Examining the impact of immunosuppressive drugs on antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood natural killer (NK) cells and gamma delta (γ8) T cells

<bold>Background: </bold>Human natural killer (NK) cells and gamma delta (gamma delta) T cells may impact outcomes of solid organ transplantation (SOT) such as lung transplantation (LTx) following the differential engagement of an array of activating and inhibitory receptors. Amongst these, CD16 may be particularly important due to its capacity to bind IgG to trigger antibody-dependent cellular cytotoxicity (ADCC) and the production of proinflammatory cytokines. While the use of immunosuppressive drugs (ISDs) is an integral component of SOT practice, their relative impact on various immune cells, especially gamma delta T cells and CD16-induced functional responses, is still unclear.<bold>Methods: </bold>The ADCC responses of peripheral blood NK cells and gamma delta T cells from both healthy blood donors and adult lung transplant recipients (LTRs) were assessed by flow cytometry. Specifically, the degranulation response, as reflected in the expression of CD107a, and the capacity of both NK cells and gamma delta T cells to produce IFN-gamma and TNF-alpha was assessed following rituximab (RTX)-induced activation. Additionally, the effect of cyclosporine A (CsA), tacrolimus (TAC), prednisolone (Prdl) and azathioprine (AZA) at the concentration of 1 ng/ml, 10 ng/ml, 100 ng/ml, and 1000 ng/ml on these responses was also compared in both cell types.<bold>Results: </bold>Flow cytometric analyses of CD16 expresion showed that its expression on gamma delta T cells was both at lower levels and more variable than that on peripheral blood NK cells. Nevertheless functional analyses showed that despite these differences, gamma delta T cells like NK cells can be readily activated by engagement with RTX to degranulate and produce cytokines such as IFNg and TNF-a. RTX-induced degranulation by either NK cells or gamma delta T cells from healthy donors was not impacted by co-culture with individual ISDs. However, CsA and TAC but not Prdl and AZA did inhibit the production of IFN-gamma and TNF-alpha by both cell types. Flow cytometric analyses of RTX-induced activation of NK cells and gamma delta T cells from LTRs suggested their capacity to degranulate was not markedly impacted by transplantation with similar levels of cells expressing CD107 pre- and post-LTx. However an impairment in the ability of NK cells to produce cytokines was observed in samples obtained post LTx whereas gamma delta T cell cytokine responses were not significantly impacted.<bold>Conclusions: </bold>In conclusion, the findings show that despite differences in the expression levels of CD16, gamma delta T cells like NK cells can be readily activated by engagement with RTX and that in vitro exposure to CsA and TAC (calcineurin inhibitors) had a measurable effect on cytokine production but not degranulation by both NK cells and gdT cells from healthy donors. Finally the observation that in PBMC obtained from LTx recipients, NK cells but not gamma delta T cells exhibited impaired cytokine reponses suggests that transplantation or chronic exposure to ISDs differentially impacts their potential to respond to the introduction of an allograft and/or transplant-associated infections.