Vγ9/Vδ2 (γδ) T cells have an important effector and regulatory role in innate and adaptive immunity against microbes, stressed cells and tumor cells. They represent less than 5% of peripheral blood lymphocytes, but can be activated and expanded in vitro by aminobisphosphonates (ABP) like zoledronic acid (Zol), as surrogates of their natural ligands. In this study, we have investigated the proliferative response of γδ T cells to Zol in 59 patients with chronic lymphocytic leukemia (CLL) at diagnosis. Proliferation of γδ T cells was observed in 30 patients (51%)(responders, R), whereas 29 patients (49%) were non-responders (NR). γδ T-cell subset distribution [e.g., naive (TN), central memory (TCM), effector memory (TEM), and terminally differentiated effector memory (TEMRA)] was well balanced in R patients, whereas TEM and TEMRA were largely predominant in NR patients. TEMRA of NR patients had a unique profile of NK receptors expression, characterized by the expression of the ILT4 inhibitory receptor, whereas R patients tended to have an higher expression of the costimulatory molecule NKG2D. Notably, HLA-G, a negative prognosticator in CLL and a well known ILT4 ligand, was more expressed in tumor cells of NR patients. This correlation prompted us to determine whether other tumor cell features were different in R and NR patients. Indeed, the latter showed significantly higher tumor cell counts, higher frequency of poor-risk cytogenetic abnormalities, and a significantly shorter median time to first treatment. Lastly, a very significant association was observed with the mutational status of the tumor immunoglobulin heavy chain variable region (IgVH), which was mutated (M) in 96% of R patients, and unmutated (UM) in 74% of NR patients. To gain further insight into this association, we evaluated the activity of the mevalonate pathway in tumor cells of M and UM patients. This pathway, that can be targeted by Zol, generates the phosphoantigens naturally recognized by γδ T cells. Bioinformatic and biochemical approaches showed that this pathway is more active in tumor cells of UM than M patients. Based on these data, we propose that tumor cells of UM CLL patients can more easily engage γδ T cells and, in the long run, exhaust their immune surveillance potential by driving their differentiation into functionally impaired TEMRA. In conclusion, we have identified a novel mechanism of immune escape which can contribute to the disease progression in UM CLL patients.

Author notes

Disclosure:Research Funding: Resarch funding from Novartis Farma, Origgio, Italy. Honoraria Information: Honoraria from Novartis Farma, Origgio. Off Label Use: Zoledronic acid has been used to activate in vitro gamma/delta T cells.