RFXAP and immunodeficiency disease: The deficiency of regulatory factor X-associated protein (RFXAP), a key transcription factor of the MHC II gene, can cause severe immunodeficiency via the inhibition of MHC class II expression and the inactivation of CD4+ T lymphocytes.61, 62 Ding et al. revealed that RFXAP is inhibited by miR-212-3p transferred from PC-derived exosomes, which decreases MHC II expression when released to DCs.