Induction and expansion of an anti-tumor immune response by B7-1+ tumor cells in dependence on the anatomical site of delivery and the dose applied

Immunization with Sp6 hybridoma cells transfected with B7-1 cDNA (Sp6/B7) elicited a protective response against wild type (w.t.) Sp6 exclusively through the subcutaneous (s.c.) route. Protection could be confined to sites in the same anatomical quarter as the immunizing injection or extended to distant anatomical districts by increasing the tumor cell dose. The anatomical extention of protection correlated with an expansion of Sp6-specific cytotoxic T-lymphocyte activity. Neither P1A or gp70 tumor antigens appeared to be involved in this tumor-specific cytotoxic response. Although RT-PCR analysis of Sp6 and Sp6/B7 total RNA indicated the presence of transcripts specific for both P1A and gp70 antigens, splenocytes from Sp6/B7-immunized mice did not show any relevant cytotoxic activity specific for these antigens, indicating that the Sp6-specific cytotoxic reponse elicited by immunization with Sp6/B7 is against different tumor antigens.