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Abstract Background Emerging evidence suggests irreversible electroporation (IRE) with standard-of-care (SOC) chemotherapy may improve survival in patients with Stage 3 pancreatic ductal adenocarcinoma (PDAC) when compared to SOC alone. This study evaluates the overall survival (OS) and progression-free survival (PFS) of Stage 3 PDAC patients treated with SOC plus IRE with the NanoKnife System versus SOC alone. Methods This prospective, multicenter study included two cohorts from the DIRECT registry: an IRE cohort from sites offering IRE as part of clinical care, and a comparator SOC cohort of prospectively enrolled and contemporaneous retrospective patients. Enrollment spanned 08/05/2019 to 02/05/2023, with follow-up through at least 24 months, death, or loss to follow-up. Included were 137 patients (99 IRE; 38 SOC), aged ≥18 years with Stage 3 PDAC and no progression after three months of SOC therapy. Results Median (interquartile range) time from diagnosis to enrollment was 8 (6-10) months for IRE and 4 (3-6) for SOC (p<0.0001). Median OS and PSF from enrollment were 18 (95% confidence interval [CI]: 15-24) months and 9 (95% CI: 7-12) months for IRE, and 10 (95% CI: 8-14) months and 6 (5-8) months for SOC, respectively (p<0.0001 and p=0.009). Adverse events occurred in 80% (79/99) of IRE patients and 95% (36/38) of SOC patients; 29% (29/99) of the IRE cohort experiencing an IRE-related adverse event. Conclusions IRE was associated with improved OS versus SOC alone and may be an effective consolidative treatment for Stage 3 PDAC after three months of induction chemotherapy.

Objective Identifying eligible patients for precision oncology clinical trials is challenging, particularly for rare molecular subpopulations. To address this challenge, A2 Biotherapeutics developed BASECAMP-1 ( NCT04981119 ), a non-interventional master screening study to identify patients eligible for interventional studies of logic-gated Tmod chimeric antigen receptor T-cell therapies. Eligible patients for these interventional trials have an advanced solid malignancy and are germline human leucocyte antigen (HLA)-A*02 heterozygous, with tumour-associated HLA-A loss of heterozygosity (LOH). HLA-A LOH occurs in ~16% of advanced solid malignancies; therefore, an efficient screening strategy is required. This report describes BASECAMP-1; compares the efficiency of two screening methods; and discusses the broader advantages of BASECAMP-1 beyond efficient enrolment. Methods and analysis Patients are identified for BASECAMP-1 using two approaches. In the traditional approach, common for clinical trials, investigators consent and screen all patients who might be good candidates for cell therapy trials, with no prior knowledge of patient HLA-A type or LOH status. To further optimise our approach, we co-developed with Tempus AI (Tempus) the bioinformatic programme Aware, which identifies potentially eligible patients with tumour-associated HLA-A*02 LOH within a clinico-genomic database that includes linked genomic and transcriptomic sequencing and clinical data collected during routine care. Results Over 42 months of using a traditional approach to identify eligible patients, 1918 patients at 13 study sites were consented and screened for BASECAMP-1; of these, 30 patients with tumour-associated HLA-A*02 LOH were enrolled (~0.7 participants per month). Over the last 30 months of that same period, Tempus Aware screening was implemented and 55 patients with tumour-associated HLA-A*02 LOH were enrolled (~1.8 participants per month). The bioinformatic approach identified more patients than the traditional approach and used sequencing results produced as part of the standard clinical tumour sequencing workflow, reducing resource use and study staff burden. Additional advantages of using a screening study, such as BASECAMP-1, include manufacturing efficiencies and collection of a large dataset of molecular and clinical parameters that can be used to supplement trial analyses. Conclusions The BASECAMP-1 study demonstrates a clinico-genomic screening approach can more efficiently identify patients for precision oncology trials. Furthermore, precision oncology can be enhanced through collaborative data-sharing. Trial registration number NCT04981119 .

