EFFECTS OF LEFLUNOMIDE AND DEOXYSPERGUALIN IN THE GUINEA PIG???RAT CARDIAC MODEL OF DELAYED XENOGRAFT REJECTION

Background. If complement (C) activation is prevented or the host is C depleted, discordant vascularized xenografts undergo delayed xenograft rejection (DXR), characterized by graft infiltration by macrophages (MØ) and natural killer (NK) cells, endothelial cell activation, and widespread fibrin deposition. Given a lack of effect of T cell-directed therapies on development of DXR, we evaluated two novel agents, 15-deoxyspergualin (DSG) and leflunomide (LEF), with reported anti-B-cell and/or anti-MØ actions. Methods. DSG and LEF were administered to C-depleted, splenectomized rat recipients of guinea pig cardiac xenografts, and their effects on graft survival and production of anti-guinea pig antibodies were determined. Serial intragraft events were studied by immunohistology using monoclonal antibodies to rat leukocytes, cytokines, and novel proteins, including rat MØ lectin, which in other systems is important to MØ binding, activation, and target cell killing. Results. Median graft survival was 62 hr in cobra venom factor (CVF)-treated controls versus 108 hr (DSG), 129 hr (LEF), and 120 hr (DSG and LEF; all groups P<0.01 vs. CVF alone). LEF and DSG each decreased (immunoglobulin M [IgM]) or abrogated (IgG) posttransplant production of anti-guinea pig antibodies. Immunohistologic studies showed that each agent also inhibited graft infiltration by NK and T cells, and expression of various cytokines, including the chemokine monocyte chemoattractant protein-1 (MCP-1), but did not affect the tempo or extent of MØ infiltration. Consistent with this, the rapid induction of MØ lectin postxenografting, and induction of MØ lectin by rat MØ exposed to guinea pig cells in vitro, were unaffected by therapy with DSG and/or LEF. Conclusions. LEF or DSG along with CVF can result in the longest prolongation of xenograft survival yet reported in this model, in conjunction with a dampening of host mononuclear cell responses, including suppression of B cell activation. However, the persistent influx of MØ in this model, despite lack of C-, Fc receptor- or apparent chemokine-dependent mechanisms, suggests the presence of additional mechanisms for cell recruitment and activation. It was of importance that, in this regard, although MØ depletion is technically difficult and can lead to undesired effects, the demonstration of rapid MØ lectin induction postxenografting indicates opportunities for blockade of MØ recruitment and functions during DXR by use of anti-MØ lectin monoclonal antibodies or administration of competing sugars.