Maloney, David G.

TPS788 Background: MSLN is a desirable candidate for targeted therapy given its limited expression in normal tissues and its overexpression in several malignancies, including PANC, mesothelioma, non-small cell lung, and ovarian cancers (TCGA 2022). MSLN-targeted CAR T and T-cell receptor therapies have shown promising clinical activity; however, on-target, off-tumor toxicity, including fatal events, have occurred (1-3). Autologous logic-gated Tmod CAR T therapies address the challenges of on-target, off-tumor toxicity by combining 2 CARs: activating and blocking receptors. The activator recognizes a tumor-associated antigen present on the surface of both tumor and normal cells; the blocker prevents CAR T activity when it binds HLA-A*02, which is present in normal cells and often lost in tumor cells. Thus, in patients with tumor-associated HLA-A*02 LOH, the blocker prevents on-target, off-tumor toxicity on normal cells due to retained HLA-A*02 expression (4). HLA-A*02 LOH is observed in various solid tumors, including ~20% of PANC (5). Two autologous CAR T therapies are currently under investigation: A2B530, targeting carcinoembryonic antigen, in the EVEREST-1 trial, and A2B694, targeting MSLN, in the EVEREST-2 trial, described herein. A2B694 may provide a therapeutic window to treat patients with PANC and other MSLN-expressing solid tumors exhibiting HLA-A*02 LOH due to its unique discriminatory mechanism. Methods: EVEREST-2 (NCT06051695) is a first-in-human, phase 1/2, open-label, nonrandomized study to evaluate the safety and efficacy of A2B694 for recurrent unresectable, locally advanced, or metastatic cancers with MSLN expression, including PANC. Eligible patients must have exhausted options of potentially curative therapy and have recurrent disease. Enrollment to EVEREST-2 occurs through the prescreening study BASECAMP-1 (NCT04981119), in which patients with tumor-associated HLA-A*02 LOH are identified via next-generation sequencing (Tempus AI, Inc) and leukapheresis product is collected. 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 the primary endpoint overall response rate per RECIST v1.1 and secondary endpoints progression-free survival and overall survival. The first patient was dosed on April 24, 2024 and dose escalation is ongoing. 1. Beatty, et al. Gastroenterology . 2018. 2. Haas, et al. Mol Ther . 2023. 3. Hong, et al. ESMO 2021. Abstr 9590. 4. Hamburger, et al. Mol Immunol . 2020. 5. Hecht, et al. J Clin Oncol . 2022. Clinical trial information: NCT06051695 .

TPS2699 Background: Despite the success in hematologic cancers, chimeric antigen receptor (CAR) T-cell therapies are challenging to implement in solid tumors owing to a lack of tumor-specific targets that discriminate cancer from normal cells. MSLN expression normally is limited to the mesothelium of major body cavities but can be upregulated in diverse solid tumor types (TCGA 2022), making it a potential target for cancer therapy. MSLN-targeted cell approaches, including CAR T-cell and T-cell receptor fusion therapies, have shown promising clinical activity; however, on-target, off-tumor toxicity including fatal events have occurred (1-3). A2B694 is an autologous logic-gated, MSLN-targeted Tmod CAR T-cell 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 binds HLA-A*02 and prevents CAR T-cell activity. Thus, in patients with both germline HLA-A*02 and tumor-associated HLA-A*02 LOH, the blocker prevents on-target, off-tumor toxicity on normal cells owing to retained HLA-A*02 expression (4). Through this unique discriminatory 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 should have received ≥1 line of prior therapy such as checkpoint inhibitor, molecular targeted, or chemotherapy. 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. 1. Beatty, et al. Gastroenterology. 2018. 2. Haas, et al. Mol Ther. 2023. 3. Hong, et al. ESMO 2021. Abstract 9590. 4. Hamburger, et al. Mol Immunol. 2020. Clinical trial information: NCT06051695 .

