B7-H3 and B7-H4 Expression in Breast Cancer and Their Association with Clinicopathological Variables and T Cell Infiltration

<b><i>Objectives:</i></b> B7-H3 and B7-H4 proteins are expressed in breast cancer tissues, but their relationships with respect to tumor immune surveillance and outcomes in breast cancer are not conclusive. <b><i>Methods:</i></b> We first examined B7-H3 and B7-H4 mRNA expression in the Genotype-Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) datasets. Next, mRNA and protein expression were assessed by RNAscope in situ hybridization (ISH) and immunohistochemistry in 10 pairs of breast cancer and matched normal tissues. Immunohistochemical staining of B7-H3, B7-H4, CD3, and CD8 was performed in tissue microarray slides containing 198 breast cancer samples. Association of B7-H3 and B7-H4 expression with survival was verified using the publicly accessible BreastMark tool. <b><i>Results:</i></b> B7-H3 and B7-H4 mRNA expression were significantly higher in breast cancer samples in the TCGA dataset than in normal breast tissues in the GTEx dataset. RNAscope ISH and immunohistochemistry showed that B7-H3 and B7-H4 mRNA and protein appeared to be mainly expressed in cancer cells. Expression of B7-H3 and B7-H4 tended to be associated with low-density scores of stromal tumor-infiltrating lymphocytes (TILs) as well as molecular subtypes. Expressions of B7-H3 and B7-H4 were negatively correlated with stromal CD3+ and CD8+ T cell infiltration density. B7-H3 and B7-H4 expression was not associated with survival, which was verified by BreastMark analysis. <b><i>Conclusion:</i></b> Expression levels of B7-H3 and B7-H4 were independent of clinical outcomes of breast cancer. There was an inverse relationship between the expression of B7-H3 and B7-H4 in breast cancer and the density of stromal TILs and CD8+ T lymphocytes. This inverse relationship may represent a promising target in the field of breast cancer immunotherapy.