FOXO1 is a master regulator of memory programming in CAR T cells

A major limitation of chimeric antigen receptor (CAR) T cell therapies is the poor persistence of these cells in vivo1. The expression of memory-associated genes in CAR T cells is linked to their long-term persistence in patients and clinical efficacy2-6, suggesting that memory programs may underpin durable CAR T cell function. Here we show that the transcription factor FOXO1 is responsible for promoting memory and restraining exhaustion in human CAR T cells. Pharmacological inhibition or gene editing of endogenous FOXO1 diminished the expression of memory-associated genes, promoted an exhaustion-like phenotype and impaired the antitumour activity of CAR T cells. Overexpression of FOXO1 induced a gene-expression program consistent with T cell memory and increased chromatin accessibility at FOXO1-binding motifs. CAR T cells that overexpressed FOXO1 retained their function, memory potential and metabolic fitness in settings of chronic stimulation, and exhibited enhanced persistence and tumour control in vivo. By contrast, overexpression of TCF1 (encoded by TCF7) did not enforce canonical memory programs or enhance the potency of CAR T cells. Notably, FOXO1 activity correlated with positive clinical outcomes of patients treated with CAR T cells or tumour-infiltrating lymphocytes, underscoring the clinical relevance of FOXO1 in cancer immunotherapy. Our results show that overexpressing FOXO1 can increase the antitumour activity of human CAR T cells, and highlight memory reprogramming as a broadly applicable approach for optimizing therapeutic T cell states.

CD22 CAR T cells demonstrate high response rates and safety in pediatric and adult B-ALL: Phase 1b results

Chimeric antigen receptor (CAR) T cells targeting CD22 (CD22-CAR) provide a therapeutic option for patients with CD22+ malignancies with progression after CD19-directed therapies. Using on-site, automated, closed-loop manufacturing, we conducted parallel Phase 1b clinical trials investigating a humanized CD22-CAR with 41BB costimulatory domain in children and adults with heavily treated, relapsed/refractory (r/r) B-ALL. Of 19 patients enrolled, 18 had successful CD22-CAR manufacturing, and 16 patients were infused. High grade (3-4) cytokine release syndrome (CRS) and immune effector-cell-associated neurotoxicity syndrome (ICANS) each occurred in only one patient; however, three patients experienced immune-effector-cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS). Twelve of 16 patients (75%) achieved CR with an overall 56% MRD-negative CR rate. Duration of response was overall limited (median 77 days), and CD22 expression was downregulated in 4/12 (33%) available samples at relapse. In summary, we demonstrate that closed-loop manufacturing of CD22-CAR T cells is feasible and is associated with a favorable safety profile and high CR rates in pediatric and adult r/r B-ALL, a cohort with limited CD22-CAR reporting.

Directed evolution of genetically encoded LYTACs for cell-mediated delivery

Lysosome-targeting chimeras (LYTACs) are a promising therapeutic modality to drive the degradation of extracellular proteins. However, early versions of LYTAC contain synthetic glycopeptides that cannot be genetically encoded. Here, we present our designs for a fully genetically encodable LYTAC (GELYTAC), making our tool compatible with integration into therapeutic cells for targeted delivery at diseased sites. To achieve this, we replaced the glycopeptide portion of LYTACs with the protein insulin-like growth factor 2 (IGF2). After showing initial efficacy with wild-type IGF2, we increased the potency of GELYTAC using directed evolution. Subsequently, we demonstrated that our engineered GELYTAC construct not only secretes from HEK293T cells but also from human primary T-cells to drive the uptake of various targets into receiver cells. Immune cells engineered to secrete GELYTAC thus represent a promising avenue for spatially selective targeted protein degradation.

CAR19 monitoring by peripheral blood immunophenotyping reveals histology-specific expansion and toxicity

Chimeric antigen receptor (CAR) T cells directed against CD19 (CAR19) are a revolutionary treatment for B-cell lymphomas. CAR19 cell expansion is necessary for CAR19 function but is also associated with toxicity. To define the impact of CAR19 expansion on patient outcomes, we prospectively followed a cohort of 236 patients treated with CAR19 (brexucabtagene autoleucel or axicabtagene ciloleucel) for mantle cell (MCL), follicular (FL), and large B-cell lymphoma (LBCL) over the course of five years and obtained CAR19 expansion data using peripheral blood immunophenotyping for 188 of these patients. CAR19 expansion was higher in patients with MCL compared to other lymphoma histologic subtypes. Notably, patients with MCL had increased toxicity and required four-fold higher cumulative steroid doses than patients with LBCL. CAR19 expansion was associated with the development of cytokine release syndrome (CRS), immune effector cell associated neurotoxicity syndrome (ICANS), and the requirement for granulocyte colony stimulating factor (GCSF) after day 14 post-infusion. Younger patients and those with elevated lactate dehydrogenase (LDH) had significantly higher CAR19 expansion. In general, no association between CAR19 expansion and LBCL treatment response was observed. However, when controlling for tumor burden, we found that lower CAR19 expansion in conjunction with low LDH was associated with improved outcomes in LBCL. In sum, this study finds CAR19 expansion principally associates with CAR-related toxicity. Additionally, CAR19 expansion as measured by peripheral blood immunophenotyping may be dispensable to favorable outcomes in LBCL.

A versatile CRISPR-Cas13d platform for multiplexed transcriptomic regulation and metabolic engineering in primary human T cells

CRISPR technologies have begun to revolutionize T cell therapies; however, conventional CRISPR-Cas9 genome-editing tools are limited in their safety, efficacy, and scope. To address these challenges, we developed multiplexed effector guide arrays (MEGA), a platform for programmable and scalable regulation of the T cell transcriptome using the RNA-guided, RNA-targeting activity of CRISPR-Cas13d. MEGA enables quantitative, reversible, and massively multiplexed gene knockdown in primary human T cells without targeting or cutting genomic DNA. Applying MEGA to a model of CAR T cell exhaustion, we robustly suppressed inhibitory receptor upregulation and uncovered paired regulators of T cell function through combinatorial CRISPR screening. We additionally implemented druggable regulation of MEGA to control CAR activation in a receptor-independent manner. Lastly, MEGA enabled multiplexed disruption of immunoregulatory metabolic pathways to enhance CAR T cell fitness and anti-tumor activity in vitro and in vivo. MEGA offers a versatile synthetic toolkit for applications in cancer immunotherapy and beyond.

Inosine induces stemness features in CAR-T cells and enhances potency

Adenosine (Ado) mediates immune suppression in the tumor microenvironment and exhausted CD8+ CAR-T cells express CD39 and CD73, which mediate proximal steps in Ado generation. Here, we sought to enhance CAR-T cell potency by knocking out CD39, CD73, or adenosine receptor 2a (A2aR) but observed only modest effects. In contrast, overexpression of Ado deaminase (ADA-OE), which metabolizes Ado to inosine (INO), induced stemness and enhanced CAR-T functionality. Similarly, CAR-T cell exposure to INO augmented function and induced features of stemness. INO induced profound metabolic reprogramming, diminishing glycolysis, increasing mitochondrial and glycolytic capacity, glutaminolysis and polyamine synthesis, and reprogrammed the epigenome toward greater stemness. Clinical scale manufacturing using INO generated enhanced potency CAR-T cell products meeting criteria for clinical dosing. These results identify INO as a potent modulator of CAR-T cell metabolism and epigenetic stemness programming and deliver an enhanced potency platform for cell manufacturing.

Immune determinants of CAR-T cell expansion in solid tumor patients receiving GD2 CAR-T cell therapy

Chimeric antigen receptor T cells (CAR-Ts) have remarkable efficacy in liquid tumors, but limited responses in solid tumors. We conducted a Phase I trial (NCT02107963) of GD2 CAR-Ts (GD2-CAR.OX40.28.z.iC9), demonstrating feasibility and safety of administration in children and young adults with osteosarcoma and neuroblastoma. Since CAR-T efficacy requires adequate CAR-T expansion, patients were grouped into good or poor expanders across dose levels. Patient samples were evaluated by multi-dimensional proteomic, transcriptomic, and epigenetic analyses. T cell assessments identified naive T cells in pre-treatment apheresis associated with good expansion, and exhausted T cells in CAR-T products with poor expansion. Myeloid cell assessment identified CXCR3+ monocytes in pre-treatment apheresis associated with good expansion. Longitudinal analysis of post-treatment samples identified increased CXCR3- classical monocytes in all groups as CAR-T numbers waned. Together, our data uncover mediators of CAR-T biology and correlates of expansion that could be utilized to advance immunotherapies for solid tumor patients.

Antigen density quantification of cell-surface immunotherapy targets by flow cytometry: Multi-antigen assay of neuroblastoma bone marrow metastasis

The central role of target antigen density on chimeric antigen receptor T cell potency highlights the need for accurate measurement of antigen levels on clinical tumor samples. Here, we present a protocol for quantifying antigen density for six cell-surface antigens on neuroblastoma cells metastatic to bone marrow. We describe steps for patient sample acquisition, flow cytometry panel development, instrument setup, and compensation and detail procedures for running clinical samples and data analysis. For complete details on the use and execution of this protocol, please refer to Heitzeneder et al. (2022).1.

