The effects of differentiation inducer sodium phenylacetate on antigen expression of human breas cancer MDA-453 cells and their activity to induce allospecific cytotoxic T lymphocytes (CTL) in peripheral blood mononuclear cells (PBMC) were investigated. The results showed that sodium phenylacetate could the expression of HLA-A2 molecules, intercellular adhesion molecule-1 (ICAW-1) and protein HER-2/neu on the surface of MDA-453 cells. In mixed allogenic PBMC/MDA-453 cell (shared the same HLA-A2 locus) culture in vitro, MDA-453 cells could stimulate PBMC growth in the presence of low dose of interleukin-2 (IL-2 ), but sodium phenylacetate-treated MDA-453 cells were more potent for stimulating PBMC growth than the untreated cells. PBMC obtained from frow culture at 7th day could kill MDA-453 cells. The cytotoxicity of PBMC obtained form the culture at 21st day was restricted to MDA-453 cells (PBMC could hardly kill K562 and Raji cells), so the PBMC at this time could be called allospecific CTL. Sodium phenylacetate-treated MDA-453 cells were more potent for inducing allospecific CTL than the untreated cells in mixed allogenic PBMC/MDA-453 cell culture. In summary, sodium phenylacetate could increase the activity of breast cancer MDA-453 cells to induce allospecific CTL with a corresponding effect on antigen expression. The effects of differentiation inducer sodium phenylacetate on antigen expression of human breas cancer MDA-453 cells and their activity to induce allospecific cytotoxic T lymphocytes (CTL) in peripheral blood mononuclear cells (PBMC) were investigated. The results showed that sodium phenylacetate could the expression Of HLA-A2 molecules, intercellular adhesion molecule-1 (ICAW-1) and protein HER-2/neu on the surface of MDA-453 cells. In mixed allogenic PBMC/MDA-453 cell (shared the same HLA-A2 locus) Culture in vitro, MDA-453 cells could stimulate PBMC growth in the presence of low dose of interleukin-2 (IL-2 ), but sodium phenylacetate-treated MDA-453 cells were more potent for stimulating PBMC growth than the untreated cells. PBMC Was obtained from frow culture at 7th day could kill MDA-453 cells. The cytotoxicity of PBMC obtained form the culture at 21st day was restricted to MDA-453 cells (PBMC could hardly kill K562 and Raji cells), so the PBMC at this time could Be called allospecif Ic CTL. Sodium phenylacetate-treated MDA-453 cells were more potent for inducing allospecific CTL than the untreated cells in mixed allogenic PBMC/MDA-453 cell culture. In summary, sodium phenylacetate raised increased activity of breast cancer MDA-453 cells to Induce allospecific CTL with a corresponding effect on antigen expression.