Cooperative CAR targeting to selectively eliminate AML and minimize escape.

Acute myeloid leukemia (AML) poses a singular challenge for chimeric antigen receptor (CAR) therapy owing to its phenotypic heterogeneity and similarity to normal hematopoietic stem/progenitor cells (HSPCs). Here we expound a CAR strategy intended to efficiently target AML while minimizing HSPC toxicity. Quantification of target expression in relapsed/refractory patient samples and normal HSPCs reveals a therapeutic window for gated co-targeting of ADGRE2 and CLEC12A: We combine an attenuated ADGRE2-CAR with a CLEC12A-chimeric costimulatory receptor (ADCLEC.syn1) to preferentially engage ADGRE2posCLEC12Apos leukemic stem cells over ADGRE2lowCLEC12Aneg normal HSPCs. ADCLEC.syn1 prevents antigen escape in AML xenograft models, outperforms the ADGRE2-CAR alone and eradicates AML despite proximate myelopoiesis in humanized mice. Off-target HSPC toxicity is similar to that of a CD19-CAR and can be mitigated by reducing CAR T cell-derived interferon-γ. Overall, we demonstrate the ability of target density-adapted cooperative CAR targeting to selectively eliminate AML and potentially obviate the need for hematopoietic rescue.

CD19 CAR T-cell therapy and prophylactic anakinra in relapsed or refractory lymphoma: phase 2 trial interim results.

In preclinical models, anakinra, an IL-1 receptor antagonist (IL-1Ra), reduced immune effector cell-associated neurotoxicity syndrome (ICANS) without compromising anti-CD19 chimeric antigen receptor (CAR) T-cell efficacy. We initiated a phase 2 clinical trial of anakinra in patients with relapsed/refractory large B-cell lymphoma and mantle cell lymphoma treated with commercial anti-CD19 CAR T-cell therapy. Here we report a non-prespecified interim analysis reporting the final results from cohort 1 in which patients received subcutaneous anakinra from day 2 until at least day 10 post-CAR T-cell infusion. The primary endpoint was the rate of severe (grade ≥3) ICANS. Key secondary endpoints included the rates of all-grade cytokine release syndrome (CRS) and ICANS and overall disease response. Among 31 treated patients, 74% received axicabtagene ciloleucel, 13% received brexucabtagene ciloleucel and 4% received tisagenlecleucel. All-grade ICANS occurred in 19%, and severe ICANS occurred in 9.7% of patients. There were no grade 4 or 5 ICANS events. All-grade CRS occurred in 74%, and severe CRS occurred in 6.4% of patients. The overall disease response rate was 77% with 65% complete response rate. These initial results show that prophylactic anakinra resulted in a low incidence of ICANS in patients with lymphoma receiving anti-CD19 CAR T-cell therapy and support further study of anakinra in immune-related neurotoxicity syndromes.

Validation of a High-Sensitivity Assay for Detection of Chimeric Antigen Receptor T-Cell Vectors Using Low-Partition Digital PCR Technology.

Although in vivo engraftment, expansion, and persistence of chimeric antigen receptor (CAR) T cells are pivotal components of treatment efficacy, quantitative monitoring has not been implemented in routine clinical practice. We describe the development and analytical validation of a digital PCR assay for ultrasensitive detection of CAR constructs after treatment, circumventing known technical limitations of low-partitioning platforms. Primers and probes, designed for detection of axicabtagene, brexucabtagene, and Memorial Sloan Kettering CAR constructs, were employed to validate testing on the Bio-Rad digital PCR low-partitioning platform; results were compared with Raindrop, a high-partitioning system, as reference method. Bio-Rad protocols were modified to enable testing of DNA inputs as high as 500 ng. Using dual-input reactions (20 and 500 ng) and a combined analysis approach, the assay demonstrated consistent target detection around 1 × 10-5 (0.001%) with excellent specificity and reproducibility and 100% accuracy compared with the reference method. Dedicated analysis of 53 clinical samples received during validation/implementation phases showed the assay effectively enabled monitoring across multiple time points of early expansion (day 6 to 28) and long-term persistence (up to 479 days). CAR vectors were detected at levels ranging from 0.005% to 74% (vector versus reference gene copies). The highest levels observed in our cohort correlated strongly with the temporal diagnosis of grade 2 and 3 cytokine release syndrome diagnosis (P < 0.005). Only three patients with undetectable constructs had disease progression at the time of sampling.

