One of the difficult hurdles that must be overcome in order to allow the future implementation and assessment of protocols to induce immune tolerance in organ transplant recipients is to develop the ability to recognize when an organ transplant recipient is tolerant, i.e., when immunosuppression can be safely withdrawn without the risk of immune-mediated damage to the transplanted organ.
The primary objective of the proposed multicenter study is to determine if a specific profile or “fingerprint” can be identified for liver transplant recipients who are successfully withdrawn from immunosuppression without the occurrence of rejection, based on the ability of in vitro assays to discriminate between tolerant individuals and those at risk for rejection. Liver transplant recipients are ideal candidates for this type of empiric drug withdrawal trial because 1. Acute rejection, which may be elicited by drug withdrawal, is not a significant risk factor for graft loss in liver transplantation, unlike other organ transplants and 2. Preliminary studies suggest that 20% or more of liver transplant recipients receiving standard immunosuppression can be successfully withdrawn from drugs without eliciting rejection.
Liver transplant recipients will be treated prospectively with Campath-1H as induction therapy and tacrolimus as maintenance monotherapy and the tacrolimus slowly withdrawn. Participants will be followed closely by frequent assessment of their liver function and liver biopsies obtained to diagnose rejection if any liver dysfunction occurs. Participants developing rejection will be treated and returned to immunosuppression and followed as controls to compare to the participants who stop immunosuppression and do not reject.
Monitoring assays to be evaluated for their ability to discriminate participants who do or do not experience rejection with immunosuppression withdrawal are:
- ELISPOT for enumeration of donor reactive cytokine-producing T cells
- Cytokine detection using Luminex multianalyte profiling from serum and from donor antigen-stimulated PBL
- Flow cytometry phenotyping of PBMC
- Measurement of anti-donor HLA antibodies
- HLA genotype and matching
- Protocol biopsies for routine histology
- RNA preparation for gene expression by PCR
- PBMC RNA preparation for gene expression by PCR and microarray
- SNP analysis for gene polymorphisms
These assays will be evaluated to gain insight into the mechanism(s) by which immune tolerance is established and maintained in liver transplant recipients and determine if tolerance correlates with defined genetic markers of functional significance, has a pattern of specific gene activation and/or down-regulation, or is related to a uniquely regulated immune response to donor alloantigens.