Human Chromosome 10 open reading frame 99 is a 9.2 KDa protein encoded by the C10orf99 gene. C10orf99 has been described as a potential cytokine and a ligand Sushi Domain Containing 2 (SUSD2), inducing SUSD2 internalization upon binding. It has also been proposed to be a chemotactic factor that mediates lymphocytes recruitment to epithelia through binding and activation of the G-protein coupled receptor GPR15.