CTLA4 and acute lymphoblastic leukemia: The maximal anti-tumor effect was seen when CTLA4-CD28 was expressed in both CD4+ and CD8+ T cells.35Park et al found the CTLA4-CD28 modification of T cells enhanced the therapeutic efficacy of donor lymphocyte infusion in a mouse model of acute lymphocytic leukemia.36 Perplexingly, a CTLA4-CD28 chimera has been shown to naturally exist in some T cell lymphomas.