Reassessment of autoreactivity of the broadly neutralizing HIV antibodies 4E10 and 2F5 and retrospective analysis of clinical safety data

BACKGROUND: The broadly neutralizing recombinant human HIV-1 antibodies 4E10, 2F5 and Igh1b12 are reported to have autoreactive potential, which is significant for HIV-1 vaccine development and passive immunotherapy using these antibodies. OBJECTIVE: To investigate the clinical relevance of these findings in subjects receiving passive immunotherapy with these antibodies. METHODS: Four types of investigations were performed: (1) Investigation of clotting parameters in an ongoing clinical study with 4E10, 2F5 and 2G12. (2) Mixing experiments of pooled plasma with the same antibodies. (3) Retrospective analysis of serum from patients who received passive immunotherapy with 4E10, 2F5 and 2G12 either alone or in combination. (4) Assessment of clinical safety data obtained after 418 infusions with these antibodies. RESULTS: Standard clinical assays confirmed that 4E10 showed low-level cross-reactivity with cardiolipin, while previously reported cardiolipin cross-reactivity for 2F5 could not be confirmed. High serum titers of 4E10 induced mild prolongation of the activated partial thromboplastin time, which resolved with the wash out of 4E10. Neither 2F5 nor 2G12 affected coagulation. Repeated high-dose infusions of the monoclonal antibody combination were well tolerated with no incidence for thrombotic complications after 418 infusions in 39 subjects. CONCLUSIONS: Monoclonal antibody 4E10 but not 2F5 or 2G12 showed autoreactive binding specificities. Infusion of 4E10 resulted in transient low anticardiolipin titers. Although an increased thromboembolic risk cannot definitely be excluded, this risk appears to be low and likely depend on underlying disorders.     

Electron microscopic and immunochemical analysis of the broadly neutralizing HIV-1-specific, anti-carbohydrate antibody, 2G12

2G12 is one of only a few cloned antibodies with broadly neutralizing specificity to HIV-1 envelope proteins. Crystallographic and electron microscopic (EM) data showed that the Fab arms are locked together via a novel VH domain exchange. Both the conventional and the unprecedented additional VH-VH antigen binding sites show specificity for high mannose oligosaccharides on the silent face of gp120. We have now extended the EM and biochemical analysis of 2G12. Unligated 2G12 IgG1 molecules clearly show paired (parallel attached) Fab arms in the "doughnut" configuration attached to the Fc both in individual and computationally averaged images. A minority of the IgG molecules in the 2G12 prep showed the open "Y" configuration of conventional IgG. The averaged EM image compares well to the atomic structure model of 2G12. Papain digests of 2G12 yielded paired Fab arms (Fab dimer), as observed by EM, which dissociated into Fab-sized fragments in non-reducing SDS-PAGE. Purified 2G12 reduced and alkylated H and L chains can reassociate to form IgG molecules with the Fab dimer configuration and can combine with L and H chains from conventional human IgG to form hybrid molecules. 2G12 is heavily aggregated following brief acid exposure possibly as a result of its unique structure. A model of the aggregation process is proposed. An anti-Id MAb was shown by EM to react with neither the conventional nor additional antigen binding sites, but bound to the lateral faces of the Fab arms of intact, reduced and alkylated, and reconstructed 2G12 molecules. Efforts to identify IgG molecules with a similar intertwined Fab dimer structure in a large IgG pool were unsuccessful.     

Biochemical mechanism of keratin degradation by the actinomycete Streptomyces fradiae and the fungus Microsporum gypseum: A comparison

Two keratinolytic organisms, the procaryote Streptomyces fradiae and the fungus Microsporum gypseum, were cultured on sterile sheep's wool in a mineral solution. The loss in substrate was recorded and the degradation products in the cultivation fluid were analyzed. In M. gypseum the key reaction was the cleaving of the substrate disulfide bridges by means of sulfite excreted into the medium. Keratin denatured by ?sulfitolysis’? was further attacked by extracellular proteases. A typical finding was the accumulation of peptides containing S-sulfocysteine, the product of sulfitolysis of cystine. The overall excess of sulfur was removed by oxidation to sulfite and to sulfate, which was the main and final product. In S. fradiae the degradation was faster. The results did not prove that sulfite formed and the concentration of sulfate in the medium remained negligible. Neither could cysteine desulfhydration and hydrogen sulfide excretion be demonstrated. The medium was found to contain relatively high concentrations of sulfhydryl compounds, evidently cysteine-containing peptides. Therefore, in this microorganism, keratin was most likely denatured by the direct reduction of cystine bridges. The main product of the elimination of excess sulfur was inorganic thiosulfate, which accumulated in the medium.