Mapping the diversity of chronic lymphocytic leukemia at single-cell resolution

Chronic lymphocytic leukemia (CLL) presents a complex picture among patients, with some enduring decades without treatment while others face rapidly progressing disease. A new study from Karolinska Institutet, published in Blood Neoplasia, delves into the intricacies of CLL diversity at a single-cell resolution. Researchers compared 48,557 individual cells from 13 untreated patients, identifying three distinct subsets defined by highly similar B-cell receptors.

Subset #1 exhibited stress- and survival-related programs, subset #2 showed increased metabolic and growth-related activity, while subset #4 displayed a more quiescent profile, corresponding to its generally indolent disease course. A striking distinction emerged in small populations of cells exhibiting molecular signs of recent activation and proliferation.

These active-state cells were present in every patient but were notably more frequent in the aggressive subsets, indicating a higher cellular turnover associated with more progressive disease.

The study also unveiled diversity within individual leukemic clones, with 11 of the 13 patients showing the accumulation of additional mutations in the genes encoding their B-cell receptors, suggesting ongoing diversification. By combining gene expression with B-cell receptor information at the single-cell level, the researchers were able to discern both the different cellular states among the leukemic cells and how the clone continues to diversify.

This investigation underscores the complexity of CLL, revealing multiple layers of diversity not only between stereotyped subsets but also within cells belonging to the same leukemic clone. The findings provide valuable insights into the cellular and molecular processes underlying the varying clinical outcomes observed in CLL patients, bringing researchers closer to understanding the mechanisms behind these differences.