Advancing childhood cancer research through young investigator and advocate collaboration

Cancer advocates and researchers share the same goal of driving science forward to create new therapies to cure more patients. The power of combining cancer researchers and advocates has become of increased importance due to their complementary expertise. Therefore, advocacy is a critical component of grant structures and has become embedded into the Stand Up 2 Cancer (SU2C) applications. To date, the optimal way to combine these skillsets and experiences to benefit the cancer community is currently unknown. The Saint Baldrick's Foundation (SBF)-SU2C now called St. Baldrick's Empowering Pediatric Immunotherapies for Childhood Cancer (EPICC) Team is comprised of a collaborative network across nine institutions in the United States and Canada. Since SU2C encourages incorporating advocacy into the team structure, we have assembled a diverse team of advocates and scientists by nominating a young investigator (YI) and advocate from each site. In order to further bridge this interaction beyond virtual monthly and yearly in person meetings, we have developed a questionnaire and conducted interviews. The questionnaire is focused on understanding each member's experience at the intersection between science/advocacy, comparing to previous experiences, providing advice on incorporating advocacy into team science and discussing how we can build on our work. Through creating a YI and advocate infrastructure, we have cultivated a supportive environment for meaningful conversation that impacts the entire research team. We see this as a model for team science by combining expertise to drive innovation forward and positively impact pediatric cancer patients, and perhaps those with adult malignancies.

Significance

Questionnaire results show both advocates and YI's see this structure to be valuable and beneficial. YI's communicated their research to a non-scientific audience and learned advocate's experience. This was their first advocacy experience for most YIs. Advocates learned more about the research being conducted to provide hope. They can also aid with fundraising, publicity and lobbying. This collaboration improves science communication, designing patient-friendly clinical trials and sharing experience across institutions.

Directed Evolution of Genetically Encoded LYTACs for Cell-Mediated Delivery

Lysosome-targeting chimeras (LYTACs) are a promising therapeutic modality to drive the degradation of extracellular proteins. However, early versions of LYTAC contain synthetic glycopeptides that cannot be genetically encoded. Here we present our designs for a fully genetically encodable LYTAC (GELYTAC), making our tool compatible with integration into therapeutic cells for targeted delivery at diseased sites. To achieve this, we replaced the glycopeptide portion of LYTACs with the protein insulin like growth factor 2 (IGF2). After showing initial efficacy with wild type IGF2, we increased the potency of GELYTAC using directed evolution. Subsequently, we demonstrated that our engineered GELYTAC construct not only secretes from HEK293T cells but also from human primary T-cells to drive the uptake of various targets into receiver cells. Immune cells engineered to secrete GELYTAC thus represent a promising avenue for spatially-selective targeted protein degradation.

FOXO1 is a master regulator of CAR T memory programming

Poor CAR T persistence limits CAR T cell therapies for B cell malignancies and solid tumors1,2. The expression of memory-associated genes such as TCF7 (protein name TCF1) is linked to response and long-term persistence in patients3-7, thereby implicating memory programs in therapeutic efficacy. Here, we demonstrate that the pioneer transcription factor, FOXO1, is responsible for promoting memory programs and restraining exhaustion in human CAR T cells. Pharmacologic inhibition or gene editing of endogenous FOXO1 in human CAR T cells diminished the expression of memory-associated genes, promoted an exhaustion-like phenotype, and impaired antitumor activity in vitro and in vivo. FOXO1 overexpression induced a gene expression program consistent with T cell memory and increased chromatin accessibility at FOXO1 binding motifs. FOXO1-overexpressing cells retained function, memory potential, and metabolic fitness during settings of chronic stimulation and exhibited enhanced persistence and antitumor activity in vivo. In contrast, TCF1 overexpression failed to enforce canonical memory programs or enhance CAR T cell potency. Importantly, endogenous FOXO1 activity correlated with CAR T and TIL responses in patients, underscoring its clinical relevance in cancer immunotherapy. Our results demonstrate that memory reprogramming through FOXO1 can enhance the persistence and potency of human CAR T cells and highlights the utility of pioneer factors, which bind condensed chromatin and induce local epigenetic remodeling, for optimizing therapeutic T cell states.

Tisagenlecleucel utilisation and outcomes across refractory, first relapse and multiply relapsed B-cell acute lymphoblastic leukemia: a retrospective analysis of real-world patterns

Background

Tisagenlecleucel was approved by the Food and Drug Administration (FDA) in 2017 for refractory B-cell acute lymphoblastic leukemia (B-ALL) and B-ALL in ≥2nd relapse. Outcomes of patients receiving commercial tisagenlecleucel upon 1st relapse have yet to be established. We aimed to report real-world tisagenlecleucel utilisation patterns and outcomes across indications, specifically including patients treated in 1st relapse, an indication omitted from formal FDA approval.

Methods

We conducted a retrospective analysis of real-world tisagenlecleucel utilisation patterns across 185 children and young adults treated between August 30, 2017 and March 6, 2020 from centres participating in the Pediatric Real-World CAR Consortium (PRWCC), within the United States. We described definitions of refractory B-ALL used in the real-world setting and categorised patients by reported Chimeric Antigen Receptor (CAR) T-cell indication, including refractory, 1st relapse and ≥2nd relapse B-ALL. We analysed baseline patient characteristics and post-tisagenlecleucel outcomes across defined cohorts.

Findings

Thirty-six percent (n = 67) of our cohort received tisagenlecleucel following 1st relapse. Of 66 evaluable patients, 56 (85%, 95% CI 74-92%) achieved morphologic complete response. Overall-survival (OS) and event-free survival (EFS) at 1-year were 69%, (95% CI 58-82%) and 49%, (95% CI 37-64%), respectively, with survival outcomes statistically comparable to remaining patients (OS; p = 0.14, EFS; p = 0.39). Notably, toxicity was increased in this cohort, warranting further study. Interestingly, of 30 patients treated for upfront refractory disease, 23 (77%, 95% CI 58-90%) had flow cytometry and/or next-generation sequencing (NGS) minimum residual disease (MRD)-only disease at the end of induction, not meeting the historic morphologic definition of refractory.

Interpretation

Our findings suggested that tisagenlecleucel response and survival rates overlap across patients treated with upfront refractory B-ALL, B-ALL ≥2nd relapse and B-ALL in 1st relapse. We additionally highlighted that definitions of refractory B-ALL are evolving beyond morphologic measures of residual disease.

Funding

St. Baldrick's/Stand Up 2 Cancer, Parker Institute for Cancer Immunotherapy, Virginia and D.K. Ludwig Fund for Cancer Research.

Preclinical development of a chimeric antigen receptor T cell therapy targeting FGFR4 in rhabdomyosarcoma

Pediatric patients with relapsed or refractory rhabdomyosarcoma (RMS) have dismal cure rates, and effective therapy is urgently needed. The oncogenic receptor tyrosine kinase fibroblast growth factor receptor 4 (FGFR4) is highly expressed in RMS and lowly expressed in healthy tissues. Here, we describe a second-generation FGFR4-targeting chimeric antigen receptor (CAR), based on an anti-human FGFR4-specific murine monoclonal antibody 3A11, as an adoptive T cell treatment for RMS. The 3A11 CAR T cells induced robust cytokine production and cytotoxicity against RMS cell lines in vitro. In contrast, a panel of healthy human primary cells failed to activate 3A11 CAR T cells, confirming the selectivity of 3A11 CAR T cells against tumors with high FGFR4 expression. Finally, we demonstrate that 3A11 CAR T cells are persistent in vivo and can effectively eliminate RMS tumors in two metastatic and two orthotopic models. Therefore, our study credentials CAR T cell therapy targeting FGFR4 to treat patients with RMS.

HLH-like toxicities predict poor survival after the use of tisagenlecleucel in children and young adults with B-ALL

Chimeric antigen receptor-associated hemophagocytic lymphohistiocytosis (HLH)-like toxicities (LTs) involving hyperferritinemia, multiorgan dysfunction, coagulopathy, and/or hemophagocytosis are described as occurring in a subset of patients with cytokine release syndrome (CRS). Case series report poor outcomes for those with B-cell acute lymphoblastic leukemia (B-ALL) who develop HLH-LTs, although larger outcomes analyses of children and young adults (CAYAs) with B-ALL who develop these toxicities after the administration of commercially available tisagenlecleucel are not described. Using a multi-institutional database of 185 CAYAs with B-ALL, we conducted a retrospective cohort study including groups that developed HLH-LTs, high-grade (HG) CRS without HLH-LTs, or no to low-grade (NLG) CRS without HLH-LTs. Primary objectives included characterizing the incidence, outcomes, and preinfusion factors associated with HLH-LTs. Among 185 CAYAs infused with tisagenlecleucel, 26 (14.1%) met the criteria for HLH-LTs. One-year overall survival and relapse-free survival were 25.7% and 4.7%, respectively, in those with HLH-LTs compared with 80.1% and 57.6%, respectively, in those without. In multivariable analysis for death, meeting criteria for HLH-LTs carried a hazard ratio of 4.61 (95% confidence interval, 2.41-8.83), controlling for disease burden, age, and sex. Patients who developed HLH-LTs had higher pretisagenlecleucel disease burden, ferritin, and C-reactive protein levels and lower platelet and absolute neutrophil counts than patients with HG- or NLG-CRS without HLH-LTs. Overall, CAYAs with B-ALL who developed HLH-LTs after tisagenlecleucel experienced high rates of relapse and nonrelapse mortality, indicating the urgent need for further investigations into prevention and optimal management of patients who develop HLH-LTs after tisagenlecleucel.

Homology-independent targeted insertion (HITI) enables guided CAR knock-in and efficient clinical scale CAR-T cell manufacturing

BACKGROUND

Chimeric Antigen Receptor (CAR) T cells are now standard of care (SOC) for some patients with B cell and plasma cell malignancies and could disrupt the therapeutic landscape of solid tumors. However, access to CAR-T cells is not adequate to meet clinical needs, in part due to high cost and long lead times for manufacturing clinical grade virus. Non-viral site directed CAR integration can be accomplished using CRISPR/Cas9 and double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) via homology-directed repair (HDR), however yields with this approach have been limiting for clinical application (dsDNA) or access to large yields sufficient to meet the manufacturing demands outside early phase clinical trials is limited (ssDNA).

