IMPORTANCE Patients who experience progression of advanced human papillomavirus (HPV)-associated cancers and who have previously received first-line systemic treatment have a poor prognosis and limited therapeutic options. OBJECTIVE To assess the clinical activity of the combination of the HPV type 16 therapeutic vaccine PDS0101, the tumor-targeting interleukin 12 antibody-drug conjugate PDS01ADC, and the bifunctional anti-programmed cell death ligand 1 (PD-L1)/transforming growth factor beta (TGF-beta) bintrafusp alfa in advanced HPV-associated cancers. DESIGN, Setting, and Participants This nonrandomized clinical trial was phase 1/2 and investigator initiated, and was conducted at a single US cancer research center between June 2020 and July 2022. Patients with advanced or metastatic HPV-associated cancers were eligible, including patients who were both immune checkpoint blockade (ICB) naive and ICB resistant. The cutoff date for data analysis was May 13, 2024. INTERVENTION Patients received 1 mL of PDS0101 subcutaneously every 4 weeks for 6 doses then every 12 weeks for 2 additional doses, PDS01ADC, 16.8 mu g/kg, subcutaneously every 4 weeks or PDS01ADC, 8 mu g/kg, subcutaneously every 2 weeks, and bintrafusp alfa, 1200 mg, intravenously every 2 weeks. MAIN OUTCOMES AND MEASURES Objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors version 1.1 in ICB-naive patients. RESULTS Of the 50 eligible patients, 26 (52%) were men and the median age was 56 years (range, 28-80 years). The median (IQR) follow-up was 37.7 (30.6-42.0) months. Fourteen patients (28%) were ICB naive, with an ORR of 35.7% (95% CI, 12.8%-64.9%), and median overall survival (OS) 42.4 months (95% CI, 8.3 months-not estimable); in ICB-resistant patients, the ORR was 16.7% (6 of 36 patients; 95% CI, 6.4%-32.8%) and median OS was 15.8 months (95% CI, 9.0-21.3 months). Among patients with HPV-16-positive tumors (37 patients [74%]), in the ICB-naive group (8 patients [21.6%]) the ORR was 62.5% (95% CI, 24.5%-91.5%) and a median OS measure was not reached. Grade 3 and 4 treatment-related adverse events occurred in 26 of 50 patients (52%). There were no treatment-related deaths. CONCLUSIONS AND RELEVANCE In this trial, the combination of PDS0101, PDS01ADC, and bintrafusp alfa showed an acceptable safety profile and promising antitumor activity and improved OS in patients with HPV-16-positive cancers, in both ICB-naive and ICB-resistant patients, warranting further evaluation of the combination of PDS0101 and PDS01ADC with simultaneous PD-L1/TGF-beta inhibition in these populations.

Background Prostate cancer is the most diagnosed cancer in men worldwide, making up 21% of all cancer cases.1 Although this disease is slow growing, 370,000 men die from prostate cancer every year. Prostate cancer is mostly a cold tumor, lacking infiltrating immune cells.2 To switch the tumor immune microenvironment phenotype from cold to inflamed we used Prostvac, a therapeutic cancer vaccine that targets prostate-specific antigen (PSA) in monotherapy and in combination with Nivolumab, a PD1 inhibitor. Methods Patients with localized prostate cancer were enrolled in 2 distinct clinical trials. In the 1st trial, patients received subcutaneously neoadjuvant Prostvac vaccine alone for 4 doses (NCT02153918). In the 2nd trial, patients received Prostvac and Nivolumab (NCT 02933255). We studied the T cells infiltration in matched paired samples from pre-treatment biopsies and post-treatment Radical prostatectomy from patients enrolled in these trials (26 patients had monotherapy and 12 patients had combination therapy). Using multiplex immunofluorescence technique and opals, we immune-stained formalin fixed paraffin-embedded sections with a validated lymphocyte panel of markers that included DAPI, CD4, CD8, FOXP3, Ki67, Pan CK and PD-L1. We analyzed the data by measuring the cell densities in Invasive margin, center of the tumor and normal regions. Results In both trials and using Prostvac alone or in combination with Nivolumab, CD4 and CD8 T cells increased in the overall prostate tumor tissues, the invasive margins and the center of the tumors. These increases are more predominant and frequent in patients who received Prostvac and Nivolumab. CD4 and CD8 densities increased by at least 2-fold