Publications by authors named "Calman A MacLennan"

100 Publications

Outer membrane vesicle vaccines.

Semin Immunol 2020 08 9;50:101433. Epub 2020 Dec 9.

Bill & Melinda Gates Foundation, 62 Buckingham Gate, London, United Kingdom; Jenner Institute, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom.

Outer Membrane Vesicles (OMV) have received increased attention in recent years as a vaccine platform against bacterial pathogens. OMV from Neisseria meningitidis serogroup B have been extensively explored. Following the success of the MeNZB OMV vaccine in controlling an outbreak of N. meningitidis B in New Zealand, additional research and development resulted in the licensure of the OMV-containing four-component 4CMenB vaccine, Bexsero. This provided broader protection against multiple meningococcal B strains. Advances in the field of genetic engineering have permitted further improvements in the platform resulting in increased yields, reduced endotoxicity and decoration with homologous and heterologous antigens to enhance immuno genicity and provide broader protection. The OMV vaccine platform has been extended to many other pathogens. In this review, we discuss progress in the development of the OMV vaccine delivery platform, highlighting successful applications, together with potential challenges and gaps.
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http://dx.doi.org/10.1016/j.smim.2020.101433DOI Listing
August 2020

Short Vi-polysaccharide abrogates T-independent immune response and hyporesponsiveness elicited by long Vi-CRM conjugate vaccine.

Proc Natl Acad Sci U S A 2020 09 8;117(39):24443-24449. Epub 2020 Sep 8.

Technology Platform Unit, GSK Vaccines Institute for Global Health (GVGH), 53100 Siena, Italy.

Polysaccharide-protein conjugates have been developed to overcome the T-independent response, hyporesponsiveness to repeated vaccination, and poor immunogenicity in infants of polysaccharides. To address the impact of polysaccharide length, typhoid conjugates made with short- and long-chain fractions of Vi polysaccharide with average sizes of 9.5, 22.8, 42.7, 82.0, and 165 kDa were compared. Long-chain-conjugated Vi (165 kDa) induced a response in both wild-type and T cell-deficient mice, suggesting that it maintains a T-independent response. In marked contrast, short-chain Vi (9.5 to 42.7 kDa) conjugates induced a response in wild-type mice but not in T cell-deficient mice, suggesting that the response is dependent on T cell help. Mechanistically, this was explained in neonatal mice, in which long-chain, but not short-chain, Vi conjugate induced late apoptosis of Vi-specific B cells in spleen and early depletion of Vi-specific B cells in bone marrow, resulting in hyporesponsiveness and lack of long-term persistence of Vi-specific IgG in serum and IgG antibody-secreting cells in bone marrow. We conclude that while conjugation of long-chain Vi generates T-dependent antigens, the conjugates also retain T-independent properties, leading to detrimental effects on immune responses. The data reported here may explain some inconsistencies observed in clinical trials and help guide the design of effective conjugate vaccines.
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http://dx.doi.org/10.1073/pnas.2005857117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7533886PMC
September 2020

Typhoid Conjugate Vaccines and Enteric Fever Control: Where to Next?

Clin Infect Dis 2020 Jul;71(Supplement_2):S185-S190

Enteric and Diarrheal Diseases, Bill & Melinda Gates Foundation, Seattle, Washington, USA.

After the unprecedented success and acceleration of the global agenda towards typhoid fever control with a strong World Health Organization recommendation and the approval of funding from Gavi, the Vaccine Alliance (Gavi), for the use of a new typhoid conjugate vaccine (TCV), we should turn our minds to the challenges that remain ahead. Despite the evidence showing the safety and clinical efficacy of TCV in endemic populations in developing countries, we should remain vigilant and explore hurdles for the full public health impact of TCV, including vaccine supply for the potential global demand, immunization strategies to optimize the effectiveness and long-term protection provided by the vaccines, potential use of TCV in outbreak settings, and scenarios for addressing chronic carriers. Finally, challenges face endemic countries with poor surveillance systems concerning awareness of the need for TCV and the extent of the issue across their populations, and how to target immunization strategies appropriately.
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http://dx.doi.org/10.1093/cid/ciaa343DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7388705PMC
July 2020

Gonococcal vaccines: Public health value and preferred product characteristics; report of a WHO global stakeholder consultation, January 2019.

Vaccine 2020 06 28;38(28):4362-4373. Epub 2020 Apr 28.

World Health Organization, Geneva, Switzerland.

Renewed interest in developing vaccines against Neisseria gonorrhoeae has been sparked by the increasing threat of gonococcal antimicrobial resistance (AMR) and growing optimism that gonococcal vaccines are biologically feasible. Evidence suggests serogroup B Neisseria meningitidis vaccines might provide some cross-protection against N. gonorrhoeae, and new gonococcal vaccine candidates based on several approaches are currently in preclinical development. To further stimulate investment and accelerate development of gonococcal vaccines, greater understanding is needed regarding the overall value that gonococcal vaccines might have in addressing public health and societal goals in low-, middle-, and high-income country contexts and how future gonococcal vaccines might be accepted and used, if available. In January 2019, the World Health Organization (WHO) convened a multidisciplinary international group of experts to lay the groundwork for understanding the potential health, economic, and societal value of gonococcal vaccines and their likely acceptance and use, and for developing gonococcal vaccine preferred product characteristics (PPCs). WHO PPCs describe preferences for vaccine attributes that would help optimize vaccine value and use in meeting the global public health need. This paper describes the main discussion points and conclusions from the January 2019 meeting of experts. Participants emphasized the need for vaccines to control N. gonorrhoeae infections with the ultimate goals of preventing adverse sexual and reproductive health outcomes (e.g., infertility) and reducing the impact of gonococcal AMR. Meeting participants also discussed important PPC considerations (e.g., vaccine indications, target populations, and potential immunization strategies) and highlighted crucial research and data needs for guiding the value assessment and PPCs for gonococcal vaccines and advancing gonococcal vaccine development.
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http://dx.doi.org/10.1016/j.vaccine.2020.02.073DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7273195PMC
June 2020

Outer membrane protein size and LPS O-antigen define protective antibody targeting to the Salmonella surface.

