Exploring new immunosuppressive strategies inducing donor-specific hyporesponsiveness is an important challenge in transplantation. For this purpose, a careful immune monitoring and graft histology assessment is mandatory. Here, we report the results of a pilot study conducted in twenty renal transplant recipients, analyzing the immunomodulatory effects of a protocol based on induction therapy with rabbit anti-thymocyte globulin low doses, sirolimus, and mofetil mycophenolate. Evolution of donor-specific cellular and humoral alloimmune response, peripheral blood lymphocyte subsets and apoptosis was evaluated. Six-month protocol biopsies were performed to assess histological lesions and presence of FOXP3⁺ regulatory T cells (Tregs) in interstitial infiltrates. After transplantation, there was an early and transient apoptotic effect, mainly within the CD8⁺HLADR⁺ T cells, combined with a sustained enhancement of CD4⁺CD25^+high lymphocytes in peripheral blood. The incidence of acute rejection was 35%, all steroid sensitive. Importantly, only pretransplant donor-specific cellular alloreactivity could discriminate patients at risk to develop acute rejection. Two thirds of the patients became donor-specific hyporesponders at 6 and 24 mo, and the achievement of this immunologic state was not abrogated by prior acute rejection episodes. Remarkably, donor-specific hyporesponders had the better renal function and less chronic renal damage. Donor-specific hyporesponsiveness was inhibited by depleting CD4⁺CD25^+high T cells, which showed donor-Ag specificity. FOXP3⁺CD4⁺CD25^+high Tregs both in peripheral blood and in renal infiltrates were higher in donor-specific hyporesponders than in nonhyporesponders, suggesting that the recruitment of Tregs in the allograft plays an important role for renal acceptance. In conclusion, reaching donor-specific hyporesponsiveness is feasible after renal transplantation and associated with Treg recruitment in the graft.

In renal transplantation, chronic allograft nephropathy is the leading cause of long-term graft losses, transplant glomerulopathy being its glomerular form. Differential diagnosis from recurrent or de novo membranoproliferative glomerulonephritis should be established. Whether hepatitis C virus is associated with cryoglobulinemia and glomerular damage in renal allograft recipients, as in native kidneys, is not known. We identified six hepatitis C virus-infected renal allograft recipients with proteinuria higher than 1.5 g/day, microhematuria, and membranoproliferative glomerulonephritis. Virologic and immunologic studies were conducted. Low serum levels of circulating immune complexes and cryoglobulins were observed, which were type II immunoglobulin G polyclonal-immunoglobulin Mk monoclonal in all six patients. Classical serum complement pathway activation and at least one type of autoantibodies were present in all of them. Hepatitis C virus RNA was found in higher concentrations in cryoprecipitate than in serum (percentage of enrichment ranged from 341 to 18,200%). Hepatitis C virus genotype was 1b in 4 of 6 patients, 1a in 1 of 6 patients, and 2a in 1 of 6 patients. In renal histology prominent parietal diffuse deposition of immunoglobulin M was the rule. Glomerular subendothelial electron-dense deposits with fibrillar appearance were observed in the two patients in which electron microscopy provided information about glomeruli. In renal allograft recipients hepatitis C virus infection may be associated with type II cryoglobulinemia which may lead to membranoproliferative glomerulonephritis. Immunologic and virologic studies may help to differentiate hepatitis C virus-associated membranoproliferative glomerulonephritis from transplant glomerulopathy.