in 91% and 83%, respectively and in patients who received the combination therapy, whereas this increase was found in 71% and 58% in patients who received only the vaccine. Ki67 was found higher in CD8 T-cells (Mean from 2.9 cells/mm2 to 4.16 cells/mm2, p=0.09) and significantly higher in CD4 T-cells in the overall tissues (Mean from 7.63 cells/mm2 to 15.68 cells/mm2, p=0.0019) only after the combination treatment, suggesting a role of blocking PD1 in activating these lymphocytes. T-regulatory T cells were found low in all samples (average of 10 cells/mm2). Conclusions Immunotherapy is standard therapy for many tumors, however PD-1 inhibitors as single agents have no clinical role in prostate cancer outside MSI high cancer. Combination immunotherapies could change the tumor immune-microenvironment landscape and enhance immune response by increasing T-cells activation and infiltration and therefore overcoming tumor immune evasion. Trial Registration NCT: 02153918 and NCT: 02933255 References Sung H, Ferlay J, Siegel RL, Laversanne M, Soerjomataram I, Jemal A, Bray F. Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries. CA Cancer J Clin. 2021;71(3):209−249. Yarchoan, M., Johnson, B., Lutz, E. et al. Targeting neoantigens to augment antitumour immunity. Nat Rev Cancer 2017; 17:209–222. Ethics Approval The study obtained ethics approval by NIH IRB. All participants gave informed consent before taking part in these trials.

2501 Background: There are more than 630,000 cases of HPV associated malignancies including cervical, oropharyngeal and anal cancer worldwide annually. HPV 16 is responsible for the majority of these cases. About 15-20% of HPV associated malignancies respond to PD-(L)1 inhibitors, but for the overwhelming majority of patients who progress on these immunotherapies there is no effective standard of care therapy. Preclinical studies have shown that the triple combination of PDS0101 (Versamune-HPV), a liposomal multipeptide therapeutic vaccine targeting HPV 16 E6/E7, M9241, a tumor-targeting immunocytokine composed of IL-12 heterodimers fused to a monoclonal antibody targeting free DNA in necrotic tumor regions, and bintrafusp alfa, a bifunctional fusion protein targeting TGF-β and PD-L1, resulted in maximum HPV-specific T cell responses, T cell tumor infiltration and tumor reduction as compared to any one or two of these agents alone. Methods: Fourteen pts with HPV 16+ relapsed or refractory advanced cancer were enrolled to the triple combination of PDS0101, M9241 and bintrafusp alfa (NCT04287868). Pts received bintrafusp alfa at 1200 mg flat dose i.v. every 2 weeks, M9241 at 16.8 mcg/kg s.c. every 4 weeks and PDS0101 given as two separate 0.5 ml s.c. injections every 4 weeks. Dose reductions of M9241 to 8 mcg/kg were allowed as well as skipped doses of any agent for ongoing toxicities. Results: Fourteen pts with advanced HPV 16+ cancers (5 cervical, 2 vaginal/vulvar, 4 anal, 3 oropharyngeal) were treated. 4/14 (28.6%) pts had a grade 3 treatment related toxicity including grade 3 hematuria in 2 pts with cervical ca and prior pelvic radiation and grade 3 AST/ALT elevation in 2 pts, one with anal ca and one with vaginal ca. For one patient with grade 3 AST/ALT elevation dose reduction of M9241 from 16.8 to 8 mcg/kg allowed for continued treatment with AST/ALT remaining at grade 1 or less. One additional patient had transient asymptomatic grade 4 neutropenia. No other treatment related grade 3 or greater toxicities were noted. 10/14 (71%) pts have had objective responses: 1 CR (anal ca) and 9 PRs (3 cervical, 2 vulvar/vaginal, 2 anal, 2 oropharyngeal) with 9/10 of these responses ongoing after a median 5 month of follow up. Of the 14 pts, 6 pts have checkpoint naïve disease and 8 pts have checkpoint refractory disease. 5/6 (83%) pts with checkpoint naïve disease and 5/8 (63%) pts with checkpoint refractory disease have had objective responses. Analyses of immune responses and other immune correlates are ongoing. Conclusions: Triple combination of PDS0101, M9241 and bintrafusp alfa appears to have a manageable safety profile along with early evidence of notable clinical activity for pts with both checkpoint naïve as well as checkpoint refractory HPV 16+ advanced malignancies. Clinical trial information: NCT04287868.

