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Introduction: Therapeutic options for relapsed/refractory (r/r) acute myeloid leukemia (AML) and hypomethylating agent (HMA) failure higher risk myelodysplastic syndrome (MDS) are limited with a median overall survival of < 6 months. Although chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of B-cell malignancies, significant challenges exist in myeloid CAR development. PRGN-3006 UltraCAR-T are engineered using non-viral gene delivery to simultaneously express CD33 CAR, membrane bound IL-15 (mbIL15) and kill switch to be effective against AML with improved safety profile. UltraCAR-T cells are manufactured at medical center's cGMP facility using autologous T cells in < 48 hours without ex vivo expansion. Methods: A Phase 1/1b first-in-human dose escalation/dose expansion clinical trial (NCT03927261) of PRGN-3006 in adult pts with r/r AML, HMA failure higher risk MDS or chronic myelomonocytic leukemia (CMML) with ≥ 5% blasts. Pts who have relapsed post allogeneic stem cell transplant (SCT) are allowed if > 3 months out from transplant without evidence of active graft versus host disease (GvHD) and off immunosuppression for 6 weeks. Ps receive PRGN-3006 infusion without (Cohort 1) or with lymphodepletion (fludarabine 30mg/m 2 and cyclophosphamide 500mg/m 2 days -5 to -3; Cohort 2). Dose escalation of Cohorts 1 and 2 occur in parallel with initial clearance of Cohort 1 at each dose level (DL; Table 1). Results: As of July 25, 2021, data cut-off, 15 r/r AML pts have been treated in Cohort 1 (n=9) and Cohort 2 (n=6) with a median age of 60 years (33-77). Pts were heavily pre-treated with a median of 3 prior regimens (1-7), with 93% and 80% of pts being r/r to a HMA + venetoclax or intensive chemotherapy, respectively. Additionally, 40% of pts (n=6) had relapsed after SCT. 93% of pts were int/adv by ELN 2017 criteria (60% adverse). PRGN-3006 infusion at doses up to 1x10 6 cells/kg was well tolerated. There have been no deaths, DLTs, bone marrow aplasia, neurotoxicity or unexpected on-target/off-target toxicities related to PRGN-3006, and no use of the kill switch to date. One incidence of grade 2 GvHD was observed in a post-SCT patient (Cohort 2) on day 31, which resolved completely with corticosteroid therapy, and notably this patient responded to therapy. Cytokine release syndrome (CRS) occurred in 47% of pts (n=7; G1 in 5 pts) with only 1 transient grade 3 event (DL 1, Cohort 1) that resolved in < 24 hours with tocilizumab and dexamethasone. Median onset to maximum CRS was 11 days (range 4-15 days). Peak CRP and ferritin levels occurred at a median of days 8 and 9, respectively. No significant increase in plasma levels of inflammatory cytokines, including IL-6 and TNFa, was observed post treatment. The plasma levels of IL-15 did not increase with treatment confirming mbIL15 is not shed. In Cohort 1, dose escalation through DL3 has been completed. Dose-dependent expansion of PRGN-3006 was observed in all patients with mean peak copy numbers following DL1, DL2 and DL3 in peripheral blood at approximately 600, 9,700 and 28,000 copies/µg DNA, respectively, with persistence up to 7 months post-infusion in a pt with stable disease/blast reduction. No objective responses in cohort 1 have been observed to date. In Cohort 2, dose escalation through DL2 has been completed. Expansion of PRGN-3006 was higher in Cohort 2 compared to Cohort 1 with mean peak copy numbers following DL1 and DL2 in peripheral blood at approximately 11,000 and 120,000 copies/µg DNA, respectively, and persistence 3+ months post-infusion. The objective response rate (ORR) for Cohort 2 was 50% (3/6). At DL1, 1 of 3 pts obtained CRi and was bridged to SCT and remains in a measurable residual disease negative CR 6 months post-SCT. At DL2, 2 post-SCT relapse patients also obtained response: 1 CRh with complete cytogenetic remission and NGS clearance with a remission length of 2 months; and 1 PR that lasted 3 months in a patient with isolated extramedullary leukemia (Figure 1). All 3 responders remain alive at data cut-off (5-10 months). Conclusion: PRGN-3006 UltraCAR-T cells targeting CD33 have been well tolerated with low grade CRS. In the setting of mbIL15, there has been a dose-dependent robust expansion and durable persistence of PRGN-3006 with encouraging responses (50%) in patients treated following lymphodepletion. Enrollment is ongoing to DL4, and updated safety, efficacy, PK/PD and cytokine data to be presented. Figure 1 Figure 1. Disclosures Sallman: AbbVie: Membership on an entity's Board of Directors or advisory committees; Syndax: Membership on an entity's Board of Directors or advisory committees; Intellia: Membership on an entity's Board of Directors or advisory committees; Incyte: Speakers Bureau; Kite: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Magenta: Consultancy; Aprea: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shattuck Labs: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees. Sweet: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees. Talati: AbbVie: Honoraria; BMS: Honoraria; Pfizer: Honoraria; Jazz: Speakers Bureau; Astellas: Speakers Bureau. Mishra: Novartis: Research Funding. Semnani: Precigen: Current Employment. Shah: Precigen: Current Employment, Current equity holder in publicly-traded company. Sabzevari: