Production of human monoclonal antibodies to B lymphocyte cell surface antigens by in vitro immunization and human-human hybridoma technology

We attempted to produce human monoclonal IgM antibodies to class II HLA antigens by in vitro immunization of human splenocytes with affinity purified HLA or irradiated whole lymphoblastoid B cells using the adjuvant muramyl dipeptide and IL-2. Two fusions where affinity purified HLA was used to stimulate the in vitro immunization produced no hybrids secreting antibodies against the stimulating antigen. However, 13.1% of 381 hybrids from eight fusions were positive by CELISA when whole cells were used to immunize. These antibodies were reactive with a wide range of cell types and were not directed to HLA. It proved difficult to characterize them, possibly because of low affinity. One reacted in Western blots with a 200 kD antigen, but this was exceptional. Most bound to a small percentage of cells in flow cytometry and did not lyse target cells in cytotoxicity assays. Control fusions were performed and similar antibodies were obtained from 2.6% of235 hybrids. These data suggest that in vitro immunization using the protocol outlined can increase the frequency of some antibodies, but that they may represent a very primitive lineage which does not have the specificity and affinity required to prove useful as diagnostic or therapeutic agents.