In epithelial cells and fibroblasts, activation of CD99-related ligands can inhibit endothelial barrier invasion and migration activity of the endothelial barrier 33; at the same time, in epithelial cells, the SEMA4A-PLXNB2 ligand receptor for activation of immune cells, such as T cells, B cells, and the CCL 5-CCR 1 ligand receptor in macrophages can direct chemotactic T cells, NK cells, and other immune cells, and in turn, activation of these ligand receptors enhances the immune response to tumors and plays a certain role in tumor metastasis 34. This evidence concerns the gene CD99 and neoplasm.