Unraveling barriers to iPSC-derived CAR-T cell differentiation.

The generation of off-the-shelf CAR-T cells from TiPSCs has been hindered by the difficulty to recapitulate adaptive T cell development and lower therapeutic efficacy compared to peripheral blood CAR-T cells. Ueda et al. address these issues in a triple-engineering strategy, combining optimized CAR expression with cytolytic and persistence enhancements.

Programming CAR T Cell Tumor Recognition: Tuned Antigen Sensing and Logic Gating.

The success of chimeric antigen receptor (CAR) T cells targeting B-cell malignancies propelled the field of synthetic immunology and raised hopes to treat solid tumors in a similar fashion. Antigen escape and the paucity of tumor-restricted CAR targets are recognized challenges to fulfilling this prospect. Recent advances in CAR T cell engineering extend the toolbox of chimeric receptors available to calibrate antigen sensitivity and combine receptors to create adapted tumor-sensing T cells. Emerging engineering strategies to lower the threshold for effective antigen recognition, when needed, and enable composite antigen recognition hold great promise for overcoming tumor heterogeneity and curbing off-tumor toxicities. SIGNIFICANCE: Improving the clinical efficacy of CAR T cell therapies will require engineering T cells that overcome heterogeneous and low-abundance target expression while minimizing reactivity to normal tissues. Recent advances in CAR design and logic gating are poised to extend the success of CAR T cell therapies beyond B-cell malignancies.

Replication competent retrovirus testing (RCR) in the National Gene Vector Biorepository: No evidence of RCR in 1,595 post-treatment peripheral blood samples obtained from 60 clinical trials.

The clinical impact of any therapy requires the product be safe and effective. Gammaretroviral vectors pose several unique risks, including inadvertent exposure to replication competent retrovirus (RCR) that can arise during vector manufacture. The US FDA has required patient monitoring for RCR, and the National Gene Vector Biorepository is an NIH resource that has assisted eligible investigators in meeting this requirement. To date, we have found no evidence of RCR in 338 pre-treatment and 1,595 post-treatment blood samples from 737 patients associated with 60 clinical trials. Most samples (75%) were obtained within 1 year of treatment, and samples as far out as 9 years after treatment were analyzed. The majority of trials (93%) were cancer immunotherapy, and 90% of the trials used vector products produced with the PG13 packaging cell line. The data presented here provide further evidence that current manufacturing methods generate RCR-free products and support the overall safety profile of retroviral gene therapy.

GPRC5D-Targeted CAR T Cells for Myeloma.

BACKGROUND: B-cell maturation antigen (BCMA)-directed chimeric antigen receptor (CAR) T-cell therapies have generated responses in patients with advanced myeloma, but relapses are common. G protein-coupled receptor, class C, group 5, member D (GPRC5D) has been identified as an immunotherapeutic target in multiple myeloma. Preclinical studies have shown the efficacy of GPRC5D-targeted CAR T cells, including activity in a BCMA antigen escape model. METHODS: In this phase 1 dose-escalation study, we administered a GPRC5D-targeted CAR T-cell therapy (MCARH109) at four dose levels to patients with heavily pretreated multiple myeloma, including patients with relapse after BCMA CAR T-cell therapy. RESULTS: A total of 17 patients were enrolled and received MCARH109 therapy. The maximum tolerated dose was identified at 150×106 CAR T cells. At the 450×106 CAR T-cell dose, 1 patient had grade 4 cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome (ICANS), and 2 patients had a grade 3 cerebellar disorder of unclear cause. No cerebellar disorder, ICANS of any grade, or cytokine release syndrome of grade 3 or higher occurred in the 12 patients who received doses of 25×106 to 150×106 cells. A response was reported in 71% of the patients in the entire cohort and in 58% of those who received doses of 25×106 to 150×106 cells. The patients who had a response included those who had received previous BCMA therapies; responses were observed in 7 of 10 such patients in the entire cohort and in 3 of 6 such patients who received 25×106 to 150×106 cells. CONCLUSIONS: The results of this study of a GPRC5D-targeted CAR T-cell therapy (MCARH109) confirm that GPRC5D is an active immunotherapeutic target in multiple myeloma. (Funded by Juno Therapeutics/Bristol Myers Squibb; ClinicalTrials.gov number, NCT04555551.).