METHODS

We applied homology-independent targeted insertion (HITI) or HDR using CRISPR/Cas9 and nanoplasmid DNA to insert an anti-GD2 CAR into the T cell receptor alpha constant (TRAC) locus and compared both targeted insertion strategies in our system. Next, we optimized post-HITI CRISPR EnrichMENT (CEMENT) to seamlessly integrate it into a 14-day process and compared our knock-in with viral transduced anti-GD2 CAR-T cells. Finally, we explored the off-target genomic toxicity of our genomic engineering approach.

RESULTS

Here, we show that site directed CAR integration utilizing nanoplasmid DNA delivered via HITI provides high cell yields and highly functional cells. CEMENT enriched CAR T cells to approximately 80% purity, resulting in therapeutically relevant dose ranges of 5.5 × 10⁸-3.6 × 10⁹ CAR + T cells. CRISPR knock-in CAR-T cells were functionally comparable with viral transduced anti-GD2 CAR-T cells and did not show any evidence of off-target genomic toxicity.

CONCLUSIONS

Our work provides a novel platform to perform guided CAR insertion into primary human T-cells using nanoplasmid DNA and holds the potential to increase access to CAR-T cell therapies.

The future of CAR T-cell therapy for B-cell acute lymphoblastic leukemia in pediatrics and adolescents

INTRODUCTION

Antigen down-regulation and early chimeric antigen receptor (CAR) T cell loss have emerged as 2 major challenges threatening outcomes following CD19-specific CAR T cell therapy for children and young adults with B-cell acute lymphoblastic leukemia (B-ALL). In addressing the future of CAR T cell therapy for B-ALL, innovative strategies to avert antigen downregulation and enhance CAR persistence warrant prioritized focus.

AREAS COVERED

We describe promising engineering strategies to refine CAR constructs to reverse exhaustion, develop regulatable CARs, optimize manufacturing, enrich for immune memory and disrupt immune inhibition. We additionally focus on alternative targeting to CD19-monospecific targeting and contextualize possibilities for expanded CAR utilization.

EXPERT OPINION

We describe research advances as they are independently reported, however anticipate an integrative strategy incorporating complementary modifications will be required to effectively address CAR loss, overcome antigen downregulation and enhance reliability and durability of CAR T cell responses for B-ALL.

Inosine Induces Stemness Features in CAR T cells and Enhances Potency

Adenosine (Ado) mediates immune suppression in the tumor microenvironment and exhausted CD8+ CAR T cells mediate Ado-induced immunosuppression through CD39/73-dependent Ado production. Knockout of CD39, CD73 or A2aR had modest effects on exhausted CAR T cells, whereas overexpression of Ado deaminase (ADA), which metabolizes Ado to inosine (INO), induced stemness features and potently enhanced functionality. Similarly, and to a greater extent, exposure of CAR T cells to INO augmented CAR T cell function and induced hallmark features of T cell stemness. INO induced a profound metabolic reprogramming, diminishing glycolysis and increasing oxidative phosphorylation, glutaminolysis and polyamine synthesis, and modulated the epigenome toward greater stemness. Clinical scale manufacturing using INO generated enhanced potency CAR T cell products meeting criteria for clinical dosing. These data identify INO as a potent modulator of T cell metabolism and epigenetic stemness programming and deliver a new enhanced potency platform for immune cell manufacturing.

Abstract 1128: Lineage tracing of CAR T cells in patients with B cell malignancies

Autologous T cells genetically engineered to express a chimeric antigen receptor (CAR) targeting CD19 and/or CD22 have achieved high complete response rates in patients with hematologic malignancies, but >50% of patients progress following therapy. Here, we sought to understand key T cell intrinsic factors impacting efficacy: CAR T cell expansion, persistence, and homing to the tumor. Using an endogenous T cell receptor (TCR) sequence as a ‘barcode’, we followed individual T cell clonotypes at the single-cell level from pre-manufacture apheresis and infusion products to tumor-involved lymph node and blood at peak and late expansion in 22 adult patients with relapsed or refractory large B cell lymphoma (LBCL) or acute lymphoblastic leukemia (ALL) treated with axicabtagene ciloleucel, an FDA-approved CD19-CAR T cell immunotherapy, or bispecific CD19/CD22 CAR T cells on an investigator-initiated trial (NCT03233854). The resulting CAR T cell atlas comprises matched transcriptome (scRNA-seq) and surface protein expression (CITE-seq) for 846,344 cells from 97 samples, with 215,045 unique TCR clonotypes identified, including 8,747 clonotypes that could be traced across 2+ timepoints in CAR mRNA+ cells. This atlas enabled us to ask: “What were the phenotypes of ‘successful’ CAR T cell clonotypes with optimal homing, expansion, and persistence properties at the time of infusion or pre-manufacture apheresis?” We found that successful T cell clonotypes at apheresis had juvenile features, including IL7R expression. Conversely, successful clonotypes in the infusion product had elevated interferon pathway activity and effector signatures, including GZMB expression. Further, we built a cell-cell interactome using all live cells from on-treatment biopsies and identified a set of 149 specific ligand-receptor pairs significantly enriched in patients who progressed. Finally, we defined dynamics of TCR clonotypes with predicted specificities for viral and self-antigens. These analyses pinpoint the identities of source T cells and infusion CAR T cells with properties impacting efficacy, and also identify ligand-receptor pairs that could be modulated to enhance CAR T cell response in the tumor at the genetic or pharmacological level. This work was supported in part by the Parker Institute for Cancer Immunotherapy, California Institute for Regenerative Medicine, Kite Pharma, and Stanford Cancer Institute.

Citation Format: Zinaida Good, Mark P. Hamilton, Jay Y. Spiegel, Sreevidya Kurra, Moksha H. Desai, Snehit Prabhu, Shin-Heng Chiou, Christine Y. Yeh, Yiyun Chen, Eric Yang, Michael G. Ozawa, Fang Wu, Matthew J. Frank, Lori Muffly, Gursharan K. Claire, Juliana Craig, Maria I. Iglesias, Sushma Bharadwaj, Katherine A. Kong, Dhananjay Wagh, John Coller, Mark M. Davis, Sylvia K. Plevritis, Bita Sahaf, David B. Miklos, Crystal L. Mackall. Lineage tracing of CAR T cells in patients with B cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1128.

Tonic-signaling chimeric antigen receptors drive human regulatory T cell exhaustion

Regulatory T cell (Treg) therapy is a promising approach to improve outcomes in transplantation and autoimmunity. In conventional T cell therapy, chronic stimulation can result in poor in vivo function, a phenomenon termed exhaustion. Whether or not Tregs are also susceptible to exhaustion, and if so, if this would limit their therapeutic effect, was unknown. To "benchmark" exhaustion in human Tregs, we used a method known to induce exhaustion in conventional T cells: expression of a tonic-signaling chimeric antigen receptor (TS-CAR). We found that TS-CAR-expressing Tregs rapidly acquired a phenotype that resembled exhaustion and had major changes in their transcriptome, metabolism, and epigenome. Similar to conventional T cells, TS-CAR Tregs upregulated expression of inhibitory receptors and transcription factors such as PD-1, TIM3, TOX and BLIMP1, and displayed a global increase in chromatin accessibility-enriched AP-1 family transcription factor binding sites. However, they also displayed Treg-specific changes such as high expression of 4-1BB, LAP, and GARP. DNA methylation analysis and comparison to a CD8+ T cell-based multipotency index showed that Tregs naturally exist in a relatively differentiated state, with further TS-CAR-induced changes. Functionally, TS-CAR Tregs remained stable and suppressive in vitro but were nonfunctional in vivo, as tested in a model of xenogeneic graft-versus-host disease. These data are the first comprehensive investigation of exhaustion in Tregs and reveal key similarities and differences with exhausted conventional T cells. The finding that human Tregs are susceptible to chronic stimulation-driven dysfunction has important implications for the design of CAR Treg adoptive immunotherapy strategies.

Abstract 5741: Harnessing macrophages, while protecting T cells, enhances anti-tumor efficacy

Chimeric antigen receptor T (CAR T) cells are synthetically engineered to target specific tumor antigens. CD47 is a ubiquitous receptor that serves as a “don’t eat me” signal by binding to SIRPɑ on macrophages and is often over-expressed by cancer cells. Despite individual promise of CAR T and anti-CD47 therapies, neither has demonstrated clear efficacy in treating solid tumors in the clinic and there is thus an urgent need to develop novel approaches that enhance the potency of these therapies. We interrogated the potential pairing of CAR T with anti-CD47 therapy to overcome tumor resistance mechanisms inherent to each therapy alone, by engaging non-redundant properties of two arms of the immune system. However, upon coadministration of anti-CD47 therapy and CAR T cells across multiple tumor models in vivo, we observed potent and consistent macrophage-mediated clearance of CAR-T cells via on-target, off-tumor binding of anti-CD47 therapies to CAR T cells. This anti-CD47 mediated CAR T cell depletion blunts the therapeutic benefits of treatment and renders the pairing of the current versions of the two agents impractical.To overcome this challenge, we used directed evolution and yeast surface display to engineer a novel variant of CD47 (eCD47) with selective binding, identifying mutations that resulted in loss of binding to the anti-CD47 antibody B6H12, while maintaining the CD47 “don’t eat me” function through binding to SIRPɑ, which is essential for T cell persistence in vivo. T cells engineered to express eCD47, but not native, wild-type CD47, were resistant to targeting by multiple anti-CD47 antibodies but maintained binding to SIRPɑ. These T cells were no longer susceptible to anti-CD47 mediated macrophage phagocytosis in vitro, nor were they depleted in vivo after B6H12 administration. We demonstrated a striking improvement in therapeutic efficacy upon treatment of multiple solid tumor models when anti-CD47 therapy was combined with CAR T cells expressing eCD47, compared to combination with CAR T cells expressing wild-type CD47. We interrogated a mechanistic basis for this improved efficacy in an osteosarcoma model through single-cell RNA-sequencing of isolated tumors. We discovered that CAR T treatment led to a large influx of unique populations of macrophages into the tumor, which were lost upon CAR T depletion after anti-CD47 treatment. These T cell recruited-macrophages were maintained after anti-CD47 treatment in the presence of CAR T cells expressing eCD47, harnessing macrophage mediated anti-tumor activity after combination treatment. Thus, for the first time, eCD47 allows for effective pairing of CAR T therapy and anti-CD47 therapy for cancer treatment, by sparing T cells from macrophage mediated depletion, and revealing impressive synergy when adoptive T cell therapy is combined with macrophage activation.