Nat Commun 2020 02 12;11(1):851. Epub 2020 Feb 12.

Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, B15 2TT, UK.

Lipopolysaccharide (LPS) O-antigen (O-Ag) is known to limit antibody binding to surface antigens, although the relationship between antibody, O-Ag and other outer-membrane antigens is poorly understood. Here we report, immunization with the trimeric porin OmpD from Salmonella Typhimurium (STmOmpD) protects against infection. Atomistic molecular dynamics simulations indicate this is because OmpD trimers generate footprints within the O-Ag layer sufficiently sized for a single IgG Fab to access. While STmOmpD differs from its orthologue in S. Enteritidis (SEn) by a single amino-acid residue, immunization with STmOmpD confers minimal protection to SEn. This is due to the OmpD-O-Ag interplay restricting IgG binding, with the pairing of OmpD with its native O-Ag being essential for optimal protection after immunization. Thus, both the chemical and physical structure of O-Ag are key for the presentation of specific epitopes within proteinaceous surface-antigens. This enhances combinatorial antigenic diversity in Gram-negative bacteria, while reducing associated fitness costs.
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http://dx.doi.org/10.1038/s41467-020-14655-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7015928PMC
February 2020

Consensus Report on Shigella Controlled Human Infection Model: Conduct of Studies.

Clin Infect Dis 2019 12;69(Suppl 8):S580-S590

Enteric Disease Department, Naval Medical Research Center, Silver Spring, Maryland.

Shigella causes morbidity and mortality worldwide, primarily affecting young children living in low-resource settings. It is also of great concern due to increasing antibiotic resistance, and is a priority organism for the World Health Organization. A Shigella vaccine would decrease the morbidity and mortality associated with shigellosis, improve child health, and decrease the need for antibiotics. Controlled human infection models (CHIMs) are useful tools in vaccine evaluation for early up- or down-selection of vaccine candidates and potentially useful in support of licensure. Over time, the methods employed in these models have become more uniform across sites performing CHIM trials, although some differences in conduct persist. In November 2017, a Shigella CHIM workshop was convened in Washington, District of Columbia. Investigators met to discuss multiple aspects of these studies, including study procedures, clinical and immunological endpoints, and shared experiences. This article serves as a uniform procedure by which to conduct Shigella CHIM studies.
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http://dx.doi.org/10.1093/cid/ciz892DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6901126PMC
December 2019

Consensus Report on Shigella Controlled Human Infection Model: Immunological Assays.

Clin Infect Dis 2019 12;69(Suppl 8):S596-S601

Bill & Melinda Gates Foundation, London, United Kingdom.

Moderate to severe diarrhea caused by Shigella is a global health concern due to its substantial contribution to morbidity and mortality in children aged <5 years in low- and middle-income countries. Although antibiotic treatment can be effective, emerging antimicrobial resistance, limited access, and cost affirm the role of vaccines as the most attractive countermeasure. Controlled human infection models (CHIMs) represent a valuable tool for assessing vaccine efficacy and potentially accelerating licensure. Currently, immunological analysis during CHIM studies is customized based on vaccine type, regimen, and administration route. Additionally, differences in type of immunoassays and procedures used limit comparisons across studies. In November 2017, an expert working group reviewed Shigella CHIM studies performed to date and developed consensus guidelines on prioritization of immunoassays, specimens, and collection time points. Immunoassays were ranked into 3 tiers, with antibodies to Shigella lipopolysaccharide (LPS) being the highest priority. To facilitate comparisons across clinical studies, a second workshop was conducted in December 2017, which focused on the pathway toward a recognized enzyme-linked immunosorbent assay (ELISA) to determine serum immunoglobulin G titers against Shigella LPS. The consensus of the meeting was to establish a consortium of international institutions with expertise in Shigella immunology that would work with the National Institute for Biological Standards and Control to establish a harmonized ELISA, produce a reference sera, and identify a reliable source of Shigella LPS for global utilization. Herein we describe efforts toward establishing common procedures to advance Shigella vaccine development, support licensure, and ultimately facilitate vaccine deployment and uptake.
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http://dx.doi.org/10.1093/cid/ciz909DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6901123PMC
December 2019

Consensus Report on Shigella Controlled Human Infection Model: Introduction and Overview.

Clin Infect Dis 2019 12;69(Suppl 8):S577-S579

Bill & Melinda Gates Foundation, Seattle, Washington.

In recent years, controlled human infection models (CHIMs) have become available for a range of infectious agents and have proved invaluable for understanding the disease process, pathogenesis, and mechanisms of immunity. CHIM studies have also contributed significantly to advancing development of a number of vaccines by providing an indication of vaccine efficacy. The Shigella CHIM has been established in 3 sites in the United States, and it is likely that the CHIM will play an important regulatory role for advancing the range of Shigella vaccine candidates that are currently in development. This supplement describes the harmonization of best practices across sites, with a view to maximizing the contribution that CHIM studies can make to Shigella vaccine development.
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http://dx.doi.org/10.1093/cid/ciz886DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6901124PMC
December 2019

Consensus Report on Shigella Controlled Human Infection Model: Clinical Endpoints.

Clin Infect Dis 2019 12;69(Suppl 8):S591-S595

Enteric Disease Department, Naval Medical Research Center, Silver Spring, Maryland.

