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 atthe cell surface of RMA‐S. Rauscher peptides are presented tovirus‐specific CTL in the groove of both the class I H2K^b and D^b molecules, but at a low level. Culture of RMA‐S cells at room temperature increases theirsusceptibility to CTL. The RMA‐S defect thus affects, but not totally abrogates, Rauscher peptide presentation by MHC class I molecules via the endogenous pathway. Thisindicates that the RMA‐S antigen processing deficit is not absolute.