Induction of NK cell reactivity against acute myeloid leukemia by Fc-optimized CD276 (B7-H3) antibody

Acute myeloid leukemia (AML) remains a therapeutic challenge despite recent therapeutic advances. Although monoclonal antibodies (mAbs) engaging natural killer (NK) cells via antibody-dependent cellular cytotoxicity (ADCC) hold promise in cancer therapy, almost none have received clinical approval for AML, so far. Recently, CD276 (B7-H3) has emerged as a promising target for AML immunotherapy, due to its high expression on leukemic blasts of AML patients. Here, we present the preclinical development of the Fc-optimized CD276 mAb 8H8_SDIE with enhanced CD16 affinity. We demonstrate that 8H8_SDIE specifically binds to CD276 on AML cell lines and primary AML cells and induces pronounced NK cell activation and degranulation as measured by CD69, CD25, and CD107a. Secretion of IFNγ, TNF, granzyme B, granulysin, and perforin, which mediate NK cell effector functions, was induced by 8H8_SDIE. A pronounced target cell-restricted lysis of AML cell lines and primary AML cells was observed in cytotoxicity assays using 8H8_SDIE. Finally, xenograft models with 8H8_SDIE did not cause off-target immune activation and effectively inhibited leukemia growth in vivo. We here present a novel attractive immunotherapeutic compound that potently induces anti-leukemic NK cell reactivity in vitro and in vivo as treatment option for AML.

Soluble NKG2DLs Are Elevated in Breast Cancer Patients and Associate with Disease Outcome

Ligands of the natural killer group 2D (NKG2DL) family are expressed on malignant cells and are usually absent from healthy tissues. Recognition of NKG2DLs such as MICA/B and ULBP1-3 by the activating immunoreceptor NKG2D, expressed by NK and cytotoxic T cells, stimulates anti-tumor immunity in breast cancer. Upregulation of membrane-bound NKG2DLs in breast cancer has been demonstrated by immunohistochemistry. Tumor cells release NKG2DLs via proteolytic cleavage as soluble (s)NKG2DLs, which allows for effective immune escape and is associated with poor prognosis. In this study, we collected serum from 140 breast cancer (BC) and 20 ductal carcinoma in situ (DCIS) patients at the time of initial diagnosis and 20 healthy volunteers (HVs). Serum levels of sNKG2DLs were quantified through the use of ELISA and correlated with clinical data. The analyzed sNKG2DLs were low to absent in HVs and significantly higher in BC patients. For some of the ligands analyzed, higher sNKG2DLs serum levels were associated with the classification of malignant tumor (TNM) stage and grading. Low sMICA serum levels were associated with significantly longer progression-free (PFS) and overall survival (OS). In conclusion, we provide the first insights into sNKG2DLs in BC patients and suggest their potential role in tumor immune escape in breast cancer. Furthermore, our observations suggest that serum sMICA levels may serve as a prognostic parameter in the patients analyzed in this study.

FusionVAC22_01: a phase I clinical trial evaluating a DNAJB1-PRKACA fusion transcript-based peptide vaccine combined with immune checkpoint inhibition for fibrolamellar hepatocellular carcinoma and other tumor entities carrying the oncogenic driver fusion

The DNAJB1-PRKACA fusion transcript was identified as the oncogenic driver of tumor pathogenesis in fibrolamellar hepatocellular carcinoma (FL-HCC), also known as fibrolamellar carcinoma (FLC), as well as in other tumor entities, thus representing a broad target for novel treatment in multiple cancer entities. FL-HCC is a rare primary liver tumor with a 5-year survival rate of only 45%, which typically affects young patients with no underlying primary liver disease. Surgical resection is the only curative treatment option if no metastases are present at diagnosis. There is no standard of care for systemic therapy. Peptide-based vaccines represent a low side-effect approach relying on specific immune recognition of tumor-associated human leucocyte antigen (HLA) presented peptides. The induction (priming) of tumor-specific T-cell responses against neoepitopes derived from gene fusion transcripts by peptide-vaccination combined with expansion of the immune response and optimization of immune function within the tumor microenvironment achieved by immune-checkpoint-inhibition (ICI) has the potential to improve response rates and durability of responses in malignant diseases. The phase I clinical trial FusionVAC22_01 will enroll patients with FL-HCC or other cancer entities carrying the DNAJB1-PRKACA fusion transcript that are locally advanced or metastatic. Two doses of the DNAJB1-PRKACA fusion-based neoepitope vaccine Fusion-VAC-XS15 will be applied subcutaneously (s.c.) with a 4-week interval in combination with the anti-programmed cell death-ligand 1 (PD-L1) antibody atezolizumab starting at day 15 after the first vaccination. Anti-PD-L1 will be applied every 4 weeks until end of the 54-week treatment phase or until disease progression or other reason for study termination. Thereafter, patients will enter a 6 months follow-up period. The clinical trial reported here was approved by the Ethics Committee II of the University of Heidelberg (Medical faculty of Mannheim) and the Paul-Ehrlich-Institute (P-00540). Clinical trial results will be published in peer-reviewed journals.

Trial registration numbers

EU CT Number: 2022-502869-17-01 and ClinicalTrials.gov Registry (NCT05937295).

Immunocytokines with target cell-restricted IL-15 activity for treatment of B cell malignancies

Despite the advances in cancer treatment achieved, for example, by the CD20 antibody rituximab, an urgent medical need remains to optimize the capacity of such antibodies to induce antibody-dependent cellular cytotoxicity (ADCC) that determines therapeutic efficacy. The cytokine IL-15 stimulates proliferation, activation, and cytolytic capacity of NK cells, but broad clinical use is prevented by short half-life, poor accumulation at the tumor site, and severe toxicity due to unspecific immune activation. We here report modified immunocytokines consisting of Fc-optimized CD19 and CD20 antibodies fused to an IL-15 moiety comprising an L45E-E46K double mutation (MIC+ format). The E46K mutation abrogated binding to IL-15Rα, thereby enabling substitution of physiological trans-presentation by target binding and thus conditional IL-15Rβγ stimulation, whereas the L45E mutation optimized IL-15Rβγ agonism and producibility. In vitro analysis of NK activation, anti-leukemia reactivity, and toxicity using autologous and allogeneic B cells confirmed target-dependent function of MIC+ constructs. Compared with Fc-optimized CD19 and CD20 antibodies, MIC+ constructs mediated superior target cell killing and NK cell proliferation. Mouse models using luciferase-expressing human NALM-6 lymphoma cells, patient acute lymphoblastic leukemia (ALL) cells, and murine EL-4 lymphoma cells transduced with human CD19/CD20 as targets and human and murine NK cells as effectors, respectively, confirmed superior and target-dependent anti-leukemic activity. In summary, MIC+ constructs combine the benefits of Fc-optimized antibodies and IL-15 cytokine activity and mediate superior NK cell immunity with potentially reduced side effects. They thus constitute a promising new immunotherapeutic approach shown here for B cell malignancies.

Protocol of a first-in-human clinical trial to evaluate the safety, tolerability, and preliminary efficacy of the bispecific CD276xCD3 antibody CC-3 in patients with colorectal cancer (CoRe_CC-3)

Introduction

Colorectal cancer (CRC) is the third most common cancer worldwide in men and women. In the metastasized stage, treatment options and prognosis are limited. To address the high medical need of this patient population, we generated a CD276xCD3 bispecific antibody termed CC-3. CD276 is expressed on CRC cells and on tumor vessels, thereby allowing for a "dual" anticancer effect.

Methods and analysis

This first-in-human clinical study is planned as a prospective multicenter trial, enrolling patients with metastatic CRC after three lines of therapy. During the dose-escalation part, initially, an accelerated titration design with single-patient cohorts is employed. Here, each patient will receive a fixed dose level (starting with 50 µg for the first patient); however, between patients, dose level may be increased by up to 100%, depending on the decision of a safety review committee. Upon occurrence of any adverse events (AEs) grade ≥2, dose-limiting toxicity (DLT), or reaching a dose level of ≥800 µg, the escalation will switch to a standard 3 + 3 dose design. After maximum tolerated dose (MTD) has been determined, defined as no more than one of the six patients experiencing DLT, an additional 14 patients receive CC-3 at the MTD level in the dose-expansion phase. Primary endpoints are incidence and severity of AEs, as well as the best objective response to the treatment according to response evaluation criteria in solid tumors (RECIST) 1.1. Secondary endpoints include overall safety, efficacy, survival, quality of life, and pharmacokinetic investigations.

Ethics and dissemination

The CD276xCD3 study was approved by the Ethics Committee of the Medical Faculty of the Heinrich Heine University Düsseldorf and the Paul-Ehrlich-Institut (P00702). Clinical trial results will be published in peer-reviewed journals. Trial registration numbers: ClinicalTrials.cov Registry (NCT05999396) and EU ClinicalTrials Registry (EU trial number 2022-503084-15-00).

Long-term efficacy of the peptide-based COVID-19 T cell activator CoVac-1 in healthy adults

OBJECTIVES

T cell immunity is key for the control of viral infections including SARS-CoV-2, in particular with regard to immune memory and protection against arising genetic variants.

METHODS

We recently evaluated a peptide-based SARS-CoV-2 T cell activator termed CoVac-1 in a first-in-human trial in healthy adults. Here, we report on long-term safety and efficacy data of CoVac-1 until month 12.

RESULTS

CoVac-1 is well tolerated without long-term immune-related side effects and induces long-lasting anti-viral T cell responses in 100% of study participants, with potent expandability of clusters of differentiation (CD4+) and CD8+ T cells targeting multiple different CoVac-1 T cell epitopes. T cell responses were associated with stronger injection site reaction. Beyond induction of T cell immunity, 89% of subjects developed CoVac-1-specific immunoglobulin G antibodies which associated with the intensity of the T cell response, indicating that CoVac-1-specific CD4+ T cells support the induction of B-cell responses. Vaccination with approved COVID-19 vaccines boosted CoVac-1-specific T cell responses. Overall, a low SARS-CoV-2 infection rate (8.3%) was observed.

CONCLUSION

Together, a single application of CoVac-1 elicits long-lived and broad SARS-CoV-2-specific T cell immunity, which further supports the current evaluation of our T cell activator in patients with congenital or acquired B-cell defects.

TOFIMS mass spectrometry-based immunopeptidomics refines tumor antigen identification

T cell recognition of human leukocyte antigen (HLA)-presented tumor-associated peptides is central for cancer immune surveillance. Mass spectrometry (MS)-based immunopeptidomics represents the only unbiased method for the direct identification and characterization of naturally presented tumor-associated peptides, a key prerequisite for the development of T cell-based immunotherapies. This study reports on the implementation of ion mobility separation-based time-of-flight (TOFIMS) MS for next-generation immunopeptidomics, enabling high-speed and sensitive detection of HLA-presented peptides. Applying TOFIMS-based immunopeptidomics, a novel extensive benignTOFIMS dataset was generated from 94 primary benign samples of solid tissue and hematological origin, which enabled the expansion of benign reference immunopeptidome databases with > 150,000 HLA-presented peptides, the refinement of previously described tumor antigens, as well as the identification of frequently presented self antigens and not yet described tumor antigens comprising low abundant mutation-derived neoepitopes that might serve as targets for future cancer immunotherapy development.

