Abstract P3-09-15: A phase 1b study of PVX-410 (PVX) vaccine plus durvalumab (DUR) as adjuvant therapy in HLA-A2+ early stage triple negative breast cancer (eTNBC) to assess safety and immune response

Background: eTNBC remains at high risk for recurrence despite modern (neo)adjuvant chemotherapy. Immunotherapy with checkpoint inhibition is active in early and metastatic TNBC, and vaccines may further induce host immune response. PVX-410 (PVX, OncoPep) is a novel tetra-peptide vaccine with 3 of the 4 antigens (XBP1 [2 splice variants] and CD138) commonly overexpressed in TNBC. Here we present results from a phase1b study evaluating safety, tolerability and immune response of PVX and durvalumab (DUR) as adjuvant therapy in eTNBC. Methods: Eligibility for this phase 1b multi-center, single arm study included: HLA-A2+ female patients (pts) with TNBC and tumor size at least 1 cm or node positive; treatment with at least 4 cycles of adjuvant or neoadjuvant chemotherapy; completion of all planned therapy 1-6 months prior to study entry. Pts with local-regional recurrence without evidence of distant metastases treated with curative were also eligible. Pts received 6 doses of 800ug PVX (subcutaneously) emulsified in Montanide and co-administered with Hiltonol (IM) every 2 weeks, and 2 doses of 1500mg DUR (IV) concurrent with the 4th and 6th vaccine treatments. The study included a 6 pt run-in to assess for dose limiting toxicity (DLT), followed by a 14 pt expansion. Blood samples were collected for immune response assessment via flow cytometry at week 0 (Baseline) and at weeks 6, 10, 14, and 24 post-treatment. The primary objective was safety and tolerability. The key secondary objective was PVX specific immune response assessment defined at week 14 as a 2-fold or greater change over baseline in the proportion of CD3+CD8+ T cells that expressed IFNγ and the proportion of CD3+CD8+ T cells positive for PVX tetramers following an in vitro stimulation of PBMC with PVX peptides and a flow cytometric determination. Other immune response assessments included the proportion of CD3+CD8+ T cells expressing TNFα, IL-2, and CD137 following the in vitro peptide stimulation. Results: Among 22 pts enrolled, median age was 48 yrs (range 34-68) and anatomical stage at diagnosis was: Stage 1 = 1 (4.5%), Stage 2 = 14 (64%), and Stage 3 = 7 (32%). Among 20 pts evaluable for week 14 immune response, all planned PVX doses were given, and 1 DUR dose was held due to toxicity (tox). No DLTs were observed in the 6 pt run-in. The most common adverse events (all grades) include: injection site reaction (96%), flu-like symptoms, fatigue (41% each), arthralgia, pruritis (36% each), ALT elevation (32%), myalgia (27%), pain, diarrhea, AST and amylase elevation (23% each). One pt had grade 3 diarrhea and 1 pt had grade 3 hyponatremia, AST and ALT elevation. There were no grade 4 or 5 events. Immune response assessment for the first 12 pts are available at the time of abstract submission. Comparing baseline to week 14, 10 of 12 patients demonstrated a PVX specific immune response (as defined above). Immune response persisted in all patient samples tested at 6 months. Additionally, most pts tested to date had increases over baseline in the proportions of CD3+CD8+ T cells that expressed TNFα, IL-2, and CD137 following the in vitro stimulation with PVX peptides. Final immune response assessment in all 20 evaluable patients will be updated for presentation. At the time of data cut off (4/29/19), with a median follow up of 15.4 months, 4 of 22 (18%) pts had a local (1) or metastatic (3) recurrence and 2 (9%) have died. Conclusions: PVX plus DUR is safe and tolerable in pts with eTNBC with no new unexpected toxicities identified. Immune response data demonstrate that PVX induces antigen-specific T cell expansion and activation in these pts as observed by increases in PVX tetramer, IFNγ, TNFα, IL-2 and CD137 positive T cells. These immune responses to PVX persisted for up to 6 months in most patients, indicating a prolonged immune response. Citation Format: Steven J Isakoff, Sylvia Adams, Hatem H Soliman, Nadine Tung, William T Barry, Jiani Hu, Lorenzo Trippa, Rachel Deering, Joanne Parker, Hannah Park, Elena F Brachtel, Leif W Ellisen, Mariano Severgnini, Doris Peterkin, Sara M Tolaney. A phase 1b study of PVX-410 (PVX) vaccine plus durvalumab (DUR) as adjuvant therapy in HLA-A2+ early stage triple negative breast cancer (eTNBC) to assess safety and immune response [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-09-15.