From Computer Tyme Support Wiki

My Immune Therapy Plan

Nivolumab (Opdivo) and other immunotherapy drugs work by both boosting the immune system and targeting cancer using "checkpoint inhibitors". Some cancers put put a substance called PD-L1 that makes the adaptive immune system (T Cells) not be able to see the cancer. PD-L1 is an "I'm a friend - don't kill me" signal that hides the cancer from attack. Opdivo removes the mask allowing the immune system to see the cancer and attack it. In some cases even leading to a complete cure.

However ...

You can't unmask something that isn't masked in the first place so if you have PD-L1 then that's great. But I don't have it so a drug that removes a mask that isn't there isn't likely to work.

Nivolumab apparently does more that just remove the mask. Although the literature focuses on PD-L1, the list of possible side effects look similar to people who have autoimmune problems. In other words - it looks like it also stimulates the immune system to the point where it might attack your body's good cells. It appears that Nivolumab has more than one function - to unmask the cancer - and to stimulate the immune system and put it in learn mode so that the T cells can identify the cancer and attack it.