We initiated a phase I/II R3 peptide vaccination for patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) overexpressing the receptor for hyaluronic acid mediated motility (RHAMM). RHAMM is a leukemia associated antigen (LAA) that is strongly expressed in several hematological malignancies and induces humoral and cellular immune responses. In this study, patients with AML, MDS, MM or CLL were included with RHAMM expression but with a limited tumor load or a minimal residual disease. To date, 25 patients were enrolled. The first 12 patients were vaccinated with 300 mcg and further patients with 1000 mcg R3 peptide emulsified with the incomplete Freund’s adjuvant. The vaccine was given four times at a biweekly interval and GM-CSF was added for five days each vaccination. Only mild drug-related adverse events were observed such as erythema and induration of the skin at the site of injection. Immunological analysis were performed using enzyme linked immunospot (ELISpot) assays for Interferon gamma and Granzyme B, tetramer staining and chromium release assays. We detected specific immune responses in 70% of patients. In most patients, we found an increase of CD8+/HLA-A2/RHAMM R3 tetramer+/CD45RA+/CCR7−/CD27−/CD28− effector T cells in flow cytometry in accordance with an increase of R3-specific CD8+ T cells in ELISpot assays. In chromium release assays, a specific lysis of RHAMM-positive leukemic blasts was shown. Moreover, we measured IL-2 and IL-10 levels in sera before and after vaccination. While IL-10 levels remained at a rather low level, we detected an increase of IL-2 in four of ten patients who showed also clinical responses. RHAMM transcripts in bone marrow and peripheral blood were quantified by real-time RT-PCR. Responding patients showed a decrease of RHAMM after vaccination. We detected positive clinical effects in several patients with myeloid disorders showing a reduction of blasts in the bone marrow. One MDS patient did not need any longer erythrocyte transfusions. Two patients with MM showed a reduction of free light chain serum levels. Taken together, RHAMM-R3 peptide vaccination induced both immunological and clinical responses. Therefore, RHAMM constitutes a promising structure for further targeted immunotherapies in patients with different hematological malignancies.
Disclosure: No relevant conflicts of interest to declare.