Hu8F4-CAR T cells with mutated Fc spacer segment improve target-specificity and mediate anti-leukemia activity in vivo

Hu8F4 is a T cell receptor (TCR)-like antibody with high affinity for leukemia-associated antigen PR1/HLA-A2 epitope. Adapted into a chimeric antigen receptor (CAR) format, Hu8F4-CAR is comprised of the Hu8F4 scFv, the human IgG1 CH2CH3 extracellular spacer domain, a human CD28 costimulatory domain, and the human CD3ζ signaling domain. We have demonstrated high efficacy of Hu8F4-CAR-T cells against PR1/HLA-A2-expressing cell lines and leukemic blasts from AML patients in vitro. Previous studies have shown that modification of the Fc domains of IgG4 CH2CH3 spacer regions can eliminate activation-induced cell death and off-target killing mediated by mouse Fc gamma receptor (FcgR)-expressing cells. We generated Hu8F4-CAR(PQ) with mutated Fc receptor binding sites on the CH2 domain of Hu8F4-CAR to prevent unwanted interactions with FcgR-expressing cells in vivo. The primary human T cells transduced with Hu8F4-CAR(PQ) can specifically lyse HLA-A2+ PR1-expressing leukemia cell lines in vitro. Furthermore, both adult donor-derived and cord blood-derived Hu8F4-CAR(PQ)-T cells are active and can eliminate U937 leukemia cells in NSG mice. Herein, we demonstrate that modification of the IgG1-based spacer can eliminate Fc receptor-binding-induced adverse effects and Hu8F4-CAR(PQ)-T cells can kill leukemia in vivo.

Novel myeloperoxidase-derived HLA-A2-restricted peptides as therapeutic targets against myeloid leukemia

BACKGROUND AIMS

Human myeloperoxidase has been shown to be overexpressed in many types of leukemia, such as chronic myeloid leukemia, acute myeloid leukemia and myelodysplastic syndrome. The authors identified two myeloperoxidase-derived HLA-A2-restricted peptides, MY4 and MY8, as novel leukemia-associated antigens.

METHODS

Ex vivo-elicited MY4- and MY8-specific cytotoxic T lymphocytes were generated, and tested for leukemia cell lysis in vitro and in NOD/SCID AML xenograft model.

RESULTS

These MY4- and MY8-specific cytotoxic T lymphocytes killed leukemic blasts while sparing healthy donor bone marrow cells. In addition, co-injection of MY4- and MY8-specific cytotoxic T lymphocytes into nonobese diabetic/severe combined immunodeficiency mice with acute myeloid leukemia drastically reduced tumor burden in vivo. The authors also found that MY4- and MY8-specific T cells could be detected in the peripheral blood mononuclear cells of allogeneic stem cell transplant recipients.

CONCLUSIONS

These antigen-specific T cells were significantly increased in blood samples from patients compared with healthy donors, suggesting that both MY4 and MY8 are immunogenic and that MY4- and MY8-specific cytotoxic T lymphocytes may play a role in reducing leukemia in vivo. Thus, the discovery of MY4 and MY8 as novel leukemia-associated antigens paves the way for targeting these antigens in immunotherapy against myeloid leukemia.

Two unique HLA-A*0201 restricted peptides derived from cyclin E as immunotherapeutic targets in leukemia

Immunotherapy targeting leukemia-associated antigens has shown promising results. Because of the heterogeneity of leukemia, vaccines with a single peptide have elicited only a limited immune response. Targeting several peptides together elicited peptide-specific cytotoxic T lymphocytes (CTLs) in leukemia patients, and this was associated with clinical responses. Thus, the discovery of novel antigens is essential. In the current study, we investigated cyclin E as a novel target for immunotherapy. Cyclin E1 and cyclin E2 were found to be highly expressed in hematologic malignancies, according to reverse transcription polymerase chain reaction and western blot analysis. We identified two HLA-A*0201 binding nonameric peptides, CCNE1M from cyclin E1 and CCNE2L from cyclin E2, which both elicited the peptide-specific CTLs. The peptide-specific CTLs specifically kill leukemia cells. Furthermore, CCNE1M and CCNE2L CTLs were increased in leukemia patients who underwent allogeneic hematopoietic stem cell transplantation, and this was associated with desired clinical outcomes. Our findings suggest that cyclin E1 and cyclin E2 are potential targets for immunotherapy in leukemia.

