Characterization of heteromyeloma fusion partners which promote the outgrowth of porcine hybridomas

Abstract

Production of porcine monoclonal antibodies for use in research and immunotherapy has been hampered by the lack of suitable fusion partners which promote high efficiencies of hybridoma out-growth and immunoglobulin synthesis. To overcome these obstacles, five heteromyeloma fusion partners (HM-1,2,3,4 and 5) were constructed by successively fusing porcine lymphocytes with murine myeloma cells or murine x bovine heteromyeloma cells. Following section of hypoxanthine/aminopterin/thymidine (HAT)-sensitive mutants, karyotypes, growth rates and surface phenotypes of the heteromyelomas were determined. Karyotyping revealed an increase in the mean number of chromosomes present in HM-1,4 and 5 cells. Peak doubling times of the parental and HM cells ranged between 12.2 and 17.4 h. Uisng flow microfluorimetry and monoclonal antibodies specific for class I/II major histocompatability antigens, it was determined that the surface phenotype of HM-1,2,3,4 and 5 resembled that of the parental murine X63 myeloma cells. HM 1,2,3,4 and 5 were evaluated for their abilities to serve as fusion partners. Highest percentages of hybrid outgrowth (37%) and immunoglobulin synthesis (52%) were observed when HM-1 was fused with procine lymphocytes. When cloned, percentage of outgrowth and immunoglobulin synthesis increased if HM-1 and HM-2 were used as fusion partners. Cryopreservation of HM-1 and HM-2 did not adversely affect their abilities to promote hybrid outgrowth or immunoglobulin synthesis. During the first week following fusion of porcine lymphocytes with heteromyelomas, murine thymocytes were found to be essential for survival of the nascent hybrids. To confirm that immunoglobulin secreted by hybridomas was of porcine and not murine or bovine origin, culture supernates were subjected to SDS gel electrophoresis, electroblotted and identified. using species-specific isotyping reagents. Two of four cell lines tested secreted porcine light chains and one of four cell lines secreted whole IgM molecules. This paper is the first to describe porcine heteromyelomas for use as fusion partners. Similar to findings of human and bovine studies, our data suggest that heteromyeloma fusion partners perform better than rodent myelomas for creating hybridomas synthesizing porcine immunoglobulin.