The Shigella controlled human infection model (CHIM) is valuable for assessing candidate Shigella vaccine efficacy and potentially accelerating regulatory approval. The Shigella CHIM is currently being conducted at 3 sites in the United States using Shigella flexneri 2a strain 2457T and Shigella sonnei strain 53G. Shigellosis can present variably as watery diarrhea alone or with dysentery, and can be accompanied by manifestations including fever, abdominal cramps, tenesmus, and malaise. For comparability, it is important to harmonize the primary clinical endpoint. An expert working group was convened on 2 February 2018 to review clinical data from Shigella CHIM studies performed to date and to develop a consensus primary endpoint. The consensus endpoint enabled "shigellosis" to present as severe diarrhea or moderate diarrhea or dysentery. The latter 2 criteria are met when concurrent with fever of 38.0°C and/or vomiting, and/or a constitutional/enteric symptom graded at least as "moderate" severity. The use of a blinded independent committee to adjudicate the primary endpoint by subject was also regarded as important. As safety of volunteers in challenge studies is of paramount importance and treatment timing can affect primary outcomes, a standard for early antibiotic administration was established as follows: (1) when the primary endpoint is met; (2) if a fever of ≥39.0°C develops; or (3) if the study physician deems it appropriate. Otherwise, antibiotics are given at 120 hours postinfectious challenge. The working group agreed on objective and subjective symptoms to be solicited, and standardized methods for assessing subject-reported severity of symptoms.
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http://dx.doi.org/10.1093/cid/ciz891DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6901125PMC
December 2019

The Severe Typhoid Fever in Africa Program: Study Design and Methodology to Assess Disease Severity, Host Immunity, and Carriage Associated With Invasive Salmonellosis.

Clin Infect Dis 2019 10;69(Suppl 6):S422-S434

International Vaccine Institute, Seoul National University Research Park, Republic of Korea.

Background: Invasive salmonellosis is a common community-acquired bacteremia in persons residing in sub-Saharan Africa. However, there is a paucity of data on severe typhoid fever and its associated acute and chronic host immune response and carriage. The Severe Typhoid Fever in Africa (SETA) program, a multicountry surveillance study, aimed to address these research gaps and contribute to the control and prevention of invasive salmonellosis.

Methods: A prospective healthcare facility-based surveillance with active screening of enteric fever and clinically suspected severe typhoid fever with complications was performed using a standardized protocol across the study sites in Burkina Faso, the Democratic Republic of Congo (DRC), Ethiopia, Ghana, Madagascar, and Nigeria. Defined inclusion criteria were used for screening of eligible patients for enrollment into the study. Enrolled patients with confirmed invasive salmonellosis by blood culture or patients with clinically suspected severe typhoid fever with perforation were eligible for clinical follow-up. Asymptomatic neighborhood controls and immediate household contacts of each case were enrolled as a comparison group to assess the level of Salmonella-specific antibodies and shedding patterns. Healthcare utilization surveys were performed to permit adjustment of incidence estimations. Postmortem questionnaires were conducted in medically underserved areas to assess death attributed to invasive Salmonella infections in selected sites.

Results: Research data generated through SETA aimed to address scientific knowledge gaps concerning the severe typhoid fever and mortality, long-term host immune responses, and bacterial shedding and carriage associated with natural infection by invasive salmonellae.

Conclusions: SETA supports public health policy on typhoid immunization strategy in Africa.
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http://dx.doi.org/10.1093/cid/ciz715DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6821161PMC
October 2019

Genomic characterization of novel Neisseria species.

Sci Rep 2019 09 24;9(1):13742. Epub 2019 Sep 24.

Department of Zoology, University of Oxford, Oxford, UK.

Of the ten human-restricted Neisseria species two, Neisseria meningitidis, and Neisseria gonorrhoeae, cause invasive disease: the other eight are carried asymptomatically in the pharynx, possibly modulating meningococcal and gonococcal infections. Consequently, characterizing their diversity is important for understanding the microbiome in health and disease. Whole genome sequences from 181 Neisseria isolates were examined, including those of three well-defined species (N. meningitidis; N. gonorrhoeae; and Neisseria polysaccharea) and genomes of isolates unassigned to any species (Nspp). Sequence analysis of ribosomal genes, and a set of core (cgMLST) genes were used to infer phylogenetic relationships. Average Nucleotide Identity (ANI) and phenotypic data were used to define species clusters, and morphological and metabolic differences among them. Phylogenetic analyses identified two polyphyletic clusters (N. polysaccharea and Nspp.), while, cgMLST data grouped Nspp isolates into nine clusters and identified at least three N. polysaccharea clusters. ANI results classified Nspp into seven putative species, and also indicated at least three putative N. polysaccharea species. Electron microscopy identified morphological differences among these species. This genomic approach provided a consistent methodology for species characterization using distinct phylogenetic clusters. Seven putative novel Neisseria species were identified, confirming the importance of genomic studies in the characterization of the genus Neisseria.
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http://dx.doi.org/10.1038/s41598-019-50203-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6760525PMC
September 2019

Cross-sectional study of IgG antibody levels to invasive nontyphoidal LPS O-antigen with age in Uganda.

Gates Open Res 2019 26;3:1501. Epub 2019 Jun 26.

Nuffield Department of Medicine, University of Oxford, Oxford, OX3 7DQ, UK.

Invasive nontyphoidal (iNTS) disease is a major cause of deaths among children and HIV-infected individuals in sub-Saharan Africa. Acquisition of IgG to iNTS lipopolysaccharide (LPS) O-antigen in Malawi in early childhood corresponds with a fall in cases of iNTS disease suggesting that vaccines able to induce such antibodies could confer protection. To better understand the acquisition of IgG to iNTS in other African settings, we performed a cross-sectional seroepidemiological study using sera from 1090 Ugandan individuals aged from infancy to old age. Sera were analysed for IgG to LPS O-antigen of . Typhimurium and . Enteritidis using an in-house ELISA. Below 18 months of age, most children lacked IgG to both serovars. Thereafter, specific IgG levels increased with age, peaking in adulthood, and did not wane noticeably in old age. There was no clear difference in antibody levels between the sexes and the few HIV-infected individuals in the study did not have obviously different levels from uninfected subjects. While IgG to iNTS is acquired at a younger age in Malawian compared with Ugandan children, it is not clear whether this is due to differences in the populations themselves, their exposure to iNTS, or variations between assays used. In conclusion, there is a need to develop a harmonised method and standards for measuring antibodies to iNTS across studies and to investigate acquisition of such antibodies with age across different sites in sub-Saharan Africa.
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http://dx.doi.org/10.12688/gatesopenres.13034.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640003PMC
June 2019

How can controlled human infection models accelerate clinical development and policy pathways for vaccines against Shigella?

