CD8(+) lymphocytes suppress human immunodeficiency virus 1 replication by secreting type I interferons

CD8+ Lymphocytes from Healthy Blood Donors Secrete Antiviral Levels of Interferon-Alpha

The adaptive immune response to viral infections features the antigen-driven expansion of CD8+ T cells. These cells are widely recognized for their cytolytic activity that is mediated through the secretion of cytokines such as perforin and granzymes. Less appreciated is their ability to secrete soluble factors that restrict virus replication without killing the infected cells. In this study we measured the ability of primary anti-CD3/28-stimulated CD8+ T cells from healthy blood donors to secrete interferon-alpha. Supernatants collected from CD8+ T cell cultures were screened for their ability to suppress HIV-1 replication in vitro and their interferon-alpha concentrations were measured by ELISA. Interferon-alpha concentrations in the CD8+ T cell culture supernatants ranged from undetectable to 28.6 pg/mL. The anti-HIV-1 activity of the cell culture supernatants was observed to be dependent on the presence of interferon-alpha. Appreciable increases in the expression levels of type 1 interferon transcripts were observed following T cell receptor stimulation, suggesting that the secretion of interferon-alpha by CD8+ T cells is an antigen-driven response. In 42-plex cytokine assays, the cultures containing interferon-alpha were also found to contain elevated levels of GM-CSF, IL-10, IL-13, and TNF-alpha. Together, these results demonstrate that the secretion of anti-viral levels of interferon-alpha is a common function of CD8+ T cells. Furthermore, this CD8+ T cell function likely plays broader roles in health and disease.

HLA-DQB1*06 and breadth of Nef core region-specific T-cell response are associated with slow disease progression in antiretroviral therapy-naive Chinese HIV-1 subtype B patients

Vaccines still are an important way to prevent and treat acquired immunodeficiency syndrome (AIDS). ¹ For developing an effective T cell-based AIDS vaccine, it is critical to define the human leukocyte antigen (HLA) type and epitope that elicit the most potent responses. This study involved 29 antiretroviral therapy-naive and chronic human immunodeficiency virus (HIV)-1 subtype B-infected individuals. A polymerase chain reaction-sequence-specific primer was used to detect the HLA typing, and the enzyme-linked immunospot assay to quantify the T-cell immune function. The results showed that the HLA-DQB1*06-positive group had higher CD4 counts and lower viral load (VL) compared with the HLA-DQB1*06-negative group; A higher magnitude of HIV-1-specific T-cell response and breadth were observed in the HLA-DQB1*06-positive group; the T-cell response was proportional to VL (R² = 0.488, P = 0.0368) in the HLA-DQB1*06-positive group. The total T-cell responses to HIV-1 Nef core region were quantified at the single-peptide level. Nine (90%) peptides were recognized in 18 (62.1%) individuals. The breath of Nef core region-specific T-cell response was correlated positively with CD4⁺ T cell count and inversely with VL, which improved disease outcomes. These data revealed that HLA-DQB1*06 had a protective effect on the course of HIV-1 and T-cell targeting of certain specific Nef epitopes, contributing to HIV-1 suppression. The results suggested the potential use of HLA-DQB1*06 and Nef core region in HIV-1 T-cell vaccine design.

Prior Puma Lentivirus Infection Modifies Early Immune Responses and Attenuates Feline Immunodeficiency Virus Infection in Cats

We previously showed that cats that were infected with non-pathogenic Puma lentivirus (PLV) and then infected with pathogenic feline immunodeficiency virus (FIV) (co-infection with the host adapted/pathogenic virus) had delayed FIV proviral and RNA viral loads in blood, with viral set-points that were lower than cats infected solely with FIV. This difference was associated with global CD4⁺ T cell preservation, greater interferon gamma (IFN-γ) mRNA expression, and no cytotoxic T lymphocyte responses in co-infected cats relative to cats with a single FIV infection. In this study, we reinforced previous observations that prior exposure to an apathogenic lentivirus infection can diminish the effects of acute infection with a second, more virulent, viral exposure. In addition, we investigated whether the viral load differences that were observed between PLV/FIV and FIV infected cats were associated with different immunocyte phenotypes and cytokines. We found that the immune landscape at the time of FIV infection influences the infection outcome. The novel findings in this study advance our knowledge about early immune correlates and documents an immune state that is associated with PLV/FIV co-infection that has positive outcomes for lentiviral diseases.

