CD4 and leukemia: To address this issue, we employed tripartite in vitro co-cultures comprizing NALM-6 leukemia, CD19 CAR-T cells and autologous monocytes (figure 2A), as previously described.28 Of note, we observed increased monocyte activation levels when including CD4 rather than CD8 CAR-T cells, independently of the endodomain incorporated (figure 2B).