Chronic Lymphocytic Leukemia in Venezuela: VH Mutation Status, Expression of ZAP-70, CD38 and Phenotypic Prevalence Among the Venezuelan Population.

Abstract 4395

CLL- B patients have a heterogeneous evolution, while some follow an indolent disease free of complications, others develop a severe disease and die within a few years disregarding of treatment. Recent studies have revealed that the expression of ZAP-70, CD38 high and unmutated immunoglobulin heavy chain variable region genes (U-IgVH) are useful markers for severe disease. Most of these studies have been done in Caucasian and Asian populations. The objective of our study was to find out if such markers are also of prognostic value in Venezuelan CLL patients. We consider this of interest since the Venezuelan population is and admixture of Amerindians, Europeans and Africans. IgVH sequences were done in 82 patients using standard techniques. Sequences with less than 98% homology with the corresponding germ line IgVH were considered mutated. Criteria for ZAP-70 positivity were established by flow cytometry in our laboratory based on the fluorescence intensity values found for B cells in relation with reference values for T cells. Isotypic background was considered. Patients were considered CD38 positive when 20% or more leukemic B cells expressed the marker. We were able to study all the 3 parameters in 55 patients. According to the clinical staging method described by Rai et al. at the time of diagnosis, 53.64% of patients were identified in stage 0; 26.83% in stage I; 7.32% in stage II, 4,88% in stage III and 7.32% in stage IV. Thirty-six (43,9%) patients had U-IgVH, and 46 (56,1%) had mutated M-IgVH. The most frequently expressed VH gene family was found to be VH3 (48,8%) followed by VH1 (24,4%), VH4 (20,7%) and VH5 (6,1%), with no expression of VH2, VH6 or VH7 gene families. VH3-21 were high (9.76%) in our cohort, the VH3-21 gene usage is an unfavorable prognostic marker independent of the IgVH mutational status. Out of the 55 patients studied, 47,3% were ZAP-70 positive and 43,6% patients were CD38 positive. Among ZAP-70 positive patients, 65.4% had U-IgVH; similarly a higher percentage of CD38 positive patients expressed U-IgVH. The majority of patients who required treatment, expressed U-IgVH (62.5%) and ZAP-70 (68,7%) and 43.7% of treated patients expressed both markers. Remarkably, 47.5% of our CLL patients were of European origin which is a clear overrepresentation of Europeans in the Venezuelan population admixture. In conclusion, our results support the prognostic value of ZAP-70 expression and of U-IgVH status for CLL patient evolution and an increased usage of the VH3 gene family, consistent with previous findings elsewhere. Additionally, our study suggest differential susceptibility of CLL in the Venezuelan population being European descendant more prone to suffer the disease.