4-1BB Costimulatory Domain Research Articles

FGFR4-specific CAR-T cells with inducible caspase-9 suicide gene as an approach to treat rhabdomyosarcoma.

Metastatic rhabdomyosarcoma is associated with poor survival and unsatisfactory treatment outcomes. Therefore, new immunotherapeutic methods are urgently required. Fibroblast growth factor receptor 4 (FGFR4), a new therapeutic target for rhabdomyosarcoma, plays a crucial role in its onset and development. This study aimed to generate FGFR4 single-chain variable fragment-based chimeric antigen receptor (CAR) T cells without causing evident toxicity and incorporating an inducible caspase-9 (iCasp9) suicide gene system to enhance their safety. FGFR4 antigen expression was evaluated in normal murine tissues, normal human tissues, and specimens from patients with rhabdomyosarcoma. Combined with a 4-1BB co-stimulatory domain, a CD3ζ signaling domain, and an iCasp9 suicide gene, CAR-T cells with an FGFR4-specific single-chain variable fragment were developed. The specific cytotoxic effects, T-cell proliferation, cytokine secretion, apoptosis induction by chemical dimerization (AP20187), and toxicity of FGFR4 CAR-T cells were investigated in vitro and in vivo. FGFR4 CAR-T cells generated a variety of immune-promoting cytokines, including tumor necrosis factor α, interleukin 2, and interferon γ, and displayed effective cytotoxic activity against FGFR4-overexpressing rhabdomyosarcoma cells in vitro. FGFR4 CAR-T cells were relatively effective against FGFR4-overexpressing rhabdomyosarcoma, with tumor regression and poor survival in a subcutaneous xenograft model. The iCasp9 gene was incorporated into FGFR4 CAR-T cells and it was demonstrated that effective and reliable suicide gene activity depends on the administration of AP20187. By making use of the cross-reaction of FGFR4 CAR-T cells with murine FGFR4 in a syngeneic tumor model, this study found that FGFR4 CAR-T cells could regulate the growth of tumors without evident toxicity. Our study demonstrates that FGFR4 is a prospective target for CAR-T cell therapy in rhabdomyosarcoma without serious on-target off-tumor toxicity. FGFR4 CAR-T cells with the iCasp9 suicide gene system as a safety switch to limit toxicity may broaden the clinical applications of cellular therapy.

High specificity of engineered T cells with third generation CAR (CD28-4-1BB-CD3-ζ) based on biotin-bound monomeric streptavidin for potential tumor immunotherapy.

Immunotherapy has revolutionized cancer treatment, and Chimeric Antigen Receptor T cell therapy (CAR-T) is a groundbreaking approach. Traditional second-generation CAR-T therapies have achieved remarkable success in hematological malignancies, but there is still room for improvement, particularly in developing new targeting strategies. To address this limitation, engineering T cells with multi-target universal CARs (UniCARs) based on monomeric streptavidin has emerged as a versatile approach in the field of anti-tumor immunotherapy. However, no studies have been conducted on the importance of the intracellular signaling domains of such CARs and their impact on efficiency and specificity. Here, we developed second-generation and third-generation UniCARs based on an extracellular domain comprising an affinity-enhanced monomeric streptavidin, in addition to CD28 and 4-1BB co-stimulatory intracellular domains. These UniCAR structures rely on a biotinylated intermediary, such as an antibody, for recognizing target antigens. In co-culture assays, we performed a functional comparison between the third-generation UniCAR construct and two second-generation UniCAR variants, each incorporating either the CD28 or 4-1BB as co-stimulatory domain. We observed that components in culture media could inhibit the binding of biotinylated antibodies to monomeric streptavidin-CARs, potentially compromising their efficacy. Furthermore, third-generation UniCAR-T cells showed robust cytolytic activity against cancer cell lines upon exposure to specific biotinylated antibodies like anti-CD19 and anti-CD20, underscoring their capability for multi-targeting. Importantly, when assessing engineered UniCAR-T cell activation upon encountering their target cells, third-generation UniCAR-T cells exhibited significantly enhanced specificity compared to second-generation CAR-T cells. First, optimizing culture conditions would be essential before deploying UniCAR-T cells clinically. Moreover, we propose that third-generation UniCAR-T cells are excellent candidates for preclinical research due to their high specificity and multi-target anti-tumor cytotoxicity.

