Avila, Monica

TPS2673 Background: The main challenge for developing CAR T therapies for solid tumors is the lack of targets that distinguish tumor from normal cells, resulting in on-target, off-tumor toxicity. Tmod logic-gated CAR T therapy addresses this challenge by incorporating 2 CARs on the same T cell: an activator targeting a marker on both tumor and normal cells, and a blocker targeting HLA-A*02 that inhibits CAR T activity against normal cells while allowing activation against tumor cells (with HLA-A*02 LOH), improving tumor selectivity and decreasing toxicity. Early safety results from 3 ongoing phase 1/2 clinical trials of logic-gated, Tmod CAR T therapy (EVEREST-1, EVEREST-2, and DENALI-1) have demonstrated manageable safety and tolerability in patients with advanced solid tumors (Grierson et al, SITC , 2024; Ward et al, SITC 2025; Specht et al, SABCS , 2025). Early efficacy results include the first ever reported complete response in a patient with non-small cell lung cancer following treatment with a CAR T-cell therapy (A2B694). A2B543 is an autologous Tmod CAR T therapy that contains the same Tmod construct as A2B694 with an added membrane-tethered IL-12 (memIL12) booster. Specifically, A2B543 is comprised of autologous Tmod cells transduced with 2 lentiviral vectors: one expressing both the HLA-A*02-targeted blocker and the mesothelin-targeted CAR activator; and a second expressing the memIL12 booster. Interleukin 12 (IL-12) is a potent, pro-inflammatory cytokine that plays a crucial role in inducing antitumor immune responses; however, systemic IL-12 can be prohibitively toxic (Jia et al, Front Immunol , 2022). In A2B543, expression of the memIL12 cassette is under the control of an NFAT promoter and is induced during antigen engagement or T cell activation. This inducible memIL12 is designed to reduce the toxicity associated with systemic IL-12 while enhancing the long-term potency and persistence of Tmod (Zhang et al, J Immunother Cancer , 2025). Methods: EVEREST-2 (NCT06051695) is a phase 1/2, open-label, nonrandomized study evaluating the safety and efficacy of A2B543 in adults with recurrent/metastatic mesothelin-expressing cancers with tumor-associated HLA-A*02 LOH, including mesothelioma, colorectal, non-small cell lung, pancreatic, or ovarian cancer. Patients are enrolled through BASECAMP-1 (NCT04981119), a master prescreening study that identifies patients with HLA LOH via next-generation sequencing and cryopreserves leukapheresis product. Upon progression, A2B543 is manufactured and then administered after lymphodepletion. The phase 1 primary objective is to evaluate the safety and tolerability of A2B543 and identify a recommended phase 2 dose (RP2D). The phase 2 primary objective is to assess overall response rate. Clinical trial information: NCT06051695 .

8579 Background: LOH may provide a means to target tumor versus normal cells, to augment the efficacy and safety of MSLN-targeted programs (Hecht et al. JCO . 2022). A2B694 is an autologous, logic-gated, Tmod CAR T therapy designed to improve tumor selectivity and decrease toxicity by integrating an MSLN CAR activator with an HLA-A*02 blocker (Hamburger et al. Mol Imm. 2020). Methods: The first-in-human, open-label, phase 1/2 EVEREST-2 (NCT06051695) study of A2B694 in patients with recurrent/metastatic MSLN-expressing cancers with tumor-associated HLA-A*02 LOH. The prescreening study BASECAMP-1 (NCT04981119) identifies eligible patients and cryopreserves leukapheresis product. Upon progression, A2B694 is manufactured and administered after lymphodepletion. Phase 1 primary objective: evaluate the safety and tolerability of A2B694 and identify a recommended phase 2 dose. Results: As of 05 January 2026, 13 patients were enrolled: 8 women/5 men, median age 59 years, 11 non-Hispanic White/2 Hispanic with unknown race. Tumor types included colorectal (n = 4), ovarian (n = 3), pancreatic (n = 3), non–small cell lung adenocarcinoma (NSCLC), gastro-esophageal, and mesothelioma (n = 1 each). A2B694 dose level (DL) groups were: DL1: 1×10 8 cells (n = 3), DL2: 2×10 8 cells (n = 4), DL3: 4×10 8 cells (n = 5), and DL4: 6×10 8 cells plus low-dose IL-2 (n = 1). Lymphodepletion prior to administration of A2B694 was