Expression of CD226 on γδ T cells is lower in advanced chronic lymphocytic leukemia and correlates with IgA, IgG and LDH levels.

Background: Gamma-delta (γδ) T cells comprise an important subset of human T cells, responding to viral and bacterial infections, and are significant for cancer immunosurveillance. Human γδ T cells are divided into 5 major subsets, namely Vδ1-Vδ5, of which the latter 3 have limited available literature. At present, Vδ2 is the most studied subpopulation.

Objectives: In the current paper, we focused on non-Vδ2 cells in chronic lymphocytic leukemia (CLL). We assessed the expression of co-inhibitory checkpoint receptors (CTLA-4, PD-1 and TIGIT) and co-stimulatory (CD226 and NKp30) molecules separately on Vδ1 and Vδ3-Vδ5 cells.

Material And Methods: We assessed γδ T cells for their expression of both cytotoxicity-related (NKp30, CD226) and co-inhibitory (PD-1, TIGIT) molecules with flow cytometry in CLL patients. Moreover, we evaluated the expression of TIGIT and CD226 ligand (PVR , CD155) in neoplastic B cells in CLL patients with quantitative real-time polymerase chain reaction (qPCR).

Results: A significant accumulation of Vδ1 T cells was noted, while no difference was observed in the total percentage of Vδ2 cells. Contrary to our initial hypothesis, the impact of CLL burden on CD226 and TIGIT expression was lower than anticipated. The former tends to be lower in more advanced disease. Finally, a strong upregulation of CD155 (PVR) was noted on CLL-derived B cells when compared to healthy B cells.

Conclusions: Chronic lymphocytic leukemia regulates the expression of the CD155-CD226/TIGIT axis. Contrary to expectations, the ligand is significantly more affected than the receptors. Nevertheless, the relatively high expression of CD155 and TIGIT makes CLL an interesting target for anti-TIGIT immunotherapy.