CAR T-cells targeting FGFR4 and CD276 simultaneously show potent antitumor effect against childhood rhabdomyosarcoma

Chimeric antigen receptor (CAR) T-cells targeting Fibroblast Growth Factor Receptor 4 (FGFR4), a highly expressed surface tyrosine receptor in rhabdomyosarcoma (RMS), are already in the clinical phase of development, but tumour heterogeneity and suboptimal activation might hamper their potency. Here we report an optimization strategy of the co-stimulatory and targeting properties of a FGFR4 CAR. We replace the CD8 hinge and transmembrane domain and the 4-1BB co-stimulatory domain with those of CD28. The resulting CARs display enhanced anti-tumor activity in several RMS xenograft models except for an aggressive tumour cell line, RMS559. By searching for a direct target of the RMS core-regulatory transcription factor MYOD1, we identify another surface protein, CD276, as a potential target. Bicistronic CARs (BiCisCAR) targeting both FGFR4 and CD276, containing two distinct co-stimulatory domains, have superior prolonged persistent and invigorated anti-tumor activities compared to the optimized FGFR4-specific CAR and the other BiCisCAR with the same 4-1BB co-stimulatory domain. Our study thus lays down the proof-of-principle for a CAR T-cell therapy targeting both FGFR4 and CD276 in RMS.

Outpatient administration of CAR T-cell therapies using a strategy of no remote monitoring and early CRS intervention

AbstractRecent studies demonstrating the feasibility of outpatient chimeric antigen receptor (CAR)–modified T-cell therapy administration are either restricted to CARs with 41BB costimulatory domains or use intensive at-home monitoring. We report outcomes of outpatient administration of all commercially available CD19- and B-cell maturation antigen (BCMA)–directed CAR T-cell therapy using a strategy of no remote at-home monitoring and an early cytokine release syndrome (CRS) intervention strategy. Patients with hematologic malignancies who received CAR T-cell therapy in the outpatient setting during 2022 to 2023 were included. Patients were seen daily in the cancer center day hospital for the first 7 to 10 days and then twice weekly through day 30. The primary end point was to determine 3-, 7-, and 30-day post–CAR T-cell infusion hospitalizations. Early CRS intervention involved administering tocilizumab as an outpatient for grade ≥1 CRS. Fifty-eight patients received outpatient CAR T-cell infusion (33 myeloma, 24 lymphoma, and 1 acute lymphoblastic leukemia). Of these, 17 (41%), 16 (38%), and 9 patients (21%) were admitted between days 0 to 3, 4 to 7, and 8 to 30 after CAR T-cell infusion, respectively. The most common reason for admission was CAR T-cell–related toxicities (33/42). Hospitalization was prevented in 15 of 35 patients who received tocilizumab for CRS as an outpatient. The nonrelapse mortality rates were 1.7% at 1 month and 3.4% at 6 months. In conclusion, we demonstrate that the administration of commercial CAR T-cell therapies in an outpatient setting is safe and feasible without intensive remote monitoring using an early CRS intervention strategy.

Zevorcabtagene Autoleucel: First Approval.

Zevorcabtagene autoleucel () is a fully humanised B cell maturation antigen (BCMA)-targeting specific chimeric antigen receptor (CAR) T-cell therapy being developed by CARsgen for the treatment of multiple myeloma. Zevorcabtagene autoleucel is an autologous CAR T cell comprising a fully human BCMA-specific scFv (25C2), a CD8α hinge region and transmembrane domain, a 4-1BB costimulatory domain and a CD3-ζ T cell activation domain. Zevorcabtagene autoleucel recognizes and induces selective toxicity against BCMA-expressing tumour cells leading to their elimination. In February 2024, zevorcabtagene autoleucel received its first approval in China for the treatment of adults with relapsed or refractory multiple myeloma who have progressed after ≥ 3 prior lines of therapy (including ≥ 1 proteasome inhibitor and an immunomodulatory agent). Clinical studies of zevorcabtagene autoleucel are underway in Canada and the US. This article summarizes the milestones in the development of zevorcabtagene autoleucel leading to this first approval for relapsed or refractory multiple myeloma.

Comparative analysis of Bcl-2 family protein overexpression in CAR T cells alone and in combination with BH3 mimetics.

Approximately 50% of patients with hematologic malignancies relapse after chimeric antigen receptor (CAR) T cell treatment; mechanisms of failure include loss of CAR T persistence and tumor resistance to apoptosis. We hypothesized that both of these challenges could potentially be overcome by overexpressing one or more of the Bcl-2 family proteins in CAR T cells to reduce their susceptibility to apoptosis, both alone and in the presence of BH3 mimetics, which can be used to activate apoptotic machinery in malignant cells. We comprehensively investigated overexpression of different Bcl-2 family proteins in CAR T cells with different signaling domains as well as in different tumor types. We found that Bcl-xL and Bcl-2 overexpression in CAR T cells bearing a 4-1BB costimulatory domain resulted in increased expansion and antitumor activity, reduced exhaustion, and decreased apoptotic priming. In addition, CAR T cells expressing either Bcl-xL or a venetoclax-resistant Bcl-2 variant led to enhanced antitumor efficacy and survival in murine xenograft models of lymphoma and leukemia in the presence or absence of the BH3 mimetic venetoclax, a clinically approved BH3 mimetic. In this setting, Bcl-xL overexpression had stronger effects than overexpression of Bcl-2 or the Bcl-2(G101V) variant. These findings suggest that CAR T cells could be optimally engineered by overexpressing Bcl-xL to enhance their persistence while opening a therapeutic window for combination with BH3 mimetics to prime tumors for apoptosis.