well-tolerated, with expected, transient cytopenias. The only adverse event reported in more than 1 patient was grade 3 neutropenia. One patient had grade 3 ICANS and 1 patient had grade 1 CRS. There were no dose-limiting toxicities or new safety signals after up to 17 months follow-up. All 13 patients received A2B694, were efficacy-evaluable, and had A2B694 detected post-infusion in peripheral blood. While A2B694 was not detected in tumor biopsies collected in patients treated at DL1 (0/2), all patients treated at DL2-DL4 with available biopsies (3/3) had detectable A2B694 in the tumor microenvironment. A patient with KRAS G12V /STK11 co-mutated NSCLC who had progressed on carboplatin, pemetrexed, and pembrolizumab achieved a complete response (CR) at D90 post-infusion per RECIST 1.1 by central review and had a confirmed CR at D180. In addition, PET-CT scan and ctDNA on D190 demonstrated no evidence of disease. On D243, the patient had a CNS relapse, with an ongoing non-CNS CR per RANO-BM at D284. At M12, the patient's CT showed no new findings and persistence of A2B694 in the blood was confirmed by ddPCR. Conclusions: We report the first patient with NSCLC to have a CR after CAR T. Overall, A2B694 demonstrated manageable safety and tolerability in patients with advanced solid MSLN-expressing tumors with tumor-associated HLA-A*02 LOH. The maximum tolerated dose has not been reached; dose-escalation continues. Clinical trial information: NCT06051695 .

3040 Background: EVEREST-2 is a first-in-human, phase 1/2 trial to assess the safety and efficacy of A2B694, an autologous, logic-gated Tmod CAR T therapy targeted to MSLN, which is normally expressed in the mesothelium and can be upregulated in many solid tumors. A2B694 is designed to overcome challenges of on-target, off-tumor toxicity that have limited other MSLN-targeted approaches by combining a CAR-activating receptor targeting MSLN with a blocker CAR that recognizes HLA-A*02, to distinguish between normal and tumor cells (Tokatlian, et al. J Immunother Cancer. 2022). Methods: Adults with recurrent unresectable, locally advanced, or metastatic cancers with MSLN expression who have progressed after standard-of-care therapy are eligible for EVEREST-2. Enrollment to EVEREST-2 and collection of T-cells occurs through the ongoing prescreening study BASECAMP-1 (NCT04981119). When clinically appropriate, A2B694 is manufactured from cryopreserved T cells, and patients undergo lymphodepletion before A2B694 infusion. The dose-escalation phase is evaluating the safety and tolerability of A2B694 to identify the recommended phase 2 dose (RP2D). Dose escalation was started at 1x10 8 Tmod positive cells (dose level [DL] 1) and will increase up to 14x10 8 in combination with low-dose IL-2 (DL 5). The dose-expansion phase will confirm RP2D and collect biomarker data to further characterize A2B694. Results: As of January 15, 2025, 5 participants (median age: 60 years; range, 50-84) have enrolled on EVEREST-2 and received A2B694 at DLs 1-2; participants had ovarian cancer (n = 3), pancreatic cancer (n = 1), and non-small cell lung cancer (n = 1) and had received a median of 4 prior lines of therapy (range, 1-7). Lymphodepleting chemotherapy was well tolerated with no significant cytopenias observed. The most common adverse events were lymphopenia (7 [14.6%]) and decreased appetite (6 [12.5%]). There were no dose-limiting toxicities, cytokine release syndrome, nor related neurotoxicity. One participant was admitted to the hospital for decreased appetite. No long-term toxicities have been noted up to 7.5 months post-infusion. Of the participants who have received A2B694, 5 were efficacy evaluable at DLs 1-2. A2B694 was detected post-infusion in the peripheral blood in all patients. Additionally, A2B694 was detected in an abdominal tumor biopsy from a patient with pancreatic cancer 42 days post-infusion. Conclusions: The logic-gated approach was successful at reducing toxicity seen with prior MSLN-targeted CAR T therapies, and A2B694 showed successful CAR T expansion and tumor infiltration. The maximum tolerated dose has not been reached, and results from the dose-escalation phase continue to determine the RP2D. Clinical trial information: NCT06051695 .

