Second-generation Chimeric Antigen Receptor Research Articles

Simultaneous targeting of Tim3 and A2a receptors modulates MSLN-CAR T cell antitumor function in a human cervical tumor xenograft model.

Chimeric antigen receptor (CAR) T cell therapy has transformed the treatment of hematological malignancies. However, its efficacy in solid tumors is limited by the immunosuppressive tumor microenvironment that compromises CAR T cell antitumor function in clinical settings. To overcome this challenge, researchers have investigated the potential of inhibiting specific immune checkpoint receptors, including A2aR (Adenosine A2 Receptor) and Tim3 (T cell immunoglobulin and mucin domain-containing protein 3), to enhance CAR T cell function. In this study, we evaluated the impact of genetic targeting of Tim3 and A2a receptors on the antitumor function of human mesothelin-specific CAR T cells (MSLN-CAR) in vitro and in vivo. Second-generation anti-mesothelin CAR T cells were produced using standard cellular and molecular techniques. A2aR-knockdown and/or Tim3- knockdown anti-mesothelin-CAR T cells were generated using shRNA-mediated gene silencing. The antitumor function of CAR T cells was evaluated by measuring cytokine production, proliferation, and cytotoxicity in vitro through coculture with cervical cancer cells (HeLa cell line). To evaluate in vivo antitumor efficacy of manufactured CAR T cells, tumor growth and mouse survival were monitored in a human cervical cancer xenograft model. In vitro experiments demonstrated that knockdown of A2aR alone or in combination with Tim3 significantly improved CAR T cell proliferation, cytokine production, and cytotoxicity in presence of tumor cells in an antigen-specific manner. Furthermore, in the humanized xenograft model, both double knockdown CAR T cells and control CAR T cells could effectively control tumor growth. However, single knockdown CAR T cells were associated with reduced survival in mice. These findings highlight the potential of concomitant genetic targeting of Tim3 and A2a receptors to augment the efficacy of CAR T cell therapy in solid tumors. Nevertheless, caution should be exercised in light of our observation of decreased survival in mice treated with single knockdown MSLN-CAR T cells, emphasizing the need for careful efficacy considerations.

Abstract B017: Novel mesothelin-based CAR T cells targeting MUC16 as an intravesical bladder cancer therapy

Abstract Intravesical therapies have been the mainstay of non-muscle invasive bladder cancer (BC) management; however, their efficacy is limited by toxicities, recurrences, and supply shortages. Consequently, many patients are recommended cystectomy, which is fraught with high complication rates. Thus, bladder-sparing treatments present a major, unmet clinical need. Chimeric antigen receptor (CAR) T cell therapy, wherein T cells are engineered to express an artificial receptor to a target, is an immunotherapeutic approach with efficacy in hematologic malignancies. Similar success in solid tumors has been hindered by a lack of suitable targets, reduced T cell infiltration/activity, and major toxicities, including on-target off-tumor effects and cytokine release syndromes. To overcome these limitations, locoregional delivery of CAR T cells is being investigated. Yet, to date, no studies have examined their potential as intravesical therapies. In this study, we used a computational pipeline using large-scale BC transcriptomics data to discover potential CAR targets which met strict criteria of high cell-surface expression on BC and minimal expression on normal tissue. We identified MUC16, a surface-bound mucinous glycoprotein, as a top candidate from this pipeline, which has more reduced pan-tissue expression than targets of precision-guided therapies in BC. Consistent with prior reports, MUC16 transcript and protein levels increase with grade and T stage and correlates with chemotherapeutic resistance. We also find MUC16 expression persists in recurrent tumors after BCG-therapy. To target MUC16, we designed second-generation CARs based on scFv derived from the antibody 3a5 (3a5-28z) and natural-ligands based on the high-affinity MUC16-mesothelin interaction (MSLN-28z) or its truncated binding domain (truncMSLN-28z) which were fused to CD28 co-stimulatory domains and CD3z chains of the T cell receptor. Using human BC lines with a broad range of MUC16 levels, we show MSLN-28z more effectively lyses MUC16+, but not MUC16−, cells than compared to 3a5-28z or truncMSLN-28z CAR T cells. Ablation of MUC16 by CRISPR/Cas9 or modification of MSLN-based CAR to lack signaling domains abolishes the cytotoxicity of MSLN-28z CAR T cells, demonstrating dependency on MUC16 engagement. Using multiplex assays and intracellular cytokine staining, we further demonstrate MSLN-28z CAR T cells have potent polyfunctionality through secretion of cytokines IL-2, IFN-g, and TNF-a by both CD4+ and CD8+ subsets. Last, in immunodeficient mice orthotopically xenografted with HT1376 cells, intravesical delivery of MSLN-28z CAR T cells enhances survival compared to CAR T cells delivered intravenously. This enhanced anti-tumor response correlates with reduced tumor weights and increased T cell infiltration. Notably, intravesically delivered CAR T cells are not detectable in peripheral circulation of tumor-bearing mice. Together, our findings substantiate MUC16 as a targetable antigen in BC and validate MSLN-based CAR T cells as a potential intravesical therapy. Citation Format: Parwiz Abrahimi, Jonathan Khan, Renier Brentjens, Taha Merghoub, Jedd Wolchok. Novel mesothelin-based CAR T cells targeting MUC16 as an intravesical bladder cancer therapy [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B017.

Genetically Engineered CLDN18.2 CAR-T Cells Expressing Synthetic PD1/CD28 Fusion Receptors Produced Using a Lentiviral Vector.

This study aimed to develop synthetic Claudin18.2 (CLDN18.2) chimeric antigen receptor (CAR)-T (CAR-T) cells as a treatment for advanced gastric cancer using lentiviral vector genetic engineering technology that targets the CLDN18.2 antigen and simultaneously overcomes the immunosuppressive environment caused by programmed cell death protein 1 (PD-1). Synthetic CAR T cells are a promising approach in cancer immunotherapy but face many challenges in solid tumors. One of the major problems is immunosuppression caused by PD-1. CLDN18.2, a gastric-specific membrane protein, is considered a potential therapeutic target for gastric and other cancers. In our study, CLDN18.2 CAR was a second-generation CAR with inducible T-cell costimulatory (CD278), and CLDN18.2-PD1/CD28 CAR was a third-generation CAR, wherein the synthetic PD1/CD28 chimeric-switch receptor (CSR) was added to the second-generation CAR. In vitro, we detected the secretion levels of different cytokines and the killing ability of CAR-T cells. We found that the secretion of cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) secreted by three types of CAR-T cells was increased, and the killing ability against CLDN18.2-positive GC cells was enhanced. In vivo, we established a xenograft GC model and observed the antitumor effects and off-target toxicity of CAR-T cells. These results support that synthetic anti-CLDN18.2 CAR-T cells have antitumor effect and anti-CLDN18.2-PD1/CD28 CAR could provide a promising design strategy to improve the efficacy of CAR-T cells in advanced gastric cancer.

