We hypothesized that they would promote the recognition of tumor cells by T cells to exert anti-tumor effects, but the co-stimulatory molecule CTLA4 is also highly expressed, and CTLA4 competes with CD28 to bind ligands such as CD80 and CD86 in T cells and has higher affinity, thereby overcoming the positive effects of CD28 and placing T cells in an immunosuppressive state. Here, CTLA4 is linked to neoplasm.