Immune Surveillance of Acute Myeloid Leukemia Is Mediated by HLA-Presented Antigens on Leukemia Progenitor Cells

Therapy-resistant leukemia stem and progenitor cells (LSC) are a main cause of acute myeloid leukemia (AML) relapse. LSC-targeting therapies may thus improve outcome of patients with AML. Here we demonstrate that LSCs present HLA-restricted antigens that induce T-cell responses allowing for immune surveillance of AML. Using a mass spectrometry-based immunopeptidomics approach, we characterized the antigenic landscape of patient LSCs and identified AML- and AML/LSC-associated HLA-presented antigens absent from normal tissues comprising nonmutated peptides, cryptic neoepitopes, and neoepitopes of common AML driver mutations of NPM1 and IDH2. Functional relevance of shared AML/LSC antigens is illustrated by presence of their cognizant memory T cells in patients. Antigen-specific T-cell recognition and HLA class II immunopeptidome diversity correlated with clinical outcome. Together, these antigens shared among AML and LSCs represent prime targets for T cell-based therapies with potential of eliminating residual LSCs in patients with AML.

SIGNIFICANCE

The elimination of therapy-resistant leukemia stem and progenitor cells (LSC) remains a major challenge in the treatment of AML. This study identifies and functionally validates LSC-associated HLA class I and HLA class II-presented antigens, paving the way to the development of LSC-directed T cell-based immunotherapeutic approaches for patients with AML. See related commentary by Ritz, p. 430 . This article is featured in Selected Articles from This Issue, p. 419.

Randomized phase-III study of low-dose cytarabine and etoposide + /- all-trans retinoic acid in older unfit patients with NPM1-mutated acute myeloid leukemia

The aim of this randomized clinical trial was to evaluate the impact of all-trans retinoic acid (ATRA) in combination with non-intensive chemotherapy in older unfit patients (> 60 years) with newly diagnosed NPM1-mutated acute myeloid leukemia. Patients were randomized (1:1) to low-dose chemotherapy with or without open-label ATRA 45 mg/m2, days 8-28; the dose of ATRA was reduced to 45 mg/m2, days 8-10 and 15 mg/m2, days 11-28 after 75 patients due to toxicity. Up to 6 cycles of cytarabine 20 mg/day s.c., bid, days 1-7 and etoposide 100 mg/day, p.o. or i.v., days 1-3 with (ATRA) or without ATRA (CONTROL) were intended. The primary endpoint was overall survival (OS). Between May 2011 and September 2016, 144 patients (median age, 77 years; range, 64-92 years) were randomized (72, CONTROL; 72, ATRA). Baseline characteristics were balanced between the two study arms. The median number of treatment cycles was 2 in ATRA and 2.5 in CONTROL. OS was significantly shorter in the ATRA compared to the CONTROL arm (p = 0.023; median OS: 5 months versus 9.2 months, 2-years OS rate: 7% versus 10%, respectively). Rates of CR/CRi were not different between treatment arms; infections were more common in ATRA beyond treatment cycle one. The addition of ATRA to low-dose cytarabine plus etoposide in an older, unfit patient population was not beneficial, but rather led to an inferior outcome.The clinical trial is registered at clinicaltrialsregister.eu (EudraCT Number: 2010-023409-37, first posted 14/12/2010).

Targeting NKG2DL with Bispecific NKG2D-CD16 and NKG2D-CD3 Fusion Proteins on Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a particularly aggressive subtype of breast cancer with a poor response rate to conventional systemic treatment and high relapse rates. Members of the natural killer group 2D ligand (NKG2DL) family are expressed on cancer cells but are typically absent from healthy tissues; thus, they are promising tumor antigens for novel immunotherapeutic approaches. We developed bispecific fusion proteins (BFPs) consisting of the NKG2D receptor domain targeting multiple NKG2DLs, fused to either anti-CD3 (NKG2D-CD3) or anti-CD16 (NKG2D-CD16) Fab fragments. First, we characterized the expression of the NKG2DLs (MICA, MICB, ULBP1-4) on TNBC cell lines and observed the highest surface expression for MICA and ULBP2. Targeting TNBC cells with NKG2D-CD3/CD16 efficiently activated both NK and T cells, leading to their degranulation and cytokine release and lysis of TNBC cells. Furthermore, PBMCs from TNBC patients currently undergoing chemotherapy showed significantly higher NK and T cell activation and tumor cell lysis when stimulated with NKG2D-CD3/CD16. In conclusions, BFPs activate and direct the NK and T cells of healthy and TNBC patients against TNBC cells, leading to efficient eradication of tumor cells. Therefore, NKG2D-based NK and T cell engagers could be a valuable addition to the treatment options for TNBC patients.

Phase I/II trial of a peptide-based COVID-19 T-cell activator in patients with B-cell deficiency

T-cell immunity is central for control of COVID-19, particularly in patients incapable of mounting antibody responses. CoVac-1 is a peptide-based T-cell activator composed of SARS-CoV-2 epitopes with documented favorable safety profile and efficacy in terms of SARS-CoV-2-specific T-cell response. We here report a Phase I/II open-label trial (NCT04954469) in 54 patients with congenital or acquired B-cell deficiency receiving one subcutaneous CoVac-1 dose. Immunogenicity in terms of CoVac-1-induced T-cell responses and safety are the primary and secondary endpoints, respectively. No serious or grade 4 CoVac-1-related adverse events have been observed. Expected local granuloma formation has been observed in 94% of study subjects, whereas systemic reactogenicity has been mild or absent. SARS-CoV-2-specific T-cell responses have been induced in 86% of patients and are directed to multiple CoVac-1 peptides, not affected by any current Omicron variants and mediated by multifunctional T-helper 1 CD4+ T cells. CoVac-1-induced T-cell responses have exceeded those directed to the spike protein after mRNA-based vaccination of B-cell deficient patients and immunocompetent COVID-19 convalescents with and without seroconversion. Overall, our data show that CoVac-1 induces broad and potent T-cell responses in patients with B-cell/antibody deficiency with a favorable safety profile, which warrants advancement to pivotal Phase III safety and efficacy evaluation. ClinicalTrials.gov identifier NCT04954469.

Phase I study evaluating the Fc-optimized FLT3 antibody FLYSYN in AML patients with measurable residual disease

BACKGROUND

About half of AML patients achieving complete remission (CR) display measurable residual disease (MRD) and eventually relapse. FLYSYN is an Fc-optimized antibody for eradication of MRD directed to FLT3/CD135, which is abundantly expressed on AML cells.

METHODS

This first-in-human, open-label, single-arm, multicenter trial included AML patients in CR with persisting or increasing MRD and evaluated safety/tolerability, pharmacokinetics and preliminary efficacy of FLYSYN at different dose levels administered intravenously (cohort 1-5: single dose of 0.5 mg/m2, 1.5 mg/m2, 5 mg/m2, 15 mg/m2, 45 mg/m2; cohort 6: 15 mg/m2 on day 1, 15 and 29). Three patients were treated per cohort except for cohorts 4 and 6, which were expanded to nine and ten patients, respectively. Primary objective was safety, and secondary efficacy objective was ≥ 1 log MRD reduction or negativity in bone marrow.

RESULTS

Overall, 31 patients were treated, of whom seven patients (22.6%) experienced a transient decrease in neutrophil count (two grade 3, others ≤ grade 2). No infusion-related reaction or dose-limiting toxicity was observed. Adverse events (AEs) were mostly mild to moderate, with the most frequent AEs being hematologic events and laboratory abnormalities. Response per predefined criteria was documented in 35% of patients, and two patients maintained MRD negativity until end of study. Application of 45 mg/m2 FLYSYN as single or cumulative dose achieved objective responses in 46% of patients, whereas 28% responded at lower doses.

CONCLUSIONS

FLYSYN monotherapy is safe and well-tolerated in AML patients with MRD. Early efficacy data are promising and warrant further evaluation in an up-coming phase II trial. Trial registration This clinical is registered on clinicaltrials.gov (NCT02789254).

In vivo kinetics of early, non-random methylome and transcriptome changes induced by DNA-hypomethylating treatment in primary AML blasts

Despite routine use of DNA-hypomethylating agents (HMAs) in AML/MDS therapy, their mechanisms of action are not yet unraveled. Pleiotropic effects of HMAs include global methylome and transcriptome changes. We asked whether in blasts and T-cells from AML patients HMA-induced in vivo demethylation and remethylation occur randomly or non-randomly, and whether gene demethylation is associated with gene induction. Peripheral blood AML blasts from patients receiving decitabine (20 mg/m² day 1-5) were serially isolated for methylome analyses (days 0, 8 and 15, n = 28) and methylome-plus-transcriptome analyses (days 0 and 8, n = 23), respectively. T-cells were isolated for methylome analyses (days 0 and 8; n = 16). We noted massive, non-random demethylation at day 8, which was variable between patients. In contrast, T-cells disclosed a thousand-fold lesser, random demethylation, indicating selectivity of the demethylation for the malignant blasts. The integrative analysis of DNA demethylation and transcript induction revealed 87 genes displaying a significant inverse correlation, e.g. the tumor suppressor gene IFI27, whose derepression was validated in two AML cell lines. These results support HMA-induced, non-random early in vivo demethylation events in AML blasts associated with gene induction. Larger patient cohorts are needed to determine whether a demethylation signature may be predictive for response to this treatment.

An optimized IgG-based B7-H3xCD3 bispecific antibody for treatment of gastrointestinal cancers

T cell-based immunotherapy has revolutionized oncological treatment. However, many patients do not respond to treatment, and long-term remissions remain rare, particularly in gastrointestinal cancers like colorectal cancer (CRC). B7-H3 is overexpressed in multiple cancer entities including CRC on both tumor cells and tumor vasculature, the latter facilitating influx of effector cells into the tumor site upon therapeutic targeting. We generated a panel of T cell-recruiting B7-H3xCD3 bispecific antibodies (bsAbs) and show that targeting a membrane-proximal B7-H3 epitope allows for a 100-fold reduction of CD3 affinity. In vitro, our lead compound CC-3 showed superior tumor cell killing, T cell activation, proliferation, and memory formation, whereas undesired cytokine release was reduced. In vivo, CC-3 mediated potent antitumor activity in three independent models using immunocompromised mice adoptively transferred with human effector cells with regard to prevention of lung metastasis and flank tumor growth as well as elimination of large established tumors. Thus, fine-tuning of both target and CD3 affinities as well as binding epitopes allowed for the generation of a B7-H3xCD3 bsAbs with promising therapeutic activity. CC-3 is presently undergoing good manufacturing practice (GMP) production to enable evaluation in a clinical "first-in-human" study in CRC.

