Acute cellular allograft rejection in homozygous CCR5 Delta32 patients after renal transplantation.

We report that three of four patients who were identified as carriers of the homozygous CCR5 32 mutation developed acute cellular allograft rejection after renal transplantation. Despite the lack of a functional CCR5, dense Tcell infiltration into the allograft was detectable. Interestingly, the vast majority of recruited T cells expressed CXCR3, indicating that alternative chemokine pathways can promote T-cell trafficking in acute renal allograft rejection. Approximately 10–20% of whites are heterozygous and about 1% are homozygous carriers of a 32-base pair deletion mutation in the chemokine receptor 5 gene (CCR5 32) leading to a nonfunctional receptor. CCR5 is highly expressed on the cell surface of Th1-polarized T cells and monocytes. CCR5 is activated by three chemokines: RANTES/CCL5, MIP-1 / CCL3, and MIP-1 /CCL4. Each of these ligands is induced under inflammatory conditions in the kidney. Acute allograft rejection after renal transplantation is characterized by recruitment of activated T cells into the allograft. Data from experimental and human studies support that the process of leukocyte recruitment in acute allograft rejection is controlled by chemokines and their cognate receptors (1). In particular, the receptors CCR5 and CXCR3, both predominantly expressed on Th1 cells, are supposed to be involved in the pathophysiology of cellmediated allograft rejection in renal transplantation (2). In a recent multicenter study, Fischereder et al. demonstrated that patients carrying the homozygous CCR5 32 genotype had a significantly longer renal transplant survival time than heterozygous CCR5 32 and CCR5 wild-type individuals (3). Despite the improved graft survival, biopsy-proven acute rejection occurred in 9 of the 21 CCR5 32 patients in this study. As it remains unclear to what extend the lack of CCR5 impairs the development of acute allograft rejection, we screened 187 patients who had undergone renal transplantation in our center for the CCR5 32 genotype by polymerase chain reaction screening. Of the 187 patients, 162 (86.6%) had a CCR5 wild-type genotype, 21 (11.2%) were heterozygous, and four patients had a homozygous CCR5 32 genotype (2.1%). Clinical basic data of the four CCR5 / patients are given in Table 1. Three of these homozygous CCR5 32 patients (75%) developed biopsy-proven acute renal allograft rejection with characteristic infiltration of T cells and monocytes into the allograft (Banff 1A), while the rejection rate in the wild-type population was 33% and 29% in the heterozygous patients. Overall rejection rate was 33%. Immunohistochemical staining of patients carrying the CCR5 32 genotype with acute allograft rejection (n 3) demonstrated dense infiltrates of CD3positive T cells which could be subclassified as CD4 or CD8 positive and CD 68-positive monocytes (Fig. 1 and Table 1). As expected, CCR5 immunostaining was almost completely negative in the allografts of the homozygous CCR5 32 individuals (Fig. 1). Only in one allograft from a CCR5 32 carrier few CCR5 positive cells could be detected. As fluorescenceactivated cell sorting analysis of leukocytes from the peripheral blood of this patient showed complete absence of the CCR5 (data not shown), these infiltrating cells are probably donor derived. CCR5 wild-type carriers with acute rejection, by contrast, showed strong CCR5 positivity confined to infiltrating T cells and monocytes (2). In a next step, we performed immunohistological staining for the Th1-characteristic receptor CXCR3. In homozygous CCR5 32 patients, the vast majority of infiltrating CD3-positive T cells were CXCR3 positive (Fig. 1). The number of infiltrating (CXCR3 ) CD3 positive T cells per tubulointerstitial high-power field in this group (Table 1) was comparable to that of 13 wild-type patients with early acute allograft rejection (2), thus suggesting that CXCR3-mediated T-cell recruitment is a mechanism to compensate for the lack of functional CCR5. These results indicate that the lack of CCR5 does not substantially attenuate the recruitment of activated T cells in acute allograft rejection, underscoring the functional redundancy of the chemokine system. The effects leading to the longer transplant survival in CCR5 32 therefore remain largely unknown. Indeed we believe that the benefit of CCR5 32 on the long-term transplant survival is probably explained by several complex mechanisms, some of which cannot be functionally replaced by CXCR3. As has been reported recently, CCR5 exerts an important role in the immunological synapse were it helps to establish an effective crosstalk between antigen-presenting cells and T cells (4). Moreover, it has been described that the CCR5 plays an important role in longterm CD8 memory T cell generation in secondary lymphatic organs, thus probably influencing the chronic rejection process (5). On the basis of these data and our own findings, it is questionable whether the blockade of CCR5 alone is a useful strategy for prevention of acute allograft rejection in the early period after renal transplantation, which is of central interest because CCR5 blockade is now therapeutically used in the clinical setting (6). However, it seems more rewarding to target either CXCR3, the lack of which has been shown to effectively prevent acute rejection in a mouse model of cardiac transplantation (7), or even more promising, CXCR3 and CCR5 simultaneously in a double blockade to