CD274 and neoplasm: Because the target antigens in successful solid tumor cell therapies have been tumor-restricted antigens (eg, neoantigens, viral antigens, or cancer germline antigens), tumor models were based on tumor-restricted antigens.6–8 Finally, due to complex interactions of PD-1 blockade with therapeutic T cells and host cells, syngeneic mouse model systems with intact PD-1 and PD-L1 expression by therapeutic cells and host cells were utilized.