Therapeutic potential of third-generation chimeric antigen receptor T cells targeting B cell maturation antigen for treating multiple myeloma

Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the rapid proliferation of malignant plasma cells within the bone marrow. Standard therapies often fail due to patient resistance. The US FDA has approved second-generation chimeric antigen receptor (CAR) T cells targeting B-cell maturation antigen (anti-BCMA-CAR2 T cells) for MM treatment. However, achieving enduring clinical responses remains a challenge in CAR T cell therapy. This study developed third-generation T cells with an anti-BCMA CAR (anti-BCMA-CAR3). The CAR incorporated a fully human scFv specific to BCMA, linked to the CD8 hinge region. The design included the CD28 transmembrane domain, two co-stimulatory domains (CD28 and 4-1BB), and the CD3ζ signaling domain (28BBζ). Lentiviral technology generated these modified T cells, which were compared against anti-BCMA-CAR2 T cells for efficacy against cancer. Anti-BCMA-CAR3 T cells exhibited significantly higher cytotoxic activity against BCMA-expressing cells (KMS-12-PE and NCI-H929) compared to anti-BCMA-CAR2 T cells. At an effector-to-target ratio of 10:1, anti-BCMA-CAR3 T cells induced lysis in 75.5 ± 3.8% of NCI-H929 cells, whereas anti-BCMA-CAR2 T cells achieved 56.7 ± 3.4% (p = 0.0023). Notably, after twelve days of cultivation, anti-BCMA-CAR3 T cells nearly eradicated BCMA-positive cells (4.1 ± 2.1%), while anti-BCMA-CAR2 T cells allowed 36.8 ± 20.1% to survive. This study highlights the superior efficacy of anti-BCMA-CAR3 T cells against both low and high BCMA-expressing MM cells, surpassing anti-BCMA-CAR2 T cells. These findings suggest potential for advancing anti-BCMA-CAR3 T cells in chimeric antigen receptor T (CAR-T) therapy for relapsed/refractory MM.

Scrutiny of chimeric antigen receptor activation by the extracellular domain: experience with single domain antibodies targeting multiple myeloma cells highlights the need for case-by-case optimization.

Multiple myeloma (MM) remains incurable, despite the advent of chimeric antigen receptor (CAR)-T cell therapy. This unfulfilled potential can be attributed to two untackled issues: the lack of suitable CAR targets and formats. In relation to the former, the target should be highly expressed and reluctant to shedding; two characteristics that are attributed to the CS1-antigen. Furthermore, conventional CARs rely on scFvs for antigen recognition, yet this withholds disadvantages, mainly caused by the intrinsic instability of this format. VHHs have been proposed as valid scFv alternatives. We therefore intended to develop VHH-based CAR-T cells, targeting CS1, and to identify VHHs that induce optimal CAR-T cell activation together with the VHH parameters required to achieve this. CS1-specific VHHs were generated, identified and fully characterized, in vitro and in vivo. Next, they were incorporated into second-generation CARs that only differ in their antigen-binding moiety. Reporter T-cell lines were lentivirally transduced with the different VHH-CARs and CAR-T cell activation kinetics were evaluated side-by-side. Affinity, cell-binding capacity, epitope location, in vivo behavior, binding distance, and orientation of the CAR-T:MM cell interaction pair were investigated as predictive parameters for CAR-T cell activation. Our data show that the VHHs affinity for its target antigen is relatively predictive for its in vivo tumor-tracing capacity, as tumor uptake generally decreased with decreasing affinity in an in vivo model of MM. This does not hold true for their CAR-T cell activation potential, as some intermediate affinity-binding VHHs proved surprisingly potent, while some higher affinity VHHs failed to induce equal levels of T-cell activation. This could not be attributed to cell-binding capacity, in vivo VHH behavior, epitope location, cell-to-cell distance or binding orientation. Hence, none of the investigated parameters proved to have significant predictive value for the extent of CAR-T cell activation. We gained insight into the predictive parameters of VHHs in the CAR-context using a VHH library against CS1, a highly relevant MM antigen. As none of the studied VHH parameters had predictive value, defining VHHs for optimal CAR-T cell activation remains bound to serendipity. These findings highlight the importance of screening multiple candidates.

Abstract LB071: Weaponizing CAR T-cells to attack PD-L1 presenting cells in solid tumors

Abstract Despite its success in treating blood cancers, chimeric antigen receptor (CAR) T-cell therapy has not yielded anticipated clinical outcomes in patients with solid tumors. This discrepancy is primarily attributed to the lack of dependable antigens and the immunosuppressive nature of the tumor microenvironment (TME). A pivotal evasion mechanism employed by tumor to counter antitumor immunity involves the upregulation of programmed death ligand 1 (PD-L1), which interacts with PD1 on T cells, deactivating effector T cells. A variety of immunosuppressive cells within the TME employ similar mechanisms to inhibit T-cell functions. These findings provide a rationale for targeting PD-L1 in both tumors and the immunosuppressive cells. Using a humanized anti-PD-L1 monoclonal antibody, we engineered a second-generation PD-L1 CAR, namely MC9999. MC9999 CAR T-cells exhibited antigen-specific cytotoxicity in vitro and elicited potent in vivo antitumor effects against PD-L1-expressing MDA-MD-232 breast cancer cells. The effectiveness of MC9999 CAR T-cells was confirmed across three other solid tumor models: non-small cell lung cancer, melanoma and glioblastoma (GBM). Notably, intravenous administration of MC9999 CAR T-cells eradicated intracranially established LN229 GBM tumors, suggesting the potential to penetrate the blood-brain barrier. In addition to targeting tumor cells, MC9999 CAR T-cells exhibited cytotoxicity against three immunosuppressive cell models, including HMC3 microglia cells, M2 macrophages, and importantly, primary tumor-associated macrophages (TAMs) isolated from GBM. Furthermore, we engineered patient-derived MC9999 CAR T-cells and demonstrated their effectiveness against two primary tumor cell lines derived from GBM tumors and HMC3 cells. Collectively, these proof-of-principle study findings substantiate the viability of targeting PD-L1 against both tumors and their immunosuppressive microenvironment. This prototype MC9999 CAR lays the groundwork for further development of clinically applicable CAR T-cell therapy against solid tumors. Citation Format: Yaqing Qie, Emiliano Sanchez Garavito, Maria J. Ulloa Navas, Tanya Hundal, Alfredo Quinones-Hinojosa, Hong Qin, Yan Luo. Weaponizing CAR T-cells to attack PD-L1 presenting cells in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB071.

