Antigenic expression in somatic hybrids and the use of cell fusion in tumor xenogenization

The evidence has been reviewed on antigenic expression in somatic cell hybrids. Genetically determined antigens, such as H-2, HLA, and β₂-microglobulin show a codominant (autonomous) expression, with one exception: Hybrids produced by fusing the virtually H-2-negative Ehrlich ascites tumor with other cells, In this case, the antigenic expression of the partner is suppressed but can reappear after chromosome losses. Fushion of β₂-microglobulin and HLA negative cells (Daudi) with microglobulin-positive mouse or human cells leads to a reexpression of the missing HLA. Another situation of minor histocompatibility complex (MHC) antigen reexpression concerns the TA3/Hauschka ascites tumor, low in H-2 antigens, where fusion with normal fibroblast partners of a different H-2 specificity leads to full reexpression of the minimally expressed H-2^a. Antigens and other markers related to differentiation are usually suppresed when expressor cells of a given lineage are fused with non-expressor cells of a different lineage. In contrast, when expressor and non-expressor cells of the same linage are fused, co-dominant expression appears to be the rule, like in the genetically determined antigen systems. Virally determined and tumor-associated antigens show a whole range of behaviour. This has been discussed for polyoma T antigen and tumor specific transplantation antigen TSTA), Epstein-Barr virus (EBV)-associated antigens, and murine C-type virus-determined antigens. The usefulness, or otherwise, of somatic hybrids as an approach to xenogenization, i.e., augmentation of tumor immunogenicity, has been discussed. Examples will be given for both positive and negative findings. It appears that while certain somatic hybrids can show an increased immunogenicity, this is by no means the rule and the relevant variables are not yet understood.