Citation Format: Sean A. Yamada-Hunter, Johanna Theruvath, Molly T. Radosevich, Brianna J. McIntosh, Katherine A. Freitas, Naiara Martinez-Velez, Elena Sotillo, Amaury Leruste, Peng Xu, Moksha H. Desai, Bita Sahaf, Allison Banuelos, Savannah L. Wasserman, Irving L. Weissman, Jennifer R. Cochran, Crystal L. Mackall. Harnessing macrophages, while protecting T cells, enhances anti-tumor efficacy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5741.

Abstract 959: Immune signatures of GD2 CAR T cell activity in H3K27M+ diffuse midline glioma patients

Introduction: H3K27M-mutated diffuse intrinsic pontine glioma (DIPG) and spinal cord diffuse midline glioma (DMG) are universally lethal central nervous system (CNS) tumors in children and young adults. We previously demonstrated safety and activity of GD2.41BB.z chimeric antigen receptor T cells (CAR-Ts) at dose level 1, 1x106 GD2 CAR-T/kg (Majzner/Ramakrishna et al. Nature 2022) and reported results of dose level 2, 3x106 GD2 CAR-T/kg (Majzner et al. AACR 2022). Here, we present in depth high-dimensional analyses to define the immune states that contribute to CAR-T activity in patients.

Methods: Thirteen patients (10 DIPG/3 spinal DMG; 4-30 years old; 7F/6M) were enrolled in this GD2 CAR-T phase 1 clinical trial (NCT04196413). GD2 CAR-Ts were administered to 12/13 enrolled patients. In the first cohort, CAR-Ts were administered initially intravenously (IV), followed by serial intracerebroventricular infusions (ICV; range 0-11 infusions/patient). Patient GD2 CAR-T product, peripheral blood, and cerebrospinal fluid (CSF) samples were evaluated for CAR-T expansion (qPCR; flow cytometry), cytokine signatures (Multiplex Luminex), and immune cell profiles (single cell RNA-sequencing). Data were analyzed in the context of clinical trajectory and patient response.

Results: 10/12 infused subjects demonstrated clinical and/or radiographic benefit, with less systemic toxicity following ICV compared to IV infusion. CAR-T expansion was noted in the periphery and CSF of all treated patients and following serial ICV infusions. In peripheral blood, cytokine concentrations, including IFN-gamma, IL6, and CXCL9, were higher after IV compared to ICV CAR-T infusions, correlating with increased systemic inflammation. Conversely in CSF, cytokine concentrations, such as CCL2 and CXCL9, were higher following ICV compared to IV CAR-T infusions. Transcriptomic analysis was conducted on 576,199 single cells from 91 samples, including GD2 CAR-T products and patient CSF. This is the largest CAR-T dataset in CNS tumors. Patient CSF samples were dominated by T cell and myeloid populations. After IV CAR-T infusion, patient CSF exhibited an increased fraction of regulatory T cells and suppressive myeloid populations from baseline. These immune suppressive cells reduced after ICV infusion. Ongoing analyses are underway to explore the relation of these immune populations to patient response.

Conclusions: H3K27M-mutated DIPG/DMG patients demonstrate continued clinical response with serial ICV GD2 CAR-T infusions, with heterogeneity in the durability of response across patients. In-depth correlative analyses profile distinct immune populations and demonstrate population shifts depending on route of administration and over the course of treatment. Key findings from these data will allow for iterative improvement in CAR-T therapies for H3K27M+ DIPG/DMG patients, providing hope to shift the paradigm of this fatal disease.

Citation Format: Sneha Ramakrishna, Zinaida Good, Moksha Desai, Daniel Zamler, Rebecca Mancusi, Jasia Mahdi, Robbie Majzner, Liora Schultz, Rebecca Richards, Jennifer Kamens, Valentin Barsan, Cynthia Campen, Sonia Partap, Zachary Ehlinger, Warren Reynolds, Yiyun Chen, Mark P. Hamilton, Jennifer Moon, Christina Baggott, Michael Kunicki, Michelle Fujimoto, Amy Li, Sneha Jariwala, Sharon Mavroukakis, Emily Egeler, Ashley Jacobs, Courtney Erickson, Karen Yamabe-Kwong, Snehit Prabhu, Kara Davis, Steve Feldman, Bita Sahaf, Crystal L. Mackall, Michelle Monje. Immune signatures of GD2 CAR T cell activity in H3K27M+ diffuse midline glioma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 959.

Tumor inflammation-associated neurotoxicity

Cancer immunotherapies have unique toxicities. Establishment of grading scales and standardized grade-based treatment algorithms for toxicity syndromes can improve the safety of these treatments, as observed for cytokine release syndrome (CRS) and immune effector cell associated neurotoxicity syndrome (ICANS) in patients with B cell malignancies treated with chimeric antigen receptor (CAR) T cell therapy. We have observed a toxicity syndrome, distinct from CRS and ICANS, in patients treated with cell therapies for tumors in the central nervous system (CNS), which we term tumor inflammation-associated neurotoxicity (TIAN). Encompassing the concept of 'pseudoprogression,' but broader than inflammation-induced edema alone, TIAN is relevant not only to cellular therapies, but also to other immunotherapies for CNS tumors. To facilitate the safe administration of cell therapies for patients with CNS tumors, we define TIAN, propose a toxicity grading scale for TIAN syndrome and discuss the potential management of this entity, with the goal of standardizing both reporting and management.

Co-opting signalling molecules enables logic-gated control of CAR T cells

Although chimeric antigen receptor (CAR) T cells have altered the treatment landscape for B cell malignancies, the risk of on-target, off-tumour toxicity has hampered their development for solid tumours because most target antigens are shared with normal cells1,2. Researchers have attempted to apply Boolean-logic gating to CAR T cells to prevent toxicity3-5; however, a truly safe and effective logic-gated CAR has remained elusive6. Here we describe an approach to CAR engineering in which we replace traditional CD3ζ domains with intracellular proximal T cell signalling molecules. We show that certain proximal signalling CARs, such as a ZAP-70 CAR, can activate T cells and eradicate tumours in vivo while bypassing upstream signalling proteins, including CD3ζ. The primary role of ZAP-70 is to phosphorylate LAT and SLP-76, which form a scaffold for signal propagation. We exploited the cooperative role of LAT and SLP-76 to engineer logic-gated intracellular network (LINK) CAR, a rapid and reversible Boolean-logic AND-gated CAR T cell platform that outperforms other systems in both efficacy and prevention of on-target, off-tumour toxicity. LINK CAR will expand the range of molecules that can be targeted with CAR T cells, and will enable these powerful therapeutic agents to be used for solid tumours and diverse diseases such as autoimmunity7 and fibrosis8. In addition, this work shows that the internal signalling machinery of cells can be repurposed into surface receptors, which could open new avenues for cellular engineering.

Role of peripheral blood MRD and 18F-FDG PET in the post-CAR relapse setting: a case study of discordant peripheral blood and bone marrow MRD

BACKGROUND

Chimeric antigen receptor (CAR) T cell therapy is an effective salvage therapy for pediatric relapsed B-cell acute lymphoblastic leukemia (B-ALL), yet is challenged by high rates of post-CAR relapse. Literature describing specific relapse patterns and extramedullary (EM) sites of involvement in the post-CAR setting remains limited, and a clinical standard for post-CAR disease surveillance has yet to be established. We highlight the importance of integrating peripheral blood minimal residual disease (MRD) testing and radiologic imaging into surveillance strategies, to effectively characterize and capture post-CAR relapse.

MAIN BODY

Here, we describe the case of a child with multiply relapsed B-ALL who relapsed in the post-CAR setting with gross non-contiguous medullary and EM disease. Interestingly, her relapse was identified first from peripheral blood flow cytometry MRD surveillance, in context of a negative bone marrow aspirate (MRD <0.01%). Positron emission tomography with 18F-fluorodeoxyglucose revealed diffuse leukemia with innumerable bone and lymph node lesions, interestingly sparing her sacrum, the site of her bone marrow aspirate sampling.

CONCLUSIONS

We highlight this case as both peripheral blood MRD and 18F-fluorodeoxyglucose positron emission tomography imaging were more sensitive than standard bone marrow aspirate testing in detecting this patient's post-CAR relapse. Clinical/Biologic Insight: In the multiply relapsed B-ALL setting, where relapse patterns may include patchy medullary and/or EM disease, peripheral blood MRD and/or whole body imaging, may carry increased sensitivity at detecting relapse in patient subsets, as compared with standard bone marrow sampling.

CAR immune cells: design principles, resistance and the next generation

The remarkable clinical activity of chimeric antigen receptor (CAR) therapies in B cell and plasma cell malignancies has validated the use of this therapeutic class for liquid cancers, but resistance and limited access remain as barriers to broader application. Here we review the immunobiology and design principles of current prototype CARs and present emerging platforms that are anticipated to drive future clinical advances. The field is witnessing a rapid expansion of next-generation CAR immune cell technologies designed to enhance efficacy, safety and access. Substantial progress has been made in augmenting immune cell fitness, activating endogenous immunity, arming cells to resist suppression via the tumour microenvironment and developing approaches to modulate antigen density thresholds. Increasingly sophisticated multispecific, logic-gated and regulatable CARs display the potential to overcome resistance and increase safety. Early signs of progress with stealth, virus-free and in vivo gene delivery platforms provide potential paths for reduced costs and increased access of cell therapies in the future. The continuing clinical success of CAR T cells in liquid cancers is driving the development of increasingly sophisticated immune cell therapies that are poised to translate to treatments for solid cancers and non-malignant diseases in the coming years.

