a-Fetoprotein (AFP) is a self protein expressed by fetal liver at high levels, but is transcriptionally repressed at birth. AFP is up-regulated in hepatocellular carcinomas, and patients with active disease could have plasma levels as high as1mg/mL.We previously identified four immunodominant HLA-A*0201-restricted peptides [hAFP [137][138][139][140][141][142][143][144][145] (PLFQVPEPV), hAFP [158][159][160][161][162][163][164][165][166] (FMNKFIYEI), hAFP [325][326][327][328][329][330][331][332][333][334] (GLSPNLNRFL), and hAFP 542-550 (GVALQTMKQ)] derived from human AFP that could stimulate specific T cell responses in healthy donor peripheral blood lymphocytes in vitro. We conducted a phase I/II clinical trial in which HLA-A*0201patients with AFP-positive hepatocellular carcinoma were immunized with three biweekly intradermal vaccinations of the four AFP peptides pulsed onto autologous dendritic cells (DC). DCs were prepared from adherent peripheral blood mononuclear cells cultured with granulocyte-macrophage colony-stimulating factor and interleukin-4 for 7 days. Sixteen subjects were enrolled and 10 were treated. Peripheral blood lymphocytes were isolated from these patients before, during, and afterAFP peptide/DC immunization and were tested ex vivo with MHC tetramer and IFNg ELISPOTanalysis. Six of 10 subjects expanded statistically significant levels of AFP-specificTcells postvaccine to at least one peptide by MHC tetramer. Also, 6 of10 subjects increased IFNg producing AFP-specificTcell responses to at least one of the peptides postvaccination, by ELISPOT. We conclude that the humanTcell repertoire is capable of responding to the AFP self antigen after the administration of AFP peptidepulsed DC even in an environment of high circulating levels of this oncofetal antigen.We originally reported that the self antigen a-fetoprotein (AFP) could be recognized by both murine and human T cells and serve as a tumor rejection antigen in a murine tumor model (1, 2). AFP is produced by 50% to 80% of hepatocellular carcinomas (HCC), and its measurement in serum has played an important role in diagnosis and monitoring responses to treatment for the last several decades (3). AFP is expressed by the fetal liver with serum levels of 1 mg/mL, but is transcriptionally repressed shortly after birth (4 -6). Our ability to generate potent AFP-specific T cell immunity to murine AFP in mice and to human AFP in in vitro human T cell cultures clearly indicates that, despite being exposed to high plasma levels of this protein during embryonic development, some AFP-specific T cells are not deleted during ontogeny.Using a combination of strategies (HLA-A*0201/K b transgenic mice, human T cell cultures, and mass spectrometric analysis), we identified four immunodominant AFP-derived peptides that are naturally processed and presented in the context of HLA-A*0201 (1, 7 -9). At least three of these peptides could be isolated from the surface of an HLA-A*0201/AFP-positive human HCC cell line, HepG2. These peptides can stimulate T ...