Generation of T-cell-receptor-negative CD8αß-positive CAR T cells from T-cell-derived induced pluripotent stem cells.

The production of autologous T cells expressing a chimaeric antigen receptor (CAR) is time-consuming, costly and occasionally unsuccessful. T-cell-derived induced pluripotent stem cells (TiPS) are a promising source for the generation of 'off-the-shelf' CAR T cells, but the in vitro differentiation of TiPS often yields T cells with suboptimal features. Here we show that the premature expression of the T-cell receptor (TCR) or a constitutively expressed CAR in TiPS promotes the acquisition of an innate phenotype, which can be averted by disabling the TCR and relying on the CAR to drive differentiation. Delaying CAR expression and calibrating its signalling strength in TiPS enabled the generation of human TCR- CD8αß+ CAR T cells that perform similarly to CD8αß+ CAR T cells from peripheral blood, achieving effective tumour control on systemic administration in a mouse model of leukaemia and without causing graft-versus-host disease. Driving T-cell maturation in TiPS in the absence of a TCR by taking advantage of a CAR may facilitate the large-scale development of potent allogeneic CD8αß+ T cells for a broad range of immunotherapies.

Gut microbiome correlates of response and toxicity following anti-CD19 CAR T cell therapy.

Anti-CD19 chimeric antigen receptor (CAR) T cell therapy has led to unprecedented responses in patients with high-risk hematologic malignancies. However, up to 60% of patients still experience disease relapse and up to 80% of patients experience CAR-mediated toxicities, such as cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. We investigated the role of the intestinal microbiome on these outcomes in a multicenter study of patients with B cell lymphoma and leukemia. We found in a retrospective cohort (n = 228) that exposure to antibiotics, in particular piperacillin/tazobactam, meropenem and imipenem/cilastatin (P-I-M), in the 4 weeks before therapy was associated with worse survival and increased neurotoxicity. In stool samples from a prospective cohort of CAR T cell recipients (n = 48), the fecal microbiome was altered at baseline compared to healthy controls. Stool sample profiling by 16S ribosomal RNA and metagenomic shotgun sequencing revealed that clinical outcomes were associated with differences in specific bacterial taxa and metabolic pathways. Through both untargeted and hypothesis-driven analysis of 16S sequencing data, we identified species within the class Clostridia that were associated with day 100 complete response. We concluded that changes in the intestinal microbiome are associated with clinical outcomes after anti-CD19 CAR T cell therapy in patients with B cell malignancies.

CD19-directed chimeric antigen receptor T cell therapy in Waldenström macroglobulinemia: a preclinical model and initial clinical experience.

BACKGROUND: Waldenström macroglobulinemia (WM) is an incurable disease and, while treatable, can develop resistance to available therapies and be fatal. Chimeric antigen receptor (CAR) T cell therapy directed against the CD19 antigen has demonstrated efficacy in relapsed or refractory B lymphoid malignancies, and is now approved for B cell acute lymphoblastic leukemia and certain B cell lymphomas. However, CAR T therapy has not been evaluated for use in WM. METHODS AND RESULTS: We performed preclinical studies demonstrating CAR T cell activity against WM cells in vitro, and developed an in vivo murine model of WM which demonstrated prolonged survival with use of CAR T therapy. We then report the first three patients with multiply relapsed and refractory WM treated for their disease with CD19-directed CAR T cells on clinical trials. Treatment was well tolerated, and observed toxicities were consistent with those seen in CAR T treatment for other diseases, and no grade 3 or higher cytokine release syndrome or neurotoxicity events occurred. All three patients attained at least a clinical response to treatment, including one minimal residual disease-negative complete response, though all three eventually developed recurrent disease between 3 and 26 months after initial treatment. CONCLUSIONS: This report summarizes preclinical and clinical activity of CD19-directed CAR T therapy in WM, demonstrating early tolerability and efficacy in patients with WM, and representing a possible treatment option in patients with heavily pretreated and relapsed or refractory WM. Larger studies evaluating CAR T therapy in WM are warranted, along with further evaluation into mechanisms of resistance to CAR T therapy.

HLA-independent T cell receptors for targeting tumors with low antigen density.

