Abstract
PD-1/PD-L1 inhibitors have shown clinical benefit in lung adenocarcinoma (LUAD). However, the immunotherapy strategy is less effective in patients with EGFR-activating mutations (EGFR MT). Studies showed that besides low expression of PD-L1, the absence of TILs and distinct expression profile of immune checkpoint molecules might be associated with low response of the patient subset. In this study, we first compared CD8A, GZMB and PRF1 mRNA levels in different LUAD subtypes harboring different driver mutations by dataset analyses and investigated the association between 15 well-defined B7-CD28 family members and driver mutations. The results showed that the decreases in the density and function of CD8+ TILs, CD274 (PD-L1 gene), and CD86 and increases in VTCN1 (B7-H4 gene) and HHLA2 were associated with LUAD with EGFR-activating mutations. Immunohistochemical staining studies further supported that PD-L1 was downregulated and B7-H4 was upregulated in the subtype. Furthermore, PD-L1 expression was positively associated with levels of CD8A and granzyme B, while B7-H4 expression was negatively associated with granzyme B levels. In lung cancer cell lines, EGFR-activating mutations effectively upregulated B7-H4 and downregulated PD-L1. MEK/ERK-pathway activation upregulated B7-H4, and PI3K/Akt activation upregulated PD-L1. EGFR 19Del mutation was associated with inhibition of CD8+ T-cell function, while knocking down B7-H4 could reverse the inhibition, and further showed tumor-growth inhibition and longer survival in vivo. Taken together, this study shed light on that B7-H4 might be an alternative immune-checkpoint molecule and a potential therapeutic target for LUAD with EGFR MT.