By serving as the sole output of the cerebellar cortex, integrating a myriad of afferent stimuli, Purkinje cells (PCs) constitute the principal neuron in cerebellar circuits. Several neurodegenerative cerebellar ataxias feature a selective cell-autonomous loss of PCs, warranting the development of regenerative strategies. To date, very little is known as to the regulatory cascades controlling PC development. During central nervous system development, the proneural gene neurogenin 2 (Neurog2) contributes to many distinct neuronal types by specifying their fate and/or dictating development of their morphological features. By analyzing a mouse knock-in line expressing Cre recombinase under the control of Neurog2 cis-acting sequences we show that, in the cerebellar primordium, Neurog2 is expressed by cycling progenitors cell-autonomously fated to become PCs, even when transplanted heterochronically. During cerebellar development, Neurog2 is expressed in G1 phase by progenitors poised to exit the cell cycle. We demonstrate that, in the absence of Neurog2, both cell-cycle progression and neuronal output are significantly affected, leading to an overall reduction of the mature cerebellar volume. Although PC fate identity is correctly specified, the maturation of their dendritic arbor is severely affected in the absence of Neurog2, as null PCs develop stunted and poorly branched dendrites, a defect evident from the early stages of dendritogenesis. Thus, Neurog2 represents a key regulator of PC development and maturation.

Natural killer (NK) and hepatitis B virus (HBV)‐specific T cells are functionally impaired in chronic hepatitis B (CHB). Understanding to what extent nucleos(t)ide analogue (NUC) therapy can improve T‐ and NK‐cell responses is important in the perspective of immunomonitoring strategies for a safe and earlier NUC withdrawal and of novel combination therapies based on modulation of antiviral immunity. To gain further insights into T/NK‐cell interplay, we studied NK‐cell phenotype and function in hepatitis B e antigen–negative chronic HBV patients either untreated (25) or NUC treated (36 hepatitis B surface antigen [HBsAg]⁺ and 10 HBsAg^–/hepatitis B surface antibody [anti‐HBs]⁺). Interferon‐gamma, interleukin‐2, and tumor necrosis factor alpha (TNF‐α) production by HBV‐specific T cells was also analyzed in NUC‐treated patients. NK cells from chronic naïve patients showed an “inflammatory” phenotype defined by increased expression of TNF‐related apoptosis‐inducing ligand (TRAIL), CD38, and Ki67 that significantly declined upon viremia suppression and alanine aminotransferase normalization induced by NUC therapy. Reversion to a quiescent NK‐cell phenotype was associated with restoration of the HBV‐specific T‐cell function. T‐ and NK‐cell responses showed an inverse correlation, with an opposite behavior in individual NUC‐treated patients. NK‐cell depletion as well as TRAIL and NKG2D pathway blockade induced a significant improvement of the HBV‐specific T‐cell function. Conclusions: NK cells can express regulatory activity on T cells in NUC‐treated patients with prevalent inhibition of CD4 T cells, likely needed to limit persistent T‐cell activation. NK‐cell phenotype is modulated by NUC therapy and its reversion to quiescence mirrors efficient HBV‐specific T‐cell responses. Thus, changes of NK‐cell phenotype may predict acquisition of antiviral control before anti‐HBs seroconversion and represent the groundwork for future studies aimed at assessing whether NK phenotyping can be translated into the clinical practice to guide NUC suspension.(Hepatology 2015;62:1697–1709)

Chronic hepatitis B virus (HBV) infection represents a worldwide public health concern with approximately 250 million people chronically infected and at risk of developing liver cirrhosis and hepatocellular carcinoma. Nucleos(t)ide analogues (NUC) are the most widely used therapies for HBV infection, but they often require long-lasting administration to avoid the risk of HBV reactivation at withdrawal. Therefore, there is an urgent need to develop novel treatments to shorten the duration of NUC therapy by accelerating virus control, and to complement the effect of available anti-viral therapies. In chronic HBV infection, virus-specific T cells are functionally defective, and this exhaustion state is a key determinant of virus persistence. Reconstitution of an efficient anti-viral T cell response may thus represent a rational strategy to treat chronic HBV patients. In this perspective, the enhancement of adaptive immune responses by a checkpoint inhibitor blockade, specific T cell vaccines, lymphocyte metabolism targeting, and autologous T cell engineering, including chimeric antigen receptor (CAR) and TCR-redirected T cells, constitutes a promising immune modulatory approach for a therapeutic restoration of protective immunity. The advances of the emerging immune-based therapies in the setting of the HBV research field will be outlined.

Background Hepatitis C virus (HCV) persistence is associated with impaired CD8 functions. Whether functional restoration of CD8 T cells chronically exposed to antigen can be obtained once the antigen is removed remains to be clarified. Objective To determine whether clearance of HCV by antiviral treatment can fully restore the antiviral function of HCV-specific CD8 cells. Design Peripheral blood HCV-, Flu- and cytomegalovirus (CMV)-specific CD8 cells were quantified by tetramer staining in 28 patients whose HCV infection resolved after peginterferon or peginterferon/ribavirin treatment for either acute or chronic hepatitis and in eight subjects with acute HCV infection which resolved spontaneously for comparison. HCV-specific CD8 cells were evaluated for their phenotypic and functional characteristics by comparing different patient groups and CD8 cells with different viral specificities in the same patients. Results Sustained viral response (SVR) did not lead to full maturation of a functional memory CD8 cell response. In particular, SVR in chronic infection was associated with a greater level of T cell dysfunction than responders after acute infection, who showed HCV-specific CD8 responses comparable to those of spontaneous resolvers but weaker than those of Flu-specific CD8 cells. Higher programmed death (PD)-1 expression was detected on HCV than on Flu- and CMV-specific CD8 cells and the effect of PD-1/PD-L1 blockade was better in SVRs after chronic than after acute HCV infection. Conclusion A better restoration of HCV-specific CD8 function was detectable after SVR in patients with acute hepatitis than in those with chronic disease. Thus, the difficulty in achieving a complete restoration of the antiviral T cell function should be considered in the design of immunomodulatory therapies.