Prolongation of murine vascularized heart allograft survival by recipient-specific anti-major histocompatibility complex class II antibody

Treatment with anti-MHC-class-II antibody postpones kidney allograft rejection in primates but increases the risk of CMV activation

Treatment of kidney graft recipients with antibodies that may specifically suppress the anti-donor response would be an ideal situation to prevent graft rejection. MHC class-II-specific antibodies and, in particular, DR specific antibodies have often been proposed as treatment to prevent antigen presentation, and thus graft destruction. Here we report an attempt to prevent graft rejection using a humanized MHC class-II-specific monoclonal antibody CDP855 in a cynomolgus monkey kidney graft model. A modest delay in graft rejection was observed when the antibody was given only on days 0, 1 and 2 after transplantation. Unexpectedly 50% of the animals succumbed of a viral infection, most likely CMV in two of three cases, prior to graft rejection in the first week post-transplantation. We speculate that the antibody treatment triggered CMV activation, possibly as a consequence of the activation of factors such as NF-kappab by the interaction of the antibody and its target cells.

Evaluating the validity of animal models for research into therapies for immune-based disorders

The last few decades of the 20th century have shown an intensified search for safer and more effective medications against chronic diseases that burden ageing societies of the western world. The impressive development of biotechnological production techniques has greatly facilitated the pharmaceutical development of relatively non-toxic biological molecules. However, despite the huge investments, only a few effective therapies for immune-based diseases have reached the clinic. In this article we use examples from monoclonal antibody trials to discuss the validity and predictive strength of the animal models currently used for the development of effective therapies.

Anti-major histocompatibility complex class II treatment prevents graft rejection in the hamster-to-rat cardiac xenograft

BACKGROUND

Several groups have achieved graft acceptance in the concordant hamster to rat model by using a combination of anti-proliferative drugs and conventional immunosuppressive therapy. However, such aggressive treatment often leads to the recipient dying with a functional xenograft, as a result of opportunistic infections. This study aimed to investigate the effects of a short course of therapy with an anti-MHC class II monoclonal antibody treatment (chimeric OX6 [cOX6]) in combination with cyclosporin A (CyA) in a concordant hamster-to-rat xenograft model.

METHODS

Rats receiving hamster cardiac xenografts were given CyA or cOX6 alone or in combination and were monitored daily to assess the effect of treatment on graft survival. Additional studies monitored the effect of treatment on the production of cytolytic anti-hamster antibodies by the recipient and the deposition of immunoglobulin (Ig)M and complement factors within the xenograft.

RESULTS

Treatment with CyA only had no effect on graft survival, whereas treatment with cOX6 increased graft survival time by 2 days. The median graft survival time for cOX6+CyA was 76 days. cOX6 treatment of rats having undergone transplants inhibited the rise in cytotoxic anti-hamster antibodies in peripheral blood until day 5, whereas combination therapy completely inhibited anti-hamster antibody formation. Fluorescence-activated cell sorter analysis showed treatment with cOX6 significantly reduced circulating B cell numbers until day 5. Anti-MHC class II treatment also markedly reduced the deposition of both IgM and C3. Anti-MHC class II treatment with CyA gives long term survival in concordant xenografts without severe side effects.

CONCLUSIONS

The mechanism of action of this combination is complex and could be caused by an initial inhibition of B cell function by the anti-MHC class II treatment and the subsequent inhibition of T cell dependent pathways by CyA.

Induction of immunologic tolerance for transplantation

In the second half of the 20th century, the transplantation of replacement organs and tissues to cure disease has become a clinical reality. Success has been achieved as a direct result of progress in understanding the cellular and molecular biology of the immune system. This understanding has led to the development of immunosuppressive pharmaceuticals that are part of nearly every transplantation procedure. All such drugs are toxic to some degree, however, and their chronic use, mandatory in transplantation, predisposes the patient to the development of infection and cancer. In addition, many of them may have deleterious long-term effects on the function of grafts. New immunosuppressive agents are constantly under development, but organ transplantation remains a therapy that requires patients to choose between the risks of their primary illness and its treatment on the one hand, and the risks of life-long systemic immunosuppression on the other. Alternatives to immunosuppression include modulation of donor grafts to reduce immunogenicity, removal of passenger leukocytes, transplantation into immunologically privileged sites like the testis or thymus, encapsulation of tissue, and the induction of a state of immunologic tolerance. It is the last of these alternatives that has, perhaps, the most promise and most generic applicability as a future therapy. Recent reports documenting long-term graft survival in the absence of immunosuppression suggest that tolerance-based therapies may soon become a clinical reality. Of particular interest to our laboratory are transplantation strategies that focus on the induction of donor-specific T-cell unresponsiveness. The basic biology, protocols, experimental outcomes, and clinical implications of tolerance-based transplantation are the focus of this review.