Natural carriage of Streptococcus pneumoniae is associated with increased experimental pneumococcal carriage but reduced conjugate vaccine efficacy in a human challenge model.

BACKGROUND: In Malawi, the national pneumococcal conjugate vaccine (PCV13) demonstrated less herd immunity than the USA, likely due to higher natural pneumococcal carriage rates. We assessed PCV13 efficacy against experimental pneumococcal carriage in healthy Malawian adults. We explored how natural carriage (pneumococcal carriage of any other serotype apart from 6B) influenced experimental carriage rates and vaccine efficacy. METHODS: Healthy adults aged 18-40 were randomly assigned PCV13 (n=98) or saline (n=106), followed by intranasal SPN 6B inoculation at 20,000 (n=40), 80,000 (n=74), or 160,000 (n=90) CFU/100µl, 28 days post-vaccination. We evaluated natural and experimental pneumococcal carriage before and after vaccination on days 2, 7, and 14 post-inoculation using culture and multiplex qPCR targeting lytA/cpsA genes and compared carriage rates by vaccination status. RESULTS: Of 204 participants, 19.6% (40) exhibited experimental carriage, detected by culture and 25.5% (52) by qPCR. Vaccinated individuals had lower experimental carriage rates (10.2%, n=10/98) compared to the placebo group (28.3%, n=30/106). This difference in vaccine efficacy was more pronounced in participants without natural carriage (PCV13=8% n=6/75 vs. placebo=25.9%, n=21/81) compared to those with natural carriage (PCV13=14.8%, n=4/27 vs. placebo=26.5%, n=9/34). Using a log-binomial model, vaccine effectiveness (VE) was 62%, whether assessed by culture or qPCR. Natural carriers had a lower VE of 52% compared to participants with no natural carriage (VE=69%). CONCLUSION: We have shown that PCV13 VE estimate (62%) is robust whether carriage is assessed by culture or qPCR. PCV13 had lower VE in natural carriers compared to those without natural carriage at the inoculation visit.

Fourth Controlled Human Infection Model (CHIM) meeting - CHIMs in endemic countries, May 22-23, 2023.

Earlier meetings laid the foundations for Controlled Human Infection Models (CHIMs), also known as human challenge studies and human infection studies, including Good Manufacturing Practice (GMP) production of the challenge agent, CHIM ethics, environmental safety in CHIM, recruitment, community engagement, advertising and incentives, pre-existing immunity, and clinical, immunological, and microbiological endpoints. The fourth CHIM meeting focused on CHIM studies being conducted in endemic countries. Over the last ten years we have seen a vast expansion of the number of countries in Africa performing CHIM studies, as well as a growing number of different challenge organisms being used. Community and public engagement with assiduous ethical and regulatory oversight has been central to successful introductions and should be continued, in more community-led or community-driven models. Valuable initiatives for regulation of CHIMs have been undertaken but further capacity building remains essential.

A comparison of four epidemic waves of COVID-19 in Malawi; an observational cohort study.

BACKGROUND: Compared to the abundance of clinical and genomic information available on patients hospitalised with COVID-19 disease from high-income countries, there is a paucity of data from low-income countries. Our aim was to explore the relationship between viral lineage and patient outcome. METHODS: We enrolled a prospective observational cohort of adult patients hospitalised with PCR-confirmed COVID-19 disease between July 2020 and March 2022 from Blantyre, Malawi, covering four waves of SARS-CoV-2 infections. Clinical and diagnostic data were collected using an adapted ISARIC clinical characterization protocol for COVID-19. SARS-CoV-2 isolates were sequenced using the MinION™ in Blantyre. RESULTS: We enrolled 314 patients, good quality sequencing data was available for 55 patients. The sequencing data showed that 8 of 11 participants recruited in wave one had B.1 infections, 6/6 in wave two had Beta, 25/26 in wave three had Delta and 11/12 in wave four had Omicron. Patients infected during the Delta and Omicron waves reported fewer underlying chronic conditions and a shorter time to presentation. Significantly fewer patients required oxygen (22.7% [17/75] vs. 58.6% [140/239], p < 0.001) and steroids (38.7% [29/75] vs. 70.3% [167/239], p < 0.001) in the Omicron wave compared with the other waves. Multivariable logistic-regression demonstrated a trend toward increased mortality in the Delta wave (OR 4.99 [95% CI 1.0-25.0 p = 0.05) compared to the first wave of infection. CONCLUSIONS: Our data show that each wave of patients hospitalised with SARS-CoV-2 was infected with a distinct viral variant. The clinical data suggests that patients with severe COVID-19 disease were more likely to die during the Delta wave.

