Inhibition of HLA antibody cytotoxicity by intravenous immunoglobulin G F(ab ')(2) dimers, monomers, and monovalent F(ab)

IVIgG preparations are clinically relevant to sensitized transplant candida tes because they inhibit HLA alloantibody in vitro and in vivo. We hypothes ized chat IVIgG F(ab')(2) idiotypic-antiidiotypic dimers may possess a grea ter immunomodulatory capacity when remonomerized than non-dimerizable F(ab' )(2) monomers in IVIgG. We reasoned that when 60-75% of potential antiidiot ypic IVIgG monomers fail to bind to IVIgG molecules in a large pool of plas ma donors (>10,000), IVIgG monomers may fill to inhibit HLA idiotypic antib odies of sensitized transplant candidates. In the first series of AHG T cel l crossmatches, non-fractionated IVIgG F(ab')(2) was found to inhibit titer ed HLA antibodies in 13 out of 29 (45%) crossmatch combinations. Crossmatch inhibition was incomplete, i.e., a particular titered HLA antibody specifi city was not always inhibited by IVIgG F(ab')(2) in every HLA antigen-match ed target cell crossmatch. Next, the IVIgG F(ab')(2) product was fractionat ed into F(ab')(2) dimers, F(ab')(2) monomers and Fab monovalent components by size exclusion high pressure liquid chromatography (HPLC) and retested i n cross-marches which previously demonstrated inhibition. The percent of cr ossmatches that were inhibited by HPLC F(ab')(2) IVIgG fractions ill three separate experiments was statistically similar for pH 4.0 remonomerized dim ers, 82%; pH 6.0 dimers, 50%; monomers, 64%; and monovalent Fab, 64% (p = 0 .50). Soluble class I HLA antigen was undetectable in IVIgG F(ab')(2) by an ELISA assay. In conclusion, IVIgG dimers and monomers appear to have simil ar immunomodulatory capacities, and separation of whole IVIgG products into dimer and monomer fractions does not appear to be warranted. Further, IVIg G produces should be tested for optimal HLA antibody inhibition ill vitro p rior to in vivo therapy. 492-499 (1999). (C) American Society for Histocomp atibility and Immunogenetics, 1999. Published by Elsevier Science Inc.