Interestingly, when CAR-T cells were stimulated with antigen-positive leukemia cells, expression of the CD19/CD20 tandem constructs resulted in less cytokine production than CD20 CAR alone, suggesting some attenuation of signaling when the CD19 and CD20 receptors were co-expressed in tandem on the same CAR. The gene discussed is MS4A1; the disease is leukemia.