Bedu‐Addo, Frank

6041 Background: Human papillomavirus (HPV) E6/E7 oncoproteins mediate immune evasion by down-regulating Type 1 interferons, TLR9, MHC Class I/II as well as other mechanisms, resulting in persistent infection and initiation of ̃5% of all cancers globally. Similarly, established cancers evade immune surveillance utilizing parallel mechanisms including the expression of checkpoint proteins. PDS0101 is a molecularly targeted immunotherapeutic based on an enantiospecific cationic lipid nanoparticle platform containing HPV16 neoantigens that exhibits anti-tumor activity with checkpoint inhibitors (CPIs) by upregulating Type I interferons and promoting antigen processing and cross presentation. This allows generation of high levels of polyfunctional HPV16-specific CD8 and CD4 T cells in vivo as well as immune memory. VERSATILE-002 (NCT04260126) is a phase 2 study of the combination of PDS0101 and pembrolizumab in treatment of CPI naïve and refractory patients with recurrent or metastatic HPV16-related HNSCC. Herein, we report preliminary safety and efficacy data for CPI naïve patients at a prespecified interim analysis. Methods: Subjects are treated with pembrolizumab 200mg IV every three weeks plus SC PDS0101 following pembrolizumab on days one of Cycles1-4 and Cycle12; pembrolizumab continues up until 35 cycles, disease progression or intolerance to therapy. Results: Eighteen CPI naïve subjects with confirmed HPV16 tumors and a CPS score > = 1, median age 62 yrs (range 46-71), all male, 17 (94%) of whom were White and 16 (88.9%) not Hispanic or Latino, received at least one cycle of combination therapy. At the time of analysis, 17 (94%) subjects had received > = 4 doses of PDS0101 (median 4, range 1-5) and pembrolizumab (median 7, range 1-14). There were no Grade 3 or greater treatment-related toxicities and no drug discontinuation related to toxicity or immune-related AEs. Clinical activity (CR+PR+SD) was seen in 13 (72.2%) of 18 subjects, with best overall reponse per RECIST1.1 documenting: OR in 7 (38.9%; 2 CR, 5PR); stable disease (SD) in 6 (33.3%) and progressive disease in 3 (16.7%); 2 subjects had missing data. Tumor reduction was seen in 4 of 6 (67%) subjects with SD. Nine-month PFS and OS rates (95% CI) were 52% (22.5, 74.7) and 81% (37.8, 95.5) respectively; median PFS and OS have not been reached. Conclusions: The combination of PDS0101 and pembrolizumab demonstrates an excellent safety profile with preliminary evidence of clinical activity in the majority of CPI naïve patients with HPV-related HNSCC. Clinical trial information: NCT04260126.