Vaccine 2019 08;37(34):4778-4783

Enteric & Diarrheal Diseases, Global Health, Bill & Melinda Gates Foundation, Seattle, WA, USA.

Controlled Human Infection Models (CHIMs) now exist for several infectious diseases. CHIMs offer significant insight into disease pathogenesis, as well the potential to rapidly test clinical proof-of-concept of vaccine candidates. The application of CHIMs to identify a correlate of protection that may reduce the sample size of, or obviate the need for clinical efficacy studies to achieve licensure is of considerable interest to vaccine developers and public health stakeholders. This topic was the subject of a workshop at the 2018 Vaccines Against Shigella and ETEC (VASE) conference, in the context of O-antigen-based Shigella vaccines.
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http://dx.doi.org/10.1016/j.vaccine.2019.03.036DOI Listing
August 2019

Rapid transcriptional responses to serum exposure are associated with sensitivity and resistance to antibody-mediated complement killing in invasive Typhimurium ST313.

Wellcome Open Res 2019 25;4:74. Epub 2019 Apr 25.

Institute of Immunology and Immuotherapy, University of Birmingham, Birmingham, UK.

: Typhimurium ST313 exhibits signatures of adaptation to invasive human infection, including higher resistance to humoral immune responses than gastrointestinal isolates. Full resistance to antibody-mediated complement killing (serum resistance) among nontyphoidal is uncommon, but selection of highly resistant strains could compromise vaccine-induced antibody immunity. Here, we address the hypothesis that serum resistance is due to a distinct genotype or transcriptome response in . Typhimurium ST313. : Six . Typhimurium ST313 bloodstream isolates, three of which were antibody resistant, were studied. Genomic content (single nucleotide polymorphisms and larger chromosomal modifications) of the strains was determined by Illumina and PACBIO sequencing, and functionally characterized using RNA-seq, transposon directed insertion site sequencing (TraDIS), targeted gene deletion and transfer of selected point mutations in an attempt to identify features associated with serum resistance.   : Sequence polymorphisms in genes from strains with atypical serum susceptibility when transferred from strains that were highly resistant or susceptible to a strain that exhibited intermediate susceptibility did not significantly alter serum killing phenotype. No large chromosomal modifications typified serum resistance or susceptibility. Genes required for resistance to serum identified by TraDIS and RNA-seq included those involved in exopolysaccharide synthesis, iron scavenging and metabolism. Most of the down-regulated genes were associated with membrane proteins. Resistant and susceptible strains had distinct transcriptional responses to serum, particularly related to genes responsible for polysaccharide biosynthesis. There was higher upregulation of locus genes, involved in the biosynthesis of colanic acid exopolysaccharide, in susceptible strains and increased expression of , a regulator of very long-chain lipopolysaccharide in resistant strains. : Clinical isolates of . Typhimurium ST313 exhibit distinct antibody susceptibility phenotypes that may be associated with changes in gene expression on exposure to serum.
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http://dx.doi.org/10.12688/wellcomeopenres.15059.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6560496PMC
April 2019

Bacterial flagellin promotes viral entry via an NF-kB and Toll Like Receptor 5 dependent pathway.

Sci Rep 2019 05 27;9(1):7903. Epub 2019 May 27.

Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK.

Viruses and bacteria colonize hosts by invading epithelial barriers. Recent studies have shown that interactions between the microbiota, pathogens and the host can potentiate infection through poorly understood mechanisms. Here, we investigated whether diverse bacterial species could modulate virus internalization into host cells, often a rate-limiting step in establishing infections. Lentiviral pseudoviruses expressing influenza, measles, Ebola, Lassa or vesicular stomatitis virus envelope glycoproteins enabled us to study entry of viruses that exploit diverse internalization pathways. Salmonella Typhimurium, Escherichia coli and Pseudomonas aeruginosa significantly increased viral uptake, even at low bacterial frequencies. This did not require bacterial contact with or invasion of host cells. Studies determined that the bacterial antigen responsible for this pro-viral activity was the Toll-Like Receptor 5 (TLR5) agonist flagellin. Exposure to flagellin increased virus attachment to epithelial cells in a temperature-dependent manner via TLR5-dependent activation of NF-ΚB. Importantly, this phenotype was both long lasting and detectable at low multiplicities of infection. Flagellin is shed from bacteria and our studies uncover a new bystander role for this protein in regulating virus entry. This highlights a new aspect of viral-bacterial interplay with significant implications for our understanding of polymicrobial-associated pathogenesis.
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http://dx.doi.org/10.1038/s41598-019-44263-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6536546PMC
May 2019

Invasive Nontyphoidal Disease in Africa.

EcoSal Plus 2019 01;8(2)

Jenner Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK.

