Abstract: Objective To explore the effect of human epidermal growth factor receptor-2 （Her-2） on immune cell infiltration in gastric cancer tissues and its possible mechanism. Methods The RNA-Seq data of 354 patients with complete information were downloaded from the TCGA. The CIBERSORT algorithm was used to investigate the proportion of infiltrating immune cells in the microenvironment of gastric cancer，and its correlation with Her-2 expression was analyzed to screen the potential types of Her-2 genes regulating infiltrating immune cells. Gene set variation analysis（GSVA） was used to evaluate the set of signal pathways related to Her-2 expression in gastric cancer tissues，and gastric transcriptome data collected by Gene Expression Omnibus（GEO） was used to further verify the relationship between Her-2 gene expression and the degree of gastric cancer immune cell infiltration. Results CIBERSORT analysis of gastric cancer samples from the TCGA database found that CD8+ T cells，resting memory CD4⁺ T cells，M0 macrophages，and mast cells infiltrated differentially in Her-2 high- and low-expression groups（P=0.029，0.049，0.027，0.008）. High expression of Her-2 gene was related to the development，induction，differentiation，and migration regulation of CD8⁺ T cells，resting memory CD4⁺ T cells，M0 macrophages and mast cells（P<0.05），and affected the infiltration capacity and proportion of some immune cells in gastric cancer tissues. Conclusion High expression of Her-2 gene in gastric cancer may have an inhibitory effect on the formation and function of some immune cells.

Key words: Gastric cancer, Her-2, Tumor immune cells infiltration, Molecular mechanism, Bioinformatics