Infection with Epstein-Barr virus (EBV) affects most humans worldwide and persists life-long in the presence of robust virus-specific T-cell responses. In both immunocompromised and some immunocompetent people, EBV causes several cancers and lymphoproliferative diseases. EBV transforms B cells in vitro and encodes at least 44 microRNAs (miRNAs), most of which are expressed in EBV-transformed B cells, but their functions are largely unknown. Recently, we showed that EBV miRNAs inhibit CD4 + T-cell responses to infected B cells by targeting IL-12, MHC class II, and lysosomal proteases. Here we investigated whether EBV miRNAs also counteract surveillance by CD8 + T cells. We have found that EBV miRNAs strongly inhibit recognition and killing of infected B cells by EBV-specific CD8 + T cells through multiple mechanisms. EBV miRNAs directly target the peptide transporter subunit TAP2 and reduce levels of the TAP1 subunit, MHC class I molecules, and EBNA1, a protein expressed in most forms of EBV latency and a target of EBV-specific CD8 + T cells. Moreover, miRNAmediated down-regulation of the cytokine IL-12 decreases the recognition of infected cells by EBV-specific CD8 + T cells. Thus, EBV miRNAs use multiple, distinct pathways, allowing the virus to evade surveillance not only by CD4 + but also by antiviral CD8 + T cells.adaptive immunity | immune evasion | herpesvirus | CD8 T cells | microRNA E pstein-Barr virus (EBV) is a ubiquitous herpesvirus that infects the majority of the human population worldwide. Although EBV infection persists for life, most carriers remain asymptomatic due to a stringent control by virus-specific immunity. An important component of this immunity is EBV-specific CD8 + T cells, which often expand to high numbers in healthy carriers or after primary infection. Conversely, the absence of EBV-specific CD8 + T cells predicts the emergence of EBVassociated disease in patients after stem cell transplantation or when afflicted with AIDS (1-3). Dangerous EBV-mediated complications can be reversed or prevented by transfer of EBVspecific T cells (4, 5), which further confirms the important role of continuous T-cell control of EBV infection. Among EBVspecific T cells, CD8 + T cells predominate; about 0.05-1% of all CD8 + T cells in healthy donors are typically specific for EBV latent antigens and about twice as many for lytic antigens (6, 7).EBV predominantly infects B cells and establishes a latent infection before production of progeny virus becomes possible (8). Four distinct programs of EBV latent infection have been defined according to their expression profiles of latent viral genes (9-11). One of these programs, known as latency III or the "growth program," is characterized by the expression of a restricted set of approximately eight viral proteins, which activate B cells and drive their proliferation, thus increasing the viral reservoir. Latency III is found in EBV-associated malignancies in immunosuppressed patients (9) and likely reemerges continuously in healthy carriers (9, 12), indicati...

