Somatically mutated immunoglobulin VH genes without intraclonal heterogeneity indicate a post germinal center origin of primary intraocular diffuse large B-cell lymphomas

Abstract

8072 Background: Primary intraocular lymphoma (PIOL) is a very rare high grade malignant non-Hodgkin lymphoma, usually of the diffuse large B cell lymphoma (DLBCL) type, which presents in the vitreous, retina and/or the optic nerve. Sixty to 80% of patients with PIOL eventually disseminate to the brain, whereas up to 15% of primary central nervous system lymphoma (PCNSL) patients exhibit ocular involvement. For these reasons, PIOL is regarded as a subtype of PCNSL. Analysis of the immunoglobulin heavy chain (VH) sequences in PCNSL tumors demonstrated biased overrepresentation of the VH4–34 gene and indicated derivation of these tumors from highly mutated germinal center (GC) B cells with ongoing mutational activity. Whether PIOL tumors are of similar or different origin is presently unknown. Methods: Immunoglobulin VH genes were examined in vitrectomy specimens of 4 PIOL patients, 1 patient with concomitant PCNSL and 1 patient with systemic DLBCL involving the eye. The extracted DNA was amplified by PCR using VH family specific primers, cloned and sequenced. Results: Seven clonal VH rearrangements belonging to the VH4, VH3 and VH1 families were cloned from the analyzed cases. In concordance with previous reports, the lymphomatous eye infiltrate from the PCNSL patient revealed a mutated clonal VH4–34 gene with intraclonal heterogeneity -a manifestation of active ongoing mutational activity. All the PIOL clonal VH rearrangements also exhibited mutated sequences with homology to the germline sequences ranging between 76 to 95%. However, in contrast to PCNSL, 3 out of 4 PIOL cases exhibited no intraclonal heterogeneity while the remaining case demonstrated ongoing somatic mutations in one of the 2 clonal VH rearrangements detected in this tumor. Interestingly, the clinical course of this patient was highly unusual, since he exhibited systemic dissemination during follow-up. Conclusions: Analysis of VH gene sequences from PIOL tumors indicate a post- GC derivation and suggest that they belong to the activated B cell (ABC)-like subtype of DLBCL. This is in contrast to the GC-origin of closely related PCNSL. No significant financial relationships to disclose.