Development of a compact bidirectional promoter-driven dual chimeric antigen receptor (CAR) construct targeting CD19 and CD20 in the Sleeping Beauty (SB) transposon system

BackgroundA bidirectional promoter-driven chimeric antigen receptor (CAR) cassette provides the simultaneous expression of two CARs, which significantly enhances dual antigen-targeted CAR T-cell therapy.MethodsWe developed a second-generation CAR directing CD19 and...

Abstract 60: Functional mapping of glioblastoma recurrence reveals targetable dependencies in an axonal guidance pathway in highly invasive brain cancers

Abstract Resistance to genotoxic therapies and tumor recurrence are hallmarks of glioblastoma (GBM), an aggressive brain tumor. Here, we explore the functional drivers of post-treatment recurrent GBM. By conducting genome-wide CRISPR-Cas9 screens in patient-derived GBM models, we uncover distinct genetic dependencies in recurrent tumor cells that were absent in their patient-matched primary predecessors, accompanied by increased mutational burden and differential transcript and protein expression. These analyses map a multilayered genetic response to drive tumor recurrence, identifying protein tyrosine phosphatase 4A2 (PTP4A2) as a novel modulator of self-renewal, proliferation and tumorigenicity at GBM recurrence. Genetic perturbation or small molecule inhibition of PTP4A2 represses axon guidance activity through a dephosphorylation axis with roundabout guidance receptor 1 (ROBO1), exploiting a functional dependency on ROBO signaling. Importantly, engineered anti-ROBO1 single-domain antibodies also mimic effects of PTP4A2 inhibition. Since a pan-PTP4A inhibitor was limited by poor penetrance across the blood brain barrier (BBB) in vivo, a second-generation chimeric antigen receptor (CAR)-T cell therapy was engineered against ROBO1 that elicits specific and potent anti-tumor responses in vivo. A single dose of anti-ROBO1 CAR-T cells doubles median survival in patient-derived xenograft (PDX) models of recurrent glioblastoma, and also eradicates tumors in around 50% of mice engrafted with PDX models of lung-to-brain metastases and pediatric relapsed medulloblastoma. We conclude that functional reprogramming drives tumorigenicity and dependence on a multi-targetable PTP4A-ROBO1 signaling axis at GBM recurrence, with potential in other malignant brain tumors. Citation Format: Sheila Kumari Singh, Chirayu Chokshi, Vaseem Shaikh, Benjamin Brakel, Alisha Anand, Chitra Venugopal, Thomas Kislinger, Kevin Henry, Martin Rossotti, Kevin Brown, John Lazo, Jason Moffat. Functional mapping of glioblastoma recurrence reveals targetable dependencies in an axonal guidance pathway in highly invasive brain cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 60.

Abstract 3993: A tunable safety switch for solid tumor CAR T-cell therapy

Abstract On-target off-tumor toxicity, cytokine release syndrome (CRS), and immune effector cell-associated neurotoxicity syndrome (ICANS) are severe immune-related adverse events (irAEs) that are frequently associated with Chimeric Antigen Receptor (CAR) T-cell therapy. Current efforts to manage such therapy-related toxicities involve incorporation of an inducible suicide agent within CAR constructs, such as iCaspase-9 or herpes simplex virus type 1 thymidine kinase that can be selectively activated to produce toxic effects within CAR T cells and attenuate their activity. However, while activation of these agents helps to mitigate or overcome such unwarranted toxicities, the therapeutic benefit of CAR T cells anti-tumor activity is also compromised. Therefore, to continue maintenance of CAR T cells’ therapeutic function while minimizing irAEs, an ideal safety switch should 1) rapidly inhibit the activation and proliferation of CAR T cells exposed to the target antigen, 2) reversibly inhibit activity without inducing CAR T cell elimination and 3) be clinically translatable for safe application in patients. Our laboratory investigated one such safety switch to inhibit CAR T-cell activity while maintaining their therapeutic function. We showed that incorporating a mutant variant of c-KIT D816V (KITv) in the intracellular domain of mesothelin-targeting second-generation CAR T cells (M28z-KITv) improved efficacy in solid tumors with low antigen, or an immunosuppressive environment. Herein, we evaluate the use of Dasatinib, a clinically available multitarget (BCR, SRC, c-KIT) tyrosine kinase inhibitor (TKI), as a tunable safety switch to reversibly inhibit M28z-KITv CAR T-cell functional activity. In cohorts of mice established with lung adenocarcinoma, daily administration of Dasatinib starting on day 1 or day 3 after CAR T-cell administration stabilized tumor growth, which otherwise continued to regress in untreated mice, indicating inhibition of CAR T-cell functional activity. Upon discontinuation of Dasatinib, tumors regressed, indicating reversal of CAR T-cell functional activity. In an experiment conducted to investigate functional persistence of CAR T cells upon long-term exposure to Dasatinib (1 month), we noted uninhibited activity of CAR T cells to rechallenged tumors. Dasatinib, thus may act as a tunable safety switch to regulate M28z-KITv CAR T-cell activity without compromising its therapeutic function. Citation Format: Kyohei Misawa, Meriem Taleb, Srijita Banerjee, William-Ray Vista, Navin K. Chintala, Prasad S. Adusumilli. A tunable safety switch for solid tumor CAR T-cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3993.

Regional delivery of mesothelin-targeted chimeric antigen receptor T-cell effectively and safely targets colorectal cancer liver metastases in mice.

