AstraZeneca COVID-19 vaccine induces robust broadly cross-reactive antibody responses in Malawian adults previously infected with SARS-CoV-2.

BACKGROUND: Binding and neutralising anti-Spike antibodies play a key role in immune defence against SARS-CoV-2 infection. Since it is known that antibodies wane with time and new immune-evasive variants are emerging, we aimed to assess the dynamics of anti-Spike antibodies in an African adult population with prior SARS-CoV-2 infection and to determine the effect of subsequent COVID-19 vaccination. METHODS: Using a prospective cohort design, we recruited adults with prior laboratory-confirmed mild/moderate COVID-19 in Blantyre, Malawi, and followed them up for 270 days (n = 52). A subset of whom subsequently received a single dose of the AstraZeneca COVID-19 vaccine (ChAdOx nCov-19) (n = 12). We measured the serum concentrations of anti-Spike and receptor-binding domain (RBD) IgG antibodies using a Luminex-based assay. Anti-RBD antibody cross-reactivity across SARS-CoV-2 variants of concern (VOC) was measured using a haemagglutination test. A pseudovirus neutralisation assay was used to measure neutralisation titres across VOCs. Ordinary or repeated measures one-way ANOVA was used to compare log10 transformed data, with p value adjusted for multiple comparison using Sídák's or Holm-Sídák's test. RESULTS: We show that neutralising antibodies wane within 6 months post mild/moderate SARS-CoV-2 infection (30-60 days vs. 210-270 days; Log ID50 6.8 vs. 5.3, p = 0.0093). High levels of binding anti-Spike or anti-RBD antibodies in convalescent serum were associated with potent neutralisation activity against the homologous infecting strain (p < 0.0001). A single dose of the AstraZeneca COVID-19 vaccine following mild/moderate SARS-CoV-2 infection induced a 2 to 3-fold increase in anti-Spike and -RBD IgG levels 30 days post-vaccination (both, p < 0.0001). The anti-RBD IgG antibodies from these vaccinated individuals were broadly cross-reactive against multiple VOCs and had neutralisation potency against original D614G, beta, and delta variants. CONCLUSIONS: These findings show that the AstraZeneca COVID-19 vaccine is an effective booster for waning cross-variant antibody immunity after initial priming with SARS-CoV-2 infection. The potency of hybrid immunity and its potential to maximise the benefits of COVID-19 vaccines needs to be taken into consideration when formulating vaccination policies in sub-Saharan Africa, where there is still limited access to vaccine doses.

New management approaches to tuberculosis in people living with HIV.

PURPOSE OF REVIEW: People living with HIV (PLWH) are commonly coinfected with Mycobacterium tuberculosis, particularly in high-transmission resource-limited regions. Despite expanded access to antiretroviral therapy and tuberculosis (TB) treatment, TB remains the leading cause of death among PLWH. This review discusses recent advances in the management of TB in PLWH and examines emerging therapeutic approaches to improve outcomes of HIV-associated TB. RECENT FINDINGS: Three recent key developments have transformed the management of HIV-associated TB. First, the scaling-up of rapid point-of-care urine-based tests for screening and diagnosis of TB in PLWH has facilitated early case detection and treatment. Second, increasing the availability of potent new and repurposed drugs to treat drug-resistant TB has generated optimism about the treatment and outcome of multidrug-resistant and extensively drug-resistant TB. Third, expanded access to the integrase inhibitor dolutegravir to treat HIV in resource-limited regions has simplified the management of TB/HIV coinfected patients and minimized serious adverse events. SUMMARY: While it is unequivocal that substantial progress has been made in early detection and treatment of HIV-associated TB, significant therapeutic challenges persist. To optimize the management and outcomes of TB in HIV, therapeutic approaches that target the pathogen as well as enhance the host response should be explored.

Household air pollution causes dose-dependent inflammation and altered phagocytosis in human macrophages.

