CD274 and plasma cell myeloma: The immune microenvironment of MM is notoriously immunosuppressive, with a quantitative decrease in myeloma-specific lymphocytes, such as NKT cells and CD8+ T cells, coupled with an increased infiltration of T-regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSC), associated with an increase in PD-1/PD-L1 expression in MM cells and multiple immune cell types [5].