A Novel T-Cell Engaging Bi-specific Antibody Targeting the Leukemia Antigen PR1/HLA-A2

Despite substantial advances in the treatment of acute myeloid leukemia (AML), only 30% of patients survive more than 5 years. Therefore, new therapeutics are much needed. Here, we present a novel therapeutic strategy targeting PR1, an HLA-A2 restricted myeloid leukemia antigen. Previously, we have developed and characterized a novel T-cell receptor-like monoclonal antibody (8F4) that targets PR1/HLA-A2 and eliminates AML xenografts by antibody-dependent cellular cytotoxicity (ADCC). To improve the potency of 8F4, we adopted a strategy to link T-cell cytotoxicity with a bi-specific T-cell-engaging antibody that binds PR1/HLA-A2 on leukemia and CD3 on neighboring T-cells. The 8F4 bi-specific antibody maintained high affinity and specific binding to PR1/HLA-A2 comparable to parent 8F4 antibody, shown by flow cytometry and Bio-Layer Interferometry. In addition, 8F4 bi-specific antibody activated donor T-cells in the presence of HLA-A2⁺ primary AML blasts and cell lines in a dose dependent manner. Importantly, activated T-cells lysed HLA-A2⁺ primary AML blasts and cell lines after addition of 8F4 bi-specific antibody. In conclusion, our studies demonstrate the therapeutic potential of a novel bi-specific antibody targeting the PR1/HLA-A2 leukemia-associated antigen, justifying further clinical development of this strategy.

Decreases in thymopoiesis of astronauts returning from space flight

Following the advent of molecular assays that measure T cell receptor excision circles (TRECs) present in recent thymic emigrants, it has been conclusively shown that thymopoiesis persists in most adults, but that functional output decreases with age, influencing the maintenance of a diverse and functional T cell receptor (TCR) repertoire. Space flight has been shown to result in a variety of phenotypic and functional changes in human T cells and in the reactivation of latent viruses. While space flight has been shown to influence thymic architecture in rodents, thymopoiesis has not previously been assessed in astronauts. Here, we assessed thymopoiesis longitudinally over a 1-year period prior to and after long-term space flight (median duration, 184 days) in 16 astronauts. While preflight assessments of thymopoiesis remained quite stable in individual astronauts, we detected significant suppression of thymopoiesis in all subjects upon return from space flight. We also found significant increases in urine and plasma levels of endogenous glucocorticoids coincident with the suppression of thymopoiesis. The glucocorticoid induction and thymopoiesis suppression were transient, and they normalized shortly after return to Earth. This is the first report to our knowledge to prospectively demonstrate a significant change in thymopoiesis in healthy individuals in association with a defined physiologic emotional and physical stress event. These results suggest that suppression of thymopoiesis has the potential to influence the maintenance of the TCR repertoire during extended space travel. Further studies of thymopoiesis and endogenous glucocorticoids in other stress states, including illness, are warranted.

A novel TCR-like CAR with specificity for PR1/HLA-A2 effectively targets myeloid leukemia in vitro when expressed in human adult peripheral blood and cord blood T cells

BACKGROUND AIMS

The PR1 peptide, derived from the leukemia-associated antigens proteinase 3 and neutrophil elastase, is overexpressed on HLA-A2 in acute myeloid leukemia (AML). We developed a T-cell receptor (TCR)-like monoclonal antibody (8F4) that binds the PR1/HLA-A2 complex on the surface of AML cells, efficiently killing them in vitro and eliminating them in preclinical models. Humanized 8F4 (h8F4) with high affinity for the PR1/HLA-A2 epitope was used to construct an h8F4- chimeric antigen receptor (CAR) that was transduced into T cells to mediate anti-leukemia activity.