TPS2698 Background: Chimeric antigen receptor (CAR) T-cell therapies for treating solid tumors are challenging due to a lack of tumor-specific targets that discriminate cancer from normal cells. Previous studies using CEA T-cell receptors and T-cell engagers have resulted in dose-limiting, on-target, off-tumor toxicities (1,2). A2B530 is an autologous logic-gated, CEA-targeted Tmod CAR T-cell therapy that addresses the challenges of on-target, off-tumor toxicity by combining a CAR-activating receptor with a blocking receptor to discriminate tumor from normal cells (3). The activator recognizes CEA on the surface of both tumor and normal cells while specificity for tumor cells is provided by a blocker that binds HLA-A*02. In patients with both germline HLA-A*02 and tumor-associated HLA-A*02 LOH, the blocker prevents on-target, off-tumor toxicity on normal cells owing to retained HLA-A*02 expression (4). HLA-A*02 LOH can be detected using next-generation sequencing (Tempus AI, Inc.). With this definitive discriminator target, A2B530 can potentially provide a therapeutic window to treat patients with CEA-expressing solid tumors exhibiting HLA LOH. Methods: EVEREST-1 (NCT05736731) is a seamless, phase 1/2, open-label, nonrandomized study to evaluate the safety and efficacy of A2B530 in adult patients. Patients are enrolled through BASECAMP-1 (NCT04981119), a master prescreening study that identifies patients with HLA LOH at any time in the course of their disease. BASECAMP-1–eligible patients undergo leukapheresis and, when clinically appropriate, their banked T cells are manufactured for the EVEREST-1 study. The key inclusion criteria include histologically confirmed recurrent unresectable, locally advanced, or metastatic cancers associated with CEA expression: non-small cell lung, colorectal, or pancreatic cancers. Patients should have received ≥1 line of prior therapy such as checkpoint inhibitor, molecular targeted, or chemotherapy. The primary objective of phase 1 is to evaluate the safety and tolerability of A2B530 and determine the recommended phase 2 dose (RP2D). The dose-escalation portion is based on the Bayesian optimal interval design. The dose-expansion phase will confirm RP2D and collect biomarker data to further characterize A2B530. Phase 2 will assess overall response rate per RECIST v1.1. As of January 29, 2024, 8 patients have been enrolled on EVEREST-1. A2B530 was successfully manufactured for all patients, and all patients have received A2B530 infusion, with the first patient dosed in May 2023. Dose escalation is ongoing. 1. Parkhurst, et al. Mol Ther. 2022. 2. Tabernero, et al. J Clin Oncol. 2017. 3. Hamburger, et al. Mol Immunol. 2020. 4. Sandberg, et al. Sci Transl Med. 2022. Clinical trial information: NCT05736731 .

1604 Background: Diversity in clinical studies is essential to address health disparities, but racial and ethnic minorities are often underrepresented in clinical studies, especially in precision medicine studies using genetic data (1). BASECAMP-1 (NCT04981119) is an ongoing prescreening study to identify patients with unresectable advanced or metastatic solid tumors and tumor-associated HLA-A*02 LOH for the EVEREST-1 and -2 Tmod chimeric antigen receptor T-cell therapy trials. When enrollment began in 2021, eligibility for Part 1 was restricted to patients with germline HLA-A*02:01 based on preclinical data. Additional analysis revealed the blocker in the Tmod construct had activity across HLA-A*02 subtypes (Mock, et al. Mol Ther Oncolytics.2022). Eligibility for Part 1 was then expanded to all HLA-A*02 subtypes, allowing enrollment of more diverse patient populations. HLA-A*02 allele subtypes vary by ethnicity and race; the frequency of HLA-A*02:01 is 96% in non-Hispanic Whites, but ranges from 53% to 73% in other ethnicities and races. The frequency of all other HLA-A*02 allele subtypes (HLA-A*02:XX) is <5% in non-Hispanic Whites but up to 66% in other ethnicities and races (2,3). Methods: Patients eligible for BASECAMP-1 were identified at United States study sites. All patients screened before January 16, 2024, for Part 1 were included for demographic and central lab HLA-A typing. The % increase in eligibility and % of heterozygous HLA-A*02 patients with HLA-A*02:XX were calculated by ethnicity and race. Results: A total of 1124 patients were screened for germline HLA-A*02 typing; 431 patients were HLA-A*02:01 heterozygous, of whom 37 (9%) were Hispanic, 14 (3%) African American (AA), 2 (<1%) American Indian or Alaska Native, 17 (4%) Asian or Pacific Islander (API), and 324 (75%) non-Hispanic White (Table). The eligibility expansion identified 62 patients with HLA-A*02:XX heterozygosity, of whom 6 (10%) were Hispanic, 6 (10%) AA, 19 (31%) API, and 25 (40%) non-Hispanic White. Conclusions: By expanding enrollment to include HLA-A*02:XX, 16% more Hispanic, 43% more AA, and 112% more API patients were identified, improving the diversity in this trial compared with that of initial enrollment. 1. Aldrighetti, et al. JAMA Netw Open 2021. 2. Ellis, et al. Human Immunol. 2000. 3. Gragert, et al. Human Immunol.2013. Clinical trial information: NCT04981119 . [Table: see text]

