Peptide vaccination elicits leukemia-associated antigen-specific cytotoxic CD8 T-cell responses in patients with chronic lymphocytic leukemia

The receptor for hyaluronic acid-mediated motility (RHAMM) is a tumor-associated antigen in chronic lymphocytic leukemia (CLL). CD8 + T cells primed with the RHAMM-derived epitope R3, which is restricted by human leukocyte antigen (HLA)-A2, effectively lyse RHAMM + CLL cells. Therefore, we initiated a phase I clinical trial of R3 peptide vaccination. Six HLA-A2 + CLL patients were vaccinated four times at biweekly intervals with the R3 peptide (ILSLELMKL; 300 μg per dose) emulsified in incomplete Freund's adjuvant; granulocyte-macrophage colony stimulating factor (100 μg per dose) was administered concomitantly. Detailed immunological analyses were conducted throughout the course of peptide vaccination. No severe adverse events greater than CTC I° skin toxicity were observed. Four patients exhibited reduced white blood cell counts during vaccination. In five of six patients, R3-specific CD8 + T cells were detected with the corresponding peptide/HLA-A2 tetrameric complex; these populations were verified functionally in four of five patients using enzyme-linked immunosorbent spot (ELISpot) assays. In patients with clinical responses, we found increased frequencies of R3-specific CD8 + T cells that expressed high levels of CD107a and produced both interferon-γ and granzyme B in response to antigen challenge. Interestingly, vaccination was also associated with the induction of regulatory T cells in four patients. Thus peptide vaccination in six CLL patients was safe and could elicit to some extent specific CD8 + T-cell responses against the tumor antigen RHAMM.