Outcomes After Nonresponse and Relapse Post-Tisagenlecleucel in Children, Adolescents, and Young Adults With B-Cell Acute Lymphoblastic Leukemia

PURPOSE

Nonresponse and relapse after CD19-chimeric antigen receptor (CAR) T-cell therapy continue to challenge survival outcomes. Phase II landmark data from the ELIANA trial demonstrated nonresponse and relapse rates of 14.5% and 28%, respectively, whereas use in the real-world setting showed nonresponse and relapse rates of 15% and 37%. Outcome analyses describing fate after post-CAR nonresponse and relapse remain limited. Here, we aim to establish survival outcomes after nonresponse and both CD19+ and CD19- relapses and explore treatment variables associated with inferior survival.

METHODS

We conducted a retrospective multi-institutional study of 80 children and young adults with B-cell acute lymphoblastic leukemia experiencing nonresponse (n = 23) or relapse (n = 57) after tisagenlecleucel. We analyze associations between baseline characteristics and these outcomes and establish survival rates and salvage approaches.

RESULTS

The overall survival (OS) at 12 months was 19% across nonresponders (n = 23; 95% CI, 7 to 50). Ninety-five percent of patients with nonresponse had high preinfusion disease burden. Among 156 morphologic responders, the cumulative incidence of relapse was 37% (95% CI, 30 to 47) at 12 months (CD19+; 21% [15 to 29], CD19-; 16% [11 to 24], median follow-up; 380 days). Across 57 patients experiencing relapse, the OS was 52% (95% CI, 38 to 71) at 12 months after time of relapse. Notably, CD19- relapse was associated with significantly decreased OS as compared with patients who relapsed with conserved CD19 expression (CD19- 12-month OS; 30% [14 to 66], CD19+ 12-month OS; 68% [49 to 92], P = .0068). Inotuzumab, CAR reinfusion, and chemotherapy were used as postrelapse salvage therapy with greatest frequency, yet high variability in treatment sequencing and responses limits efficacy analysis across salvage approaches.

CONCLUSION

We describe poor survival across patients experiencing nonresponse to tisagenlecleucel. In the post-tisagenlecleucel relapse setting, patients can be salvaged; however, CD19- relapse is distinctly associated with decreased survival outcomes.

Determinants of resistance to engineered T cell therapies targeting CD19 in large B cell lymphomas

Most relapsed/refractory large B cell lymphoma (r/rLBCL) patients receiving anti-CD19 chimeric antigen receptor (CAR19) T cells relapse. To characterize determinants of resistance, we profiled over 700 longitudinal specimens from two independent cohorts (n = 65 and n = 73) of r/rLBCL patients treated with axicabtagene ciloleucel. A method for simultaneous profiling of circulating tumor DNA (ctDNA), cell-free CAR19 (cfCAR19) retroviral fragments, and cell-free T cell receptor rearrangements (cfTCR) enabled integration of tumor and both engineered and non-engineered T cell effector-mediated factors for assessing treatment failure and predicting outcomes. Alterations in multiple classes of genes are associated with resistance, including B cell identity (PAX5 and IRF8), immune checkpoints (CD274), and those affecting the microenvironment (TMEM30A). Somatic tumor alterations affect CAR19 therapy at multiple levels, including CAR19 T cell expansion, persistence, and tumor microenvironment. Further, CAR19 T cells play a reciprocal role in shaping tumor genotype and phenotype. We envision these findings will facilitate improved chimeric antigen receptor (CAR) T cells and personalized therapeutic approaches.

A Phase I/II Trial of Nivolumab plus Ipilimumab in Children and Young Adults with Relapsed/Refractory Solid Tumors: A Children's Oncology Group Study ADVL1412

PURPOSE

In many cancers, nivolumab in combination with ipilimumab improves response rates compared with either agent alone, but the combination has not been evaluated in childhood cancer. We conducted a phase I/II trial of nivolumab plus ipilimumab in children and young adults with recurrent/refractory solid tumors.

PATIENTS AND METHODS

ADVL1412, Part C assessed safety of nivolumab plus ipilimumab at two dose levels (DL): DL1 1 mg/kg of each drug and DL2 3 mg/kg nivolumab plus 1 mg/kg ipilimumab. Part D evaluated response at the recommended phase II dose (RP2D) in Ewing sarcoma, rhabdomyosarcoma, and osteosarcoma. Part E tested DL3 (1 mg/kg nivolumab plus 3 mg/kg ipilimumab) in Ewing sarcoma and rhabdomyosarcoma. Tumor response was measured using RECIST v1.1. Pharmacokinetics and PD-L1 expression on archival tissues were assessed.

RESULTS

Fifty-five eligible patients enrolled. Based on safety, tolerability, and similar drug exposure to the same doses administered in adults, DL2 was defined as the pediatric RP2D. Among 41 patients treated at the RP2D, 2 patients experienced dose-limiting toxicities during cycle 1, and 4 patients experienced toxicities beyond that period. Two patients had clinically significant sustained partial responses (1 rhabdomyosarcoma, 1 Ewing sarcoma) and 4 had stable disease. Among 8 patients treated at DL3, 3 dose-limiting toxicities (DLT) occurred, all immune-related adverse events; no objective responses were observed.

CONCLUSIONS

The RP2D of nivolumab (3 mg/kg) plus ipilimumab (1 mg/kg) is well tolerated in children and young adults with solid tumors and shows some clinical activity. Increased dose of ipilimumab (3 mg/kg) plus nivolumab (1 mg/kg) was associated with increased toxicity without clinical benefit.

Enhanced T cell effector activity by targeting the Mediator kinase module

T cells are the major arm of the immune system responsible for controlling and regressing cancers. To identify genes limiting T cell function, we conducted genome-wide CRISPR knockout screens in human chimeric antigen receptor (CAR) T cells. Top hits were MED12 and CCNC, components of the Mediator kinase module. Targeted MED12 deletion enhanced antitumor activity and sustained the effector phenotype in CAR- and T cell receptor-engineered T cells, and inhibition of CDK8/19 kinase activity increased expansion of nonengineered T cells. MED12-deficient T cells manifested increased core Meditator chromatin occupancy at transcriptionally active enhancers-most notably for STAT and AP-1 transcription factors-and increased IL2RA expression and interleukin-2 sensitivity. These results implicate Mediator in T cell effector programming and identify the kinase module as a target for enhancing potency of antitumor T cell responses.

Post-infusion CAR TReg cells identify patients resistant to CD19-CAR therapy

Approximately 60% of patients with large B cell lymphoma treated with chimeric antigen receptor (CAR) T cell therapies targeting CD19 experience disease progression, and neurotoxicity remains a challenge. Biomarkers associated with resistance and toxicity are limited. In this study, single-cell proteomic profiling of circulating CAR T cells in 32 patients treated with CD19-CAR identified that CD4+Helios+ CAR T cells on day 7 after infusion are associated with progressive disease and less severe neurotoxicity. Deep profiling demonstrated that this population is non-clonal and manifests hallmark features of T regulatory (TReg) cells. Validation cohort analysis upheld the link between higher CAR TReg cells with clinical progression and less severe neurotoxicity. A model combining expansion of this subset with lactate dehydrogenase levels, as a surrogate for tumor burden, was superior for predicting durable clinical response compared to models relying on each feature alone. These data credential CAR TReg cell expansion as a novel biomarker of response and toxicity after CAR T cell therapy and raise the prospect that this subset may regulate CAR T cell responses in humans.

CD19/22 CAR T cells in children and young adults with B-ALL: phase 1 results and development of a novel bicistronic CAR

Remission durability following single-antigen targeted chimeric antigen receptor (CAR) T-cells is limited by antigen modulation, which may be overcome with combinatorial targeting. Building upon our experiences targeting CD19 and CD22 in B-cell acute lymphoblastic leukemia (B-ALL), we report on our phase 1 dose-escalation study of a novel murine stem cell virus (MSCV)-CD19/CD22-4-1BB bivalent CAR T-cell (CD19.22.BBζ) for children and young adults (CAYA) with B-cell malignancies. Primary objectives included toxicity and dose finding. Secondary objectives included response rates and relapse-free survival (RFS). Biologic correlatives included laboratory investigations, CAR T-cell expansion and cytokine profiling. Twenty patients, ages 5.4 to 34.6 years, with B-ALL received CD19.22.BBζ. The complete response (CR) rate was 60% (12 of 20) in the full cohort and 71.4% (10 of 14) in CAR-naïve patients. Ten (50%) developed cytokine release syndrome (CRS), with 3 (15%) having ≥ grade 3 CRS and only 1 experiencing neurotoxicity (grade 3). The 6- and 12-month RFS in those achieving CR was 80.8% (95% confidence interval [CI]: 42.4%-94.9%) and 57.7% (95% CI: 22.1%-81.9%), respectively. Limited CAR T-cell expansion and persistence of MSCV-CD19.22.BBζ compared with EF1α-CD22.BBζ prompted laboratory investigations comparing EF1α vs MSCV promoters, which did not reveal major differences. Limited CD22 targeting with CD19.22.BBζ, as evaluated by ex vivo cytokine secretion and leukemia eradication in humanized mice, led to development of a novel bicistronic CD19.28ζ/CD22.BBζ construct with enhanced cytokine production against CD22. With demonstrated safety and efficacy of CD19.22.BBζ in a heavily pretreated CAYA B-ALL cohort, further optimization of combinatorial antigen targeting serves to overcome identified limitations (www.clinicaltrials.gov #NCT03448393).

