Normal Clinical Laboratory Ranges by Age and Sex, and Impact on Study Screening Outcomes in Rural Mali

The interpretation of a laboratory test result requires an appropriate reference range established in healthy subjects, and normal ranges may vary by factors such as geographic region, sex, and age. We examined hematological and clinical chemistry parameters in healthy residents at two rural vaccine trial sites: Bancoumana and Doneguebougou in Mali, West Africa. During screening of clinical studies in 2018 and 2019, peripheral blood samples from 1,192 apparently healthy individuals age 6 months to 82 years were analyzed at a laboratory accredited by the College of American Pathologists for a complete blood count, and creatinine and/or alanine aminotransferase levels. Based on manufacturers' reference range values, which are currently used in Malian clinical laboratories, abnormal values were common in this healthy population. In fact, 30.4% of adult participants had abnormal neutrophil levels and 19.8% had abnormal hemoglobin levels. Differences by sex were observed in those who were older, but not in those younger than 10 years, for several parameters, including hemoglobin, platelet, and absolute neutrophil counts in hematology, and creatinine in biochemistry. The site-specific reference intervals we report can be used in malaria vaccine clinical trials and other interventional studies, as well as in routine clinical care, to identify abnormalities in hematological and biochemical parameters among healthy Malian trial participants.

Malaria transmission-blocking vaccines Pfs230D1-EPA and Pfs25-EPA in Alhydrogel in healthy Malian adults; a phase 1, randomised, controlled trial

BACKGROUND

Malaria transmission-blocking vaccines target mosquito-stage parasites and will support elimination programmes. Gamete vaccine Pfs230D1-EPA/Alhydrogel induced superior activity to zygote vaccine Pfs25-EPA/Alhydrogel in malaria-naive US adults. Here, we compared these vaccines in malaria-experienced Malians.

METHODS

We did a pilot safety study then double-blind, block-randomised, comparator-controlled main-phase trial in malaria-intense Bancoumana, Mali. 18-50-year-old healthy non-pregnant, non-breastfeeding consenting adult residents were randomly assigned (1:1:1:1) to receive four doses at months 0, 1, 4·5, and 16·5 of either 47 μg Pfs25, 40 μg Pfs230D1 or comparator (Twinrix or Menactra)-all co-administered with normal saline for blinding-or 47 μg Pfs25 plus 40 μg Pfs230D1 co-administered. We documented safety and tolerability (primary endpoint in the as-treated populations) and immunogenicity (secondary endpoint in the as-treated populations: ELISA, standard-membrane-feeding assay, and mosquito direct skin feed assay). This trial is registered at ClinicalTrials.gov, NCT02334462.