Background Prostate cancer (PC) is the most common non-cutaneous diagnosed cancer among men in USA.1 Although clinical outcomes are favorable for patients with localized disease, 20–30% of patients will develop metastatic prostate cancer (mPC) and have poor prognosis. Immunotherapy, as a single agent, provides benefit to a small subset of PC patients, which is thought to be partially due to its known cold tumor immune microenvironment (TIME). Combination studies are needed to enhance benefit.2 Prostvac is a therapeutic cancer vaccine engineered to activate an immune response against prostate-specific Antigen (PSA).3 Prostvac alone could induce systemic immune response by increasing immune-cell infiltrates in and around the tumor.4 In this study, we are exploring the effect of Prostvac in combination with nivolumab in TIME in prostate cancer. Methods We treated locally advanced prostate cancer patients (n=6) undergoing radical prostatectomy (RP) with neoadjuvant Prostvac in combination with nivolumab, an immune checkpoint PD-1 inhibitor. Dynamic changes in TIME before and after treatment were studied using multiplex immunofluorescence (Opal Method). Formalin fixed paraffin-embedded sections from matched pre-treated prostate biopsies and post-treated RP samples were stained with a validated T cell panel (DAPI, CD4, CD8, FOXP3, Ki67, Pan CK and PD-L1). To analyze the data, TIME was segmented into 3 compartments: intratumoral, invasive margin and benign. Results Combination immunotherapy significantly increased CD4+ T cell density in the invasive margin (mean 211.5 cells/mm2 vs 592.2 cells/mm2, p<0.05), with similar trend in the intratumoral and the benign compartments. CD8+ T cell density increased after treatment in the invasive margin (mean 47.25 cells/mm2 vs 157cells/mm2) and the benign compartment. 5/6 and 4/6 patients showed more than 2-fold increase of CD4 and CD8 T cells in the TIME, respectively, in at least one of the three compartments. Increased proliferative indices in CD4+ and CD8+ T cells were also seen after treatment. Tregs were present in low frequencies in TIME (maximum of 12 cells/mm2) with no significant changes. Moreover, a significant drop in tumor cell Ki67 after treatment (mean 252.8 cells/mm2 vs 100.5 cells/332, p<0.05) suggests that the combination may control tumor growth. Conclusions The combination of Neoadjuvant Prostvac and nivolumab was associated with increased immune cell infiltration in a cohort of early prostate cancer patients. A broader examination of the TIME and the role immune cells undertake to control tumor growth is on-going. Trial Registration NCT02933255 References Siegel RL, Miller KD, Jemal A. Cancer statistics, 2020. CA Cancer J Clin (Internet) 2020;70:7–3 Zhao SG, Lehrer J, Chang SL, et al. The immune landscape of prostate cancer and nomination of PD-L2 as a potential therapeutic target. J Natl Cancer Inst 2018;111:301–10. Madan RA, Arlen PM, Mohebtash M, et al. Prostvac-VF: a vectorbased vaccine targeting PSA in prostate cancer. Expert Opin Investig Drugs 2009;18:1001–11 Abdul Sater H, Marté JL, Donahue RN, et al. Neoadjuvant PROSTVAC prior to radical prostatectomy enhances T-cell infiltration into the tumor immune microenvironment in men with prostate cancer. J Immunother Cancer 2020;8(1):655–64 Ethics Approval This study was performed in compliance with ethical standard and was approved by the NIH IRB, 17C-0007. All patients participating in this study gave an informed consent before taking part.

