Protection from lethal infection by adoptive transfer of CD8 T cells genetically engineered to express virus-specific innate immune receptor

CMV infection is one of the most common complications in immunocompromised individuals, such as organ and bone marrow transplant patients. Both innate and adaptive immune responses are required for defense against CMV infection. In murine CMV (MCMV) infection, strains harboring the MCMV-specific NK cell activation receptor, Ly49H (Klra8), are resistant. In contrast, MCMV infection of mice lacking Ly49H gene causes early mortality due to uncontrolled viral replication. In this study, we report the successful protection of mice from lethal MCMV infection with gene-transferred polyclonal CD8 T cells. CD8 T cells expressing a chimeric receptor comprising Ly49H extracellular and CD3zeta cytoplasmic domains are capable of killing target cells expressing the MCMV protein, m157. CD8 T cells expressing the chimeric receptor protect mice in vivo from lethality in the acute phase of MCMV infection, leading to the establishment of long-term protection. These data provide proof-of-principle evidence that a novel strategy for harnessing CD8 cytolytic function through TCR-independent yet pathogen-specific receptor can result in effective protection of hosts from pathogens.     

Cross-Presentation of a Spread-Defective MCMV Is Sufficient to Prime the Majority of Virus-Specific CD8+ T Cells

CD8+ T cells can be primed by peptides derived from endogenous proteins (direct presentation), or exogenously acquired protein (cross-presentation). However, the relative ability of these two pathways to prime CD8+ T cells during a viral infection remains controversial. Cytomegaloviruses (CMVs) can infect professional antigen presenting cells (APCs), including dendritic cells, thus providing peptides for direct presentation. However, the viral immune evasion genes profoundly impair recognition of infected cells by CD8+ T cells. Nevertheless, CMV infection elicits a very strong CD8+ T cell response, prompting its recent use as a vaccine vector. We have shown previously that deleting the immune evasion genes from murine cytomegalovirus (MCMV) that target class I MHC presentation, has no impact on the size or breadth of the CD8+ T cell response elicited by infection, suggesting that the majority of MCMV-specific CD8+ T cells in vivo are not directly primed by infected professional APCs. Here we use a novel spread-defective mutant of MCMV, lacking the essential glycoprotein gL, to show that cross-presentation alone can account for the majority of MCMV-specific CD8+ T cell responses to the virus. Our data support the conclusion that cross-presentation is the primary mode of antigen presentation by which CD8+ T cells are primed during MCMV infection.     

Non-hematopoietic cells in lymph nodes drive memory CD8 T cell inflation during murine cytomegalovirus infection

During human and murine cytomegalovirus (MCMV) infection an exceptionally large virus-specific CD8 T cell pool is maintained in the periphery lifelong. This anomalous response is only seen for specific subsets of MCMV-specific CD8 T cells which are referred to as 'inflationary T cells'. How memory CD8 T cell inflation is induced and maintained is unclear, though their activated phenotype strongly suggests an involvement of persistent antigen encounter during MCMV latency. To dissect the cellular and molecular requirements for memory CD8 T cell inflation, we have generated a transgenic mouse expressing an MHC class I-restricted T cell receptor specific for an immunodominant inflationary epitope of MCMV. Through a series of adoptive transfer experiments we found that memory inflation was completely dependent on antigen presentation by non-hematopoietic cells, which are also the predominant site of MCMV latency. In particular, non-hematopoietic cells selectively induced robust proliferation of inflationary CD8 T cells in lymph nodes, where a majority of the inflationary CD8 T cells exhibit a central-memory phenotype, but not in peripheral tissues, where terminally differentiated inflationary T cells accumulate. These results indicate that continuous restimulation of central memory CD8 T cells in the lymph nodes by infected non-hematopoietic cells ensures the maintenance of a functional effector CD8 T pool in the periphery, providing protection against viral reactivation events.     

