Abstract 1055: Evaluation of immune checkpoint inhibitor efficacy in EGFR mutant tumors

Abstract Tyrosine Kinase Inhibitor (TKI) of Epidermal Growth Factor Receptor (EGFR) is a first-line therapy for non-small cell carcinoma lung cancer patients with EGFR mutations, but patients often develop resistance to such a target therapy. Recently several PD-1 and PD-L1 inhibitors were approved for treating NSCLC, however, it remains unclear whether EGFR mutant NSCLC would benefit from PD-1/PD-L1 treatment. PD-1 response in cancer patients is closely associated with oncogenic mutation status, tumor microenvironment, PD-L1 expression and tumor mutation burden (TMB); however, the lack of pre-clinical models limited the investigation of the checkpoint inhibitors in EGFR mutant tumors. Here we use human PBMC reconstitution system for immune-humanization, and established a series of IO-Xenograft models (IO-CDX and IO-PDX) with cancer cell lines (IO-CDX) or patient-derived tissues (IO-PDX) that contain various EGFR mutations, including EGFR 19 del, L858R, T790M, and EGFR over-expression, amplification and fusion. We treated these models with either EGFR TKI (erlotinib, afatinib or osimertinib) or nivolumab, a PD-1 inhibitor. The predictive biomarkers including PD-L1 expression and TMB were analyzed by whole exom sequencing (WES) and FACS for tumor infiltrating lymphocytes (TILs), respectively. We found that 3 TKI-resistant PDX models bearing EGFR T790M mutation exhibited lower TILs than those bearing EGFR wild type or exon 19del mutation. Of the 8 IO-CDX or IO-PDX humanized models we have examined, those exhibiting higher TILs achieved better responses to nivolumab treatment. The 3 most sensitive models are EGFR amplification (wt), EGFR over-expression (wt) and EGFR exon 19del. In contrast, the EGFR T790M model from H1975 cell line was observed with hyper-progressive disease after nivolumab treatment. We will also discuss the contribution of PD-L1 expression and TMB to nivolumab in other models. In summary, these well-established IO-CDX and IO-PDX models can provide a human-resembling immune system for of immune therapeutics and combination with targeted therapies, and help to facilitate the understanding of relationship among tumor microenvironment, driver oncogenic mutations and drug response. Citation Format: Xuzhen Tang, Li Yang, Hui Qi, Xianzhi Zhai, Fuyang Wang, Xiangnan Qiang, Jie Xu, Xiaoran Qin, Qingyang Gu, Shaoyu Yan, Qunsheng Ji. Evaluation of immune checkpoint inhibitor efficacy in EGFR mutant tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1055.