Distinct NK Cell Subset Predicts Ibrutinib Response and Immune Pathway Activation in CLL

Changes to natural killer (NK) cell subsets following treatment with ibrutinib (Imbruvica; Janssen Biotech) in chronic lymphocytic leukemia (CLL) play a crucial role in disease development and progression, indicating their potential to help predict immune therapeutic responses. Researchers have identified a unique subpopulation of NK cells, known as CLL_NK, which function as a critical immunologic marker in CLL and may offer valuable prognostic insight into how patients will respond to immune-based therapies. Their findings were published in BMC Cancer.¹

3D visualization of natural killer cells | Image Credit: © N0X - stock.adobe.com

CLL is a highly heterogeneous, chronic lymphoproliferative disorder characterized by the overproduction of dysfunctional lymphocytes. Targeted therapies like ibrutinib, a Bruton’s tyrosine kinase (BTK) inhibitor, have significantly changed the treatment landscape for CLL/SLL and demonstrated meaningful efficacy in clinical trials. However, prolonged use of ibrutinib can lead to resistance and disease progression.²

NK cells are key players in the immune system that are involved in antitumor defense. A long-term study found that people with weaker NK cell activity in their blood were more likely to develop cancer. Because NK cells mostly circulate in the blood, they have shown strong effects against blood cancers like acute myeloid leukemia, multiple myeloma, non-Hodgkin lymphoma, and CLL; however, there is little understanding of how NK cells respond to immune therapies in CLL patients treated with ibrutinib.¹

This study used single-cell transcriptomics to examine NK cell changes in patients with monoclonal B-cell lymphocytosis, newly diagnosed CLL, those who responded completely or partially to treatment, and those with Richter's syndrome (RS) to better understand how NK cell subsets shift before and after ibrutinib and how that relates to treatment outcomes.¹

The researchers identified 3 key NK cell subsets: CD56bright_NK cells, CD56dim_NK cells, and a highly cytotoxic CLL_NK subset. CLL_NK stood out from other NK subsets based on their unique molecular features. These cells contained high levels of GNLY and FCGR3A but lacked markers like KLRG1, NCAM1, and SELL, making them easy to distinguish. Additionally, CLL_NK cells were more common in patients who responded well to treatment and showed strong activation of immune pathways tied to cell-killing functions.¹

Further analysis revealed that CLL_NK cells represent an early stage in NK cell development, eventually giving rise to both CD56bright and CD56dim NK cells. At different points along this developmental path, specific immune pathways were turned on. In early stages, PD-L1, IL-17, and cytotoxic signaling were featured, whereas later stages activated NF-κB and cytokine-receptor communication. Key transcription factors like NR2C2, SMARCA4, and FOXO3 appeared to guide these processes.¹

Using Mendelian randomization and colocalization methods, the researchers identified 12 genes tied to disease risk and created a CLL-NK index (CNI): SLAMF7, CST7, NKG7, and CD63 were associated with higher risk, whereas ASCL2, IL2RG, and GZMB seemed to be protective. Notably, NKG7 and ASCL2 stood out, with qPCR confirming they were expressed differently in CLL versus normal cells.¹

Increased immune cell activity and expression of genes involved in antigen presentation and immune checkpoints were linked to a high CNI score, which helped predict which drugs patients might respond to. The findings showed that those with higher CNI were more likely to be sensitive to 5-fluorouracil (Fluoroplex; Aqua Pharmaceuticals), fludarabine (Fludara; Teva Pharmaceuticals), and dasatinib (Sprycel; Bristol-Myers Squibb). Furthermore, expression levels of NKG7 and ASCL2 were associated with different responses to drugs like ibrutinib and trametinib (Mekinist; Novartis), pointing to their potential as biomarkers for treatment guidance.¹

“Our study revealed the existence of a novel CLL_NK cell subset in patients exhibiting favorable responses to ibrutinib treatment, underscoring its pivotal role in the therapeutic efficacy of ibrutinib for CLL,” the researchers wrote. “By identifying NKG7 and ASCL2 as genes significantly associated with the development and progression of CLL, we highlight a new avenue for investigations in which targeting these molecules could represent innovative strategies for CLL management.”¹

REFERENCES

1. Liu C, Ding T, Zou R, et al. Unravelling NK cell subset dynamics and specific gene signatures post-ibrutinib therapy in chronic lymphocytic leukaemia via single-cell transcriptomics. BMC Cancer. April 21, 2025. doi:10.1186/s12885-025-14166-0

2. Real-world study shows comparable survival outcomes with first-line ibrutinib in high-risk and non-high-risk CLL/SLL. Pharmacy Times. May 15, 2025. Accessed May 22, 2025. https://www.pharmacytimes.com/view/real-world-study-shows-comparable-survival-outcomes-with-first-line-ibrutinib-in-high-risk-and-non-high-risk-cll-sll