Benton Lawson

CD8+ Lymphocytes Control Viral Replication in SIVmac239-Infected Rhesus Macaques without Decreasing the Lifespan of Productively Infected Cells

While CD8+ T cells are clearly important in controlling virus replication during HIV and SIV infections, the mechanisms underlying this antiviral effect remain poorly understood. In this study, we assessed the in vivo effect of CD8+ lymphocyte depletion on the lifespan of productively infected cells during chronic SIVmac239 infection of rhesus macaques. We treated two groups of animals that were either CD8+ lymphocyte-depleted or controls with antiretroviral therapy, and used mathematical modeling to assess the lifespan of infected cells either in the presence or absence of CD8+ lymphocytes. We found that, in both early (day 57 post-SIV) and late (day 177 post-SIV) chronic SIV infection, depletion of CD8+ lymphocytes did not result in a measurable increase in the lifespan of either short- or long-lived productively infected cells in vivo. This result indicates that the presence of CD8+ lymphocytes does not result in a noticeably shorter lifespan of productively SIV-infected cells, and thus that direct cell killing is unlikely to be the main mechanism underlying the antiviral effect of CD8+ T cells in SIV-infected macaques with high virus replication.

Depletion of CD4+ T cells abrogates post-peak decline of viremia in SIV-infected rhesus macaques

CD4+ T cells play a central role in the immunopathogenesis of HIV/AIDS, and their depletion during chronic HIV infection is a hallmark of disease progression. However, the relative contribution of CD4+ T cells as mediators of antiviral immune responses and targets for virus replication is still unclear. Here, we have generated data in SIV-infected rhesus macaques (RMs) that suggest that CD4+ T cells are essential in establishing control of virus replication during acute infection. To directly assess the role of CD4+ T cells during primary SIV infection, we in vivo depleted these cells from RMs prior to infecting the primates with a pathogenic strain of SIV. Compared with undepleted animals, CD4+ lymphocyte-depleted RMs showed a similar peak of viremia, but did not manifest any post-peak decline of virus replication despite CD8+ T cell- and B cell-mediated SIV-specific immune responses comparable to those observed in control animals. Interestingly, depleted animals displayed rapid disease progression, which was associated with increased virus replication in non-T cells as well as the emergence of CD4-independent SIV-envelopes. Our results suggest that the antiviral CD4+ T cell response may play an important role in limiting SIV replication, which has implications for the design of HIV vaccines.

Availability of activated CD4+ T cells dictates the level of viremia in naturally SIV-infected sooty mangabeys

Naturally SIV-infected sooty mangabeys (SMs) remain asymptomatic despite high virus replication. Elucidating the mechanisms underlying AIDS resistance of SIV-infected SMs may provide crucial information to better understand AIDS pathogenesis. In this study, we assessed the determinants of set-point viremia in naturally SIV-infected SMs, i.e., immune control of SIV replication versus target cell limitation. We depleted CD4+ T cells in 6 naturally SIV-infected SMs by treating with humanized anti-CD4 mAb (Cdr-OKT4A-huIgG1). CD4+ T cells were depleted almost completely in blood and BM and at variable levels in mucosal tissues and LNs. No marked depletion of CD14+ monocytes was observed. Importantly, CD4+ T cell depletion was associated with a rapid, significant decline in viral load, which returned to baseline level at day 30-45, coincident with an increased fraction of proliferating and activated CD4+ T cells. Throughout the study, virus replication correlated with the level of proliferating CD4+ T cells. CD4+ T cell depletion did not induce any changes in the fraction of Tregs or the level of SIV-specific CD8+ T cells. Our results suggest that the availability of activated CD4+ T cells, rather than immune control of SIV replication, is the main determinant of set-point viral load during natural SIV infection of SMs.

Immune activation alters cellular and humoral responses to yellow fever 17D vaccine

BACKGROUNDnDefining the parameters that modulate vaccine responses in African populations will be imperative to design effective vaccines for protection against HIV, malaria, tuberculosis, and dengue virus infections. This study aimed to evaluate the contribution of the patient-specific immune microenvironment to the response to the licensed yellow fever vaccine 17D (YF-17D) in an African cohort.nnnMETHODSnWe compared responses to YF-17D in 50 volunteers in Entebbe, Uganda, and 50 volunteers in Lausanne, Switzerland. We measured the CD8+ T cell and B cell responses induced by YF-17D and correlated them with immune parameters analyzed by flow cytometry prior to vaccination.nnnRESULTSnWe showed that YF-17D-induced CD8+ T cell and B cell responses were substantially lower in immunized individuals from Entebbe compared with immunized individuals from Lausanne. The impaired vaccine response in the Entebbe cohort associated with reduced YF-17D replication. Prior to vaccination, we observed higher frequencies of exhausted and activated NK cells, differentiated T and B cell subsets and proinflammatory monocytes, suggesting an activated immune microenvironment in the Entebbe volunteers. Interestingly, activation of CD8+ T cells and B cells as well as proinflammatory monocytes at baseline negatively correlated with YF-17D-neutralizing antibody titers after vaccination. Additionally, memory T and B cell responses in preimmunized volunteers exhibited reduced persistence in the Entebbe cohort but were boosted by a second vaccination.nnnCONCLUSIONnTogether, these results demonstrate that an activated immune microenvironment prior to vaccination impedes efficacy of the YF-17D vaccine in an African cohort and suggest that vaccine regimens may need to be boosted in African populations to achieve efficient immunity.nnnTRIAL REGISTRATIONnRegistration is not required for observational studies.nnnFUNDINGnThis study was funded by Canadas Global Health Research Initiative, Defense Threat Reduction Agency, National Institute of Allergy and Infectious Diseases, Bill & Melinda Gates Foundation, and United States Agency for International Development.

