Abstract: Introduction: PVX-410 Multi-Peptide Vaccine (OncoPep, Inc.) is being developed for the treatment of SMM. PVX-410 consists of 4 human leukocyte antigen-A2 (HLA-A2), synthetic 9-mer peptides from unique regions of 3 multiple myeloma (MM)-associated antigens (XBP1 US184-192; XBP1 SP367-375; CD138260-268; and CS1239-247) emulsified in Montanide® ISA-720 VG (Seppic). Adults with SMM at high risk of progression to active MM who were HLA-A2-positive were eligible. The primary objective was to determine the tolerability of PVX-410, initially as monotherapy and then in combination with lenalidomide (len). Immune and disease response also were assessed. Methods: All patients received 6 bi-weekly subcutaneous injections of PVX-410, initially at the low-dose of 0.4 mg (0.1 mg/peptide or 0.4 mg total) and then at the target dose of 0.8 mg (0.2 mg/peptide or 0.8 mg total). In the PVX-410+len cohort, patients received 3 standard cycles of len (25 mg orally on Days 1-21 every 28 days, without dexamethasone). All patients also received 0.5 mL (1 mg) Hiltonol® (poly-ICLC) (2 mg/mL) via intramuscular injection at the time of PVX-410 administration. Patients were followed for 12 months post-treatment. Blood samples for immune response evaluation were collected at Week 0 (Baseline; pre-dose), 2, 4, and 8 weeks during treatment and at Months 1, 3, 6, 9, and 12 post-treatment. Disease response was assessed at the same time points, except Weeks 0 and 2, using International Myeloma Working Group and modified European Group for Blood and Bone Marrow Transplant criteria. Results: Overall, 22 patients with high-risk SMM were enrolled (age range 39 to 82 years), of whom 12 received PVX-410 monotherapy (3 low-dose; 9 target dose) and 10 received PVX-410 (target dose) + len. All 22 patients have either completed the study through post-treatment Month 12 (N=15) or discontinued before that time (N=7). PVX-410 was well-tolerated, with a treatment-emergent adverse event (TEAE) profile consistent with that expected, based on previous clinical studies with peptide vaccines. All (100%) 22 patients experienced at least 1 TEAE. Among monotherapy patients, the most common TEAEs were injection site pain (50%); fatigue (33%); and injection site erythema, pyrexia, and rash (each 25%). The TEAE profile of PVX-410+len was generally similar to that see with PVX-410 alone, although the incidence of commonly reported TEAEs was higher with the combination than with PVX-410 alone. The majority of TEAEs were Grade 1 in intensity and occurred within 2 days after study vaccine injection. No deaths or study drug-related serious adverse events were reported. PVX-410 was immunogenic as monotherapy (10/11 patients) and in combination with len (9/9), as demonstrated by an increase in the percentage of tetramer+ cells (≥1.5-fold increase over baseline) and interferon-gamma+ (IFN-γ) cells (≥2.0-fold increase over baseline) in the CD3+CD8+ cell population. This increase was statistically higher for IFN-γ+ cells after 2 vaccinations in the combination group. The CD8+ T-lymphocyte response was also characterized by increases from baseline in interleukin-2-, tumor necrosis factor-alpha-, and CD137-positive cells in both treatment groups. Furthermore, decreases in the naïve memory cell population and increases in the effector memory cell population were seen post-vaccination; this response was enhanced by the addition of len. Among the 12 monotherapy patients, 5 (2 low-dose; 3 target-dose) experienced progression to active disease within 9 months post-treatment, and 7 had stable disease (SD) at follow-up Month 12. Among the 9 evaluable PVX-410+len patients, 5 achieved at least a minimal response, with 1 patient achieving a partial response; 1 of these 5 patients then progressed to MM by Month 5 post-treatment. Four patients had SD at follow-up Month 12. Conclusions: Six doses of PVX-410 were well tolerated in 22 patients with high-risk SMM, with an expected AE profile both as monotherapy and in combination with len. An immune response to PVX-410 was seen with PVX-410 alone, which was enhanced by the addition of len. Based on these promising findings to date, investigation of PVX-410 in combination with immunogenic agents is continuing. Disclosures Nooka: Spectrum, Novartis, Onyx pharmaceuticals: Consultancy. Wang:Acerta: Consultancy, Research Funding; Asana biosciences, Beigene, Celgene, Juno, Kite, Onyx, Pharmacyclics: Research Funding; BeiGene: Research Funding; Juno Therapeutics: Research Funding; Kite Pharma: Research Funding; Dava Oncology: Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Asana BioSciences: Research Funding. Kaufman:Incyte: Consultancy; Pharmacyclics: Consultancy; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding. Peterkin:OncoPep: Employment. Lonial:Celgene: Consultancy; Onyx: Consultancy; Janssen: Consultancy; BMS: Consultancy; Onyx: Consultancy; Celgene: Consultancy; Novartis: Consultancy; Novartis: Consultancy; BMS: Consultancy; Janssen: Consultancy; Merck: Consultancy; Millenium: Consultancy. Richardson:Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees. Raje:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Research Funding; Eli Lilly: Research Funding.

