INDUCTION OF FUNCTIONAL EMPTY CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX GLYCOPROTEINS BY PHOTOACTIVATED 8-METHOXYPSORALEN

CD8+ cytotoxic T lymphocytes (CTLs) bind to and selectively lyse tumor cells via T-cell receptor recognition of distinctive peptide antigens presented in the context of surface major histocompatibility complex class I(MHC class I) glycoproteins. Several human and experimental ani mal tumors express distinctive MHC class I-associated peptides, which can be selectively targeted by specific CD8+ CTLs. Malignant cells exp ressing low quantities of these peptides are poor inducers of CTL resp onses. Therefore, we have developed a method of externally loading inc reased amounts of antigenic peptides onto MHC class I molecules. In or der to induce ''empty'' fillable MHC class I molecules capable of bind ing antigenic peptides, we exposed transformed murine T cells (RMA) to low dose (3 joules/cm(2)) ultraviolet A energy and 8-methoxypsoralen (100 ng per mi). Presence of ''empty'' class I molecules was ascertain ed by ''meltdown'' or loss of the thermodynamically unstable cold-indu ced ''empty'' molecules as identified by cytofluorography at 37 degree s C. Retained function of ''empty'' molecules was determined by their stabilization through addition of peptides of the correct size and seq uence motif, prior to exposure to physiologic temperature.