Chimeric antigen receptors (CARs) are receptors for antigen that direct potent immune responses. Tumor escape associated with low target antigen expression is emerging as one potential limitation of their efficacy. Here we edit the TRAC locus in human peripheral blood T cells to engage cell-surface targets through their T cell receptor-CD3 complex reconfigured to utilize the same immunoglobulin heavy and light chains as a matched CAR. We demonstrate that these HLA-independent T cell receptors (HIT receptors) consistently afford high antigen sensitivity and mediate tumor recognition beyond what CD28-based CARs, the most sensitive design to date, can provide. We demonstrate that the functional persistence of HIT T cells can be augmented by constitutive coexpression of CD80 and 4-1BBL. Finally, we validate the increased antigen sensitivity afforded by HIT receptors in xenograft mouse models of B cell leukemia and acute myeloid leukemia, targeting CD19 and CD70, respectively. Overall, HIT receptors are well suited for targeting cell surface antigens of low abundance.

Lentiviral globin gene therapy with reduced-intensity conditioning in adults with ß-thalassemia: a phase 1 trial.

ß-Thalassemias are inherited anemias that are caused by the absent or insufficient production of the ß chain of hemoglobin. Here we report 6-8-year follow-up of four adult patients with transfusion-dependent ß-thalassemia who were infused with autologous CD34+ cells transduced with the TNS9.3.55 lentiviral globin vector after reduced-intensity conditioning (RIC) in a phase 1 clinical trial ( NCT01639690) . Patients were monitored for insertional mutagenesis and the generation of a replication-competent lentivirus (safety and tolerability of the infusion product after RIC-primary endpoint) and engraftment of genetically modified autologous CD34+ cells, expression of the transduced ß-globin gene and post-transplant transfusion requirements (efficacy-secondary endpoint). No unexpected safety issues occurred during conditioning and cell product infusion. Hematopoietic gene marking was very stable but low, reducing transfusion requirements in two patients, albeit not achieving transfusion independence. Our findings suggest that non-myeloablative conditioning can achieve durable stem cell engraftment but underscore a minimum CD34+ cell transduction requirement for effective therapy. Moderate clonal expansions were associated with integrations near cancer-related genes, suggestive of non-erythroid activity of globin vectors in stem/progenitor cells. These correlative findings highlight the necessity of cautiously monitoring patients harboring globin vectors.

Depletion of high-content CD14+ cells from apheresis products is critical for successful transduction and expansion of CAR T cells during large-scale cGMP manufacturing.

With the US Food and Drug Administration (FDA) approval of four CD19- and one BCMA-targeted chimeric antigen receptor (CAR) therapy for B cell malignancies, CAR T cell therapy has finally reached the status of a medicinal product. The successful manufacturing of autologous CAR T cell products is a key requirement for this promising treatment modality. By analyzing the composition of 214 apheresis products from 210 subjects across eight disease indications, we found that high CD14+ cell content poses a challenge for manufacturing CAR T cells, especially in patients with non-Hodgkin's lymphoma and multiple myeloma caused by the non-specific phagocytosis of the magnetic beads used to activate CD3+ T cells. We demonstrated that monocyte depletion via rapid plastic surface adhesion significantly reduces the CD14+ monocyte content in the apheresis products and simultaneously boosts the CD3+ content. We established a 40% CD14+ threshold for the stratification of apheresis products across nine clinical trials and demonstrated the effectiveness of this procedure by comparing manufacturing runs in two phase 1 clinical trials. Our study suggests that CD14+ content should be monitored in apheresis products, and that the manufacturing of CAR T cells should incorporate a step that lessens the CD14+ cell content in apheresis products containing more than 40% to maximize the production success.

A Phase I Trial of Regional Mesothelin-Targeted CAR T-cell Therapy in Patients with Malignant Pleural Disease, in Combination with the Anti-PD-1 Agent Pembrolizumab.

