Removal Of Baboon And Human Antiporcine Igg And Igm Natural Antibodies By Immunoadsorption

Abstract

The safe and effective removal of xenoreactive antibodies in the peritransplant period is likely to be critical for the clinical application of xenotransplantation involving disparate donor species, such as the pig. In an effort to develop an improved method for antibody removal in xenotransplantation, we have studied reusable antihuman antibody (Ig) columns in vitro and in vivo. Two types of columns were tested: (1) an antihuman Ig column containing polyclonal sheep antihuman IgG (heavy- and light-chain-specific) conjugated to sepharose CL-4B (Ig-Therasorb), and (2) an antihuman Ig column using polyclonal antihuman IgM (mu-chain-specific) conjugated to sepharose. Passage of human or baboon plasma through the Ig-Therasorb column resulted in 97.5% and 78.4% mean reductions in total IgG and IgM, respectively. Reductions in total IgG and IgM correlated with lowering of antipig IgG (54-486 fold) and IgM (9-54 fold) antibody titers as assessed by pig endothelial cell ELISA. The ability of the Ig-Therasorb to significantly reduce IgM may be attributed to the light chain specificity of this column. With the anti-IgM column, marked reductions in total (82.6-83.9%) and antipig (27-54 fold) IgM in human and baboon plasma occurred, while levels of total and xenoreactive IgG were slightly affected. Other than a dilutional effect, neither column resulted in significant reduction in albumin, fibrinogen, factor 5, and factor 8. Repeated in vivo use of either column in baboons achieved reductions in IgG and IgM that closely followed the results of our in vitro studies. No subject morbidity or mortality occurred. Use of the Ig-Therasorb column with immunosuppression in two baboons receiving pig renal xenografts achieved sustained reductions in antipig antibodies and prevented hyperacute rejection. Subjects were sacrificed at 11 and 13 days posttransplant with functioning xenografts and were found to have no evidence of vascular xenograft rejection. We conclude that anti-Ig columns represent a safe and effective method for antibody removal, without several of the limitations of other antibody removal techniques. Also, columns appear to be safe for repeated antibody removal in the posttransplant period.