Nontyphoidal salmonellae (NTS) are a major cause of invasive (iNTS) disease in sub-Saharan Africa, manifesting as bacteremia and meningitis. Available epidemiological data indicate that iNTS disease is endemic in much of the region. Antimicrobial resistance is common and case fatality rates are high. There are well-characterized clinical associations with iNTS disease, including young age, HIV infection, malaria, malnutrition, anemia, and sickle cell disease. However, the clinical presentation of iNTS disease is often with fever alone, so clinical diagnosis is impossible without blood culture confirmation. No vaccine is currently available, making this a priority area for global health research. Over the past ten years, it has emerged that iNTS disease in Africa is caused by distinct pathovars of Typhimurium, belonging to sequence type ST313, and Enteritidis. These are characterized by genome degradation and appear to be adapting to an invasive lifestyle. Investigation of rare patients with primary immunodeficiencies has suggested a key role for interferon gamma-mediated immunity in host defense against NTS. This concept has been supported by recent population-based host genetic studies in African children. In contrast, immunoepidemiological studies from Africa indicate an important role for antibody for protective immunity, supporting the development of antibody-inducing vaccines against iNTS disease. With candidate O-antigen-based vaccines due to enter clinical trials in the near future, research efforts should focus on understanding the relative contributions of antibody and cell-mediated immunity to protection against iNTS disease in humans.
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http://dx.doi.org/10.1128/ecosalplus.ESP-0007-2018DOI Listing
January 2019

HIV infection compounds the lymphopenia associated with cerebral malaria in Malawian children.

J Blood Med 2019 19;10:9-18. Epub 2018 Dec 19.

Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, Blantyre, Malawi,

Aim: Cerebral malaria (CM), unlike severe malarial anemia (SMA), has previously been characterized by pan-lymphopenia that normalizes in convalescence, while HIV infection is associated with depletion of CD4 T cells. In this study, we investigate whether HIV infection in Malawian children exacerbates the pan-lymphopenia associated with CM.

Methods: We investigated the absolute and percentage lymphocyte-subset counts and their activation and memory status in Malawian children presenting with either CM who were HIV-uninfected (n=29), HIV-infected (n=9), or SMA who were HIV-uninfected (n=30) and HIV-infected (n=5) in comparison with HIV-uninfected children without malaria (n=42) and HIV-infected children without malaria (n=4).

Results: HIV-infected CM cases had significantly lower absolute counts of T cells (=0.006), CD4 T cells (=0.0008), and B cells (=0.0014) than HIV-uninfected CM cases, and significantly lower percentages of CD4 T cells than HIV-uninfected CM cases (=0.005). HIV-infected SMA cases had significantly lower percentages of CD4 T cells (=0.001) and higher CD8 T cells (=0.003) in comparison with HIV-uninfected SMA cases. HIV-infected SMA cases had higher proportions of activated T cells (=0.003) expressing CD69 than HIV-uninfected SMA cases.

Conclusion: HIV infection compounds the perturbation of acute CM and SMA on lymphocytes, exacerbating subset-specific lymphopenia in CM and increasing activation status in SMA, potentially exacerbating host immunocompromise.
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http://dx.doi.org/10.2147/JBM.S187081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6305159PMC
December 2018

Morbidity and mortality due to shigella and enterotoxigenic Escherichia coli diarrhoea: the Global Burden of Disease Study 1990-2016.

Lancet Infect Dis 2018 11 25;18(11):1229-1240. Epub 2018 Sep 25.

Institute for Health Metrics and Evaluation, Seattle WA, USA. Electronic address:

Background: Shigella and enterotoxigenic Escherichia coli (ETEC) are bacterial pathogens that are frequently associated with diarrhoeal disease, and are a significant cause of mortality and morbidity worldwide. The Global Burden of Diseases, Injuries, and Risk Factors study 2016 (GBD 2016) is a systematic, scientific effort to quantify the morbidity and mortality due to over 300 causes of death and disability. We aimed to analyse the global burden of shigella and ETEC diarrhoea according to age, sex, geography, and year from 1990 to 2016.

Methods: We modelled shigella and ETEC-related mortality using a Bayesian hierarchical modelling platform that evaluates a wide range of covariates and model types on the basis of vital registration and verbal autopsy data. We used a compartmental meta-regression tool to model the incidence of shigella and ETEC, which enforces an association between incidence, prevalence, and remission on the basis of scientific literature, population representative surveys, and health-care data. We calculated 95% uncertainty intervals (UIs) for the point estimates.

Findings: Shigella was the second leading cause of diarrhoeal mortality in 2016 among all ages, accounting for 212 438 deaths (95% UI 136 979-326 913) and about 13·2% (9·2-17·4) of all diarrhoea deaths. Shigella was responsible for 63 713 deaths (41 191-93 611) among children younger than 5 years and was frequently associated with diarrhoea across all adult age groups, increasing in elderly people, with broad geographical distribution. ETEC was the eighth leading cause of diarrhoea mortality in 2016 among all age groups, accounting for 51 186 deaths (26 757-83 064) and about 3·2% (1·8-4·7) of diarrhoea deaths. ETEC was responsible for about 4·2% (2·2-6·8) of diarrhoea deaths in children younger than 5 years.

Interpretation: The health burden of bacterial diarrhoeal pathogens is difficult to estimate. Despite existing prevention and treatment options, they remain a major cause of morbidity and mortality globally. Additional emphasis by public health officials is needed on a reduction in disease due to shigella and ETEC to reduce disease burden.

Funding: Bill & Melinda Gates Foundation.
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http://dx.doi.org/10.1016/S1473-3099(18)30475-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6202441PMC
November 2018

Comparative immunogenicity and efficacy of equivalent outer membrane vesicle and glycoconjugate vaccines against nontyphoidal .

Proc Natl Acad Sci U S A 2018 10 27;115(41):10428-10433. Epub 2018 Sep 27.

Jenner Institute, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7DQ, United Kingdom.