Evasion of MAIT cell recognition by the African Salmonella Typhimurium ST313 pathovar that causes invasive disease.

Mucosal-associated invariant T (MAIT) cells are innate T lymphocytes activated by bacteria that produce vitamin B2 metabolites. Mouse models of infection have demonstrated a role for MAIT cells in antimicrobial defense. However, proposed protective roles of MAIT cells in human infections remain unproven and clinical conditions associated with selective absence of MAIT cells have not been identified. We report that typhoidal and nontyphoidal Salmonella enterica strains activate MAIT cells. However, S. Typhimurium sequence type 313 (ST313) lineage 2 strains, which are responsible for the burden of multidrug-resistant nontyphoidal invasive disease in Africa, escape MAIT cell recognition through overexpression of ribB This bacterial gene encodes the 4-dihydroxy-2-butanone-4-phosphate synthase enzyme of the riboflavin biosynthetic pathway. The MAIT cell-specific phenotype did not extend to other innate lymphocytes. We propose that ribB overexpression is an evolved trait that facilitates evasion from immune recognition by MAIT cells and contributes to the invasive pathogenesis of S. Typhimurium ST313 lineage 2.

Defective Monocyte Enzymatic Function and an Inhibitory Immune Phenotype in Human Immunodeficiency Virus-Exposed Uninfected African Infants in the Era of Antiretroviral Therapy.

BACKGROUND: Human immunodeficiency virus-exposed uninfected (HEU) infants are a rapidly expanding population in sub-Saharan Africa and are highly susceptible to encapsulated bacterial disease in the first year of life. The mechanism of this increased risk is still poorly understood. We investigated whether human immunodeficiency virus (HIV)-exposure dysregulates HEU immunity, vaccine-antibody production, and human herpes virus amplify this effect. METHODS: Thirty-four HIV-infected and 44 HIV-uninfected pregnant women were recruited into the birth cohort and observed up to 6 weeks of age; and then a subsequent 43 HIV-infected and 61 HIV-uninfected mother-infant pairs were recruited into a longitudinal infant cohort at either: 5-7 to 14-15; or 14-15 to 18-23 weeks of age. We compared monocyte function, innate and adaptive immune cell phenotype, and vaccine-induced antibody responses between HEU and HIV-unexposed uninfected (HU) infants. RESULTS: We demonstrate (1) altered monocyte phagosomal function and B-cell subset homeostasis and (2) lower vaccine-induced anti-Haemophilus influenzae type b (Hib) and anti-tetanus toxoid immunoglobulin G titers in HEU compared with HU infants. Human herpes virus infection was similar between HEU and HU infants. CONCLUSIONS: In the era of antiretroviral therapy-mediated viral suppression, HIV exposure may dysregulate monocyte and B-cell function, during the vulnerable period of immune maturation. This may contribute to the high rates of invasive bacterial disease and pneumonia in HEU infants.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Africa: Current Considerations and Future Projections.

The burden of severe Covid-19 has been relatively low in sib-Saharan Africa compared to Europe and the Americas. However, SARS-CoV-2 sero-prevalence data has demonstrated that there has been more widespread transmission than can be deduced from reported cases. This could be attributed to under reporting due to low testing capacity or high numbers of asymptomatic SARS-CoV-2 infection in communities. Recent data indicates that prior SARS-CoV-2 exposure is protective against reinfection and that vaccination of previously SARS-CoV-2 infected individuals induces robust cross-reactive antibody responses. Considering these data, calls for a need for a re-think of the COVID-19 vaccination strategy in sub-Saharan African settings with high SARSCoV-2 population exposure but limited available vaccine doses. A potential recommendation would be to prioritize rapid and widespread vaccination of the first dose, while waiting for more vaccines to become available.

