Pharmacologic immunosuppressive therapy and extracorporeal immunoadsorption in the suppression of anti-alpha Gal antibody in the baboon

The aim of this study was to deplete baboons of anti-alpha galactosyl (alph a Gal] antibody and attempt to maintain depletion by pharmacologic immunosu ppressive therapy (PI). In 12 experiments, involving nine baboons, repeated extracorporeal immunoadsorption (EIA) was carried out by plasma perfusion through immunoaffinity columns of synthetic alpha Gal trisaccharide type 6. Five of the baboons were immunologically naive and four had undergone vari ous procedures at least 6 months previously. All, however, had recovered ly mphohematopoietic function and (with one exception) had levels of anti-alph a Gal antibody within the normal range. Eleven protocols included continuou s i.v. cyclosporine (to maintain whole blood levels of approximately 1,600 ng/ml). In addition, in ten protocols, the baboon received one or more of t he following drugs: cyclophosphamide (1-20 mg/kg/day), mycophenolate mofeti l (70-700 mg/kg/day), brequinar sodium (1-12 mg/kg/day), prednisolone (1 mg /kg/day), melphalan (0.15-0.6 mg/kg/day), methylprednisolone (125 mg/day x3 ), and antilymphocyte globulin (ATG) (50 mg/kg/day x3). EIA was carried out on 1-9 occasions in each study and was temporarily successful in removing all antibody. When no PI was administered, antibody returned close to pre-E IA levels within 48 hr. Cyclosporine alone delayed the rate of antibody ret urn only slightly. While EIA was continuing on a daily or alternate day sch edule, antibody levels (both IgM and IgG) were maintained at 20-45% of pre- EIA levels. Once EIA was discontinued but PI maintained, IgM rose to 40-90% and IgG to 30-60% of pre-EIA levels. In vitro testing demonstrated signifi cant cytotoxicity to pig cells at these antibody levels. We conclude that i ) EIA utilizing columns of alpha Gal trisaccharide is successful in tempora rily depleting baboons of anti-alpha Gal antibody, but ii) none of the PI r egimens tested suppressed antibody production to levels which would be expe cted to prevent antibody-mediated rejection of pig xenografts. Additional s trategies will therefore be required if xenotransplantation is to become a clinical reality.