Three billion people are exposed to household air pollution from biomass fuel use. Exposure is associated with higher incidence of pneumonia, and possibly tuberculosis. Understanding mechanisms underlying these defects would improve preventive strategies. We used human alveolar macrophages obtained from healthy Malawian adults exposed naturally to household air pollution and compared them with human monocyte-derived macrophages exposed in vitro to respirable-sized particulates. Cellular inflammatory response was assessed by IL-6 and IL-8 production in response to particulate challenge; phagosomal function was tested by uptake and oxidation of fluorescence-labeled beads; ingestion and killing of Streptococcus pneumoniae and Mycobacterium tuberculosis were measured by microscopy and quantitative culture. Particulate ingestion was quantified by digital image analysis. We were able to reproduce the carbon loading of naturally exposed alveolar macrophages by in vitro exposure of monocyte-derived macrophages. Fine carbon black induced IL-8 release from monocyte-derived and alveolar macrophages (P < 0.05) with similar magnitude responses (log10 increases of 0.93 [SEM = 0.2] versus 0.74 [SEM = 0.19], respectively). Phagocytosis of pneumococci and mycobacteria was impaired with higher particulate loading. High particulate loading corresponded with a lower oxidative burst capacity (P = 0.0015). There was no overall effect on killing of M. tuberculosis. Alveolar macrophage function is altered by particulate loading. Our macrophage model is comparable morphologically to the in vivo uptake of particulates. Wood smoke-exposed cells demonstrate reduced phagocytosis, but unaffected mycobacterial killing, suggesting defects related to chronic wood smoke inhalation limited to specific innate immune functions.

Bronchoalveolar CD4+ T cell responses to respiratory antigens are impaired in HIV-infected adults.

RATIONALE: HIV-infected adults are at an increased risk of lower respiratory tract infections. HIV infection impairs systemic acquired immunity, but there is limited information in humans on HIV-related cell-mediated immune defects in the lung. OBJECTIVE: To investigate antigen-specific CD4(+) T cell responses to influenza virus, Streptococcus pneumoniae and Mycobacterium tuberculosis antigens in bronchoalveolar lavage (BAL) and peripheral blood between HIV-infected individuals and HIV-uninfected Malawian adults. METHODS: We obtained BAL fluid and blood from HIV-infected individuals (n=21) and HIV-uninfected adults (n=24). We determined the proportion of T cell subsets including naive, memory and regulatory T cells using flow cytometry, and used intracellular cytokine staining to identify CD4(+) T cells recognising influenza virus-, S pneumoniae- and M tuberculosis-antigens. MAIN RESULTS: CD4(+) T cells in BAL were predominantly of effector memory phenotype compared to blood, irrespective of HIV status (p<0.001). There was immune compartmentalisation with a higher frequency of antigen-specific CD4(+) T cells against influenza virus, S pneumoniae and M tuberculosis retained in BAL compared to blood in HIV-uninfected adults (p<0.001 in each case). Influenza virus- and M tuberculosis-specific CD4(+) T cell responses in BAL were impaired in HIV-infected individuals: proportions of total antigen-specific CD4(+) T cells and of polyfunctional IFN-γ and TNF-α-secreting cells were lower in HIV-infected individuals than in HIV-uninfected adults (p<0.05 in each case). CONCLUSIONS: BAL antigen-specific CD4(+) T cell responses against important viral and bacterial respiratory pathogens are impaired in HIV-infected adults. This might contribute to the susceptibility of HIV-infected adults to lower respiratory tract infections such as pneumonia and tuberculosis.

Something Old, Something New: Ion Channel Blockers as Potential Anti-Tuberculosis Agents.

Tuberculosis (TB) remains a challenging global health concern and claims more than a million lives every year. We lack an effective vaccine and understanding of what constitutes protective immunity against TB to inform rational vaccine design. Moreover, treatment of TB requires prolonged use of multi-drug regimens and is complicated by problems of compliance and drug resistance. While most Mycobacterium tuberculosis (Mtb) bacilli are quickly killed by the drugs, the prolonged course of treatment is required to clear persistent drug-tolerant subpopulations. Mtb's differential sensitivity to drugs is, at least in part, determined by the interaction between the bacilli and different host macrophage populations. Therefore, to design better treatment regimens for TB, we need to understand and modulate the heterogeneity and divergent responses that Mtb bacilli exhibit within macrophages. However, developing drugs de-novo is a long and expensive process. An alternative approach to expedite the development of new TB treatments is to repurpose existing drugs that were developed for other therapeutic purposes if they also possess anti-tuberculosis activity. There is growing interest in the use of immune modulators to supplement current anti-TB drugs by enhancing the host's antimycobacterial responses. Ion channel blocking agents are among the most promising of the host-directed therapeutics. Some ion channel blockers also interfere with the activity of mycobacterial efflux pumps. In this review, we discuss some of the ion channel blockers that have shown promise as potential anti-TB agents.

Single cell analysis of M. tuberculosis phenotype and macrophage lineages in the infected lung.

