Coexistence of Mutated and Unmutated IgVH Forms in Patients with Chronic Lymphocytic Leukemia.

The mutation status of the immunoglobulin heavy chain variable region (IgVH) gene is an independent prognostic indicator in patients with chronic lymphocytic leukemia (CLL). Unmutated IgVH is associated with rapid disease progression and shorter survival. The assay for determining IgVH mutation status depends on specific amplification of the mRNA of the expressed clonal IgVH. The presence of more than 1 clone in patients with CLL has been speculated and can be documented when the 2 clones express different light chains. Determining the IgVH gene family that is expressed in subclones also allows the confirmation of the presence of two clones in some cases. We describe 3 patients with two clones of CLL discovered in the process of determining the IgVH mutation status. PCR amplification of the expressed IgVH mRNA yielded 2 distinct bands. Sequencing each band separately revealed 2 different clones in each patient. Interestingly, each clone had a different mutation profile. In 2 of the 3 patients, the 2 clones were from completely different IgVH gene families (VH1-2 with VH2-5 and VH4-34 with VH5-51); both of these patients showed kappa light chain restriction. In the third patient the expressed IgVH gene family was VH3-21 in both clones, but 1 was mutated (6.8%) and the second was unmutated. Two of the 3 patients had evidence of aggressive disease with hepatosplenomegaly and lymphadenopathy; 1 of these patients expressed the VH3-21 gene family, which is known to be associated with aggressive disease irrespective of its mutation status. The other patient had a 9-year history of indolent disease without therapy. The intensity of the expressed IgVH clones as determined by PCR indicated that the mutated clones were dominant in 2 patients (approximately 80%). In the patient with VH3-21 expression, the unmutated clone accounted for 80% of total expressed IgVH. These data suggest that the presence of more than 1 clone should be considered when testing for IgVH mutation status and, more importantly, that evolution of a more aggressive second clone should be suspected. The presence of 2 clones—1 arising in naïve cells and the second in memory cells—suggests the possibility that the first hit occurred very early in the ontogeny of lymphocytes and that a second hit occurred at a later stage. However, the presence of naïve and memory clones in the same family raises the possibility that the naïve leukemic cells might still go through the germinal center programming process.