Evelyn Gitau

Prime-boost vaccination with chimpanzee adenovirus and modified vaccinia Ankara encoding TRAP provides partial protection against Plasmodium falciparum infection in Kenyan adults

Vaccination with the recombinant viral vectors chimpanzee adenovirus 63 followed by modified vaccinia Ankara both encoding the malaria sequence ME-TRAP conferred 67% protection against infection with Plasmodium falciparum in Kenyan adults. Setting a TRAP for the malaria parasite Previous studies have shown that T cells induced by vaccines can clear liver-stage malaria parasites, but these vaccines have not been effective in field trials. In a new study, Bejon et al. randomly allocated 121 healthy adult male volunteers to receive either a T cell–inducing vaccine or rabies vaccine as a control. They gave antimalarials to clear malaria parasites from the subjects’ blood and then did frequent blood tests to identify new infections with the malaria parasite Plasmodium falciparum. They found that the volunteers receiving the T cell vaccine had a 67% reduction in the risk of malaria infection during 8 weeks of follow-up. Protective immunity to the liver stage of the malaria parasite can be conferred by vaccine-induced T cells, but no subunit vaccination approach based on cellular immunity has shown efficacy in field studies. We randomly allocated 121 healthy adult male volunteers in Kilifi, Kenya, to vaccination with the recombinant viral vectors chimpanzee adenovirus 63 (ChAd63) and modified vaccinia Ankara (MVA), both encoding the malaria peptide sequence ME-TRAP (the multiple epitope string and thrombospondin-related adhesion protein), or to vaccination with rabies vaccine as a control. We gave antimalarials to clear parasitemia and conducted PCR (polymerase chain reaction) analysis on blood samples three times a week to identify infection with the malaria parasite Plasmodium falciparum. On Cox regression, vaccination reduced the risk of infection by 67% [95% confidence interval (CI), 33 to 83%; P = 0.002] during 8 weeks of monitoring. T cell responses to TRAP peptides 21 to 30 were significantly associated with protection (hazard ratio, 0.24; 95% CI, 0.08 to 0.75; P = 0.016).

Translating the Immunogenicity of Prime-boost Immunization With ChAd63 and MVA ME-TRAP From Malaria Naive to Malaria-endemic Populations

To induce a deployable level of efficacy, a successful malaria vaccine would likely benefit from both potent cellular and humoral immunity. These requirements are met by a heterologous prime-boost immunization strategy employing a chimpanzee adenovirus vector followed by modified vaccinia Ankara (MVA), both encoding the pre-erythrocytic malaria antigen ME-thrombospondin-related adhesive protein (TRAP), with high immunogenicity and significant efficacy in UK adults. We undertook two phase 1b open-label studies in adults in Kenya and The Gambia in areas of similar seasonal malaria transmission dynamics and have previously reported safety and basic immunogenicity data. We now report flow cytometry and additional interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) data characterizing pre-existing and induced cellular immunity as well as anti-TRAP IgG responses. T-cell responses induced by vaccination averaged 1,254 spot-forming cells (SFC) per million peripheral blood mononuclear cells (PBMC) across both trials and flow cytometry revealed cytokine production from both CD4(+) and CD8(+) T cells with the frequency of CD8(+) IFN-γ-secreting monofunctional T cells (previously shown to associate with vaccine efficacy) particularly high in Kenyan adults. Immunization with ChAd63 and MVA ME-TRAP induced strong cellular and humoral immune responses in adults living in two malaria-endemic regions of Africa. This prime-boost approach targeting the pre-erythrocytic stage of the malaria life-cycle is now being assessed for efficacy in a target population.

Review Article: blood-brain barrier in falciparum malaria.

Plasmodium falciparum malaria is the most important parasitic disease infecting the central nervous system of humans worldwide. The pathogenesis of the neurological complications of falciparum malaria remains unclear. In particular, how do asexual parasites confined to the vascular space of the brain cause neuronal impairment? The evidence for a breakdown in the blood–brain barrier (BBB) is conflicting. In some animal models of malaria, there is evidence of breakdown of the BBB, but the data from humans suggests the BBB is mildly impaired only, with few morphological changes. Whether these changes in the BBB are sufficient to account for the neurological complications remains to be determined.

Discovery and Validation of Biomarkers to Guide Clinical Management of Pneumonia in African Children

Lipocalin 2 distinguishes severe and bacterial pneumonia from nonsevere and nonbacterial pneumonia with a high level of precision. The clinical impact of this biomarker requires large-scale clinical evaluation.

