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

B cell neoplasias descending from germinal center cells harbor the hallmark of intraclonal diversity resulting from ongoing mutation in the variable parts of their immunoglobulin-encoding genes. To characterize a primary cutaneous follicle center B cell lymphoma in more detail, we analyzed the respective VH and VL genes in single cells mobilized from four sequential biopsies, three taken from the skin and one obtained after internal dissemination from a retrobulbar infiltrate. The lymphoma cells were found to contain V5-51/D6-12/JH5b (heavy chain) and A27/Jkappa2 (light chain) gene rearrangements detected on both the genomic and the transcriptional level. To provide an accurate mutation analysis, the specific VH gene counterpart (V5-51UK) was cloned from the patient's germline. Analyzing 226 single cells, we found: (i) complete nucleotide identity when VH and VL genes of lymphoma cells from one particular biopsy were compared among each other; (ii) intraclonal diversity due to ongoing mutation comparing the sequences obtained from sequential biopsies; (iii) both VH and VL genes to be highly mutated. Deducing from the sequence data, we propose a scenario of the clonal evolution of the B cell tumor in this patient. From the molecular-biological point of view, this primary cutaneous follicle center B cell lymphoma shows the features of a germinal center cell lymphoma. To draw this conclusion from single cell PCR data, however, a sample of sequential biopsies had to be analyzed.