Gene-modified spontaneous Epstein-Barr virus-transformed lymphoblastoid cell lines as autologous cancer vaccines: Mutated p21 ras oncogene as a model

The transfer of genes coding for tumor antigens (Ags) into Ag-presenting ce lls is a promising strategy to develop cancer vaccines for patients not lim ited by major histocompatibility complex restriction. To test whether autol ogous lymphoblastoid cell lines (LCL) can be used as an alternative to dend ritic cells for Ag presentation, we established LCL by spontaneous growth i n cyclosporin-containing medium in vitro (SP-LCL). SP-LCL, which have an ad vantage over B95-8-transfected LCL in that they carry no risk of introducin g a new infectious agent when used for vaccination, served as a permanent s ource for transfection with an episomal Epstein-Barr virus-based expression vector encoding the Ki-ras p21 oncogene carrying a point mutation at codon 12 (muRas) as a model tumor Ag. The ability of mu Ras-transfected SP-LCL ( muRas-LCL) to induce immunoreactivity was determined in vitro. After electr oporation with an optimized protocol, muRas-LCL expressed mutated ras pepti des for a considerable period of time (at least 8 weeks) on the cell surfac e. The transfection procedure did not affect the expression of the costimul atory molecules B7.1, intercellular adhesion molecule-1, and leukocyte func tion associated Ag-3 by SP-LCL. muRas-LCL were able to induce muRas-specifi c cytotoxic T lymphocytes from three of th ree healthy donors and one of on e patient with pancreatic carcinoma. Our results suggest that the gene tran sfer of muRas sequences to SP-LCL leads to an endogenous processing of this Ag in the major histocompatibility complex class I pathway and to function al presentation of antigenic peptides to CD8(+) T lymphocytes. Autologous S P-LCL can serve as an unlimited renewable source for autologous cellular va ccines and appear to be good candidates as presenters for a wide range of h uman tumor Ags.