The COVID-19 pandemic in the African continent.

In December 2019, a new coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and associated disease, coronavirus disease 2019 (COVID-19), was identified in China. This virus spread quickly and in March, 2020, it was declared a pandemic. Scientists predicted the worst scenario to occur in Africa since it was the least developed of the continents in terms of human development index, lagged behind others in achievement of the United Nations sustainable development goals (SDGs), has inadequate resources for provision of social services, and has many fragile states. In addition, there were relatively few research reporting findings on COVID-19 in Africa. On the contrary, the more developed countries reported higher disease incidences and mortality rates. However, for Africa, the earlier predictions and modelling into COVID-19 incidence and mortality did not fit into the reality. Therefore, the main objective of this forum is to bring together infectious diseases and public health experts to give an overview of COVID-19 in Africa and share their thoughts and opinions on why Africa behaved the way it did. Furthermore, the experts highlight what needs to be done to support Africa to consolidate the status quo and overcome the negative effects of COVID-19 so as to accelerate attainment of the SDGs.

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.

Inhibition of the lncRNA SAF drives activation of apoptotic effector caspases in HIV-1-infected human macrophages.

Long noncoding RNAs (lncRNAs) impart significant regulatory functions in a diverse array of biological pathways and manipulation of these RNAs provides an important avenue to modulate such pathways, particularly in disease. Our knowledge about lncRNAs' role in determination of cellular fate during HIV-1 infection remains sparse. Here, we have identified the impact of the lncRNA SAF in regulating apoptotic effector caspases in macrophages, a long-lived cellular reservoir of HIV-1, that are largely immune to virus-induced cell death. Expression of SAF is significantly up-regulated in HIV-1-infected human monocyte-derived macrophages (MDM) compared with bystander and virus-nonexposed cells. A similar enhancement in SAF RNA expression is also detected in the HIV-1-infected airway macrophages obtained by bronchoalveolar lavage of HIV-1-infected individuals. Down-regulation of SAF with siRNA treatment increases caspase-3/7 activity levels in virus-infected MDMs. This induction of apoptotic caspases occurs exclusively in HIV-1-infected macrophages and not in bystander cells, leading to a significant reduction in HIV-1 replication and overall viral burden in the macrophage culture. This study identifies targeting of the lncRNA SAF as a potential means to specifically induce cell death in HIV-1-infected macrophages.

SARS-CoV-2 exposure in Malawian blood donors: an analysis of seroprevalence and variant dynamics between January 2020 and July 2021.

BACKGROUND: By August 2021, the COVID-19 pandemic has been less severe in sub-Saharan Africa than elsewhere. In Malawi, there have been three subsequent epidemic waves. We therefore aimed to describe the dynamics of SARS-CoV-2 exposure in Malawi. METHODS: We measured the seroprevalence of anti-SARS-CoV-2 antibodies amongst randomly selected blood transfusion donor sera in Malawi from January 2020 to July 2021 using a cross-sectional study design. In a subset, we also assessed in vitro neutralisation against the original variant (D614G WT) and the Beta variant. RESULTS: A total of 5085 samples were selected from the blood donor database, of which 4075 (80.1%) were aged 20-49 years. Of the total, 1401 were seropositive. After adjustment for assay characteristics and applying population weights, seropositivity reached peaks in October 2020 (18.5%) and May 2021 (64.9%) reflecting the first two epidemic waves. Unlike the first wave, both urban and rural areas had high seropositivity in the second wave, Balaka (rural, 66.2%, April 2021), Blantyre (urban, 75.6%, May 2021), Lilongwe (urban, 78.0%, May 2021), and Mzuzu (urban, 74.6%, April 2021). Blantyre and Mzuzu also show indications of the start of a third pandemic wave with seroprevalence picking up again in July 2021 (Blantyre, 81.7%; Mzuzu, 71.0%). More first wave sera showed in vitro neutralisation activity against the original variant (78% [7/9]) than the beta variant (22% [2/9]), while more second wave sera showed neutralisation activity against the beta variant (75% [12/16]) than the original variant (63% [10/16]). CONCLUSION: The findings confirm extensive SARS-CoV-2 exposure in Malawi over two epidemic waves with likely poor cross-protection to reinfection from the first on the second wave. The dynamics of SARS-CoV-2 exposure will therefore need to be taken into account in the formulation of the COVID-19 vaccination policy in Malawi and across the region. Future studies should use an adequate sample size for the assessment of neutralisation activity across a panel of SARS-CoV-2 variants of concern/interest to estimate community immunity.

