New paper in PNAS describing how the micropolymorphisms that distinguish different HLA proteins within a superfamily can have a profound impact on TCR recognition of cancer neoantigens, altering specifcity without any perceptible impact on static structures or peptide binding affinity. In this case, the two polymorphisms that distinguish HLA-*0301 from HLA-A*0302 exert their effect by changing the ability of the peptide to move in a way that is needed for TCR binding. Congratulations to super star former graduate student and postoc Jiaqi Ma, pinch hitters Gihan Perera and Bassant Eldaly, and all the rest of the team. Also a big shout out to Christopher Klebanoff and his team at MSKCC for their crucial contributions.