The Power of Malaria Vaccine Trials Using Controlled Human Malaria Infection

Controlled human malaria infection (CHMI) in healthy human volunteers is an important and powerful tool in clinical malaria vaccine development. However, power calculations are essential to obtain meaningful estimates of protective efficacy, while minimizing the risk of adverse events. To optimize power calculations for CHMI-based malaria vaccine trials, we developed a novel non-linear statistical model for parasite kinetics as measured by qPCR, using data from mosquito-based CHMI experiments in 57 individuals. We robustly account for important sources of variation between and within individuals using a Bayesian framework. Study power is most dependent on the number of individuals in each treatment arm; inter-individual variation in vaccine efficacy and the number of blood samples taken per day matter relatively little. Due to high inter-individual variation in the number of first-generation parasites, hepatic vaccine trials required significantly more study subjects than erythrocytic vaccine trials. We provide power calculations for hypothetical malaria vaccine trials of various designs and conclude that so far, power calculations have been overly optimistic. We further illustrate how upcoming techniques like needle-injected CHMI may reduce required sample sizes

A monoclonal antibody-based immunoassay to measure the antibody response against the repeat region of the circumsporozoite protein of Plasmodium falciparum

Background: The malaria vaccine candidate RTS, S/AS01 (GSK Vaccines) induces high IgG concentration against the circumsporozoite protein (CSP) of Plasmodium falciparum. In human vaccine recipients circulating anti-CSP antibody concentrations are associated with protection against infection but appear not to be the correlate of protection. However, in a humanized mouse model of malaria infection prophylactic administration of a human monoclonal antibody (MAL1C), derived from a RTS, S/AS01-immunized volunteer, directed against the CSP repeat region, conveyed full protection in a dose-dependent manner suggesting that antibodies alone are able to prevent P. falciparum infection when present in sufficiently high concentrations. A competition ELISA was developed to measure the presence of MAL1C-like antibodies in polyclonal sera from RTS, S/AS01 vaccine recipients and study their possible contribution to protection against infection. Results: MAL1C-like antibodies present in polyclonal vaccine-induced sera were evaluated for their ability to compete with biotinylated monoclonal antibody MAL1C for binding sites on the capture antigen consisting of the recombinant protein encompassing 32 NANP repeats of CSP (R32LR). Serum samples were taken at different time points from participants in two RTS, S/AS01 vaccine studies (NCT01366534 and NCT01857869). Vaccine-induced protection status of the study participants was determined based on the outcome of experimental challenge with infected mosquito bites after vaccination. Optimal conditions were established to reliably detect MAL1C-like antibodies in polyclonal sera. Polyclonal anti-CSP antibodies and MAL1C-like antibody content were measured in 276 serum samples from RTS, S/AS01 vaccine recipients using the standard ELISA and MAL-1C competition ELISA, respectively. A strong correlation was observed between the results from these assays. However, no correlation was found between the results of either assay and protection against infection. Conclusions: The competition ELISA to measure MAL1C-like antibodies in polyclonal sera from RTS, S/AS01 vaccine recipients was robust and reliable but did not reveal the elusive correlate of protection

PfHPRT: a new biomarker candidate of acute Plasmodium falciparum infection.

Plasmodium falciparum is a protozoan parasite that causes human malaria. This parasitic infection accounts for approximately 655,000 deaths each year worldwide. Most deaths could be prevented by diagnosing and treating malaria promptly. To date, few parasite proteins have been developed into rapid diagnostic tools. We have combined a shotgun and a targeted proteomic strategy to characterize the plasma proteome of Gambian children with severe malaria (SM), mild malaria, and convalescent controls in search of new candidate biomarkers. Here we report four P. falciparum proteins with a high level of confidence in SM patients, namely, PF10_0121 (hypoxanthine phosphoribosyltransferase, pHPRT), PF11_0208 (phosphoglycerate mutase, pPGM), PF13_0141 (lactate dehydrogenase, pLDH), and PF14_0425 (fructose bisphosphate aldolase, pFBPA). We have optimized selected reaction monitoring (SRM) assays to quantify these proteins in individual patients. All P. falciparum proteins were higher in SM compared with mild cases or control subjects. SRM-based measurements correlated markedly with clinical anemia (low blood hemoglobin concentration), and pLDH and pFBPA were significantly correlated with higher P. falciparum parasitemia. These findings suggest that pHPRT is a promising biomarker to diagnose P. falciparum malaria infection. The diagnostic performance of this marker should be validated prospectively

Paths to a malaria vaccine illuminated by parasite genomics.

