Immunoglobulin VH Gene Analysis of Splenic Marginal Zone Lymphoma Histologic Variants
DW Bahler, P Szankasi, SD Dufresne, RE Felgar, SH Swerdlow. University of Utah, Salt Lake City, UT; University of Pittsburgh, Pittsburgh, PA
Background: Splenic marginal zone lymphomas (SMZL) are typically CD5-, CD10- B-cell neoplasms that classically display a biphasic growth pattern in the white pulp with marginal zone-like cells merging with a more central zone of smaller lymphocytes. However, many cases lack a biphasic pattern but show nodules composed mostly of marginal zone-like cells. Other less easily classified cases have mostly just small lymphocytes. To evaluate whether there may be molecular correlates to these histological differences related to direct antigen stimulation, lymphoma immunoglobulin heavy chain variable (VH) genes were analyzed.
Design: 23 splenic small B-cell lymphoma cases were identified that had available frozen tissue and were not HCL, CLL, FL, or MCL. Diagnoses were established by morphologic analysis and immunohistochemical staining. Rearranged lymphoma VH genes were amplified from the isolated DNA and the resultant PCR products could be directly sequenced in 19/23 cases.
Results: The 19 successfully sequenced cases consisted of 5 having a biphasic pattern, 7 having monophasic marginal zone-like nodules, and 7 unclassifiable cases. A single functional VH gene without stop codons was identified in all 19 sequenced cases. VH1 family gene segments were used in 4 cases, VH3 segments in 5, and VH4 family gene segments in 10. All 4 VH1 cases used the same V1-2 segment, and 5/10 VH4 cases used the V4-34 gene segment. Although cases using V4-34 were distributed among all 3 morphologic types, most (3/4) cases using V1-2 showed a biphasic pattern. The lymphoma VH genes were mutated from the most closely related germline gene segments (98% or less homology) in 13 cases, with 4 being heavily mutated (mean germline homology 83.0% 5.9%), and unmutated (greater than 98% homology) in 6 cases. The presence or absence of somatic mutations did not appear to correlate with the use of specific VH gene segments or histologic types.
Conclusions: Splenic marginal zone lymphomas appear to preferentially express VH4 family genes and specific VH gene segments, V1-2 (4/4 VH1 cases) and V4-34 (5/10 VH4 cases). These findings are consistent with direct antigen stimulation playing an important role in lymphoma growth and recognition of similar antigens. In addition, our study suggests the high use of V1-2 previously reported in SMZL may be mostly restricted to those cases showing a classic biphasic growth pattern.
Tuesday, March 10, 2009 9:30 AM
Poster Session III # 138, Tuesday Morning