Abstract: TPS1126 Background: Stage 2-3 triple negative breast cancer (TNBC) remains at high risk for recurrence despite modern adjuvant therapy. An important role for the immune system in TNBC has recently emerged. Tumor infiltrating lymphocytes (TILs) are correlated with improved prognosis and several PD-1/PD-L1 checkpoint inhibitors, including Durvalumab (DUR), demonstrated activity in metastatic TNBC. Vaccines are a promising approach to further enhance the immune response in many cancers including TNBC. PVX-410 (PVX) is a novel tetra-peptide vaccine against XBP1 (2 splice variants), CD138 and CS1 that was safe and induced immune responses in a phase 1b study in smoldering myeloma. XBP1 and CD138 are also over-expressed in TNBC. Methods: This Phase 1b multi-center, single arm study will enroll 20 HLA-A2+ female patients (pts) following completion of all adjuvant therapy for stage 2-3 TNBC. Pts will receive 6 doses of 800ug PVX (emulsified in Montanide (SC) and co-administered with Hiltonol (IM)) at 2-week intervals, and 2 doses of DUR 1500mg IV at the 4 th and 6 th vaccine visits. Eligible pts must be between 1-6 months from completing adjuvant therapy, have no prior autoimmune disease, and have residual disease if neoadjuvant therapy was used. The primary objective is to determine the safety and tolerability of the combination, and the key secondary objective is to determine the immune response to PVX + DUR. If ≤1 pt in the first 6 has a protocol defined dose limiting toxicity within 4 weeks after the first DUR dose, accrual will continue to 20 pts. Immune response will be assessed at baseline, pre-dose 4 PVX/dose 1 DUR, and 4 weeks after completing protocol therapy. Paired data in 20 pts provides 90% power to see a shift of 0.75 standardized units from baseline to 4 weeks post treatment with the signed rank test. Immune response will be determined by a FACs based assay of antigen specific CD3+CD8+ T lymphocyte response and IFN-γ production (intracellular staining) in patient PBMCs. Additional correlative studies, including T-cell PD-1 and tissue PD-L1, XBP1, and CD138, are planned. Currently 4 pts are enrolled. Clinical trial information: NCT02826434.

Abstract: Background: Immunotherapy with checkpoint inhibition is active in mTNBC. Both pembrolizumab and atezolizumab are FDA approved for programmed cell death ligand 1 positive (PDL1+) mTNBC. Vaccines may further induce host immune response and enhance therapeutic activity of checkpoint inhibitors. PVX-410 (PVX) (OncoPep, Inc.) is a novel, HLA-A2 restricted, tetra-peptide vaccine, with 3 of its 4 antigens (XBP1[2 splice variants] and CD138) commonly overexpressed in TNBC. We present results from a phase 1b study evaluating the immune response, safety and tolerability, and clinical activity of PVX and pembrolizumab (PEM) in mTNBC. Methods: Eligibility for this phase 1b multi-center, single-arm study included HLA-A2+, PD-L1 unselected female patients (pts) ≥18 years with metastatic or inoperable locally advanced TNBC, measurable disease, and any number of prior therapies, including prior checkpoint inhibitor therapy. Pts received 6 doses of 800µg PVX emulsified in Montanide ISA 720 VG by subcutaneous injection co-administered with intramuscular Hiltonol weekly for 6 weeks (wks) followed by booster vaccine doses at wks 10 and 28, with concurrent intravenous 200 mg PEM every 3 wks starting with the second PVX dose. Therapy was given until progressive disease, unacceptable toxicity or a maximum of 24 months. Blood samples were scheduled for immune response assessment at baseline and at weeks 2, 5, 10, 28, and 52 post-treatment initiation. The primary objective was PVX- specific immune response at week 10. Immune response was defined as a ≥2-fold 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 using a flow cytometric assay. Secondary objectives were immune response at wk 28, safety and tolerability, and clinical endpoints (RR, CBR, DCR, DoR, PFS, and OS). Results: Between 3/2018 and 8/2020, 19 pts enrolled. Median age was 62 yrs (range 46-79), with median 2 (range 0-9) lines of prior therapy for metastatic disease. Median disease-free interval among 16 pts with prior early TNBC was 3.3 years. Among 19 enrolled patients, 16 were available for analysis at the time of abstract submission. Among the 16, 10 pts were evaluable at week 10 and 7(70%) demonstrated a PVX specific immune response. There were 6 patients who progressed before week 10, of whom 3 (50%) had a positive immune response at the EOT visit. Immune response persisted in all evaluable pts assessed at week 28 (n=4). Immune response data for all evaluable patients will be updated at the presentation. Among 19 patients evaluable for safety analysis, the most common adverse events (AEs) attributable to PVX (grade ≥2) included: fatigue (21%), arthralgia (11%) injection site reaction (5 %) pain (5%) lymphocyte count decreased (5%), maculopapular rash (5%) and skin infection (5%) . There were two grade 3 AEs attributed to PEM (AST elevation, hyponatremia) and one grade 4 AE (ALT elevation). There were no grade 5 AEs. The clinical benefit rate (CR+PR+SD for ≥16 weeks) was 31.6% with no confirmed partial or complete responses. Best overall response was SD in 9 (47%) patients. Analysis of additional clinical endpoints including PFS and OS is ongoing and will be presented at the meeting. Conclusions: PVX plus PEM is safe with manageable toxicity in pts with mTNBC. No new unexpected adverse events were identified. Immune response data show PVX induces antigen-specific T cell expansion as observed by increases in PVX tetramer and IFN positive T cells. Clinical disease control was observed with a CBR of 31.6%. Based on these promising immune response results in this pretreated population, a phase 2 study with PVX+PEM in combination with standard chemotherapy in treatment naïve, PD-L1+ mTNBC is underway (NCT04634747). Citation Format: Steven J Isakoff, Nadine M. Tung, Jun Yin, Nabihah Tayob, Joanne Parker, Julie Rosenberg, Aditya Bardia, Laura Spring, Hannah Park, Maya Collins, William T. Barry, Mariano Severgnini, Doris Peterkin, Sara M. Tolaney. A phase 1b study of PVX-410 vaccine in combination with pembrolizumab in metastatic triple negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-14-17.

Abstract: 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.