More human death and disease is caused by malaria parasites than by all other eukaryotic pathogens combined. As early as the sequencing of the first human genome, malaria parasite genomics was prioritized to fuel the discovery of vaccine candidate antigens. This stimulated increased research on malaria, generating new understanding of the cellular and molecular mechanisms of infection and immunity. This review of recent developments illustrates how new approaches in parasite genomics, and increasingly large amounts of data from population studies, are helping to identify antigens that are promising lead targets. Although these results have been encouraging, effective discovery and characterization need to be coupled with more innovation and funding to translate findings into newly designed vaccine products for clinical trials

Evidence of blood stage efficacy with a virosomal malaria vaccine in a Phase IIa clinical trial

Background Previous research indicates that a combination vaccine targeting different stages of the malaria life cycle is likely to provide the most effective malaria vaccine. This trial was the first to combine two existing vaccination strategies to produce a vaccine that induces immune responses to both the pre-erythrocytic and blood stages of the P. falciparum life cycle. Methods This was a Phase I/IIa study of a new combination malaria vaccine FFM ME-TRAP+PEV3A. PEV3A includes peptides from both the pre-erythrocytic circumsporozoite protein and the blood-stage antigen AMA-1. This study was conducted at the Centre for Clinical Vaccinology and Tropical Medicine, University of Oxford, Oxford, UK. The participants were healthy, malaria naïve volunteers, from Oxford. The interventions were vaccination with PEV3A alone, or PEV3A+FFM ME-TRAP. The main outcome measure was protection from malaria in a sporozoite challenge model. Other outcomes included measures of parasite specific immune responses induced by either vaccine; and safety, assessed by collection of adverse event data. Results We observed evidence of blood stage immunity in PEV3A vaccinated volunteers, but no volunteers were completely protected from malaria. PEV3A induced high antibody titres, and antibodies bound parasites in immunofluorescence assays. Moreover, we observed boosting of the vaccine-induced immune response by sporozoite challenge. Immune responses induced by FFM ME-TRAP were unexpectedly low. The vaccines were safe, with comparable side effect profiles to previous trials. Although there was no sterile protection two major observations support an effect of the vaccine-induced response on blood stage parasites: (i) Lower rates of parasite growth were observed in volunteers vaccinated with PEV3A compared to unvaccinated controls (p = 0.012), and this was reflected in the PCR results from PEV3A vaccinated volunteers. These showed early control of parasitaemia by some volunteers in this group. One volunteer, who received PEV3A alone, was diagnosed very late, on day 20 compared to an average of 11.8 days in unvaccinated controls. (ii). Morphologically abnormal parasites were present in the blood of all (n = 24) PEV3A vaccinated volunteers, and in only 2/6 controls (p = 0.001). We describe evidence of vaccine-induced blood stage efficacy for the first time in a sporozoite challenge study

Vaccine innovation, translational research and the management of knowledge accumulation

What does it take to translate research into socially beneficial technologies like vaccines? Current policy that focuses on expanding research or strengthening incentives overlooks how the supply and demand of innovation is mediated by problem-solving processes that generate knowledge which is often fragmented and only locally valid. This paper details some of the conditions that allow fragmented, local knowledge to accumulate through a series of structured steps from the artificial simplicity of the laboratory to the complexity of real world application. Poliomyelitis is used as an illustrative case to highlight the importance of experimental animal models and the extent of co-ordination that can be required if they are missing. Implications for the governance and management of current attempts to produce vaccines for HIV, TB and Malaria are discussed. Article Outlin

Evaluation of the immune response to RTS,S/AS01 and RTS,S/AS02 adjuvanted vaccines : randomized, double-blind study in malaria-naïve adults