e16408 Background: A2B530 is a logic-gated CEA-targeting Tmod CAR T therapy being evaluated in the EVEREST-1 (NCT05736731) phase 1/2 study. Tmod CAR T therapy addresses challenges of on-target, off-tumor toxicity that have limited application of CAR T therapy to solid tumors (Tabernero, et al. J Clin Oncol. 2017); through use of a CEA-targeted CAR-activating receptor combined with a blocking receptor recognizing HLA-A*02, A2B530 can distinguish between tumor and normal cells (Sandberg, et al. Sci Transl Med. 2022). Methods: Patients with unresectable locally advanced or metastatic solid tumors expressing CEA and tumor-associated HLA-A*02 LOH are enrolled through the ongoing prescreening study BASECAMP-1 (NCT04981119). Eligible patients undergo leukapheresis and, when clinically appropriate, A2B530 is manufactured for the EVEREST-1 study. Patients undergo lymphodepletion before A2B530 infusion. The phase 1 dose escalation will evaluate safety, tolerability, manufacturing feasibility, and biomarkers starting at 1x10 8 Tmod positive cells (dose level [DL] 1) up to 6x10 8 cells and higher doses of lymphodepleting chemotherapy (LDC; DL 5). After the recommended phase 2 dose has been established, dose expansion will confirm safety and activity. Results: As of January 15, 2025, 14 total participants were enrolled on EVEREST-1 and had received A2B530 infusion at DLs 1-5, 4 (29%) with pancreatic (PANC) and 10 (71%) with colorectal cancer. Median age was 57 years (range, 34-76), with a median of 2 prior lines of therapy (range, 1-6). LDC was well tolerated: neutropenia nadired at days 7-10, with recovery in all patients, and no significant episodes of prolonged cytopenia. There were no dose-limiting toxicities, grade > 3 serious adverse events (AEs), or episodes of related neurotoxicity. Most gastrointestinal AEs occurred early and were grade 1 or 2. One patient in DL 2 (2x10 8 cells) experienced possible grade 2 cytokine release syndrome (CRS), which started on day 15 and resolved with supportive therapy within 2 days; later the CRS diagnosis was confounded by a positive blood culture from the participant’s central line. The low rate of CRS is consistent with the low levels of serum cytokines measured up to 28 days post-infusion. Central response assessment has been completed for the 6 participants in DLs 1-2, with a partial response observed in 1 of 3 (33%) of participants with PANC. Peak expansion shows a possible dose response. Conclusions: Treatment with A2B530 was well tolerated, showing potential clinical efficacy and a potential dose response, although these are initial results. Maximum tolerated dose has not been reached, and dose escalation continues to determine the optimal phase 2 dosing of this treatment regimen. Clinical trial information: NCT05736731 .

766 Background: BASECAMP-1 (NCT04981119) is a pre-screening study to identify patients with tumor-associated human leukocyte antigen (HLA)-A*02 loss of heterozygosity (LOH) for interventional studies, such as EVEREST-2 (NCT06051695), a phase 1/2 study of logic-gated chimeric antigen receptor T-cell (CAR T) therapy for MSLN-expressing cancers. MSLN is a cell surface protein expressed in several cancer types, including mesothelioma (MESO), colorectal (CRC), non-small cell lung (NSCLC), ovarian (OVCA), and pancreatic (PANC) cancer, which can be associated with poor prognosis (1). Longitudinal clinical, genomic, and biomarker data were collected from patients enrolled in BASECAMP-1, providing a large dataset for translational discovery and propensity scoring. The aim of this analysis was to determine whether MSLN expression measured by RNAseq and IHC are correlated among patients with solid tumors. Methods: In BASECAMP-1, tumor tissue from patients with germline heterozygous HLA-A*02 is tested for HLA-A*02 LOH using an investigational next generation sequencing device codeveloped with Tempus Labs (Lozac'hmeur, et al. NPJ Precis Oncol. 2024) that detects somatic alterations, including HLA LOH, and generates RNAseq data (eg, MSLN expression). Gene-level transcripts per million read (TPM) values were determined and the log2 TPM +1 was displayed in a scatter plot (the mean and standard deviation [SD] are provided in the Table). Patients with HLA-A*02 LOH also submit tissue for IHC testing for exploratory biomarkers (eg, MSLN expression using anti-MSLN clone 5B2). Statistical significance was determined with ANOVA or t-tests. Results: As of June 1, 2024, 314 patients had been screened for BASECAMP-1 and had RNAseq results; 34 patients also had MSLN IHC results. MSLN expression by RNAseq was consistently higher in patients with PANC or OVCA vs CRC or NSCLC ( P <0.001). MSLN expression by RNAseq and IHC were correlated overall ( P <0.001), particularly among patients with PANC and OVCA. Among the 8 patients with OVCA or PANC who were IHC+ for MSLN, only 1 had an RNAseq value below 6 log2 TPM+1; this patient had mesonephric-like ovarian adenocarcinoma, which may account for the low value. The one MESO sample with both RNAseq and IHC available was IHC+ and had a high RNAseq value. Conclusions: This analysis demonstrated high correlation between RNAseq and IHC MSLN expression in tumor tissue. 1. Faust, et al. Cancers. 2022. Clinical trial information: NCT04981119 . MSLN expression by RNASeq by tumor type and IHC status. Tumor Overall (N=314) IHC data available (n=34) MSLN Positive MSLN Negative n Mean TPM a (SD) n Mean TPM a (SD) n Mean TPM a (SD) All 314 5.1 (2.3) 20 6.0 (2.1) 14 2.3 (1.7) adNSCLC 33 3.8 (2.4) 2 4.7 (1.7) 7 1.5 (1.3) sqNSCLC 4 3.1 (1.8) 0 0 MESO 4 4.5 (4.2) 1 5.7 0 CRC 148 4.4 (2.0) 8 5.1 (2.1) 7 3.1 (1.6) PANC 100 6.1 (1.8) 3 7.8 (0.6) 0 OVCA 25 7.2 (2.1) 5 6.6 (2.8) 0 a MSLN log2 transcripts per million+1. ad, adenocarcinoma; sq, squamous.

