FU-266, a mutant human myeloma cell line sensitive to hypoxanthine/aminopterin/thymidine (HAT), was transfected by protoplast fusion with DNA of the recombinant plasmid vector pSV2-neo , thus acquiring a dominant marker conferring resistance to the antibiotic G418. One of the resultant neoR clones, E-1, was fused to irradiated (500 rads) or unirradiated cells of the HAT-sensitive, G-418-sensitive, nonproducer mouse myeloma line X63-Ag8.653. Hybrid clones were selected in G-418 plus ouabain, thus preserving their HAT sensitivity. Small numbers of human chromosomes were retained in all such hybrids, but most of them ceased secreting human myeloma IgE(A). Selected hybrid clones were then tested as malignant fusion partners in a series of fusions with polyclonally activated human B lymphocytes and with antigen-primed human B lymphocytes, in some instances after transformation of the latter with Epstein-Barr virus. The yield of viable chimeric hybridomas has been consistently high, as has the proportion of hybridomas secreting human immunoglobulin molecules unpermuted with mouse or human myeloma heavy or light chains. Secretion by many subcloned hybridomas has been stable for over 6 months, and several antigen-specific human monoclonal antibodies have been generated. Thus these heteromyeloma cell lines appear to have significant advantages for human monoclonal antibody production.The development by Kohler and Milstein (1, 2) of the hybridoma procedure for mouse monoclonal antibody production has opened a new era in immunology. The fact that the cell lines thus derived are cloned and immortal assures the monoclonality and permanent availability of their antibody products, and antibody yield is limited only by cell culture volume. However, clinical use of xenoantibodies in human patients is likely to be severely limited by the fact that they will be treated as foreign proteins by the human immune system. Thus, for diagnostic and therapeutic applications in man, the production of human rather than mouse or other rodent monoclonal antibodies would clearly be desirable.Early attempts to generate immortalized human immunoglobulin-producing cells involved the fushion of human lymphoid cells with mouse myeloma cells to create chimeric hybridomas (3-9). However, with rare exceptions (6-8), such mouse-human hybridomas have tended to cease human immunoglobulin production due to the selective loss of human chromosomes (10, 11), or to disturbances of gene expression (12). Transformation of antigen-primed human B lymphocytes with the Epstein-Barr virus (EBV) (13-20) has had some success, but such cultures usually secrete low levels of antibody and have tended to cease antibody production entirely after a variable period (13). These problems have also been encountered in most, though not all, of the fusions of antigen-primed human B lymphocytes with EBV-transformed B lymphoblastoid cell. lines (LCL) (8,(21)(22)(23)(24)(25)(26)(27)(28). Moreover, such hybridomas usually secrete permuted immunoglobulin molecules derived from...

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