Chronic viral infections often result in ineffective CD8 T-cell responses due to functional exhaustion or physical deletion of virus-specific T cells. However, how persisting virus impacts various CD8 T-cell effector functions and influences other aspects of CD8 T-cell dynamics, such as immunodominance and tissue distribution, remains largely unknown. Using different strains of lymphocytic choriomeningitis virus (LCMV), we compared responses to the same CD8 T-cell epitopes during acute or chronic infection. Persistent infection led to a disruption of the normal immunodominance hierarchy of CD8 T-cell responses seen following acute infection and dramatically altered the tissue distribution of LCMV-specific CD8 T cells in lymphoid and nonlymphoid tissues. Most importantly, CD8 T-cell functional impairment occurred in a hierarchical fashion in chronically infected mice. Production of interleukin 2 and the ability to lyse target cells in vitro were the first functions compromised, followed by the ability to make tumor necrosis factor alpha, while gamma interferon production was most resistant to functional exhaustion. Antigen appeared to be the driving force for this loss of function, since a strong correlation existed between the viral load and the level of exhaustion. Further, epitopes presented at higher levels in vivo resulted in physical deletion, while those presented at lower levels induced functional exhaustion. A model is proposed in which antigen levels drive the hierarchical loss of different CD8 T-cell effector functions during chronic infection, leading to distinct stages of functional impairment and eventually to physical deletion of virus-specific T cells. These results have implications for the study of human chronic infections, where similar T-cell deletion and functional dysregulation has been observed.Considerable evidence suggests that an effective CD8 T-cell response can control or eradicate viral infections. CD8 T cells appear to be particularly important in the immune response to chronic infections and in the long-term control of latent and reactivating viruses (2, 26). Indeed, potent human immunodeficiency virus (HIV)-specific CD8 T-cell responses correlate with acute viral control and long-term nonprogression (16,42,55,56,61,66). Further, rhesus macaques infected with simian immunodeficiency virus (SIV) show significantly higher viral loads if CD8 T cells are eliminated by antibody-mediated depletion (38). Evidence also suggests that CD8 T cells are important for the acute phase as well as long-term control of other persistent viruses, such as Epstein-Barr virus (EBV), cytomegalovirus, hepatitis B virus (HBV), and hepatitis C virus (HCV) (18,24,63,83). However, in many patients CD8 T cells fail to contain viral replication, particularly during HIV, HBV, and HCV infections. Recent studies suggest that functional impairment (exhaustion) and/or physical deletion of CD8 T cells can accompany ineffective viral control (44, 85). However, the impact of chronic viral infection on the induction and m...

R us se ll -L od ri gue, C hr is to ph er Monjure,

RTS,S is an advanced malaria vaccine candidate and confers significant protection against Plasmodium falciparum infection in humans. Little is known about the molecular mechanisms driving vaccine immunity. Here, we applied a systems biology approach to study immune responses in subjects receiving three consecutive immunizations with RTS,S (RRR), or in those receiving two immunizations of RTS,S/AS01 following a primary immunization with adenovirus 35 (Ad35) (ARR) vector expressing circumsporozoite protein. Subsequent controlled human malaria challenge (CHMI) of the vaccinees with Plasmodium-infected mosquitoes, 3 wk after the final immunization, resulted in ∼50% protection in both groups of vaccinees. Circumsporozoite protein (CSP)-specific antibody titers, prechallenge, were associated with protection in the RRR group. In contrast, ARR-induced lower antibody responses, and protection was associated with polyfunctional CD4 + T-cell responses 2 wk after priming with Ad35. Molecular signatures of B and plasma cells detected in PBMCs were highly correlated with antibody titers prechallenge and protection in the RRR cohort. In contrast, early signatures of innate immunity and dendritic cell activation were highly associated with protection in the ARR cohort. For both vaccine regimens, natural killer (NK) cell signatures negatively correlated with and predicted protection. These results suggest that protective immunity against P. falciparum can be achieved via multiple mechanisms and highlight the utility of systems approaches in defining molecular correlates of protection to vaccination. malaria | vaccine | systems vaccinology | systems biology | immune

Recombinant vaccinia viruses (rVV) have been extensively used as vaccines, but there is little information about the total magnitude of the VV-specific T-cell response and how this compares to the immune response to the foreign gene(s) expressed by the rVV. To address this issue, we quantitated the T-cell responses to both the viral vector and the insert following the infection of mice with VV expressing a cytotoxic T lymphocyte (CTL) epitope (NP118-126) from lymphocytic choriomeningitis virus (LCMV). The LCMV epitope-specific response was quantitated by intracellular cytokine staining after stimulation with the specific peptide. To analyze the total VV-specific response, we developed a simple intracellular cytokine staining assay using VV-infected major histocompatibility complex class I and II matched cells as stimulators. Using this approach, we made the following determinations. (i) VV-NP118 induced potent and long-lasting CD8 and CD4 T-cell responses to the vector; at the peak of the response (ϳ1 week), there were ϳ10 7 VV-specific CD8 T cells (25% of the CD8 T cells) and ϳ106 VV-specific CD4 T cells (ϳ5% of the CD4 T cells) in the spleen. These numbers decreased to ϳ5 ؋ 10 5 CD8 T cells (ϳ5% frequency) and ϳ10 5 CD4 T cells (ϳ0.5% frequency), respectively, by day 30 and were then stably maintained at these levels for >300 days. The size of this VV-specific T-cell response was comparable to that of the T-cell response induced following an acute LCMV infection. (ii) VV-specific CD8 and CD4 T cells were capable of producing gamma interferon (IFN-␥), tumor necrosis factor alpha (TNF-␣), and interleukin-2; all cells were able to make IFN-␥, a subset produced both IFN-␥ and TNF-␣, and another subset produced all three cytokines. (iii) The CD8 T-cell response to the foreign gene (LCMV NP118-126 epitope) was coordinately regulated with the response to the vector during all three phases (expansion, contraction, and memory) of the T-cell response. The total number of CD8 T cells responding to NP118-126 were ϳ20-to 30-fold lower than the number responding to the VV vector (ϳ1% at the peak and 0.2% in memory). This study provides a better understanding of T-cell immunity induced by VV-based vaccines, and in addition, the technique described in the study can be readily extended to other viral vectors to determine the ratio of the T-cell response to the insert versus the vector. This information will be useful in optimizing prime-boost regimens for vaccination.Recombinant vaccinia viruses expressing foreign genes from different pathogens have been extensively used in various experimental studies and also in clinical trials (2,20). Despite the widespread use of vaccinia virus (VV) as a viral vector, there is little to no information available about the total size of the VV-specific T-cell response. The major impediment to such studies has been the absence of well-defined CD4 and CD8 T-cell epitopes of VV. This has prevented a detailed quantitative analysis of T-cell immunity to VV. Although there is information about the...

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