Performance of phase-I dose finding designs with and without a run-in intra-patient dose escalation stage

Dose-finding designs for phase-I trials aim to determine the recommended phase-II dose (RP2D) for further phase-II drug development. If the trial includes patients for whom several lines of standard therapy failed or if the toxicity of the investigated agent does not necessarily increase with dose, optimal dose-finding designs should limit the frequency of treatment with suboptimal doses. We propose a two-stage design strategy with a run-in intra-patient dose escalation part followed by a more traditional dose-finding design. We conduct simulation studies to compare the 3 + 3 design, the Bayesian Optimal Interval Design (BOIN) and the Continual Reassessment Method (CRM) with and without intra-patient dose escalation. The endpoints are accuracy, sample size, safety, and therapeutic efficiency. For scenarios where the correct RP2D is the highest dose, inclusion of an intra-patient dose escalation stage generally increases accuracy and therapeutic efficiency. However, for scenarios where the correct RP2D is below the highest dose, intra-patient dose escalation designs lead to increased risk of overdosing and an overestimation of RP2D. The magnitude of the change in operating characteristics after including an intra-patient stage is largest for the 3 + 3 design, decreases for the BOIN and is smallest for the CRM.

Activity of decitabine combined with all-trans retinoic acid in oligoblastic AML: Results from a randomized 2x2 phase II trial (DECIDER)

Not available.

Novel ACE2 fusion protein with adapting activity against SARS-CoV-2 variants in vitro

Despite the successful development of vaccines and neutralizing antibodies to limit the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerging variants prolong the pandemic and emphasize the persistent need to develop effective antiviral treatment regimens. Recombinant antibodies directed to the original SARS-CoV-2 have been successfully used to treat established viral disease. However, emerging viral variants escape the recognition by those antibodies. Here we report the engineering of an optimized ACE2 fusion protein, designated ACE2-M, which comprises a human IgG1 Fc domain with abrogated Fc-receptor binding linked to a catalytically-inactive ACE2 extracellular domain that displays increased apparent affinity to the B.1 spike protein. The affinity and neutralization capacity of ACE2-M is unaffected or even enhanced by mutations present in the spike protein of viral variants. In contrast, a recombinant neutralizing reference antibody, as well as antibodies present in the sera of vaccinated individuals, lose activity against such variants. With its potential to resist viral immune escape ACE2-M appears to be particularly valuable in the context of pandemic preparedness towards newly emerging coronaviruses.

IgG-based B7-H3xCD3 bispecific antibody for treatment of pancreatic, hepatic and gastric cancer

T cell-based immunotherapy has significantly improved treatment options for many malignancies. However, despite these and other therapeutic improvements over the last decades, gastrointestinal cancers, in particular pancreatic, hepatic and gastric cancer, are still characterized by high relapse rates and dismal prognosis, with an accordingly high unmet medical need for novel treatment strategies. We here report on the preclinical characterization of a novel bispecific antibody in an IgG-based format termed CC-3 with B7-H3xCD3 specificity. In many cancer entities including pancreatic, hepatic and gastric cancers, B7-H3 (CD276) is overexpressed on tumor cells and also on the tumor vasculature, the latter allowing for improved access of immune effector cells into the tumor site upon therapeutic targeting. We demonstrate that CC-3 induces profound T cell reactivity against various pancreatic, hepatic and gastric cancer cell lines as revealed by analysis of activation, degranulation and secretion of IL2, IFNγ as well as perforin, resulting in potent target cell lysis. Moreover, CC-3 induced efficient T cell proliferation and formation of T cell memory subsets. Together, our results emphasize the potential of CC-3, which is presently being GMP-produced to enable clinical evaluation for treatment of pancreatic, hepatic and gastric cancer.

The oncogenic fusion protein DNAJB1-PRKACA can be specifically targeted by peptide-based immunotherapy in fibrolamellar hepatocellular carcinoma

The DNAJB1-PRKACA fusion transcript is the oncogenic driver in fibrolamellar hepatocellular carcinoma, a lethal disease lacking specific therapies. This study reports on the identification, characterization, and immunotherapeutic application of HLA-presented neoantigens specific for the DNAJB1-PRKACA fusion transcript in fibrolamellar hepatocellular carcinoma. DNAJB1-PRKACA-derived HLA class I and HLA class II ligands induce multifunctional cytotoxic CD8⁺ and T-helper 1 CD4⁺ T cells, and their cellular processing and presentation in DNAJB1-PRKACA expressing tumor cells is demonstrated by mass spectrometry-based immunopeptidome analysis. Single-cell RNA sequencing further identifies multiple T cell receptors from DNAJB1-PRKACA-specific T cells. Vaccination of a fibrolamellar hepatocellular carcinoma patient, suffering from recurrent short interval disease relapses, with DNAJB1-PRKACA-derived peptides under continued Poly (ADP-ribose) polymerase inhibitor therapy induces multifunctional CD4⁺ T cells, with an activated T-helper 1 phenotype and high T cell receptor clonality. Vaccine-induced DNAJB1-PRKACA-specific T cell responses persist over time and, in contrast to various previous treatments, are accompanied by durable relapse free survival of the patient for more than 21 months post vaccination. Our preclinical and clinical findings identify the DNAJB1-PRKACA protein as source for immunogenic neoepitopes and corresponding T cell receptors and provide efficacy in a single-patient study of T cell-based immunotherapy specifically targeting this oncogenic fusion.

B7-H3-targeting Fc-optimized antibody for induction of NK cell reactivity against sarcoma

Natural killer (NK) cells largely contribute to antibody-dependent cellular cytotoxicity (ADCC), a central factor for success of monoclonal antibodies (mAbs) treatment of cancer. The B7 family member B7-H3 (CD276) recently receives intense interest as a novel promising target antigen for immunotherapy. B7-H3 is highly expressed in many tumor entities, whereas expression on healthy tissues is rather limited. We here studied expression of B7-H3 in sarcoma, and found substantial levels to be expressed in various bone and soft-tissue sarcoma subtypes. To date, only few immunotherapeutic options for treatment of sarcomas that are limited to a minority of patients are available. We here used a B7-H3 mAb to generate chimeric mAbs containing either a wildtype Fc-part (8H8_WT) or a variant Fc part with amino-acid substitutions (S239D/I332E) to increase affinity for CD16 expressing NK cells (8H8_SDIE). In comparative studies we found that 8H8_SDIE triggers profound NK cell functions such as activation, degranulation, secretion of IFNγ and release of NK effector molecules, resulting in potent lysis of different sarcoma cells and primary sarcoma cells derived from patients. Our findings emphasize the potential of 8H8_SDIE as novel compound for treatment of sarcomas, particularly since B7-H3 is expressed in bone and soft-tissue sarcoma independent of their subtype.

Expression of the immune checkpoint modulator OX40 indicates poor survival in acute myeloid leukemia

Despite therapeutic advances, mortality of Acute Myeloid Leukemia (AML) is still high. Currently, the determination of prognosis which guides treatment decisions mainly relies on genetic markers. Besides molecular mechanisms, the ability of malignant cells to evade immune surveillance influences the disease outcome and, among others, the expression of checkpoints modulators contributes to this. In AML, functional expression of the checkpoint molecule OX40 was reported, but the prognostic relevance of OX40 and its ligand OX40L axis has so far not been investigated. Here we described expression and prognostic relevance of the checkpoint modulators OX40 and OX40L, analyzed on primary AML cells obtained from 92 therapy naïve patients. Substantial expression of OX40 and OX40L on AML blasts was detected in 29% and 32% of the investigated subjects, respectively, without correlation between the expression of the receptor and its ligand. Whereas OX40L expression was not associated with different survival, patients with high expression levels of the receptor (OX40^high) on AML blasts survived significantly shorter than OX40^low patients (p = 0.009, HR 0.46, 95% CI 0.24–0.86), which identifies OX40 as novel prognostic marker and a potential therapeutic target in AML patients.

Controversial Role of the Immune Checkpoint OX40L Expression on Platelets in Breast Cancer Progression

In conventional T cells, OX40 has been identified as a major costimulating receptor augmenting survival and clonal expansion of effector and memory T cell populations. In regulatory T cells, (Treg) OX40 signaling suppresses cellular activity and differentiation. However, clinical trials investigating OX40 agonists to enhance anti-tumor immunity, showed only limited success so far. Here we show that platelets from breast cancer patients express relevant levels of OX40L and platelet OX40L (pOX40L) inversely correlates with platelet-expressed immune checkpoint molecules GITRL (pGITRL) and TACI (pTACI). While high expression of pOX40L correlates with T and NK cell activation, elevated pOX40L levels identify patients with higher tumor grades, the occurrence of metastases, and shorter recurrence-free survival (RFS). Of note, OX40 mRNA levels in breast cancer correlate with enhanced expression of anti-apoptotic, immune-suppressive, and tumor-promoting mRNA gene signatures. Our data suggest that OX40L on platelets might play counteracting roles in cancer and anti-tumor immunity. Since pOX40L reflects disease relapse better than the routinely used predictive markers CA15-3, CEA, and LDH, it could serve as a novel biomarker for refractory disease in breast cancer.

Abstract 2865: CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers

Despite substantial improvements over the last decades, survival rates in metastatic gastrointestinal cancer are still far from satisfactory, with an accordingly high medical need for new treatment strategies. B7-H3 (CD276) is a member of the B7 immune checkpoint family. Initially thought to act as co-stimulator, recent studies revealed that B7-H3 rather has an inhibitory role for T cells and contributes to tumor immune evasion. Clinically, its overexpression has been linked to invasive and metastatic potential as well as poor prognosis. Due to its expression on both, tumor cells and tumor vasculature, in a variety of cancer entities including colorectal cancer, B7-H3 attracted our interest as therapeutic target for T cell-recruiting bispecific antibodies (bsAbs). We postulate that “dual targeting” of both, the cancer cells and the tumor vasculature may support the influx of T cells into the tumor site, a critical prerequisite for successful immunotherapy of solid tumors allowing for subsequent destruction of antigen-positive malignant cells. We generated a panel of monoclonal antibodies directed to different epitopes of the B7-H3 molecule. After biochemical characterization, we selected two antibodies with distinct binding proprieties and subsequently used them for the construction of Tcell-recruiting B7-H3xCD3 bsAbs in an IgG-based (IgGsc) format. To reduce side effects, constructs were cloned using a UCHT-1 derived low affinity anti-CD3 sequence. In vitro characterization using colorectal and other carcinoma cells allowed for selection of a construct with optimal functional properties (thereafter termed CC-3) as revealed by target cell-restricted induction of T cell activation, proliferation and tumor cell killing. In vivo, potent efficacy of CC-3 was documented in a lung metastasis model and by its ability to eliminate large established flank tumors using immunocompromised NSG mice adoptively transferred with human effector cells. Despite the high therapeutic efficacy of CC-3, no toxicity was observed in the absence of target cells. In summary, CC-3 is a bsAb with promising therapeutic activity against B7-H3 positive tumors. GMP compliant production of CC-3 is presently ongoing to enable evaluation in a clinical “first in human” study in patients with colorectal cancer.

Citation Format: Latifa Zekri, Martina S. Lutz, Ilona Hagelstein, Timo Manz, Monika Engel, Boris Klimovich, Nisha Prakash, Anna Chashchina, Sebastian Hörner, Stefanie Müller, Melanie Märklin, Martin Pflügler, Gundram Jung, Helmut R. Salih. CC-3, an IgG-based B7-H3xCD3 bispecific antibody for targeting of gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2865.

