CTLA4 and neoplasm: Recently, the human cell receptor ACE2 of SARS-CoV-2 has received extensive attention due to its role in SARS Co V-2 infection, and the up-regulation of ACE2 is related to the anti-tumor immune characteristics, the increase of PD-L1 expression and the good anti-PD-1/PD-L1/CTLA-4 immunotherapy response.