While for CD19-directed therapies it remains unclear whether the inclusion of defined proportions of CD4+ T cells leads to enhanced efficacy, for a distinct CAR-T targeting B cell maturation antigen (BCMA) on multiple myeloma cells, a post hoc analysis indicated that responses to this therapy were associated with a higher CD4:CD8 ratio in the pre-manufacturing leukapheresis product (Cohen et al., 2019). Here, CD4 is linked to plasma cell myeloma.