2640 Background: Brachyury, a transcription factor, plays an integral role in epithelial-to-mesenchymal transition, metastasis, poor prognosis, and resistance to chemotherapy. It is expressed in many tumor types, and rare in normal tissue, making it an ideal immunologic target. BN-Brachyury comprises heterologous vaccination with recombinant MVA priming followed by FPV boosting, each encoding transgenes for brachyury and three costimulatory molecules (B7-1, ICAM1, and LFA-3). Heterologous prime boost approach is intended to optimize immunogenicity, as previously observed. Methods: Pts with metastatic solid tumors were treated with 2 monthly doses of MVA-brachyury SC at the previously tested dose, 2.2 x 10 9 infectious units (IU), followed by FPV-brachyury SC, 1 x 10 9 IU, for 6 monthly doses and then every 3 months for up to 2 years. The primary objective was to determine safety and tolerability and establish the RP2D. Immune assays were conducted to evaluate immunogenicity. Results: In 10 pts (3 chordoma, 6 GI, 1 papillary thyroid), no dose-limiting toxicities or serious treatment-related adverse events (TRAEs) were observed. The only Grade 3 TRAE was sedation associated with fever, which resolved spontaneously and did not recur with subsequent cycles. All other TRAEs were Grade 1 or 2; the most common was injection-site reaction in all patients. Five pts have had stable disease for > 24 wks (per RECIST v1.1) and remain on treatment. One pt with chordoma, for which BN-Brachyury was granted orphan drug designation, has had a 13.2% reduction in tumor size. As previously demonstrated, brachyury-specific T cell responses were observed, as were responses against cascade antigens (non-encoded antigens) CEA and MUC-1. Conclusions: Heterologous MVA- and FPV-brachyury is well tolerated and induced immune responses to brachyury and cascade antigens, suggesting induction of immunologically relevant tumor cell destruction. These data have informed combining BN-Brachyury with checkpoint inhibition (NCT03493945) and radiation (NCT03595228) to evaluate potential for synergetic activity in selected populations. Clinical trial information: NCT03349983.

3007 Background: Therapies targeting PD-1/L1 have produced response rates of 15-20% in patients (pts) with HPV associated cancers (HAC) including cervical (cerv), anal or head and neck squamous cell carcinoma (HNSCC). Another potential target for these diseases is transforming growth factor-β (TGF-β) as genome wide association studies in HPV+ cancers have shown TGF-β to be significantly overexpressed. M7824 is a bifunctional fusion protein targeting PD-L1 and TGF-β comprised of a human IgG1 monoclonal antibody against PD-L1 fused to 2 extracellular domains of TGF-β receptor II, which functions as a TGF-β “trap”. We report data from pts with HAC on a fully enrolled dose escalation portion of a phase 1 trial of M7824. Methods: NCT02517398 is a phase 1, 3+3 dose-escalation study. Pts received M7824 at 1, 3, 10, 20, or 30 mg/kg Q2W until PD or unacceptable toxicity. The primary objective was safety and maximum tolerated dose (MTD). A key secondary objective was best overall response per RECIST v1.1. Results: As of Feb 5 2018, 16 pts with HAC (9 cerv, 4 anal and 3 HNSCC) were enrolled. HPV was + in 11 pts and unknown (uk) in 5 pts. Grade 3 treatment related adverse events (TRAEs) occurred in 3/16 (colitis, cystitis, gastroparesis; all cerv). Notably all 3 also had disease reduction. Grade 4 hypokalemia accompanied the gastroparesis. No other grade 4-5 TRAEs were seen. The only DLT was colitis (at 20 mg/kg) and no MTD was reached. 9/16 (56%) have had disease reduction on treatment including 1 pt (cerv; HPV+) with a durable CR, 4 pts (2 HNSCC, 2 anal; all HPV+) with durable PRs, 1 pt (cerv; HPV uk) with an unconfirmed PR, 2 pts (2 cerv; both HPV uk) with near PRs (-25%, -27%) and 1 pt (anal; HPV uk) with modest reduction (-9%). In all, 6/16 (37.5%) have ongoing responses, 5/6 confirmed. Of pts with known HPV+ disease, 5/11 (45.5%) have ongoing confirmed responses. Conclusions: Data from a phase 1 trial of M7824 suggests a manageable safety profile and an ORR of 37.5% in pts with HAC including a confirmed ORR of 45.5% in pts with known HPV+ disease. M7824 is a promising drug for pts with HAC or HPV+ cancers and continues to be evaluated in phase I and II trials. Clinical trial information: NCT02517398.