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.

Nasal Pneumococcal Density Is Associated with Microaspiration and Heightened Human Alveolar Macrophage Responsiveness to Bacterial Pathogens.

Rationale: Pneumococcal pneumonia remains a global health problem. Colonization of the nasopharynx with Streptococcus pneumoniae (Spn), although a prerequisite of infection, is the main source of exposure and immunological boosting in children and adults. However, our knowledge of how nasal colonization impacts on the lung cells, especially on the predominant alveolar macrophage (AM) population, is limited.Objectives: Using a controlled human infection model to achieve nasal colonization with 6B serotype, we investigated the effect of Spn colonization on lung cells.Methods: We collected BAL from healthy pneumococcal-challenged participants aged 18-49 years. Confocal microscopy and molecular and classical microbiology were used to investigate microaspiration and pneumococcal presence in the lower airways. AM opsonophagocytic capacity was assessed by functional assays in vitro, whereas flow cytometry and transcriptomic analysis were used to assess further changes on the lung cellular populations.Measurements and Main Results: AMs from Spn-colonized individuals exhibited increased opsonophagocytosis to pneumococcus (11.4% median increase) for approximately 3 months after experimental pneumococcal colonization. AMs also had increased responses against other bacterial pathogens. Pneumococcal DNA detected in the BAL samples of Spn-colonized individuals were positively correlated with nasal pneumococcal density (r = 0.71; P = 0.029). Similarly, AM-heightened opsonophagocytic capacity was correlated with nasopharyngeal pneumococcal density (r = 0.61, P = 0.025).Conclusions: Our findings demonstrate that nasal colonization with pneumococcus and microaspiration prime AMs, leading to brisker responsiveness to both pneumococcus and unrelated bacterial pathogens. The relative abundance of AMs in the alveolar spaces, alongside their potential for nonspecific protection, render them an attractive target for novel vaccines.

Inflammatory Phenotypes Predict Changes in Arterial Stiffness Following Antiretroviral Therapy Initiation.

BACKGROUND: Inflammation drives vascular dysfunction in HIV, but in low-income settings causes of inflammation are multiple, and include infectious and environmental factors. We hypothesized that patients with advanced immunosuppression could be stratified into inflammatory phenotypes that predicted changes in vascular dysfunction on ART. METHODS: We recruited Malawian adults with CD4 <100 cells/µL 2 weeks after starting ART in the REALITY trial (NCT01825031). Carotid femoral pulse-wave velocity (cfPWV) measured arterial stiffness 2, 12, 24, and 42 weeks post-ART initiation. Plasma inflammation markers were measured by electrochemiluminescence at weeks 2 and 42. Hierarchical clustering on principal components identified inflammatory clusters. RESULTS: 211 participants with HIV grouped into 3 inflammatory clusters representing 51 (24%; cluster-1), 153 (73%; cluster-2), and 7 (3%; cluster-3) individuals. Cluster-1 showed markedly higher CD4 and CD8 T-cell expression of HLADR and PD-1 versus cluster-2 and cluster-3 (all P < .0001). Although small, cluster-3 had significantly higher levels of cytokines reflecting inflammation (IL-6, IFN-γ, IP-10, IL-1RA, IL-10), chemotaxis (IL-8), systemic and vascular inflammation (CRP, ICAM-1, VCAM-1), and SAA (all P < .001). In mixed-effects models, cfPWV changes over time were similar for cluster-2 versus cluster-1 (relative fold-change, 0.99; 95% CI, .86-1.14; P = .91), but greater in cluster-3 versus cluster-1 (relative fold-change, 1.45; 95% CI, 1.01-2.09; P = .045). CONCLUSIONS: Two inflammatory clusters were identified: one defined by high T-cell PD-1 expression and another by a hyperinflamed profile and increases in cfPWV on ART. Further clinical characterization of inflammatory phenotypes could help target vascular dysfunction interventions to those at highest risk. CLINICAL TRIALS NETWORK: NCT01825031.

