Integrative multi-omics reveals a regulatory and exhausted T-cell landscape in CLL and identifies galectin-9 as an immunotherapy target.

T-cell exhaustion contributes to immunotherapy failure in chronic lymphocytic leukemia (CLL). Here, we analyze T cells from CLL patients' blood, bone marrow, and lymph nodes, as well as from a CLL mouse model, using single-cell RNA sequencing, mass cytometry, and tissue imaging. T cells in CLL lymph nodes show the most distinct profiles, with accumulation of regulatory T cells and CD8(+) T cells in various exhaustion states, including precursor (T(PEX)) and terminally exhausted (T(EX)) cells. Integration of T-cell receptor sequencing data and use of the predicTCR classifier suggest an enrichment of CLL-reactive T cells in lymph nodes. Interactome studies reveal potential immunotherapy targets, notably galectin-9, a TIM3 ligand. Inhibiting galectin-9 in mice reduces disease progression and TIM3(+) T cells. Galectin-9 expression also correlates with worse survival in CLL and other cancers, suggesting its role in immune evasion and potential as a therapeutic target.