Antigen presentation by B7^- nonprofessional APC does not prevent responses to solid tumor cells

The growth of tumors in vivo often is associated with immune suppression. In this report we tested whether the expression of a known antigen by tumor cells would inhibit the development of antitumor responses when the antigen was subsequently expressed in an immunogenic form. For this, we expressed a well-characterized surrogate tumor antigen, the nucleoprotein (NP) of the PR8 virus, in solid tumor cells. Although the NP⁺ tumor cells were not rejected in vivo and stimulated nondetectable CTL response in vitro, T cells from these mice differentiated in CTL following ip inoculation of PR8 virus and their tumors regressed. The results suggested that prior presentation of tumors antigens by tumors cells does not necessary preclude a response if the peptide is subsequently presented appropriately.