Kim Blom

High Levels of Chronic Immune Activation in the T-Cell Compartments of Patients Coinfected with Hepatitis C Virus and Human Immunodeficiency Virus Type 1 and on Highly Active Antiretroviral Therapy Are Reverted by Alpha Interferon and Ribavirin Treatment

ABSTRACT Chronic immune activation is a driver of human immunodeficiency virus type 1 (HIV-1) disease progression. Here, we describe that subjects with chronic hepatitis C virus (HCV)/HIV-1 coinfection display sharply elevated immune activation as determined by CD38 expression in T cells. This occurs, despite effective antiretroviral therapy, in both CD8 and CD4 T cells and is more pronounced than in the appropriate monoinfected control groups. Interestingly, the suppression of HCV by pegylated alpha interferon and ribavirin treatment reduces activation. High HCV loads and elevated levels of chronic immune activation may contribute to the high rates of viral disease progression observed in HCV/HIV-1-coinfected patients.

Expansion of Functionally Skewed CD56-Negative NK Cells in Chronic Hepatitis C Virus Infection: Correlation with Outcome of Pegylated IFN-α and Ribavirin Treatment

NK cells are important innate immune effector cells, normally characterized as CD56+CD3− lymphocytes. In this study, we report that CD56−CD16+ NK cells expand in many patients with chronic hepatitis C virus infection. These CD56− NK cells were functionally impaired with respect to cytokine production upon target cell recognition, in comparison to CD56dim and CD56bright NK cell subsets. In particular, CD56− NK cells were strikingly defective in their polyfunctional response as measured by the coexpression of MIP-1β, IFN-γ, TNF-α, and CD107a degranulation. The ability of these cells to mediate three or four of these functions was poor; expression of MIP-1β alone dominated their response. CD56− NK cells retained expression of receptors such as the natural cytotoxicity receptors and NKG2D, whereas the expression of CD57 and perforin was lower when compared with CD56dim NK cells. Interestingly, pretreatment levels of CD56− NK cells correlated with the outcome of pegylated IFN-α and ribavirin treatment. In patients with CD56− NK cells in the range of healthy subjects, 80% reached a sustained virological response to treatment, whereas only 25% of patients with levels clearly above those in healthy subjects experienced a sustained virological response. Thus, chronic hepatitis C virus infection is associated with an expansion of CD56− NK cells functionally skewed toward MIP-1β production only. Furthermore, high levels of these cells reveal a disturbance in innate cellular immunity that is associated with an impaired ability to respond to antiviral treatment with IFN-α and ribavirin.

Temporal Dynamics of the Primary Human T Cell Response to Yellow Fever Virus 17D As It Matures from an Effector- to a Memory-Type Response

The live attenuated yellow fever virus (YFV) 17D vaccine provides a good model to study immune responses to an acute viral infection in humans. We studied the temporal dynamics, composition, and character of the primary human T cell response to YFV. The acute YFV-specific effector CD8 T cell response was broad and complex; it was composed of dominant responses that persisted into the memory population, as well as of transient subdominant responses that were not detected at the memory stage. Furthermore, HLA-A2– and HLA-B7–restricted YFV epitope–specific effector cells predominantly displayed a CD45RA−CCR7−PD-1+CD27high phenotype, which transitioned into a CD45RA+CCR7−PD-1−CD27low memory population phenotype. The functional profile of the YFV-specific CD8 T cell response changed in composition as it matured from an effector- to a memory-type response, and it tended to become less polyfunctional during the course of this transition. Interestingly, activation of CD4 T cells, as well as FOXP3+ T regulatory cells, in response to YFV vaccination preceded the kinetics of the CD8 T cell response. The present results contribute to our understanding of how immunodominance patterns develop, as well as the phenotypic and functional characteristics of the primary human T cell response to a viral infection as it evolves and matures into memory.