Liver metastasis is the major cause of colorectal cancer related death. Mesothelin (MSLN)-targeted chimeric antigen receptor (CAR) T-cell therapy has been illustrated effective and safe through regional delivery of breast cancer, ovarian cancer and malignant mesothelioma tumors. Herein, we investigated the safety, efficacy, and immune microenvironment of regional delivery of MSLN (CAR) T-cell in the treatment of colorectal carcinoma liver metastases (CRLM). Second-generation MSLN CAR T-cells were administered by portal vein (PV) or caudal vein (CV, systemic administration) delivery in an orthotopic MSLN+ CRLM nonobese diabetic (NOD)/severe combined immunodeficient (SCID)/γc-/- (NSG) mouse model. A total of 20 mice were randomly divided into control group, non-transduced T cell (NT)-CV group, NT-PV group, MSLN CAR T-cell CV (MSLN-CV) group, and MSLN CAR T-cell PV (MSLN-PV) group, with each group containing four mice to examine the safety and efficacy. The bioluminescence intensity (BLI) of tumor burden, tumor tissue macroscopic and microscopic observation were used to evaluate treatment efficacy. The safety was examined by body weight, survival time, and vital organ damage of mice. CAR T-cell infiltration and cytokine concentration were analyzed by flow cytometry, and immunostaining. The change of immune microenvironment between regional delivery and systemic delivery was investigated on an immune reconstructed CRLM patient-derived xenograft (PDX) model. Additionally, T cell subsets and immunosuppressive markers were examined. PV administration of 1×107/100 μL MSLN CAR T-cells in 20 NSG mice was well tolerated, and no overt toxicity was observed. The tumor burden in the PV group was obviously alleviated. The BLI was (0.73±0.52)×109 in PV group and (1.97±0.11)×109 in CV group (P<0.05), CD8+ granzyme B (GB)+ T cell percentage (MSLN-CV 4.42%±0.47% vs. MSLN-PV 13.5%±4.67%, P<0.01) and cytokine concentration were obviously increased in the MSLN-PV group. In the immune reconstituted CRLM PDX model, intratumor (IT) delivery of MSLN CAR T-cells exhibited much more infiltration of CD4+ and CD8+ T cells accompanied with elevated expression levels of PD-1, LAG-3, and TIM-3. Regional delivery of MSLN-targeted CAR T-cell therapy has encouraging results in the orthotopic CRLM NSG mouse model and PDX model, and converts the tumor microenvironment from cold to hot. This study may provide a new therapeutic approach for CRLM. Further clinical study is needed.

Abstract A042: Quantitative multiplex immunoprecipitation reveals distinct protein interaction networks responsible for discrepant in vivo activity exhibited by two second generation CD22-targeted chimeric antigen receptors

Abstract The Pediatric Leukemia Adoptive Therapy (PLAT) trials at Seattle Children’s Hospital have pioneered the use of chimeric antigen receptor (CAR) T cell (CAR-T) therapies in pediatric patients with B cell Acute Lymphoblastic Leukemia. The landmark PLAT-02 trial (n=45), utilizing a second-generation CD19-directed CAR, observed a 93% remission rate following CAR-T infusion. However, approximately half of these subjects relapsed within one year and nearly a third of those tumors no longer expressed the CD19 target. The PLAT-04 trial (n=4) was subsequently conceived with a second-generation CAR (SCRI-C22v1) engineered to target CD22, an alternative antigen expressed on the B cell surface. Despite promising preclinical data, SCRI-C22v1 failed to generate anti-leukemic activity in all four subjects and the trial was halted. In response, a different second-generation CD22-directed CAR (SCRI-C22v2) was engineered, replacing the CD28 transmembrane domain and IgG4 hinge domain in SCRI-C22v1 with a continuous CD8 hinge and transmembrane domain while retaining identical 4-1BB and CD3ζ intracellular signaling domains. The modified SCRI-C22v2 displayed improved anti-tumor activity in preclinical models and was ultimately tested in patients in the PLAT-07 trial (n=4), where it exhibited strong in vivo expansion and persistence while inducing complete remission after 1 month in all four subjects. To investigate the molecular signaling responsible for clinical differences observed between SCRI-C22v1 and SCRI-C22v2, we applied an emerging proteomic technology, Quantitative Multiplex Immunoprecipitation (QMI), that captures medium-throughput quantitative data about fold changes in protein interaction networks downstream of the CAR. CAR-T products from healthy donors expressing either SCRI-C22v1 or SCRI-C22v2 were stimulated with fixed K562 cells expressing CD22 and protein interaction networks were profiled with QMI, revealing distinct differences in signal transduction downstream of the CAR. Contrary to expectation, it was the ineffective SCRI-C22v1 that exhibited significantly enhanced signalosome formation, engaging more strongly than SCRI-C22v2 with both the classical CD3ζ-ZAP70-LAT-SLP76 pathway as well as the non-classical TRAF pathway. Interestingly, the clinically successful SCRI-C22v2 demonstrated stronger baseline engagement with inhibitory molecules that attenuate canonical TCR signaling such as SHP2 and UBASH3A, suggesting regulatory control of CAR signaling is crucial for optimal clinical responses. Since the CAR is a synthetic receptor, it should be possible to bioengineer optimized signal transduction to some extent, and our group continues to work towards identifying an optimized QMI signature that can be used as a CAR-tune network for the rational design of more effective CAR-T therapies. Citation Format: Eric Bueter, Corinne Summers, Isabella Draper, Joshua Gustafson, Stephen EP Smith, Kamila Gwiazda, Julie Park, Colleen Annesley, Rebecca Gardner, Michael Jensen. Quantitative multiplex immunoprecipitation reveals distinct protein interaction networks responsible for discrepant in vivo activity exhibited by two second generation CD22-targeted chimeric antigen receptors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr A042.

CRISPR Activation Screen to Optimize Chimeric Antigen Receptor (CAR) T Cell Immunophenotype

