TCR clonality and Treg frequency as predictors of outcome in stage III NSCLC treated with durvalumab.

Abstract

3050 Background: Novel blood-based biomarkers evaluating T-cell receptor (TCR) clonality as well as the frequency/activation of immune populations hold significant potential for predicting response and elucidating the biology of anti-tumor immunity in stage 3 NSCLC treated with durvalumab. In this study, we sought to characterize clinical and immunologic predictors of durable response to therapy with a specific focus on TCR clonality and peripheral immune populations. Methods: Stage 3 NSCLC patients undergoing chemoradiation (CRT) and durvalumab were prospectively recruited and underwent baseline and serial blood collections. TCR repertoire analysis was performed on cfDNA using hybrid-capture TCR sequencing and TCR diversity estimated using Shannon’s entropy index. Viably preserved peripheral blood mononuclear cells (PBMC) were analyzed by high-dimensional flow cytometry using validated panels to evaluate T/B/NK-cell, Treg and myeloid populations. Correlations between cell populations were examined using linear and cox regression. Results: 134 stage 3 NSCLC patients who received durvalumab had a median PFS was 15.4 months, with worse PFS in patients with PD-L1 1-49% (HR 2.4, p = 0.03) and PD-L1 < 1% (HR 2.6, p = 0.03). Smoking and EGFR/ALK mutations were not predictors of PFS. Immune profiling was performed in a pilot of 19 patients. Baseline TCR diversity did not associate with clinical factors or outcome. However, lack of clonal expansion after CRT indicated by a higher Shannon’s index was significantly associated with increased frequency of Tregs after durvalumab (p < 0.05). In turn, this elevation in Tregs was associated with significantly reduced PFS in EGFR/ALK wt patients (p = 0.03) and a trend towards reduced PFS in the overall cohort (HR 5.2, p = 0.1). Conclusions: Clonal expansion of T cells after CRT may influence the likelihood of an anti-tumor immune response following PD-L1 blockade in stage 3 NSCLC. Similarly, expansion of peripheral Treg populations is associated with increased likelihood of disease recurrence. Further characterization of TCR clonality, minimal residual disease and T cell subpopulations using serially collected blood is ongoing.