We have demonstrated immunological responses and positive clinical effects of a peptide vaccination for patients with AML, MDS, MM and CLL with a limited tumor load or a minimal residual disease over-expressing RHAMM using 300 μg RHAMM-R3 peptide (Schmitt et al., Blood 2008; Giannopoulos et al., abstract submitted). To date, 26 patients were enrolled in this clinical peptide vaccination trial. Here, we report on the second cohort of nine patients with AML, MDS and MM vaccinated with a higher peptide dose (1000 μg RHAMM-R3 peptide). The vaccine was given four times at a biweekly interval and GM-CSF was added for five days each vaccination. Similar to the patients vaccinated with 300 μg peptide only mild drug-related adverse events were observed such as erythema and induration of the skin. Immunomonitoring was performed using ELISpot assays for Interferon gamma and Granzyme B, tetramer-based flow cytometry and chromium release assays. Moreover, the frequency of regulatory T cells was quantified at different time points of vaccination. In this second cohort of patients treated with 1,000 μg peptide we detected specific immune responses in a lower frequency (4/9 patients) in contrast to patients in the 300 μg cohort (7/10 patients). In these patients with immune responses 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. Two patients with positive immune responses showed a significant decrease of regulatory T cells. One patient without positive immune and clinical effects showed an increase of the frequency of regulatory T cells (5.03% to 15.9%). Three out of nine patients treated with 1,000 μg showed positive clinical effects: One patient with MDS RAEB-2 showed a reduction of leukemic blasts in the bone morrow to lower than 5%, one MDS patient achieved a normalization of the peripheral blood counts and one patient with multiple myeloma experienced a reduction of light chain in serum. The patients in the 300 μg cohort showed also a higher frequency of positive clinical effects (5 out of 10 patients).

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. However, higher doses of peptide do not improve the frequency and intensity of immune responses in this clinical trial.

Disclosures: No relevant conflicts of interest to declare.

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