Maintenance of intestinal Th17 cells and reduced microbial translocation in SIV-infected rhesus macaques treated with interleukin (IL)-21.

In pathogenic HIV and SIV infections of humans and rhesus macaques (RMs), preferential depletion of CD4+ Th17 cells correlates with mucosal immune dysfunction and disease progression. Interleukin (IL)-21 promotes differentiation of Th17 cells, long-term maintenance of functional CD8+ T cells, and differentiation of memory B cells and antibody-secreting plasma cells. We hypothesized that administration of IL-21 will improve mucosal function in the context of pathogenic HIV/SIV infections. To test this hypothesis, we infected 12 RMs with SIVmac239 and at day 14 post-infection treated six of them with rhesus rIL-21-IgFc. IL-21-treatment was safe and did not increase plasma viral load or systemic immune activation. Compared to untreated animals, IL-21-treated RMs showed (i) higher expression of perforin and granzyme B in total and SIV-specific CD8+ T cells and (ii) higher levels of intestinal Th17 cells. Remarkably, increased levels of Th17 cells were associated with reduced levels of intestinal T cell proliferation, microbial translocation and systemic activation/inflammation in the chronic infection. In conclusion, IL-21-treatment in SIV-infected RMs improved mucosal immune function through enhanced preservation of Th17 cells. Further preclinical studies of IL-21 may be warranted to test its potential use during chronic infection in conjunction with antiretroviral therapy.

The amino acid sensor GCN2 controls gut inflammation by inhibiting inflammasome activation

The integrated stress response (ISR) is a homeostatic mechanism by which eukaryotic cells sense and respond to stress-inducing signals, such as amino acid starvation. General controlled non-repressed (GCN2) kinase is a key orchestrator of the ISR, and modulates protein synthesis in response to amino acid starvation. Here we demonstrate in mice that GCN2 controls intestinal inflammation by suppressing inflammasome activation. Enhanced activation of ISR was observed in intestinal antigen presenting cells (APCs) and epithelial cells during amino acid starvation, or intestinal inflammation. Genetic deletion of Gcn2 (also known as Eif2ka4) in CD11c+ APCs or intestinal epithelial cells resulted in enhanced intestinal inflammation and T helper 17 cell (TH17) responses, owing to enhanced inflammasome activation and interleukin (IL)-1β production. This was caused by reduced autophagy in Gcn2−/− intestinal APCs and epithelial cells, leading to increased reactive oxygen species (ROS), a potent activator of inflammasomes. Thus, conditional ablation of Atg5 or Atg7 in intestinal APCs resulted in enhanced ROS and TH17 responses. Furthermore, in vivo blockade of ROS and IL-1β resulted in inhibition of TH17 responses and reduced inflammation in Gcn2−/− mice. Importantly, acute amino acid starvation suppressed intestinal inflammation via a mechanism dependent on GCN2. These results reveal a mechanism that couples amino acid sensing with control of intestinal inflammation via GCN2.

CD8+ Lymphocytes Are Required for Maintaining Viral Suppression in SIV-Infected Macaques Treated with Short-Term Antiretroviral Therapy

Infection with HIV persists despite suppressive antiretroviral therapy (ART), and treatment interruption results in rapid viral rebound. Antibody-mediated CD8(+) lymphocyte depletion in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) shows that these cells contribute to viral control inxa0untreated animals. However, the contribution of CD8(+) lymphocytes to maintaining viral suppression under ART remains unknown. Here, we have shown that in SIV-infected RMs treated with short-term (i.e., 8-32xa0week) ART, depletion of CD8(+) lymphocytes resulted in increased plasma viremia in all animals and that repopulation of CD8(+) Txa0cells was associatedxa0with prompt reestablishment of virus control. Although the number of SIV-DNA-positive cells remained unchanged after CD8 depletion and reconstitution, the frequency of SIV-infected CD4(+) Txa0cells before depletion positively correlated with both the peak and area under the curve of viremia after depletion. These results suggest a role for CD8(+) Txa0cells inxa0controlling viral production during ART, thus providing a rationale for exploring immunotherapeutic approaches in ART-treated HIV-infected individuals.

