The Immunologic Paradox of BTK Inhibitors in Chronic Lymphocytic Leukemia: Selectivity, Hypogammaglobulinemia, and Infection Risk

Bruton’s tyrosine kinase (BTK) inhibitors have revolutionized B-cell malignancy treatment but paradoxically increase infection susceptibility. Covalent BTK inhibitors (Ibrutinib, Acalabrutinib, Zanubrutinib) induce sustained BTK blockade but disrupt immune homeostasis through off-target effects on T-cell and myeloid signaling, contributing to hypogammaglobulinemia and increased risk of bacterial, viral, and opportunistic fungal infections. Non-covalent inhibitors (Pirtobrutinib) and emerging BTK degraders offer more selective inhibition, preserving T-cell function and potentially mitigating infection risk, though their long-term immunological impact requires further study. Infection susceptibility varies across BTK inhibitor generations, reflecting differences in kinase selectivity, modulation of humoral and cellular immunity, and disease-intrinsic immune dysfunction in chronic lymphocytic leukemia. This review examines the mechanistic basis of BTK inhibitor-associated immune dysfunction, compares generational differences in selectivity and safety profiles, and provides evidence-based recommendations for infection risk mitigation in clinical practice.