Preclinical specificity & activity of a fully human 41BB-expressing anti-CD19 CART- therapy for treatment-resistant autoimmune disease

Over 4% of the global population is estimated to live with autoimmune disease, necessitating immunosuppressive treatment that is often chronic, not curative, and carries associated risks. B cells have emerged as key players in disease pathogenesis, as evidenced by partial responsiveness to B cell depletion by antibody-based therapies. However, these treatments often have transient effects due to incomplete depletion of tissue-resident B cells. Chimeric antigen receptor (CAR) Tcells targeting B cells have demonstrated efficacy in refractory systemic lupus erythematosus. To this end, we developed an anti-CD19 CAR Tcell product candidate, CABA-201, containing a clinically evaluated fully human CD19 binder (IC78) with a 4-1BB costimulatory domain and CD3 zeta stimulation domain for treatment refractory autoimmune disease. Here, we demonstrate specific cytotoxic activity of CABA-201 against CD19+ Nalm6 cells with no off-target effects on primary human cells. Novel examination of CABA-201 generated from primary Tcells from multiple patients with autoimmune disease displayed robust CAR surface expression and effective elimination of the intended target autologous CD19+ B cells invitro. Together, these findings support the tolerability and activity of CABA-201 for clinical development in patients with autoimmune disease.

Toll-like receptor 4 signaling activation domains promote CAR T cell function against solid tumors

Chimeric antigen receptor (CAR) Tcell therapy has emerged as a powerful therapeutic approach against a range of hematologic malignancies. While the incorporation of CD28 or 4-1BB costimulatory signaling domains into CARs revolutionized immune responses, there is an exciting prospect of further enhancing CAR functionality. Here, we investigated the design of CD19 CARs enriched with distinct Toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 (MyD88), or Toll/IL-1 domain-containing adaptor-inducing interferon (IFN)-β (TRIF) costimulatory domains. Screening of various designs identified several candidates with no tonic activity but with increased CD19 target cell-dependent interleukin (IL)-2 production. Human Tcells transduced with the selected CAR construct exhibited augmented hIL-2 and hIFN-γ induction and cytotoxicity when cocultured with CD19-positive lymphoma and solid-tumor cell lines. RNA sequencing (RNA-seq) analysis demonstrated the upregulation of some genes involved in the innate immune response and Tcell activation and proliferation. In experiments on a xenogeneic solid-tumor mice model, MyD88 and TLR4 CAR Tcells exhibited prolonged remission. This study demonstrates that the integration of a truncated TLR4 signaling costimulatory domain could provide immunotherapeutic potential against both hematologic malignancies and solid tumors.

TOP CAR with TMIGD2 as a safe and effective costimulatory domain in CAR cells treating human solid tumors.

Chimeric antigen receptor (CAR)-T cell therapy shows impressive efficacy treating hematologic malignancies but requires further optimization in solid tumors. Here, we developed a TMIGD2 optimized potent/persistent (TOP) CAR that incorporated the costimulatory domain of TMIGD2, a T and NK cell costimulator, and monoclonal antibodies targeting the IgV domain of B7-H3, an immune checkpoint expressed on solid tumors and tumor vasculature. Comparing second- and third-generation B7-H3 CARs containing TMIGD2, CD28, and/or 4-1BB costimulatory domains revealed superior antitumor responses in B7-H3.TMIGD2 and B7-H3.CD28.4-1BB CAR-T cells in vitro. Comparing these two constructs using in vivo orthotopic human cancer models demonstrated that B7-H3.TMIGD2 CAR-T cells had equivalent or superior antitumor activity, survival, expansion, and persistence. Mechanistically, B7-H3.TMIGD2 CAR-T cells maintained mitochondrial metabolism; produced less cytokines; and established fewer exhausted cells, more central memory cells, and a larger CD8/CD4 T cell ratio. These studies demonstrate that the TOP CAR with TMIGD2 costimulation offered distinct benefits from CD28.41BB costimulation and is effective against solid tumors.