Nontyphoidal cause a devastating burden of invasive disease in sub-Saharan Africa with high levels of antimicrobial resistance. Vaccination has potential for a major global health impact, but no licensed vaccine is available. The lack of commercial incentive makes simple, affordable technologies the preferred route for vaccine development. Here we compare equivalent Generalized Modules for Membrane Antigens (GMMA) outer membrane vesicles and O-antigen-CRM glycoconjugates to deliver lipopolysaccharide O-antigen in bivalent Typhimurium and Enteritidis vaccines. strains were chosen and deleted to induce GMMA production. O-antigens were extracted from wild-type bacteria and conjugated to CRM Purified GMMA and glycoconjugates were characterized and tested in mice for immunogenicity and ability to reduce infection. GMMA and glycoconjugate O-antigen had similar structural characteristics, O-acetylation, and glucosylation levels. Immunization with GMMA induced higher anti-O-antigen IgG than glycoconjugate administered without Alhydrogel adjuvant. With Alhydrogel, antibody levels were similar. GMMA induced a diverse antibody isotype profile with greater serum bactericidal activity than glycoconjugate, which induced almost exclusively IgG1. Immunization reduced bacterial colonization of mice subsequently infected with Typhimurium numbers were lower in tissues of mice vaccinated with GMMA compared with glycoconjugate. Enteritidis burden in the tissues was similar in mice immunized with either vaccine. With favorable immunogenicity, low cost, and ability to induce functional antibodies and reduce bacterial burden, GMMA offer a promising strategy for the development of a nontyphoidal vaccine compared with established glycoconjugates. GMMA technology is potentially attractive for development of vaccines against other bacteria of global health significance.
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http://dx.doi.org/10.1073/pnas.1807655115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6187145PMC
October 2018

The essential role of complement in antibody-mediated resistance to Salmonella.

Immunology 2019 01 10;156(1):69-73. Epub 2018 Oct 10.

Department of Veterinary Medicine, University of Cambridge, Cambridge, UK.

Vaccines can serve as essential tools to prevent bacterial diseases via the induction of long-lasting IgG responses. The efficacy of such vaccines depends on the effector mechanisms triggered by IgG. The complement system and Fc-gamma receptors (FcγRs) can potentially play a crucial role in IgG-mediated immunity against bacterial diseases. However, their relative importance in vivo is unclear, and has been the object of controversy and debate. In this brief study, we have used gene-targeted mice lacking either FcγRI, II, II and IV or the C3 complement component as well as a novel mouse strain lacking both C3 and FcγRs to conclusively show the essential role of complement in antibody-mediated host resistance to Salmonella enterica systemic infection. By comparing the effect of IgG2a antibodies against Salmonella O-antigen in gene-targeted mice, we demonstrate that the complement system is essential for the IgG-mediated reduction of bacterial numbers in the tissues.
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http://dx.doi.org/10.1111/imm.13000DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6283648PMC
January 2019

Risk of nontyphoidal Salmonella bacteraemia in African children is modified by STAT4.

Nat Commun 2018 03 9;9(1):1014. Epub 2018 Mar 9.

Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, OX3 7BN, UK.

Nontyphoidal Salmonella (NTS) is a major cause of bacteraemia in Africa. The disease typically affects HIV-infected individuals and young children, causing substantial morbidity and mortality. Here we present a genome-wide association study (180 cases, 2677 controls) and replication analysis of NTS bacteraemia in Kenyan and Malawian children. We identify a locus in STAT4, rs13390936, associated with NTS bacteraemia. rs13390936 is a context-specific expression quantitative trait locus for STAT4 RNA expression, and individuals carrying the NTS-risk genotype demonstrate decreased interferon-γ (IFNγ) production in stimulated natural killer cells, and decreased circulating IFNγ concentrations during acute NTS bacteraemia. The NTS-risk allele at rs13390936 is associated with protection against a range of autoimmune diseases. These data implicate interleukin-12-dependent IFNγ-mediated immunity as a determinant of invasive NTS disease in African children, and highlight the shared genetic architecture of infectious and autoimmune disease.
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http://dx.doi.org/10.1038/s41467-017-02398-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844948PMC
March 2018

IgG Responses to Porins and Lipopolysaccharide within an Outer Membrane-Based Vaccine against Nontyphoidal Develop at Discordant Rates.

mBio 2018 03 6;9(2). Epub 2018 Mar 6.

Institute for Microbiology and Infection, School of Immunology and Immunotherapy, Institute for Biomedical Research, University of Birmingham, Birmingham, United Kingdom

Antibodies acquired after vaccination or natural infection with Gram-negative bacteria, such as invasive serovar Typhimurium, can protect against disease. Immunization with naturally shed outer membrane vesicles from Gram-negative bacteria is being studied for its potential to protect against many infections, since antigens within vesicles maintain their natural conformation and orientation. Shedding can be enhanced through genetic modification, and the resulting particles, generalized modules for membrane antigens (GMMA), not only offer potential as vaccines but also can facilitate the study of B-cell responses to bacterial antigens. Here we show that the response to immunization with GMMA from  Typhimurium (STmGMMA) provides B-cell-dependent protection and induces antibodies to two immunodominant antigens, lipopolysaccharide (LPS) and porins. Antibodies to LPS O antigen (O-Ag) markedly enhance protection in the spleen, but this effect is less marked in the liver. Strikingly, IgG responses to LPS and porins develop with distinct kinetics. In the first week after immunization, there is a dramatic T-cell-independent B1b-cell-associated induction of all IgG isotypes, except IgG1, to porins but not to LPS. In contrast, production of IgG1 to either antigen was delayed and T cell dependent. Nevertheless, after 1 month, cells in the bone marrow secreting IgG against porins or LPS were present at a similar frequency. Unexpectedly, immunization with O-Ag-deficient STmGMMA did not substantially enhance the anti-porin response. Therefore, IgG switching to all antigens does not develop synchronously within the same complex and so the rate of IgG switching to a single component does not necessarily reflect its frequency within the antigenic complex. Vaccines save millions of lives, yet for some infections there are none. This includes some types of infections, killing hundreds of thousands of people annually. We show how a new type of vaccine, called GMMA, that is made from blebs shed from the cell wall, works to protect against infection in mice by inducing host proteins (antibodies) specifically recognizing bacterial components (antigens). The rate of development of IgG antibody to antigens within GMMA occurred with different kinetics. However, the antibody response to GMMA persists and is likely to provide prolonged protection for those who need it. These results help show how antibody responses to bacterial antigens develop and how vaccines like GMMA can work and help prevent infection.
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http://dx.doi.org/10.1128/mBio.02379-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844998PMC
March 2018

Presentation of life-threatening invasive nontyphoidal Salmonella disease in Malawian children: A prospective observational study.

