A Potential Role for NKG2C+ γδ T Cells as a Cellular Therapy in Combating Post-Lung Transplant Cytomegalovirus Infection

PURPOSE: Cytomegalovirus (CMV) is the most clinically significant pathogen following lung transplantation (LTx). While currently used anti-viral treatments are efficacious, their use is associated with toxicity and antiviral resistance. Given early promising results, immunotherapy is an attractive option to complement current antiviral therapies. We assessed the phenotype of circulating T cells following LTx with the aim of identifying novel cell subsets that may be candidate population as anti-viral immunotherapy. METHODS: Peripheral blood mononuclear cells (PBMC) were isolated from lung transplant patients from a single centre at pre-transplant, 0.5, 1.5, 3, 6, 9, 12- and 18-months post-LTx. Patients that were at risk of developing CMV disease were included in the study and were stratified based on the risk - moderate risk (Recipient CMV positive, n=15) or high risk (Recipient CMV negative/Donor CMV positive, n =11). CMV reactivation was classified as CMV PCR positive (>150 copies/ml) in blood and/or BAL within the first 12-months post-LTx. The phenotype of T cells in PBMC was assessed by multi-colour flow cytometry with a particular focus on γδT cells. RESULTS: We observed that recipient's γδT cell subset increased markedly following cessation of anti-viral prophylaxis and in CMV seropositive recipients, this subset is prominent pre-LTx, being highest in those who did not experience CMV reactivation. These cells are enriched in Vδ1 TCR-expressing population. Furthermore, a strong bias towards NKG2C+ cells was observed. NKG2C is a well-defined activation marker on NK cells and has been implicated in CMV immunity. In vitro assays showed that NKG2C+Vδ1+ γδT cells from healthy individuals exhibit functional capacity in line with anti-viral immunity. Our results indicate that NKG2C+Vδ1+ cells may be a suitable target for immunotherapy. CONCLUSION: The increase of blood NKG2C+Vδ1+ γδT cells in the presence of CMV indicates their contribution in this infection. As these cells could act in HLA-independent manner, we propose they may be an ideal target for cellular therapy against CMV in the transplant setting.