In more recent studies, it has been indicated that Tregs navigate tumor antigen presentation and immunosuppressive signaling in MM by inducing the production of TGF-β1, downregulating the gene expression of members of the class I major histocompatibility complex (MHC) molecules, and increasing PD-L1 expression in myeloma cells [135]. Here, TGFB1 is linked to plasma cell myeloma.