CD4+ T cell-independent production of allo-antibodies in transplantation: mechanisms and therapeutic potential – ESPRIT

Work force:
2 MD wer full time on the project (master degree)
One engineer has been recruited in september 2012

Experimental strategy:
A new mouse model has been developed wher HLA A2 transgenic animals (B6 background are used as donor for B6 recipients. The only allogenic target is therefore the HLA A2 molecule, which allow us to use clinical tools to monitor the antibody response in recipients.
CD4+ T cells are depleted by genetic manipulation (MHC II KO).
Skin graft and heterotopic heart transplantations models has been used to sensitize the recipients

Clinical strategy:
ESPRIT is a translationnal project. We have developed a platform aiming at performing the monitoring of the phenotype of circulating CD4+ T cells of the renal transplant recipients followed in Edouard Herriot Hospital.

In contrast with WT controls, CD4+ T cell deficient recipients did not develop a detectable antibody response against their grafts nor their transplants.

To test the effect of:
-the amount of CD4+ T cell help (partial depletion)
-the quality of CD4+ T cell help (immunosuppressive drugs)
on the antibody response against an allogenic graft/transplant

NR

Renal transplantation represents currently the best treatment for patients with terminal kidney failure, a life threatening condition the incidence of which is currently rocketing worldwide. Although renal transplantation save thousands of lives and transform the quality of life of thousands more, many people will die or remain on renal replacement therapy because the organ supply falls drastically short of demand. Advance in transplantation over the last decades has only marginally improved the long term graft outcomes and prolonging graft life appears therefore has the most straightforward strategy to reduce organ shortage.
Unlike T cells, which have increasingly come under pharmacologic control, B cells have remained relatively untamed by modern immunosuppressive drugs. As a result, antibody-mediated rejection has emerged has the first cause of allograft failure.
This is somewhat surprising because the prevalent immunologic dogma predicts that without CD4+ T cell help, B cells should be unable to respond to donor specific HLA molecules, which are typical T cell-dependent antigens. This clinical observation, together with recent basic immunologic findings, suggest that a CD4+ T cell-independent allo-antibody response can develop in immunosuppressed renal transplanted patients and this process might play a crucial role in allograft failure.
The ESPRIT project represents a translational attempt, combining murine experimental models with in depth clinical analysis of human samples, aiming at :
i) demonstrating that an allo-Ab response can develop in the absence of conventional CD4+ T cell help, ii) providing an exhaustive characterization of such allo-Ab response, iii) identifying the mechanisms allowing CD4+ T cell-independent allo-Ab response to develop, and iv) establishing the proof of concept that CD4+ T cell-independent allo-Ab response represents a potential target to prolong graft survival in graft recipients.
Evidence that CD4+ T cells from immunosuppressed kidney recipients are functionally blocked and unable to provide efficient help to B cells will be provided in ex vivo assays.
A simple murine model will be used to perform a dissection of the mechanisms allowing CD4+ T cell-independent allo-Ab response to develop. CD4+ T cell deficient mice (either due to genetic modification: CD4 KO, MHC II KO, or induce by anti-CD4 depleting mAbs) will be grafted with skin from donor with the same genetic background but transgenic for the human MHC I molecule HLA A2. In this model the CD4+ T cell-independent anti-HLA A2 Ab response will be easily monitored with tools available in routine clinical practice. This model will serve as basis for the identification of i) the molecular signals required for B cells to respond to HLA A2 in the absence of conventional CD4+ T cell help, and ii) the alternative cell partners able to provide these signals. Based on recent basic immunological discovery, we will focus our first investigations on cells of the innate immune system, in particular NKT cells. The latter interact with B cells and have been shown to be potent display potent helper capacities.
Our results will pave the way to design innovative therapeutic strategies aiming at blocking the CD4+ T cell-independent Ab responses. A murine preclinical model of heterotopic heart transplantation in immunosuppressed recipients will be used to establish the proof of concept that these therapeutic strategies effectively prolong graft survival.