Changes in circulating immune biomarkers following nivolumab with or without ipilimumab for metastatic anal cancer (NCI9673).

Background: Approximately 25% of patients (pts) with squamous cell carcinoma of the anal canal (SCCA) develop metastatic disease. The ETCTN-led NCI9673 phase II trial evaluated PFS of the anti-PD-1 antibody nivolumab (N) with or without the anti-CTLA-4 antibody ipilimumab (I) in metastatic SCCA. We analyzed serial blood samples from NCI9673 for immune biomarker profiling following N or N+I. Methods: PBMCs from 47 pts (24 N, 23 N+I) were collected at pretreatment (N=47), week 9 (N=26), and at progression (N=15). Immune cell populations - effector CD4 T cells, CD8 T cells, natural killer (NK) cells, and regulatory T cells - were analyzed by flow cytometry for immune inhibitory (PD-1, CTLA-4, TIM-3, LAG-3, TIGIT) and immune stimulatory (OX40, ICOS) expression. Mean expression (as percentage of cells with any expression) for each biomarker at a matched time point was compared between the N and N+I arms by a corrected student’s t test, with an alpha= .10 for significance. Changes in mean expression for each biomarker were compared by one-way ANOVA. Results: Mean TIGIT expression at baseline was highest on CD4 and CD8 T-cells relative to other immune checkpoint biomarkers (p, .0001 for all subsets; see Table). N+I was associated with higher TIGIT expression on CD4 cells at progression than for N alone (21.3% vs. 10.9%, p=.08). Among NK cells, TIGIT expression decreased at progression relative to baseline for N (14.1% vs. 5.9%, p=.06). Relative to non-responders, responders to N had OX40 expression that increased on CD4 T cells but decreased on NK cells at week 9 relative to baseline. Conclusions: In previously metastatic SCCA pts, TIGIT expression was greater on CD4 and CD8 T cells and was modulated on differing immune cell populations according to treatment arm. These data not only implicate T and NK cells in mediating treatment effect following single agent and/or combination immunotherapy, but also support the exploration of TIGIT as a potential novel target for treatment of metastatic SCCA.