Establishing an immunocompetent mouse model of CAR T anti-tumor efficacy for studies of therapeutic resistance

Abstract Chimeric antigen receptor (CAR) T cell therapies redirect a patient's T-cells to recognize tumor antigens, and are an effective clinical strategy in the treatment of several hematological malignancies. However, targeting of solid tumors remains challenging, in part due to features of the solid tumor microenvironment that impair the expansion, persistence, and function of CAR T cells. To date, most studies employ xenograft models, thus limiting a mechanistic understanding of CAR T biology in the context of an intact immune system. To model the resistance of solid tumors to CAR T therapy and dissect how endogenous immune populations impact this process, we have generated an immunocompetent mouse model of CAR T therapy. Murine CARs recognizing human CD20 have been engineered with an extracellular scFv domain and intracellular CD3z signaling and 4-1BB costimulatory domains. Using flow cytometry and live-cell imaging assays, we demonstrate potent, antigen-dependent in vitro cytotoxicity and cytokine release by huCD20-targeting CAR T cells against solid (MC38) or heme (EL4) tumor cells engineered to express cell-surface huCD20. Moreover, huCD20 CAR T cells exhibit in vivo efficacy against both EL4-huCD20 and MC38-huCD20 tumor models, while CAR T that recognize an irrelevant antigen do not affect tumor growth. These results highlight a platform to explore resistance mechanisms and potential immune cell interactions that may impair CAR T therapy directed against solid tumors.

Abstract CT096: Phase I first-in-human MUC1* targeted autologous CAR T cells for the treatment of metastatic breast cancers

Abstract Purpose: First-in-human Phase I study for advanced MUC1* positive breast cancer with autologous T cells engineered to express either a chimeric antigen receptor, huMNC2-CAR44 or huMNC2-CAR22, which specifically bind to a cleaved form of MUC1 (MUC1*); evaluate the safety and preliminary anti-tumor activity. Methods: MUC1* (muk 1 star) is the growth factor receptor form of MUC1, created by cleavage and release of the N-terminal portion of MUC1. The targeting antibody, huMNC2, only recognizes the conformational epitope created when MUC1 is cleaved by specific tumor-associated enzymes that are correlated with poor prognosis. huMNC2 does not bind to full-length MUC1, which is expressed on all normal epithelial cells. huMNC2-scFv was incorporated into huMNC2-CAR44, comprising a CD8 hinge and transmembrane region, 4-1BB costimulatory domain and wild-type CD3z. huMNC2-scFv was also incorporated into huMNC2-CAR22 wherein the hinge, transmembrane and co-stimulatory portions were derived from CD28 and CD3z bears the 1XX mutations to increase in vivo persistence. Inclusion criteria require that the patient’s tumor is at least 30% MUC1* positive and that patient has progressed through 2 or 3 prior therapies, while in the metastatic setting. Patients receive standard Cy/Flu lymphodepletion approximately 3-days before CAR T treatment, administered at 1 of 4 dose levels ranging from 3.3X10^5 up to 1.0X10^7 CAR+ T cells. Results: To date, 8 patients have been treated with huMNC2-CAR44. No patients experienced neuro toxicities. No off-target toxicities were observed. 3 patients experienced CRS Grade 1-3. In 6 of the 8 patients, side effects were non-existent or minimal. However, one patient experienced a Grade 5 SAE that was deemed to be possibly related to the treatment. Best responses include Partial Responses and Stable Disease at a low CAR-T dose. Greatest efficacy was observed for patients whose biopsy showed H Scores >120. Patients are currently being enrolled for treatment with huMNC2-CAR22, where the 1XX mutations are expected to increase in vivo persistence, durability of response and reduced incidence of CRS. Conclusions: These data support a conclusion that the MUC1* antibody, huMNC2, is safe and could have high therapeutic value as a CAR T treatment for solid tumors with moderate to high antigen density. As the huMNC2-CAR22 (1XX) trial proceeds, we will assess if patient responses mirror our animal results that show that the 1XX mutations confer increased persistence, reduced exhaustion and the ability to kill tumors with low antigen density. Citation Format: Cynthia Carol Bamdad, Joanne E. Mortimer, Yuan Yuan, Jennifer M. Specht, Andrew K. Stewart, Benoit J. Smagghe, Stephen C. Lin, Mark G. Carter, Tim W. Synold, Mark D. Fleming, Stanley R. Hamilton, Vishwas Parekh, Danica M. Walkley, Qing Liu-Michael, Kevin R. Yi, Jac-Leen S. Nash, Michael J. Nash, Stephen J. Forman. Phase I first-in-human MUC1* targeted autologous CAR T cells for the treatment of metastatic breast cancers [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 CT096.

