COMBINATION OF CCR5 BLOCKADE AND CYCLOSPORINE A ATTENUATES CARDIAC ALLOGRAFT VASCULOPATHY IN NON-HUMAN PRIMATES.:

P1003 Aims: CCR5, the receptor for the chemokines MIP-1α, MIP-1β and RANTES, is expressed constitutively on monocytes, macrophages and activated T cells. In vivo studies in rodent demonstrate that this receptor plays an important role in both acute and chronic allograft rejection. We have previously reported that CCR5 inhibition with a highly selective antagonist prevents infiltration of CCR5+ and CXCR3+ cells into a rejecting allograft. Here we explore its role in chronic rejection in non-human primates when used in the context of conventional immunosuppression with Cyclosporine A (CsA). Methods: Three reference cynomolgus monkeys were treated with daily CsA monotherapy dosed to achieve a “therapeutic” trough level of 500ng/ml. Six study animals were treated with additional CCR5 antagonist (5-10mg/kg IV BID); most were dosed with CsA so as to achieve “subtherapeutic” CsA levels. Protocol graft biopsies were performed weekly for two weeks, at one month, and then for clinical indications (fever, diminished graft function by telemetry or ultrasound exam). When diagnosed by histology (findings consistent with cellular rejection) or clinical observation of graft dysfunction (fever, depressed graft function), acute rejection was treated with IV steroids. The grafts were explanted when acute rejection did not respond to steroid treatment, or electively at 90 days. Donor specific alloantibody titer was measured regularly (weekly or biweekly) in protocol serum samples. Cardiac allograft vasculopathy (CAV) was assessed in all biopsies and at the time of graft explant. Antigen-specific T cell response in peripheral blood was analyzed using MLR and ELISPOT. Results: Although graft survival was similar with the addition of CCR5 blockade relative to reference CsA controls (MST 35 ± 14 days versus 37 ± 20 days), the mode of graft loss differed. Moderate or severe CAV was consistently observed with CsA monotherapy in most biopsy samples at or after day 14, and was always prominent at subsequent graft failure when that occurred after 30 days. In stark contrast, although acute rejection was common in animals additionally receiving CCR5 blockade, CAV was not observed or was mild. High levels of alloantibody were consistently found in CsA-treated animals at day 14, but not usually until about 30 days in animals treated with additional αCCR5. Notably, elaboration of IgG isotype anti-donor antibody was typically suppressed in αCCR5-treated animals. Antigen-specific T cell response measured by MLR and ELISPOT showed a rise at the time of acute rejection and explant, similarly in both groups. Conclusions: Although not effective to prevent acute allograft injury, addition of CCR5 blockade to conventional immunosuppression with CsA suppressed the production of anti-donor alloantibody, and strikingly inhibited development of CAV in non-human primates, suggesting a pivotal role of CCR5 in these processes. We conclude that CCR5 blockade is a promising adjuvant approach to attenuate chronic allograft rejection in primates, and may be similarly effective in man.