CD4 and neoplasm: In a mouse B-cell lymphoma model, Boulch et al. [15] reported the impact of CD4 and CD8 CAR-T cells on the host immune system and the possible role of cytokines released in vivo, underlining the importance of the crosstalk between CAR-T cells and the tumor microenvironment in order to enable an optimal anti-tumor CAR-T-cell efficacy.