Treatment of SIV-infected sooty mangabeys with a type-I IFN agonist results in decreased virus replication without inducing hyperimmune activation

A key feature differentiating nonpathogenic SIV infection of sooty mangabeys (SMs) from pathogenic HIV/SIV infections is the rapid resolution of type I IFN (IFN-I) responses and IFN-stimulated gene expression during the acute-to-chronic phase transition and the establishment of an immune quiescent state that persists throughout the chronic infection. We hypothesized that low levels of IFN-I signaling may help to prevent chronic immune activation and disease progression in SIV-infected SMs. To assess the effects of IFN-I signaling in this setting, in the present study, we administered recombinant rhesus macaque IFNα2-IgFc (rmIFNα2) to 8 naturally SIV-infected SMs weekly for 16 weeks. Gene-expression profiling revealed a strong up-regulation of IFN-stimulated genes in the blood of treated animals, confirming the reagents bioactivity. Interestingly, we observed an approximately 1-log decrease in viral load that persisted through day 35 of treatment. Flow cytometric analysis of lymphocytes in the blood, lymph nodes, and rectal biopsies did not reveal a significant decline of CD4(+) T cells, a robust increase in lymphocyte activation, or change in the level of SIV-specific CD8(+) T cells. The results of the present study indicate that administration of type I IFNs in SIV-infected SMs induces a significant anti-viral effect that is not associated with a detectable increase in chronic immune activation.

Mother-to-Infant Transmission of Simian Immunodeficiency Virus Is Rare in Sooty Mangabeys and Is Associated with Low Viremia

ABSTRACT Mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1) occurs in utero, intrapartum, and through breastfeeding, with a cumulative rate of transmission of 35 to 40%. As a result, ∼400,000 children become infected each year. Little is known about mother-to-infant transmission (MTIT) during natural simian immunodeficiency virus (SIV) infection of sooty mangabeys (SMs) that typically is nonpathogenic despite high viral loads. In this study, we retrospectively investigated the rates of MTIT in a large colony of naturally SIV-infected SMs using serological (anti-SIV antibody by enzyme-linked immunosorbent assay [ELISA] and Western blot analysis) and virological (SIVsmm real-time reverse transcription-PCR) methods. We examined 161 SM infants born to SIV-infected mothers and found that 150 (93.2%) were infected by non-MTIT (n = 120) or remained uninfected (n = 30). The remaining 11 SM infants (6.8%) were defined as acquiring SIV by presumptive MTIT based on (i) the presence of anti-SIV antibodies without seroreversion and (ii) a viral load of >500 copies/ml of serum in the first year of life. SM infants infected with SIV by presumptive MTIT did not show any increased morbidity or mortality, indicating that the infection is nonpathogenic even when acquired early in life. Interestingly, viral loads of SIV-infected SM infants with presumptive MTIT were 2-log lower than those of SIV-infected adult SMs living in the same colony (i.e., ∼1,000 and 100,000 copies/ml, respectively). These results indicate that MTIT is substantially less frequent in naturally SIV-infected SMs than in HIV-1-infected humans and results in nonpathogenic infection associated with low SIV viremia. Evolutionary pressure to reduce MTIT may have contributed to the restriction of SIV pathogenesis in natural hosts.

Initial viral load determines the magnitude of the human CD8 T cell response to yellow fever vaccination

Significance Current vaccine development against persistent infections such as HIV and tuberculosis focuses on eliciting CD8 T cell immunity through the use of replication-incompetent or single-cycle vectors. Although inherently safe, these vectors deliver limited amounts of antigen. We investigate how antigen load affects the CD8 response by analyzing the viral load and the magnitude of the specific CD8 response after immunization with the live attenuated yellow fever vaccine (YFV-17D). Our results show that the magnitude of the CD8 response is proportional to the amount of antigen when virus load is below a threshold value and saturates above. This finding highlights the requirement that T cell-based vaccines deliver sufficient antigen to elicit a large CD8 response that may be needed for protection. CD8 T cells are a potent tool for eliminating intracellular pathogens and tumor cells. Thus, eliciting robust CD8 T-cell immunity is the basis for many vaccines under development. However, the relationship between antigen load and the magnitude of the CD8 T-cell response is not well-described in a human immune response. Here we address this issue by quantifying viral load and the CD8 T-cell response in a cohort of 80 individuals immunized with the live attenuated yellow fever vaccine (YFV-17D) by sampling peripheral blood at days 0, 1, 2, 3, 5, 7, 9, 11, 14, 30, and 90. When the virus load was below a threshold (peak virus load < 225 genomes per mL, or integrated virus load < 400 genome days per mL), the magnitude of the CD8 T-cell response correlated strongly with the virus load (R2 ∼ 0.63). As the virus load increased above this threshold, the magnitude of the CD8 T-cell responses saturated. Recent advances in CD8 T-cell–based vaccines have focused on replication-incompetent or single-cycle vectors. However, these approaches deliver relatively limited amounts of antigen after immunization. Our results highlight the requirement that T-cell–based vaccines should deliver sufficient antigen during the initial period of the immune response to elicit a large number of CD8 T cells that may be needed for protection.