Recovery and assessment of leukocytes from LR Express filters

Leukocytes, or white blood cells, are used for a variety of investigational purposes and they offer advantages over laboratory-adapted cell lines. Leukocytes that are typically discarded by blood banks during the collection of red blood cells, platelets, and plasma can often be obtained for research use. However, the available leukocytes are frequently contained within a blood filtration device, such as the Terumo LR Express (TLRE) filter. In this study, procedures were evaluated for the ability to elute viable leukocytes from TLRE filters. The recovered leukocytes were assessed for composition, growth, and functionality. The large majority (>70%) of leukocytes were eluted with a single reverse-elution procedure and the recovered cells contained representative populations of the major leukocyte subsets. Purified T cells exhibited diverse T cell receptor repertoires, characteristic growth upon mitogen stimulation, and CD4⁺ T cells were able to support HIV-1 propagation. Purified monocytes were able to be differentiated into phenotypically characteristic populations of macrophages and dendritic cells. Overall, TLRE filters offer an attractive source of primary human cells for research and possibly clinical purposes.

Brief Report: Increased Expression of the Type I Interferon Receptor on CD4+ T Lymphocytes in HIV-1-Infected Individuals

BACKGROUND

Type I interferons (IFN1s; eg, interferon-alpha and interferon-beta) are potent cytokines that inhibit the replication of human immunodeficiency virus-1 (HIV-1) and other viruses. The antiviral and immunoregulatory activities of IFN1 are mediated through ligand-receptor interactions with the IFN1 receptor complex (IFNAR). Variation in the cell-surface density of IFNAR could play a role in HIV-1 pathogenesis.

METHODS

In this cross-sectional study of fresh whole blood, we used flow cytometry to evaluate the expression of IFNAR2 on lymphocyte subsets from HIV-1-infected (n = 33) and HIV-1-uninfected (n = 22) individuals.

RESULTS

In comparison with healthy blood bank donors, we observed that the HIV-1-infected individuals, particularly those having advanced to disease, exhibited the increased expression of IFNAR2 on CD4 T cells (relative fluorescence intensity 6.9 vs. 9.0; P = 0.027). The CD4:CD4 T-cell IFNAR2 expression-level ratio provides an internally standardized measure of this alteration. The observed increased expression of IFNAR2 was largely restricted to CD4 T cells that expressed the chemokine receptor CXCR4 and lacked the expression of CCR5.

CONCLUSIONS

HIV-1-infected individuals exhibit an increased expression of the IFN1 receptor on CD4 T cells. The level of IFNAR2 expression seems to increase with disease progression. These findings provide insight for the immunologic alterations associated with HIV-1 infection and possibly new therapeutic approaches.

Pre-infection transcript levels of FAM26F in peripheral blood mononuclear cells inform about overall plasma viral load in acute and post-acute phase after simian immunodeficiency virus infection

CD8⁺ cells from simian immunodeficiency virus (SIV)-infected long-term non-progressors and some uninfected macaques can suppress viral replication in vitro without killing the infected cells. The aim of this study was to identify factors responsible for non-cytolytic viral suppression by transcriptional profiling and to investigate their potential impact on SIV replication. Results of microarray experiments and further validation with cells from infected and uninfected macaques revealed that FAM26F RNA levels distinguished CD8⁺ cells of controllers and non-controllers (P=0.001). However, FAM26F was also expressed in CD4⁺ T-cells and B-cells. FAM26F expression increased in lymphocytes after in vitro IFN-γ treatment on average 40-fold, and ex vivo FAM26F RNA levels in peripheral blood mononuclear cells correlated with plasma IFN-γ but not with IFN-α. Baseline FAM26F expression appeared to be stable for months, albeit the individual expression levels varied up to tenfold. Investigating its role in SIV-infection revealed that FAM26F was upregulated after infection (P<0.0008), but did not directly correlate with viral load in contrast to MX1 and CXCL10. However, pre-infection levels of FAM26F correlated inversely with overall plasma viral load (AUC) during the acute and post-acute phases of infection (e.g. AUC weeks post infection 0–8; no AIDS vaccine: P<0.0001, Spearman rank correlation coefficient (rs)=−0.89, n=16; immunized with an AIDS vaccine: P=0.033, rs=−0.43; n=25). FAM26F transcript levels prior to infection can provide information about the pace and strength of the antiviral immune response during the early stage of infection. FAM26F expression represented, in our experiments, one of the earliest prognostic markers, and could supplement major histocompatibility complex (MHC)-typing to predict disease progression before SIV-infection.

