Slow clearance of histidine-rich protein-2 in Gabonese with uncomplicated malaria.

Malaria rapid diagnostic tests (RDTs), which detect Plasmodium falciparum (Pf)-specific histidine-rich protein-2 (HRP2), have increasing importance for the diagnosis and control of malaria, especially also in regions where routine diagnosis by microscopy is not available. HRP2-based RDTs have a similar sensitivity to expert microscopy, but their reported low specificity can lead to high false positivity rates, particularly in high-endemic areas. Despite the widespread use of RDTs, models investigating the dynamics of HRP2 clearance following Pf treatment focus rather on short-term clearance of the protein. The goal of this observational cohort study was to determine the long-term kinetic of HRP2-levels in peripheral blood after treatment of uncomplicated malaria cases with Pf mono-infection using a 3-day course of artesunate/amodiaquine. HRP2 levels were quantified at enrollment and on days 1, 2, 3, 5, 7, 12, 17, 22, and 28 post-treatment initiation. The findings reveal an unexpectedly prolonged clearance of HRP2 after parasite clearance from capillary blood. Terminal HRP2 half-life was estimated to be 9 days after parasite clearance using a pharmacokinetic two-compartmental elimination model. These results provide evidence that HRP2 clearance has generally been underestimated, as the antigen remains detectable in capillary blood for up to 28 days following successful treatment, influencing RDT-based assessment following a malaria treatment for weeks. A better understanding of the HRP2 clearance dynamics is critical for guiding the diagnosis of malaria when relying on RDTs. IMPORTANCE: Detecting Plasmodium falciparum, the parasite responsible for the severest form of malaria, typically involves microscopy, polymerase chain reaction (PCR), or rapid diagnostic tests (RDTs) targeting the histidine-rich protein 2 or 3 (HRP2/3). While microscopy and PCR quickly turn negative after the infection is cleared, HRP2 remains detectable for a prolonged period. The exact duration of HRP2 persistence had not been well defined. Our study in Gabon tracked HRP2 levels over 4 weeks, resulting in a new model for antigen clearance. We discovered that a two-compartment model accurately predicts HRP2 levels, revealing an initial rapid reduction followed by a much slower elimination phase that can take several weeks. These findings are crucial for interpreting RDT results, as lingering HRP2 can lead to false positives, impacting malaria diagnosis and treatment decisions.

Machine learning prediction of malaria vaccine efficacy based on antibody profiles.

Immunization through repeated direct venous inoculation of Plasmodium falciparum (Pf) sporozoites (PfSPZ) under chloroquine chemoprophylaxis, using the PfSPZ Chemoprophylaxis Vaccine (PfSPZ-CVac), induces high-level protection against controlled human malaria infection (CHMI). Humoral and cellular immunity contribute to vaccine efficacy but only limited information about the implicated Pf-specific antigens is available. Here, we examined Pf-specific antibody profiles, measured by protein arrays representing the full Pf proteome, of 40 placebo- and PfSPZ-immunized malaria-naïve volunteers from an earlier published PfSPZ-CVac dose-escalation trial. For this purpose, we both utilized and adapted supervised machine learning methods to identify predictive antibody profiles at two different time points: after immunization and before CHMI. We developed an adapted multitask support vector machine (SVM) approach and compared it to standard methods, i.e. single-task SVM, regularized logistic regression and random forests. Our results show, that the multitask SVM approach improved the classification performance to discriminate the protection status based on the underlying antibody-profiles while combining time- and dose-dependent data in the prediction model. Additionally, we developed the new fEature diStance exPlainabilitY (ESPY) method to quantify the impact of single antigens on the non-linear multitask SVM model and make it more interpretable. In conclusion, our multitask SVM model outperforms the studied standard approaches in regard of classification performance. Moreover, with our new explanation method ESPY, we were able to interpret the impact of Pf-specific antigen antibody responses that predict sterile protective immunity against CHMI after immunization. The identified Pf-specific antigens may contribute to a better understanding of immunity against human malaria and may foster vaccine development.

Immune responses associated with protection induced by chemoattenuated PfSPZ vaccine in malaria-naive Europeans.

