Multiple Myeloma (MM) patients treated with B-cell maturation antigen (BCMA)-specific CAR-T cells usually relapse with BCMA+ disease, indicative of CAR-T cell supression. CD200 is an immune checkpoint that is overexpressed on aberrant plasma cells (aPCs) in MM and is an independent negative prognostic factor for survival. However, CD200 is not present on MM cell lines, a potential limitation of current preclinical models. We engineered MM cell lines to express CD200 at levels equivalent to …