In this study, we detail a novel approach that combines bacterial fitness fluorescent reporter strains with scRNA-seq to simultaneously acquire the host transcriptome, surface marker expression, and bacterial phenotype for each infected cell. This approach facilitates the dissection of the functional heterogeneity of M. tuberculosis-infected alveolar (AMs) and interstitial macrophages (IMs) in vivo. We identify clusters of pro-inflammatory AMs associated with stressed bacteria, in addition to three different populations of IMs with heterogeneous bacterial phenotypes. Finally, we show that the main macrophage populations in the lung are epigenetically constrained in their response to infection, while inter-species comparison reveals that most AMs subsets are conserved between mice and humans. This conceptual approach is readily transferable to other infectious disease agents with the potential for an increased understanding of the roles that different host cell populations play during the course of an infection.

Generation of hiPSC-derived low threshold mechanoreceptors containing axonal termini resembling bulbous sensory nerve endings and expressing Piezo1 and Piezo2.

Somatosensory low threshold mechanoreceptors (LTMRs) sense innocuous mechanical forces, largely through specialized axon termini termed sensory nerve endings, where the mechanotransduction process initiates upon activation of mechanotransducers. In humans, a subset of sensory nerve endings is enlarged, forming bulb-like expansions, termed bulbous nerve endings. There is no in vitro human model to study these neuronal endings. Piezo2 is the main mechanotransducer found in LTMRs. Recent evidence shows that Piezo1, the other mechanotransducer considered absent in dorsal root ganglia (DRG), is expressed at low level in somatosensory neurons. We established a differentiation protocol to generate, from iPSC-derived neuronal precursor cells, human LTMR recapitulating bulbous sensory nerve endings and heterogeneous expression of Piezo1 and Piezo2. The derived neurons express LTMR-specific genes, convert mechanical stimuli into electrical signals and have specialized axon termini that morphologically resemble bulbous nerve endings. Piezo2 is concentrated within these enlarged axon termini. Some derived neurons express low level Piezo1, and a subset co-express both channels. Thus, we generated a unique, iPSCs-derived human model that can be used to investigate the physiology of bulbous sensory nerve endings, and the role of Piezo1 and 2 during mechanosensation.

Airway CD8+CD161++TCRvα7.2+ T Cell Depletion During Untreated HIV Infection Targets CD103 Expressing Cells.

HIV-infected adults are at an increased risk to lower respiratory tract infections (LRTIs). CD8+CD161++TCRvα7.2+ T cells are an innate-like T cell subset that are thought to play an important role in early defense against pathogens in the respiratory tract. HIV infection leads to irreversible depletion of these cells in peripheral blood, however, its impact on this subset in the human airway is still unclear. Here, we show presence of CD103 expressing CD8+CD161++TCRvα7.2+ T cells in the airway that exhibited a distinct cytokine functional profile compared to their CD103- airway counterparts and those from peripheral blood. These CD103 expressing airway CD8+CD161++TCRvα7.2+ T cells were selectively depleted in untreated HIV-infected adults compared to healthy controls. Their frequency was positively correlated with frequency of airway CD4+ T cells. Furthermore, the frequency of airway CD8+CD161++TCRvα7.2+ T cells was also inversely correlated with HIV plasma viral load, while suppressive antiretroviral therapy (ART) resulted in restoration of airway CD8+CD161++TCRvα7.2+ T cells. Our findings show that CD103 expressing airway CD8+CD161++TCRvα7.2+ T cells are functionally distinct and are preferentially depleted during untreated asymptomatic HIV infection. Depletion of CD103 expressing airway CD8+CD161++TCRvα7.2+ T cells, at a major portal of pathogen entry, could partly contribute to the increased propensity for opportunistic LRTIs observed in untreated HIV-infected adults.

Application of light sheet microscopy for qualitative and quantitative analysis of bronchus-associated lymphoid tissue in mice.

Bronchus-associated lymphoid tissue (BALT) develops at unpredictable locations around lung bronchi following pulmonary inflammation. The formation and composition of BALT have primarily been investigated by immunohistology that, due to the size of the invested organ, is usually restricted to a limited number of histological sections. To assess the entire BALT of the lung, other approaches are urgently needed. Here, we introduce a novel light sheet microscopy-based approach for assessing lymphoid tissue in the lung. Using antibody staining of whole lung lobes and optical clearing by organic solvents, we present a method that allows in-depth visualization of the entire bronchial tree, the lymphatic vasculature and the immune cell composition of the induced BALT. Furthermore, three-dimensional analysis of the entire lung allows the qualitative and quantitative enumeration of the induced BALT. Using this approach, we show that a single intranasal application of the replication-deficient poxvirus MVA induces BALT that constitutes up to 8% of the entire lung volume in mice deficient in CCR7, in contrast to wild type mice (WT). Furthermore, BALT induced by heat-inactivated E. coli is dominated by a pronounced T cell infiltration in Cxcr5-deficient mice, in contrast to WT mice.

