Abstract LB-144: Immunotherapy targeting PSA and PSMA in patients with biochemically recurrent prostate cancer expands antigen-specific T cell receptor repertoire in a PhI/II trial

Abstract

Abstract Introduction: About one-third of prostate cancer (PCa) patients will experience rising prostate specific antigen levels, a condition known as biochemical recurrence. INO-5150 is a DNA-based immunotherapy targeting PSA and PSMA previously tested with or without plasmid-encoded cytokine adjuvant IL-12 (INO-9012) in a phase 1/2, open-label, multi-center study. Treatment was well-tolerated and safe, with no treatment-related serious adverse events. Here we sought to characterize the T cell receptor (TCR) repertoire of treated patients before and after INO-5150. Experimental Procedures: 62 post-prostatectomy/radiation therapy patients with rising PSA were enrolled in the trial. INO-5150±INO-9012 was administered IM followed by electroporation with the CELLECTRA® device on day 0, weeks 3, 12 and 24. Peripheral blood mononuclear cells (PBMCs) were collected before and after treatment from a subset of patients (n=19) and stimulated with PSA or PSMA peptides, negative or positive controls. After 5 days the Complementary Determining Region 3 (CDR3) of the TCR beta chain was sequenced. Results: TCR sequences that expanded after PSA or PSMA stimulation only were considered antigen specific sequences. On average, >70% of antigen specific TCR sequences were expanded following treatment with INO-5150 +/- INO-9012, including fold increases of up to 327 fold for PSA and 471 fold for PSMA over pretreatment frequencies. All treated patients had a Shannon's entropy (H) index >3.5 for TCR diversity. Previous examination of these patients using flow cytometry suggested that half of them demonstrated expansion of a PSA/PSMA specific CD8+ T cell subset harboring lytic potential (CD38+PD1+Prf+). TCR analysis performed by grouping patients based on the presence or absence of these cells suggested PSA/PSMA specific TCR expansion occurred for both groups. Deeper analysis suggested differences in the degree of expansion, as 56% of patients with the CD38+PD1+Prf+ phenotype were found to have at least 150 TCRs with a 10 fold expansion over baseline, whereas only 20% of patients without this cell population met this criteria. Conclusions: Treatment with INO-5150 +/- INO-9012 in PCa patients drove the expansion of a diverse pool of antigen specific T cells with a high Shannon's Entropy value suggesting high TCR diversity. Patients with immune reactivity by flow cytometry were more likely to have a higher frequency of PSA/PSMA specific TCRs that expanded >10 fold over their pre-treatment value; however patients without immune reactivity also demonstrated expansion in TCRs. These data suggest that INO-5150 induced PSA/PSMA specific T cells and that TCR sequencing is a valuable tool for assessment of immune responses induced by immunotherapy that does not bias towards a specific T cell function. Citation Format: Kimberly A. Kraynyak, Matthew P. Morrow, Albert J. Sylvester, Snehal Wani, Jean Boyer, Kamal Bhatt, Trevor McMullan, Jessica Lee, Brian Sacchetta, Samantha Rosencranz, Jeffrey Skolnik, Neal Shore. Immunotherapy targeting PSA and PSMA in patients with biochemically recurrent prostate cancer expands antigen-specific T cell receptor repertoire in a PhI/II trial [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-144.