Arias, Victor

5555 Background: Platinum-resistant/refractory ovarian cancer presents a significant therapeutic challenge and despite several attempts, immunotherapies have not delivered satisfactory results to be approved. Identifying biomarkers of response to novel therapies is crucial for personalizing treatments and improving patient outcomes, especially since certain patients do experience long term benefit after the treatment with pembrolizumab and igrelimogene litadenorepvec (TILT-123; an oncolytic adenovirus coding for TNF and IL-2). Methods: Tumor biopsies (n=62), ascites (n=8) and blood (n=234) were collected from 15 patients treated in the PROTA trial (Phase I, NCT05271318). These patients received pembrolizumab intravenously plus igrelimogene litadenorepvec intravenously, followed by local administration intratumorally or intraperitoneally. Sampling took place prior to therapy, during therapy and after it. Tumor proteome (IHC, mIF) and transcriptome was analyzed to assess immune changes and virus presence. Ascites and blood samples were assayed to measure cell counts, phenotypes, cytokine and protein counts, as well as for the presence of antiviral neutralizing antibodies (NAbs). Biological parameters were correlated with overall survival (OS), RECIST 1.1 evaluations and tumor size changes. For analysis of OS, logrank test was used. For group comparisons two-tailed Mann-Whitney U-test was used. Pearson or Spearman tests were used for correlations. Results: Patients experiencing a drop in circulating lymphocytes 8-24 hours after treatment were more likely to experience longer OS (p=0.044). Additionally, patients with a higher lymphocyte count at baseline experienced similar OS benefit (p=0.018) plus a positive correlation with disease control (p=0.023). Most patients (11/15) showed antiviral immunity at baseline but eventually all patients developed neutralizing activity, and the same was observed in ascites. The presence of NAbs at baseline as well as development of highest titers were positively correlated with longer OS (p=0.004) and disease control (p=0.003). Conclusions: Igrelimogene litadenorepvec and pembrolizumab are therapies designed to attract, activate and/or protect lymphocyte-mediated antitumor activity. These findings suggest that having a fit immune system able to mobilize effector immune cells as well as responding to immunostimulant agents increases therapeutic success. As a disease with few therapeutic options, ovarian cancer patients often receive multiple lines of chemotherapy that might decrease the efficacy of immediate immunotherapies. The potential use of these biomarkers will be studied in larger studies to validate their utility in guiding the use of immunotherapy in this challenging patient population. Clinical trial information: NCT05271318 .

Abstract Background: Ad5/3-E2F-D24-hTNFa-IRES-hIL-2 (TILT-123) is an oncolytic adenovirus armed with TNFa and IL-2. The cytokine pairing demonstrated superior tumor immunomodulation in preclinical studies. Subsequent studies supported evaluation of TILT-123 in PROTA, a phase 1 study of TILT-123 in combination with pembrolizumab in platinum resistant or refractory ovarian cancer patients. Biomarker analysis is ongoing. Experimental procedures: In this phase 1a dose escalation trial (NCT05271318), 15 patients received an initial single intravenous dose of TILT-123 ranging from 3x1011 to 4x1012 VPs, followed by intratumoural and/or intraperitoneal injections ranging from 1x1011 to 5x1011 VPs. Patients also received i.v. pembrolizumab (200mg) every three weeks starting on day 36. The primary endpoint was safety by day 92, while efficacy by RECIST1.1 and overall survival (OS) were secondary endpoints. Collection of tumour biopsies and blood, including PBMCs and serum, enabled evaluation of MoA and identification of preliminary biomarkers. Summary of data: ORR was 7.1% in evaluable patients (1/14). Disease control rate was 64% in evaluable patients (n = 14) and median OS was 190 days (n =15). Patients with disease control and no disease control by 92 achieved a median OS of 571 days and 138 days respectively. Correlations of complete blood count with differential to OS (n =15) and imaging response (n = 14) revealed a greater drop in lymphocyte count after treatment, as well as baseline lymphocyte count positively correlated with OS and disease control (PR/SD vs PD). Correlation of prothrombin INR to OS revealed patients with a slower blood-clotting rate at baseline and post-treatment positively correlated with OS. Analysis of anti-adenovirus neutralizing antibody (nAb) titer revealed 77% of all patients were positive for nAbs prior to treatment. All patients developed nAbs in blood and ascites (ascites n = 3). Patients presenting with nAbs at baseline achieved longer OS than those not positive. Additionally, a higher titer post-treatment positively correlated with OS and disease control. Percentage and fold change increase in IgM expression on plasma cells on day 36 positively correlated with OS. In addition, a higher expression of IgM on the surface of plasma cells at baseline was observed in patients achieving disease control. Conclusion: These preliminary results identify a key role of circulating lymphocyte re-distribution and humoral immune response as markers of treatment benefit. Initial phenotyping implicates IgM producing plasma cells as a potentially relevant immune cell population. Additionally we observed a correlation between the coagulation cascade and OS. Citation Format: James H. Clubb, Matthew Block, Johanna Mäenpää, Victor Arias, Mirte van der Heijden, Santeri Pakola, Dafne C. Quixabeira, Tatiana Kudling, Elise Jirovec, Lyna Haybout, Tuomo Alanko, Daniel Adamo, Susan Ramadan, Jorma Sormunen, Juha Kononen, Michael J. Chisamore, Julia W. Cohen, Nadena Singh, John Goldfinch, Suvi Sorsa, Riikka Havunen, Claudia Kistler, João M. Santos, Víctor Cervera-Carrascon, Akseli Hemminki. Clinical-immunological correlates in platinum resistant or refractory ovarian cancer patients treated with chimeric oncolytic adenovirus encoding TNFa and IL-2 (TILT-123) in combination with pembrolizumab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2035.