Vaccination of malaria-naive volunteers with a high dose of Plasmodium falciparum sporozoites chemoattenuated by chloroquine (CQ) (PfSPZ-CVac [CQ]) has previously demonstrated full protection against controlled human malaria infection (CHMI). However, lower doses of PfSPZ-CVac [CQ] resulted in incomplete protection. This provides the opportunity to understand the immune mechanisms needed for better vaccine-induced protection by comparing individuals who were protected with those not protected. Using mass cytometry, we characterized immune cell composition and responses of malaria-naive European volunteers who received either lower doses of PfSPZ-CVac [CQ], resulting in 50% protection irrespective of the dose, or a placebo vaccination, with everyone becoming infected following CHMI. Clusters of CD4+ and γδ T cells associated with protection were identified, consistent with their known role in malaria immunity. Additionally, EMRA CD8+ T cells and CD56+CD8+ T cell clusters were associated with protection. In a cohort from a malaria-endemic area in Gabon, these CD8+ T cell clusters were also associated with parasitemia control in individuals with lifelong exposure to malaria. Upon stimulation with P. falciparum-infected erythrocytes, CD4+, γδ, and EMRA CD8+ T cells produced IFN-γ and/or TNF, indicating their ability to mediate responses that eliminate malaria parasites.

Evaluating Malaria Rapid Diagnostic Tests and Microscopy for Detecting Plasmodium Infection and Status of Plasmodium falciparum Histidine-Rich Protein 2/3 Gene Deletions in Southeastern Nigeria.

Delays in malaria diagnosis increase treatment failures and deaths. In endemic regions, standard diagnostic methods are microscopy and malaria rapid diagnostic tests (mRDTs) detecting Plasmodium falciparum histidine-rich protein 2/3 (PFHRP2/PFHRP3), but gene deletions can allow certain parasites to remain undetected. We enlisted a cohort comprising 207 symptomatic individuals, encompassing both children and adults, at a hospital in Nnewi, Nigeria. The prevalence of parasites was determined using a highly sensitive, species-specific quantitative polymerase chain reaction (SS-qPCR). Within a subset of 132 participants, we assessed the sensitivity and specificity of microscopy and HRP2-mRDTs in comparison to SS-qPCR for the detection of P. falciparum. We also investigated the prevalence of pfhrp2/pfhrp3 gene deletions. Greater sensitivity was achieved with mRDTs (95%) compared with microscopy (77%). Also, mRDTs exhibited greater specificity (68%) than microscopy (44%). The positive predictive value of mRDTs (89%) surpassed that of microscopy (80%), suggesting a greater probability of accurately indicating the presence of infection. The negative predictive value of mRDTs (82%) was far greater than microscopy (39%). Of the 165 P. falciparum-positive samples screened for pfhrp2/pfhrp3 gene deletions, one gene deletion was detected in one sample. Regarding infection prevalence, 84% were positive for Plasmodium spp. (by reverse transcription [RT]-qPCR), with P. falciparum responsible for the majority (97%) of positive cases. Thus, exclusive reliance on microscopy in endemic areas may impede control efforts resulting from false negatives, underscoring the necessity for enhanced training and advocating for high-throughput molecular testing such as RT-qPCR or qPCR at referral centers to address limitations.

Mucosal response of inactivated and recombinant COVID-19 vaccines in Congolese individuals.