Abstract 3957: Receptor Activator of NF-κB (RANK) confers resistance to chemotherapy in AML and associates with dismal disease course

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Untreated, AML leads to death within months after first symptoms. Combinatorial chemotherapy, mostly using a pyrimidine analog together with an anthracycline, made this previously incurable disease medicable, and response to remission-inducing chemotherapy strongly correlates with patient outcome. Despite advances in treatment over the recent years, AML still has a poor prognosis with an average 5-year survival rate of 30%. A better understanding of the molecular mechanisms predicting and affecting treatment efficacy is key to improve disease control and outcome. Here we studied the expression, prognostic relevance and functional role of the tumor necrosis factor receptor (TNFR) family member Receptor Activator of Nuclear Factor (NF)-κB (RANK) in AML. We conducted an experimental ex vivo study using leukemic cells of 54 AML patients. Substantial surface expression of RANK was detected on the primary AML cells in 35% of the analyzed patients. We further found that RANK signaling induced the release of the cytokines IL-6, IL-8, TNF and IL-10 acting as growth and survival factors for the leukemic cells and mediated resistance of AML cells to treatment with doxorubicin and cytarabine, the most commonly used cytostatic compounds in AML treatment. In line, prevalence of RANK expression on leukemic cells correlated with dismal disease course of patients as revealed by reduced overall survival. Together, our results show that RANK plays a yet unrecognized role in AML pathophysiology and resistance to treatment. Moreover, the association of RANK expression with adverse disease course identifies RANK as potential “functional” prognostic marker and putative target for therapeutic intervention to improve treatment response of AML patients.

Citation Format: Kim L. Clar, Lisa M. Weber, Bastian J. Schmied, Jonas S. Heitmann, Maddalena Marconato, Claudia Tandler, Pascal Schneider, Helmut R. Salih. Receptor Activator of NF-κB (RANK) confers resistance to chemotherapy in AML and associates with dismal disease course [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3957.

Abstract 2886: Antigen internalization and its prevention during treatment with bispecific antibodies

Antigen-mediated antibody internalization is an important factor influencing kinetics and efficacy of antibody-based therapeutics. Antibodies directed against HER2, CD20, FLT3, EGFR, CD10 and CD22 have been shown to undergo internalization upon binding to their target antigens. Although antibody-induced internalization may be desirable under some circumstances, for example in case of antibody-drug conjugates, it can subvert the therapeutic efficacy of ADCC-inducing antibodies and bispecific antibodies (bsAbs) aiming to mobilize T cells against cancer. Here we examined the turnover of PSMA, a target antigen widely used for diagnostic and therapeutic interventions in prostate cancer. As a model system, we used prostate cancer cell lines expressing varying levels of PSMA in functional analyses with our PSMAxCD3 bsAb CC-1 which is currently being evaluated in two clinical trials (NCT04104607 and NCT04496674). Antigen internalization kinetics was analyzed by flow cytometric-internalization assays and live-cell imaging of antibody internalization. These analyses revealed that surface PSMA expression is rapidly downregulated after binding of PSMAxCD3 bsAb. Internalization occured in a dose-dependent manner, with complete negativity observed at concentrations ≥0.1 µg/ml. After withdrawal of the bsAb, antigen surface levels were fully restored within 24 hours. PSMA internalization was found to be partially prevented by inhibiting clathrin-dependent endocytosis. Currently, we are screening various clinically approved clathrin-dependent endocytosis inhibitors (e.g. statins and chloroquine) to identify compounds for combinatorial approaches to prevent undesired PSMA internalization in patients receiving PSMAxCD3 bsAbs. Altogether, our results document the involvement of clathrin-dependent endocytosis in bsAbs-driven PSMA internalization and provide a basis for combinatorial approaches to increase the efficacy of PSMA-directed therapeutics.

Citation Format: Maria Klimovich, Latifa Zekri, Gundram Jung, Helmut R. Salih. Antigen internalization and its prevention during treatment with bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2886.

Abstract 2104: NK cell immunosurveillance of tumors is regulated by NFAT1 and NFAT2

NK cells are lymphoid components of innate immunity and play an important role in tumor immunosurveillance. One of the major transcriptional regulators in lymphoid cells is NFAT (Nuclear Factor of Activated T cells), controlling lymphocyte development and activity. However, while the role of NFAT signaling is well defined in T cells, the cytotoxic lymphocytes of adaptive immunity, surprisingly little is known regarding the relevance of this transcription factor family in NK cells as effector cells of innate immunity. Available data indicate that NFAT activity is dispensable for development of NK cells. However, several lines of evidence including reports on the effects of the immunosuppressive drugs cyclosporin A and tacrolimus, which mediate their effects through inhibition of calcineurin and consecutively NFAT, implicate an involvement of the NFAT family in NK cell function. We here employed different genetic mouse models to unravel the role of NFAT1 (NFATc2) and NFAT2 (NFATc1) in NK cell reactivity.

When NK cells with knockout (KO) of NFAT1 or NFAT2 compared to NK cells of control mice (WT) were employed in in vitro analyses, lack of either NFAT was found to surprisingly result in enhanced NK cell degranulation as well as increased production of granzyme B and perforin upon stimulation of activating receptors like NK1.1 or Nkp46 or upon co-culture with different leukemia and solid tumor tumor cells. In line, cytotoxicity assays revealed increased lysis of YAC-1 and B16F10 tumor cells by both NFAT1- and NFAT2-deficient NK cells as compared to WT controls. The inhibitory effect of NFAT transcription factors on NK cell effector function could also be confirmed in vivo by employing WT and NFAT KO animals in syngeneic B16F10 melanoma and RMA-S flank tumor models, which revealed a significantly reduced tumor burden in NFAT1 and NFAT2 KO mice. Comparative analyses with single NFAT as well as NFAT1+NFAT2 double KO and WT animals further confirmed the inhibitory effect of NFAT1 and NFAT2 and pointed to additive effects of NFAT1 and NFAT2 in NK cell tumor immunosurveillance.

Taken together, our results provide the first evidence for the direct functional involvement of NFAT1 and NFAT2 in NK cell antitumor reactivity and, in contrast to T and B cells, identify NFAT as a negative regulator of NK cell function.

Citation Format: Melanie Märklin, Samuel Holzmayer, Kübra Kaban, Martin R. Müller, Helmut R. Salih. NK cell immunosurveillance of tumors is regulated by NFAT1 and NFAT2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2104.

Abstract 3168: Immunopeptidome-defined acute myeloid leukemia progenitor cell-associated antigens are targeted in vivo by AML patients’ T cells

Despite recent advances and the approval of novel molecular therapies in acute myeloid leukemia (AML), the disease is still characterized by high relapse rates and poor overall survival due to the persistence of therapy-resistant residual leukemic progenitor cells (LPCs). T cell-based immunotherapy has been suggested as a novel therapeutic option to eliminate minimal residual disease and achieve long-lasting remissions. One main prerequisite for immunotherapy development is the selection of immunogenic targets that show natural, high-frequent, and tumor-exclusive presentation on the cell surface of malignant cells. In a previous study we characterized the antigenic landscape of AML by mass spectrometry to identify AML-specific T cell epitopes (Berlin et al. Leukemia 2015). Here, we aimed to analyze the immunopeptidome of primary AML progenitor cells (n = 10, purity >80% CD34+CD38-) to identify LPC-associated antigens that enable the specific targeting of AML LPCs. Additionally, we analyzed an extended set of AML patient samples (n = 47) to screen for naturally presented neoepitopes and to identify broadly applicable AML-associated target antigens that are presented on both AML blasts and LPCs.

We identified more than 16,000 HLA class I- and 17,000 HLA class II-presented peptides on LPCs and 72,000 HLA class I and 61,000 HLA class II peptides in the total AML cohort. Comparative profiling of LPCs, AML blasts, and a benign tissue database (n = 332) revealed HLA class I- and HLA class II-presented LPC-exclusive as well as frequently presented AML-associated antigens on both AML blasts and LPCs. Besides these tumor-exclusive self-peptides, we detected naturally presented neoepitopes derived from two frequent mutations (NPM1 and IDH2) in this low-mutational burden malignancy.

For immunogenicity analyses we selected 16 HLA class I- and 15 HLA class II-restricted peptides comprising unmutated as well as mutation-derived antigens. In vitro priming experiments showed the induction of peptide-specific, multi-functional, and cytotoxic CD8+ effector cells in samples of healthy volunteers and AML patients.

We were able to detect strong preexisting memory T cell responses targeting LPC-associated antigens in AML patients with detection frequencies of up to 20%. Retrospective analyses revealed that patients with preexisting peptide-specific T cell responses showed improved overall survival compared to patients without any memory responses against our targets.

Taken together, we identified novel, naturally presented, LPC-exclusive, and AML-associated self-antigens and neoepitopes presented on both AML blasts and LPCs. We could demonstrate the immunogenicity of 14/16 (88%) HLA class I and 13/15 (87%) HLA class II antigens highlighting their potential as promising targets for T cell-based immunotherapy approaches to eliminate minimal residual disease in AML patients.

Citation Format: Annika Nelde, Heiko Schuster, Tatjana Bilich, Jens Bauer, Malte Roerden, Sarah Schroeder, Jonas S. Heitmann, Elke Rücker-Braun, Hans-Georg Rammensee, Helmut R. Salih, Juliane S. Walz. Immunopeptidome-defined acute myeloid leukemia progenitor cell-associated antigens are targeted in vivo by AML patients’ T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3168.

Abstract CT258: Interim safety and immunogenicity results of a phase I trial evaluating the multi-peptide COVID-19 vaccine candidate CoVac-1 for induction of SARS-CoV-2 T cell immunity in cancer patients with disease- or treatment-related immunoglobulin deficiency

Individuals with impaired ability to mount a humoral immune response, either during natural infection or upon prophylactic vaccination, are at high risk for a severe course of COVID-19. Besides humoral immunity mediated by B cells, T cell immunity is key for the control of viral infections. We developed the peptide-based vaccine candidate CoVac-1, which primarily aims for the induction of SARS-CoV-2-specific T cells. CoVac-1 comprises six promiscuous HLA-DR-binding SARS-CoV-2-derived T cell epitopes from various viral proteins proven (i) to be frequently and HLA-independently recognized by T cells in COVID-19 convalescents, (ii) to be of pathophysiological relevance for T cell immunity to combat COVID-19, and (iii) to mediate long-term immunity after infection (Nelde et al. Nat Immunol 2021, Bilich et al. Sci Transl Med 2021). CoVac-1 vaccine peptides are adjuvanted with the novel toll-like receptor 1/2 agonist XS15 emulsified in Montanide࣪ ISA51 VG. In a first-in-human clinical trial in healthy adults (NCT04546841), CoVac-1 showed a favorable safety profile and induced profound and long-lasting T cell immunity after single dose administration in 100% of the study subjects, mediated by multifunctional T-helper 1 CD4+ and CD8+ T cells. CoVac-1-induced T cell responses surpassed those after SARS-CoV-2 infection as well as those after vaccination with approved vaccines and were unaffected by current SARS-CoV-2 variants of concern (Heitmann et al. Nature 2021). Here we present the interim safety and immunogenicity results of our Phase I/II trial evaluating CoVac-1 in patients with congenital or acquired B cell deficiency, mainly comprising leukemia and lymphoma patients (NCT04954469). 64% of study subjects had previously been vaccinated with approved vaccines without developing any humoral immune response. Alike in the healthy adults, CoVac-1 showed a good safety and tolerability profile without relevant systemic adverse events. CoVac-1-specific T cell responses could be documented in 93% of study subjects on day 28 after CoVac-1 application, with earliest responses evidenced at day 14 (71%). Vaccine-induced T cell responses were mediated by multifunctional T-helper 1 CD4+ T cells. Of note, CoVac-1 induced T cell responses in this highly immune compromised study population were similar to those occurring in healthy volunteers after natural infection or induced by approved vaccines. These results identify CoVac-1 as promising vaccine candidate for cancer and other immunocompromised patients with immunoglobulin deficiency. Recruitment of the Phase II part of the trial is ongoing with results expected for March 2022.

