Induction of antibody response to liposome-associated Gross-virus cell-surface antigen (GCSAa).

The immunogenicity of a soluble fraction containing Gross-virus-associated cell-surface antigen (GCSAa) obtained from (C58NT)D lymphoma cells either by detergent (NP40) solubilization or by 3M KCl extraction, was studied in syngeneic W/Fu rats. Rats immunized by 2 s.c. injections of soluble antigen or soluble antigen mixed with empty liposomes and emulsified in complete Freund's adjuvant (CFA) failed to produce significant levels of cytotoxic antibodies to GCSAa. On the other hand, rats similarly immunized by negatively charged liposomes containing NP40-solubilized GCSAa, and emulsified in CFA, developed high and persistent levels of cytotoxic antibodies, and their response could even mimic that induced by viable (C58NT)D cells. A similar response could also be obtained in rats immunized with liposome-associated NP40-solubilized GCSAa, but without CFA. Rats immunized by comparable amounts of liposome-assocated 3M KCl-extracted GCSAa developed only low levels of cytotoxic antibodies, and their response was of shorter duration. These results strongly suggest that inclusion into liposomes of a solubilized proteic tumour-associated cell-surface antigen can provide an immunogen as potent as viable tumour cells in inducing an antibody response, and that the solubilization method may be critical.