TLR9-dependent migration identifies different Chronic Lymphocytic Leukemia signaling states under BTK inhibition.

Fri, 16 Oct 2026 09:00:00 +0000

Summary

In recent years, B-cell receptor (BCR) inhibitors (such as ibrutinib) have transformed the treatment landscape for CLL. However, a significant challenge remains: some patients experience incomplete responses or eventually develop resistance to these drugs, even without acquiring the common BTK genetic mutations typically associated with drug failure. Our team set out to understand why this happens by investigating an alternative signalling route: the Toll-like receptor 9 (TLR9) pathway.

Our Key Discoveries

By analysing over 100 TLR9-stimulated patient samples using in-silico modelling, transcriptomics, and protein analyses, we uncovered diversity between use of the BCR and TLR9 signalling pathways.

We identified two distinct groups of CLL cells based on how they migrate when TLR9 is activated:

The “Reverse-Responders” (RR): In these patients, the baseline BCR signalling is highly active, which naturally suppresses the TLR9 pathway. When treated with standard BTK inhibitor monotherapy, preliminary data suggests these patients have good clinical outcomes.
The “Responders” (R): In these patients, baseline BCR signalling is low, allowing the TLR9 pathway to fully activate. This allows the leukaemia cells to migrate and survive using a pathway that can bypass BTK inhibitor drugs.

When we examined CLL cells from patients who had developed clinical resistance to BTK inhibitors, we found a clear shift: their BCR signalling had decreased, while their TLR9-associated (NF-κB) signalling had increased.

Clinical Impact

This study fundamentally redefines how we view CLL subgroups, showing that different patients rely on distinct survival pathways (BCR vs. TLR9).

Most importantly, in an exploratory cohort, we found that the “Reverse-Responder” phenotype is strongly associated with superior clinical outcomes following ibrutinib monotherapy—including shorter lymphocyte halving times, deeper Minimal Residual Disease (MRD) clearance, and longer progression-free survival.

Moving forward, and following analysis in a larger clinical cohort, measuring this TLR9-dependent migratory phenotype could serve as a powerful new functional biomarker, helping clinicians predict the depth of a patient’s response to BTK inhibitor monotherapy. It also paves the way for new therapeutic targets for those who develop resistance.

Read the full paper in Blood here

Fabio Simoes | Pepper Lab

TLR9-dependent migration identifies different Chronic Lymphocytic Leukemia signaling states under BTK inhibition.

Summary