Precigen: Current Employment, Current equity holder in publicly-traded company; Compass Therapeutics: Current equity holder in publicly-traded company; Kinnate BioPharma: Membership on an entity's Board of Directors or advisory committees. Chakiath: Precigen: Current Employment. Lankford: Precigen: Current Employment, Current equity holder in publicly-traded company. Padron: Stemline: Honoraria; Kura: Research Funding; Incyte: Research Funding; Blueprint: Honoraria; BMS: Research Funding; Taiho: Honoraria. Kuykendall: PharmaEssentia: Honoraria; Abbvie: Honoraria; Protagonist: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Prelude: Research Funding; BluePrint Medicines: Honoraria, Speakers Bureau; Celgene/BMS: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Incyte: Consultancy; CTI Biopharma: Honoraria. Komrokji: Geron: Consultancy; Taiho Oncology: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; BMSCelgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees; Acceleron: Consultancy; Jazz: Consultancy, Speakers Bureau. Lancet: AbbVie: Consultancy; Daiichi Sankyo: Consultancy; Millenium Pharma/Takeda: Consultancy; ElevateBio Management: Consultancy; Astellas: Consultancy; Agios: Consultancy; Celgene/BMS: Consultancy; BerGenBio: Consultancy; Jazz: Consultancy. Davila: Precigen: Research Funding. Bejanyan: Medexus: Consultancy, Membership on an entity's Board of Directors or advisory committees; Avrobio (Spouse disclosure): Current equity holder in publicly-traded company; Magenta: Consultancy, Membership on an entity's Board of Directors or advisory committees; Humanigen (Spouse disclosure): Consultancy, Membership on an entity's Board of Directors or advisory committees; Crispr Therapeutics (Spouse disclosure): Current equity holder in publicly-traded company; Teladoc Health (Spouse disclosure): Current equity holder in publicly-traded company; Organon (Spouse disclosure): Current equity holder in publicly-traded company; Kadmon (Spouse disclosure): Consultancy; Merck (Spouse disclosure): Current equity holder in publicly-traded company; American Well Corp (Spouse disclosure): Current equity holder in publicly-traded company; Thermo Fisher (Spouse disclosure): Current equity holder in publicly-traded company; Unitedhealth Group (Spouse disclosure): Current equity holder in publicly-traded company.

BackgroundPRGN-2009 is a novel gorilla adenovirus vaccine containing 35 non-HLA-restricted epitopes of HPV 16 and 18 which is being tested in an open-label, NCI-sponsored, single-center Phase I/II study alone and combined with the bifunctional TGF-β ”trap”/anti-PD-L1 fusion protein bintrafusp alfa (BA) (NCT04432597).MethodsFor the Phase I of the trial, eligible patients are adults with previously treated (checkpoint blockade allowed) recurrent/metastatic HPV-associated cancers. Objectives are to assess the safety and determine the recommended phase 2 dose (RP2D) of PRGN-2009 alone and combined with BA. Treatment followed a single-agent 3+3 dose escalation at two dose levels of PRGN-2009 (dose level 1: 1x1011 viral particle units (VPU), dose level 2: 5x1011 VPU) subcutaneously Q2W for 3 times, then Q4W for up to one year in total. After determination of RP2D, a combination cohort of 10 patients treated with PRGN-2009 at the RP2D combined with BA (1200 mg IV Q2W for 52 weeks) opened. Peripheral blood mononuclear cells collected from patients before and after vaccination with PRGN-2009 were stimulated with overlapping peptide pools and assessed by intracellular cytokine staining to identify HPV-16 and HPV-18 specific T-cells, as well as T-cells targeting cascade antigens not encoded by the vaccine.ResultsSix patients were enrolled in the single-agent PRGN-2009 dose-escalation phase (3 with cervical cancer, 2 with anal cancer, 1 with vaginal cancer). Observed adverse events were Grade 1-2 flu-like syndrome (headache, body aches), injection site reactions (erythema, pruritus, soreness, localized edema), fatigue, and rash. There were no dose limiting toxicities, and 5x1011 VPU was selected as RP2D. Four patients had stable disease as best response, (one ongoing, 10 months on treatment).T-cells targeting HPV-16 and/or HPV-18 were increased after vaccination in 100% of patients, with 3/6 (50%) developing HPV-16 T cells and 5/6 (83%) developing HPV-18 T cells. In some patients, the magnitude and breadth of HPV-16 and HPV-18 specific T cells were notably increased after repeated vaccination. T cells that target the cascade antigens brachyury and MUC1 were also increased in all patients evaluated. Multifunctional T-cell responses against all these antigens were also developed after vaccination in the majority of patients. No differences in immunogenicity were noted between the two dose levels. Enrollment is underway in combination with BA. Updated data will be presented.ConclusionsThe Phase 1 results demonstrate the safety of single-agent PRGN-2009 and induction of anti-HPV T-cell immune responses, supporting the hypothesis that PRGN-2009 could potentially induce anti-tumor effects in HPV-associated cancers.AcknowledgementsThis research was supported in part by the Intramural Research Program of the NIH, NCI.Trial RegistrationNCT04432597Ethics ApprovalApproved by the NIH IRB (Ref No 543876). All participants have given informed consent before taking part in the study.