Citation Format: Claudia Tandler, Jonas S. Heitmann, Maddalena Marconato, Yacine Maringer, Monika Denk, Marion Richter, Annika Nelde, Imma Fischer, Markus W. Löffler, Hans-Georg Rammensee, Helmut R. Salih, Juliane S. Walz. Interim safety and immunogenicity results of a phase I trial evaluating the multi-peptide COVID-19 vaccine candidate CoVac-1 for induction of SARS-CoV-2 T cell immunity in cancer patients with disease- or treatment-related immunoglobulin deficiency [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT258.

Abstract 1972: Clinical implications of HLA expression and immunopeptidome-presented tumor antigens in ovarian carcinoma

Ovarian carcinoma (OvCa) is the seventh most common malignancy in women and the eighth leading cause of cancer-related deaths worldwide. In a previous study, we characterized the antigenic landscape of ovarian carcinoma by mass spectrometry-based immunopeptidomics and identified novel OvCa-associated tumor antigens, including Mucin-16 (MUC-16) and Mesothelin (MSLN) with the aim to develop novel T cell-based immunotherapies (Schuster et al. PNAS 2017). Here, we analyzed the immunopeptidomics data of this OvCa cohort in relation to clinical patient characteristics and disease outcome. Analysis included 43 OvCa patients with respective immunopeptidomics and RNA sequencing data, comprising immunopeptidome diversity, tumor antigen presentation and expression (MUC16, MSLN) as well as HLA mRNA expression.Analyzing HLA class I-restricted tumor antigen presentation in relation to clinical data, we could show that nodal-positive patients presented more frequently HLA-restricted peptides derived from the tumor antigen MUC16 (p = 0.0087) and showed significantly increased numbers of unique MUC16-derived HLA-presented peptides within the total immunopeptidome (p = 0.042) compared to nodal-negative patients. No significant difference in HLA class I immunopeptidome diversity, overall tumor antigen presentation, and expression was observed for histological subtypes, grading, or the prevalence of distant metastases. For HLA class II-restricted tumor antigen presentation and HLA expression in relation to clinical data, we observed a more diverse HLA class II immunopeptidome in terms of different HLA class II-presented peptides (p = 0.011) for patients with high tumor grading (G3) compared to low/intermediate (G1/G2) grading. In line, the tumors of these patients also presented an increased number of different MSLN-derived HLA class II-restricted peptides (p = 0.021). No significant difference in HLA class II immunopeptidome diversity, tumor antigen presentation and expression was seen for the prevalence of distant metastasis, histological subtypes, or nodal positivity.Of note, patients presenting MSLN-derived peptides in their immunopeptidome showed a significantly prolonged recurrence-free survival (RFS, p = 0.011). In addition, patients exhibiting a high expression of HLA-DR showed a significantly increased RFS (p = 0.018 for HLA-DRA, p = 0.0031 for HLA-DRB).In conclusion, this work provides first insights on the relation of immunopeptidomic characteristics, comprising HLA expression and tumor antigen presentation, with clinical characteristics and disease outcome of OvCa patients. The observed correlation of HLA-DR expression and HLA class II tumor antigen presentation with prolonged RFS indicates a central role of CD4+ T cell responses for anti-tumor immune surveillance in ovarian cancer.

Citation Format: Christian M. Tegeler, Jonas S. Heitmann, Helmut R. Salih, Juliane S. Walz, Annika Nelde. Clinical implications of HLA expression and immunopeptidome-presented tumor antigens in ovarian carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1972.

Abstract 2864: A CLEC12A immunocytokine with target cell-restricted IL-15 activity shows a favorable toxicity profile and high potency in AML

IL-15, often referred to as the “anti-cancer cytokine”, potently stimulates proliferation and activation of NK and T cells, but unlike its close relative IL-2, does neither promote activation-induced death of lymphocytes nor activity of immunoinhibitory Tregs. So far, short half-life, poor accumulation at the tumor site and severe toxicity upon systemic application limit IL-15 efficacy in patients. Fusion of IL-15 to antibodies directed to tumor antigens (classical immunocytokines, ICs) improves on accumulation at the tumor site and pharmacokinetics. However, since the activity of the cytokine moiety within classical ICs does not depend on antigen binding, the application of clinically effective doses is still prevented by toxicity due to unspecific immune activation. To overcome this problem, we took advantage of the unique mechanism of action of IL-15 which stimulates IL-15Rβ/γ on NK and T cells as a membrane-bound complex with IL-15Rα on monocytes and DCs (trans-presentation). We used an Fc-optimized antibody directed to CLEC12A, a surface antigen abundantly expressed on AML cells and leukemic stem cells but not on healthy stem cells. This antibody termed 33C2-SDIE was fused to an IL-15E46K mutant with abolished binding to IL-15Rα, allowing to substitute physiological trans-presentation of IL-15 by binding of the construct to its tumor-expressed target. Antigen-specific binding of the resulting modified immunocytokine (MIC12) was confirmed using multiple CLEC12A-expressing cell lines and primary AML samples from patients. Functional analysis of activation, cytokine release, and target cell lysis demonstrated that MIC proteins, in contrast to classical IC, stimulate cytotoxic lymphocytes in a highly target cell-restricted manner, allowing for the desired reduction of unspecific immune activation. At the same time, significantly superior NK cell reactivity against AML cells as compared to even the Fc-optimized antibody was observed. Both, IL-15 signaling and engagement of Fc-receptors by the optimized Fc-domain were found to be essential for optimal activity of our MIC constructs. Importantly, only treatment with MIC12 was capable to induce NK cell proliferation, which is required to overcome unfavorable target to effector ratios that prevail in overt cancer disease. In summary, our novel CLEC12A-targeting immunocytokine allows for tumor-restricted stimulation of cytotoxic lymphocytes and reduced toxicity while displaying superior anti-leukemic activity and constitutes a promising compound for the treatment of AML.

Citation Format: Boris Klimovich, Leonard Anton, Yangmi Lim, Jonghwa Won, Anna Chashchina, Martin Pflügler, Latifa Zekri, Gundram Jung, Helmut R. Salih. A CLEC12A immunocytokine with target cell-restricted IL-15 activity shows a favorable toxicity profile and high potency in AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2864.

Abstract 3555: Immunopeptidomics-guided tumor antigen warehouse design for peptide-based immunotherapy in head and neck squamous cell carcinomas

Head and neck squamous cell carcinomas (HNSCC) are the sixth most common malignancies worldwide. 45% of patients are diagnosed at a late tumor stage associated with poor survival. For metastatic, unresectable or recurrent (m/uR) HNSCC, immune checkpoint inhibition (ICI) was recently approved as a novel therapeutic option showing significant survival benefits compared to standard chemotherapy-based treatment. However, response to ICI is still limited to a small number of patients calling for further improvement of T cell-based immunotherapies. Peptide-based approaches, which rely on the specific immune recognition of tumor-associated human leukocyte antigen (HLA) presented peptides, represent promising and low side effect treatment options. Peptide vaccination has been shown to enhance and induce long-term anti-tumoral immune responses and even clinical responses in HNSCC patients. However, current vaccines are either monovalent, based on patient-individual tumor-specific mutations or restricted to a single HLA allotype and therefore neither widely applicable nor suitable for reliable studies and large-scale production. In this study, using mass spectrometry (MS) -based immunopeptidome analysis of a large cohort of HNSCC patient (n = 30) tumor and adjacent benign samples, we established a tumor-associated off-the-shelf peptide warehouse for broadly applicable personalized therapies. The malignant dataset, comprising 91651 HLA ligands, was compared to adjacent benign and various benign tissues (www.hla-ligand-atlas.org) to identify tumor-exclusive antigens. Further antigen selection was based on allotype-specific high frequent presentation. In total, 23 frequently presented and tumor-exclusive HNSCC-associated peptides were selected for six of the most common HLA class I allotypes (A*01, A*02, A*24, B*15, B*35, B*40) covering >75% of the world population, as well as five HLA class II presented peptides binding various different HLA class II allotypes. Immunogenicity was validated by IFN-γ ELISPOT screening for spontaneous preexisting T cell responses targeting the respective peptides as well as by in vitro priming experiments of naïve T cells in HNSCC patients and healthy volunteers. Furthermore, immunopeptidome analyses identified these antigens in patient plasma samples providing first evidence for “liquid biopsy” immunopeptidome analysis without the need of primary tumor tissue. A phase I study evaluating safety, immunogenicity as well as first efficacy of this warehouse-based vaccine in combination with ICI in HNSCC patients is currently being set up, with personalized peptide selection based on individual HLA-allotype and MS analysis of patient tumor/plasma sample. In conclusion, we here designed a peptide warehouse that enables a polyvalent and widely applicable but still personalized peptide vaccination in HNSCC patients.

Citation Format: Sarah Schroeder, Thorben Gross, Annika Nelde, Marcel Wacker, Jens Bauer, Jonas Rieth, Marissa Dubbelaar, Lena Muehlenbruch, Yacine Maringer, Paul-Stefan Mauz, Martin Sailer, Julia Philipp, Sven Becker, Thomas Breuer, Helmut R. Salih, Hans-Georg Rammensee, Hubert Löwenheim, Juliane S. Walz. Immunopeptidomics-guided tumor antigen warehouse design for peptide-based immunotherapy in head and neck squamous cell carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3555.