Viral interference with antigen presentation does not alter acute or chronic CD8 T cell immunodominance in murine cytomegalovirus infection

Both human CMV and murine CMV (MCMV) elicit large CD8 T cell responses, despite the potent effects of viral genes that interfere with the MHC class I (MHC I) pathway of Ag presentation. To investigate the impact of immune evasion on CD8 T cell priming, we infected mice with wild-type (wt) MCMV or a mutant lacking its MHC I immune evasion genes, Deltam4+m6+m152 MCMV. In acute infection, the two viruses elicited a CD8 T cell response to 26 peptide epitopes that was virtually identical in total size, kinetics, and immunodominance hierarchy. This occurred despite results demonstrating that primary DCs are susceptible to the effects of MCMV's MHC I immune evasion genes. Eight months later, responses to both wt and mutant MCMV displayed the same CD8 T cell "memory inflation" and altered immunodominance that characterize the transition to chronic MCMV infection in C57BL/6 mice. Taken together, these findings suggest either that cross-priming dominates over direct CD8 T cell priming in both acute and chronic MCMV infection, or else that the MHC I immune evasion genes of MCMV are unable to alter direct CD8 T cell priming in vivo. At 2 years postinfection, differences in CD8 T cell immunodominance emerged between individual mice, but on average there were only slight differences between wt and mutant virus infections. Overall, the data indicate that the presence or absence of MHC I immune evasion genes has remarkably little impact on the size or specificity of the MCMV-specific CD8 T cell response over an entire lifetime of infection.     

The dynamics of mouse cytomegalovirus-specific CD4 T cell responses during acute and latent infection

The dynamics of mouse cytomegalovirus (MCMV)-specific CD4 T cell responses and the mechanisms by which these cells contribute to viral control are not well understood, mainly due to lack of appropriate tools to characterize MCMV-specific CD4 T cells. We therefore generated MCMV-specific CD4 T cell hybridomas, then used an MCMV expression library and overlapping peptides to identify CD4 T cell epitopes. We used these novel tools to study the long-term kinetics and organ distribution of MCMV-specific CD4 T cells in comparison to MCMV-specific CD8 T cell responses. We demonstrate that the overall MCMV-specific CD4 T cell response stabilizes during the latent stage, which stands in contrast to subpopulations of MCMV-specific CD8 T cells and HCMV-specific CD4 T cells which accumulate over the course of CMV latency. Furthermore, MCMV-specific CD4 T cells displayed a Th1 phenotype, secreting high levels of IFN-gamma and TNF-alpha and to some extent IL-2, cytokines which are involved in protection from CMV disease.     

Kinetics of ocular and systemic antigen-specific T-cell responses elicited during murine cytomegalovirus retinitis

Cytomegalovirus (CMV) reactivation in the retina of immunocompromized patients is a cause of significant morbidity as it can lead to blindness. The adaptive immune response is critical in controlling murine CMV (MCMV) infection in MCMV-susceptible mouse strains. CD8(+) T cells limit systemic viral replication in the acute phase of infection and are essential to contain latent virus. In this study, we provide the first evaluation of the kinetics of anti-viral T-cell responses after subretinal infection with MCMV. The acute response was characterized by a rapid expansion phase, with infiltration of CD8(+) T cells into the infected retina, followed by a contraction phase. MCMV-specific T cells displayed biphasic kinetics with a first peak at day 12 and contraction by day 18 followed by sustained recruitment of these cells into the retina at later time points post-infection. MCMV-specific CD8(+) T cells were also observed in the draining cervical lymph nodes and the spleen. Presentation of viral epitopes and activation of CD8(+) T cells was widespread and could be detected in the spleen and the draining lymph nodes, but not in the retina or iris. Moreover, after intraocular infection, antigen-specific cytotoxic activity was detectable and exhibited kinetics equivalent to those observed after intraperitoneal infection with the same viral dose. These data provide novel insights of how and where immune responses are initiated when viral antigen is present in the subretinal space.     

Human cytomegalovirus differentially controls B cell and T cell responses through effects on plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDCs), the main producers of type I IFN in response to viral infection, are essential in antiviral immunity. In this study, we assessed the effect of human CMV (HCMV) infection on PDC function and on downstream B and T cell responses in vitro. HCMV infection of human PDCs was nonpermissive, as immediate-early but not late viral Ags were detected. HCMV led to partial maturation of PDCs and up-regulated MHC class II and CD83 molecules but not the costimulatory molecules CD80 and CD86. Regardless of viral replication, PDCs secreted cytokines after contact with HCMV, including IFN-alpha secretion that was blocked by inhibitory CpG, suggesting an engagement of the TLR7 and/or TLR9 pathways. In the presence of B cell receptor stimulation, soluble factors produced by HCMV-matured PDCs triggered B cell activation and proliferation. Through PDC stimulation, HCMV prompted B cell activation, but only induced Ab production in the presence of T cells or T cell secreted IL-2. Conversely, HCMV hampered the allostimulatory ability of PDCs, leading to decreased proliferation of CD4(+) and CD8(+) T cells. These findings reveal a novel mechanism by which HCMV differentially controls humoral and cell-mediate immune responses through effects on PDCs.     