Delayed reconstitution of B cell immunity to pneumococcus in HIV-infected Malawian children on antiretroviral therapy.

OBJECTIVE: Despite CD4(+) count restoration and viral load suppression with antiretroviral therapy (ART), HIV-infected children remain at increased risk of life-threatening infections including invasive pneumococcal disease (IPD). We therefore investigated whether persistent susceptibility to IPD following ART is associated with incomplete recovery of B-cell function. METHODS: 41 HIV-infected Malawian children commencing ART were followed-up for a 1 year period during which time blood samples were collected at 0, 3, 6 and 12 months for comprehensive immunophenotyping and pneumomococcal-specific Memory B-cell Enzyme-Linked Immunospot assays. In addition, nasopharyngeal swab samples were cultured to determine pneumococcal carriage rates. RESULTS: Normalization of major lymphocyte subsets such as CD4(+) percentages was evident following 3 months of ART. The proportions of mature naïve B cells (CD19(+) CD10(-) CD27(-) CD21(hi)) and resting memory B cells (CD19(+) CD27(+) CD21(hi)) increased and apoptosis-prone mature activated B cells (CD19(+) CD21(lo) CD10(-)) decreased markedly by 12 months. However, in the context of high nasopharyngeal pneumococcal carriage rates (83%), restoration of pneumococcal protein antigen-specific B-cell memory was more delayed. CONCLUSIONS: These data show that, in chronically HIV-infected children receiving ART, improvement in B-cell memory profiles and function is slower than CD4(+) T-cells. This supports early initiation of ART and informs research into optimal timing of immunization with pneumococcal vaccines.

Kinetics of Mycobacterium tuberculosis-specific IFN-γ responses and sputum bacillary clearance in HIV-infected adults during treatment of pulmonary tuberculosis.

In HIV-uninfected adults with pulmonary tuberculosis (TB), anti-TB treatment is associated with changes in Mycobacterium tuberculosis (Mtb)-specific immune responses, which correlate with sputum bacillary load. It is unclear if this occurs in HIV-infected TB patients. We investigated changes in Mtb-specific immune responses and sputum bacillary clearance during anti-TB treatment in HIV-infected and HIV-uninfected adults with pulmonary TB. Sputum bacillary load was assessed by smear microscopy and culture. Mtb-specific IFN-γ secreting peripheral blood mononuclear cells were enumerated using an ELISPOT assay following stimulation with PPD, ESAT-6 and CFP-10. The baseline frequency of Mtb-specific IFN-γ secreting cells was lower in HIV-infected than HIV-uninfected patients (median PPD 32 vs. 104 Spot Forming Units (SFU), p = 0.05; CFP-10 19 vs. 74 SFU, p = 0.01). ESAT-6-specific IFN-γ secreting cells and sputum bacillary load declined progressively during treatment in both HIV-infected and HIV-uninfected patients. HIV infection did not influence the 2-month sputum culture conversion rate (Odds Ratio 0.89, p = 0.95). These findings suggest that changes in ESAT-6-specific immune responses during anti-TB treatment correspond with changes in sputum bacillary load irrespective of host HIV infection status. The utility of Mtb-specific IFN-γ responses as a proxy measure of treatment response in HIV-infected TB patients warrants further evaluation in other settings.

Incomplete recovery of pneumococcal CD4 T cell immunity after initiation of antiretroviral therapy in HIV-infected malawian adults.

