Development of consensus fluorogenically labeled probes of the immunoglobulin heavy-chain gene for detecting minimal residual disease in B-cell non-Hodgkin lymphomas

We have examined 72 patients with B-cell non-Hodgkin lymphoma (B-NHL) in order to search for consensus sequences of the immunoglobulin heavy chain (IgH) gene, and developed consensus fluorogenically labeled probes for use in an allele-specific oligonucleotide (ASO) real-time quantitative polymerase chain reaction (RQ-PCR) assay of minimal residual disease (MRD). We detected a clonal IgH variable region (VH) sequence in 51 (70.8%) of the 72 B-NHLs, the most frequent VH gene usages being VH3 and VH4 (45/51, 88.2%). it was possible to design three consensus fluorogenic probes for the VH3 gene and one for the VH4 gene avoiding these hypermutations. Our sequencing results suggested that consensus fluorogenic probes would be best based on the 5'-side of the framework region 3 (FR3) because the frequency of somatic hypermutations was significantly lower in the regions on which the probes were based than in the remaining parts of FR3 (P<0.05). Nineteen (54.3%) of 35 B-NHLs with the VH3 gene and 5 (50%) of 10 with the VH4 gene had sequences identical to at least one of these probes. We found that probes containing one base substitution were still applicable for a MRD study, whereas those containing two or more were not. Therefore, our four probes were applicable for 37 (82.2%) of the 45 patients with VH3 or VH4. This limited number of probes makes a large-scale study of MRD in B-NHL more feasible.