Functional and clinical relevance of CD44 variant isoform expression on B-cell chronic lymphocytic leukemia cells

Recent studies have shown that expression of adhesion molecules of the Ig superfamily, of integrins and of selectins allows definition of high vs low risk B-cell chronic lymphocytic leukemia (B-CLL). The proteoglycan CD44 is an adhesion molecule that may be expressed as a standard form of 85-95 KD or as several variant isoforms. The presence of certain CD44 variant (v) isoforms on neoplastic cells indicates poor prognosis in epithelial and lymphoid malignancies, as it is associated with tumor progression and metastasis.

The expression of CD44 v3, 4, 5, 6, 7, 9 and 10 was analyzed in cells from 85 B-CLL patients. Indirect immunofluorescence and flow cytometry were used to identify CD44v. Functional studies were performed by analysis of adhesion to hyaluronate (HA), one CD44 ligand, and HA-induced Ca2+ influx. A variety of statistical methods were used to define phenotypic and functional differences between the various clones, to calculate survival curves, and for multivariate analyses.

In 17/85 B-CLL (20%), one or more CD44v were detectable by indirect immunofluorescence, whereas in 68/85 cases (80%) this technique yielded negative results. However, moAb "mixes" against CD44v and patching of surface molecules on B-CLL cells have shown that all B-CLL clones express CD44v. This has been confirmed by Western blot in a number of cases. Thus, two groups of patients whose cells bear CD44v at high or low density, are distinguished. Functions of the two clonotypes were investigated, namely their adhesion to a CD44 ligand and hyaluronate (HA), and effect on HA-induced Ca2+ influx. Cells expressing high density CD44v adhere to HA-coated substrates more efficiently than cells with low density CD44v. In all clones, HA-signaling via CD44 yields Ca2+ influx. This indicates that CD44 mediates activatory signals following interaction with the ligand.

The clinical relevance of these findings has been ascertained. The 17/85 cases whose cells bore high density CD44v had significantly worse prognostic features than those of patients with low density CD44v, namely more advanced disease stage, LDT < 12 months and therapy requirement. Moreover, the median survival in the former group of patients was < 5 years as opposed to > 12 years in the latter. Therefore, analysis of CD44v expression provides indications of biological and clinical relevance also in low grade lymphoproliferative disorders.