Anti-CD4 monoclonal antibody reduces the dose of cyclophosphamide required to induce tolerance to H-2 haplotype identical skin allografts in mice

IFN-gamma is an absolute requirement for spontaneous acceptance of liver allografts

Experimental liver allografts undergo spontaneous acceptance despite undergoing rejection during the first few weeks post transplant. We explored the role of interferon-gamma (IFN-gamma) in the spontaneous acceptance of mouse liver allografts. Strain of mouse (CBA) liver allografts transplanted into normal BALB/c mice developed histologic changes typical of rejection that spontaneously regressed, permitting long-term survival of these allografts similar to that of syngeneic grafts. In contrast, CBA liver allografts in IFN-gamma-deficient hosts manifested not only infiltration but also hemorrhage and necrosis, with no survival beyond 14 days. Despite differences in survival, local expression of cytotoxic T-cell genes in the transplant was not increased in IFN-gamma-deficient hosts, but livers in interferon-gamma-deficient mice (GKO) hosts displayed much less induction of major histocompatibility complex (MHC) class I and II expression. To determine whether the difference in survival was secondary to the direct effects of IFN-gamma on the liver, we transplanted livers from IFN-gamma-receptor-deficient mice into normal hosts. Liver allografts lacking IFN-gamma receptors also developed hemorrhage and necrosis with minimal induction of MHC expression. Thus IFN-gamma mediates a direct effect on rejecting liver allografts that reduces hemorrhage and necrosis, induces MHC expression, and is absolutely required for spontaneous acceptance.

CD40 ligand-specific antibodies synergize with cyclophosphamide to promote long-term transplantation tolerance across MHC barriers but inhibit graft-vs-leukemia effects of transplanted cells

OBJECTIVES

We previously demonstrated that allogeneic bone marrow transplantation (BMT) after low-dose total lymphoid irradiation (200 cGy) and depletion of donor-reactive cells with cyclophosphamide (Cy) converted recipients to graft-vs-host disease (GVHD)-free chimeras tolerant to donor skin grafts. BMT also generated strong graft-vs-leukemia (GVL) response. However, clinical application of the protocol was hampered by the requirement for a relatively high dose of Cy (200 mg/kg). In this study we have tried to minimize the Cy dose by a concomitant blockade of CD40-CD40L interaction.

MATERIALS AND METHODS

Mildly irradiated BALB/c mice were primed with C57BL/6 BM cells (BM(1)) and skin graft on day 0, injected with Cy (200 mg/kg or less) on day 1, and transplanted with a second C57BL/6 BM cell inoculum (BM(2)) on day 2. CD40L-specific antibody (MR1) was given with BM(1), BM(2), and 2 days later. Treated animals were monitored for survival, chimerism, and skin allograft rejection. The GVL potential of transplanted cells was examined in mice inoculated with BCL1 leukemia cells before irradiation.

RESULTS

Blocking CD40-CD40L interaction with MR1 mAb allowed the reduction of a tolerance-generating Cy dose by 50%. Unfortunately, adding MR1 to the protocol reduced the GVL potential of the transplanted cells. Neither low-dose Cy nor antibodies alone could downregulate donor or recipient immune response.

CONCLUSIONS

CD40L-specific antibodies synergize with Cy to induce bilateral transplantation tolerance. Therefore, their use may be beneficial for safer allogeneic BMT for nonmalignant indications. However, due to MR1-associated reduction of GVL effects, MR1 should be considered with caution as conditioning for BMT for leukemia-bearing recipients.

Down-modulation of host reactivity by anti-CD44 in skin transplantation

BACKGROUND

A major goal in transplantation medicine is to achieve donor-specific tolerance while sustaining unaltered immunoreactivity toward donor-independent stimuli. Pretransplant immunization and concomitant blockade of costimulatory molecules may be one way to achieve this goal. We investigated whether transplant acceptance could be achieved by sensitization with semiallogeneic blood and blockade of CD44s (standard isoform) or CD44v6 (variant exon 6), since the adhesion molecule CD44 is known to function as a costimulatory molecule in T-cell activation.

METHODS

Immunoregulatory regimens were examined in BDX rats that had received full-thickness (DA x BDX)F1 skin grafts by controlling graft acceptance and immunoreactivity.

RESULTS

When BDX rats received full-thickness (DA x BDX)F1 skin grafts together with either anti-CD44s or anti-CD44v6, graft rejection was delayed, but none of the animals accepted the graft. An analysis of immunoreactivity revealed reduced numbers of infiltrating lymphocytes in anti-CD44s- as well as anti-CD44v6-treated rats. Expansion of donor-specific helper and cytotoxic T cells was particularly impaired in anti-CD44v6-treated rats. The effect of anti-CD44s could not be intensified by presensitization with donor-derived blood. However, when rats received anti-CD44v6 concomitantly with presensitization, 75% permanently accepted the graft and 50% accepted a second graft provided they were continuously treated with anti-CD44v6 and received a low dose of cyclosporine (CsA) during the first weeks after grafting. The frequency of graft-reactive helper T cells was reduced to less than 10% of the level in controls, and cytotoxic T cells could hardly be detected.

CONCLUSION

According to the in vivo and the vitro analyses of the graft and the draining lymph nodes, anti-CD44s blocked homing of activated lymphocytes into the graft, while anti-CD44v6 inhibited clonal expansion of donor-specific T cells. Suppression by anti-CD44v6 apparently functioned distinctly to cyclosporine and was most effective in combination with presensitization. Since expression of CD44v6 on lymphocytes is restricted to a short period during lymphocyte activation, anti-CD44v6 treatment could lead to a quite specific immunosuppression during a limited time period.