FINDINGS

Between March 19, and June 2, 2015, we screened 471 individuals. Of 225 enrolled for the pilot and main cohorts, we randomly assigned 25 participants to pilot safety cohort groups of five (20%) to receive a two-dose series of Pfs25-EPA/Alhydrogel (16 μg), Pfs230D1-EPA/Alhydrogel (15 μg) or comparator, followed by Pfs25-EPA/Alhydrogel (16 μg) plus Pfs230D1-EPA/Alhydrogel (15 μg) or comparator plus saline. For the main cohort, we enrolled 200 participants between May 11 and June 2, 2015, to receive a four-dose series of 47 μg Pfs25-EPA/Alhydrogel plus saline (n=50 [25%]; Pfs25), 40 μg Pfs230D1-EPA/Alhydrogel plus saline (n=49 [25%]; Pfs230D1), 47 μg Pfs25-EPA/Alhydrogel plus 40 μg Pfs230D1-EPA/Alhydrogel (n=50 [25%]; Pfs25 plus Pfs230D1), or comparator (Twinrix or Menactra) plus saline (n=51 [25%]). Vaccinations were well tolerated in the pilot safety and main phases. Most vaccinees became seropositive after two Pfs230D1 or three Pfs25 doses; peak titres increased with each dose thereafter (Pfs230D1 geometric mean: 77·8 [95% CI 56·9-106·3], 146·4 [108·3-198·0], and 410·2 [301·6-558·0]; Pfs25 geometric mean 177·7 [130·3-242·4] and 315·7 [209·9-474·6]). Functional activity (mean peak transmission-reducing activity) appeared for Pfs230D1 (74·5% [66·6-82·5]) and Pfs25 plus Pfs230D1 (68·6% [57·3-79·8]), after the third dose and after the fourth dose (88·9% [81·7-96·2] for Pfs230D1 and 85·0% [78·4-91·5] Pfs25 plus Pfs230D1) but not for Pfs25 (58·2% [49·1-67·3] after the third dose and 58·2% [48·5-67·9] after the fourth dose). Pfs230D1 transmission-reducing activity (73·7% [64·1-83·3]) persisted 10 weeks after the fourth dose. Transmission-reducing activity of 80% was estimated at 1659 ELISA units for Pfs25, 218 for Pfs230D1, and 223 for Pfs230D1 plus Pfs25. After 3850 direct skin feed assays, 35 participants (12 Pfs25, eight Pfs230D1, five Pfs25 plus Pfs230D1, and ten comparator) had transmitted parasites at least once. The proportion of positive assays in vaccine groups (Pfs25 33 [3%] of 982 [-0·013 to 0·014], Pfs230D1 22 [2%] of 954 [-0·005 to 0·027], and combination 11 [1%] of 940 [-0·024 to 0·002]) did not differ from that of the comparator (22 [2%] of 974), nor did Pfs230D1 and combination groups differ (-0·024 to 0·001).

INTERPRETATION

Pfs230D1 but not Pfs25 vaccine induces durable serum functional activity in Malian adults. Direct skin feed assays detect parasite transmission to mosquitoes but increased event rates are needed to assess vaccine effectiveness.

FUNDING

Intramural Research Program of the National Institute of Allergy and Infectious Diseases and US National Institutes of Health.

Preclinical evaluations of Pfs25-EPA and Pfs230D1-EPA in AS01 for a vaccine to reduce malaria transmission

Malaria transmission-blocking vaccine candidates Pfs25-EPA and Pfs230D1-EPA target sexual stage development of Plasmodium falciparum parasites in the mosquito host, thereby reducing mosquito infectivity. When formulated on Alhydrogel, Pfs25-EPA has demonstrated safety and immunogenicity in a phase 1 field trial, while Pfs230D1-EPA has shown superior activity to Pfs25-EPA in a phase 1 US trial and has entered phase 2 field trials. Development continues to enhance immunogenicity of these candidates toward producing a vaccine to reduce malaria transmission (VRMT) with both pre-erythrocytic (i.e., anti-infection) and transmission-blocking components. GSK Adjuvant Systems have demonstrated successful potency in pre-erythrocytic vaccine trials and might offer a common platform for VRMT development. Here, we describe preclinical evaluations of Pfs25-EPA and Pfs230D1-EPA nanoparticles with GSK platforms. Formulations were stable after a series of assessments and induced superior antibody titers and functional activity in CD-1 mice, compared to Alhydrogel formulations of the same antigens.

Fetal Cytokine Balance, Erythropoietin and Thalassemia but Not Placental Malaria Contribute to Fetal Anemia Risk in Tanzania