Value of Plasmodium falciparum histidine-rich protein 2 level and malaria retinopathy in distinguishing cerebral malaria from other acute encephalopathies in Kenyan children.

Background. The diagnosis of cerebral malaria is problematic in malaria-endemic areas because encephalopathy in patients with parasitemia may have another cause. Abnormal retinal findings are thought to increase the specificity of the diagnosis, and the level of histidine-rich protein 2 (HRP2) may reflect the parasite biomass. Methods. We examined the retina and measured plasma HRP2 levels in children with acute nontraumatic encephalopathy in Kenya. Logistic regression, with HRP2 level as an independent variable and World Health Organization–defined cerebral malaria and/or retinopathy as the outcome, was used to calculate malaria-attributable fractions (MAFs) and retinopathy-attributable fractions (RAFs). Results. Of 270 children, 140 (52%) had peripheral parasitemia, 80 (30%) had malaria retinopathy, and 164 (61%) had an HRP2 level of >0 U/mL. During 2006–2011, the incidence of HRP2 positivity among admitted children declined by 49 cases per 100 000 per year (a 78% reduction). An HRP2 level of >0 U/mL had a MAF of 93% for cerebral malaria, with a MAF of 97% observed for HRP2 levels of ≥10 U/mL (the level of the best combined sensitivity and specificity). HRP2 levels of >0 U/mL had a RAF of 77% for features of retinopathy combined, with the highest RAFs for macular whitening (99%), peripheral whitening (98%), and hemorrhages (90%). Conclusion. HRP2 has a high attributable fraction for features of malarial retinopathy, supporting its use in the diagnosis of cerebral malaria. HRP2 thresholds improve the specificity of the definition.

Plasma and Cerebrospinal Proteomes From Children With Cerebral Malaria Differ From Those of Children With Other Encephalopathies

Clinical signs and symptoms of cerebral malaria in children are nonspecific and are seen in other common encephalopathies in malaria-endemic areas. This makes accurate diagnosis difficult in resource-poor settings. Novel malaria-specific diagnostic and prognostic methods are needed. We have used 2 proteomic strategies to identify differentially expressed proteins in plasma and cerebrospinal fluid from children with a diagnosis of cerebral malaria, compared with those with a diagnosis of malaria-slide-negative acute bacterial meningitis and other nonspecific encephalopathies. Here we report the presence of differentially expressed proteins in cerebral malaria in both plasma and cerebrospinal fluid that could be used to better understand pathogenesis and help develop more-specific diagnostic methods. In particular, we report the expression of 2 spectrin proteins that have known Plasmodium falciparum–binding partners involved in the stability of the infected red blood cell, suppressing further invasion and possibly enhancing the red blood cells ability to sequester in microvasculature.

Challenges in Retaining Research Scientists beyond the Doctoral Level in Kenya

An important goal of modern-day African governments should be to develop a sustainable research culture in higher education in order to provide human resources and expertise toward better health and scientific national policies. Regrettably, research in Kenya is mainly funded by Northern collaborators, with the Kenyan government spending only 6.2% of total government expenditure on health in 2001 [1], and even less on health-related research. As a result, the local institutions are not carrying out the bulk of research in the country; instead, most research conducted in Kenya is funded by Northern collaborators: for example, Kenya Medical Research Institute (KEMRI) programs are funded by the Wellcome Trust (United Kingdom), Centers for Disease Control and Prevention (United States of America), and Walter Reed Army Institute of Research (United States of America). These partnerships have contributed to the changing landscape of research in Kenya, and they continue to play an important role in training local scientists. Ongoing programs and projects culminating from these partnerships have significant components designed to build individual and institutional national capacities in a variety of disciplines at all levels. One of the ways this has been done is to provide postgraduate training to young scientists to the doctoral level both at local and overseas academic institutions. However, the issue of capacity retention following training has not been comprehensively tackled. In this Viewpoint, we highlight three competitive doctoral tracks available in Kenya and how the choices students make ultimately play a role in their search for postdoctoral training. Our Viewpoint is related to A. I. Leshners Editorial in Science last year, which focuses on a change in American and British government funding strategies toward new investigators in research [2].

