Differential graft-versus-leukaemia effect by CD28 and CD40 co-stimulatory blockade after graft-versus-host disease prophylaxis.

Co-stimulatory blockade may be a promising strategy for tolerance induction in transplantation. In allogeneic bone marrow transplantation (BMT) for leukaemia treatment, however, preservation of the graft-versus-leukaemia (GVL) effect is another critical requirement for clinical application. In this study, we have compared the effect on GVL of using CD28 and CD40 co-stimulatory blockades as graft-versus-host disease (GVHD) prophylaxis in a murine allogeneic BMT model with simultaneous transfer of BCL1 leukaemia. Despite the relative improvement of GVHD as assessed by survival and body weight in both treatment regimes, treatment with anti-CD154 moAb clearly diminished the GVL effect, whereas treatment with anti-CD80 and CD86 MoAbs maintained this effect. Although T cell-mediated effector function at 14 days post-BMT assessed by IFNgamma expression and cytotoxicity against host alloantigen was comparable between both co-stimulatory blockades, IL-12 mRNA expression was preferentially reduced by CD40 blockade. Our results suggest the differential involvement of the CD28 and CD40 co-stimulatory pathways in the development of GVHD and GVL effects. CD28 blockade may be a favourable strategy for tolerance induction in leukaemia patients undergoing BMT.