Heart allograft acceptance induced by anti-CD3 antibody in high-responder rats: Effect on foxp3 and cytokine expression and graft infiltration

New generation CD3 monoclonal antibodies: are we ready to have them back in clinical transplantation?

PURPOSE OF REVIEW

The continuing problem of late graft loss and immunosuppressive drug toxicity forces us to explore new treatments for the induction of transplant tolerance. Monoclonal antibodies targeting molecules implicated in lymphocyte activation, in particular CD3/TCR, constitute a promising strategy.

RECENT FINDINGS

Promising results were obtained from the use of antibodies targeting CD3/TCR, coreceptors or costimulatory pathways as tolerance-promoting tools in experimental transplantation. These antibodies do not uniformly depress the immune system but act in an antigen-specific manner by preferentially targeting effector T cells while preserving regulatory T cells. However, translation to the clinic proved to be more difficult than expected. New generation CD3 antibodies, currently used in phase II/III trials in autoimmunity, constitute a promising approach as, beside their immunosuppressive effect, they also express potent tolerogenic capacities. Importantly, CD3 therapy is effective especially when applied in primed hosts, highlighting the importance of the therapeutic window for tolerance induction.

SUMMARY

Further investigations are required for adapting to the clinic monoclonal antibodies as substitutes for current immunosuppression. Our aim is to show that development of new therapeutic strategies/molecules may come from transversal-type research, in particular from experience in autoimmunity, as immune responses leading to autoimmunity and graft rejection involve similar pathways.

Accelerated antibody-mediated graft loss of rodent pancreatic islets after pretreatment with dexamethasone-treated immature donor dendritic cells

BACKGROUND

Allogeneic islets of Langerhans transplantation is hampered in its success as a curative treatment of type 1 diabetes by the absence of potent, specific, and nontoxic immunosuppressive drugs. Here, we assessed whether donor bone marrow-derived dexamethasone-treated dendritic cells (dexDCs) could prolong islet allograft survival in a full major histocompatibility complex mismatch rat model.

METHODS

Rodent allogeneic islet transplantation was performed from DA rats to Lewis rats and vice versa. Permanently immature dendritic cells were generated from the bone marrow of DA and Lewis rats by treatment with dexamethasone. Animals were either vehicle or donor dexDCs pretreated. Serum was used to monitor glucose, C-peptide, and alloreactive antibodies.

RESULTS

The transplantation of DA islets into Lewis recipients showed direct graft failure with reduced numbers of β-cells when rats were pretreated with donor dexDCs. In the reverse model (Lewis islets into DA recipients), dexDC-treated DA recipients even showed a significantly accelerated rejection of Lewis islets. Immunohistochemical analysis of allograft tissue of dexDC-treated recipients showed a predominant natural killer cell infiltration and a presence of antibody reactivity in the absence of complement deposition. Alloreactive antibodies were solely found in dexDC-treated recipients.

CONCLUSION

Our study shows that pretreatment with donor-derived dexDCs induces an antibody-mediated rejection in this islet transplantation rodent model.

Induction of allograft tolerance by monoclonal CD3 antibodies: a matter of timing

Despite remarkable progress in organ transplantation through the development of a wealth of immunosuppressive drugs highly effective at controlling acute rejection, two major problems still remain, the loss of transplants due to chronic rejection and the growing number of sensitized recipients due to previous transplants, transfusions or pregnancies. Induction of immune tolerance appears to be the only way to curb this complex situation. Here we describe that a therapy, already successfully used to restore immune tolerance to self-antigens in overt autoimmunity, is effective at promoting transplant tolerance. We demonstrate that a short low-dose course with CD3 antibodies started after transplantation, at the time of effector T cell priming to alloantigens, induces permanent acceptance of fully mismatched islet allografts. Mechanistic studies revealed that antigen-specific regulatory and effector T cells are differentially affected by the treatment. CD3 antibody treatment preferentially induces apoptosis of activated alloreactive T cells which is mandatory for tolerance induction. In contrast, regulatory T cells are relatively spared from CD3 antibody-induced depletion and can transfer antigen-specific tolerance thus arguing for their prominent role in sustaining long-term graft survival.

Donor IL-4-treatment induces alternatively activated liver macrophages and IDO-expressing NK cells and promotes rat liver allograft acceptance

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVG donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000U/day) for 5days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although B cells, T cells and natural killer (NK) cells also increased. IL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). IL-4 also induced IDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic IL-2, IFN-gamma and IDO expression 24h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immunosuppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues.