Peripheral CD4+ CD25+ Treg cell expansion in lung transplant recipients is not affected by calcineurin inhibitors

CD4+CD25+ regulatory T (Treg) cells have been shown to play a role in allograft tolerance and their peripheral counts vary according to the degree of graft acceptance in lung transplant recipients (LTR). Recent studies demonstrate that certain drugs might modulate generation, expansion and activity of Treg cells. Aim of this study was to evaluate the effect of therapeutic regimens used in our institution on peripheral CD4+CD25highCD69− Treg cell numbers in a group of 51 LTR with stable clinical conditions. They were treated with standard immunosuppression: calcineurin inhibitor (CNI) + azathioprine (AZA) + steroids (n = 28) or with CNI + mycophenolate mofetil (MMF) + steroids (n = 11) or with CNI + steroids (n = 12). These stable LTR were compared with age-matched healthy controls (n = 35) and with 19 LTR who developed bronchiolitis obliterans syndrome (BOS) and were treated analogously. Stable LTR showed higher peripheral Treg cell counts with respect to age-matched healthy controls (59.9 ± 31.8/μl versus 42.1 ± 16.9/μl, respectively; p < 0.05). This increase was detectable in all patients treated with CNI either in association with AZA or MMF. During these treatments a significant expansion of Treg cell counts was detectable during acute rejection (AR) episodes (86.03 ± 26.6/μl during AR versus 36.34 ± 7.6 before AR; p < 0,05). Moreover, the development of BOS was associated to a significant decrease of Treg cell counts irrespective to the immunosuppressive regimen used. In conclusion, therapeutic regimens based on CNI seem to allow a certain degree of peripheral Treg cell expansion in stable LTR.