TPS6092 Background: R/M HPVC (cervical, anal, oropharyngeal, etc.) are incurable by current therapies. For newly diagnosed LA HPV-OPSCC standard-of-care (SOC) is radiotherapy ± chemotherapy (C/RT) or surgery ± adjuvant C/RT, with considerable risk of relapse. Newly diagnosed LA SNSCC treatment follows the OPSCC paradigm, and detection of HPV appears to confer improved prognosis. Neoadjuvant PD-1 immune checkpoint blockade (ICB) before surgery may improve RFS and is being evaluated in a multicenter phase III clinical trial (Keynote-689). PRGN-2009 (P) is a novel gorilla adenovirus vaccine containing 35 non-HLA-restricted epitopes of HPV 16 and 18 shown to induce HPV specific responses (preclinical models). Bintrafusp alfa (BA) is a bifunctional fusion protein targeting TGF-β and PD-L1 with promising activity in HPVC. This trial will evaluate the safety and activity of P/ P + BA in patients with previously treated R/M HPVC and as neoadjuvant/induction therapy before SOC surgery or C/RT in newly diagnosed LA HPV-OPSCC and HPV-SNSCC. Methods: This is a first-in-human, investigator-initiated, single-center phase I/II trial. Pts with previously treated (incl. ICB) R/M HPVC are eligible for Phase I: P dose escalation arm (3+3 design, 6-12 patients) testing 2 dose levels (1x1011, 5x1011 viral particle units, SC Q2W three times, then Q4W), and combination arm (10 patients) testing P (recommended phase 2 dose (RP2D), same schedule) + BA (1200 mg IV Q2W). Treatment (both arms) will continue until disease progression, unacceptable toxicity, decision to withdraw. Primary endpoint is safety. Secondary endpoints include ORR (RECIST 1.1), PFS, and OS. For Phase II, patients with newly diagnosed stage II/III (AJCC Cancer Staging Manual, 8th ed.) HPV-OPSCC and stage II/III/IVA/IVB HPV-SNSCC planned for SOC C/RT or surgery will be eligible for two treatment arms of 20+2 patients each (sequential): P arm and P + BA, to evaluate the treatment activity. All patients will have pre-treatment biopsy, receive two cycles of the study treatment at the NCI Clinical Center two weeks apart, followed by post-treatment biopsy and SOC treatment (at the referring institution) 4 weeks after the first study treatment. Primary endpoint is post-treatment ≥2-fold increase in tumor-infiltrating CD3+ cells. Secondary endpoints include RFS, OS. Exploratory endpoints for both arms include analyses of immune subsets, soluble factors, and HPV-specific immune responses in peripheral blood and tissue where available, and in Phase II sequencing (exome, scRNA), immune spatial profiling with multiplex immunofluorescence, and salivary HPV DNA. Clinical trial registry: NCT04432597. Clinical trial information: NCT04432597.

1 It was investigated how A(1)-adenosine receptor overexpression alters the effects of carbachol on force of contraction and beating rate in isolated murine atria. Moreover, the influence of pertussis toxin on the inotropic and chronotropic effects of adenosine and carbachol in A(1)-adenosine receptor overexpressing atria was studied. 2 Adenosine and carbachol alone exerted negative inotropic and chronotropic effects in electrically driven left atrium or spontaneously beating right atrium of wild-type mice. 3 These effects were abolished or reversed by pre-treatment of animals with pertussis toxin which can interfere with signal transduction through G-proteins. 4 Adenosine and carbachol exerted positive inotropic but negative chronotropic effects in atrium overexpressing A(1)-adenosine receptors from transgenic mice. 5 The positive inotropic effects of adenosine and carbachol were qualitatively unaltered whereas the negative chronotropic effects were abolished or reversed in atrium overexpressing A(1)-adenosine receptors after pre-treatment by pertussis toxin. 6 Qualitatively similar effects for adenosine and carbachol were noted in the presence of isoprenaline, beta-adrenoceptor agonist. 7 It is concluded that overexpression of A(1)-adenosine receptors also affects the signal transduction of other heptahelical, G-protein coupled receptors like the M-cholinoceptor in the heart. The chronotropic but not the inotropic effects of adenosine and carbachol in transgenic atrium were mediated via pertussis toxin sensitive G-proteins.