Forssman antigen and phase specific fetal antigens: an evaluation of their role in SV40 tumor immunity

Forssman antigen in BK virus-induced tumor cell lines

A complement-mediated microcytotoxicity assay was used to detect Forssman antigen in BK virus (BKV)-induced tumor cells. BKT-1B, a transplantable hamster tumor cell line, contained Forssman antigen as did some other hamster cell lines tested for comparison. A rat embryo cell line transformed by BKV in vitro was negative for Forssman antigen. The presence of forssman antigen in hamster cell lines was confirmed by absorption experiments of rabbit forssman antiserum with the tumor cells, although in quantitative terms the results obtained by the two techniques were somewhat different. Immunization of rabbits with tumor cells also induced production of Forssman antibody; a much weaker response was observed in hamsters and rats.

SV40 tumor rejection induced by vesicular stomatitis virus bearing SV40 tumor-specific transplantation antigen (SV40-TSTA). I. Specificity of immunoprotection and effect of enzyme treatment on TSTA activity

Highly purified vesicular stomatitis virus (VSV) was obtained from VSV-infected SV40-transformed hamster cell lines. Immunization with this virus protected hamsters against challenge with SV40-transformed cells (TSV5-cl2). This protection was obtained regardless of the source of the SV40-transformed cells (e.g. cat, rat, hamster) used to produce VSV, and was therefore associated with the SV40 tumor-specific transplantation antigen (SV40-TSTA). Furthermore, when grown on spontaneously transformed cell lines or on cells transformed by a different oncogenic DNA virus, such as polyoma virus, the VSV failed to protect against the SV40-induced tumor. It was concluded that the SV40-TSTA activity of purified VSV is due to the incorporation of SV40-TSTA within the viral envelope. When VSV was treated with proteolytic enzymes (bromelain, trypsin) no loss of TSTA-induced tumor rejection was observed, although VSV had lost its ability to induce virus-neutralizing antibody. This clearly demonstrates that the TSTA activity is not related to the viral spikes. Phospholipase C suppressed the TSTA activity but neutralizing activity was still detectable in the anti-VSV sera. The results presented here demonstrate that the protection afforded by VSV is highly specific. It is particularly interesting that SV40-TSTA activity may be conveyed by the lipid core of the viral envelope.