KRAS G12D mutation predicts lower TMB and drives immune suppression in lung adenocarcinoma

The efficacy of anti- programmed cell death 1 (PD-1)/PD-1 ligand (PD-L1) immune checkpoint inhibitors remains controversial in patients with KRAS mutation. In addition, whether and how KRAS gene and its mutant subtypes might influence immunity has not been clarified yet. Here we examine some important biomarkers for the efficacy of immunotherapy in specific KRAS subtypes.We conducted a bioinformatics analysis on somatic mutations data, transcriptome sequencing data and proteomic data from The Cancer Genome Atlas (TCGA) database. CIBERSORT was used to provide an estimation of the abundances of immune cells using gene expression data.From a cohort of 567 patients with lung adenocarcinoma (LUAD) based on TCGA, the overall mutation rate of KRAS was 26.29 %, including KRAS/TP53 co-mutation rate of 9.7 %. We observed increased Tumor mutation burden (TMB) in KRAS mutant group compared with wild type, while no difference in PD-L1 expression and immune cell infiltration. More importantly, TP53 and KRAS/TP53 co-mutation group not only significantly increased tumor mutation burden, but also had higher PD-L1 protein level and immune cell infiltration. We further focused on influence of KRAS mutant subtype on immune biomarker. The most prevalent mutant subtype of KRAS in lung adenocarcinoma was G12C(9.88 %,56/567), followed by G12 V(5.82 %,33/567), G12D(3.00 %,17/567), G12A(3.00 %,17/567), respectively. Among them, G12D mutation appeared to be a special mutant subtype with an obviously lower TMB. This low mutation load was more significant when co-mutation with TP53. Besides, our results also revealed significantly decreased expressions of PD-L1 protein level and immune cell infiltration (activated CD4 memory T cell, helper T cell, M1 macrophage and NK cell) in KRAS G12D/TP53 mutant group.KRAS G12D/TP53 co-mutation drives immune suppression and might be a negative predictive biomarker for anti-PD-1/PD-L1 immune checkpoint inhibitors in patients with lung adenocarcinoma.