Genome-wide CRISPR screens of T cell exhaustion identify chromatin remodeling factors that limit T cell persistence

T cell exhaustion limits antitumor immunity, but the molecular determinants of this process remain poorly understood. Using a chronic stimulation assay, we performed genome-wide CRISPR-Cas9 screens to systematically discover regulators of T cell exhaustion, which identified an enrichment of epigenetic factors. In vivo CRISPR screens in murine and human tumor models demonstrated that perturbation of the INO80 and BAF chromatin remodeling complexes improved T cell persistence in tumors. In vivo Perturb-seq revealed distinct transcriptional roles of each complex and that depletion of canonical BAF complex members, including Arid1a, resulted in the maintenance of an effector program and downregulation of exhaustion-related genes in tumor-infiltrating T cells. Finally, Arid1a depletion limited the acquisition of exhaustion-associated chromatin accessibility and led to improved antitumor immunity. In summary, we provide an atlas of the genetic regulators of T cell exhaustion and demonstrate that modulation of epigenetic state can improve T cell responses in cancer immunotherapy.

Abstract 1362: Metabolic engineering of CAR-T cells overcomes suppressive adenosine signaling and enhances functionality

Chimeric Antigen Receptor (CAR) T cell therapy has resulted in remarkable clinical outcomes in the context of acute and chronic lymphoblastic leukemia, but remains unsuccessful in the treatment of solid tumors. One reason for this failure is thought to be T cell dysfunction or exhaustion promoted by suppressive soluble factors within the tumor microenvironment (TME). High extracellular levels of the immunosuppressive factor adenosine (Ado) are generated in the TME via breakdown of ATP by ecto-enzymes CD39 and CD73 expressed on tumor-infiltrating immune cells. Binding of extracellular Ado to its receptor A2a on T cells results in inhibition of proliferation and effector function. Interestingly, CD39 has recently been described as a surrogate marker of exhaustion on human CAR-T cells and non-engineered T cells. Therefore, we hypothesized that CD39 expression on exhausted CAR-T cells promotes dysfunction through generation of extracellular adenosine.

Using an in vitro model of T cell exhaustion, whereby human T cells express a CAR that tonically signals in an antigen-independent manner (HA CAR), we demonstrate that exhausted HA CAR T cells actively hydrolyze extracellular ATP via their elevated expression of CD39 and CD73. Moreover, exhausted CD39+ CAR T cells upregulate several genes associated with a Treg phenotype at the mRNA and protein levels, suggesting that this cell population might be suppressive. To assess whether CD39+/CD73+ CAR T cells exhibit suppressive functions, we co-cultured them with non-exhausted CD19-CAR T cells. Indeed, proliferation and secretion of IL-2 by CD19 CAR T cells were diminished when they were co-cultured with exhausted CD39+ CAR T cells, and that this suppression is dependent on the A2a receptor. Using this knowledge, we used gene-editing and overexpression approaches to engineer CAR-T cells with resistance to suppressive adenosine signaling. In contrast to genetic deletion of CD39 or CD73, which did not alleviate CAR T cell dysfunction, genetic deletion of adenosine receptor A2aR in exhausted CAR T cells resulted in phenotypic changes and a modest improvement in tumor-specific killing. Further, ectopic overexpression of adenosine deaminase (ADA) in CAR T cells led to decreased exhaustion marker expression and significantly enhanced effector function. These data indicate that ADA overexpression is an innovative approach to increase the functionality of CAR T cells through avoidance of suppressive adenosine signaling, and provides proof-of-concept that metabolic engineering of CAR-T cells can pave the way for responses in patients with solid tumors.

Citation Format: Dorota Klysz, Meena Malipatlolla, Katherine Freitas, Malek Bashti, Louai Labanieh, Peng Xu, Cecilia Ramello, Amaury Lerust, Hyatt Balke Want, Kaithlen Zen Pacheco, Evan W. Weber, Shabnum Patel, Steven Feldman, Elena Sotillo, Crystal L. Mackall. Metabolic engineering of CAR-T cells overcomes suppressive adenosine signaling and enhances functionality [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 1362.

Abstract 3603: Reverse fate mapping of CD19-targeted CAR T cells in patients with large B-cell lymphoma

Autologous T cells genetically engineered to express a chimeric antigen receptor targeting CD19 (CD19-CAR) have achieved high complete response rates in patients with hematologic malignancies, but &gt;50% of patients progress following therapy. Here, we sought to understand key T-cell intrinsic factors impacting efficacy, namely CAR T-cell expansion, persistence, and homing to the tumor. Using an approach called reverse fate mapping, we followed individual T-cell clones at the single-cell level from pre-manufacture apheresis to the infusion product, tumor-involved lymph node, and blood at peak and late expansion in 12 adult patients with relapsed or refractory large B-cell lymphoma treated with axicabtagene ciloleucel, an FDA-approved CD19-CAR T-cell immunotherapy. The resulting CAR T-cell atlas comprises matched transcriptome (scRNA-seq) and surface protein expression (CITE-seq) for 322,028 cells from 44 samples, with 119,397 unique T-cell receptor (TCR) clonotypes identified. This atlas enabled us to ask questions like: “What were the phenotypes of the most successful CAR T-cell clones at the time of infusion or pre-manufacture apheresis?” We found that T-cell clonotypes with juvenile features at apheresis, including IL7R expression, were the most successful at expansion to higher frequencies in the infusion product, while clones with effector gene expression programs, such as those encoding perforin and granzymes, contracted between apheresis and product. Conversely, it was GZMK-expressing T cells in pre-manufacture apheresis that were dominant in the tumor early following CAR T-cell infusion. Further, T-cell clonotypes with active effector programs at infusion dominated at peak expansion. Finally, we defined active expression modules and pathways in the infusion product for CAR T-cell clones that homed to the tumor or became dominant at late expansion. These analyses pinpoint the molecular mechanisms that could be modulated to rationally steer CAR T-cell differentiation trajectories at the genetic or pharmacological level. This work was supported in part by the Parker Institute for Cancer Immunotherapy, California Institute for Regenerative Medicine, Kite Pharma, and Stanford Cancer Institute.

Citation Format: Zinaida Good, Mark P. Hamilton, Jay Y. Spiegel, Sreevidya Kurra, Moksha Desai, Snehit Prabhu, Eric Yang, Michael G. Ozawa, Paul J. Hanson, Fang Wu, Matthew J. Frank, John H. Baird, Lori Muffly, Gursharan K. Claire, Juliana Craig, Katherine A. Kong, Dhananjay Wagh, John Coller, Sylvia K. Plevritis, Bita Sahaf, David B. Miklos, Crystal L. Mackall. Reverse fate mapping of CD19-targeted CAR T cells in patients with large B-cell lymphoma [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 3603.

Abstract 2815: Exploring the role of telomerase in senescence and exhaustion in CAR T cell immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has revolutionized oncology through engineered targeting of antigens on previously untreatable cancers. However, less than half of patients on CAR T cell therapy experience long-term disease control, with better outcomes observed in pediatric compared to adult populations. Senescent T cells have been shown to manifest defective killing abilities and the development of negative regulatory functions, with evidence suggesting that senescence may play a role in decreasing CAR T cell efficacy and persistence. Moreover, levels of telomerase have been shown to control the lifespan of human T cells, with increased levels delaying senescence. It has been shown that T cell exhaustion limits CAR T cell efficacy in the context of solid tumors, where CAR T cells have yet to demonstrate sustained responses. Using a model of CAR T cell exhaustion developed in our lab, and CAR T cells manufactured from younger and older donors, we have developed a comprehensive method to profile T cell functionality, phenotype, and proliferation. We are able to characterize features of senescence via cell surface markers, intracellular activity, telomere length, and telomerase activity as well as features of exhaustion. Using CRISPR/Cas9, we have inactivated TERT in primary human T cells and CAR T cells and interrogated the effects of hTERT knockout as well as of hTERT overexpression on key markers of T cell identity, exhaustion, senescence, and cytotoxic activity. Understanding telomerase in the context of CAR T cell therapy will provide mechanistic insights into senescence and exhaustion cellular programs and has the potential to inform increasingly effective CAR T cell cancer treatments.

Citation Format: Tara Murty, Maria C. Ramello, Elena Sotillo, Lu Chen, Steven A. Artandi, Crystal L. Mackall. Exploring the role of telomerase in senescence and exhaustion in CAR T cell immunotherapy [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 2815.

Abstract CT001: Major tumor regressions in H3K27M-mutated diffuse midline glioma (DMG) following sequential intravenous (IV) and intracerebroventricular (ICV) delivery of GD2-CAR T cells

Background: H3K27M-mutated DMGs are universally lethal central nervous system tumors that express high levels of the disialoganglioside GD2. IV administered GD2-CAR T cells (GD2-CART) regress DMG in preclinical models, and locoregionally delivered CARs demonstrate enhanced activity in xenograft models of brain tumors.

Methods: NCT04196413 is a 3+3 Phase I dose escalation trial testing GD2-CART in patients with H3K27M DMG, with dose-limiting toxicities (DLT) considered independently for DIPG and spinal DMG (sDMG). Arm A tested escalating doses of IV GD2-CART (DL1: 1e6 GD2-CART/kg; DL2=3e6 GD2-CART/kg) following lymphodepletion (LD). After the DLT period, patients with clinical and/or radiographic benefit were eligible for subsequent ICV GD2-CART (10-30e6 GD2-CART) administered via Ommaya catheter without LD every 4-8 weeks for a maximum of 12 doses. We previously reported early results from 4 patients treated on DL1, which demonstrated clinical activity and manageable toxicity. Here we provide updated results for DL1 and DL2.

