iwCLL 2017 | Clonal Chronic Lymphocytic Leukemia mutations can occur extremely early in the hematopoietic lineage

The second session at this year’s iwCLL was titled “Role of Non-Leukemic Cells and the Microenvironment in CLL Development”, and was jointly chaired by Silvia Deaglio (University of Turin, Torino, Italy) and Christopher Pepper (Cardiff University, Wales, UK).

Sonia Marsilio, PhD, from the Weill Cornell Medical College, New York, USA, gave a talk titled “CLL Mutations in the Earliest Cells of the Hematopoietic Lineage: Documentation and Need for Caution.”

The group aimed to analyze the genomes of immature members of the hematopoietic lineage, while preventing contamination from mature CLL cells and controlling for deep sequencing noise.

FACS was used to isolate cell populations containing Hematopoietic Stem Cells (HSCs), Multi-Potent Progenitor (MPP) cells, downstream Hematopoietic Progenitor Cell (HPC) populations, and mature T-cells and monocytes from granulocyte-colony stimulating factor mobilized peripheral blood of 9 patients. CLL cells were also identified and subjected to Whole Exome Sequencing (WES).

In 6 paired CLL samples, 87 coding mutation were identified (average = 14.5 mutations per sample) and went on to be validated by Sanger sequencing.

Using the MRD method defined by van der Velden et al. in Leukemia in 2007, 9 pure samples were identified (0.01–0.04% of B-CLL cells = 11; 0.05–1.4% B-CLL cells = 9).

In one patient, an SF3B1-K700E mutation was present in the HSC+MPP fraction (VAF >0.15%) as well as in CLL B-cells (VAF >0.15%) of the patient in mutually exclusive clones. The SF3B1-I704F mutation was only identified in later stages of hematopoietic differentiation (CLL B-cells, VAF = 47%).

However, in some cases HSC+MPP and HPC fractions defined as “pure” by MRD analysis potentially were still contaminated with CLL B-cells.

 Sonia Marsilio concluded her presentation with a succinct summary slide: