Several human lymphoblastoid cell lines and human myeloma cell lines have been suggested for fusion with human B lymphocytes. Fushion partners of purely human origin are particularly advantageous because the monoclonal antibodies produced by hybridomas prepared from such fusion partners and human B lymphocytes are more likely to be compatible with the natural human immune response system than antibodies produced by non-human or mixed hybridomas. Mouse-human hybridomas, for example, tend to lose their human chromosomes quite quickly, while hybridomas of human origin typically exhibit good stability with respect to human chromosomes.
Of available human myeloma fusion partners, the plasmacytomas have a well-established cell morphology characterized by abundant rough endoplasmic recticulum, few free polyribosomes, numerous mitochondria and a well-developed Golgi appartus. Plasmacytomas also exhibit a high rate of immunoglobulin secretion. Unfortunately, plasmacytoma cells only rarely can be continuously maintained in vitro. Additionally, most plasmacytomas have doubling times between 36 and 73 hours and may require a plasmacyte-stimulating factor for proliferation in tissue culture. The frequency of hybrid formation using such cells also generally is quite low.
While available human lymphoblastoid cells exhibit higher fusion frequencies, are more easily maintained in tissue culture and have doubling times of about 20 to 30 hours, these cells do not have a well-developed rough endoplasmic recticulum and secrete much less immunoglobulin.
A purely human cell exhibiting some of the desirable characteristics of both plasmacytoma and lymphoblastoid cells would be particularly advantageous.