Neoantigen screening identifies EGFR L858R mutation immunogenicity in 1862 Chinese NSCLC patients.

e21512 Background: Therapeutic vaccines targeting mutation-derived neoantigens prime T-cell responses and deliver long-term clinical benefit to patients. Last year we reported EGFR L858R mutation could be a possible target for individual-independent vaccine in 799 Chinese patients with non-small cell lung cancer (NSCLC). Here we verified the findings and explored possible immunological mechanisms in a larger sample size of 1862 Chinese NSCLC. Peripheral blood or normal tissue was used as control. Methods: DNA sequencing data was acquired using our targeted 1021-gene panel and HLA-I genotyping was determined based on DNA sequencing by OptiType v1.0. The peptide-HLA binding affinity was predicted with netMHCpan v4.0. Neoantigen was identified if the IC50 MT < 500 nM and IC50 WT > 500 nM, furthermore, IC50 MT < 50 nM was considered as strong-binders. Results: EGFR (50.05%) was the most prevalent mutated gene, with 22.61% and 13.16% harboring L858R mutations and E746_A750del respectively. HLA typing showed HLA-A*11:01(42.59%) was the top one allele and HLA-A*33:03(12.94%) ranked 12th. The combination of EGFR L858R and HLA-A*33:03 had both relatively strongest binding affinity (IC50 MT = 22.9 nM and IC50 WT = 12734.0 nM, 2.93%) and highest shared frequency (2.93%). In terms of mechanism, we examined 7 of 1862 (0.37%) B2M gene mutation and 1092 of 1731 (63.1%) HLA-I LOH (loss of heterozygosity) in our population, but didn’t see any statistical difference between L858R subtype and other position mutations in EGFR. We also calculated 26 immune cell types’ signature scores from Chinese CHOICE study and found L858R subtype was associated with elevated level of pDC (KW-test p = 0.02) and lower level of neutrophils signature(KW-test p = 0.07) compared with exon 19 deletion and other uncommon mutations of EGFR. Conclusions: (1) Targeting EGFR L858R mutation in patients with HLA-A*33:03 allele appeared to be valuable for the neoantigen-based vaccine designed for Chinese NSCLC patients. (2) The specific immunogenicity of L858R seemed to be little influenced by B2M mutation and HLA-I LOH which were important factors for neoantigen presentation. (3) High pDC and low neutrophils infiltration might contribute to the inhibitive microenvironment associated with L858R mutation.