METHODS

Human T cells were transduced to express the PR1/HLA-A2-specific CAR (h8F4-CAR-T cells) containing the scFv of h8F4 fused to the intracellular signaling endo-domain of CD3 zeta chain through the transmembrane and intracellular costimulatory domain of CD28.

RESULTS

Adult human normal peripheral blood (PB) T cells were efficiently transduced with the h8F4-CAR construct and predominantly displayed an effector memory phenotype with a minor population (12%) of central memory cells in vitro. Umbilical cord blood (UCB) T cells could also be efficiently transduced with the h8F4-CAR. The PB and UCB-derived h8F4-CAR-T cells specifically recognized the PR1/HLA-A2 complex and were capable of killing leukemia cell lines and primary AML blasts in an HLA-A2-dependent manner.

CONCLUSIONS

Human adult PB and UCB-derived T cells expressing a CAR derived from the TCR-like 8F4 antibody rapidly and efficiently kill AML in vitro. Our data could lead to a new treatment paradigm for AML in which targeting leukemia stem cells could transfer long-term immunity to protect against relapse.

Abstract LB-222: Long-term subclonal evolution of CLL from immune selective pressure after allogeneic stem cell transplant and donor lymphocyte infusion

Next-generation sequencing (NGS) has revealed that the malignant subclones comprising a patient's cancer can possess tremendous genetic heterogeneity at different sites of disease and over time. In leukemia, chemotherapy can hasten subclonal evolution allowing for rare leukemic subclones with aggressive driver mutations to gain a competitive advantage and to predominate at relapse, often portending an inferior treatment response. The impact of immunotherapy on subclonal evolution is less well studied. To determine the effects of allogeneic stem cell transplant (alloSCT) and donor lymphocyte infusion (DLI) on subclonal evolution, we performed whole exome sequencing (WES) on longitudinal peripheral blood and bone marrow from 4 patients with CLL. Specifically, timepoints analyzed included pre-transplant, post-transplant relapse, and post-DLI relapse over a period of up to 8.5 years. B-CLL cells (CD19+CD5+) and normal T cells (CD3+) were sort-purified by fluorescence-activated cell sorting prior to genomic DNA extraction. Libraries for WES were constructed and sequenced to an average depth of 300x on an Illumina HiSeq 2000 using 76 bp paired-end reads. Somatic single nucleotide variants (sSNVs) and indels were called using MuTect and Pindel, respectively, and copy number changes were assessed using an in-house algorithm. In general, these patients had more nonsynonymous mutations per pre-alloSCT sample than reported in other CLL NGS studies (average 30.3; range 8-45), likely related to the significant amount of pre-transplant therapies. Heterogeneous patterns of linear and branched subclonal evolution were seen after alloSCT and DLI in both responders and non-responders. Mutations in several candidate CLL driver genes were seen in this cohort, including SF3B1, SAMHD1, BCOR, EGR2, TP53, and DDX3X. Interestingly, sSNVs in multiple recurrently mutated CLL or cancer census genes (e.g. MAP2K1) rose to levels of detection only after alloSCT or DLI, suggesting they may play a role in immune evasion. In addition, several subclonal genetic variants, including missense mutations in FAM126B and LTBP3, were no longer detected after alloSCT or DLI and may thus represent potential neoantigens. In one treatment-refractory patient, a somatic nonsynonymous clonal CHEK2 mutation was found in 8 longitudinal samples and may represent a novel unique driver mutation. Finally, in one patient who experienced a durable complete remission after DLI, concurrent CLL WES and T-cell receptor beta chain CDR3 NGS was performed, which demonstrated a rapidly evolving T-cell repertoire at the time of complete remission after DLI. For CLL, alloSCT and DLI offer a potentially curative treatment strategy and a better understanding of the genes that confer susceptibility or resistance to these immunotherapies may help unlock the mechanisms that underlie these durable responses.

