Mystery Checkpoint Revealed: KIR3DL3 Finally Found a Ligand in HHLA2.

Inhibitory killer cell immunoglobulin-like receptors (iKIR) tolerize natural killer cells and some T cells upon detecting classical HLA class I molecules. In this issue, Bhatt and colleagues identify the B7 family member HHLA2 as an unanticipated ligand for a peculiar iKIR family member, KIR3DL3. These data establish a new inhibitory checkpoint pathway that may protect HHLA2+ tumor cells from immune attack.See article by Bhatt et al., p. 156.