Background Adoptive cellular therapies (ACT) offer potential cures for a wide range of human diseases. Immune cells genetically engineered with chimeric antigen receptors (CAR) have a clear role in B cell malignancies, and broader applications to other malignancies are under investigation. Significant obstacles to the long-term durability and potency of these therapies remain. As CAR T-cells remain persistently activated and exposed to the tumor microenvironment, they may become functionally impaired. This exhaustion can result in reduced production of cytokines, cytotoxic molecules, and other factors necessary for effective tumor cell killing. While CAR T-cell exhaustion remains a challenge, ongoing research and clinical trials aim to further understand the underlying mechanisms and develop strategies to overcome this limitation. Clinical studies have demonstrated that sustained in vivo persistence and function of CAR T-cells is correlated with infusion product phenotype. Persistence is associated with a less differentiated, memory-like phenotype. Naive (T N), Central Memory (T CM) and Stem Cell Memory (T SCM) are related to good proliferative potential and durability. CRISPR technologies offer powerful, functional genomic screens that permit the inference and modification of gene regulatory networks to optimize CAR T-cell persistence and function. Genome-wide CRISPR knock out screens have identified the CD2-CD58 axis as critical to T-cell potency and the knock-out of the mediator kinase module as beneficial to potency. Here we report on in vitro CRISPR activation screening of human CAR T-cells for gene expression that enhances T cell phenotypes associated with durable function. Method We designed 9,983 single guide RNA (sgRNA) to target the transcription start sites (TSS) of all known human transcription factors as well as a select set of genes with critical functions in T-cells. The vast majority of genes was targeted with 5 different sgRNA. To this we added a pool of 1,000 non-targeting sgRNA. We lentivirally transduced the sgRNA in tandem to a second-generation anti-CD20 CAR into primary T cells from healthy human donors. In a second lentiviral transduction we integrated catalytically dead Cas9 (dCas9) fused to the strong transcription activator, VP64 and in tandem to a puromycin resistance gene. After puromycin selection, we cultured the CRISPR activated CAR T-cells either alone or together with Raji or K562 cells for nine days before immunophenotypically sorting the CAR T-cells into CD8 + Naive, CD8 + Transitional Memory, CD8 + Central Memory, CD8 + Stem Cell Memory, CD8 + Transitional Effector, CD8 + Effector Memory, CD4 + Naive and CD4 + Memory T-cell populations. We extracted DNA from the sorted cells and prepared sequencing libraries targeting the sgRNA. We carried out two-way ANOVA analysis on the experimental conditions (trivial, Raji or K562 co-culture versus addition of CD2/CD28 activation beads) and T-cell subset to determine which genes targeted by CRISPRa resulted in favorable phenotypes. Result Across the different culture conditions, sgRNA activating IL23A and KLF4 were enriched in Transitional Memory versus Stem Cell Memory T-cells. Across the different CAR T-cell immunophenotypes, sgRNA targeting the TGFß (including KLF10), TNFα (including NFATC4) and FOXO signaling pathways were enriched in CAR T-cells cultured alone compared to CAR T-cells activated with CD2/CD28. Conclusion In this study we have investigated genes whose activation results in CAR T-cell immunophenotypes that are associated with more potent and durable CAR T-cell therapies. Our experiment suggests that the activation of genes, such as IL23 and KLF4, enriches for a Transitional Memory over Stem Cell Memory phenotype in a manner that is largely independent of environment (culture conditions). The activation of other genes, such as KLF10 and NFATC4, results in enrichment of CAR T-cells across all T-cell subsets, but in a manner that is dependent on environment. Gene expression requires coordinated control of gene-proximal and -distal cis-regulatory elements (CREs), whose state varies as cells differentiate or respond to environmental signals. Abrogating or adding CRE may result in more durable and potent adoptive cellular therapies independent of environment.

CD28 CAR T Cells for the Treatment of T Cell Malignancies

CONCLUSION While synthetic immunotherapy has been introduced into the standard of care treatment of patients with B-lineage malignancies, patients with T-lineage malignancies have not gained benefit from this novel approach, yet. The main reason is the challenging choice of target antigen in T-lineage malignancies such as pediatric T cell acute lymphoblastic leukemia (T-ALL). As activating mutations of CD28 have already been described in T cell malignancies, we set out to quantify surface expression of CD28 and other costimulatory molecules on primary pediatric T-ALL samples and explore the utility of this functionally relevant molecule as a novel target antigen. Bone marrow (BM) samples of pediatric T-ALL patients (n=54) at time of diagnosis and healthy control individuals (n=14) were collected. We quantified surface expression of CD28 and 25 additional co-stimulatory or co-inhibitory molecules by flow cytometry after gating on T cell precursors (living singlets, CD45 dim/SSC-A low and CD7 +). Subsequently, we generated a set of 20 CD28 directed second-generation chimeric antigen receptors (CARs) based on five different monoclonal antibodies with variation in hinge domain and light chain / heavy chain chronology. We analyzed specific CAR activity against CD28 expressing T-ALL cell lines after retroviral transduction into primary human T cells. Additional CD28 knockout (KO) by CRISPR/Cas9 could prevent T cell fratricide. CAR constructs were subjected to in vivo testing in a T-ALL NSG mouse model with transplantation of 7.5e4 CCRF-CEM cells transduced with firefly luciferase on day 0 and transfer of 2.5e6 CD28 KO T cells on day 3 harboring either of both CD28 CAR molecules. We used CD7 CAR T cells as positive control, CD19 CAR T cells and CD28 KO T cells without CAR as negative controls. We observed significant upregulation of CD28 on T-ALL leukemia when compared to healthy BM donors (Figure 1A, mean 68.8% vs. 3.7%, p=0.0002). We confirmed upregulation of CD28 in published T-ALL RNA-expression data sets. Interestingly, other co-stimulatory molecules such as CD127 were upregulated, too (mean 50.0% vs. 14.6%, p=0.0001), while co-inhibitory molecules such as CD160, TIGIT and TIM-3 were strongly downregulated (&amp;gt;10fold and p&amp;lt;0.0001 each). We hypothesized that this could imply a functional relevance of CD28 in T-ALL. Therefore, we performed co-culture assays of monocyte derived dendritic cells (CDs) expressing CD28 ligands CD80 and CD86 with different T-lineage leukemia cell lines. The presence of DCs significantly increased proliferation of CD28 + T-ALL cell lines under stress conditions. In order to test the feasibility of CD28 CAR T cells, we generated CD28 KO primary T cells without CAR. When tested in co-culture assays with leukemia cells and T cell engagers, CD28 KO T cells showed unchanged cytotoxic capacity and target-dependent activation illustrating that CD28 KO T cells retain short-term effector functions. Based on cytotoxic capacity and CAR T cell expansion, we identified two lead CD28 CAR candidates out of a pool of 20 CD28 CARs. After CD28 KO, CD28 CAR-T cells showed in vitro expansion comparable to CD19 CAR T cells. Next, we asked how CD28 CAR T cells compare to CD7 CAR T cells, which are currently evaluated clinical trials for T-ALL therapy. Therefore, we generated CD7 KO T cells that were subsequently transduced with a functional CD7 CAR. In vitro, both CD28 CAR T cells and CD7 CAR T cells showed killing of CD28 +CD7 + CCRF-CEM cells of &amp;gt;90% at an effector:target (E:T) ratio of 0.2:1, with CD7 being outperformed by one of the CD28 CARs while outperforming the other CD28 CAR at an E:T ratio of 0.04:1 (Figure 1B). Finally, we went on to validate the functionality of CD28 CAR T cells in vivo. We observed significantly prolonged survival of mice treated with CD28 CAR T cells and CD7 CAR T cells when compared to CD19 CAR T cells or control T cells. No difference in survival between CD7 and CD28 CAR T cell treated mice could be observed in two independent experiments. We identify CD28 as novel target antigen for pediatric T-ALL and provide evidence that CD28 is an immunotarget with functional relevance for T-ALL. We demonstrate the feasibility of CD28 CAR T cell generation and that these novel CAR T cells perform equally well as CD7 CAR T cells both in vitro and in vivo. Novel and functionally relevant CAR targets will facilitate clinical development of immunotherapy for T-lineage malignancies.