Results: Thirteen subjects were enrolled and 11 treated [n=4 DL1 (3 DIPG/1 sDMG); n=9 DL2 (7 DIPG/2 sDMG)]. Two subjects were removed prior to treatment due to rapid progression. No DLTs were observed on DL1. Three subjects experienced DLT on DL2 (2 DIPG/1 sDMG) due to grade 4 cytokine release syndrome (CRS), successfully managed with tocilizumab, anakinra, and corticosteroids. CRS occurred earlier on DL2 vs. DL1 (Day 3 vs 7). On both dose levels, all subjects exhibited transient symptoms related to on-tumor inflammation, termed Tumor Inflammation-Associated Neurotoxicity (TIAN), which was successfully managed with anakinra and, in some cases, CSF drainage and dexamethasone. No DLT due to TIAN has occurred.

Ten patients have had adequate follow-up to assess benefit. Nine experienced radiographic and/or clinical benefit after IV infusion, and they received subsequent ICV GD2-CART infusions (median= 4 ICV infusions/pt, range 1-6). ICV infusions were not associated with high-grade CRS, although some subjects developed transient fever, headache, meningismus, nausea, and/or vomiting, and several subjects developed TIAN. Four patients continue to receive ICV infusions on study and have experienced continued clinical and radiographic benefit at 11+, 9.5+, 8+ and 7+ months following enrollment. A 31-year-old with sDMG has experienced a near-complete (&gt;95%) reduction in tumor volume and a 17-year-old with DIPG experienced a near-complete (&gt;98%) reduction in volume of a pontine tumor.

Conclusions: IV treatment of DIPG and sDMG with GD2-CART is safe at a dose of 1e6/kg, but associated with unacceptable rates of high-grade CRS at 3e6/kg. ICV GD2-CART without LD, administered following a previous course of IV GD2-CART with LD, has been well tolerated and has mediated impressive sustained clinical benefit in some patients with DIPG/sDMG. Given these findings, we are launching a new arm to assess safety and activity and to define the recommended phase 2 dose for ICV delivery of GD2-CART without LD. Patients are eligible for up to 12 ICV infusions of GD2-CART administered every 4-6 weeks. Clinical benefit will be formally assessed using patient-reported outcomes. GD2-CART has the potential to transform therapy for patients with H3K27M+ DIPG/sDMG.

Citation Format: Robbie G. Majzner, Jasia Mahdi, Sneha Ramakrishna, Shabnum Patel, Harshini Chinnasamy, Kristen Yeom, Liora Schultz, Valentin Barsan, Rebecca Richards, Cynthia Campen, Agnes Reschke, Angus Martin Shaw Toland, Christina Baggott, Sharon Mavroukakis, Emily Egeler, Jennifer Moon, Ashley Jacobs, Karen Yamabe-Kwong, Lindsey Rasmussen, Esther Nie, Sean Green, Michael Kunicki, Michelle Fujimoto, Zach Ehlinger, Warren Reynolds, Snehit Prabhu, Katherine E. Warren, Tim Cornell, Sonia Partap, Paul Fisher, Gerald Grant, Hannes Vogel, Bita Sahaf, Kara Davis, Steven Feldman, Michelle Monje, Crystal L. Mackall. Major tumor regressions in H3K27M-mutated diffuse midline glioma (DMG) following sequential intravenous (IV) and intracerebroventricular (ICV) delivery of GD2-CAR 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 CT001.

Delivery of CAR-T cells in a transient injectable stimulatory hydrogel niche improves treatment of solid tumors

Adoptive cell therapy (ACT) has proven to be highly effective in treating blood cancers, but traditional approaches to ACT are poorly effective in treating solid tumors observed clinically. Novel delivery methods for therapeutic cells have shown promise for treatment of solid tumors when compared with standard intravenous administration methods, but the few reported approaches leverage biomaterials that are complex to manufacture and have primarily demonstrated applicability following tumor resection or in immune-privileged tissues. Here, we engineer simple-to-implement injectable hydrogels for the controlled co-delivery of CAR-T cells and stimulatory cytokines that improve treatment of solid tumors. The unique architecture of this material simultaneously inhibits passive diffusion of entrapped cytokines and permits active motility of entrapped cells to enable long-term retention, viability, and activation of CAR-T cells. The generation of a transient inflammatory niche following administration affords sustained exposure of CAR-T cells, induces a tumor-reactive CAR-T phenotype, and improves efficacy of treatment.

Disease Burden Affects Outcomes in Pediatric and Young Adult B-Cell Lymphoblastic Leukemia After Commercial Tisagenlecleucel: A Pediatric Real-World Chimeric Antigen Receptor Consortium Report

PURPOSE

Tisagenlecleucel is a CD19-specific chimeric antigen receptor T-cell therapy, US Food and Drug Administration-approved for children, adolescents, and young adults (CAYA) with relapsed and/or refractory (RR) B-cell acute lymphoblastic leukemia (B-ALL). The US Food and Drug Administration registration for tisagenlecleucel was based on a complete response (CR) rate of 81%, 12-month overall survival (OS) of 76%, and event-free survival (EFS) of 50%. We report clinical outcomes and analyze covariates of outcomes after commercial tisagenlecleucel.

METHODS

We conducted a retrospective, multi-institutional study of CAYA with RR B-ALL across 15 US institutions, who underwent leukapheresis shipment to Novartis for commercial tisagenlecleucel. A total of 200 patients were included in an intent-to-treat response analysis, and 185 infused patients were analyzed for survival and toxicity.

RESULTS

Intent-to-treat analysis demonstrates a 79% morphologic CR rate (95% CI, 72 to 84). The infused cohort had an 85% CR (95% CI, 79 to 89) and 12-month OS of 72% and EFS of 50%, with 335 days of median follow-up. Notably, 48% of patients had low-disease burden (< 5% bone marrow lymphoblasts, no CNS3, or other extramedullary disease), or undetectable disease, pretisagenlecleucel. Univariate and multivariate analyses associate high-disease burden (HB, ≥ 5% bone marrow lymphoblasts, CNS3, or non-CNS extramedullary) with inferior outcomes, with a 12-month OS of 58% and EFS of 31% compared with low-disease burden (OS; 85%, EFS; 70%) and undetectable disease (OS; 95%, EFS; 72%; P < .0001 for OS and EFS). Grade ≥ 3 cytokine release syndrome and neurotoxicity rates were 21% and 7% overall and 35% and 9% in patients with HB, respectively.

CONCLUSION

Commercial tisagenlecleucel in CAYA RR B-ALL demonstrates efficacy and tolerability. This first analysis of commercial tisagenlecleucel stratified by disease burden identifies HB preinfusion to associate with inferior OS and EFS and increased toxicity.

Neurotoxicity following CD19/CD28ζ CAR T-cells in children and young adults with B-cell malignancies

BACKGROUND

Neurotoxicity is an established toxicity of CD19 CAR T-cell therapy; however, there is little information on neurotoxicity in children, adolescents, and young adults (CAYA) receiving CD19/CD28ζ CAR T-cells for B-cell malignancies.

METHODS

We analyzed neurotoxicity of CD19/CD28ζ CAR T-cells in CAYA treated on a phase I study (NCT01593696). Assessments included daily inpatient monitoring, caregiver-based neuro-symptom checklist (NSC), exploratory neurocognitive assessments, clinically-indicated imaging, CSF analysis, and systematic cytokine profiling, outcomes of which were associated with cytokine release syndrome (CRS) and treatment response postinfusion. Patients with active CNS leukemia were included.

RESULTS

Amongst 52 patients treated, 13 patients had active CNS leukemia at infusion. Neurotoxicity was seen in 11/52 (21.2%) patients, with an incidence of 29.7% (11/37) in patients with CRS. Neurotoxicity was associated with the presence and severity of CRS. Those with neurotoxicity had higher levels of peak serum IL-6, IFNγ, and IL-15. Additionally, CNS leukemia was effectively eradicated in most patients with CRS. Pilot neurocognitive testing demonstrated stable-to-improved neurocognitive test scores in most patients, albeit limited by small patient numbers. The NSC enabled caregiver input into the patient experience.

CONCLUSIONS

This is the first systematic analysis of neurotoxicity utilizing a CD19/CD28ζ CAR construct in CAYA, including in those with active CNS involvement. The experience demonstrates that the neurotoxicity profile was acceptable and reversible, with evidence of anti-leukemia response and CNS trafficking of CAR T-cells. Additionally, neurocognitive testing, while exploratory, provides an opportunity for future studies to employ systematic evaluations into neurotoxicity assessments and validation is needed in future studies.

GD2-CAR T cell therapy for H3K27M-mutated diffuse midline gliomas

Diffuse intrinsic pontine glioma (DIPG) and other H3K27M-mutated diffuse midline gliomas (DMGs) are universally lethal paediatric tumours of the central nervous system¹. We have previously shown that the disialoganglioside GD2 is highly expressed on H3K27M-mutated glioma cells and have demonstrated promising preclinical efficacy of GD2-directed chimeric antigen receptor (CAR) T cells², providing the rationale for a first-in-human phase I clinical trial (NCT04196413). Because CAR T cell-induced brainstem inflammation can result in obstructive hydrocephalus, increased intracranial pressure and dangerous tissue shifts, neurocritical care precautions were incorporated. Here we present the clinical experience from the first four patients with H3K27M-mutated DIPG or spinal cord DMG treated with GD2-CAR T cells at dose level 1 (1 × 10⁶ GD2-CAR T cells per kg administered intravenously). Patients who exhibited clinical benefit were eligible for subsequent GD2-CAR T cell infusions administered intracerebroventricularly³. Toxicity was largely related to the location of the tumour and was reversible with intensive supportive care. On-target, off-tumour toxicity was not observed. Three of four patients exhibited clinical and radiographic improvement. Pro-inflammatory cytokine levels were increased in the plasma and cerebrospinal fluid. Transcriptomic analyses of 65,598 single cells from CAR T cell products and cerebrospinal fluid elucidate heterogeneity in response between participants and administration routes. These early results underscore the promise of this therapeutic approach for patients with H3K27M-mutated DIPG or spinal cord DMG.