CD4+ T Cell Responses to the Plasmodium falciparum Erythrocyte Membrane Protein 1 in Children with Mild Malaria

The immune response against the variant surface Ag Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against malaria. We have investigated the development and maintenance of CD4+ T cell responses to a small semiconserved area of the Duffy binding–like domain (DBL)α–domain of PfEMP1, the DBLα-tag. Young children were followed up longitudinally, and parasites and PBMCs were isolated from 35 patients presenting with an acute case of uncomplicated malaria. The DBLα-tag from the PfEMP1 dominantly expressed by the homologous parasite isolate was cloned and expressed as recombinant protein. The recombinant DBLα-tag was used to activate PBMCs collected from each acute episode and from an annual cross-sectional survey performed after the acute malaria episode. In this article, we report that CD4+ T cell responses to the homologous DBLα-tag were induced in 75% of the children at the time of the acute episode and in 62% of the children at the following cross-sectional survey on average 235 d later. Furthermore, children who had induced DBLα-tag–specific CD4+IL-4+ T cells at the acute episode remained episode free for longer than children who induced other types of CD4+ T cell responses. These results suggest that a wide range of DBLα-tag–specific CD4+ T cell responses were induced in children with mild malaria and, in the case of CD4+IL-4+ T cell responses, were associated with protection from clinical episodes.

Endotoxaemia is common in children with Plasmodium falciparum malaria

BackgroundChildren presenting to hospital with recent or current Plasmodium falciparum malaria are at increased the risk of invasive bacterial disease, largely enteric gram-negative organisms (ENGO), which is associated with increased mortality and recurrent morbidity. Although incompletely understood, the most likely source of EGNO is the bowel. We hypothesised that as a result of impaired gut-barrier function endotoxin (lipopolysaccharide), present in the cell-wall of EGNO and in substantial quantities in the gut, is translocated into the bloodstream, and contributes to the pathophysiology of children with severe malaria.MethodsWe conducted a prospective study in 257 children presenting with malaria to two hospitals in Kenya and Uganda. We analysed the clinical presentation, endotoxin and cytokine concentration.ResultsEndotoxaemia (endotoxin activity ≥0.4 EAA Units) was observed in 71 (27.6%) children but its presence was independent of both disease severity and outcome. Endotoxaemia was more frequent in children with severe anaemia but not specifically associated with other complications of malaria. Endotoxaemia was associated with a depressed inflammatory and anti-inflammatory cytokine response. Plasma endotoxin levels in severe malaria negatively correlated with IL6, IL10 and TGFβ (Spearman rho: TNFα: r=−0.122, p=0.121; IL6: r=−0.330, p<0.0001; IL10: r=−0.461, p<0.0001; TGFβ: r=−0.173, p<0.027).ConclusionsEndotoxaemia is common in malaria and results in temporary immune paralysis, similar to that observed in patients with sepsis and experimentally-induced endotoxaemia. Intense sequestration of P. falciparum-infected erythrocytes within the endothelial bed of the gut has been observed in pathological studies and may lead to gut-barrier dysfuction. The association of endotoxaemia with the anaemia phenotype implies that it may contribute to the dyserythropoesis accompanying malaria through inflammation. Both of these factors feasibly underpin the susceptibility to EGNO co-infection. Further research is required to investigate this initial finding, with a view to future treatment trials targeting mechanism and appropriate antimicrobial treatment.

Differential Plasmodium falciparum surface antigen expression among children with Malarial Retinopathy

Retinopathy provides a window into the underlying pathology of life-threatening malarial coma (“cerebral malaria”), allowing differentiation between 1) coma caused by sequestration of Plasmodium falciparum-infected erythrocytes in the brain and 2) coma with other underlying causes. Parasite sequestration in the brain is mediated by PfEMP1; a diverse parasite antigen that is inserted into the surface of infected erythrocytes and adheres to various host receptors. PfEMP1 sub-groups called “DC8” and “DC13” have been proposed to cause brain pathology through interactions with endothelial protein C receptor. To test this we profiled PfEMP1 gene expression in parasites from children with clinically defined cerebral malaria, who either had or did not have accompanying retinopathy. We found no evidence for an elevation of DC8 or DC13 PfEMP1 expression in children with retinopathy. However, the proportional expression of a broad subgroup of PfEMP1 called “group A” was elevated in retinopathy patients suggesting that these variants may play a role in the pathology of cerebral malaria. Interventions targeting group A PfEMP1 may be effective at reducing brain pathology.