Gp350-Targeted CAR-T Therapy in EBV-Positive NK/T-Cell Lymphoma: Pre-Clinical Development of gp350CAR-T

Introduction: Epstein-Barr virus (EBV) positive NK/T cell lymphoma is a subtype of non-Hodgkin's lymphoma strongly associated with EBV infection. EBV infection has been reported in 85-100% of cases. It has been suggested to be central in pathogenesis. The incidence of EBV+ NK/T cell lymphoma is increasing worldwide, particularly in Asia and Latin America, and it has a poor prognosis with few effective treatment options. Therefore, novel approaches for treating EBV-associated NK/T cell lymphoma are urgently needed. Developing chimeric antigen receptor (CAR)-T cells therapy targeting EBV specific protein in the context of this EBV-positive aggressive lymphoma will provide a novel therapeutic strategy for patients with limited treatment options. Targeting EBV lytic protein for control EBV in vivo replication and tumorigenesis have been explored lately. The gp350 protein is a major glycoprotein on the surface of EBV during its lytic phase, after fusion between virus and host cell membrane, gp350 is left on the host cell surface. The distinct surface distribution pattern of gp350 in both freshly infected host cells and the lytic phase host cells renders it an attractive target for immunotherapy. Method and Result: We developed EBV specific CAR-T cells targeting gp350. We utilized single-chain variable fragments (scFvs) derived from four novel, gp350-binding, neutralizing monoclonal antibodies (mAbs) (12C10, 7D11, 6A12, 7A8) to generate the CAR constructs. We demonstrated that these scFvs, when fused to a second-generation CAR backbone consisting of 4-1BB and CD3ζ signal domains, are efficiently expressed on the surface of transduced T cells. These gp350 CAR-T cells exhibit specific activation and cytotoxic effects in vitro. Of note, the clone 6A12 scFv of CAR displayed the most potent cytotoxicity effects in gp350 positive cancer coculture toxicity assays. To optimize the CAR structure further, we designed various linker and transmembrane domains based on the clone 6A12 scFv, including CD8 linker, IgG4 hinge, IgG1 Fc linker, and CD28 linker and transmembrane domains. Our cytotoxicity assay screening indicated that the CD8 linker and transmembrane domain resulted in the most advanced cytotoxicity and target specificity (Figure A, B). To assess gp350 CAR-T efficacy in vivo, we established a T-cell leukaemia animal model in NOD immune-deficient mice through intravenous injection of Jurkat-gp350-luc cells. On post xenograft day 7, the Jurkat-gp350-luc xenografted mice were separated into three groups and each group with 5 mice (except PBS group with 2 mice). CAR-T and T cell were infused by tail vein injection with mock T 2x10^6/mouse, 6A12CAR-T 2x10^6/mouse and PBS control. The tumor growth in mice was monitored by in vivo luminescence with IVIS imaging system. Upon engraftment, Jurkat-gp350-luc cells established disseminated leukaemia expanding preferentially in the spine, femur, head, and pelvis, with few cells in peripheral blood. Mice receiving control mock T cells or without T cell PBS control developed rapid disease progression and were euthanized by day 35 after Jurkat-gp350-luc engraftment. In contrast, mice receiving gp350 CART cells were significantly protected from rapid progression (Figure C, D). Conclusion: In pre-clinical development, we designed, constructed, and screened gp350 CAR-T cells to demonstrate its efficacy in vitro and in vivo against and kill gp350 positive leukaemia cells and prevent formation and development leukaemia in xenograft mice model.

EXTH-80. A SYSTEMIC COMPARISON OF CAR T CELLS, CAR NK CELLS AND CAR MACROPHAGES FOR GLIOMA TREATMENT

Abstract Adoptive transfer of engineered immune cells expressing chimeric antigen receptors (CAR) is an emerging cancer immunotherapy that is also being investigated for glioblastoma. Many separate studies focus on either CAR T or CAR NK cells, and CAR macrophages are in early stages of development. However, a systemic cross-comparison of engineered immune effector cells against solid tumors, including glioblastoma, is lacking. Here, we generated second-generation NKG2D CAR mouse and human T cells, NK cells and macrophages and characterized them in vitro in co-culture assays with glioma cells and in vivo in orthotopic glioma mouse models. In vitro, mouse and human CAR T cells and CAR NK cells exhibited the highest tumor-killing activity. In contrast, in vivo, only CAR T cells exhibited anti-tumor activity in two immunocompetent orthotopic glioma-bearing mouse models, whereas CAR NK cells and CAR macrophages failed to prolong survival. More in-depth characterizations using flow cytometry, in vivo imaging and 3D microscopy, revealed that CAR T cells had the best tumor migration properties upon i.v. administration with distinct spatial distribution within the tumor compared to CAR NK cells and CAR macrophages. To profile the effects on bystander immune cells within the tumor microenvironment, we employed flow cytometry and single-cell RNA sequencing. This revealed effector cell-specific effects on the tumor microenvironment and provided insights into why the effective in vitro activity did not translate to in vivo. To unleash the anti-tumor potential of CAR immune effector cells, we engineered them to co-express the pro-inflammatory cytokines IL-12/IFNα2. This improved the in vivo anti-tumor activity of all effector cells and led to the highest fraction of long-term surviving mice with CAR NK cells. This study offers the first cross-comparison of different CAR immune effector cells against gliomas, providing valuable insights for the design of future adoptive cell therapies targeting malignant brain tumors.

Poliovirus receptor-based chimeric antigen receptor T cells combined with NK-92 cells exert potent activity against glioblastoma.

