4A–D). Since phenotypic analysis of NK cells (including CD56brightCD16± and CD56dimCD16+ NK-cell subsets) from PTLD patients has identified PD-1 up-regulation (Fig. 3), we next investigated whether disrupting PD-1 receptor binding during NK-cell stimulation may result in NK-cell function restoration in this cohort. To test the mechanism of PD-1

regulation, we incubated NK cells with autologous LCL in the presence or absence of PD-1 blocking mAb (or isotype control). This HM781-36B supplier treatment restored the IFN-γ response by CD56brightCD16± (Fig. 5A) NK cells, while CD107a release by CD56dimCD16+ (Fig. 5B) was only partially increased in PTLD patients. Interestingly, similar experiments performed on NK cells from LVL patients, who displayed low levels of PD-1 expression but maintained high NKp46 and NKG2D expression, have showed that blocking PD-1 resulted in increased IFN-γ and CD107a expression (Fig. 5A and B). NK cells, as part of innate Carfilzomib ic50 immunity, play an important role in the initial immunologic defense against viral infections 6, 7. However, the role of NK-cell surveillance during EBV latency, or chronic EBV infection with increased viral loads after Tx, or during PTLD remains elusive. Overall, our results show that NK-cell

phenotype and function are profoundly impaired in pediatric Tx PTLD patients (with a similar trend for chronic HVL carriers), indicating a possible NK-cell contribution to the Demeclocycline immunopathogenesis of EBV complications in the Tx setting. Here, we have identified for the first time significant differences in NK-cell subset distribution between EBV seropositive HC and pediatric Tx patients carrying, or not, an EBV load. On one hand, the CD56brightCD16± subset was increased in asymptomatic

Tx patients, suggesting possible differences in the NK functional (IFN-γ) requirements in pediatric Tx recipients versus HC. In contrast, PTLD patients showed decreased CD56brightCD16± and CD56dimCD16+ subset levels with an accumulation of CD56dimCD16− and CD56−CD16+ NK subsets. These changes in the NK-cell subset levels may be a consequence of high EBV challenge of NK cells seen with PTLD patients, leading to the possible CD56 receptor down-modulation on the conventional “functional” NK-cell subsets. Interestingly, recent studies have also described unusual accumulation of circulating dysfunctional CD56dimCD16− and CD56−CD16+ NK-cell subsets in patients with complications of chronic HIV and HCV infections, indicating a direct correlation between NK-cell subset defective function and chronic viral uncontrolled challenge 19–21. Early protection against EBV replication and against proliferation of EBV-infected targets was shown to rely on NK-cell ability to release IFN-γ and to mediate cytotoxicity in response to cytokine milieu instructions and to triggering receptor ligation by molecules on EBV-infected target cells 15, 16.