IDO1 and lymphoma: In a lymphoma murine model, IDO+ MSCs could enhance tumor growth, which could be reversed by the IDO inhibitor D-1-methyl-tryptophan (D1-MT).418 Since MSCs secrete IDO to further suppress T-cell immune responses, umbilical cord-derived MSCs genetically secrete TandAb (a tetravalent bispecific antibody with two CD3 and two CD19 binding sites).