Noncytolytic CD8+ Cell Mediated Antiviral Response Represents a Strong Element in the Immune Response of Simian Immunodeficiency Virus-Infected Long-Term Non-Progressing Rhesus Macaques

The ability of long term non progressors to maintain very low levels of HIV/SIV and a healthy state, involves various host genetic and immunological factors. CD8+ non-cytolytic antiviral response (CNAR) most likely plays an important role in this regard. In order to gain a deeper insight into this unique phenomenon, the ability of CD8+ T cells to suppress viral replication in vitro was investigated in 16 uninfected, longitudinally in 23 SIV-infected long-term non-progressing (LTNPs), and 10 SIV-infected rhesus macaques with progressing disease. An acute infection assay utilizing CD4⁺ cells from MHC-mismatched monkeys to avoid cytolytic responses was employed. The study has identified CNAR as a long-term stable activity that inversely correlated with plasma viral load. The activity was also detected in CD8⁺ cells of uninfected macaques, which indicates that CNAR is not necessarily a virus specific response but increases after SIV-infection. Physical contact between CD4⁺ and CD8⁺ cells was mainly involved in mediating viral inhibition. Loss of this activity appeared to be due to a loss of CNAR-expressing CD8+ cells as well as a reduction of CNAR-responsive CD4+ cells. In contrast, in vitro viral replication did not differ in CD4+ cells from un-infected macaques, CNAR(+) and CNAR(-) LTNPs. A role for transitional memory cells in supporting CNAR in the macaque model of AIDS was questionable. CNAR appears to represent an important part of the immune response displayed by CD8+ T cells which might be underestimated up to now.

SAMHD1 Limits HIV-1 Antigen Presentation by Monocyte-Derived Dendritic Cells

Monocyte-derived dendritic cells (MDDC) stimulate CD8 cytotoxic T lymphocytes (CTL) by presenting endogenous and exogenous viral peptides via major histocompatibility complex class I (MHC-I) molecules. MDDC are poorly susceptible to HIV-1, in part due to the presence of SAMHD1, a cellular enzyme that depletes intracellular deoxynucleoside triphosphates (dNTPs) and degrades viral RNA. Vpx, an HIV-2/SIVsm protein absent from HIV-1, antagonizes SAMHD1 by inducing its degradation. The impact of SAMHD1 on the adaptive cellular immune response remains poorly characterized. Here, we asked whether SAMHD1 modulates MHC-I-restricted HIV-1 antigen presentation. Untreated MDDC or MDDC pretreated with Vpx were exposed to HIV-1, and antigen presentation was examined by monitoring the activation of an HIV-1 Gag-specific CTL clone. SAMHD1 depletion strongly enhanced productive infection of MDDC as well as endogenous HIV-1 antigen presentation. Time-lapse microscopy analysis demonstrated that in the absence of SAMHD1, the CTL rapidly killed infected MDDC. We also report that various transmitted/founder (T/F) HIV-1 strains poorly infected MDDC and, as a consequence, did not stimulate CTL. Vesicular stomatitis virus glycoprotein (VSV-G) pseudotyping of T/F alleviated a block in viral entry and induced antigen presentation only in the absence of SAMHD1. Furthermore, by using another CTL clone that mostly recognizes incoming HIV-1 antigens, we demonstrate that SAMHD1 does not influence exogenous viral antigen presentation. Altogether, our results demonstrate that the antiviral activity of SAMHD1 impacts antigen presentation by DC, highlighting the link that exists between restriction factors and adaptive immune responses.

IMPORTANCE

Upon viral infection, DC may present antigens derived from incoming viral material in the absence of productive infection of DC or from newly synthesized viral proteins. In the case of HIV, productive infection of DC is blocked at an early postentry step. This is due to the presence of SAMHD1, a cellular enzyme that depletes intracellular levels of dNTPs and inhibits viral reverse transcription. We show that the depletion of SAMHD1 in DCs strongly stimulates the presentation of viral antigens derived from newly produced viral proteins, leading to the activation of HIV-1-specific cytotoxic T lymphocytes (CTL). We further show in real time that the enhanced activation of CTL leads to killing of infected DCs. Our results indicate that the antiviral activity of SAMHD1 not only impacts HIV replication but also impacts antigen presentation by DC. They highlight the link that exists between restriction factors and adaptive immune responses.