A Longitudinal Study of γδ T Cell Subsets Post Lung Transplant: Potential Players in CMV Immunity

Abstract

Purpose Cytomegalovirus (CMV) is the predominant opportunistic infection in lung transplant (LTx) recipients and there is a need to develop biomarkers that indicate CMV immunity. To this end, we have recently reported that natural killer (NK) cells expressing the activating receptor, CD94-NKG2C, may be important in the control of CMV following LTx. γδ T cells can also aid in CMV immunity, yet their role following LTx is unknown. In this study, we longitudinally assessed the phenotype of γδ T cells in the blood of LTx recipients with and without CMV reactivation. Methods Cryopreserved peripheral blood mononuclear cells (PBMC) from LTx recipients treated at the Alfred Hospital were examined by multicolour flow cytometry. Patients were stratified by risk of CMV infection into low risk (CMV donor (D) negative (-), CMV recipient (R) -, n=6), moderate risk (CMV R positive (+), n=13 (n=6 no CMV reactivation, n=7 with CMV reactivation) or high risk (CMV D+, R-) n=12 (n=5 no CMV reactivation, n=7 with CMV reactivation). CMV reactivation was classified as CMV PCR positive (>150 copies/ml) in blood and/or BAL within the first 12-months following LTx. The phenotype of γδ T cells from the LTx recipients was assessed at pre-LTx and 0.5, 1.5, 3, 6, 9, 12- and 18-months post-LTx (where available). We then compared γδ T cell phenotype between LTx recipients with and without CMV reactivation to healthy non-transplant donors (n=12). Results There was an increase in the proportion of γδ T cells expressing the Vδ1 receptor in LTx recipients compared to healthy controls, reaching significance in all CMV risk groups at 18-months post-LTx. At all time-points, there was a higher proportion of γδ T cells expressing NKG2C in moderate CMV risk recipients only without CMV reactivation compared to healthy controls. Conversely, in high CMV risk recipients with CMV, an increased proportion of γδ T cells expressed NKG2C at 18-months post-transplant compared to healthy controls. Conclusion Subsets of γδ T cells could be linked with control of CMV following LTx. Moreover, the NK cell receptor CD94-NKG2C is seemingly important in the control of CMV by multiple cell types. In conclusion, we have demonstrated that γδ T cells are an active and dynamic component of the LTx environment and may have utility as a biomarker following LTx, particularly when used in combination with NK cell analysis.