Citation Format: Haven R. Garber, Hannah Beird, Yu Cao, Jianhua Zhang, Rachel Sargent, Pei Lin, Sahil Seth, Xingzhi Song, Huandong Sun, Xizeng Mao, Lisa St John, Karen Clise-Dwyer, Gheath Alatrash, P. Andrew Futreal, Jeffrey J. Molldrem. Long-term subclonal evolution of CLL from immune selective pressure after allogeneic stem cell transplant and donor lymphocyte infusion. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-222. doi:10.1158/1538-7445.AM2015-LB-222

Common minor histocompatibility antigen discovery based upon patient clinical outcomes and genomic data

Background

Minor histocompatibility antigens (mHA) mediate much of the graft vs. leukemia (GvL) effect and graft vs. host disease (GvHD) in patients who undergo allogeneic stem cell transplantation (SCT) [1], [2], [3], [4]. Therapeutic decision making and treatments [5] based upon mHAs will require the evaluation of multiple candidate mHAs and the selection of those with the potential to have the greatest impact on clinical outcomes. We hypothesized that common, immunodominant mHAs, which are presented by HLA-A, B, and C molecules, can mediate clinically significant GvL and/or GvHD, and that these mHAs can be identified through association of genomic data with clinical outcomes.

Methodology/Principal Findings

Because most mHAs result from donor/recipient cSNP disparities, we genotyped 57 myeloid leukemia patients and their donors at 13,917 cSNPs [6]. We correlated the frequency of genetically predicted mHA disparities with clinical evidence of an immune response and then computationally screened all peptides mapping to the highly associated cSNPs for their ability to bind to HLA molecules. As proof-of-concept, we analyzed one predicted antigen, T4A, whose mHA mismatch trended towards improved overall and disease free survival in our cohort. T4A mHA mismatches occurred at the maximum theoretical frequency for any given SCT. T4A-specific CD8+ T lymphocytes (CTLs) were detected in 3 of 4 evaluable post-transplant patients predicted to have a T4A mismatch.

Conclusions/Significance

Our method is the first to combine clinical outcomes data with genomics and bioinformatics methods to predict and confirm a mHA. Refinement of this method should enable the discovery of clinically relevant mHAs in the majority of transplant patients and possibly lead to novel immunotherapeutics [5].

Head and neck squamous cell growth suppression using adenovirus-p53-FLAG: a potential marker for gene therapy trials

The recombinant wild-type p53 adenovirus has been proven effective against the growth of human head and neck squamous cell cancer (SCCHN) cell lines iir vitro and in a nude mouse model. The addition of a FLAG peptide sequence was used in this study, along with the p53 adenovirus vector as a marker of the site of the gene therapy activity. It provides clear evidence of the exogenous gene product within the transduced carcinoma cells. No alterations in transcription or translation of the p53 gene product were noted with the addition of the FLAG sequence to the original p53 adenovirus vector. Immunohistochemical analysis displayed simultaneous expression of the p53 and FLAG proteins in the infected cells. The p53 protein remained localized to the nucleus, whereas the FLAG protein was additionally noted in the cytoplasm. In vitro growth suppression assays and in vivo microscopic residual tumor model experiments in nude mice showed a similar tumoricidal effect with the p53-FLAG adenovirus vector to that with the previously studied p53 adenovirus vector without the addition of the FLAG sequence. We conclude that the addition of the FLAG octapeptide sequence allows identification of those cells that have been affected by the molecular therapy independent of the endogenous gene expression of the cells. This novel molecular tracer may prove useful in characterizing infection efficiency and in gene therapy trials.