Malignant pleural diseases, comprising metastatic lung and breast cancers and malignant pleural mesothelioma (MPM), are aggressive solid tumors with poor therapeutic response. We developed and conducted a first-in-human, phase I study of regionally delivered, autologous, mesothelin-targeted chimeric antigen receptor (CAR) T-cell therapy. Intrapleural administration of 0.3M to 60M CAR T cells/kg in 27 patients (25 with MPM) was safe and well tolerated. CAR T cells were detected in peripheral blood for >100 days in 39% of patients. Following our demonstration that PD-1 blockade enhances CAR T-cell function in mice, 18 patients with MPM also received pembrolizumab safely. Among those patients, median overall survival from CAR T-cell infusion was 23.9 months (1-year overall survival, 83%). Stable disease was sustained for ≥6 months in 8 patients; 2 exhibited complete metabolic response on PET scan. Combination immunotherapy with CAR T cells and PD-1 blockade agents should be further evaluated in patients with solid tumors. SIGNIFICANCE: Regional delivery of mesothelin-targeted CAR T-cell therapy followed by pembrolizumab administration is feasible, safe, and demonstrates evidence of antitumor efficacy in patients with malignant pleural diseases. Our data support the investigation of combination immunotherapy with CAR T cells and PD-1 blockade agents in solid tumors.See related commentary by Aldea et al., p. 2674.This article is highlighted in the In This Issue feature, p. 2659.

CAR T cells: Building on the CD19 paradigm.

Spearheaded by the therapeutic use of chimeric antigen receptors (CARs) targeting CD19, synthetic immunology has entered the clinical arena. CARs are recombinant receptors for antigen that engage cell surface molecules through the variable region of an antibody and signal through arrayed T-cell activating and costimulatory domains. CARs allow redirection of T-cell cytotoxicity against any antigen of choice, independent of MHC expression. Patient T cells engineered to express CARs specific for CD19 have yielded remarkable outcomes in subjects with relapsed/refractory B- cell malignancies, setting off unprecedented interest in T-cell engineering and cell-based cancer immunotherapy. In this review, we present the challenges to extend the use of CAR T cells to solid tumors and other pathologies. We further highlight progress in CAR design, cell manufacturing, and genome editing, which in aggregate hold the promise of generating safer and more effective genetically instructed immunity. Novel engineered cell types, including innate T-cell types, natural killer (NK) cells, macrophages, and induced pluripotent stem cell-derived immune cells, are on the horizon, as are applications of CAR T cells to treat autoimmunity, severe infections, and senescence-associated pathologies.

Interventions and outcomes of adult patients with B-ALL progressing after CD19 chimeric antigen receptor T-cell therapy.

CD19-targeted chimeric antigen receptor (CAR) T-cell therapy has become a breakthrough treatment of patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, despite the high initial response rate, the majority of adult patients with B-ALL progress after CD19 CAR T-cell therapy. Data on the natural history, management, and outcome of adult B-ALL progressing after CD19 CAR T cells have not been described in detail. Herein, we report comprehensive data of 38 adult patients with B-ALL who progressed after CD19 CAR T therapy at our institution. The median time to progression after CAR T-cell therapy was 5.5 months. Median survival after post-CAR T progression was 7.5 months. A high disease burden at the time of CAR T-cell infusion was significantly associated with risk of post-CAR T progression. Thirty patients (79%) received salvage treatment of post-CAR T disease progression, and 13 patients (43%) achieved complete remission (CR), but remission duration was short. Notably, 7 (58.3%) of 12 patients achieved CR after blinatumomab and/or inotuzumab administered following post-CAR T failure. Multivariate analysis revealed that a longer remission duration from CAR T cells was associated with superior survival after progression following CAR T-cell therapy. In summary, overall prognosis of adult B-ALL patients progressing after CD19 CAR T cells was poor, although a subset of patients achieved sustained remissions to salvage treatments, including blinatumomab, inotuzumab, and reinfusion of CAR T cells. Novel therapeutic strategies are needed to reduce risk of progression after CAR T-cell therapy and improve outcomes of these patients.

Preclinical Efficacy and Safety of a Human Embryonic Stem Cell-Derived Midbrain Dopamine Progenitor Product, MSK-DA01.

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra leading to disabling deficits. Dopamine neuron grafts may provide a significant therapeutic advance over current therapies. We have generated midbrain dopamine neurons from human embryonic stem cells and manufactured large-scale cryopreserved dopamine progenitors for clinical use. After optimizing cell survival and phenotypes in short-term studies, the cell product, MSK-DA01, was subjected to an extensive set of biodistribution, toxicity, and tumorigenicity assessments in mice under GLP conditions. A large-scale efficacy study was also performed in rats with the same lot of cells intended for potential human use and demonstrated survival of the grafted cells and behavioral amelioration in 6-hydroxydopamine lesioned rats. There were no adverse effects attributable to the grafted cells, no obvious distribution outside the brain, and no cell overgrowth or tumor formation, thus paving the way for a future clinical trial.