Isolation of human monoclonal antibodies binding to B fragment of diphtheria toxin

Abstract

Human tonsillar lymphocytes immunized in vitro with diphtheria toxoid were fused with the heteromyeloma cell line SP2/HPT. Hybrids were selected on hypoxanthine-thymidine aminopterin (HAT) medium and assayed for antibody production both by ELISA and Western blotting. Four stable hybridoma cell lines producing 3–7 μg/mL of human IgG₁ antibodies were isolated. In Western blotting studies these antibodies show binding to the B fragment of diphtheria toxin. Cells from the subclone P2-13/G35 were injected i.p. in pristane-primed nude mice, and ascites fluid was collected after 4–6 weeks. The monoclonal antibody neutralized the cytotoxicity of diphtheria toxin in the Vero cell assay system. This human monoclonal antibody may have a potential in the immunotherapy of diphtheric disease.