Porkchop. PS does not take the brake off of the immune system. PS in NORMAL BODILY FUNCTIONS is a STOP SIGN or a DINNER BELL for macrophage and dendritic cells which in turn notify the immune system if they find something different. The PD-1s simply turn on t-cells with no specific target which leads to side effects...ie..immune cascade...IMHO
Everyone seems to think PS is bad...it is not. It is cancer, viruses and other terrible diseases that take advantage of PS to remain undiscovered.
The big question is the PS threshold between dead cell and cancer cell.