Tolerance to heart and kidney grafts induced by nondepleting anti-CD4 monoclonal antibody (RIB 5/2) versus depleting anti-CD4 monoclonal antibody (OX-38) with donor antigen administration

Donor brain death significantly interferes with tolerance induction protocols

Studies in rodents showed that antibodies are able to induce tolerance of allografts. As clinical results are unsatisfactory and deceased donors are still the main source of organ transplants, we investigated whether donor brain-death impacts on tolerance induction after experimental kidney transplantation. Anti-CD4 monoclonal antibodies (RIB 5/2; 2.5 mg/kg x 5 days) treated and untreated recipients of brain-dead donor grafts were compared with RIB 5/2 treated and untreated recipients of living donor grafts (F344-to-Lewis). All recipients received low-dose CsA (1.5 mg/kg x 10 days). Kidneys were recovered 4, 16 and 40 weeks after transplantation and examined by morphology, immunohistology and flow cytometry. Renal function was monitored monthly. RIB 5/2 treatment significantly decreased proteinuria in recipients of living donor allografts when compared with living donor controls. After 40 weeks, inflammatory cell infiltration and MHC class II expression were reduced while morphologic alterations were minimal. In contrast, treatment of brain-dead graft recipients had no impact on graft function. Structural changes and graft infiltration were comparable to brain-dead donor controls at all time points. RIB 5/2 treatment significantly improved graft function in recipients of living donor grafts; however, it was not effective in recipients of brain-dead donor organs.

Use of a non-depleting anti-CD4 antibody to modulate the immune response to coagulation factors VIII and IX

The generation of antibodies to therapeutic factors VIII or IX is a major problem in the management of haemophilia and places potential limitations on the application of gene therapy. We have investigated the administration of a non-depleting anti-CD4 antibody for modulation of the immune response to human recombinant coagulation factors VIII and IX. In mice given these clotting factors, co-administration of anti-CD4 antibody significantly reduced the appearance of factor-specific antibodies. These data provide evidence that the neutralizing antibody response to exogenous coagulation factors may be controllable if non-depleting anti-CD4 antibody is co-administered at the time of initial replacement therapy.

Organ Transplant Specificity of Tolerance to Skin Grafts with Heart or Kidney Grafts Plus Nondepleting Anti-CD4 Monoclonal Antibody (RIB 5/2) and Intravenous Donor Alloantigen Administration

BACKGROUND

CD4+ T cells play an essential role in allograft rejection. Monoclonal anti-rat CD4 antibody, RIB 5/2, has been shown to modulate the CD4 glycoprotein without eliminating recipient T cells. A single dose of monoclonal anti-rat CD4 antibody RIB 5/2 plus donor splenocytes results in donor-specific unresponsiveness to heart and kidney allografts, but not skin allografts. This study examined whether tolerance to the more resistant skin graft could also be achieved with RIB 5/2.

METHODS

Buffalo (RT1(b)) recipients were given a single dose (20 mg/kg) of monoclonal antibody RIB 5/2 IP plus IV Lewis (RT1(l)) splenocytes (25 x 10(6)) 21 days before Lewis heart, kidney, or skin grafts. In addition, Lewis skin was grafted either simultaneously with or after long- term Lewis heart or kidney allograft acceptance (>50 days).

RESULTS

While IV alloantigen plus RIB 5/2 results in long-term acceptance of both heart and kidney, skin allografts are rejected when transplanted alone. Simultaneous transplantation with a Lewis kidney, but not with a Lewis heart, resulted in long-term Lewis skin graft acceptance. However, recipients tolerant to Lewis kidney or heart alone will not accept subsequent Lewis skin grafts, while recipients of simultaneous Lewis skin and kidney grafts subsequently accept a second Lewis, but not third-party Brown Norway (RT1(n)), skin graft.

CONCLUSION

RIB 5/2 plus Lewis donor splenocytes tolerize for donor-specific heart and kidney but not skin grafts. However, Lewis skin grafted simultaneously with a Lewis kidney, but not Lewis heart, is accepted and protects a subsequent donor-specific Lewis skin graft.

Recent advances in immunosuppressants

In recent years, a large number of structurally diverse immunosuppressants have been discovered that are effective for the treatment of organ transplantation. Some of them are undergoing clinical trials and may soon enter into routine clinical practice. These compounds are either chemical entities obtained from natural sources/synthetic means or biomaterials such as monoclonal antibodies/gene products/proteins. They have been found to interfere at different stages of T cell activation and proliferation, and can be identified as inhibitors of nucleotide synthesis, growth factor signal transduction and differentiation. Newer strategies involving combination of new agents with traditional immunosuppressants, monoclonal antibodies and gene therapy offer enormous potential, not only for the investigation of mechanisms pertaining to graft rejection, but also for its therapeutic prevention.