The general principle for tumor cells to escape from immune surveillance is to prevent tumor antigens frombeing recognized by the immune system.Many methods have been developed to increase the immunogenecityof the tumor cells.The most efficient methods are able to force tumor cells to present their own tumor antigensto the immune system.Stimulating Th cells by converting tumor cells into MHC class II+/Ii-antigen presentingcells is one of the most efficient technologies.Using antisense methods,we suppress the expression of the Iiprotein that normally co-expresses with MHC class II molecules and blocks the antigenic peptide binding siteof MHC class II molecules during synthesis in the endoplasmic reticulum.In such tumor cells,the“unprotected”MHC class II molecules pick up endogenous tumor antigenic peptides,which have beentransported into the ER for binding to MHC class I molecules.Simultaneous presentation of tumor antigens byboth MHC class I and II molecules generates a robust and long-lasting anti-tumor immune response.MHCclass II+/Ii-tumor cells are potent tumor cell vaccines and also cure a significant number of animals with renaland prostate tumors.We have developed analogous human gene vectors that are suitable for most patients andcancers.Cellular & Molecular Immunology.2004;1(3):180-185. The general principle for tumor cells to escape from immune surveillance is to prevent tumor antigens from being developed by the immune system. Many methods have been developed to increase the immunogenecityof the tumor cells. The most efficient methods are able to force tumor cells to present their own tumor antigensto the immune system .timulating Th cells by converting tumor cells into MHC class II + / Ii-antigen presenting cells is one of the most efficient technologies. Using Anti-sense methods, we suppress the expression of the Iiprotein that normally co-expresses with MHC class II molecules and blocks the antigenic peptide binding site of MHC class II molecules during synthesis in the endoplasmic reticulum. Such tumor cells, the “unprotected” MHC class II molecules pick up endogenous tumor antigenic peptides, which have beentransported into the ER for binding to MHC class I molecules. Simultaneous presentation of tumor antigens byboth MHC class I and II molecules generate a robust and long-lasting anti-tumor immune response. MHC Class II + / Ii-tumor cells are potent tumor cell vaccines and also cure a significant number of animals with renaland prostate tumors. We have developed analogous human gene vectors that are suitable for most patients and patients. Cellular & Molecular Immunology. 2004; 1 (3): 180-185.