Memory inflation: continuous accumulation of antiviral CD8+ T cells over time

CD8+ T lymphocytes play an important role in the control of intracellular pathogens during both acute and persistent infections. This is particularly true in the case of persistent herpesviruses such as human CMV, which are typified by large virus-specific CD8+ T cell populations during viral latency. To understand the origin of these populations and the factors shaping them over time, we investigated the CD8+ T cell response after murine CMV (MCMV) infection. The kinetics of the acute response were characterized by rapid expansion of activated T cells, followed by a contraction phase. Thereafter, we observed a striking pattern, where MCMV-specific memory CD8+ T cells steadily accumulated over time, with 20% of all CD8+ T cells at 1 year specific for one MCMV epitope. Accumulation of MCMV-specific CD8+ T lymphocytes was seen in all organs tested and was associated with continuous activation of specific CD8+ T lymphocytes, primarily within lymph nodes. The pattern of accumulation was observed in only two of five epitopes tested, and was accompanied by a gradual restriction in usage of the variable region of the TCR beta-chain over time. This novel pattern of a virus-specific CD8+ T cell response suggests that continuous or repetitive exposure to Ag can slowly mold memory T cell populations over time. This may be relevant for understanding the evolution of the large human CMV-specific CD8+ T cell populations seen in humans.     

Zwitterionic polysaccharides stimulate T cells by MHC class II-dependent interactions

Polysaccharides of pathogenic extracellular bacteria commonly have negatively charged groups or no charged groups at all. These molecules have been considered classic T cell-independent Ags that do not elicit cell-mediated immune responses in mice. However, bacterial polysaccharides with a zwitterionic charge motif (ZPSs), such as the capsular polysaccharides of many strains of Bacteroides fragilis, Staphylococcus aureus, and Streptococcus pneumoniae type 1 elicit potent CD4(+) T cell responses in vivo and in vitro. The cell-mediated response to ZPS depends on the presence of both positively charged and negatively charged groups on each repeating unit of the polysaccharide. In this study, we define some of the requirements for the presentation of ZPS to CD4(+) T cells. We provide evidence that direct interactions of T cells with APCs are essential for T cell activation by ZPS. Monocytes, dendritic cells, and B cells are all able to serve as APCs for ZPS-mediated T cell activation. APCs lacking MHC class II molecules do not support this activity. Furthermore, mAb to HLA-DR specifically blocks ZPS-mediated T cell activation, while mAbs to other MHC class II and class I molecules do not. Immunoprecipitation of lysates of MHC class II-expressing cells following incubation with ZPS shows binding of ZPS and HLA-DR. Electron microscopy reveals colocalization of ZPS with HLA-DR on the cell surface and in compartments of the endocytic pathway. These results indicate that MHC class II molecules expressing HLA-DR on professional APCs are required for ZPS-induced T cell activation. The implication is that binding of ZPS to HLA-DR may be required for T cell activation.     

Presentation of soluble antigens to CD8+ T cells by CpG oligodeoxynucleotide-primed human naive B cells

Naive B lymphocytes are generally thought to be poor APCs, and there is limited knowledge of their role in activation of CD8(+) T cells. In this article, we demonstrate that class I MHC Ag presentation by human naive B cells is enhanced by TLR9 agonists. Purified naive B cells were cultured with or without a TLR9 agonist (CpG oligodeoxynucleotide [ODN] 2006) for 2 d and then assessed for phenotype, endocytic activity, and their ability to induce CD8(+) T cell responses to soluble Ags. CpG ODN enhanced expression of class I MHC and the costimulatory molecule CD86 and increased endocytic activity as determined by uptake of dextran beads. Pretreatment of naive B cells with CpG ODN also enabled presentation of tetanus toxoid to CD8(+) T cells, resulting in CD8(+) T cell cytokine production and granzyme B secretion and proliferation. Likewise, CpG-activated naive B cells showed enhanced ability to cross-present CMV Ag to autologous CD8(+) T cells, resulting in proliferation of CMV-specific CD8(+) T cells. Although resting naive B cells are poor APCs, they can be activated by TLR9 agonists to serve as potent APCs for class I MHC-restricted T cell responses. This novel activity of naive B cells could be exploited for vaccine design.     