Fetal anemia is common in malaria-endemic areas and a risk factor for anemia as well as mortality during infancy. Placental malaria (PM) and red cell abnormalities have been proposed as possible etiologies, but the relationship between PM and fetal anemia has varied in earlier studies, and the role of red cell abnormalities has not been studied in malaria-endemic areas. In a Tanzanian birth cohort study designed to elucidate the pathogenesis of severe malaria in young infants, we performed a cross-sectional analysis of risk factors for fetal anemia. We determined PM status, newborn red cell abnormalities, and maternal and cord blood levels of iron regulatory proteins, erythropoietin (EPO), cytokines and cytokine receptors. We examined the relationship between these factors and fetal anemia. Fetal anemia was present in 46.2% of the neonates but was not related to PM. Maternal iron deficiency was common (81.6%), most frequent in multigravidae, and interacted with parity to modify risk of fetal anemia, but it was not directly related to risk. Among offspring of iron-deficient women, the odds of fetal anemia increased with fetal α⁺-thalassemia, as well as these patterns of cord blood cytokines: increased cord IL-6, decreased TNF-RI, and decreased sTfR. The EPO response to fetal anemia was low or absent and EPO levels were significantly decreased in newborns with the most severe anemia. This study from an area of high malaria transmission provides evidence that 1) fetal α⁺-thalassemia and cytokine balance, but not PM at delivery, are related to fetal anemia; 2) maternal iron deficiency increases the risk that other factors may cause fetal anemia; and 3) fetal anemia has a multifactorial etiology that may require a variety of interventions, although measures that reduce maternal iron deficiency may be generally beneficial.

Malaria vaccines since 2000: progress, priorities, products

Malaria vaccine development entered a new era in 2015 when the pre-erythrocytic Plasmodium falciparum candidate RTS,S was favorably reviewed by the European Medicines Agency and subsequently introduced into national pilot implementation programs, marking the first human anti-parasite vaccine to pass regulatory scrutiny. Since the first trials published in 1997, RTS,S has been evaluated in a series of clinical trials culminating in Phase 3 testing, while testing of other pre-erythrocytic candidates (that target sporozoite- or liver-stage parasites), particularly whole sporozoite vaccines, has also increased. Interest in blood-stage candidates (that limit blood-stage parasite growth) subsided after disappointing human efficacy results, although new blood-stage targets and concepts may revive activity in this area. Over the past decade, testing of transmission-blocking vaccines (that kill mosquito/sexual-stage parasites) advanced to field trials and the first generation of placental malaria vaccines (that clear placenta-sequestering parasites) entered the clinic. Novel antigen discovery, human monoclonal antibodies, structural vaccinology, and improved platforms promise to expand on RTS,S and improve existing vaccine candidates.

Safety and tolerability of a live oral Salmonella typhimurium vaccine candidate in SIV-infected nonhuman primates

Nontyphoidal Salmonella (NTS) serovars are a common cause of acute food-borne gastroenteritis worldwide and can cause invasive systemic disease in young infants, the elderly, and immunocompromised hosts, accompanied by high case fatality. Vaccination against invasive NTS disease is warranted where the disease incidence and mortality are high and multidrug resistance is prevalent, as in sub-Saharan Africa. Live-attenuated vaccines that mimic natural infection constitute one strategy to elicit protection. However, they must particularly be shown to be adequately attenuated for consideration of immunocompromised subjects. Accordingly, we examined the safety and tolerability of an oral live attenuated Salmonella typhimurium vaccine candidate, CVD 1921, in an established chronic simian immunodeficiency virus (SIV)-infected rhesus macaque model. We evaluated clinical parameters, histopathology, and measured differences in mucosal permeability to wild-type and vaccine strains. Compared to the wild-type S. typhimurium strain I77 in both SIV-infected and SIV-uninfected nonhuman primate hosts, this live-attenuated vaccine shows reduced shedding and systemic spread, exhibits limited pathological disease manifestations in the digestive tract, and induces low levels of cellular infiltration in tissues. Furthermore, wild-type S. typhimurium induces increased intestinal epithelial damage and permeability, with infiltration of neutrophils and macrophages in both SIV-infected and SIV-uninfected nonhuman primates compared to the vaccine strain. Based on shedding, systemic spread, and histopathology, the live-attenuated S. typhimurium strain CVD 1921 appears to be safe and well-tolerated in the nonhuman primate model, including chronically SIV-infected rhesus macaques.

