Are you interested in MHCs?
If you aren't, I bet there is some guy in your department who won't stop talking about them if you get on the topic!
If you can identify the antigens that are present on the surface of cells that you don't want in a system with a functioning immune system (for example cancer cells, intracellular parasites, those sorts of things) then you can utilize the immune system to go ahead and get rid of those cells for you. It's totally
Flip to the method section in this brand new paper and you'll be filled with confidence that you, too, can identify the essential peptides that will make great new immunotherapeutic targets!
In all seriousness, they do make this sound quite straight-forward and present some very positive findings in the tumors that they analyze here. I don't know enough about the biology to contribute anything meaningful, but the authors seem excited about it. What I do know is that if I wanted to start looking for immunogenic antigen presenting peptides (or whatever they're called -- come on, my job would just be to identify a bunch of them, right?) I'd start by following the very clear method section in this paper!