The Receptor for Hyaluronic Acid Mediated Motility (RHAMM): Characterization as an Immunotherapeutical Target in Chronic Lymphocytic Leukemia (CLL) and First Results of RHAMM-Derived Peptide Vaccination Trial.

Background and Aims: The increased expression of receptor of hyaluronic acid mediated motility (RHAMM) was noted in CLL. The defective expression of RHAMM-exon4 splice variant that correlated with chromosomal instability was found to bear negative prognostic value in patients with multiple myeloma. Therefore, here we characterized expression of RHAMM with its splice variants and correlated it with prognosis in CLL. Moreover, based on our previous results we initiated a RHAMM-derived R3 peptide vaccination study for patients with B-CLL in early stages of disease.

Methods: Messenger RNA expression of RHAMM/CD168 was assessed by quantitative RT-PCR in blood samples from 65 B-CLL patients, at the time of diagnosis. The splice variant expression was measured using fluorescence capillary electrophoresis. Three hundred mcg RHAMM R3 peptide (ILSLELMKL) emulsified with the incomplete Freund’s adjuvant (ISA-51) day 3, as well as GM-CSF days 1–5, was administrated four times subcutaneously at a biweekly interval.

Results: The real-time RT-PCR results revealed higher RHAMM/TBP expression rates in patients with unmutated IgVH status compared with mutated CLL cases (0.047 vs. 0.029, p=0.012). Both splice variants RHAMMFL as well as RHAMM-exon4 showed significantly higher expression in unmutated CLL cases. Increased expression of RHAMM/TBP was noted in advanced stages of disease. A tendency towards higher RHAMM/TBP expression ratios was observed in B-CLL cases with del11q. CLL patients with a RHAMM/TBP ratio >0.028 showed a significantly shorter median treatment-free survival (TFS) (16 vs. 38 months, p=0.0019). In a bivariate analysis, patients with VH mutated status and lower amounts of RHAMM presented longer TFS compared to unmutated cases with a high RHAMM expression (110 vs. 8 months, respectively). An enhanced RHAMM expression was observed in bone marrow samples of 5 B-CLL patients compared with the results obtained in blood (RHAMM/TBP 0.102 vs 0.032). Similar tendency to higher RHAMM/TBP ratios was observed after CD40L stimulation (RHAMM/TBP 0.025 vs.0.113). In five patients who completed all four doses of R3 peptide vaccine no toxicity related to vaccine was observed. Reduction of leukemic cells was noted in 3 patients but no clinical responses meeting NCI criteria was observed. Immunological responses were observed in patients who achieved hematological improvement. Conclusion: RHAMM/CD168 is a novel LAA in B-CLL patients, and its expression levels are correlated with the clinical course of the disease. RHAMM expression might indicate the proliferative potential of leukemic cells. First results of peptide vaccination using RHAMM-derived peptide showed limited reduction of tumor burden.