This phase II, randomized, double-blind study evaluated the immunogenicity of RTS, S vaccines containing Adjuvant System AS 01 or AS 02 as compared with non-adjuvanted RTS, S in healthy, malaria-naive adults (NCT00443131). Thirty-six subjects were randomized (1:1:1) to receive RTS, S/AS 01, RTS, S/AS 02, or RTS, S/saline at months 0, 1, and 2. Antibody responses to Plasmodium falciparum circumsporozoite (CS) and hepatitis B surface (HBs) antigens were assessed and cell-mediated immune responses evaluated by flow cytometry using intracellular cytokine staining on peripheral blood mononuclear cells. Anti-CS antibody avidity was also characterized. Safety and reactogenicity after each vaccine dose were monitored. One month after the third vaccine dose, RTS, S/AS 01 (160.3 EU/mL [95%CI: 114.1-225.4]) and RTS, S/AS 02 (77.4 EU/mL (95%CI: 47.3-126.7)) recipients had significantly higher anti-CS antibody geometric mean titers (GMTs) than recipients of RTS, S/saline (12.2 EU/mL (95%CI: 4.8-30.7); P < 0.0001 and P = 0.0011, respectively). The anti-CS antibody GMT was significantly higher with RTS, S/AS 01 than with RTS, S/AS 02 (P = 0.0135). Anti-CS antibody avidity was in the same range in all groups. CS- and HBs-specific CD4(+) T cell responses were greater for both RTS, S/AS groups than for the RTS, S/saline group. Reactogenicity was in general higher for RTS, S/AS compared with RTS, S/saline. Most grade 3 solicited adverse events (AEs) were of short duration and grade 3 solicited general AEs were infrequent in the 3 groups. No serious adverse events were reported. In conclusion, in comparison with non-adjuvanted RTS, S, both RTS, S/AS vaccines exhibited better CS-specific immune responses. The anti-CS antibody response was significantly higher with RTS, S/AS 01 than with RTS, S/AS 02. The adjuvanted vaccines had acceptable safety profiles

Emerging Challenges and Opportunities in Infectious Disease Epidemiology.

Much of the intellectual tradition of modern epidemiology stems from efforts to understand and combat chronic diseases persisting through the 20th century epidemiologic transition of countries such as the United States and United Kingdom. After decades of relative obscurity, infectious disease epidemiology has undergone an intellectual rebirth in recent years amid increasing recognition of the threat posed by both new and familiar pathogens. Here, we review the emerging coalescence of infectious disease epidemiology around a core set of study designs and statistical methods bearing little resemblance to the chronic disease epidemiology toolkit. We offer our outlook on challenges and opportunities facing the field, including the integration of novel molecular and digital information sources into disease surveillance, the assimilation of such data into models of pathogen spread, and the increasing contribution of models to public health practice. We next consider emerging paradigms in causal inference for infectious diseases, ranging from approaches to evaluating vaccines and antimicrobial therapies to the task of ascribing clinical syndromes to etiologic microorganisms, an age-old problem transformed by our increasing ability to characterize human-associated microbiota. These areas represent an increasingly important component of epidemiology training programs for future generations of researchers and practitioners

Misoprostol in the management of the third stage of labour in the home delivery setting in rural Gambia: a randomised controlled trial.

OBJECTIVE: To assess the effectiveness of 600 microg oral misoprostol on postpartum haemorrhage (PPH) and postpartum anaemia in a low income country home birth situation. DESIGN: Double blind randomised controlled trial. SETTING: Twenty-six villages in rural Gambia with 52 traditional birth attendants (TBAs). SAMPLE: One thousand, two hundred and twenty-nine women delivering at home under the guidance of a trained TBA. METHODS: Active management of the third stage of labour using three 200-microg misoprostol tablets and placebo or four 0.5-mg ergometrine tablets (standard treatment) and placebo. Tablets were taken orally immediately after delivery. MAIN OUTCOME MEASURES: Measured blood loss, postpartum haemoglobin (Hb), difference between Hb at the last antenatal care visit and three to five days postpartum. RESULTS: The misoprostol group experienced lower incidence of measured blood loss > or =500 mL and postpartum Hb or = 2 g/dL was 16.4% with misoprostol and 21.2% with ergometrine [relative risk 0.77; 95% confidence interval (CI) 0.60-0.98; P= 0.02]. Shivering was significantly more common with misoprostol, while vomiting was more common with ergometrine. Only transient side effects were observed. CONCLUSIONS: Six hundred micrograms of oral misoprostol is a promising drug to prevent life-threatening PPH in this setting