Molecular and Clinical Analysis of a Midwest Cohort of B-CLL Patients Utilizing the Immunoglobulin VH 1-69 Gene.

Abstract

The prognostic power of immunoglobulin (Ig) somatic mutation status in B cell chronic lymphocytic leukemia (B-CLL) is widely appreciated and has served as the rationale to systematically determine this molecular feature in B-CLL patients. Consistent with other reports, our study of Ig mutation status in a large cohort of B-CLL patients (n=599) found the most commonly used Ig heavy chain variable (VH) region gene was VH 1–69. The VH1–69 gene is of particular interest as there are numerous reports demonstrating that VH1–69 expressing B-CLL cells predominantly express the 51p1-like allele in an unmutated (UM) form and it is frequently associated with use of the D gene segment, D3-3; the J gene segment, JH6; and a relatively long third, complementarity-determining region (CDR3). Despite molecular definition of a commonly used form of VH1–69 in B-CLL, the clinical significance of CLL B cell usage of this prototypic form of VH1–69 remains to be determined. The goal of this study, therefore, was to perform a molecular and clinical analysis on our cohort of B-CLL patients expressing the VH1–69 gene. Our cohort consisted of 19 females and 55 males, with 89.5% expressing UM Ig VH. The 51p1-like allele was present in 75.7% of patients and the predominant D region used was D3 (64.7%). Patients in our cohort were classified by Rai risk as follows: 20 low (28.2%), 40 intermediate (56.3%), and 11 high (15.5%). For those patients with Rai stage available, analysis of specific D and J regions resulted in 16 D3-3/JH6 (26.7%); 14 D3-3/non-JH6 (23.3%); 16 non-D3-3/JH6 (26.7%); and 14 non-D3-3/non-JH6 (23.3%). Despite observing an overwhelming majority of leukemic cells with UM Ig VH, and the known relationship between mutation status and disease progression, it is interesting that our cohort included almost 30% with a low Rai risk. Of note, Ig VH mutation status did not segregate with Rai risk group or VH1–69 allele use (although few patients overall were mutated). However, an UM Ig VH status was associated with a CDR3 length >20 (p = 0.001) and with use of the JH6 segment (p = 0.003). When mutation status was analyzed in concert with specific use of the D3-3 allele, no relationship emerged; however, when this D region allele was analyzed for JH6 vs non-JH6 usage, combination of the D3-3 allele with JH6 was significantly associated with an UM Ig VH status (p = 0.004). Moreover, when J and D segment usage was analyzed in concert with Rai stage group, a significant (p = 0.019) relationship emerged between paired use of D3-3 and a JH6 segment and advanced (intermediate/high) Rai stage. Strikingly, only 1 of 18 VH1–69 patients with low Rai risk for whom D and J data were available expressed the specific combination of D3-3 and JH6. Although analysis of a larger cohort is clearly required to more formally and fully evaluate these relationships, to our knowledge, this is the first suggestion that D and J usage in VH1-69 expressing B-CLL patients correlates with advanced stages of disease. Because Ig VH usage is not believed to change over the course of disease, it is tempting to speculate that VH1–69 B-CLL patients that do not express the prototypic VH1–69 receptor may have a more favorable disease course. In summary, these data add further support to the notion that there is selection for specific Ig receptors in B-CLL and that the antigenic specificity of certain receptors may be associated with risk of progression.