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4569 Background: Although PD-1 blockade is active in varied mUC treatment settings, predicting response and overcoming resistance remain unmet needs. We hypothesized that immunosuppressive M-MDSCs (CD14 + Lin-/HLA-DR low/- ) and TCR dynamics in tumors and blood may correlate with outcomes from NIVO in pts with platinum-refractory mUC (NCT02553642). Methods: 69 pts with mUC were treated with NIVO 240mg intravenously every 2 weeks (wks). Pre-treatment peripheral M-MDSCs among lineage-negative CD14+ monocytes (%) were estimated by flow cytometry using an algorithm that calculates MDSC frequencies based on HLA-DR mean fluorescence intensity (Kitano et al. 2014). High throughput DNA sequencing of the CDR3 region of the TCR beta chain was performed on baseline tumors (N = 57) and pre and post-treatment (wk 2) peripheral blood mononuclear cells using Adaptive Immunosequencing (Adaptive Biotechnologies). M-MDSC levels and TCR metrics were correlated with clinical outcomes: complete or partial response (CR, PR) vs. stable or progressive disease (SD, PD) by RECIST 1.1, clinical benefit (CR + PR + SD), and progression-free and overall survival (PFS, OS). Groups were compared using Wilcoxon signed rank (paired), Wilcoxon rank sum tests (unpaired), and log-rank tests (time-to-event). Cox proportional hazards and logistic regression models were used to analyze binary and time-to-event outcomes, respectively. Results: Higher pre-treatment M-MDSCs were associated with worse PFS and OS univariably (PFS HR 1.07; 95% CI, 1.01-1.14; p = 0.025; OS HR 1.07; 95% CI, 1.00-1.14; p = 0.038), and after adjustment for liver disease and PD-L1 at baseline (PFS HR 1.12; 95% CI, 1.04-1.21, p = 0.004; OS HR 1.11; 95% CI, 1.03-1.20, p = 0.010). Baseline M-MDSCs did not significantly differ between responders and non-responders, but were significantly lower in patients with clinical benefit (median 12.8 IQR: 10.7-15.9 vs. median 15.6 IQR: 13.5-18.3; p = 0.039), and remained significantly associated after adjustment for PD-L1 score in a multivariable model (OR 0.82; 95% CI, 0.67-0.97; p = 0.037). A higher number of tumor-associated clones in the blood (BTACs) at baseline was associated with response (p = 0.049). Overall, BTACs significantly increased at wk 2 (p median 2,012 clones) and low groups at wk 2, with improved PFS in the high group (log-rank p = 0.026). OS rate for the BTAC high group was 34% vs. 16% for the low group at wk 2, but this did not achieve significance (p = 0.098). Conclusions: Peripheral M-MDSCs may promote resistance to PD-1 blockade in pts with mUC. NIVO stimulated tumor-specific TCR clones in the blood, which correlated with improved response and outcomes. Clinical trial information: NCT02553642 .
Gupta et al. (Sat,) studied this question.