Previous analyses showed that monoclonal B-cell lymphocytosis (MBL), a CLL precursor state, has been detected up to 6 years before CLL diagnosis, the investigators explained, noting that “[a]nother prognostically relevant immunogenetic feature of CLL concerns the stereotype of the B-cell receptor immunoglobulins (BcR IG).”
“Indeed, distinct stereotyped subsets can be defined by the expression of shared sequence motifs and are associated with particular presentation and outcomes,” P. Martijn Kolijn, PhD, a researcher in the department of immunology at Erasmus Medical Center, Rotterdam, the Netherlands, and colleagues wrote in a brief report published online in Blood. In an effort to “gain insight into the composition of the BcR IG repertoire during the early stages of CLL,” the investigators utilized next-generation sequencing to analyze 124 blood samples taken from healthy individuals up to 22 years before they received a diagnosis of CLL or small lymphocytic leukemia (SLL). An additional 118 matched control samples were also analyzed.
Study subjects were participants in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort.
“First, unsurprisingly, we observed a significant difference in the frequency of the dominant clonotype in CLL patients versus controls with a median frequency of 54.9%, compared to only 0.38% in controls,” they wrote.
Among 28 patients whose lymphocyte counts were measured at baseline, 10 showed evidence of lymphocytosis up to 8 years before CLL diagnosis.
This suggests undiagnosed instances of high-count MBL (cases with a cell count above 0.5x 109 cells/L, which can progress to CLL) or asymptomatic CLL, they explained.
“In contrast, next-generation sequencing results showed detectable skewing of the IGH gene repertoire in 21/28 patients up to 15 years before CLL diagnosis, often in the absence of elevated lymphocyte counts,” they wrote. “Remarkably, some patients with CLL requiring treatment and clinical transformation to an aggressive B-cell lymphoma displayed considerable skewing in the IGH gene repertoire even 16 years before CLL diagnosis.”
Patients with a prediagnostic IGHV-unmutated dominant clonotype had significantly shorter overall survival after CLL diagnosis than did those with an IGHV-mutated clonotype, they noted.
“Furthermore, at early timepoints (>10 years before diagnosis), patients with a high dominant clonotype frequency were more likely to be IGHV mutated, whereas closer to diagnosis this tendency was lost, indicating that the prediagnostic phase may be even longer than 16 years for [mutated] CLL patients,” they added.
The investigators also found that:
- Twenty-five patients carried stereotyped BcR IG up to 17 years prior to CLL diagnosis, and of these, 10 clonotypes were assigned to minor subsets and 15 to major CLL subsets. Among the latter, 14 of the 15 belonged to high-risk subsets, and most of those showed a trend for faster disease evolution.
- High frequency of the dominant clonotype was evident in samples obtained less than 6 years before diagnosis, whereas high-risk stereotyped clonotypes found longer before diagnosis (as early as 16 years) tended to have a lower dominant clonotype frequency (<20% of IGH gene repertoire)
- The stereotyped BcR IG matched the clonotype at diagnosis for both patients with diagnostic material.
- No stereotyped subsets were identified among the dominant clonotypes of the healthy controls.