Clonal evolution in a primary cutaneous follicle center B cell lymphoma revealed by single cell analysis in sequential biopsies

A comparison of hydraulic and laser capture microdissection methods for collection of single B cells, PCR, and sequencing of antibody VDJ

During the development of B lymphocytes, a series of gene rearrangements assemble the sequences that encode immunoglobulin heavy and light chains (VDJ). Earlier studies of VDJ sequence diversification during expansion of cells in splenic or appendix germinal centers used hydraulic micromanipulation (HM) to collect single B cells for PCR amplification of rearranged antibody heavy and light chain genes. PCR products were directly sequenced without a cloning step. Hydraulic micromanipulation is a very tedious method. Once capability to collect single cells by laser capture microdissection (LCM) was developed, we modified previous tissue staining and fixation methods so that we could collect cells from a given stained tissue section by HM and LCM and directly compare our success rates using these two methods. Cells were alkaline lysed and after two rounds of nested PCR products were recovered and directly sequenced. Because each rearrangement of genomic DNA that occurs to form the immunoglobulin heavy-chain-encoding sequence in developing B cells is unique, this system allowed us to verify our success rate in recovering single lymphocytes from tissue sections and amplifying a single allele. The methods developed have now made LCM an efficient alternative to HM for the collection of single B cells.

Primary cutaneous follicle center cell lymphomas and large B cell lymphomas of the leg descend from germinal center cells. A single cell polymerase chain reaction analysis

Primary cutaneous B cell lymphomas are defined as non-Hodgkin lymphomas that occur in the skin without extracutaneous involvement for 6 mo after diagnosis. They are characterized by a less aggressive course and better prognosis than their nodal counterparts. According to the European Organization for Research and Treatment of Cancer classification, the major subentities of primary cutaneous B cell lymphoma are follicle center cell lymphomas, immunocytomas, and large B cell lymphomas of the leg, which differ considerably regarding their clinical behavior, the former two being indolent, the latter being of intermediate malignancy. In this study, we applied a single cell polymerase chain reaction approach to analyze immunoglobulin V(H)/V(L) genes in 532 individual B lymphocytes from histologic sections of four follicle center cell lymphomas localized on the head and trunk, and four large B cell lymphomas on the leg. We found: (i) in six of eight patients a clonal heavy chain, and in seven of eight patients a clonal light chain rearrangement, all being potentially productive; (ii) no bias in VH gene usage, in four of seven light chain rearrangements the V kappa germline gene IGVK3-20*1 was used; (iii) no biallelic rearrangements; (iv) all V(H)/V(L) genes are extensively mutated (mutation rate 5.4-16.3%); (v) intraclonal diversity in six of eight cases (three of each group); and (vi) low replacement vs silent mutation ratios in framework regions indicating preservation of antigen-receptor structure, as in normal B cells selected for antibody expression. Our data indicate a germinal center cell origin of primary cutaneous follicle center cell lymphomas and large B cell lymphomas independent of those belonging to one of these subentities.

Primary cutaneous follicle center cell lymphoma

The exact classification of primary cutaneous follicle center cell lymphomas (FCCLs) has been the subject of ongoing debate. In the classification of cutaneous lymphomas proposed by the European Organization for Research and Treatment of Cancer (EORTC)-Cutaneous Lymphoma Project Group, cutaneous follicle center cell lymphoma (FCCL) is defined as a proliferation of centrocytes and centroblasts showing a diffuse pattern of growth in the great majority of cases, and presenting only rarely a true follicular pattern. CD10 and Bcl-2 are usually not expressed by neoplastic cells, and the t(14:18) is absent. By contrast, nodal follicular lymphoma is a tumor with a follicular pattern, characterized by the proliferation of CD10+, Bcl-2+ follicular cells, and by the presence of the t(14;18) in most cases. In this review we outline the clinicopathologic, phenotypic, and molecular features of primary cutaneous FCCL, reviewing criteria for diagnosis and differential diagnosis of this peculiar variant of cutaneous B-cell lymphoma.

Cutaneous follicular B-cell lymphoma: description of a series of 18 cases

The lack of precise and homogeneous criteria for the recognition of primary cutaneous follicular lymphoma has hindered gaining data on the frequency and clinical and molecular features of this entity. In the course of a review of a series of primary cutaneous lymphoma from different Spanish hospitals, we collected a series of 18 cases of primary cutaneous follicular lymphoma and analyzed its clinical, morphologic, and biologic characteristics. In this review only cases with a follicular pattern of growth, germinal center cytology, and restriction to the skin in a minimum follow-up of 6 months have been included. Cases of primary cutaneous follicular lymphoma were characterized by the expression of classic markers of the germinal center, such as bcl6, CD10, and the presence of aggregates of follicular dendritic cells. They frequently express bcl2 protein, although classical t(14;18) was not found in any of the cases analyzed. Analysis of the bcl6 noncoding first exon showed somatic mutations in two of four cases analyzed, as would be expected in lymphoma deriving from the germinal center. Clinically, most cases showed initial involvement of the head and neck, with relapses in eight cases (involving the skin in five cases, both skin and lymph node in two cases, and lymph node in one case). No death attributable to the tumor was recorded. These data seem to imply that follicular lymphoma may present initially in the skin, lacking the characteristic t(14;18) and having a relatively indolent course. Recognition of these tumors and elucidation of their molecular alterations could lead to properly adapted staging and treatment protocols for these patients.