Abstract Background: Chimeric antigen receptor T-cell (CAR T) therapies have demonstrated significant clinical efficacy in hematologic malignancies, but have proven challenging in solid tumors, in part owing to a lack of tumor-specific targets and unmanageable toxicity. Mesothelin (MSLN) expression normally is limited to the mesothelium of major body cavities but can be upregulated in diverse solid tumor types (cancer.gov/tcga), making it a potential target for cancer therapy. MSLN-targeted cell therapy approaches, including CAR T and T-cell receptor fusion therapies, have shown promising clinical activity; however, on-target, off-tumor toxicity including fatal events have occurred (Beatty, et al. Gastroenterology. 2018.; Haas, et al. Mol Ther. 2023.; Hong, et al. ESMO 2021. Abstract 9590.). A2B694 is an autologous logic-gated, MSLN-targeted Tmod CAR T therapy that addresses the challenges of on-target, off-tumor toxicity by combining 2 CARs: an activating and blocking receptor. The activator recognizes MSLN present on the surface of both tumor and normal cells; the blocker inhibits the CAR T activator when it binds human leukocyte antigen (HLA)-A*02, which is present in normal cells and often lost in tumor cells. Thus, in patients with tumor-associated HLA-A*02 loss of heterozygosity (LOH), the blocker prevents on-target, off-tumor toxicity on normal cells owing to retained HLA-A*02 expression (Hamburger, et al. Mol Immunol. 2020). Through this unique selective mechanism, A2B694 may provide a therapeutic window to treat patients with MSLN-expressing solid tumors exhibiting HLA-A*02 LOH. Methods: EVEREST-2 (NCT06051695) is a first-in-human, phase 1/2, open-label, nonrandomized study to evaluate the safety and efficacy of A2B694 in adults with recurrent unresectable, locally advanced, or metastatic cancers with MSLN expression, including non-small cell lung cancer, colorectal cancer, pancreatic cancer, ovarian cancer, mesothelioma, or other solid tumors with MSLN expression. Eligible patients must have progressed following standard of care therapy. Enrollment to EVEREST-2 occurs through the prescreening study BASECAMP-1 (NCT04981119), which identifies patients with tumor-associated HLA-A*02 LOH via next-generation sequencing (Tempus AI, Inc). Eligible patients enroll in the BASECAMP-1 study and undergo leukapheresis. A2B694 is manufactured from cryopreserved T cells when clinically appropriate for patients. The primary objective of phase 1 is to evaluate the safety and tolerability of A2B694 and identify the recommended phase 2 dose (RP2D). The dose-expansion phase will confirm RP2D and collect biomarker data to further characterize A2B694. Phase 2 will assess overall response rate per RECIST v1.1. The first patient was enrolled on EVEREST-2 in April 2024. Dose escalation is ongoing. Citation Format: Julian R. Molina, Antonious Hazim, Oliver Dorigo, Salman R. Punekar, Monica Avila, Diane M. Simeone, Kedar Kirtane, Gottfried E. Konecny, Jeffrey Ward, Matthew Block, Jennifer Specht, Leslie Boyd, Yanyan Lou, Jong Chul Park, Jacqueline D. Xuan, Ramez N. Eskander, Gayanie Ong, Marco Davila, Wendy Langeberg, Marcela Maus, Armen Mardiros, Frederick L. Locke, Andrea Wise, David G. Maloney, John Welch, J. Randolph Hecht. EVEREST-2: A seamless phase 1/2 study of A2B694, a logic-gated Tmod CAR T-cell therapy, in patients with mesothelin-expressing solid tumors with human leukocyte antigen-A*02 loss of heterozygosity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT186.