Aerosolized adenovirus-vectored vaccine as an alternative vaccine delivery method

Conventional parenteral injection of vaccines is limited in its ability to induce locally-produced immune responses in the respiratory tract, and has logistical disadvantages in widespread vaccine administration. Recent studies suggest that intranasal delivery or vaccination in the respiratory tract with recombinant viral vectors can enhance immunogenicity and protection against respiratory diseases such as influenza and tuberculosis, and can offer more broad-based generalized protection by eliciting durable mucosal immune responses. Controlled aerosolization is a method to minimize vaccine particle size and ensure delivery to the lower respiratory tract. Here, we characterize the dynamics of aerosolization and show the effects of vaccine concentration on particle size, vector viability, and the actual delivered dose of an aerosolized adenoviral vector. In addition, we demonstrate that aerosol delivery of a recombinant adenoviral vaccine encoding H1N1 hemagglutinin is immunogenic and protects ferrets against homologous viral challenge. Overall, aerosol delivery offers comparable protection to intramuscular injection, and represents an attractive vaccine delivery method for broad-based immunization campaigns.

Comparative efficacy of hemagglutinin, nucleoprotein, and matrix 2 protein gene-based vaccination against H5N1 influenza in mouse and ferret

Efforts to develop a broadly protective vaccine against the highly pathogenic avian influenza A (HPAI) H5N1 virus have focused on highly conserved influenza gene products. The viral nucleoprotein (NP) and ion channel matrix protein (M2) are highly conserved among different strains and various influenza A subtypes. Here, we investigate the relative efficacy of NP and M2 compared to HA in protecting against HPAI H5N1 virus. In mice, previous studies have shown that vaccination with NP and M2 in recombinant DNA and/or adenovirus vectors or with adjuvants confers protection against lethal challenge in the absence of HA. However, we find that the protective efficacy of NP and M2 diminishes as the virulence and dose of the challenge virus are increased. To explore this question in a model relevant to human disease, ferrets were immunized with DNA/rAd5 vaccines encoding NP, M2, HA, NP+M2 or HA+NP+M2. Only HA or HA+NP+M2 vaccination conferred protection against a stringent virus challenge. Therefore, while gene-based vaccination with NP and M2 may provide moderate levels of protection against low challenge doses, it is insufficient to confer protective immunity against high challenge doses of H5N1 in ferrets. These immunogens may require combinatorial vaccination with HA, which confers protection even against very high doses of lethal viral challenge.

A gene-based avian influenza vaccine in poultry

Highly pathogenic avian influenza A (HPAI) viruses, specifically H5N1 strains, cause widespread morbidity and mortality in domestic and wild bird populations, and recent outbreaks have resulted in severe economic losses. Although still largely confined to birds, more than 300 human cases resulting in deaths have been reported to the World Health Organization. These sporadic human cases result from direct transmission from infected birds; however, a sustained outbreak of HPAI H5N1 increases the potential for the emergence of a human pandemic strain. One approach to the containment of HPAI H5N1 is the development of vaccines for use in poultry. Currently, the majority of avian influenza vaccines for poultry are traditional whole-virus vaccines produced in eggs. Although highly efficacious, these vaccines are hindered by long production times, inflexibility in quickly altering antigenic composition, and limited breadth of protection. Newer vaccines with more efficient manufacturing processes, enhanced efficacy, and cross-protection against multiple strains would improve preparedness. Reverse genetics technology has provided one such method, and emerging gene-based vaccines offer another approach that reduces dependence on egg-based production and human exposure to pathogenic viruses. Gene-based vaccines also provide rapid manufacturing, enhanced precision and versatility, and the capacity to protect against a broad range of viral subtypes. Vectors for these vaccines include replication-defective viruses, bacterial vectors, and DNA. Here we review the features of gene-based vaccination that may facilitate the control of HPAI H5N1 in poultry, and highlight the development of a hemagglutinin-based multivalent DNA vaccine that confers protection in mice and chickens.