Formation of SV40 specific and H–2 restricted target cell antigen by somatic cell fusion

Abstract

Cytotoxic T lymphocytes (CTLs) to syngeneic Simian virus-40 (SV40)-transformed target cells lyse only SV40-transformed cells which are identical to the killer cells at the K and/or D loci of the H–2 complex in mice^1,2. In fact, CTLs have been shown to require autologous H–2 antigen expression for target cell lysis in a variety of syngeneic systems³. The dual specificity of these lymphocytes could indicate that both virus-coded and H–2 gene products are recognised and that interaction between viral and H–2 antigens on the tumour cell surface may be required to form the target antigen. However, serologically detectable SV40-specific antigens have not been found on the transformed cell surface. In addition, antisera to viral proteins do not block T-cell mediated lysis (CML) of syngeneic transformants⁴. If an SV40-specific moiety does not actually exist at the cell membrane, T-cell recognition might occur via an ‘altered self’ antigen where the virus codes for some activity which alters the H–2 antigens at the level of transcription or translation. To test this hypothesis the following experiments were designed: target cells were ‘manufactured’ by polyethylene glycol (PEG)-induced fusion of two cell lines; one being syngeneic to the CTL but not SV40 transformed and the other possessing the SV40 genome but differing from the effectors at the H–2 locus. The resulting multinucleated cells (heterokaryons) were then used as targets in the CML assay. Membrane components of heterokaryon cells have been shown to intermix⁵. In the present experiments we reasoned that if the target antigen is an H–2K or H–2D molecule which has been altered in transcription or translation, then simple mixing of membrane components would not lead to target antigen formation and cell lysis. If, on the other hand, separate SV40 induced and H–2 molecules are required for recognition then heterokaryon formation should lead to target antigen expression. Results described below support the latter hypothesis. Furthermore, these results show the simple mixing of cellular components is sufficient for a recognisable target antigen to form, and that protein synthesis is not required.