Stakeholder views on the acceptability of human infection studies in Malawi.

BACKGROUND: Human infection studies (HIS) are valuable in vaccine development. Deliberate infection, however, creates challenging questions, particularly in low and middle-income countries (LMICs) where HIS are new and ethical challenges may be heightened. Consultation with stakeholders is needed to support contextually appropriate and acceptable study design. We examined stakeholder perceptions about the acceptability and ethics of HIS in Malawi, to inform decisions about planned pneumococcal challenge research and wider understanding of HIS ethics in LMICs. METHODS: We conducted 6 deliberative focus groups and 15 follow-up interviews with research staff, medical students, and community representatives from rural and urban Blantyre. We also conducted 5 key informant interviews with clinicians, ethics committee members, and district health government officials. RESULTS: Stakeholders perceived HIS research to have potential population health benefits, but they also had concerns, particularly related to the safety of volunteers and negative community reactions. Acceptability depended on a range of conditions related to procedures for voluntary and informed consent, inclusion criteria, medical care or support, compensation, regulation, and robust community engagement. These conditions largely mirror those in existing guidelines for HIS and biomedical research in LMICs. Stakeholder perceptions pointed to potential tensions, for example, balancing equity, safety, and relevance in inclusion criteria. CONCLUSIONS: Our findings suggest HIS research could be acceptable in Malawi, provided certain conditions are in place. Ongoing assessment of participant experiences and stakeholder perceptions will be required to strengthen HIS research during development and roll-out.

HIV-Related Arterial Stiffness in Malawian Adults Is Associated With the Proportion of PD-1-Expressing CD8+ T Cells and Reverses With Antiretroviral Therapy.

BACKGROUND: The contribution of immune activation to arterial stiffness and its reversibility in human immunodeficiency virus (HIV)-infected adults in sub-Saharan Africa is unknown. METHODS: HIV-uninfected and HIV-infected Malawian adults initiating antiretroviral therapy (ART) with a CD4+ T-cell count of <100 cells/µL were enrolled and followed for 44 weeks; enrollment of infected adults occurred 2 weeks after ART initiation. We evaluated the relationship between carotid femoral pulse wave velocity (cfPWV) and T-cell activation (defined as HLA-DR+CD38+ T cells), exhaustion (define as PD-1+ T cells), and senescence (defined as CD57+ T cells) and monocyte subsets, using normal regression. RESULTS: In 279 HIV-infected and 110 HIV-uninfected adults, 142 (37%) had hypertension. HIV was independently associated with a 12% higher cfPWV (P = .02) at baseline and a 14% higher cfPWV at week 10 (P = .02), but the increases resolved by week 22. CD4+ and CD8+ T-cell exhaustion were independently associated with a higher cfPWV at baseline (P = .02). At 44 weeks, arterial stiffness improved more in those with greater decreases in the percentage of CD8+ T cells and the percentage of PD-1+CD8+ T cells (P = .01 and P = .03, respectively). When considering HIV-infected participants alone, the adjusted arterial stiffness at week 44 tended to be lower in those with higher baseline percentage of PD-1+CD8+ T cells (P = .054). CONCLUSIONS: PD-1+CD8+ T-cells are associated with HIV-related arterial stiffness, which remains elevated during the first 3 months of ART. Resources to prevent cardiovascular disease in sub-Saharan Africa should focus on blood pressure reduction and individuals with a low CD4+ T-cell count during early ART.

Human alveolar macrophages predominately express combined classical M1 and M2 surface markers in steady state.

Alveolar macrophages (AM) are critical to the homeostasis of the inflammatory environment in the lung. Differential expression of surface markers classifies macrophages to either classically (M1) or alternatively activated (M2). We investigated the phenotype of human alveolar macrophages (AM) in adults living in two different geographical locations: UK and Malawi. We show that the majority of AM express high levels of M1 and M2 markers simultaneously, with the M1/M2 phenotype being stable in individuals from different geographical locations. The combined M1/M2 features confer to AM a hybrid phenotype, which does not fit the classic macrophage classification. This hybrid phenotype may confer to alveolar macrophages an ability to quickly switch between M1 or M2 associated functions allowing for appropriate responses to stimuli and tissue environment.

