The Proliferative Response to CpG ODN Stimulation Predicts Disease Progression in B-Cell Chronic Lymphocytic Leukemia.

Chronic lymphocytic leukemia (CLL) B-cells from certain patients exhibit marked proliferation following stimulation with unmethylated CpG-oligodeoxynucleotides (CpG-ODN). In a recent study we observed that CpG-ODN induced proliferation occurs primarily in leukemic B-cells from patients with progressive disease and unmutated immunoglobulin (Ig) V_H genes. To further investigate whether the proliferative response following CpG-ODN stimulation can be used as a prognostic marker in CLL, we evaluated progression-free survival (PFS) and treatment-free survival (TFS) in a larger series of well characterized patients that had been followed for an extended period. In addition, we correlated the proliferative response with other prognostic factors, including Ig V_H gene mutation status, ZAP-70 expression and the presence of “high risk” cytogenetic abnormalities. Analysis of ³H thymidine incorporation in purified CLL B-cells stimulated for 72 hours with CpG-ODN 2006 revealed a proliferative response in 23 (40%) of the 58 evaluated cases. Eighteen (78%) of the proliferating cases had unmutated and 5 (22%) had mutated (M) Ig V_H genes, whereas among the 34 non-proliferating cases with available Ig V_H gene data 8 (24%) had unmutated and 26 (76%) mutated Ig V_H genes (P=<0.001 by chi-square test). ZAP-70 was expressed by 16 of the proliferating (70%) and 14 of the non-proliferating cases (40%), but this difference was not statistically significant (P = 0.053). The high-risk risk cytogenetic abnormalities del(17p13.1) and del(11q22.3) were detected in 6 of the 21 evaluated proliferating (29%) and in 3 of the 30 evaluated non-proliferating cases (10%) (P = 0.136). Median PFS was 25 months in the proliferating and 72 months in the non-proliferating subset (P=0.001). Similarly, median TFS was significantly shorter in the proliferating (30 months) than in the non-proliferating subset (114 months, P=0.001). In summary, these data confirm that the proliferative response to CpG-ODN stimulation is strongly correlated with Ig V_H gene mutation status, but does not depend on ZAP-70 expression. Although high-risk cytogenetic abnormalities were more frequent in the proliferating subset, the difference was not significant. Cases with a positive proliferative response had significantly shorter PFS and TFS, indicating that the proliferative capacity of the leukemic cells is an important determinant of the clinical course in CLL. Elucidation of the mechanisms that underlie the different proliferative capacity of CLL B-cells should provide additional insight in the pathogenesis of CLL and may lead to the identification of novel and clinically useful prognostic markers.