IDO2 and lymphoma: This is an indication that Treg are converted to pathological Treg and can become less suppressive under pathological conditions; third, lymphomas “push” physiological Treg into four different types of “lymphoma Treg” (2); fourth, self-reactive T cells, termed anti-Treg, that can recognize MHC class I-restricted antigen peptide epitopes derived from Treg markers (such as indoleamine 2,3-dioxygenase (IDO), tryptophan 2,6-dioxygenase (TDO), programmed death ligand 1 (PDL1), and forkhead box P3 (FOXP3)) were identified.