CD70-specific CAR NK cells expressing IL-15 for the treatment of CD19-negative B-cell malignancy

AbstractChimeric antigen receptor (CAR) natural killer (NK) cells can eliminate tumors not only through the ability of the CAR molecule to recognize antigen-expressed cancer cells but also through NK-cell receptors themselves. This overcomes some of the limitations of CAR T cells, paving the way for CAR NK cells for safer and more effective off-the-shelf cellular therapy. In this study, CD70-specific (a pan-target of lymphoma) fourth-generation CAR with 4-1BB costimulatory domain and interleukin-15 (IL-15) was constructed and transduced into cord blood–derived NK cells by Baboon envelope pseudotyped lentiviral vector. CD70-CAR NK cells displayed superior cytotoxic activity in vitro and in vivo against CD19-negative B-cell lymphoma when compared with nontransduced NK cells and CD19-specific CAR NK cells. Importantly, mice that received 2 doses of CD70-CAR NK cells showed effective eradication of tumors, accompanied by increased concentration of plasma IL-15 and enhanced CAR NK cell proliferation and persistence. Our study suggests that repetitive administration-based CAR NK-cell therapy has clinical advantage compared with a single dose of CAR NK cells for the treatment of B-cell lymphoma.

Abstract 2368: Intratumoral delivery of HER-2-CD3hFc mRNA-LNP inhibits ovarian tumor growth

Abstract Her-2 is a well-known driver of carcinogenesis that is overexpressed in breast, ovarian and other tumors. Immunotherapy with bispecific antibodies is a promising cancer therapy approach. Her-2 (Herceptin) antibody was used to test bispecific antibody against ovarian cancer cells. First, Her-2-CAR-T cells with Her-2 (4D5) ScFv and 4-1BB costimulatory domain were generated and tested using in vitro killing and IFN-gamma assays, and in vivo efficacy SKOV-3 xenograft NSG mouse model. Her-2-CAR-T cells killed SKBR-3 breast and SKOV-3 ovarian cancer cells and stopped SKOV-3 xenograft tumor growth. This Her-2-ScFv was used to generate bispecific Her-2 ScFv-CD3-ScFv human Fc antibody using in vitro transcribed mRNA. The 5’capped Her-2-CD3-hFc mRNA with 5’UTR, 3’UTR and poly A tail was generated by in vitro transcription using DNA template. The mRNA was embedded into lipid nanoparticles (LNP) using microfluidic PreciGenome Flex S NanoGenerator. Western blotting detected >160 kDa bispecific antibody secreted from A1847 and 293 cells transfected with mRNA-LNPs. The bispecific antibody was binding Her-2-positive A1847 ovarian cancer cell lines and T cells by FACS analysis. The Her-2-CD3-hFc bispecific antibody with T cells effectively killed Her-2-positive target cells in a dose-dependent manner in RTCA assay and produced high level of IFN-gamma. Moreover, intratumoral delivery of Her-2-CD3-hFc mRNA-LNP with intravenous injection of T cells completely blocked A1847 xenograft tumor growth. In conclusion. intratumoral delivery of Her-2-CD3 mRNA-LNP blocks ovarian xenograft tumor growth and provides a solid basis for future pre-clinical and clinical studies. Citation Format: Vita M. Golubovskaya, John Sienkiewicz, Jinying Sun, Shiming Zhang, Yanwei Huang, Liang Hu, Hua Zhou, Hizkia Harto, Shirley Xu, Robert Berahovich, Lijun Wu. Intratumoral delivery of HER-2-CD3hFc mRNA-LNP inhibits ovarian tumor growth [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 2368.

Abstract 6322: CCTx-001 CAR T-cells targeting the AML specific antigen IL-1RAP show robust pre-clinical anti-tumor efficacy

Abstract Despite significant advancements in acute myeloid leukemia (AML) treatment, patients with relapsed/refractory (r/r) AML have limited therapeutic options. Novel approaches are urgently needed. CAR T-cell therapy has shown remarkable success in hematological malignancies. However, its application in AML has been hampered by the absence of highly AML-specific antigens, making current CAR T-cell AML therapies under development poorly tolerated and effective. This pre-clinical study introduces a novel CAR T-cell therapy, CCTx-001, specifically designed to target IL-1RAP, a 78-kDa transmembrane glycoprotein. IL-1RAP, is highly expressed on AML cells but not on healthy hematopoietic stem and progenitor cells (CD34+ HSPC). Additionally, transcriptomic analyses reveal a correlation between high IL-1RAP expression and poor prognosis in AML patients. IL-1RAP's predominant presence on myeloid leukemia cells, coupled with their dependence to IL-1RAP-related pathways for their survival, presents a promising avenue for CAR T-cell therapy without the risk of treatment-induced antigen loss. CCTx-001, an autologous CAR T-cell therapy, was developed to target IL-1RAP on AML cells. It comprises CD8+ and CD4+ T-cells transduced with a highly specific anti-IL-1RAP Single-Chain Variable Fragment (scFv), an IgG1 hinge region, CD28, 4-1BB co-stimulatory domains, and a CD3ζ activation domain. In vitro experiments confirmed CCTx-001's efficacy in killing AML cell lines and primary AML cells of varying IL-1RAP expression levels, also demonstrating cytotoxicity and cytokine release that was dependent on the (E:T) ratio and target expression. Furthermore, in vivo studies using immunocompromised NCG mice confirmed CCTx-001's ability to target IL-1RAP and inhibit the growth of IL-1RAP-positive human AML tumor xenografts, leading to increased survival time. Biodistribution analyses confirmed the successful adoptive transfer, expansion and persistence of CCTx-001 CAR T-cells in vivo, only when injected into IL-1RAP-expressing tumor-bearing mice, which correlated with reduced levels of circulating AML cells. The promising preclinical data presented herein warrant the evaluation of CCTx-001 CAR T-cell therapy in clinical trials for r/r AML patients. CCTx-001 CAR T-cell therapy offers a potential breakthrough in addressing the unmet medical needs of AML patients with resistant or refractory disease. Citation Format: Edouard De Dreuzy, Soha Reda El Sayed, Delphine Genin, Clementine Primus, Lucie Bouquet, Alexis Collette, Olivier Favre-Bulle, Erik Rutjens, Jens Hasskarl, Ksenija Pavletic, Marina Deschamps, Christophe Ferrand, Richard C. A. Sainson. CCTx-001 CAR T-cells targeting the AML specific antigen IL-1RAP show robust pre-clinical anti-tumor efficacy [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 6322.