Oral Typhoid Vaccination With Live-Attenuated Salmonella Typhi Strain Ty21a Generates Ty21a-Responsive and Heterologous Influenza Virus-Responsive CD4+ and CD8+ T Cells at the Human Intestinal Mucosa.

BACKGROUND: Oral vaccination with live-attenuated Salmonella Typhi strain Ty21a is modestly efficacious, but the mechanisms of protection are currently unknown. While humoral and cellular immune responses are well described in peripheral blood, the cellular response at the intestinal mucosa has never been directly assessed. METHODS: We vaccinated healthy adults with Ty21a and assessed humoral and cellular immunity in vaccinated volunteers and controls after 18 days. Immunoglobulin levels were assessed in peripheral blood by an enzyme-linked immunosorbent assay. Cellular responses were assessed in peripheral blood and at the duodenal and colonic mucosa by flow cytometry. RESULTS: We demonstrate the generation of Ty21a-responsive and heterologous influenza virus-responsive CD4(+) and CD8(+) T cells at the duodenal mucosa. All duodenal responses were consistently correlated, and no responses were observed at the colonic mucosa. Peripheral anti-lipopolysaccharide immunoglobulin G and immunoglobulin A responses were significantly correlated with duodenal responses. The assessment of integrin ß7 expression intensity among peripheral and duodenal T-cell subsets revealed varied capacities for mucosal homing and residence. CONCLUSIONS: The breadth of duodenal cellular responses was not reflected peripherally. The direct evaluation of mucosal immune defense may yield functional correlates of protection and could provide insight into mechanisms that may be manipulated to enhance vaccine immunogenicity.

Heterogeneous loss of HIV transcription and proviral DNA from 8E5/LAV lymphoblastic leukemia cells revealed by RNA FISH:FLOW analyses.

8E5/LAV cells harbor a single HIV provirus, and are used frequently to generate standards for HIV genome quantification. Using flow cytometry-based in situ mRNA hybridization validated by qPCR, we find that different batches of 8E5 cells contain varying numbers of cells lacking viral mRNA and/or viral genomes. These findings raise concerns for studies employing 8E5 cells for quantitation, and highlight the value of mRNA FISH and flow cytometry in the detection and enumeration of HIV-positive cells.

Delayed acquisition of Plasmodium falciparum antigen-specific CD4(+) T cell responses in HIV-exposed uninfected Malawian children receiving daily cotrimoxazole prophylaxis.

BACKGROUND: Cotrimoxazole (CTX) prophylaxis, recommended in HIV-exposed uninfected (HEU) children primarily against HIV-related opportunistic infections, has been shown to have some efficacy against Plasmodium falciparum malaria. The effects of CTX prophylaxis on the acquisition of P. falciparum antigen specific CD4(+) T cells-mediated immunity in HEU children is still not fully understood. METHODS: Peripheral blood was collected from HEU and HIV-unexposed uninfected (HUU) children at 6, 12 and 18 months of age. Proportion of CD4(+) T cells subsets were determined by immunophenotyping. P. falciparum antigen-specific CD4(+) T cells responses were measured by intracellular cytokine staining assay. RESULTS: There were no differences in the proportions of naïve, effector and memory CD4(+) T cell subsets between HEU and HUU children at all ages. There was a trend showing acquisition of P. falciparum-specific IFN-γ and TNF-producing CD4(+) T cells with age in both HUU and HEU children. There was, however, lower frequency of P. falciparum-specific IFN-γ-producing CD4(+) T cells in HEU compared to HUU at 6 and 12 months, which normalized 6 months after stopping CTX prophylaxis. CONCLUSION: The results demonstrate that there is delayed acquisition of P. falciparum-specific IFN-γ-producing CD4(+) T cells in HEU children on daily cotrimoxazole prophylaxis, which is evident at 6 and 12 months of age in comparison to HUU age-matched controls. However, whether this delayed acquisition of P. falciparum-specific IFN-γ-producing CD4(+) T cells leads to higher risk to malaria disease remains unknown and warrants further investigation.