T Cells Detect Intracellular DNA but Fail to Induce Type I IFN Responses: Implications for Restriction of HIV Replication

HIV infects key cell types of the immune system, most notably macrophages and CD4+ T cells. Whereas macrophages represent an important viral reservoir, activated CD4+ T cells are the most permissive cell types supporting high levels of viral replication. In recent years, it has been appreciated that the innate immune system plays an important role in controlling HIV replication, e.g. via interferon (IFN)-inducible restriction factors. Moreover, innate immune responses are involved in driving chronic immune activation and the pathogenesis of progressive immunodeficiency. Several pattern recognition receptors detecting HIV have been reported, including Toll-like receptor 7 and Retinoic-inducible gene-I, which detects viral RNA. Here we report that human primary T cells fail to induce strong IFN responses, despite the fact that this cell type does express key molecules involved in DNA signaling pathways. We demonstrate that the DNA sensor IFI16 migrates to sites of foreign DNA localization in the cytoplasm and recruits the signaling molecules stimulator of IFN genes and Tank-binding kinase, but this does not result in expression of IFN and IFN-stimulated genes. Importantly, we show that cytosolic DNA fails to affect HIV replication. However, exogenous treatment of activated T cells with type I IFN has the capacity to induce expression of IFN-stimulated genes and suppress HIV replication. Our data suggest the existence of an impaired DNA signaling machinery in T cells, which may prevent this cell type from activating cell-autonomous anti-HIV responses. This phenomenon could contribute to the high permissiveness of CD4+ T cells for HIV-1.     

Role of the indigenous microbiota in maintaining the virus-specific CD8 memory T cells in the lung of mice infected with murine cytomegalovirus

The potent role of indigenous microbiota in maintaining murine CMV (MCMV)-specific memory T cells, which were measured by multimer staining, was investigated using germfree (GF) mice. When the BALB/c mice bred under specific pathogen-free (SPF) conditions were i.p. infected with 0.2 LD(50) of MCMV, high frequencies of CD69(+)/CD44(+) MCMV-specific CD8 T cells were noted in the lungs even at 6-12 mo after infection (11.1 +/- 3.2 and 9.8 +/- 0.9%, respectively). In contrast, even though the viral load and expression levels of mRNA of such cytokines as IL-2, IL-7, IL-15, and IFN-gamma in the lungs of MCMV-infected GF mice were comparable to those of infected SPF mice, the frequencies of MCMV-specific CD8 T cells in the lungs of infected GF mice were kept lower than 1% at 6-12 mo after infection. In addition, the reconstitution of microbiota of MCMV-infected GF mice by orally administering a fecal suspension prepared from SPF mice restored the frequencies of both CD8(+)/multimer(+) and CD8(+)/multimer(-) T cells to levels similar to those found in SPF mice. These results suggested the indigenous microbiota to play a crucial role in the expansion and maintenance of viral-specific CD8 memory T cells, probably by cross-reactivity between the antigenic epitope of the MCMV-specific memory T cells and the variety of peptides derived from the members of the microbiota. Such cross-reactivity may thus be a major feature of those cells.     

Susceptibility of immature and mature Langerhans cell-type dendritic cells to infection and immunomodulation by human cytomegalovirus

Human cytomegalovirus (CMV) infection initiates in mucosal epithelia and disseminates via leukocytes throughout the body. Langerhans cells (LCs), the immature dendritic cells (DCs) that reside in epithelial tissues, are among the first cells to encounter virus and may play important roles in the immune response, as well as in pathogenesis as hosts for viral replication and as vehicles for dissemination. Here, we demonstrate that CD34(+) progenitor cell-derived LC-type DCs exhibit a differentiation state-dependent susceptibility to CMV infection. In contrast to the small percentage (3 to 4%) of the immature LCs that supported infection, a high percentage (48 to 74%) of mature, LC-derived DCs were susceptible to infection with endotheliotropic strains (TB40/E or VHL/E) of CMV. These cells were much less susceptible to viral strains AD169varATCC, TownevarRIT(3), and Toledo. When exposed to endotheliotropic strains, viral gene expression (IE1/IE2 and other viral gene products) and viral replication proceeded efficiently in LC-derived mature DCs (mDCs). Productive infection was associated with downmodulation of cell surface CD83, CD1a, CD80, CD86, ICAM-1, major histocompatibility complex (MHC) class I, and MHC class II on these cells. In addition, the T-cell proliferative response to allogeneic LC-derived mDCs was attenuated when CMV-infected cultures were used as stimulators. This investigation revealed important characteristics of the interaction between CMV and the LC lineage of DCs, suggesting that LC-derived mDCs are important to viral pathogenesis and immunity through their increased susceptibility to virus replication and virus-mediated immune escape.     