Abstract 1375: The intra-tumoral spatial heterogeneity of T-cell antigens in glioblastoma: An integrated multi-omics approach

Glioblastoma is the most common primary malignant neoplasm of the central nervous system in adults. Current treatment options comprise maximal surgical resection followed by radiation and/or chemotherapy with temozolomide. However, these procedures are unable to eliminate all tumor cells, which in turn lead to disease recurrence accounting for the poor prognosis. Glioblastoma is a highly infiltrative tumor in which recurrence originates from the unresectable peritumoral infiltration zone. Thus, novel treatment options specifically targeting the tumor cells in the infiltration zone are needed to prevent relapse and enable long-lasting remission. In this work, we performed multi-omics spatial analysis of the necrotic center (NEC), the gadolinium contrast-enhanced region (T1), and the infiltration zone (INF) to assess immunological relevant aspects of tumor heterogeneity. By integrating mass spectrometry-based immunopeptidome analysis with next generation sequencing methods (whole exome and RNA sequencing, DNA methylation), we aimed to identify the intra-tumoral regional heterogeneity of T cell antigens with a special focus on the peritumoral infiltration zone. For multi-omics analysis, HLA peptides and genetic material from 15 glioblastoma patients were extracted and analyzed from the three zones NEC, T1, INF and for four patients additionally from adjacent benign (BEN) brain tissue. A total of 24,699 unique HLA class I and 17,394 HLA class II peptides were identified. Comparative profiling of peptides from our study and a benign tissue database (in-house (n=429) combined with HLA ligand atlas (https://hla-ligand-atlas.org)) revealed that 6% (970/15,579), 5% (829/16,442) and 5% (725/13,891) of HLA class I peptides were exclusively presented in the INF, T1 and NEC zone, respectively. 6% (394/7,150), 7% (589/8,736) and 13% (1,725/12,908) of HLA class II peptides showed exclusive representation in the INF, T1 and NEC zone, respectively. Importantly, due to the spatial analysis of the immunopeptidome, we revealed 970 HLA class I and 394 HLA class II peptides exclusively presented in the INF zone. Interestingly, one INF-associated HLA class I peptide, which showed frequent presentation in 36% of glioblastoma immunopeptidomes, is derived from the brain and acute leukemia cytoplasmic protein (BAALC), a highly expressed cell cycle inducer (via MEK kinase-1) in several cancers, including glioblastoma. Integrated RNA/DNA sequencing enabled a greater understanding of spatial tumor antigen presentation and lead to the identification of INF-specific neoepitopes derived from tumor-specific mutations. In summary, we identified the intra-tumoral regional heterogeneity of tumor antigens, which could be used in the future for specific immunotherapy approaches targeting the infiltration zone of glioblastoma.

Citation Format: Marcel Wacker, Gioele Medici, Marissa Dubbelaar, Jens Bauer, Annika Nelde, Luca Regli, Michael Weller, Helmut R. Salih, Hans-Georg Rammensee, Marian C. Neidert, Juliane S. Walz. The intra-tumoral spatial heterogeneity of T-cell antigens in glioblastoma: An integrated multi-omics approach [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1375.

Abstract 2102: NFAT2 determines susceptibility of chronic lymphocytic leukemia cells to constitutive and Rituximab-induced NK cell killing

Genetic loss of the transcription factor NFAT2 (NFATc1), known as important player in lymphocyte development, causes an aggressive course of CLL, as it enhances BCR signaling and leads to highly malignant and proliferative disease (Märklin et al. Nat Commun 2017). To investigate whether and how NFAT2 affects treatment resistance in CLL, we generated a CRISPR/Cas9 based NFAT2 knockout (KO) in MEC-1 CLL cells to model aggressive CLL. In immunodeficient NSG-mice, the NFAT2 KO cells showed a ten-fold higher engraftment in the bone marrow after three weeks compared to scrambled (SCR) controls. Cytotoxicity assays revealed a profoundly higher resistance of NFAT2 KO cells to NK cell killing without detectable differences at the level of recognition as revealed by analyses of NK cell activation, degranulation and IFNy release, which excluded resistance to NK cells was due to altered immunogenicity. As CLL patients are routinely treated with anti-CD20 antibody Rituximab, which mediates its therapeutic efficacy in large part by inducing antibody dependent cellular cytotoxicity (ADCC) of NK cells via secretion of perforin and granzymes. When we exposed the target cells to the cytotoxic content isolated out of NK cells, MEC-1 NFAT2 KO cells showed higher resistance for membrane permeabilization compared to SCR controls. In line, perforin blockade equalized susceptibility to membrane permeabilization of both, NFAT2 KO cells and controls, confirming the involvement of NFAT2 in maintaining membrane integrity. In addition, caspase 3/7 activation was reduced in NFAT2 KO cells upon exposure to NK cell granule content as well as upon treatment with staurosporine. This shows an important role of NFAT2 for resistance of the leukemic cells at early stages of apoptosis. The results on the role of NFAT2 in resistance to NK effector function were confirmed with primary CLL patient cells, which were grouped according to high and low NFAT2 expression followed by treatment with NK cell content. Our results demonstrate that loss of NFAT2 allows CLLs cells to evade NK cell effector function. This holds true for both, constitutive cytotoxicity and therapeutically induced ADCC and is due to lowered susceptibility of the leukemic cells to perforin mediated membrane permeabilization and intrinsic resistance to granzyme induced apoptosis. Thus, NFAT2 loss, which correlates with aggressive clinical course in patients, facilitates resistance of CLL cells to CD20 antibody-based treatment.

Citation Format: Samuel J. Holzmayer, Sarah M. Greiner, Kuebra Kaban, Jonas S. Heitmann, Helmut R. Salih, Melanie Maerklin. NFAT2 determines susceptibility of chronic lymphocytic leukemia cells to constitutive and Rituximab-induced NK cell killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2102.

Abstract 2859: Platelet-derived TGFβ undermines treatment efficacy of t cell recruiting bispecific antibodies

Immunotherapeutic strategies such as T cell-recruiting bispecific antibodies (bsAb), chimeric antigen receptor (CAR) T cells, and immune checkpoint inhibition have revolutionized oncological treatment. However, many patients do not respond to treatment with the so far available therapeutics, others for limited time only. Various tumor immune evasion mechanisms have been reported to counteract efficiency of T cell engaging therapeutics. Thrombocytes have recently been described to affect cancer biology by mediating epithelial-mesenchymal transition, tumor invasion, metastasis and notably also immune evasion. Here we report that, upon treatment of prostate cancer patients within a clinical trial evaluating a novel PSMAxCD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. Upon modelling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4+ and CD8+ T cell reactivity as revealed by impaired T cell activation, reduced secretion of perforin and ultimately inhibition of target cell lysis. The immunosuppressive effect mediated by platelets occurred in a TGFβ-dependent manner and was not restricted to the PSMAxCD3 bsAb, but was also observed with various other CD3-directed bispecific constructs including the clinically approved CD19xCD13 bsAb Blinatumomab. BsAb-mediated T cell reactivity could generally be restored by inhibiting platelets using dabigatran, but also specifically by blocking the TGFβ axis. Together, our findings unravel that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function and TGFβ as means to reinforce the effectiveness of bsAb treatment.

Citation Format: Martina S. Lutz, Boris Klimovich, Stefanie Maurer, Jonas S. Heitmann, Melanie Maerklin, Latifa Zekri, Gundram Jung, Helmut R. Salih, Clemens Hinterleitner. Platelet-derived TGFβ undermines treatment efficacy of t cell recruiting bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2859.

Abstract 2860: A CD135 immunocytokine with target cell-restricted IL-15 activity for treatment of AML

After diagnosis, a primary goal of treatment in acute myeloid leukemia (AML) is to achieve a morphological complete remission (CR) by induction chemotherapy. However, about half of the patients in CR show remaining minimal residual disease (MRD), which constitutes the basis for relapse. With the aim to eradicate MRD and thus improve long-term survival in AML, we recently conducted a phase I trial evaluating safety/tolerability and preliminary efficacy of an Fc-optimized antibody targeting CD135/FLT3 (FLYSYN, NCT02789254) to induce NK cell anti-leukemia reactivity. This trial enrolling AML patients in CR with detectable MRD revealed that FLYSYN is safe and well tolerated, with about 45% of patients achieving a molecular response after treatment with the target dose (Heitmann et al., Blood 2020). Besides by reinforcing the ADCC-inducing capability of antibodies, NK cell immunity can be further increased by cytokines like IL-15, and multiple efforts presently aim to exploit the latter cytokine for cancer treatment. However, clinical efficacy of IL-15 so far is limited as systemic application causes substantial side effects due to unspecific immune activation (Conlon et al, JCO 2015). To overcome this limitation, we aimed to develop an immunocytokine consisting of our Fc-optimized CD135 mAb fused to IL-15. However, the activity of the cytokine moiety within classical ICs does not depend on antigen binding, and thus application of clinically effective doses is still prevented by toxicity due to unspecific immune activation. To overcome this problem, we took advantage of the unique mechanism of action of IL-15, which stimulates IL-15Rβ/γ on cytotoxic lymphocytes as membrane-bound complex with IL-15Rα on monocytes and DCs (trans-presentation) and generated an IL-15 mutant with abolished IL-15Rα binding. The latter allows to substitute physiological trans-presentation by binding of the construct to the target antigen, thereby limiting side effects. Functional analysis using primary AML cells as targets revealed that our modified immunocytokine (MIC135) induced target-restricted NK cell anti-leukemia reactivity in a profoundly greater extent than the Fc-optimized FLYSYN antibody. Notably, in stark contrast to FLYSYN, MIC135 induced prominent NK cell proliferation, and target cell killing upon treatment with MIC135 was likewise clearly superior. Analyses regarding off-target toxicity confirmed the target-antigen restricted efficacy of MIC135 compared to anti-CD135 immunocytokine with wildtype IL-15 (IC135). Furthermore, our MIC135 did not induce unwanted effects against healthy FLT3 expressing cells. Taken together, MIC135 induces NK cell reactivity against leukemia cells in a highly target cell-restricted manner and displays higher efficacy than Fc-optimized antibodies, thus constituting a promising treatment option for AML.

Citation Format: Martina S. Lutz, Bastian J. Schmied, Fabian Riegg, Latifa Zekri, Jonas S. Heitmann, Melanie Maerklin, Martin Pfluegler, Gundram Jung, Helmut R. Salih. A CD135 immunocytokine with target cell-restricted IL-15 activity for treatment of AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2860.