Background/Objectives: Overall survival for patients with Stage 3 pancreatic ductal adenocarcinoma (PDAC) remains limited, with a median survival of 12 to 15 months. Irreversible electroporation (IRE) is a local tumor ablation method that induces cancerous cell death by disrupting cell membrane homeostasis. The DIRECT Registry study was designed to assess the effectiveness and safety of IRE when combined with standard of care (SOC) treatment for Stage 3 PDAC versus SOC alone in a real-world setting after at least 3 months of induction chemotherapy; Methods: Patients with Stage 3 PDAC treated with IRE plus SOC or SOC alone were prospectively enrolled in a multicenter registry study. Enrollment required 3 months of active multi-agent chemotherapy with no progression before enrollment. Endpoints were 30- and 90-day mortality and adverse events (AEs). Results: Eighty-seven IRE and 27 SOC subjects were enrolled in the registry. Mean ages were 64.0 ± 8.4 and 66.4 ± 9.9 years, and mean anterior/posterior tumor diameters were 2.2 ± 0.7 cm and 3.2 ± 1.3 for the IRE and SOC groups respectively (p = 0.0066). All IRE procedures were performed using an open approach. The 90-day all-cause mortality was 5/83 (6.0%) and 2/27 (7.4%) for the IRE and SOC groups, respectively. Two subjects in the IRE group died from treatment-related complications, and one patient in the SOC group died due to chemotherapy-related complications. Conclusions: Initial results from the DIRECT registry study indicate the use of IRE for curative intent tumor ablation in combination with induction chemotherapy has equivalent morbidity and mortality rates when compared to standard-of-care chemotherapy alone.

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 .

209 Background: Metastatic colorectal (CRC), pancreatic (PANC), and gastroesophageal cancers are the leading causes of GI cancer–related mortality (5-y survival: 15%, 3%, and 5%-6%, respectively) (ACS 2022). HLA LOH is a recurrent mechanism of immune escape observed in 15%-20% of GI cancers (Hecht R., ASCO GI 2022). The Tmod platform is a logic-gated chimeric antigen receptor (CAR) T-cell modular system, comprising a carcinoembryonic antigen (CEA)- or mesothelin (MSLN)-targeting CAR activator and a separate HLA-A*02-targeting blocker receptor. Both in vitro/in vivo, Tmod CAR T therapy kills cells with HLA-A*02 LOH (tumor) without harming cells with retained HLA-A*02 expression (normal). However, HLA-A*02 LOH can only be therapeutically exploited if patients are identifiable through a feasible and timely clinical workflow. Methods: We established a biobanking protocol (BASECAMP-1, NCT04981119) to determine whether HLA-A*02 LOH patients can be prospectively identified. Patients with CRC, PANC, or non-small cell lung cancer (NSCLC), and a high risk for incurable relapse, were screened first using a standard HLA assay. Heterozygous HLA-A*02 positive tumor samples were then assessed for LOH using a bioinformatic algorithm applied via the Tempus xT platform. Results: As of Sep 1, 2022, 83 patients were consented at 4 institutions. HLA status was obtained from 70 patients and 28 were identified as HLA-A*02:01 heterozygous (40%; expected frequency based on USA NMDP data, 27.6%). LOH results were available for 16 patients; 4 LOH-positive patients were identified (25%, 2 PANC, 2 NSCLC). The LOH assay sensitivity declines below a tumor purity of 40% (Hecht R., ASCO GI 2022). Six patients had a tumor purity of 20% (all with PANC, a tumor known for high stromal content), limiting possible LOH detection. The impact of tumor purity on LOH sensitivity was highlighted in a patient with a low initial sample tumor purity (30%) that resulted in a 41% probability of HLA-A*02:01 LOH (below positive threshold). A second sample with a higher tumor purity (70%), obtained from formalin-fixed, paraffin-embedded sections, resulted in a 92% probability of HLA-A*02:01 LOH (positive). Conclusions: BASECAMP-1 prospective identification of HLA-A*02 LOH is feasible in the real-world setting. The frequencies of the HLA-A*02 allele and of HLA-A*02 LOH in this cohort mirrored expected population frequencies. LOH results can be obtained within a clinically feasible workflow and timeframe, although samples with a < 40% tumor purity have a reduced sensitivity for LOH detection, an issue recurrently observed in patients with PANC. The BASECAMP-1 strategy enables prospective identification of appropriate patients for future therapeutic clinical trials using Tmod CEA and MSLN logic-gated CAR T cells. Clinical trial information: NCT04981119 .