The importance of human herpesvirus 6 (HHV-6) species as human pathogens is increasingly appreciated. However, we do not understand how infection is controlled in healthy virus carriers, and why control fails in patients with disease. Other persistent viruses are under continuous surveillance by antigen-specific T cells, and specific T-cell repertoires have been well characterized for some of them. In contrast, knowledge on HHV-6-specific T-cell responses is limited, and missing for CD8 + T cells. Here we identify CD8 + T-cell responses to HHV-6B, the most widespread HHV-6 species, in healthy virus carriers. HHV-6B-specific CD8 + T-cell lines and clones recognized HLA-A2-restricted peptides from the viral structural proteins U54 and U11, and displayed various antigenspecific antiviral effector functions. These CD8 + T cells specifically recognized HHV-6B-infected primary CD4 + T cells in an HLA-restricted manner, produced antiviral cytokines, and killed infected cells, whereas HHV-6A-infected cells were not recognized. Thus, HHV-6B-specific CD8 + T cells are likely to contribute to control of infection, overcoming the immunomodulatory effects exerted by the virus. Potentially, HHV-6-associated disease could be addressed by active or passive immunotherapy that reconstitutes virusspecific CD8 + T-cell responses. Keywords: CD8+ T cells r human herpesvirus 6B r infectious diseases r virology IntroductionHuman herpesvirus 6 (HHV-6) species are widespread pathogens, and more than 90% of humans are seropositive. The two species HHV-6A and HHV-6B have close sequence homology but differ in their epidemiology and pathogenicity [1,2]. Primary infection with HHV-6B, the more widespread species, usually takes place in early childhood and is often associated with a self-limiting illness known as three-day fever or exanthema subitum [3,4]. After primary infection, HHV-6 remains in a latent state in its immunocompetent host [5], and occasional reactivations are normally asymptomatic. However, HHV-6 (in most cases HHV-6B) can reactivate in immunosuppressed individuals. HHV-6B reactivation is observed in 40-50% of patients receiving stem cell transCorrespondence: Dr. Andreas Moosmann e-mail: andreas.moosmann@helmholtz-muenchen.de plantation, and viral reactivation is associated with delirium and cognitive decline, severe encephalitis, graft-versus-host disease, transplant failure, and overall mortality [6][7][8][9]. Apart from the immunosuppressed host, HHV-6 has been involved in a variety of diseases involving the CNS, such as febrile seizures, encephalitis, epilepsy, and multiple sclerosis [2,10]. Healthy humans frequently carry a number of other persistent viruses that may reactivate under immunosuppression, including the herpesvirus family members Epstein-Barr virus (EBV) and cytomegalovirus (CMV) [11]. It is assumed that these viruses are under continuous control by antigen-specific T cells, and viral reactivation results from a deficiency in virus-specific T cells caused by therapy-related immunosuppression [11]. In accorda...

Human herpesvirus 6 (HHV-6) is prevalent in healthy persons, causes disease in immunosuppressed carriers, and may be involved in autoimmune disease. Cytotoxic CD8 T cells are probably important for effective control of infection. However, the HHV-6-specific CD8 T cell repertoire is largely uncharacterized. Therefore, we undertook a virus-wide analysis of CD8 T cell responses to HHV-6. We used a simple anchor motif-based algorithm (SAMBA) to identify 299 epitope candidates potentially presented by the HLA class I molecule B*08:01. Candidates were found in 77 of 98 unique HHV-6B proteins. From peptide-expanded T cell lines, we obtained CD8 T cell clones against 20 candidates. We tested whether T cell clones recognized HHV-6-infected cells. This was the case for 16 epitopes derived from 12 proteins from all phases of the viral replication cycle. Epitopes were enriched in certain amino acids flanking the peptide. Ex vivo analysis of eight healthy donors with HLA-peptide multimers showed that the strongest responses were directed against an epitope from IE-2, with a median frequency of 0.09% of CD8 T cells. Reconstitution of T cells specific for this and other HHV-6 epitopes was also observed after allogeneic hematopoietic stem cell transplantation. We conclude that HHV-6 induces CD8 T cell responses against multiple antigens of diverse functional classes. Most antigens against which CD8 T cells can be raised are presented by infected cells. Ex vivo multimer staining can directly identify HHV-6-specific T cells. These results will advance development of immune monitoring, adoptive T cell therapy, and vaccines.

Relapsed follicular lymphoma (FL) can arise from common progenitor cells (CPCs). Conceptually, CPC-defining mutations are somatic alterations shared by the initial and relapsed tumours, mostly B-cell leukaemia/lymphoma 2 (BCL2)/immunoglobulin heavy locus (IGH) translocations and other recurrent gene mutations. Through complementary approaches for highly sensitive mutation detection, we do not find CPC-defining mutations in highly purified BCL2/IGH-negative haematopoietic progenitor cells in clinical remission samples from three patients with relapsed FL. Instead, we find cells harbouring the same BCL2/IGH translocation but lacking CREB binding protein (CREBBP), lysine methyltransferase 2D (KMT2D) and other recurrent gene mutations. Thus, (i) the BCL2/IGH translocation can precede CPCdefining mutations in human FL, and (ii) BCL2/IGH-translocated cells can persist in clinical remission.