RASA, a recombinant single-chain variable fragment (scFv) antibody directed against the human sperm surface: Implications for novel contraceptives

Abstract

Background: A recombinant single-chain variable fragment (scFv) antibody was engineered to a tissue-specific carbohydrate epitope located on human sperm agglutination antigen-1 (SAGA-1), a sperm glycoform of CD52. Methods and results: cDNAs encoding the variable regions of the S19 [IgG1κ] monoclonal antibody (mAb) were identified, linked, and cloned into the pCANTAB 5E vector. The recombinant anti-sperm antibody (RASA) was expressed in E. coli HB2151 cells as a 29 kDa monomer and, remarkably, also formed multimers of ∼60 and 90 kDa. RASA reacted with the endogenous SAGA-1 antigen by Western blot analysis, labelled the entire human sperm surface by indirect immunofluorescence, and aggregated human spermatozoa in a tangled (head-to-head, head-to-tail, tail-to-tail) pattern of agglutination, as was also observed with the native S19 mAb. Conclusions: These results demonstrate that active recombinant antibodies can be produced to a tissue-specific carbohydrate epitope on the human sperm surface, thereby opening opportunities for novel contraceptive agents.