Cytotoxic T lymphocytes against the antigen-processing-defective RMA-S tumor cell line.

RMA-S is an antigen processing-defective cell line, obtained from a Rauscher virus-induced tumor. The cells express only a low level of cell surface major histocompatibility complex (MHC) class I molecules, which are supposed to be devoid of internally derived antigenic peptides. We investigated Rauscher virus expression and Rauscher peptide presentation to virus-specific cytotoxic T lymphocytes (CTL) by this cell line. Viral proteins are expressed properly, both intracellularly and at the cell surface of RMA-S. Rauscher peptides are presented to virus-specific CTL in the groove of both the class I H-2Kb and Db molecules, but at a low level. Culture of RMA-S cells at room temperature increases their susceptibility to CTL. The RMA-S defect thus affects, but not totally abrogates, Rauscher peptide presentation by MHC class I molecules via the endogenous pathway. This indicates that the RMA-S antigen processing deficit is not absolute.