A Non-peptide Functional Antagonist of the CCR1 Chemokine Receptor Is Effective in Rat Heart Transplant Rejection

Abstract

Chemokines like RANTES appear to play a role in organ transplant rejection. Because RANTES is a potent agonist for the chemokine receptor CCR1, we examined whether the CCR1 receptor antagonist BX471 is efficacious in a rat heterotopic heart transplant rejection model. Treatment of animals with BX471 and a subtherapeutic dose of cyclosporin (2.5 mg/kg), which is by itself ineffective in prolonging transplant rejection, is much more efficacious in prolonging transplantation rejection than animals treated with either cyclosporin or BX471 alone. We have examined the mechanism of action of the CCR1 antagonist in in vitro flow assays over microvascular endothelium and have discovered that the antagonist blocks the firm adhesion of monocytes triggered by RANTES on inflamed endothelium. Together, these data demonstrate a significant role for CCR1 in allograft rejection.The classic signs of acute cellular rejection during organ transplantation include the infiltration of mononuclear cells into the interstitium (1). This cellular infiltrate consists mainly of T lymphocytes, monocytes, and macrophages that are recruited from the circulation into the transplanted tissue by chemotactic molecules known as chemokines. Chemokines belong to a large family of small (8 -10 kDa) inducible chemotactic cytokines, which are characterized by a distinctive pattern of four conserved cysteine residues (2). Currently over 40 chemokines have been identified and classified into two major groups, CXC and CC, dependent on the number and spacing of the first two conserved cysteine residues. The CXC class members include interleukin (IL-8), 1 melanoma growth stimulatory activity, and neutrophil-activating peptide-2, whereas the CC class includes RANTES, monocyte chemotactic protein-1, and MIP-1␣ (macrophage inflammatory protein-1).A number of studies have provided evidence for a role for RANTES in organ transplant rejection, particularly of the kidney. In a model of reperfusion injury in the rat, RANTES levels were increased over normal levels and remained high for more than a week, correlating with the peak of infiltrating macrophages (3). RANTES protein was detected in infiltrating mononuclear cells, tubular epithelium, and vascular endothelium of renal allograft biopsy specimens from patients with cyclosporin nephrotoxicity but not in normal kidney (1). A recent study suggests that RANTES may play a role in graft atherosclerosis (4). Increased levels of RANTES (both mRNA and protein) were detected in mononuclear cells, myofibroblasts, and endothelial cells of arteries undergoing accelerated atherosclerosis compared with normal coronary arteries. In another recent renal transplant study, the chemokine receptor antagonist Met-RANTES when given with low doses of cyclosporin significantly reduced renal injury including interstitial inflammation mainly by reducing the number of infiltrating monocytes (5).Mechanistically this appeared to be achieved by blocking the firm adhesion of these cells to the inflamed endothelium. In summary, these studies ...

Chemokine Receptor CCR1 But Not CCR5 Mediates Leukocyte Recruitment and Subsequent Renal Fibrosis after Unilateral Ureteral Obstruction

“…The fact that genetically generated CCR1 deficiency and intermittent CCR1 blockade with a specific antagonist had the same effect on renal inflammatory infiltrates and fibrosis after UUO provides powerful evidence for the role of CCR1 for macrophage and T cell recruitment after UUO and the concomitant fibrosis. Our results are consistent with the beneficial effects of CCR1 blockade on the functional outcome in renal and heart transplantation, pulmonary fibrosis, or experimental encephalomyelitis and argue for an important role of CCR1-mediated leukocyte recruitment in these models (8,23,24).…”

A chemokine receptor CCR-1 antagonist reduces renal fibrosis after unilateral ureter ligation

“…In rats, BX471 dose dependently improved the severity of the experimental allergic encephalomyelitis (EAE) model (13). In combination with cyclosporine a similar dose of BX471 effectively prolonged rat heart transplant survival, which correlated with a reduction of mononuclear cell infiltrates (10). In a rabbit model of renal transplantation BX471 was similar to cyclosporine in its ability to prevent transplant rejection and to improve mortality (11).…”

Prolonged Allograft Survival in TNF Receptor 1-Deficient Recipients Is Due to Immunoregulatory Effects, Not to Inhibition of Direct Antigraft Cytotoxicity

“…The increase in levels of CCR1 and CCR2 observed in allografts from TNF-R1 Ϫ/Ϫ recipients at day 5 suggests that the absence of TNF-R1 immunomodulatory signals delays but does not prevent up-regulation of these chemokine receptors. Enhanced expression of many chemokine receptors has been associated with allograft rejection (31,43), and early signaling by chemokines through these receptors may contribute to the more rapid rejection observed in allografts from wild-type recipients.…”