# Germinal center trajectories and transcriptional signatures define CLL subtypes and their pathway regulators

## TL;DR

This study explores how different subtypes of chronic lymphocytic leukemia (CLL) relate to germinal center B cell development and identifies potential biomarkers for distinguishing these subtypes.

## Contribution

The study identifies LPL, ZNF667, and ZNF667-AS1 as potential biomarkers for CLL subtypes and links them to cholesterol and EMT regulation pathways.

## Key findings

- CD27bright memory B cells show more transcriptional similarity to mutated CLL (M-CLL) than unmutated CLL (UM-CLL).
- UM-CLL mimics an early germinal center substage, while M-CLL mimics later substages.
- LPL, ZNF667, and ZNF667-AS1 are linked to cholesterol and EMT regulation in CLL pathology.

## Abstract

Chronic lymphocytic leukemia (CLL) is divided into unmutated (UM-CLL) and mutated (M-CLL) subtypes depending on somatic hypermutation (SHM) frequency in their immunoglobulin heavy chain V (IGHV) region. We previously demonstrated that CD27bright memory B cells (MBCs) are germinal center (GC)-dependent with higher mutation rate, whereas CD27dull MBCs accumulate fewer mutations and originate independently from the GC. We conducted a meta-transcriptomic analysis on bulk RNA data from 116 individuals combining four CLL cohorts and healthy B cell subsets (naïve, CD27dull and CD27bright MBCs) to decipher the transcriptional and mechanistic functions of CLL subtypes. CD27bright MBCs showed more transcriptional similarity to M-CLL rather than UM-CLL. Functional enrichment analysis revealed that LPL, ZNF667 and ZNF667-AS1 are potential informative biomarkers for stratification of CLL subtypes. They are part of the mechanistic regulatory pathways of CLL pathology through cholesterol and Epithelial Mesenchymal Transition (EMT) regulation. We applied markers for the GC B-cell substages to map in silico the CLL cohorts to their potential GC B cell counterpart. UM-CLL represented transcriptional mimicry to an early intermediary GC substage whereas M-CLL mimicked later substages in the GC. This could potentially explain the IGHV mutational status of M-CLL as well as hypothesize that CLL subtypes could derive from a GC-dependent pathway.