4531 Background: Vesigenurtacel-L (HS-410) is a vaccine comprised of an allogeneic cell line, selected for high expression from a series of bladder tumor antigens, and transfected with gp96-Ig. Cell-secreted gp96-Ig delivers these cell-derived antigens to a recipient's own antigen presenting cells, activating CD8+ cytotoxic T cells. Here we present the secondary immune outcomes from a randomized Phase 2 trial with HS-410 in combination with BCG in NMIBC. Trial ID NCT02010203. Methods: 78 patients with intermediate- (n = 5) or high-risk (n = 73) NMIBC who are either BCG-naïve or recurrent, with or without carcinoma in situ (CIS), were enrolled 1:1:1 to one of two doses of HS-410 (either 106 or 107cells/dose) or placebo in combination with 6 weeks of induction BCG, followed by 6 more weeks of HS-410 in the induction phase. Maintenance treatment consisted of 3-weekly treatments at the following timepoints: 3 mo., 6 mo., 12 mo. Concurrently, 16 patients (1 int. risk, 15 high-risk) were enrolled in an open-label monotherapy HS-410 arm for patients who did not receive BCG. The primary endpoint was 1-year RFS. Secondary immune evaluations include ELISPOT, tumor IHC, tumor antigen profiling, flow cytometry, urine cytokine analysis, and T cell receptor sequencing. Results: HS-410 treatment was well tolerated; AE profiles were similar across the treatment arms. HS-410 antigen expression showed prominent overlap with patient tumors. IFNγ ELISPOT assay demonstrated a high baseline response to HS-410; responses to overlapping peptide pools of HS-410 derived antigens defined immune responders (doubling of IFNγ-secreting cells). IHC demonstrated that ~60% of NMIBC patient tumor biopsies were TIL negative at baseline (n = 84), but that only ~15% of tumor biopsies were TIL negative post treatment (n = 40). Thus, TIL status may be used to define a responder and non-responder population to HS-410. Conclusions: Vesigenurtacel-L is well-tolerated, and immunologic responses consistent with vaccine mechanism of action may correlate with efficacy and suggest future biomarkers. Vesigenurtacel-L warrants further investigation as a potential treatment for NMIBC. Clinical trial information: NCT02010203.
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