PLoS Negl Trop Dis 2017 12 7;11(12):e0006027. Epub 2017 Dec 7.

Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Malawi.

Nontyphoidal Salmonellae commonly cause invasive disease in African children that is often fatal. The clinical diagnosis of these infections is hampered by the absence of a clear clinical syndrome. Drug resistance means that empirical antibiotic therapy is often ineffective and currently no vaccine is available. The study objective was to identify risk factors for mortality among children presenting to hospital with invasive Salmonella disease in Africa. We conducted a prospective study enrolling consecutive children with microbiologically-confirmed invasive Salmonella disease admitted to Queen Elizabeth Central Hospital, Blantyre, in 2006. Data on clinical presentation, co-morbidities and outcome were used to identify children at risk of inpatient mortality through logistic-regression modeling. Over one calendar year, 263 consecutive children presented with invasive Salmonella disease. Median age was 16 months (range 0-15 years) and 52/256 children (20%; 95%CI 15-25%) died. Nontyphoidal serovars caused 248/263 (94%) of cases. 211/259 (81%) of isolates were multi-drug resistant. 251/263 children presented with bacteremia, 6 with meningitis and 6 with both. Respiratory symptoms were present in 184/240 (77%; 95%CI 71-82%), 123/240 (51%; 95%CI 45-58%) had gastrointestinal symptoms and 101/240 (42%; 95%CI 36-49%) had an overlapping clinical syndrome. Presentation at <7 months (OR 10.0; 95%CI 2.8-35.1), dyspnea (OR 4.2; 95%CI 1.5-12.0) and HIV infection (OR 3.3; 95%CI 1.1-10.2) were independent risk factors for inpatient mortality. Invasive Salmonella disease in Malawi is characterized by high mortality and prevalence of multi-drug resistant isolates, along with non-specific presentation. Young infants, children with dyspnea and HIV-infected children bear a disproportionate burden of the Salmonella-associated mortality in Malawi. Strategies to improve prevention, diagnosis and management of invasive Salmonella disease should be targeted at these children.
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http://dx.doi.org/10.1371/journal.pntd.0006027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5745124PMC
December 2017

IgG1 Is Required for Optimal Protection after Immunization with the Purified Porin OmpD from Typhimurium.

J Immunol 2017 12 10;199(12):4103-4109. Epub 2017 Nov 10.

Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham B15 2TT, United Kingdom;

In mice, the IgG subclass induced after Ag encounter can reflect the nature of the Ag. Th2 Ags such as alum-precipitated proteins and helminths induce IgG1, whereas Th1 Ags, such as Typhimurium, predominantly induce IgG2a. The contribution of different IgG isotypes to protection against bacteria such as Typhimurium is unclear, although as IgG2a is induced by natural infection, it is assumed this isotype is important. Previously, we have shown that purified Typhimurium porins including outer membrane protein OmpD, which induce both IgG1 and IgG2a in mice, provide protection to Typhimurium infection via Ab. In this study we report the unexpected finding that mice lacking IgG1, but not IgG2a, are substantially less protected after porin immunization than wild-type controls. IgG1-deficient mice produce more porin-specific IgG2a, resulting in total IgG levels that are similar to wild-type mice. The decreased protection in IgG1-deficient mice correlates with less efficient bacterial opsonization and uptake by macrophages, and this reflects the low binding of outer membrane protein OmpD-specific IgG2a to the bacterial surface. Thus, the Th2-associated isotype IgG1 can play a role in protection against Th1-associated organisms such as Typhimurium. Therefore, individual IgG subclasses to a single Ag can provide different levels of protection and the IgG isotype induced may need to be a consideration when designing vaccines and immunization strategies.
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http://dx.doi.org/10.4049/jimmunol.1700952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5713499PMC
December 2017

Age- and sex-related changes in hematological parameters in healthy Malawians.

J Blood Med 2017 28;8:123-130. Epub 2017 Aug 28.

The Malaria Immunology Group, Malawi-Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, Blantyre, Malawi.

Aim: The aim of the study was to determine how values for white blood cell (WBC) counts, hemoglobin (Hb), hematocrit (Hct), mean corpuscular volume (mcv), and platelet counts vary with age and sex in healthy Malawians.

Methods: We recruited 660 (316 male and 344 female) participants in 12 different age groups. An ethylenediaminetetraacetic acid-anticoagulated blood sample collected from each participant was analyzed using a hematological analyzer.

Results: WBC counts decreased with age with the lowest counts observed in the 20 to <60 years old group. Median WBC counts for 20 to <60 year old females (5.9×10/L) were significantly higher than those for men (4.7×10/L; =0.015) of the same age. Hb and Hct increased between 5 and 10 years in males and 10 and 15 years in females to adult levels. Males aged 5 to <10 years had significantly higher Hb (13.05 g/dL) and Hct (42.50%) compared to females of the same age (10.40 g/dL and 32.55%, respectively; <0.0001 for both parameters). Platelet counts in males, which were highest between 3 and 5 years (376×10/L), decreased to lowest counts among 5 to <10 year olds (238×10/L), while in females these decreased from 402×10/L in 6 to <10 years olds to 226×10/L in 10 to <15 year olds. mcv median values were high in neonates reaching a nadir at 13-18 months and then increased throughout life. Females aged 0 to <6 months had significantly higher mcv values (81.85 fL) than males of the same age (69.3 fL; <0.0001).