2532 Background: CS is characterized by germline PTEN mutations. Because tumors from CS patients show increased activation of the PI3K/Akt/mTOR pathway, mTOR inhibitor such as S might have activity in such patients. Methods: Eligibility: subjects with germline PTEN mutation who meet international diagnostic criteria for CS, age 18, ECOG PS 0-2, and adequate organ function. Subjects were treated with a 56-day course of daily oral S (2 mg). Objective: Inhibition of the mTOR pathway in benign skin/GI lesion, as assessed by IHC (P-AKT, Total S6, P-S6, P-4E-BP1, score 0-4), changes in benign or malignant tumor by CT/MRI/PET, digital dermoscopy/endoscopy, and changes in cerebellar testing by modified SARA (Neurology 2006). Protocol was amended to allow up to 20 subjects. Results: A total of 18 pts/16 families were enrolled. Median age 42 (range 19-69). Male/Female: 9/9. Involvement in skin, thyroid, GI polyps, breast, CNS, and all of the five organs was observed in 18, 15, 13, 8, 18, 5 subjects, respectively. 7 had h/o malignancies: 3 renal cell, 4 breast, 3 thyroid, 4 others. 3 cerebellar gangliocytomas and 2 others were measurable by CT or MRI. PTEN mutations: 6 families in Exon 1-2, 1 in Exon 4, 9 in Exon 5-8. All but one (D24H) were truncating mutations. 11 of 16 pts who completed a 56-day course reported subjective improvement in energy, mood, focus or skin lesion. Pts with Ex6-8 mutation (n=4) had a median SUV decrease of 29.4%. Regression of skin and GI lesions was observed by dermoscopy or endoscopy. Cerebellar evaluation showed a significant improvement in a total SARA score at 1 month (n=9, p=0.034). 3 pts were treated for only 28 days due to voluntary withdrawal. IHC analysis in skin and GI benign lesions showed a decrease in average P-S6K, P-S6, Total S6, P-S6/Total S6 in response to S. P-S6K/Total S6 ratios at d14 and d56 were significantly lower than at baseline (p=0.0026, 0.0391, respectively). The most common AEs (all grades >25%) were LFTs/Hb (39%), fatigue/hypercholesterolemia (28%). Grade 3 AEs: 1 pt hypophosphatemia/lymphopenia. Conclusions: A 56-day course of S was well tolerated in subjects with CS and was associated with improvement in symptoms, skin/GI lesions, cerebellar function and decreased mTOR signaling. Clinical trial information: NCT00971789.

7103 Background: Belinostat is a hydroxamic acid histone deacetylase (HDAC) pan-inhibitor with single agent activity in thymic malignancies. PAC has activity against thymic cancers. Synergy between Bel and several chemotherapeutic agents, including P, A, and C, has been demonstrated in preclinical models. Methods: Patients with histologically confirmed, treatment naive advanced thymic malignancies, PS<2, measurable disease, and adequate renal, hepatic and hematopoietic functions were eligible. Ph1 evaluated safety and tolerability of the combination using increasing dose levels (DL) of Bel (1000-2000 mg/m² over 48 h CIVI) and PAC (50/50/500 mg/m² IV/cycle) (3+3 dose escalation schema), administered every 21 days for no more than 6 cycles followed by optional maintenance Bel every 4 weeks. Primary end point of Ph2 is overall response rate (ORR). Results: From March 2010 to January 2012, 13 patients were enrolled [7 thymoma (T), 6 thymic carcinoma (TC); 8 in Ph1 and 5 in Ph2; median age: 49 years (range, 23-76)]. In Ph1, 6 patients were treated at DL1 (Bel 1000 mg/m2+ PAC) and 2 patients at DL2 (Bel 2000 mg/m2+ PAC). Dose Limiting Toxicities were Grade 3 nausea and diarrhea, and Grade 4 neutropenia and thrombocytopenia. Recommended phase II dose (RP2D) was set at DL1. Most common grade 3/4 treatment-related adverse events (AE) were lymphocytopenia (100%), leucopenia (85%), neutropenia (77%) thrombocytopenia (54%), anemia (38%), hypophosphatemia (38%), hypomagnesemia, hypokalemia, elevated AST, prolonged QTc and infusion-catheter related thromboembolic complications (23% each). Outcomes included one complete response (CR; T at DL1), 6 partial responses (PR; 4 T, 2 TC; 4 in Ph1, 2 in Ph2) and 6 stable disease (SD; 2 T, 4 TC; 3 each in Ph1 and Ph2). Four patients previously deemed unresectable underwent surgical resection. Conclusions: Belinostat in combination with PAC has activity in thymic malignancies with a predicable AE profile. ORR was 54% including 33% PR in the TC subgroup. RP2D of the combination has been defined. Accrual to Ph2 part and molecular profiling of patient tumors is ongoing.