American Transplant Congress
Toronto, Canada, May 31-Jun 4,
A pilot study was performed to evaluate whether immune cell depletion with alemtuzumab would permit post-transplant weaning of maintenance immunosuppression in well-matched renal transplant recipients. Patients received alemtuzumab 30 mg intravenously on the day of the transplant and the subsequent 2 days while sirolimus and tacrolimus were started on day 1. Tacrolimus was discontinued at day 60 in all patients. Extensive immune monitoring was performed at 1 year.
At current follow-up (22 to 34 months), all patients are alive with a functioning graft (median MDRD GFR=46 ml/min). One patient experienced clinical and biopsy-proven rejection at 9 months. All other patients remain on sirolimus monotherapy. Four patients have been weaned to 1 mg of sirolimus daily as their sole immunosuppressive agent, with resulting blood levels of 3-4 ng/ml. These 4 patients have no evidence of donor-specific alloantibody, are unresponsive or hyporesponsive to donor cells by the cytokine kinetics test, and have a regulator phenotype to soluble donor antigens by trans-vivo DTH. Flow cytometry of peripheral blood demonstrated increased Foxp3 expression in the CD3+CD4+ population (p=0.002). Naive B cells (CD19/CD27neg) cells increased in 9 of 10 patients (p=0.02) and memory B cells increased in all 10 recipients (p=0.0005) when comparing pretransplant to 1 year timepoints.
Other than the patient with rejection, 12-month protocol biopsies did not show any evidence of rejection, although 2 of 9 showed focal C4d positivity and 1 diffuse positivity. These 3 patients also had evidence of alloantibody by Luminex xMAP testing.
In conclusion, the cytokine kinetics test, alloantibody testing, and trans-vivo DTH assay results correlated with clinical evolution of patients who successfully weaned both tacrolimus and sirolimus without rejection or alloantibody. The flow cytometry findings described occurred regardless of clinical evolution and may represent alterations of the immune system inherent in the treatment protocol independent of individual patient responses to the graft. However, the functional assays of cytokine kinetics assay and trans-vivo DTH may be of potential use to correlate with the clinical immune status of the kidney transplant recipient.