Conclusion: This study provides hematological values according to age and sex that are suitable for reference use in studies among Malawian subjects.
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http://dx.doi.org/10.2147/JBM.S142189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5587168PMC
August 2017

Contribution of factor H-Binding protein sequence to the cross-reactivity of meningococcal native outer membrane vesicle vaccines with over-expressed fHbp variant group 1.

PLoS One 2017 25;12(7):e0181508. Epub 2017 Jul 25.

GSK Vaccines Institute for Global Health (GVGH), Siena, Italy.

Factor H-binding protein (fHbp) is an important meningococcal vaccine antigen. Native outer membrane vesicles with over-expressed fHbp (NOMV OE fHbp) have been shown to induce antibodies with broader functional activity than recombinant fHbp (rfHbp). Improved understanding of this broad coverage would facilitate rational vaccine design. We performed a pair-wise analysis of 48 surface-exposed amino acids involved in interacting with factor H, among 383 fHbp variant group 1 sequences. We generated isogenic NOMV-producing meningococcal strains from an African serogroup W isolate, each over-expressing one of four fHbp variant group 1 sequences (ID 1, 5, 9, or 74), including those most common among invasive African meningococcal isolates. Mice were immunised with each NOMV, and sera tested for IgG levels against each of the rfHbp ID and for ability to kill a panel of heterologous meningococcal isolates. At the fH-binding site, ID pairs differed by a maximum of 13 (27%) amino acids. ID 9 shared an amino acid sequence common to 83 ID types. The selected ID types differed by up to 6 amino acids, in the fH-binding site. All NOMV and rfHbp induced high IgG levels against each rfHbp. Serum killing from mice immunised with rfHbp was generally less efficient and more restricted compared to NOMV, which induced antibodies that killed most meningococci tested, with decreased stringency for ID type differences. Breadth of killing was mostly due to anti-fHbp antibodies, with some restriction according to ID type sequence differences. Nevertheless, under our experimental conditions, no relationship between antibody cross-reactivity and variation fH-binding site sequence was identified. NOMV over-expressing different fHbp IDs belonging to variant group 1 induce antibodies with fine specificities against fHbp, and ability to kill broadly meningococci expressing heterologous fHbp IDs. The work reinforces that meningococcal NOMV with OE fHbp is a promising vaccine strategy, and provides a basis for rational selection of antigen sequence types for over-expression on NOMV.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0181508PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5526518PMC
October 2017

Role of and in Susceptibility to Antibody-Mediated Complement-Dependent Killing and Virulence of Salmonella enterica Serovar Typhimurium.

Infect Immun 2017 09 18;85(9). Epub 2017 Aug 18.

Novartis Vaccines Institute for Global Health, Siena, Italy

The ST313 pathovar of serovar Typhimurium contributes to a high burden of invasive disease among African infants and HIV-infected adults. It is characterized by genome degradation (loss of coding capacity) and has increased resistance to antibody-dependent complement-mediated killing compared with enterocolitis-causing strains of Typhimurium. Vaccination is an attractive disease-prevention strategy, and leading candidates focus on the induction of bactericidal antibodies. Antibody-resistant strains arising through further gene deletion could compromise such a strategy. Exposing a saturating transposon insertion mutant library of Typhimurium to immune serum identified a repertoire of Typhimurium genes that, when interrupted, result in increased resistance to serum killing. These genes included several involved in bacterial envelope biogenesis, protein translocation, and metabolism. We generated defined mutant derivatives using Typhimurium SL1344 as the host. Based on their initial levels of enhanced resistance to killing, and mutants were selected for further characterization. The Typhimurium mutant lost the characteristic rod-shaped appearance, exhibited increased sensitivity to osmotic and detergent stress, lacked very long lipopolysaccharide, was unable to invade enterocytes, and demonstrated decreased ability to infect mice. In contrast, the Typhimurium mutants had similar sensitivity to osmotic and detergent stress and lipopolysaccharide profile and an increased ability to infect enterocytes compared with the wild type, but it had no increased ability to cause infection. These findings indicate that increased resistance to antibody-dependent complement-mediated killing secondary to genetic deletion is not necessarily accompanied by increased virulence and suggest the presence of different mechanisms of antibody resistance.
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http://dx.doi.org/10.1128/IAI.00419-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5563563PMC
September 2017

Leukocyte counts and lymphocyte subsets in relation to pregnancy and HIV infection in Malawian women.

Am J Reprod Immunol 2017 Sep 6;78(3). Epub 2017 Apr 6.

Malawi-Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, Blantyre, Malawi.

Problem: We investigated leukocyte and lymphocyte subsets in HIV-infected or HIV-uninfected, pregnant or non-pregnant Malawian women to explore whether HIV infection and pregnancy may act synergistically to impair cellular immunity.

Method Of Study: We recruited 54 pregnant and 48 non-pregnant HIV-uninfected women and 24 pregnant and 20 non-pregnant HIV-infected Malawian women. We compared peripheral blood leukocyte and lymphocyte subsets between women in the four groups.

Results: Parturient HIV-infected and HIV-uninfected women had more neutrophils (each P<.0001), but fewer lymphocytes (P<.0001; P=.0014) than non-pregnant women. Both groups had fewer total T cells (P<.0001; P=.002) and CD8 T cells (P<.0001; P=.014) than non-pregnant women. HIV-uninfected parturient women had fewer CD4 and γδ T cells, B and NK cells (each P<.0001) than non-pregnant women. Lymphocyte subset percentages were not affected by pregnancy.

Conclusion: Malawian women at parturition have an increased total white cell count due to neutrophilia and an HIV-unrelated pan-lymphopenia.
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http://dx.doi.org/10.1111/aji.12678DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5573949PMC
September 2017