PD-1 Is a Negative Costimulatory Signal Expressed by Tumor Cells

PD-1 is a negative costimulatory signal expressed by tumor cells.What advantage would the expression of PD-1 have in a tumor cell avoiding the immune response?

A) Tumor cells can avoid being killed by activated T_C cells.
B) Tumor cells can avoid apoptosis triggered by T_H cells.
C) Tumor cells avoid phagocytosis by dendritic cells.
D) Tumor cells are stimulated to reproduce faster than tumor cells that do not express PD-1.
E) None.Tumor cells are recognized as self and, therefore, do not pose a health threat.