Abstract 1983: Modulation of immune gene expression by intra-tumoral oncolytic adenovirus ONCOS-102 is associated with clinical response in anti-PD-1 refractory/resistant melanoma

Background: Defining molecular parameters of clinical response to immune modulators may lead to development of novel biomarkers, new therapeutic targets and drug combinations in cancer treatment. We recently completed phase I/II testing of ONCOS-102, a GM-CSF-encoding oncolytic adenovirus (Ad5/3-D24-GMCSF), for therapeutic efficacy and capacity to remodel tumor micro-environment (TME) in combination with pembrolizumab (pem) in patients (pts) with non-resectable, stage III-IV, anti-PD-1 resistant/refractory (R/R) melanoma (NCT03003676). Here we report comparative, longitudinal gene expression analysis of tumor samples from pts with complete/partial response (CR/PR), stable (SD) or progressive (PD) disease by RECIST1.0. Methods: In study part 1, n=9 pts received three intra-tumoral (i.t.) injections of ONCOS-102 every 3 days during the first week of treatment. Pem was administered i.v. at 10 mg/kg from day 22 every 3 weeks for 6 months. In study part 2, n=12 pts received additional injections of ONCOS-102 at day 15 and then every 3 weeks along with pem. On-treatment tumor biopsies were collected at baseline, day 22 and 64. Total RNA sequencing followed by differential gene expression analysis using DESeq1 was conducted on n=17 pts to disclose dynamic transcriptome changes associated with ONCOS-102 administration and clinical response. Results: Baseline biopsies of CR/PR pts showed 1,5-2 fold higher levels of expression of innate and adaptive immune response-related genes compared to PD pts. Treatment with ONCOS-102 upregulated immune related genes at day 22 across most tumors with no clear PR/PD differentiation. However, at day 64 a striking distinction between pts with CR/PR compared to PD emerged, showing 4-5 fold increase in expression levels for several immune-related gene categories including check-points, co-stimulatory and cellular cytotoxicity genes. TME remodeling in CR/PR pts was sustained at least until day 64. On individual genes,higher and more sustained upregulation of several co-stimulatory molecules (4-1BB, OX40, CD28) and checkpoints (LAG-3, TIGID, TIM-3) was seen in responders. Expression of adenovirus genes was more prevalent in CR/PR (2 of 3 pts) than PD (0 of 2 pts) on day 64, suggesting that tumor susceptibility to virus entry and replication drives clinical benefit of ONCOS-102. Our findings were supported by analysis of other gene subsets and comparison of different schedules of ONCOS-102 administration. Conclusions: ONCOS-102 drives