Abstract 2008: The oncogenic fusion protein DNAJB1-PRKACA can be actively targeted by peptide-based immunotherapy in fibrolamellar hepatocellular carcinoma

Fibrolamellar hepatocellular carcinoma (FL-HCC) is a rare tumor disease, which affects children and adolescents without history of primary liver disease. Beside surgical resection established treatment options are lacking for FL-HCC. Recently, the DNAJB1-PRKACA fusion transcript was identified as the oncogenic driver of tumor pathogenesis in 100% of FL-HCC patients. Here, we investigated the role of the DNAJB1-PRKACA fusion protein as a source for immunogenic neoepitopes and showed first immunotherapeutic application of these antigens in a FL-HCC patient.HLA class I- and class II-presented neoantigens derived from the DNAJB1-PRKACA fusion protein were predicted in silico using NetMHCpan 4.1 and SYFPEITHI 1.0, or NetMHCIIpan 4.0, respectively. With this workflow nine binding cores of nine amino acid length for a total of 1290 different HLA class II alleles, as well as 13 HLA class I ligands for the 20 most frequent HLA class I allotypes (European population, iedb.org) were identified. Cellular processing and HLA presentation of DNAJB1-PRKACA-derived peptides was proven by liquid chromatography-coupled tandem mass spectrometry (LC-MS/MS) of DNAJB1-PRKACA-transduced HCC cell lines. Immunogenicity of DNAJB1-PRKACA-derived peptides was assessed for the HLA class II peptide (PII-1) and the HLA-A*24 peptide (PA*24) by in vitro priming experiments which showed an induction of multifunctional peptide-specific CD4+ and CD8+ T cells, respectively, with expression of CD107a, IFNγ, and TNF upon peptide-pulsing. Furthermore, PA*24-specific T cells showed antigen-specific lysis of autologous peptide-loaded target cells and single-cell next-generation sequencing (10x Genomics) of PA*24-specific CD8+ T cells further enabled the identification of DNAJB1-PRKACA-reactive T cell receptors. Based on these preclinical data we applied a peptide vaccine, consisting of three HLA class I ligands (PA*02, PB*44, and PC*05) and PII-1 spanning the DNAJB1-PRKACA fusion region, to a 15-year old patient with histologically confirmed FL-HCC, who experienced multiple tumor relapses after early liver transplant due to unresectable FL-HCC not responsive to chemotherapy. After two vaccinations in vivo induction of multifunctional CD4+ T cells targeting PII-1 and PB*44 was observed by IFNγ ELISPOT. Single-cell RNA sequencing of vaccine-induced CD4+ T cells revealed distinct gene expression clusters of T cell activation and high TCR clonality. DNAJB1-PRKACA-specific T cells persisted in peripheral blood and were accompanied by relapse free survival of the patient until now, more than one year post vaccination. These findings identified the DNAJB1-PRKACA fusion transcript as novel prime source for broadly applicable neoepitopes and corresponding TCRs and provide first evidence for their application in cancer immunotherapy of FL-HCC.

Citation Format: Jens Bauer, Natalie Köhler, Yacine Maringer, Philip Bucher, Tatjana Bilich, Melissa Zwick, Severin Dicks, Annika Nelde, Marissa Dubbelaar, Jonas Scheid, Marcel Wacker, Jonas J. Heitmann, Sarah Schroeder, Jonas Rieth, Monika Denk, Marion Richter, Reinhild Klein, Irina Bonzheim, Julia Luibrand, Ursula Holzer, Martin Ebinger, Ines B. Brecht, Michael Bitzer, Melanie Boerries, Helmut R. Salih, Hans-Georg Rammensee, Stephan Hailfinger, Juliane S. Walz. The oncogenic fusion protein DNAJB1-PRKACA can be actively targeted by peptide-based immunotherapy in fibrolamellar hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2008.

BCR::ABL1 tyrosine kinase inhibitors hamper the therapeutic efficacy of blinatumomab in vitro

PURPOSE

Acute B-lymphoblastic leukemia (B-ALL) is a malignant disease characterized by accumulation of clonal immature lymphocytes in the bone marrow and peripheral blood. The approval of BCR::ABL1 tyrosine kinase inhibitors (TKI) such as imatinib, dasatinib, nilotinib and ponatinib marked a milestone in targeted therapy only for a subset of patients carrying the translocation t(9;22)(q34;q11). Immunotherapy with the bispecific antibody (bsAb) blinatumomab targeting CD19xCD3 revolutionized treatment of all B-ALL cases. The combination of both TKI and bsAb, so-called "dual targeting", is currently under clinical investigation, although TKI might influence T cell effects.

METHODS

We here investigated the combination of different TKI and blinatumomab in BCR::ABL1⁺ and BCR::ABL1^- B-ALL cell lines and primary samples regarding T cell proliferation, differentiation, cytokine release and killing of tumor cells.

RESULTS

In vitro analysis revealed profound reduction of T cell proliferation, differentiation, cytokine release and killing of tumor cells upon application of BCR::ABL1 TKI with blinatumomab. Inhibition was more pronounced with dasatinib and ponatinib compared to nilotinib and imatinib. T cell signalling after CD3 stimulation was impaired by TKI mirrored by inhibition of LCK phosphorylation. This known off-target effect might influence the efficacy of bsAb therapy when combined with BCR::ABL1 TKI.

CONCLUSION

In conclusion, we propose that nilotinib and imatinib might also be suitable substances for combination with blinatumomab and suggest evaluation in clinical trials.

Prevalence of COVID-19-associated symptoms during acute infection in relation to SARS-CoV-2-directed humoral and cellular immune responses in a mild-diseased convalescent cohort

Objectives

Besides SARS-CoV-2-directed humoral immune responses, T cell responses are indispensable for effective antiviral immunity. Recent data have shown a correlation between COVID-19 symptoms and humoral immune response, but so far, little is known about the association of SARS-CoV-2-directed T cell responses and disease severity. Herein, we evaluated the prevalence of different clinical COVID-19 symptoms in relation to SARS-CoV-2-directed humoral and cellular immune responses.

Methods

The severity of eight different symptoms during acute infection were assessed using questionnaires from 193 convalescent individuals and were evaluated in relation to SARS-CoV-2 antibody levels and intensity of SARS-CoV-2-specific T cell responses 2–8 weeks after positive polymerase chain reaction.

Results

Although increased IgG serum levels could be associated with severity of most symptoms, no difference in T cell response intensity between different symptom severities was observed for the majority of COVID-19 symptoms. However, when analyzing loss of smell or taste and cough, awareness of more severe symptoms was associated with reduced T cell response intensities.

Conclusions

These data suggest that rapid virus clearance mediated by SARS-CoV-2-specific T cells prevents severe symptoms of COVID-19.

A novel IgG-based FLT3xCD3 bispecific antibody for the treatment of AML and B-ALL

BACKGROUND

In lymphoid malignancies, the introduction of chimeric antigen receptor T (CAR-T) cells and bispecific antibodies (bsAbs) has achieved remarkable clinical success. However, such immunotherapeutic strategies are not yet established for acute myeloid leukemia (AML), the most common form of acute leukemia in adults. Common targets in AML such as CD33, CD123, and CLEC12A are highly expressed on both AML blasts and on normal myeloid cells and hematopoietic stem cells (HSCs), thereby raising toxicity concerns. In B-cell acute lymphoblastic leukemia (B-ALL), bsAbs and CAR-T therapy targeting CD19 and CD22 have demonstrated clinical success, but resistance via antigen loss is common, motivating the development of agents focused on alternative targets. An attractive emerging target is FLT3, a proto-oncogene expressed in both AML and B-ALL, with low and limited expression on myeloid dendritic cells and HSCs.

METHODS

We developed and characterized CLN-049, a T cell-activating bsAb targeting CD3 and FLT3, constructed as an IgG heavy chain/scFv fusion. CLN-049 binds the membrane proximal extracellular domain of the FLT3 protein tyrosine kinase, which facilitates the targeting of leukemic blasts regardless of FLT3 mutational status. CLN-049 was evaluated for preclinical safety and efficacy in vitro and in vivo.

RESULTS

CLN-049 induced target-restricted activation of CD4+ and CD8+ T cells. AML cell lines expressing a broad range of surface levels of FLT3 were efficiently lysed on treatment with subnanomolar concentrations of CLN-049, whereas FLT3-expressing hematopoietic progenitor cells and dendritic cells were not sensitive to CLN-049 killing. Treatment with CLN-049 also induced lysis of AML and B-ALL patient blasts by autologous T cells at the low effector-to-target ratios typically observed in patients with overt disease. Lysis of leukemic cells was not affected by supraphysiological levels of soluble FLT3 or FLT3 ligand. In mouse xenograft models, CLN-049 was highly active against human leukemic cell lines and patient-derived AML and B-ALL blasts.

CONCLUSIONS

CLN-049 has a favorable efficacy and safety profile in preclinical models, warranting evaluation of its antileukemic activity in the clinic.

Platelets subvert antitumor efficacy of T cell-recruiting bispecific antibodies

T cell-based immunotherapy, for example, with T cell-recruiting bispecific antibody (bsAb), has revolutionized oncological treatment. However, many patients do not respond to treatment, and long-term remissions are still rare. Several tumor immune evasion mechanisms have been reported to counteract efficiency of T cell-engaging therapeutics. Platelets largely affect cancer pathophysiology by mediating tumor invasion, metastasis, and immune evasion. On treatment of patients in a clinical trial with a PSMA×CD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. On modeling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4⁺ and CD8⁺ T-cell reactivity as revealed by impaired T-cell degranulation, secretion of perforin, and ultimately, inhibition of target cell lysis. This effect occurred in a transforming growth factor beta (TGF-β)-dependent manner and was not restricted to PSMA×CD3 bsAb, but rather observed with various CD3-directed bispecific constructs, including the approved CD19×CD3 bsAb blinatumomab. BsAb-mediated T-cell reactivity could be restored by platelet inhibition and specifically by blocking the TGF-β axis. Together, our findings demonstrate that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function as a means to reinforce the effectiveness of bsAb treatment.

Identification of CD105 (endoglin) as novel risk marker in CLL

Several genetic and clinical markers are established as prognostic factors in chronic lymphocytic leukemia (CLL). However, additional markers are needed for risk stratification. Flow cytometric analysis is a mainstay of CLL diagnostics, thus identification of novel prognostic surface markers can improve risk assessment without increasing burden for patients and physicians. Furthermore, surface molecules preferentially expressed in high-risk cases could serve as therapeutic targets for immunotherapy. CD105 (endoglin) is a TGF-beta coreceptor and activates endothelial cells in healthy tissues and cancer. In addition, it is expressed on healthy hematopoietic precursors as well as lymphoid and myeloid leukemias. In acute myeloid leukemia (AML), a CD105 antibody is successfully applied in clinical studies. In CLL, mRNA expression of the CD105 gene ENG reportedly correlates with other risk factors but failed to show significant correlation with overall survival. However, CD105 protein expression in CLL has never been studied. We here analyzed CD105 surface expression on CLL cells from 71 patients by flow cytometry and report for the first time that substantial levels of CD105 are detectable on CLL cells in 70.4% of patients. Using receiver operating characteristics, we established a cutoff of 5.99% positive cells to distinguish between low and high CD105 levels, the latter correlating with decreased time to first treatment and overall survival. High CD105 expression further correlates with CD38 expression. Our study identified membrane expression of CD105 as a potential risk marker and therapeutic target in high-risk CLL. However, multivariant analyses of large cohorts should be performed in confirmatory studies.

Receptor Activator of NF-κB (RANK) Confers Resistance to Chemotherapy in AML and Associates with Dismal Disease Course

Simple Summary

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Despite the emergence of new therapeutic agents in recent years, curation remains challenging, and new and better treatment options are needed. In the present study, we investigated the expression, prognostic significance, and functional role of the Receptor Activator of Nuclear Factor-κB (RANK) in AML. We found that RANK is expressed on leukemic cells in a substantial proportion of AML patients and is associated with a dismal disease course. We further demonstrated that signaling via RANK induces release of factors that favor AML cell survival and confers resistance to chemotherapeutics in AML treatment. Together, our findings identify RANK as novel prognostic marker and putative candidate for therapeutic intervention in AML to enhance response to treatment.

