Characterization of T Cell Epitopes of the Receptor for Hyaluronic Acid Mediated Motility (RHAMM/CD168) in Acute Myeloid Leukemia.

To improve the clinical outcome of patients with acute myeloid leukemia (AML), immune therapies targeting leukemia associated antigens (LAAs) might be an approach complementary to chemotherapy and transplantation of hematopoetic stem cells. The receptor for hyaluronic acid mediated motility (RHAMM/CD168) has been defined as a LAA with specific expression. To define T cell epitopes of RHAMM/CD168 towards specific T cell immunotherapies, ten peptides were synthesized considering different computer algorithms and subjected to ELISPOT assays for interferon gamma and granzyme B, and to Cr-51 release assays. CD8+ T cells taken from the peripheral blood (PB) of 13 AML patients and presensitized with the RHAMM/CD168-derived peptides R3 (ILSLELMKL) or R5 (SLEENIVIL) did specifically recognize T2 cells pulsed with R3/R5. In contrast, CD8+ T cells isolated from the PB of 21 healthy volunteers were not able to lyse R3 or R5 pulsed T2 cells, even after presensitization. COS7 cells co-transfected with HLA-A*0201 and RHAMM/CD168 were lysed by R3 or R5 presensitized CD8+ T cells. Single HLA-A*0201 or RHAMM/CD168 transfected COS7 were not recognized. Cross-reactivity of the T cells was excluded by the use of unrelated peptides. K562 cells positive for RHAMM/CD168, but lacking HLA-class I molecules were not recognized indicating T cells and not NK cells as effector cells. The HLA class-I restricted lysis of COS-7 HLA-A*0201 and RHAMM/CD168 double- transfectants was confirmed by HLA class-I blocking antibody experiments. In an AML patient having received AML blast-derived dendritic cells, a higher frequency of RHAMM/CD168-peptide specific T cells was observed after four vaccinations when compared to his T cell status before vaccination. RHAMM/CD168 is also expressed in patients with other hematological malignancies which suggests a broad clinical applicability of its newly characterized T cell epitope peptides as a potential cancer vaccine.