CD28 and neoplasm: However, the high expression of partial ICPs, such as CD200R1, CD244, CD28, CD48, CD80, CD86, ICOS, PDCD1LG2, TNFRSF9, and TNFSF14, in C2 tumors suggests that the tumor microenvironment is immunosuppressive; thus, mRNA vaccine inhibition may be caused by eliciting an effective immune response.