CD3 downregulation identifies high-avidity human CD8 T cells.

CD8 T cells recognize infected and cancerous cells via their T-cell receptor (TCR), which binds peptide-MHC complexes on the target cell. The affinity of the interaction between the TCR and peptide-MHC contributes to the antigen sensitivity, or functional avidity, of the CD8 T cell. In response to peptide-MHC stimulation, the TCR-CD3 complex and CD8 co-receptor are downmodulated. We quantified CD3 and CD8 downmodulation following stimulation of human CD8 T cells with CMV, EBV, and HIV peptides spanning eight MHC restrictions, observing a strong correlation between the levels of CD3 and CD8 downmodulation and functional avidity, regardless of peptide viral origin. In TCR-transduced T cells targeting a tumor-associated antigen, changes in TCR-peptide affinity were sufficient to modify CD3 and CD8 downmodulation. Correlation analysis and generalized linear modeling indicated that CD3 downmodulation was the stronger correlate of avidity. CD3 downmodulation, simply measured using flow cytometry, can be used to identify high-avidity CD8 T cells in a clinical context.

CD8 T Cell Virus Inhibition Assay Protocol.

The human immunodeficiency virus (HIV)-1 viral inhibition assay (VIA) measures CD8+ T cell-mediated inhibition of HIV replication in CD4+ T cells and is increasingly used for clinical testing of HIV vaccines and immunotherapies. Different VIAs that differ in length of CD8:CD4 T cell culture periods (6-13 days), purity of CD4 cultures [isolated CD4+ T cells or CD8+ depleted peripheral blood mononuclear cells (PBMCs)], HIV strains (laboratory strains, isolates, reporter viruses) and read-outs of virus inhibition (p24 ELISA, intracellular measurement of p24, luciferase reporter expression, and viral gag RNA) have been reported. Here, we describe multiple modifications to a 7-day VIA protocol, the most impactful being the introduction of independent replicate cultures for both HIV infected-CD4 (HIV-CD4) and HIV-CD4:CD8 T cell cultures. Virus inhibition was quantified using a ratio of weighted averages of p24+ cells in replicate cultures and the corresponding 95% confidence intervals. We identify methodological and analysis changes that could be incorporated into other protocols to improve assay reproducibility. We found that in people living with HIV (PLWH) on antiretroviral therapy (ART), CD8 T cell virus inhibition was largely stable over time, supporting the use of this assay and/or analysis methods to examine therapeutic interventions. Graphic abstract.

Corrigendum: Reliable estimation of CD8 T cell inhibition of in vitro HIV-1 replication.

[This corrects the article DOI: 10.3389/fimmu.2021.666991.].

Vaccines: Underlying Principles of Design and Testing.

In this paper, we review the key elements that should be considered to take a novel vaccine from the laboratory through to licensure in the modern era. This paper is divided into four sections. First, we discuss the host immune responses that we engage with vaccines. Second, we discuss how in vivo and in vitro studies can inform vaccine design. Third, we discuss different vaccine modalities that have been licensed or are in testing in humans. Last, we overview the basic principles of vaccine approvals. Throughout we provide real-world examples of vaccine development against infectious diseases, including coronavirus disease 2019 (COVID-19).

Reliable Estimation of CD8 T Cell Inhibition of In Vitro HIV-1 Replication.

The HIV-1 viral inhibition assay (VIA) measures CD8 T cell-mediated inhibition of HIV replication in CD4 T cells and is increasingly used for clinical testing of HIV vaccines and immunotherapies. The VIA has multiple sources of variability arising from in vitro HIV infection and co-culture of two T cell populations. Here, we describe multiple modifications to a 7-day VIA protocol, the most impactful being the introduction of independent replicate cultures for both HIV infected-CD4 (HIV-CD4) and HIV-CD4:CD8 T cell cultures. Virus inhibition was quantified using a ratio of weighted averages of p24+ cells in replicate cultures and the corresponding 95% confidence interval. An Excel template is provided to facilitate calculations. Virus inhibition was higher in people living with HIV suppressed on antiretroviral therapy (n=14, mean: 40.0%, median: 43.8%, range: 8.2 to 73.3%; p < 0.0001, two-tailed, exact Mann-Whitney test) compared to HIV-seronegative donors (n = 21, mean: -13.7%, median: -14.4%, range: -49.9 to 20.9%) and was stable over time (n = 6, mean %COV 9.4%, range 0.9 to 17.3%). Cross-sectional data were used to define 8% inhibition as the threshold to confidently detect specific CD8 T cell activity and determine the minimum number of culture replicates and p24+ cells needed to have 90% statistical power to detect this threshold. Last, we note that, in HIV seronegative donors, the addition of CD8 T cells to HIV infected CD4 T cells consistently increased HIV replication, though the level of increase varied markedly between donors. This co-culture effect may contribute to the weak correlations observed between CD8 T cell VIA and other measures of HIV-specific CD8 T cell function.

Acute exposure to chlorpyrifos caused NADPH oxidase mediated oxidative stress and neurotoxicity in a striatal cell model of Huntington's disease.

We hypothesized that expression of mutant Huntingtin (HTT) would modulate the neurotoxicity of the commonly used organophosphate insecticide, chlorpyrifos (CPF), revealing cellular mechanisms underlying neurodegeneration. Using a mouse striatal cell model of HD, we report that mutant HD cells are more susceptible to CPF-induced cytotoxicity as compared to wild-type. This CPF-induced cytotoxicity caused increased production of reactive oxygen species, reduced glutathione levels, decreased superoxide dismutase activity, and increased malondialdehyde levels in mutant HD cells relative to wild-type. Furthermore, we show that co-treatment with antioxidant agents attenuated the CPF-induced ROS levels and cytotoxicity. Co-treatment with a NADPH oxidase (NOX) inhibitor, apocynin, also attenuated the CPF-induced ROS production and neurotoxicity. CPF caused increased NOX activity in mutant HD lines that was ameliorated following co-treatment with apocynin. Finally, CPF-induced neurotoxicity significantly increased the protein expression of nuclear factor erythroid 2-related factor (Nrf2) in mutant HD cells as compared to wild-type. This study is the first report of CPF-induced toxicity in HD pathophysiology and suggests that mutant HTT and CPF exhibit a disease-toxicant interaction wherein expression of mutant HTT enhances CPF-induced neurotoxicity via a NOX-mediated oxidative stress mechanism to cause neuronal loss in the full length HTT expressing striatal cells.