Poliovirus receptor interacts with 3 receptors: T-cell immunoglobulin immunoreceptor tyrosine-based inhibitory motif, CD96, and DNAX accessory molecule 1, which are predominantly expressed on T cells and natural killer (NK) cells. Many solid tumors, including IDH wild-type glioblastoma, have been reported to overexpress poliovirus receptor, and this overexpression is associated with poor prognosis. However, there are no preclinical or clinical trials investigating the use of cell-based immunotherapies targeting poliovirus receptor in IDH wild-type glioblastoma. We analyzed poliovirus receptor expression in transcriptome sequencing databases and specimens from IDH wild-type glioblastoma patients. We developed poliovirus receptor targeting chimeric antigen receptor T cells using lentivirus. The antitumor activity of chimeric antigen receptor T cells was demonstrated in patient-derived glioma stem cells, intracranial and subcutaneous mouse xenograft models. We verified poliovirus receptor expression in primary glioma stem cells, surgical specimens from IDH wild-type glioblastoma patients, and organoids. Accordingly, we developed poliovirus receptor-based second-generation chimeric antigen receptor T cells. The antitumor activity of chimeric antigen receptor T cells was demonstrated in glioma stem cells and xenograft models. Tumor recurrence occurred in intracranial xenograft models because of antigen loss. The combinational therapy of tyrosine-based inhibitory motif extracellular domain-based chimeric antigen receptor T cells and NK-92 cells markedly suppressed tumor recurrence and prolonged survival. Poliovirus receptor-based chimeric antigen receptor T cells were capable of killing glioma stem cells and suppressing tumor recurrence when combined with NK-92 cells.

CD19-CAR Cytokine Induced Killer Cells Armored with IL-18 Control Tumor Burden, Prolong Mouse Survival and Result in In Vivo Persistence of CAR-CIK Cells in a Model of B-Cell Acute Lymphoblastic Leukemia

Rationale: Cytokine induced killer cells (CIK) are a promising cancer immunotherapy. Recently CIK cells modified to express chimeric antigen receptors (CAR) target CD19 expressing hematological malignancies including B-cell acute lymphoblastic leukemia (B-ALL). Despite encouraging clinical trial results, insufficient CAR-CIK anti-tumor activity and persistence pose major obstacles towards improved efficacy in vivo. Therefore, we optimized our CAR-CIK platform by introducing two modifications to the CD19-CAR construct. The first modification “armored” CAR-CIK cells by inserting the IL-18 gene in a bicistronic DNA plasmid enabling simultaneous surface expression of the CAR protein and secretion of IL-18, which demonstrated improved CAR-T cell function. The second modification attenuated the CD28 cytoplasmic signaling domain of the CAR molecule to enhance anti-tumor activity and in vivo persistence since recent findings demonstrate that persistent or chronic CAR signaling can impair anti-tumor activity and in vivo persistence. Methods: CARCIK-1918 cells generated from donor-derived CIK cells are engineered to express CAR and IL-18 using the non-viral Sleeping Beauty (SB) transposon system. CIK cells were generated from donor PBMCs by the sequential addition of IFN-ϒ and stimulation with anti-CD3 antibody plus IL-2. After 2 days of stimulation CIK cells were co-electroporated with SB100X transposase mRNA and plasmid DNA containing a bicistronic transgene encoding both the anti-CD19 CAR and IL-18. This second-generation CAR contains a fusion of the CD28 transmembrane domain, intracellular CD28 and, TCR CD3ζ chain. In some instances, the cytoplasmic CD28 signaling domain is modified to attenuate CD28 signaling. This method of gene transfer results in stable surface expression of the CAR on CD3+ cells through a 17-day culture period. Day 17 cells are harvested, frozen and used for all subsequent studies. CARCIK-1918 cells are stimulated in vitro with CD19+ REH tumor cells and the phenotype of activated cells was characterized by multi-color flow cytometry. IL-18 secretion was determined by cytokine bead array analysis of supernatants collected post stimulation. CARCIK-1918 cells with or without the attenuated CD28 signaling domain were tested in vivo in a xenograft model of B-ALL, using NSG mice engrafted with CD19+ Raji tumor cells. Tumor burden was assessed weekly by bioluminescence imaging, the in vivo persistence of CARCIK-1918 cells was measured by flow cytometry, and survival was monitored throughout the study. Results: CARCIK-1918 cells express both IL-18 and CAR with or without attenuated CD28 signaling. Furthermore, stimulation of CARCIK-1918 cells with CD19+ REH tumor cells increases the frequency of CAR-CIK cells with a memory phenotype and concurrent upregulation of the high affinity IL-2 receptor, CD25, and the costimulatory receptor CD137. Expression of IL-18 leads to higher engraftment of CAR-CIK cells in tumor bearing NSG mice compared to unarmored controls. NSG mice engrafted with luciferase positive Raji cells demonstrated decreased bioluminescent signal following CARCIK-1918 treatment, consistent with CARCIK derived anti-leukemic activity. This anti-tumor activity corresponded to a statistically significant improvement in survival as mice treated with 2 nd generation CAR transgene CARCIK cells with or without attenuated CD28 signaling had a median survival of 37.5 (n=10; p=0.0001) and 38 (n=12; p =0.0001 days), respectively, compared to untreated mice that develop progressive highly disseminated tumor and succumb to disease by 3 weeks post tumor inoculation (n=11; median survival 18 days). Interestingly, mice treated with CARCIK-1918 cells with the CD28 attenuated signaling domain exhibited better tumor control and enhanced persistence in vivo, despite no significant improvement in survival compared to WT CD28 signaling CARCIK-1918 cells. Summary: This study demonstrates that administration of CAR-CIK cells armored with IL-18 results in a significant survival advantage for tumor challenged animals versus untreated animals. Furthermore, modifying the cytoplasmic CD28 domain to attenuate signaling, results in better control of tumor burden, and persistence of CARCIK-1918 cells in vivo. Our study is the first report of IL-18 armored CAR-CIK cells which may present a promising, novel strategy for the treatment of B-ALL.

Generation and Screening of Various CD70 CAR NK Cells Identify the Most Effective Construct Against Hematologic Malignancies

The ability to re-direct the intrinsic power of the immune system against cancer has resulted in unprecedented outcomes in certain patients with otherwise incurable diseases. Natural killer (NK) cells, similar to T cells, are powerful immune effectors that possess intrinsic anti-tumor properties and are capable of generating a strong cytotoxic response upon engaging tumor cells. However, unlike T cells, NK cells do not identify specific antigens and do so in a way that is HLA-independent, posing minimal risk of GvHD. Thus, NK cells have are being explored as a possible allogeneic source for over-the-counter cellular immunotherapy. CD70, the ligand for the CD27 receptor, is an attractive “pan-cancer antigen”, since in addition to being expressed in hematologic malignancies such as acute myeloid leukemia (AML) and lymphoma, it is also expressed on many solid tumors, including bladder, lung, triple negative breast cancer, renal cell carcinoma, pancreatic cancer, and melanoma. Moreover, CD70 is only transiently found on activated T and B lymphocytes and on dendritic cells. To target CD70-expressing cancers, we designed and tested a number of different chimeric antigen receptors (CAR). Briefly, we used the natural interaction between CD70 and CD27 to make a CAR construct that incorporated the extracellular domain of human CD27, which is the natural receptor for CD70. We generated various second-generation CAR constructs that differed in their transmembrane domains (CD27 vs. CD28) and costimulatory domains. We included co-stimulatory domains that are NK-centric (DAP10 and DAP12), T-cell-centric (CD28), or bi-centric (4-1BB). The CD3ζ chain was used as a signaling endodomain, and all the CAR constructs also included IL-15 to enhance in vivo proliferation and persistence. Cord blood (CB)-derived NK cells were efficiently retrovirally transduced with the different CAR constructs and subjected to an in vitro functional screen against various cancer cells to evaluate the best constructs for in vivo validation (Figure 1). The top constructs from our in vitro screen were further evaluated in multiple in vivo models, including a Raji lymphoma model and a THP-1 AML model. The best CAR construct in terms of superior tumor control and prolongation of survival was selected for GMP manufacturing. Based on these preclinical findings, a Phase I/II clinical study is now being conducted at our center to assess the safety and effectiveness of CD70 CAR NK cells against CD70-expressing hematologic malignancies (NCT05092451). Figure 1: Flow chart showing the screening process to identify the most effective CAR construct.