Abstract 23: The use of baboon envelope pseudotyped lentiviral (BaLV) vector allows high-efficiency transduction of CD8+ T cells

Abstract CAR-T (chimeric antigen receptors T) cell therapy has been proven to be effective in treating various types of cancers. To prevent graft vs. host disease, CAR-T cells are mostly produced from the patient’s own T-cells and transduced using pseudotyped vesicular stomatitis virus glycoprotein (VSV-G) lentivirus system. Typically, CD8+ effector T cells have relatively low transduction rates, compared with CD4+ T cells, and yet it is the CD8+ T cells that are the dominant effector immune cells in a CAR product. To achieve high efficacy of the CAR-positive effector T cells, a higher number of the patient’s CD8+ T cells are needed for transduction. However, cancer patients may not have enough T cells by the time they are eligible for CAR-T therapy due to multiple treatment cycles. One potential way to overcome this problem is to achieve a much higher transduction rate of the CD8+ T cells. Recently, our lab published the use of pseudotyping CAR lentivirus with baboon endogenous retroviral envelope (BaEV) for the generation of CAR transduced natural killer (NK) cells, exhibiting high transduction rates of above 50%. BaEV lentivirus targets the amino acid transporter, SLC1A5 (ASCT2), to enter the cell. SLC1A5 is highly expressed on activated NK and T cells. Therefore, we hypothesized that CAR-T transduced with BaEV lentivirus will have increased transduction rates compared with VSV-G. To assess transduction, we used anti-mesothelin (MSLN) CAR construct which consists of the mesothelin single chain variable fragment (scFv), CD8α hinge and transmembrane domain, 4-1BB costimulatory domain, and a CD3ζ activation domain, followed with GFP linked by self-cleavage P2A. The concentrated virus was titrated in Jurkat cells, resulting in 90% transduction efficiency with VSV-G and 50% with BaEV, for the same amount of virus. Primary CD8+ T cells were isolated from the peripheral blood of 3 healthy donors and activated with CD3/CD28 beads for three days prior to transduction. Then, the cells were transduced with either VSV-G or BaEV meso-CAR pseudotyped lentiviruses. Transduction rates were measured by flow cytometry, 3 days post-transduction. In addition, the CAR-T cells were expanded in vitro to evaluate their cytotoxicity against the mesothelin-positive cell line OVCAR-8, for 24 hours. VSV-G led to 10-20% transduction rates, while BaEV exhibited much higher transduction rates (55-70%), leading to improved cytotoxicity against the tumor cells. The successful increase of transduction rates for CD8+ CAR-T using our BaEV lentiviral system can be utilized in the clinic to treat patients that previously didn’t qualify for adoptive therapy, due to low lymphocyte counts. In addition, higher numbers of CD8+ CAR-T cells may result in better tumor control in both blood and solid tumor settings, compared with the traditional approach for CAR-T production. Citation Format: Isabel Kaplan, Michal Sheffer, Yasmin Abdulhamid, Eden Bobilev, Rizwan Romee. The use of baboon envelope pseudotyped lentiviral (BaLV) vector allows high-efficiency transduction of CD8+ T cells [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 23.

