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

Background and Objective. Recent studies have shown that expression of adhe sion molecules of the Ig superfamily, of integrins and of selectins allows definition of high vs low risk a-cell chronic lymphocytic leukemia (B-CLL). The proteoglycan CD44 is an adhesion molecule that may be expressed as a s tandard form of 85-95 KD or as several variant isoforms. The presence of ce rtain CD44 variant (v) isoforms on neoplastic cells indicates poor prognosi s in epithelial and lymphoid malignancies, as it is associated with tumor p rogression and metastasis. Design and Methods. The expression of CD44 v3, 4, 5, 6, 7, 9 and 10 was ana lyzed in cells from 85 B-CLL patients. Indirect immunofluorescence and flow cytometry were used to identify CD44v. Functional studies were performed b y analysts of adhesion to hyaluronate (HA), one CD44 ligand, and HA-induced Ca2+ influx. A variety of statistical methods were used to define phenotyp ic and functional differences between the various clones, to calculate surv ival curves, and for multivariate analyses. Results. In 17/85 B-CLL (20%), one or more CD44v were detectable by Indirec t immunofluorescence, whereas in 68/85 cases (80%) this technique yielded n egative results. However, moAb "mixes" against CD44v and patching of surfac e 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 gro ups of patients whose cells bear CD44v at high or low density, are distingu ished. Functions of the two clonotypes were investigated, namely their adhe sion to a CD44 ligand and hyaluronate (HA), and effect on HA-induced Ca2+ i nflux. Cells expressing high density CD44v adhere to HA-coated substrates m ore efficiently than cells with low density CD44v. In all clones, HA-signal ing via CD44 yields Ca2+ influx. This indicates that CD44 mediates activato ry signals following interaction with the ligand, Interpretation and Conclusions. The clinical relevance of these findings ha s been ascertained. The 17/85 cases whose cells bore high density CD44v had significantly worse prognostic features than those of patients with low de nsity CD44v, namely more advanced disease stage, LDT < 12 months and therap y requirement. Moreover, the median survival in the former group of patient s was < 5 years as opposed to > 12 years in the latter. Therefore, analysis of CD44v expression provides indications of biological and clinical releva nce also in low grade lymphoproliferative disorders. (C) 1998, Ferrata Stor ti Foundation.