Abstract

Although treatment options of acute myeloid leukemia (AML) have improved over the recent years, prognosis remains poor. Better understanding of the molecular mechanisms influencing and predicting treatment efficacy may improve disease control and outcome. Here we studied the expression, prognostic relevance and functional role of the tumor necrosis factor receptor (TNFR) family member Receptor Activator of Nuclear Factor (NF)-κB (RANK) in AML. We conducted an experimental ex vivo study using leukemic cells of 54 AML patients. Substantial surface expression of RANK was detected on primary AML cells in 35% of the analyzed patients. We further found that RANK signaling induced the release of cytokines acting as growth and survival factors for the leukemic cells and mediated resistance of AML cells to treatment with doxorubicin and cytarabine, the most commonly used cytostatic compounds in AML treatment. In line, RANK expression correlated with a dismal disease course as revealed by reduced overall survival. Together, our results show that RANK plays a yet unrecognized role in AML pathophysiology and resistance to treatment, and identify RANK as “functional” prognostic marker in AML. Therapeutic modulation of RANK holds promise to improve treatment response in AML patients.

CD18 Antibody Application Blocks Unwanted Off-Target T Cell Activation Caused by Bispecific Antibodies

Simple Summary

Bispecific antibodies are a very effective immunotherapy against different types of cancer since they activate T cells in the presence of tumor cells. However, they can cause severe side effects, such as a systemic inflammation called cytokine release syndrome. We aimed to clarify an important mechanism that causes cytokine release syndrome. In cocultures of T cells with endothelial cells or lymphoid cells, application of bispecific antibodies can induce T cell activation and cytokine release in the absence of tumor cells. By blocking the adhesion molecule CD18, this interaction is interrupted and the unwanted T cell activation is diminished. CD18 blockade, however, does not interfere with T cell activation when tumor cells are present. Therefore, CD18 blockade could prevent side effects of bispecific antibodies without decreasing the anti-tumor effect.

Abstract

T cell-recruiting bispecific antibodies (bsAbs) are successfully used for the treatment of cancer. However, effective treatment with bsAbs is so far hampered by severe side effects, i.e., potentially life-threatening cytokine release syndrome. Off-target T cell activation due to binding of bispecific CD3 antibodies to T cells in the absence of target cells may contribute to excessive cytokine release. We report here, in an in vitro setting, that off-target T cell activation is induced by bsAbs with high CD3 binding affinity and increased by endothelial- or lymphoid cells that act as stimulating bystander cells. Blocking antibodies directed against the adhesion molecules CD18/CD54 or CD2/CD58 markedly reduced this type of off-target T cell activation. CD18 blockade—in contrast to CD2—did not affect the therapeutic activity of various bsAbs. Since CD18 antibodies have been shown to be safely applicable in patients, blockade of this integrin holds promise as a potential target for the prevention of unwanted off-target T cell activation and allows the application of truly effective bsAb doses.

DNAM-1/CD226 is functionally expressed on acute myeloid leukemia (AML) cells and is associated with favorable prognosis

DNAM-1 is reportedly expressed on cytotoxic T and NK cells and, upon interaction with its ligands CD112 and CD155, plays an important role in tumor immunosurveillance. It has also been reported to be functionally expressed by myeloid cells, but expression and function on malignant cells of the myeloid lineage have not been studied so far. Here we analyzed expression of DNAM-1 in leukemic cells of acute myeloid leukemia (AML) patients. We found substantial levels of DNAM-1 to be expressed on leukemic blasts in 48 of 62 (> 75%) patients. Interaction of DNAM-1 with its ligands CD112 and CD155 induced release of the immunomodulatory cytokines IL-6, IL-8 IL-10 and TNF-α by AML cells and DNAM-1 expression correlated with a more differentiated phenotype. Multivariate analysis did not show any association of DNAM-1 positivity with established risk factors, but expression was significantly associated with clinical disease course: patients with high DNAM-1 surface levels had significantly longer progression-free and overall survival compared to DNAM-1^low patients, independently whether patients had undergone allogenic stem cell transplantation or not. Together, our findings unravel a functional role of DNAM-1 in AML pathophysiology and identify DNAM-1 as a potential novel prognostic maker in AML.

Tocilizumab, but not dexamethasone, prevents CRS without affecting antitumor activity of bispecific antibodies

Bispecific antibodies (bsAb) and chimeric antigen receptor (CAR) T cells allow for antibody guided recruitment of T cells against tumors. Both are successfully used for treatment of CD19 expressing leukemias, but may cause cytokine release syndrome (CRS) as a major dose-limiting side effect. For CRS prevention, steroids are recommended prior to bsAb treatment, despite their well-known lymphotoxic activity. The IL-6 receptor antibody tocilizumab is established for treatment of CRS induced by CAR T cells, but was not considered for CRS prevention in bsAb therapy. We here compared the influence of dexamethasone and tocilizumab on bsAb-mediated T cell proliferation and tumor lysis in vitro and in vivo and found that dexamethasone profoundly inhibited T cell proliferation and antitumor activity as induced by two different bsAb, particularly at low effector:target ratios, whereas tocilizumab did not affect efficacy. When we applied tocilizumab early during treatment of three patients with a newly developed PSMAxCD3 bsAb, significant CRS attenuation despite high IL-6 serum levels was observed. Thus, early IL-6 blockade may reduce the undesired sequelae of CRS upon bsAb therapy without affecting therapeutic activity, allowing in turn for safe application of effective doses.

Immunopeptidomics-Guided Warehouse Design for Peptide-Based Immunotherapy in Chronic Lymphocytic Leukemia

Antigen-specific immunotherapies, in particular peptide vaccines, depend on the recognition of naturally presented antigens derived from mutated and unmutated gene products on human leukocyte antigens, and represent a promising low-side-effect concept for cancer treatment. So far, the broad application of peptide vaccines in cancer patients is hampered by challenges of time- and cost-intensive personalized vaccine design, and the lack of neoepitopes from tumor-specific mutations, especially in low-mutational burden malignancies. In this study, we developed an immunopeptidome-guided workflow for the design of tumor-associated off-the-shelf peptide warehouses for broadly applicable personalized therapeutics. Comparative mass spectrometry-based immunopeptidome analyses of primary chronic lymphocytic leukemia (CLL) samples, as representative example of low-mutational burden tumor entities, and a dataset of benign tissue samples enabled the identification of high-frequent non-mutated CLL-associated antigens. These antigens were further shown to be recognized by pre-existing and de novo induced T cells in CLL patients and healthy volunteers, and were evaluated as pre-manufactured warehouse for the construction of personalized multi-peptide vaccines in a first clinical trial for CLL (NCT04688385). This workflow for the design of peptide warehouses is easily transferable to other tumor entities and can provide the foundation for the development of broad personalized T cell-based immunotherapy approaches.

Regulation of Platelet-Derived ADAM17: A Biomarker Approach for Breast Cancer?

Tumor progression and metastasis are critically dependent on the tumor microenvironment. A disintegrin and metalloproteinase 17 (ADAM17) is associated with shedding of several substrates involved in tumor progression and known to be expressed by platelets of healthy donors and patients with solid tumors. Here, we report that platelet-derived ADAM17 (pADAM17) is regulated upon platelet activation of breast cancer patients, but not of healthy individuals. The observed downregulation of pADAM17 on platelets of cancer patients correlated with clinical parameters related to tumor progression including tumor stage and the occurrence of metastasis. Our data identify an association between platelet activation, modulation of platelet-derived ADAM17, and metastasis. In conclusion, we demonstrate that further development of pADAM17 as a liquid biomarker is warranted for monitoring disease progression in breast cancer.

Preexisting and Post-COVID-19 Immune Responses to SARS-CoV-2 in Patients with Cancer

Patients with cancer, in particular patients with hematologic malignancies, are at increased risk for critical illness upon COVID-19. We here assessed antibody as well as CD4⁺ and CD8⁺ T-cell responses in unexposed and SARS-CoV-2-infected patients with cancer to characterize SARS-CoV-2 immunity and to identify immunologic parameters contributing to COVID-19 outcome. Unexposed patients with hematologic malignancies presented with reduced prevalence of preexisting SARS-CoV-2 cross-reactive CD4⁺ T-cell responses and signs of T-cell exhaustion compared with patients with solid tumors and healthy volunteers. Whereas SARS-CoV-2 antibody responses did not differ between patients with COVID-19 and cancer and healthy volunteers, intensity, expandability, and diversity of SARS-CoV-2 T-cell responses were profoundly reduced in patients with cancer, and the latter associated with a severe course of COVID-19. This identifies impaired SARS-CoV-2 T-cell immunity as a potential determinant for dismal outcome of COVID-19 in patients with cancer. SIGNIFICANCE: This first comprehensive analysis of SARS-CoV-2 immune responses in patients with cancer reports on the potential implications of impaired SARS-CoV-2 T-cell responses for understanding pathophysiology and predicting severity of COVID-19, which in turn might allow for the development of therapeutic measures and vaccines for this vulnerable patient population.See related commentary by Salomé and Horowitz, p. 1877.This article is highlighted in the In This Issue feature, p. 1861.

T cell and antibody kinetics delineate SARS-CoV-2 peptides mediating long-term immune responses in COVID-19 convalescent individuals

Long-term immunological memory to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial for the development of population-level immunity, which is the aim of vaccination approaches. Reports on rapidly decreasing antibody titers have led to questions regarding the efficacy of humoral immunity alone. The relevance of T cell memory after coronavirus disease 2019 (COVID-19) remains unclear. Here, we investigated SARS-CoV-2 antibody and T cell responses in matched samples of COVID-19 convalescent individuals up to 6 months after infection. Longitudinal analysis revealed decreasing and stable spike- and nucleocapsid-specific antibody responses, respectively. In contrast, functional T cell responses remained robust, and even increased, in both frequency and intensity. Single peptide mapping of T cell diversity over time identified open reading frame-independent, dominant T cell epitopes mediating long-term SARS-CoV-2 T cell responses. Identification of these epitopes may be fundamental for COVID-19 vaccine design.

Bispecific NKG2D-CD3 and NKG2D-CD16 Fusion Proteins as Novel Treatment Option in Advanced Soft Tissue Sarcomas

Soft tissue sarcoma (STS) constitutes a rare group of heterogeneous malignancies. Effective treatment options for most subtypes of STS are still limited. As a result, especially in metastatic disease, prognosis is still dismal. The ligands for the activating immunoreceptor NKG2D (NKG2DL) are commonly expressed in STS, but generally absent in healthy tissues. This provides the rationale for utilization of NKG2DL as targets for immunotherapeutic approaches. We here report on the preclinical characterization of bispecific fusion proteins (BFP) consisting of the extracellular domain of the NKG2D receptor fused to Fab-fragments directed against CD3 (NKG2D-CD3) or CD16 (NKG2D-CD16) for treatment of STS. After characterization of NKG2DL expression patterns on various STS cell lines, we demonstrated that both NKG2D-CD16 and NKG2D-CD3 induce profound T and NK cell reactivity as revealed by analysis of activation, degranulation and secretion of IFNγ as well as granule associated proteins, resulting in potent target cell lysis. In addition, the stimulatory capacity of the constructs to induce T and NK cell activation was analyzed in heavily pretreated STS patients and found to be comparable to healthy donors. Our results emphasize the potential of NKG2D-CD3 and NKG2D-CD16 BFP to target STS even in an advanced disease.