Innate and Adaptive Immune Responses Both Contribute to Pathological CD4 T Cell Activation in HIV-1 Infected Ugandans

HIV-1 disease progression is associated with persistent immune activation. However, the nature of this association is incompletely understood. Here, we investigated immune activation in the CD4 T cell compartment of chronically HIV-1 infected individuals from Rakai, Uganda. Levels of CD4 T cell activation, assessed as co-expression of PD-1, CD38 and HLA-DR, correlated directly to viral load and inversely to CD4 count. Deeper characterization of these cells indicated an effector memory phenotype with relatively frequent expression of Ki67 despite their PD-1 expression, and levels of these cells were inversely associated with FoxP3+ regulatory T cells. We therefore use the term deregulated effector memory (DEM) cells to describe them. CD4 T cells with a DEM phenotype could be generated by antigen stimulation of recall responses in vitro. Responses against HIV-1 and CMV antigens were enriched among the DEM CD4 T cells in patients, and the diverse Vβ repertoire of DEM CD4 T cells suggested they include diverse antigen-specificities. Furthermore, the levels of DEM CD4 T cells correlated directly to soluble CD14 (sCD14) and IL-6, markers of innate immune activation, in plasma. The size of the activated DEM CD4 T cell subset was predictive of the rate of disease progression, whereas IL-6 was only weakly predictive and sCD14 was not predictive. Taken together, these results are consistent with a model where systemic innate immune activation and chronic antigen stimulation of adaptive T cell responses both play important roles in driving pathological CD4 T cell immune activation in HIV-1 disease.

Specificity and Dynamics of Effector and Memory CD8 T Cell Responses in Human Tick-Borne Encephalitis Virus Infection

Tick-borne encephalitis virus (TBEV) is transferred to humans by ticks. The virus causes tick-borne encephalitis (TBE) with symptoms such as meningitis and meningoencephalitis. About one third of the patients suffer from long-lasting sequelae after clearance of the infection. Studies of the immune response during TBEV-infection are essential to the understanding of host responses to TBEV-infection and for the development of therapeutics. Here, we studied in detail the primary CD8 T cell response to TBEV in patients with acute TBE. Peripheral blood CD8 T cells mounted a considerable response to TBEV-infection as assessed by Ki67 and CD38 co-expression. These activated cells showed a CD45RA-CCR7-CD127- phenotype at day 7 after hospitalization, phenotypically defining them as effector cells. An immunodominant HLA-A2-restricted TBEV epitope was identified and utilized to study the characteristics and temporal dynamics of the antigen-specific response. The functional profile of TBEV-specific CD8 T cells was dominated by variants of mono-functional cells as the effector response matured. Antigen-specific CD8 T cells predominantly displayed a distinct Eomes+Ki67+T-bet+ effector phenotype at the peak of the response, which transitioned to an Eomes-Ki67-T-bet+ phenotype as the infection resolved and memory was established. These transcription factors thus characterize and discriminate stages of the antigen-specific T cell response during acute TBEV-infection. Altogether, CD8 T cells responded strongly to acute TBEV infection and passed through an effector phase, prior to gradual differentiation into memory cells with distinct transcription factor expression-patterns throughout the different phases.

The Human NK Cell Response to Yellow Fever Virus 17D Is Primarily Governed by NK Cell Differentiation Independently of NK Cell Education.

NK cells play an important role in the defense against viral infections. However, little is known about the regulation of NK cell responses during the first days of acute viral infections in humans. In this study, we used the live attenuated yellow fever virus (YFV) vaccine 17D as a human in vivo model to study the temporal dynamics and regulation of NK cell responses in an acute viral infection. YFV induced a robust NK cell response in vivo, with an early activation and peak in NK cell function at day 6, followed by a delayed peak in Ki67 expression, which was indicative of proliferation, at day 10. The in vivo NK cell response correlated positively with plasma type I/III IFN levels at day 6, as well as with the viral load. YFV induced an increased functional responsiveness to IL-12 and IL-18, as well as to K562 cells, indicating that the NK cells were primed in vivo. The NK cell responses were associated primarily with the stage of differentiation, because the magnitude of induced Ki67 and CD69 expression was distinctly higher in CD57− NK cells. In contrast, NK cells expressing self- and nonself-HLA class I–binding inhibitory killer cell Ig-like receptors contributed, to a similar degree, to the response. Taken together, our results indicate that NK cells are primed by type I/III IFN in vivo early after YFV infection and that their response is governed primarily by the differentiation stage, independently of killer cell Ig-like receptor/HLA class I–mediated inhibition or education.

Prospects for induction of CD8 T cell-mediated immunity to Zika virus infection by yellow fever virus vaccination

The Zika virus epidemic represents an unprecedented health crisis affecting significant parts of the world 1. On February 1st 2016, the WHO declared the reported clusters of Zika-virus induced microcephaly and other neurological disorders a Public Health Emergency of International Concern (PHEIC). The epidemic is currently ongoing in Latin America and the Caribbean, with impacts of the infection already seen in large populations of Brazil, Colombia, Mexico, Peru and beyond. No specific treatment or vaccine is available, although several candidates are under development 2. This article is protected by copyright. All rights reserved.

