Generation of a Neutralizing Human Monoclonal Antibody Fab Fragment to SAG1 of Toxoplasma gondii Tachyzoites

Infect Immun. 2010 Oct 18. [Epub ahead of print]

Generation of a Neutralizing Human Monoclonal Antibody Fab Fragment to SAG1 of Toxoplasma gondii Tachyzoites

Fu YF, Feng M, Ohnishi K, Kimura T, Itoh J, Cheng XJ, Tachibana H.

Department of Medical Microbiology and Parasitology, Fudan University School of Medicine, Shanghai 200032, China; Department of Infectious Diseases, Tokyo Metropolitan Bokutoh General Hospital, Sumida-Ku, Tokyo 130-8575, Japan; Department of Infectious Diseases and Teaching and Research Support Center, Tokai University School of Medicine, Isehara, Kanagawa 259-1193, Japan.

Abstract
A combinatorial immunoglobulin gene library was constructed from lymphocytes in peripheral blood of a patient with toxoplasmosis and screened for production of human monoclonal antibody Fab fragments to recombinant SAG1 of Toxoplasma gondii. Two Fab clones, Tox203 and Tox1403, which consisted of a common heavy chain and different light chains, showed positive staining on the entire surface of tachyzoites in confocal microscopy. Sequence analysis of the heavy chain gene revealed that the closest germline V segments were VH3-23. The germline D segment was D1-7, and the closest germline J segment was JH4. In the light chain genes, the closest germline V segment was Vκ1-17 with the Jκ1 or Jκ4 segments. The dissociation constants of these Fab fragments with recombinant SAG1 were 3.09x10(-9) M for Tox203 and 2.01x10(-8) M for Tox1403, indicating that the affinity of Tox203 was 7 times higher than that of Tox1403. Preincubation of T. gondii tachyzoites with Tox203 significantly inhibited their attachment to cultured MDBK cells. Passive immunization of mice with Tox203 also significantly reduced mortality after challenge with T. gondii tachyzoites. This is the first report of bacterial expression of human monoclonal antibody Fab fragments to SAG1 of T. gondii. These results also demonstrate that human Fab fragments to SAG1 might be applicable for immunoprophylaxis of toxoplasmosis.

PMID: 20956568 [PubMed - as supplied by publisher]