Abstract 1090: GPC2 directed CAR T cells are efficacious against fusion-positive and fusion-negative rhabdomyosarcomas

Abstract Background: Rhabdomyosarcoma (RMS) is an aggressive pediatric solid tumor with poor survival and new targeted therapies are needed. Aims: Using an integrative proteogenomic quantitative approach, we sought to identify candidate immunotherapeutic targets then validate top targets in RMS preclinical models. Methods: We first performed plasma membrane enrichment followed by mass spectrometry (MS) to define the surfaceome of 7 fusion-positive (FP) and 14 fusion-negative (FN) RMS patient-derived xenograft models. Surface proteins were scored by IMMUNOTAR, our custom pipeline which extracts and integrates quantitative features from diverse proteogenomic and annotation datasets to provide a score for each protein, using mean-average-precision for score optimization. Cell surface expression of IMMUNOTAR-prioritized proteins was validated using flow cytometry, focusing on targets with immunotherapies in development. CAR T cells targeting the lead protein were engineered and studied in RMS preclinical models. Results: A total of 847 and 882 high confidence cell surface proteins were detected in FP and FN RMS surfaceome, respectively, with 94% of proteins overlapping the phenotypes. IMMUNOTAR ranked anaplastic lymphoma kinase (ALK), a putative immunotherapeutic target in FP RMS, as the top FP target. Glypican 2 (GPC2), a differentially expressed cell surface proteoglycan identified in neuroblastoma and other neural-derived tumors, targetable with CAR T cells and antibody-drug conjugates [Bosse et al. Cancer Cell 2017], ranked as the top protein in FN and 5th protein in FP RMS. Overall, GPC2 was abundantly expressed in 16 of 21 RMS models profiled. Flow cytometry revealed expression of GPC2 comparable to neuroblastoma in 5 of 8 RMS cells lines. Additionally, both FP and FN GPC2+ RMS cell lines (FN: RH36, SMS-CTR; FP: RH41, RH30) activated GPC2 CAR T cells with either a CD28 or a 4-1BB costimulatory domain, inducing release of IFN-gamma and IL-2 upon co-incubation across different E:T ratios as quantified by ELISA. Further, GPC2 CAR T cells induced potent RMS cell cytotoxicity compared to control CD19 CAR T cells with near 100% specific cytotoxicity at 1:1 E:T ratio. In a pilot study, GPC2 CAR T cells with 4-1BB costimulatory domains induced significant tumor regression (p=0.03) and prolonged progression-free survival (p=0.01) compared to CD19 CAR T cells in an established murine RH41 flank xenograft model. Conclusion: In summary, we probed the RMS surfaceome using MS and identified candidate proteins amenable for immunotherapeutic targeting using our IMMUNOTAR algorithm. We validated GPC2 as a candidate target in FP and FN RMS and are corroborating our findings in additional pre-clinical RMS models. Demonstration of GPC2 CAR efficacy in these models could lead to inclusion of RMS in our ongoing phase 1 clinical trial (NCT05650749) in a planned expansion phase. Citation Format: Rawan Shraim, Patrick M. Schuerch, Anna Maria Giudice, Karina L. Conkrite, Amber K. Weiner, Alexander B. Radaoui, Brian Mooney, Raushan T. Kurmasheva, Peter J. Houghton, Gregg B. Morin, Yael B. Mosse, Poul H. Sorensen, Benjamin A. Garcia, Ahmet Sacan, John M. Maris, Kristopher R. Bosse, Sharon J. Diskin. GPC2 directed CAR T cells are efficacious against fusion-positive and fusion-negative rhabdomyosarcomas [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 1090.

Abstract 45: Driving AMPK signaling in CD4+ CART cells enhances metabolic capacity, memory formation, and anti-leukemia activity