Background:Patients with R/R CLL/SLL who experience intolerance to or disease progression after Bruton tyrosine kinase inhibitor (BTKi) and venetoclax treatment have no established standard of care and poor outcomes, indicating a critical unmet need. Liso-cel, an autologous, CD19-directed, 4-1BB CAR T cell product, has demonstrated efficacy in large B-cell lymphoma and CLL/SLL. In the primary analysis of the phase 1/2, single-arm, multicenter TRANSCEND CLL 004 (NCT03331198) study, a single administration of liso-cel demonstrated rapid, deep, and durable responses and a manageable safety profile in patients with R/R CLL/SLL, including those with progression on previous BTKi and venetoclax failure (Siddiqi T, et al. Lancet 2023). The primary endpoint was met in the prespecified subset of efficacy-evaluable patients with disease progression on BTKi and venetoclax failure (primary efficacy analysis set [PEAS]) at a target dose of 100 × 10 6 CAR + T cells (null hypothesis: ≤ 5%) with the rate of complete response/remission (CR) and CR with incomplete marrow recovery (CRi) by an independent review committee (IRC) per 2018 International Workshop on CLL (iwCLL) criteria at 18.4% ( P = 0.0006). Here we report results from TRANSCEND CLL 004 with a median follow-up of 23.5 months. Methods: Patients must have received ≥ 2 prior lines of therapy, including a BTKi. Eligible patients received liso-cel at a target dose of either 50 × 10 6 (dose level [DL] 1) or 100 × 10 6 (DL2) CAR + T cells after lymphodepleting chemotherapy. The primary endpoint was CR/CRi in the PEAS at DL2. Key secondary endpoints were ORR and rate of undetectable MRD (uMRD; 10 −4 by next-generation sequencing) in blood. All null hypotheses were tested at the primary analysis and not retested in this analysis. Results:Of 137 leukapheresed patients, 118 received liso-cel (safety set), 97 (DL1 = 9; DL2 = 88) were efficacy evaluable, and 54 (DL1 = 4; DL2 = 50) were in the PEAS. In the safety set, median (range) age was 65 years (49-82), 83% had high-risk cytogenetics (del[17p], 42%; TP53 mutation, 47%; unmuted immunoglobulin heavy-chain variable gene, 47%; ≥ 3 chromosomal aberrations, 61%), median (range) lines of prior therapy was 5 (2-14), and all patients had prior BTKi. As of data cutoff (February 28, 2023), median (range) on-study follow-up was 23.5 months (0.4-59.6) for the safety set. In the PEAS at DL2, CR/CRi rate was 20% (95% CI, 10.0-33.7; Table 1). ORR was 44% (95% CI, 30.0-58.7). One patient who had best overall response (BOR) of partial response/remission (PR) at primary analysis had deepened to CR/CRi at 18 months without any additional therapy. Of 9 patients who had BOR of CR/CRi at the primary analysis, 8 had ongoing CR/CRi and 1 completed the study with the last assessment as CR/CRi. The uMRD rate was 64% (95% CI, 49.2-77.1) in blood and 60% (95% CI, 45.2-73.6) in marrow. Median (95% CI) duration of response was 35.3 months (12.4-not reached [NR]) and median duration of CR/CRi was NR. Median (95% CI) PFS was 11.9 months (5.7-26.2). Median (95% CI) OS was 30.3 months (15.0-NR). The efficacy outcomes were similar in the full population at DL2. Of 16 patients who had BOR of CR/CRi at primary analysis, 10 had ongoing CR/CRi. In the safety set, rates of any-grade and grade ≥ 3 treatment-emergent AEs were similar across age groups (Table 2). The rate of any-grade cytokine release syndrome (CRS) was 85% (grade 3, 8%; no grade 4/5) and neurological events (NE) was 45% (grade 3, 18%; grade 4, 1%; no grade 5); 69% received tocilizumab and/or corticosteroids for CRS/NEs. Median (range) time to onset and resolution was 4 days (1-18) and 6 days (2-37) for CRS and 7 days (1-21) and 7 days (1-83) for NEs, respectively. Prolonged cytopenia (grade ≥ 3 at Day 30 after liso-cel infusion), grade ≥ 3 infections, hypogammaglobulinemia, tumor lysis syndrome, second primary malignancy, and macrophage activation syndrome occurred in 54%, 18%, 15%, 11%, 9%, and 3%, respectively. Forty-five (33%) of 137 leukapheresed patients died after liso-cel infusion (disease progression, n = 27 [20%]; AE, n = 6 [4%]; other reasons, n = 12 [9%]). Conclusions: With longer follow-up, liso-cel continued to demonstrate durable CR/CRi, high uMRD rates, and a manageable safety profile in patients with heavily pretreated, high-risk R/R CLL/SLL. The safety results from longer follow-up were similar to those reported in the primary analysis with no new safety signals and were consistent across age groups.