Human CD4+ T cells displaying viral epitopes elicit a functional virus-specific memory CD8+ T cell response

The Ag-specific cellular recall response to herpes virus infections is characterized by a swift recruitment of virus-specific memory T cells. Rapid activation is achieved through formation of the immunological synapse and supramolecular clustering of signal molecules at the site of contact. During the formation of the immunological synapse, epitope-loaded MHC molecules are transferred via trogocytosis from APCs to T cells, enabling the latter to function as Ag-presenting T cells (T-APCs). The contribution of viral epitope expressing T-APCs in the regulation of the herpes virus-specific CD8+ T cell memory response remains unclear. Comparison of CD4+ T-APCs with professional APCs such as Ag-presenting CD40L-activated B cells (CD40B-APCs) demonstrated reduced levels of costimulatory ligands. Despite the observed differences, CD4+ T-APCs are as potent as CD40B-APCs in stimulating herpes virus-specific CD8+ T cells resulting in a greater than 35-fold expansion of CD8+ T cells specific for dominant and subdominant viral epitopes. Virus-specific CD8+ T cells generated by CD4+ T-APCs or CD40B-APCs showed both comparable effector function such as specific lysis of targets and cytokine production and also did not differ in their phenotype after expansion. These results indicate that viral epitope presentation by Ag-specific CD4+ T cells may contribute to the rapid recruitment of virus-specific memory CD8+ T cells during a viral recall response.     

Phenotype and functional evaluation of ex vivo generated antigen-specific immune effector cells with potential for therapeutic applications

Ex vivo activation and expansion of lymphocytes for adoptive cell therapy has demonstrated great success. To improve safety and therapeutic efficacy, increased antigen specificity and reduced non-specific response of the ex vivo generated immune cells are necessary. Here, using a complete protein-spanning pool of pentadecapeptides of the latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV), a weak viral antigen which is associated with EBV lymphoproliferative diseases, we investigated the phenotype and function of immune effector cells generated based on IFN-γ or CD137 activation marker selection and dendritic cell (DC) activation. These ex vivo prepared immune cells exhibited a donor- and antigen-dependent T cell response; the IFN-γ-selected immune cells displayed a donor-related CD4- or CD8-dominant T cell phenotype; however, the CD137-enriched cells showed an increased ratio of CD4 T cells. Importantly, the pentadecapeptide antigens accessed both class II and class I MHC antigen processing machineries and effectively activated EBV-specific CD4 and CD8 T cells. Phenotype and kinetic analyses revealed that the IFN-γ and the CD137 selections enriched more central memory T (Tcm) cells than did the DC-activation approach, and after expansion, the IFN-γ-selected effector cells showed the highest level of antigen-specificity and effector activities. While all three approaches generated immune cells with comparable antigen-specific activities, the IFN-γ selection followed by ex vivo expansion produced high quality and quantity of antigen-specific effector cells. Our studies presented the optimal approach for generating therapeutic immune cells with potential for emergency and routine clinical applications.     

Polarization of host immune responses by helminth-expressed glycans

Helminth parasites bias host CD4(+) T helper (Th) cells toward Th2 responses, drive alternative activation of macrophages, and expand T regulatory cells. Helminth-expressed carbohydrates play critical roles in driving much of this immune cell biasing. Studies on helminth glycans have focused on Lewis X, LDN, LDN-DF, other fucosylated structures, chitin, tyvelose, and trehalose, which interact with host antigen presenting cells (APCs) minimally via C-type lectins and/or Toll-like receptors (TLR). Here, we review recent findings on helminth glycan activation of APCs via C-type lectin/TLRs and introduce the concept that glycosylated helminth molecules require endocytosis to function as immune modulators. Second, we describe unpublished data showing that in vivo glycoconjugates comprising multiple copies of glycans on carriers are directly immune modulatory. Lastly, we discuss the observation that CD14 negatively regulates alternative activation of APCs during helminth infection. We close with a discussion on the use of immune modulatory glycans as vaccine adjuvants and as antiinflammatory therapeutics.     