Anti-GD2 synergizes with CD47 blockade to mediate tumor eradication

The disialoganglioside GD2 is overexpressed on several solid tumors, and monoclonal antibodies targeting GD2 have substantially improved outcomes for children with high-risk neuroblastoma. However, approximately 40% of patients with neuroblastoma still relapse, and anti-GD2 has not mediated significant clinical activity in any other GD2+ malignancy. Macrophages are important mediators of anti-tumor immunity, but tumors resist macrophage phagocytosis through expression of the checkpoint molecule CD47, a so-called 'Don't eat me' signal. In this study, we establish potent synergy for the combination of anti-GD2 and anti-CD47 in syngeneic and xenograft mouse models of neuroblastoma, where the combination eradicates tumors, as well as osteosarcoma and small-cell lung cancer, where the combination significantly reduces tumor burden and extends survival. This synergy is driven by two GD2-specific factors that reorient the balance of macrophage activity. Ligation of GD2 on tumor cells (a) causes upregulation of surface calreticulin, a pro-phagocytic 'Eat me' signal that primes cells for removal and (b) interrupts the interaction of GD2 with its newly identified ligand, the inhibitory immunoreceptor Siglec-7. This work credentials the combination of anti-GD2 and anti-CD47 for clinical translation and suggests that CD47 blockade will be most efficacious in combination with monoclonal antibodies that alter additional pro- and anti-phagocytic signals within the tumor microenvironment.

Tisagenlecleucel outcomes in relapsed/refractory extramedullary ALL: a Pediatric Real World CAR Consortium Report

Chimeric antigen receptor (CAR) T cells have transformed the therapeutic options for relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia. Data for CAR therapy in extramedullary (EM) involvement are limited. Retrospective data were abstracted from the Pediatric Real World CAR Consortium (PRWCC) of 184 infused patients from 15 US institutions. Response (complete response) rate, overall survival (OS), relapse-free survival (RFS), and duration of B-cell aplasia (BCA) in patients referred for tisagenlecleucel with EM disease (both central nervous system (CNS)3 and non-CNS EM) were compared with bone marrow (BM) only. Patients with CNS disease were further stratified for comparison. Outcomes are reported on 55 patients with EM disease before CAR therapy (CNS3, n = 40; non-CNS EM, n = 15). The median age at infusion in the CNS cohort was 10 years (range, <1-25 years), and in the non-CNS EM cohort it was 13 years (range, 2-26 years). In patients with CNS disease, 88% (35 of 40) achieved a complete response vs only 66% (10 of 15) with non-CNS EM disease. Patients with CNS disease (both with and without BM involvement) had 24-month OS outcomes comparable to those of non-CNS EM or BM only (P = .41). There was no difference in 12-month RFS between CNS, non-CNS EM, or BM-only patients (P = .92). No increased toxicity was seen with CNS or non-CNS EM disease (P = .3). Active CNS disease at time of infusion did not affect outcomes. Isolated CNS disease trended toward improved OS compared with combined CNS and BM (P = .12). R/R EM disease can be effectively treated with tisagenlecleucel; toxicity, relapse, and survival rates are comparable to those of patients with BM-only disease. Outcomes for isolated CNS relapse are encouraging.

GPC2-CAR T cells tuned for low antigen density mediate potent activity against neuroblastoma without toxicity

Pediatric cancers often mimic fetal tissues and express proteins normally silenced postnatally that could serve as immune targets. We developed T cells expressing chimeric antigen receptors (CARs) targeting glypican-2 (GPC2), a fetal antigen expressed on neuroblastoma (NB) and several other solid tumors. CARs engineered using standard designs control NBs with transgenic GPC2 overexpression, but not those expressing clinically relevant GPC2 site density (∼5,000 molecules/cell, range 1-6 × 10³). Iterative engineering of transmembrane (TM) and co-stimulatory domains plus overexpression of c-Jun lowered the GPC2-CAR antigen density threshold, enabling potent and durable eradication of NBs expressing clinically relevant GPC2 antigen density, without toxicity. These studies highlight the critical interplay between CAR design and antigen density threshold, demonstrate potent efficacy and safety of a lead GPC2-CAR candidate suitable for clinical testing, and credential oncofetal antigens as a promising class of targets for CAR T cell therapy of solid tumors.

NOT-Gated CD93 CAR T Cells Effectively Target AML with Minimized Endothelial Cross-Reactivity

CD93 CAR T cells eliminate AML in preclinical models without targeting hematopoietic progenitor cells, and a NOT-gated CAR engineering strategy mitigates on-target, off-tumor toxicity to endothelial cells.

Chimeric antigen receptor (CAR) T cells hold promise for the treatment of acute myeloid leukemia (AML), but optimal targets remain to be defined. We demonstrate that CD93 CAR T cells engineered from a novel humanized CD93-specific binder potently kill AML in vitro and in vivo but spare hematopoietic stem and progenitor cells (HSPC). No toxicity is seen in murine models, but CD93 is expressed on human endothelial cells, and CD93 CAR T cells recognize and kill endothelial cell lines. We identify other AML CAR T-cell targets with overlapping expression on endothelial cells, especially in the context of proinflammatory cytokines. To address the challenge of endothelial-specific cross-reactivity, we provide proof of concept for NOT-gated CD93 CAR T cells that circumvent endothelial cell toxicity in a relevant model system. We also identify candidates for combinatorial targeting by profiling the transcriptome of AML and endothelial cells at baseline and after exposure to proinflammatory cytokines.

Gene editing to enhance the efficacy of cancer cell therapies

Adoptive T cell therapies have shown impressive signals of activity, but their clinical impact could be enhanced by technologies to increase T cell potency and diminish the cost and labor involved in manufacturing these products. Gene editing platforms are under study in this arena to (1) enhance immune cell potency by knocking out molecules that inhibit immune responses; (2) deliver genetic payloads into precise genomic locations and thereby enhance safety and/or improve the gene expression profile by leveraging physiologic promoters, enhancers, and repressors; and (3) enable off-the-shelf therapies by preventing alloreactivity and immune rejection. This review discusses gene editing approaches that have been the best studied in the context of human T cells and adoptive T cell therapies, summarizing their current status and near-term potential for translation.

A Fructo-Oligosaccharide Prebiotic Is Well Tolerated in Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplantation: A Phase I Dose-Escalation Trial

Alterations of the gut microbiota after allogeneic hematopoietic cell transplantation (allo-HCT) are a key factor in the development of transplant-related complications such as graft-versus-host disease (GVHD). Interventions that preserve the gut microbiome hold promise to improve HCT-associated morbidity and mortality. Murine models demonstrate that prebiotics such as fructo-oligosaccharides (FOSs) may increase gut levels of short-chain fatty acids (SCFAs) such as butyrate and consequently induce proliferation of immunomodulatory FOXP3+CD4+ regulatory T cells (Tregs), which impact GVHD risk. We conducted a pilot phase I trial to investigate the maximum tolerated dose of FOS in patients undergoing reduced-intensity allo-HCT (n = 15) compared with concurrent controls (n = 16). We administered the FOS starting at pretransplant conditioning and continuing for a total of 21 days. We characterized the gut microbiome using shotgun metagenomic sequencing, measured stool short-chain fatty acids (SCFAs) using liquid chromatography-mass spectrometry, and determined peripheral T cell concentrations using cytometry by time-of-flight. We found that FOS was safe and well-tolerated at 10 g/d without significant adverse effects in patients undergoing allo-HCT. Community-level gut microbiota composition differed significantly on the day of transplant (day 0) between patients receiving FOS and concurrent controls; however, FOS-associated alterations of the gut microbiota were not sustained after transplant. Although the impact of FOS was fleeting, transplantation itself impacted a substantial number of taxa over time. In our small pilot trial, no significant differences were observed in gut microbial metabolic pathways, stool SCFAs, or peripheral Tregs, although Tregs trended higher in those patients who received FOS. A marker of CD4+ T cell activation (namely, CTLA4+) was significantly higher in patients receiving FOS, whereas a non-significant trend existed for FOP3+CD4+ Treg cells, which were higher in those receiving FOS compared with controls. FOS is well tolerated at 10 g/d in patients undergoing reduced-intensity allo-HCT. Although the alterations in gut microbiota and peripheral immune cell composition in those receiving FOS are intriguing, additional studies are required to investigate the use of prebiotics in HCT recipients.

Allogeneic CAR Invariant Natural Killer T Cells Exert Potent Antitumor Effects through Host CD8 T-Cell Cross-Priming

PURPOSE

The development of allogeneic chimeric antigen receptor (CAR) T-cell therapies for off-the-shelf use is a major goal that faces two main immunologic challenges, namely the risk of graft-versus-host disease (GvHD) induction by the transferred cells and the rejection by the host immune system limiting their persistence. In this work we assessed the direct and indirect antitumor effect of allogeneic CAR-engineered invariant natural killer T (iNKT) cells, a cell population without GvHD-induction potential that displays immunomodulatory properties.

EXPERIMENTAL DESIGN

After assessing murine CAR iNKT cells direct antitumor effects in vitro and in vivo, we employed an immunocompetent mouse model of B-cell lymphoma to assess the interaction between allogeneic CAR iNKT cells and endogenous immune cells.

RESULTS

We demonstrate that allogeneic CAR iNKT cells exerted potent direct and indirect antitumor activity when administered across major MHC barriers by inducing tumor-specific antitumor immunity through host CD8 T-cell cross-priming.

CONCLUSIONS

In addition to their known direct cytotoxic effect, allogeneic CAR iNKT cells induce host CD8 T-cell antitumor responses, resulting in a potent antitumor effect lasting longer than the physical persistence of the allogeneic cells. The utilization of off-the-shelf allogeneic CAR iNKT cells could meet significant unmet needs in the clinic.