T-cell dysfunction in CLL is mediated through expression of SIGLEC-10 ligands CD24 and CD52 on CLL cells

• Presence of CLL cells delays TCR-mediated (CAR) T cell activation and impairs proliferation and re-stimulation

• Blocking CD24 and CD52 expression on CLL cells reverses T cell dysfunction.

Autologous T-cell-based therapies, such as CAR-T-cell therapy, exhibit low success rates in chronic lymphocytic leukemia (CLL) which correlates with a dysfunctional T-cell phenotype observed in patients. Despite various proposed mechanisms of T-cell dysfunction in CLL, the specific CLL-derived factors responsible remain unidentified. This study aims to investigate mechanisms by which CLL cells suppress (CAR) T-cell activation and function. We found that CLL-derived T cells get activated, albeit in a delayed fashion and that specifically re-stimulation of (CAR-) T cells in presence of CLL cells causes impaired cytokine production and reduced proliferation. Notably, co-culture of T cells with CD40-activated CLL cells did not result in T-cell dysfunction and this required direct cell contact between the CD40-stimulated CLL cells and T cells. Inhibition of kinases involved in the CD40-signaling cascade revealed that the SRC-kinase inhibitor dasatinib prevented rescue of T-cell function independent of CD40-mediated increased levels of costimulatory and adhesion ligands on CLL cells. Transcriptome profiling of CD40-stimulated CLL cells with or without dasatinib identified widespread differential gene expression. Selecting for surface receptor genes revealed CD40-mediated downregulation of SIGLEC-10-ligands CD24 and CD52, which was prevented by dasatinib; suggesting a role for these ligands in functional T-cell suppression in CLL. Indeed, blocking CD24 and/or CD52 markedly reduced (CAR) T-cell dysfunction upon co-culture with resting CLL cells. These results demonstrate that T cells derived from CLL patients can be reinvigorated by manipulating CLL-T cell interactions. Targeting CD24- and CD52-mediated CLL-T cell interaction could be a promising therapeutic strategy to enhance T-cell function in CLL. -