Abstract Background: While Chimeric Antigen Receptor (CAR)T cell therapy has seen great success in pediatric and young adult acute lymphoblastic leukemia, up to 50% of patients will relapse following treatment. Increased memory formation and mitochondrial capacity, particularly in the CD4+ subset, have been linked to improved CART cell function and enhanced in vivo persistence, leading to long-term relapse-free survival. AMP-activated protein kinase (AMPK) is a cellular energy sensor responsible for promoting metabolic efficiency and T cell memory formation. We have previously demonstrated AMPK activity can be increased in human T cells via overexpression of the AMPKγ2 domain. We hypothesized that overexpression of AMPKγ2 in CART cells would enhance their metabolic capacity and improve their anti-leukemia function. Methods: Human CART cells bearing a CD19-CAR utilizing a 41BB costimulatory domain were generated from healthy human donors via lentiviral transduction and co-transduced with AMPKγ2 (AMPK) or an empty vector (EV) control. Flow sorting for the co-transduced populations yielded >95% CD4+ CART cells. CARTs were expanded in IL-2 for approximately 2 weeks, followed by overnight stimulation and subsequent metabolic analysis using the Seahorse Metabolic Analyzer. Memory status was assessed by CD62L and CCR7 co-expression. In vitro CART function was assessed using Zs-green+ NALM6 targets, with loss of green fluorescence over time measured on the Incucyte analyzer. Where indicated, tumor conditioned media was harvested from 72-hour NALM6 cultures. For in vivo experiments, immunodeficient NOD-scid IL2Rγnull (NSG) mice were injected with luciferase+ NALM6 targets, followed one week later by AMPK- or EV-CARTs. Leukemia burden, via IVIS imaging, and survival were followed over time. Results: CD4+ CARTs co-transduced with AMPKγ2 (AMPK-CARTs) increased oxygen consumption, maximal respiration, and spare respiratory capacity following overnight stimulation by ~20% compared to CARTs co-transduced with the EV (EV-CARTs) (p<0.05). Following expansion, CD62L+CCR7+ central memory cells were 4.5-fold more abundant in the AMPK-CART group (2.4-6.2-fold, p<0.01). In vitro, while AMPK-CARTs demonstrated similar cytotoxicity against NALM6 targets as EV-CARTs in standard media, they mediated faster killing of NALM6 targets when challenged in tumor conditioned media (p<0.001). In vivo, recipients of AMPK-CARTs showed a consistent decrease in tumor burden as measured by median radiance values, translating to a significant survival advantage (p<0.05). Conclusions: Increasing AMPK signaling in CD4+ CARTs via overexpression of AMPKγ2 improved metabolic profile, increased memory generation, and enhanced toxicity against leukemia targets both in vitro and in vivo. Together, these features make elevating AMPK signaling an attractive method to increase the efficacy of CART therapy. Citation Format: Erica Braverman, Herbert Schuler, Mengtao Qin, Craig Byersdorfer. Driving AMPK signaling in CD4+ CART cells enhances metabolic capacity, memory formation, and anti-leukemia activity [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 45.

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.

Differential protein-protein interactions underlie signaling mediated by the TCR and a 4-1BB domain-containing CAR.

Cells rely on activity-dependent protein-protein interactions to convey biological signals. For chimeric antigen receptor (CAR) T cells containing a 4-1BB costimulatory domain, receptor engagement is thought to stimulate the formation of protein complexes similar to those stimulated by T cell receptor (TCR)-mediated signaling, but the number and type of protein interaction-mediating binding domains differ between CARs and TCRs. Here, we performed coimmunoprecipitation mass spectrometry analysis of a second-generation, CD19-directed 4-1BB:ζ CAR (referred to as bbζCAR) and identified 128 proteins that increased their coassociation after target engagement. We compared activity-induced TCR and CAR signalosomes by quantitative multiplex coimmunoprecipitation and showed that bbζCAR engagement led to the activation of two modules of protein interactions, one similar to TCR signaling that was more weakly engaged by bbζCAR as compared with the TCR and one composed of TRAF signaling complexes that was not engaged by the TCR. Batch-to-batch and interindividual variations in production of the cytokine IL-2 correlated with differences in the magnitude of protein network activation. Future CAR T cell manufacturing protocols could measure, and eventually control, biological variation by monitoring these signalosome activation markers.

Novel chimeric antigen receptor-expressing T cells targeting the malignant mesothelioma-specific antigen sialylated HEG1.

The selection of highly specific target antigens is critical for the development of clinically efficient and safe chimeric antigen receptors (CARs). In search of diagnostic marker for malignant mesothelioma (MM), we have established SKM9-2 monoclonal antibody (mAb) which recognizes a MM-specific molecule, sialylated Protein HEG homolog 1 (HEG1), with high specificity and sensitivity. In this study, to develop a novel therapeutic approach against MM, we generated SKM9-2 mAb-derived CARs that included the CD28 (SKM-28z) or 4-1BB (SKM-BBz) costimulatory domain. SKM-28z CAR-T cells showed continuous growth and enhanced Tim-3, LAG-3, and PD-1 expression in vitro, which might be induced by tonic signaling caused by self-activation; however, these phenotypes were not observed in SKM-BBz CAR-T cells. In addition, SKM-BBz CAR-T cells exhibited slightly stronger in vitro killing activity against MM cell lines than SKM-28z CAR-T cells. More importantly, only SKM-BBz CAR-T cells, but not SKM-28z CAR-T cells, significantly inhibited tumor growth in vivo in a MM cell line xenograft mouse model. Gene expression profiling and reporter assays revealed differential signaling pathway activation; in particular, SKM-BBz CAR-T cells exhibited enhanced NF-kB signaling and reduced NFAT activation. In addition, SKM-BBz CAR-T cells showed upregulation of early memory markers, such as TCF7 and CCR7, as well as downregulation of pro-apoptotic proteins, such as BAK1 and BID, which may be associated with phenotypical and functional differences between SKM-BBz and SKM-28z CAR-T cells. In conclusion, we developed novel SKM9-2-derived CAR-T cells with the 4-1BB costimulatory domain, which could provide a promising therapeutic approach against refractory MM.