CTLA4 has high homology to the costimulatory molecule (CD28) on the T cell, and both has the same ligand CD86 (B7-2) or CD80 (B7-1), but reverse functions. Binding of CTLA-4 to B7 molecules can inhibit T cell activation. Therefore, blockade of the immune checkpoint B7/CTLA-4 can enhance tumor-specific T cell activation. CTLA4 is highly expressed on Treg cells, and some anti-tumor activity can also be achieved by eliminating Treg cells. YH001 targeting CTLA-4 can enhance the removal of regulatory T cells (Treg cells) in the tumor microenvironment by improving the immune response against tumor cells in order to treat multiple tumors.