Differential loss of invariant natural killer T cells and FoxP3⁺ regulatory T cells in HIV-1 subtype A and subtype D infections.

Abstract:HIV-1 subtype D is associated with faster disease progression compared with subtype A. Immunological correlates of this difference remain undefined. We investigated invariant natural killer T (iNKT) cells and FoxP3+ regulatory T cells (Tregs) in Ugandans infected with either subtype. Loss of iNKT cells was pronounced in subtype D, whereas Tregs displayed more profound loss in subtype A infection. The iNKT cell levels were associated with CD4 T-cell interleukin-2 production in subtype A, but not in D, infection. Thus, these viral subtypes are associated with differential loss of iNKT cells and Tregs that may influence the quality of the adaptive immune response.

NK Cell Responses to Human Tick-Borne Encephalitis Virus Infection.

Tick-borne encephalitis virus (TBEV) is a flavivirus that is transferred to humans by infected ticks. The virus causes tick-borne encephalitis, a severe infection of the CNS with a high risk for long-lasting sequelae. Currently, no treatment exists for the disease. Understanding the cellular immune response to this infection is important to gain further understanding into the pathogenesis, treatment, and prevention of the disease. NK cells are known to participate in the control of viral infections. We performed a longitudinal analysis of the human NK cell response to TBEV infection in a cohort of infected individuals from the onset of severe clinical symptoms to the convalescence phase. NK cell activation, as measured by expression of Ki67, was apparent at the time of hospitalization. By 3 wk after hospitalization, it decreased to levels seen in healthy controls. Concomitant with the increase in NK cell activation, augmented levels of IL-12, IL-15, IL-18, IFN-γ, and TNF were detected in patient plasma. This TBEV-induced NK cell activation was restricted predominantly to differentiated CD57+CD56dim NK cells. Functionally, CD56dim NK cells responded poorly to target cells at the time of hospitalization, but they recovered functional capacity to control levels during the convalescent phase. In contrast, the responsiveness of NK cells to cytokine stimulation remained intact throughout the disease. These findings demonstrate that NK cells respond to TBEV infection with characteristics that are distinct from those of other human viral infections and provide insights into the NK cell response to clinical TBEV infection.

Breadth and Dynamics of HLA-A2– and HLA-B7–Restricted CD8+ T Cell Responses against Nonstructural Viral Proteins in Acute Human Tick-Borne Encephalitis Virus Infection

Tick-borne encephalitis virus (TBEV) is a leading cause of viral meningoencephalitis in many parts of Europe and eastwards in Asia, with high morbidity and often long-term neurologic sequelae. With no treatment available, studies of the immune response to TBEV are essential for the understanding of the immunopathogenesis of tick-borne encephalitis and for the development of therapeutics. We have previously demonstrated that CD8+ T cell responses in peripheral blood in patients with acute TBEV peak at around 7 d after hospitalization in the neuroinvasive phase of the disease. In this study, we identified six novel TBEV HLA-A2– and HLA-B7–restricted epitopes, all derived from the nonstructural proteins of TBEV. This identification allowed for a comprehensive phenotypic and temporal analysis of the HLA-A2– and HLA-B7–restricted Ag-specific CD8+ T cell response during the acute stages of human TBEV infection. HLA-A2– and HLA-B7–restricted TBEV epitope–specific effector cells predominantly displayed a CD45RA−CCR7−CD27+CD57− phenotype at day 7, which transitioned into separate distinct phenotypes for HLA-A2– and HLA-B7–restricted TBEV-specific CD8+ T cells, respectively. At day 21, the most prevalent phenotype in the HLA-A2–restricted CD8+ T cell populations was CD45RA−CCR7−CD27+CD57+, whereas the HLA-B7–restricted CD8+ T cell population was predominantly CD45RA+CCR7−CD27+CD57+. Almost all TBEV epitope–specific CD8+ T cells expressed α4 and β1 integrins at days 7 and 21, whereas the bulk CD8+ T cells expressed lower integrin levels. Taken together, human TBEV infection elicits broad responses to multiple epitopes, predominantly derived from the nonstructural part of the virus, establishing distinct maturation patterns for HLA-A2– and HLA-B7–restricted TBEV epitope–specific CD8+ T cells.