A Novel CD64 CAR-T Therapy for the Treatment of Monocytic Acute Myeloid Leukemia

Introduction: Acute Myeloid Leukemia (AML) is a difficult to treat, life threatening malignancy with overall survival remaining extremely poor, approximately 15% at 5 years. Recent advances in therapeutic approaches for AML have significantly improved outcomes, most notably venetoclax and azacitidine which induces a remission in approximately 70% of patients. Despite this, the majority of patients ultimately relapse and succumb to their disease. We and others have previously shown that more monocytic (M5 by FAB classification) AML cells demonstrate increased resistance to venetoclax therapy and that relapse after venetoclax and azacitidine treatment shows a monocytic phenotype in approximately 30% of patients (Pei, et. al. Cancer Discovery, 2020). These patients experience decreased overall survival compared to patients with non-M5 AML. Furthermore, we have demonstrated that AML with a dominant monocytic phenotype can arise from a unique subclass of leukemia stem cells (LSCs) that we have termed monocytic-LSCs (m-LSCs) due to their immunophenotype, including expression of CD64. m-LSCs are highly resistant to venetoclax-based therapies (Pei, et. al., Cancer Discovery, 2023). As venetoclax is increasingly utilized in AML treatment regimens, it is essential to identify methods of targeting this m-LSC subtype to prevent and treat relapsed and refractory disease. Methods: To more effectively target monocytic AML, we have developed a novel chimeric antigen receptor (CAR) T cell therapy targeting CD64, an antigen commonly expressed in monocytic cells and strongly expressed in the m-LSC population. We generated two second-generation CAR constructs targeting CD64, one with CD28 and the other with 41BB costimulatory domains. We expressed these CARs in healthy donor human T cells via lentiviral transduction and tested their function in vitro and in vivo. Results: We demonstrate that CD64 CAR-T cells effectively treat monocytic AML using pre-clinical models. CD64 CAR-T cells eliminate CD64+ leukemia cell lines in vitro in a dose dependent manner with an effector to target (E:T) ratio of 1:4 and higher eliminating 100% of Molm14 leukemia cells at 18 hours compared to 0-10% in mock T-cell controls. We also show that CD64 CAR-T cells eliminate established Molm14 leukemia in vivo, with 100% of CAR-T treated mice surviving over 50 days with no evidence of leukemia versus less than 30 days survival with high tumor burden in mock treated mice (p&amp;lt;0.01, Figure 1). We find that CD64 CAR-T cells with CD28 verses 41BB costimulatory domains are similarly efficacious against monocytic AML, though we find more prolonged persistence of CD64-41BBz CAR-T cells in mice with long term leukemia free survival. Furthermore, we demonstrate that CD64 CAR-T cells kill CD64+ primary patient derived AML cells in ex vivo co-culture, resulting in a 60-80% reduction in viable AML cells at 18 hours across 1:1 to 1:16 E:T ratios compared to mock T cell controls. We further show that CD64 CAR-T cells target m-LSCs and reduce the engraftment potential of primary AML cells in mice with a nearly 9-fold reduction in leukemia burden in CAR-T treated versus control mice. Finally, preliminary experiments with AML patient derived xenograft models further support the in vivo efficacy of CD64 CAR-T cell treatment. Conclusions: Our data provide promising preclinical evidence for the efficacy of a novel CD64 CAR-T therapy in the treatment of monocytic AML. We propose that using this regimen to augment AML therapy is a potentially powerful means to eradicate m-LSCs, which are inherently resistant to venetoclax, and thereby increase remission duration. This concept serves as the basis for an upcoming clinical trial of CD64-directed CAR-T cells for CD64 expressing AML. Figure 1: CD64 CAR-T cells eliminate AML in in vivo murine leukemia models. A) NSG mice leukemia models of GFP expressing Molm14, a CD64+ human leukemia cell line, experience leukemia clearance within 3 days after treatment with CD64-28z CAR-T cells, as shown by decreased bioluminescent signal in images of CAR-T treated mice. Mock transduced human T-cells from the same human donor serve as a control. B) Survival curves demonstrate 100% survival of CAR-T treated mice over the experiment (p&amp;lt;0.01).

Combining CSPG4-CAR and CD20-CCR for treatment of metastatic melanoma.

The prognosis for patients with metastatic melanoma is poor and treatment options are limited. Genetically-engineered T cell therapy targeting chondroitin sulfate proteoglycan 4 (CSPG4), however, represents a promising treatment option, especially as both primary melanoma cells as well as metastases uniformly express CSPG4. Aiming to prevent off-tumor toxicity while maintaining a high cytolytic potential, we combined a chimeric co-stimulatory receptor (CCR) and a CSPG4-directed second-generation chimeric antigen receptor (CAR) with moderate potency. CCRs are artificial receptors similar to CARs, but lacking the CD3ζ activation element. Thus, T cells expressing solely a CCR, do not induce any cytolytic activity upon target cell binding, but are capable of boosting the CAR T cell response when both CAR and CCR engage their target antigens simultaneously. Here we demonstrate that co-expression of a CCR can significantly enhance the anti-tumor response of CSPG4-CAR T cells in vitro as well as in vivo. Importantly, this boosting effect was not dependent on co-expression of both CCR- and CAR-target on the very same tumor cell, but was also achieved upon trans activation. Finally, our data support the idea of using a CCR as a powerful tool to enhance the cytolytic potential of CAR T cells, which might open a novel therapeutic window for the treatment of metastatic melanoma.