VH Gene Analysis in Splenic Marginal Zone Lymphoma Identifies Patients with Structurally Similar B Cell Receptors but Does Not Provide Prognostic Information.

Splenic marginal zone lymphoma (SMZL) is a rare indolent B cell malignancy whose diagnosis is based on splenic and/or marrow histology, lymphocyte morphology and immunophenotype. A low level paraprotein and deletion of chromosome 7q are found in approximately 40% of patients. IgV_H gene analysis has been performed in several small studies with evidence of biased V_H gene usage noted in some studies, and a poor clinical outcome for patients with unmutated V_H genes found in a single study. In order to clarify the biological and clinical significance of V_H gene usage and mutational state in SMZL we have analysed pooled data from 5 European centres. Of the172 V_H sequences analysed 53 (31%) utilised the V1-02 gene compared to a usage of 4% in 939 cases of CLL and < 4% in 315 normal B cell rearrangements. 89% of SMZL V1-02’s utilised the V1-02-04 allele compared to only 40% in CLL. D3-3 was used in 43% of the SMZL V1-02 cases compared to only 15% in the non-V1-02 cases. 51% of V1-02 cases had >97.9% homology to the germline sequence, most ranged between 96–99%. Constitutional DNA was sequenced from 6 V1-02 cases whose tumor DNA showed 98–99% homology. In each case differences in the tumor VH gene from the germline sequence were due to mutations rather than polymorphisms. The VH gene of 19/22 V1-02’s analysed showed at least 1 of 3 common mutations observed. 13/18 V1-02 cases utilised D3-3 in reading frame 3 and retained 2 aminoacids (GV) in all cases. The mean CDR3 length was 20 aminoacids (range 18–25). 4 additional cases utilising D3-3 in reading frame 1 showed conservation of 3 aminoacids (FLE) and 2 of these cases had virtually identical CDR3’s. These data suggest a role for antigen in the pathogenesis of SMZL, at least in a subset of patients.

Clinical outcome data were available in 166 patients presenting with splenomegaly of whom 130 underwent splenectomy. 98 had mutated V_H genes and 68 unmutated V_H genes using a 98% cut off. There was no difference in overall survival between mutated and unmutated cases nor between the V1-02 and non V1-02 cases. Disease progression after initial therapy occurred in 69 patients overall and in 46 who underwent splenectomy as primary therapy. In neither group of progressive cases was there a correlation between progression and V_H gene mutational status.

V_H gene data was also available on an additional 26 patients who presented with a lymphocytosis and the typical lymphocyte morphology, immunophenotype and incidence of 7q deletions found in SMZL but without splenomegaly. Only 1 case (4%) utilised the V1-02 gene. Further studies are required to determine whether these patients represent a benign subset of SMZL or a separate disorder. In conclusion, V_H gene analysis in SMZL confirms biased V_H gene usage with evidence of antigen selection but does not support the clinical use of V_H genes as a prognostic marker.