HIV-infected African adults are at a considerably increased risk of life-threatening invasive pneumococcal disease (IPD) which persists despite antiretroviral therapy (ART). Defects in naturally acquired pneumococcal-specific T-cell immunity have been identified in HIV-infected adults. We have therefore determined the extent and nature of pneumococcal antigen-specific immune recovery following ART. HIV-infected adults were followed up at 3, 6 and 12 months after initiating ART. Nasopharyngeal swabs were cultured to determine carriage rates. Pneumococcal-specific CD4 T-cell immunity was assessed by IFN-γ ELISpot, proliferation assay, CD154 expression and intracellular cytokine assay. S. pneumoniae colonization was detected in 27% (13/48) of HIV-infected patients prior to ART. The rates remained elevated after 12 months ART, 41% (16/39) (p = 0.17) and significantly higher than in HIV-uninfected individuals (HIVneg 14%(4/29); p = 0.0147). CD4+ T-cell proliferative responses to pneumococcal antigens increased significantly to levels comparable with HIV-negative individuals at 12 months ART (p = 0.0799). However, recovery of the pneumococcal-specific CD154 expression was incomplete (p = 0.0015) as were IFN-γ ELISpot responses (p = 0.0040) and polyfunctional CD4+ T-cell responses (TNF-α, IL-2 and IFN-γ expression) (p = 0.0040) to a pneumolysin-deficient mutant strain. Impaired control of pneumococcal colonisation and incomplete restoration of pneumococcal-specific immunity may explain the persistently higher risk of IPD amongst HIV-infected adults on ART. Whether vaccination and prolonged ART can overcome this immunological defect and reduce the high levels of pneumococcal colonisation requires further evaluation.

Naturally-acquired influenza-specific CD4+ T-cell proliferative responses are impaired in HIV-infected African adults.

BACKGROUND: Seasonal influenza has been associated with greater morbidity and mortality in AIDS patients. Highly-active antiretroviral therapy (HAART) has led to some reduction in influenza-related complications but the nature of naturally-acquired T-cell immunity to influenza virus in an African setting, and how this changes with immune reconstitution following HAART is unknown. We measured influenza-specific CD4(+) T-cell immunity in unimmunized HIV-infected Malawian adults and then investigated immune reconstitution following HAART. METHODS: Peripheral blood mononuclear cells were isolated from HIV-infected and HIV-uninfected Malawian adults. CFSE proliferation and CD154 expression flow cytometry-based assays were used to measure influenza-specific CD4(+) T-cell immunity. RESULTS: We found lower naturally-acquired proliferative influenza-specific CD4(+) T-cell responses in AIDS patients that was also present in asymptomatic HIV-infected adults with relatively high CD4 counts (>350 cells/µl). Influenza-specific CD4(+) T-cell immune reconstitution in HIV-infected patients on HAART for 12 months was poor despite a marked reduction in viral load and an increase in CD4 count. This poor immune reconstitution was characterised by a low influenza-specific proliferative CD4(+) T-cell response and reduced proportions of CD154-expressing influenza-specific CD4(+) T-cells in peripheral blood. CONCLUSION: Our data suggest that asymptomatic HIV-infected adults may also be at risk of influenza-related complications and that HAART alone may not circumvent this risk in AIDS patients. This study highlights the need to identify possible interventions early in HIV infection to reduce the risk of influenza and to intensify influenza surveillance in these susceptible African populations.

Impaired CD4 T cell memory response to Streptococcus pneumoniae precedes CD4 T cell depletion in HIV-infected Malawian adults.

OBJECTIVE: Invasive pneumococcal disease (IPD) is a leading cause of morbidity and mortality in HIV-infected African adults. CD4 T cell depletion may partially explain this high disease burden but those with relatively preserved T cell numbers are still at increased risk of IPD. This study evaluated the extent of pneumococcal-specific T cell memory dysfunction in asymptomatic HIV infection early on in the evolution of the disease. METHODS: Peripheral blood mononuclear cells were isolated from asymptomatic HIV-infected and HIV-uninfected Malawian adults and stained to characterize the underlying degree of CD4 T cell immune activation, senescence and regulation. Pneumococcal-specific T cell proliferation, IFN-γ, IL-17 production and CD154 expression was assessed using flow cytometry and ELISpot. RESULTS: We find that in asymptomatic HIV-infected Malawian adults, there is considerable immune disruption with an increase in activated and senescent CD4+CD38+PD-1+ and CD4+CD25(high)Foxp3+ Treg cells. In the context of high pneumococcal exposure and therefore immune stimulation, show a failure in pneumococcal-specific memory T cell proliferation, skewing of T cell cytokine production with preservation of interleukin-17 but decreased interferon-gamma responses, and failure of activated T cells to express the co-stimulatory molecule CD154. CONCLUSION: Asymptomatic HIV-infected Malawian adults show early signs of pneumococcal- specific immune dysregulation with a shift in the balance of CD4 memory, T helper 17 cells and Treg. Together these data offer a mechanistic understanding of how antigen-specific T cell dysfunction occurs prior to T cell depletion and may explain the early susceptibility to IPD in those with relatively preserved CD4 T cell numbers.