In vitro inhibition of Cryptosporidium parvum infection by human monoclonal antibodies.

Cryptosporidium parvum infection of the small epithelial intestine causes unremitting diarrhea and malabsorption that can lead to chronic and sometimes fatal illness in patients with AIDS. The illness may be ameliorated by passive oral immunoglobulin therapy. The objective of this study was to produce anti-Cryptosporidium human monoclonal antibodies for evaluation as potential therapy. All human monoclonal cell lines that produced C. parvum antibodies were originally generated from the peripheral blood lymphocytes of a human immunodeficiency virus-seronegative woman. She had recovered from C. parvum infection and had a high specific antibody titer. Hybridization of these lymphocytes with a tumor cell line was accomplished by hypo-osmolar electrofusion. Twelve clones were identified by enzyme-linked immunosorbent assay (ELISA) as secreting anti-Cryptosporidium antibodies after the initial hybridization. From the 12 positive clones, two high antibody-secreting clones, 17A and 17B, were maintained in long-term culture. A second hybridization produced two other human monoclonal cell lines, EC5 and BB2. Human monoclonal antibody from the first two cell lines bound to C. parvum sporozoites and oocysts by immunofluorescence. The ability of human monoclonal antibodies to inhibit C. parvum infection in vitro was assessed by using a human enterocyte cell line, HT29.74. The antibodies of the four different human hybridomas inhibited infection by 35 to 68% (P < 0.05) compared to a control irrelevant human monoclonal antibody derived in a similar fashion. Human monoclonal antibodies are candidate molecules for immunotherapy of C. parvum infection.