KMT2D and post-transplant lymphoproliferative disease: [7, 22, 23] Loss of function mutations in KMT2D/MLL2, a lysine specific histone methyltransferase targeting H3K4 residues that is considered to function as a tumor suppressor, have been reported in PTCL arising in immunocompetent individuals and were seen in a variety of T/NK-PTLD.