Natural killer cells and their activity as a potential biomarker for predicting response to checkpoint inhibitors in non-small cell lung cancer.

Abstract

e15559 Background: Despite the increased promise of checkpoint inhibitors in the treatment of non-small cell lung cancer, the majority of patients do not respond and the potential for severe toxicity is significant. Unfortunately, the predictive value of PD-L1 expression has not always proven to be definitive and the overall need to find better biomarkers that will optimize the selection of patients who will best respond to therapy remains. Recent evidence has pointed to Natural Killer (NK) cells as an essential mediator in overall response to checkpoint inhibitors. We explore whether NK cell populations and/or their activity have any correlation with response. Methods: Peripheral blood mononuclear cells (PBMCs) from nine patients with Stage IV non-small cell lung cancer (four adenocarcinoma, five squamous cell carcinoma) were collected pre and post six-weeks of checkpoint immunotherapy (six received pembrolizumab, and three received nivolumab). Overall, four of nine (44.5%) were diagnosed as SD or PR via RECIST 1.1. The immune cell composition of the PBMCs of all nine patients was analyzed using multi-variated single-cell analysis using mass cytometry (CyTOF) with an optimized 32-marker panel. Natural Killer (NK) cell activity was measured with the NKVue kit which detects NK-secreted IFN-γ levels using a quantitative sandwich ELISA from NK cells exposed to a specific recombinant cytokine. Results: The overall percentages of NK cell populations found in the immune cells of PBMCs were prominently elevated in patients who responded (SD or PR) to checkpoint therapy compared to those who had progressive disease (non-responders). While there were no significant differences in the population of other immune cells between these two groups, the overall NK cell activity in patients who responded was highly elevated compared to the NK cell activity in non-responders. From the analysis of NK subsets, there were no differences in the population of early NK cells between the two groups, but the functionally differentiated late NK cells were prominently high in the responder group. Conclusions: Natural Killer (NK) cells have been recently implicated to play a key role in anti-tumor response to checkpoint inhibitors and our results suggest that the overall number of NK cells and their activity could prove to be an independent and reliable predictive tool/biomarker in patients with NSCLC.