Genome-wide analysis reveals a highly diverse CD8 T cell response to murine cytomegalovirus

Human CMV establishes a lifelong latent infection in the majority of people worldwide. Although most infections are asymptomatic, immunocompetent hosts devote an extraordinary amount of immune resources to virus control. To increase our understanding of CMV immunobiology in an animal model, we used a genomic approach to comprehensively map the C57BL/6 CD8 T cell response to murine CMV (MCMV). Responses to 27 viral proteins were detectable directly ex vivo, the most diverse CD8 T cell response yet described within an individual animal. Twenty-four peptide epitopes were mapped from 18 Ags, which together account for most of the MCMV-specific response. Most Ags were from genes expressed at early times, after viral genes that interfere with Ag presentation are expressed, consistent with the hypothesis that the CD8 T cell response to MCMV is largely driven by cross-presented Ag. Titration of peptide epitopes in a direct ex vivo intracellular cytokine staining assay revealed a wide range of functional avidities, with no obvious correlation between functional avidity and the strength of the response. The immunodominance hierarchy varied only slightly between mice and between experiments. However, H-2(b)-expressing mice with different genetic backgrounds responded preferentially to different epitopes, indicating that non-MHC-encoded factors contribute to immunodominance in the CD8 T cell response to MCMV.     

Nuclear shelter: The influence of subcellular location on the processing of antigens by macroautophagy

CD4⁺ T cells recognize peptides displayed by MHC II molecules on the surface of specialized antigen-presenting cells (APCs). These peptides are generally considered to come from exogenous proteins that have been internalized by APCs and degraded in the endocytic network, thus representing a snapshot of proteins in the APC's extracellular environment. However, it is increasingly apparent that some proteins endogenously expressed within the APC itself can directly gain access to the MHC II pathway. This has particular implications for pathogens that naturally infect APCs, since such infections might therefore become visible to CD4⁺ (MHC II-restricted) effector T cells. Such a pathogen is Epstein-Barr Virus (EBV), a human herpesvirus that infects most individuals establishing life-long infection of B cells. EBV's persistence in the immune host depends upon expression of the viral nuclear protein EBNA1 to segregate the viral genome into daughter cells during homeostatic B cell turnover. Surprisingly, EBNA1 contains many CD4 epitopes, elicits strong CD4 T cell responses in most people and, in in vitro models, can be processed for CD4⁺ T cell recognition through delivery into the MHC II pathway, apparently via macroautophagy (hereafter referred to as autophagy). Taken together, these observations raise the interesting question of how does EBV persist in the B cell system given the presence of strong CD4 T cell responses directed against the one protein the virus absolutely requires for long-term persistence?     

IL-10 Suppression of NK/DC Crosstalk Leads to Poor Priming of MCMV-Specific CD4 T Cells and Prolonged MCMV Persistence

IL-10 is an anti-inflammatory cytokine that regulates the extent of host immunity to infection by exerting suppressive effects on different cell types. Herpes viruses induce IL-10 to modulate the virus-host balance towards their own benefit, resulting in prolonged virus persistence. To define the cellular and molecular players involved in IL-10 modulation of herpes virus-specific immunity, we studied mouse cytomegalovirus (MCMV) infection. Here we demonstrate that IL-10 specifically curtails the MCMV-specific CD4 T cell response by suppressing the bidirectional crosstalk between NK cells and myeloid dendritic cells (DCs). In absence of IL-10, NK cells licensed DCs to effectively prime MCMV-specific CD4 T cells and we defined the pro-inflammatory cytokines IL-12, IFN-γ and TNF-α as well as NK cell activating receptors NKG2D and NCR-1 to regulate this bidirectional NK/DC interplay. Consequently, markedly enhanced priming of MCMV-specific CD4 T cells in Il10 ^−/− mice led to faster control of lytic viral replication, but this came at the expense of TNF-α mediated immunopathology. Taken together, our data show that early induction of IL-10 during MCMV infection critically regulates the strength of the innate-adaptive immune cell crosstalk, thereby impacting beneficially on the ensuing virus-host balance for both the virus and the host.