BACKGROUND: The efficacy of immunization against an airborne pathogen depends in part on its ability to induce antibodies at the major entry site of the virus, the mucosa. Recent studies have revealed that mucosal immunity is poorly activated after vaccination with messenger RNA vaccines, thus failing in blocking virus acquisition upon its site of initial exposure. Little information is available about the induction of mucosal immunity by inactivated and recombinant coronavirus disease 2019 (COVID-19) vaccines. This study aims to investigate this topic. METHODS: Saliva and plasma samples from 440 healthy Congolese were collected including (1) fully vaccinated 2 month postvaccination with either an inactivated or a recombinant COVID-19 vaccine and (2) nonvaccinated control group. Total anti-severe acute respiratory syndrome coronavirus 2 receptor-binding domain IgG and IgA antibodies were assessed using in-house enzyme-linked immunosorbent assays for both specimens. FINDINGS: Altogether, the positivity of IgG was significantly higher in plasma than in saliva samples both in vaccinated and nonvaccinated control groups. Inversely, IgA positivity was slightly higher in saliva than in plasma of vaccinated group. The overall IgG and IgA levels were respectively over 103 and 14 times lower in saliva than in plasma samples. We found a strong positive correlation between IgG in saliva and plasma also between IgA in both specimens (r = .70 for IgG and r = .52 for IgA). Interestingly, contrary to IgG, the level of salivary IgA was not different between seropositive control group and seropositive vaccinated group. No significant difference was observed between recombinant and inactivated COVID-19 vaccines in total IgG and IgA antibody concentration release 2 months postvaccination both in plasma and saliva. CONCLUSION: Inactivated and recombinant COVID-19 vaccines in use in the Republic of Congo poorly activated mucosal IgA-mediated antibody response 2 months postvaccination.

PlasmoFAB: a benchmark to foster machine learning for Plasmodium falciparum protein antigen candidate prediction.

MOTIVATION: Machine learning methods can be used to support scientific discovery in healthcare-related research fields. However, these methods can only be reliably used if they can be trained on high-quality and curated datasets. Currently, no such dataset for the exploration of Plasmodium falciparum protein antigen candidates exists. The parasite P.falciparum causes the infectious disease malaria. Thus, identifying potential antigens is of utmost importance for the development of antimalarial drugs and vaccines. Since exploring antigen candidates experimentally is an expensive and time-consuming process, applying machine learning methods to support this process has the potential to accelerate the development of drugs and vaccines, which are needed for fighting and controlling malaria. RESULTS: We developed PlasmoFAB, a curated benchmark that can be used to train machine learning methods for the exploration of P.falciparum protein antigen candidates. We combined an extensive literature search with domain expertise to create high-quality labels for P.falciparum specific proteins that distinguish between antigen candidates and intracellular proteins. Additionally, we used our benchmark to compare different well-known prediction models and available protein localization prediction services on the task of identifying protein antigen candidates. We show that available general-purpose services are unable to provide sufficient performance on identifying protein antigen candidates and are outperformed by our models that were trained on this tailored data. AVAILABILITY AND IMPLEMENTATION: PlasmoFAB is publicly available on Zenodo with DOI 10.5281/zenodo.7433087. Furthermore, all scripts that were used in the creation of PlasmoFAB and the training and evaluation of machine learning models are open source and publicly available on GitHub here: https://github.com/msmdev/PlasmoFAB.

The exception that proves the rule: Virulence gene expression at the onset of Plasmodium falciparum blood stage infections.

Controlled human malaria infections (CHMI) are a valuable tool to study parasite gene expression in vivo under defined conditions. In previous studies, virulence gene expression was analyzed in samples from volunteers infected with the Plasmodium falciparum (Pf) NF54 isolate, which is of African origin. Here, we provide an in-depth investigation of parasite virulence gene expression in malaria-naïve European volunteers undergoing CHMI with the genetically distinct Pf 7G8 clone, originating in Brazil. Differential expression of var genes, encoding major virulence factors of Pf, PfEMP1s, was assessed in ex vivo parasite samples as well as in parasites from the in vitro cell bank culture that was used to generate the sporozoites (SPZ) for CHMI (Sanaria PfSPZ Challenge (7G8)). We report broad activation of mainly B-type subtelomeric located var genes at the onset of a 7G8 blood stage infection in naïve volunteers, mirroring the NF54 expression study and suggesting that the expression of virulence-associated genes is generally reset during transmission from the mosquito to the human host. However, in 7G8 parasites, we additionally detected a continuously expressed single C-type variant, Pf7G8_040025600, that was most highly expressed in both pre-mosquito cell bank and volunteer samples, suggesting that 7G8, unlike NF54, maintains expression of some previously expressed var variants during transmission. This suggests that in a new host, the parasite may preferentially express the variants that previously allowed successful infection and transmission. Trial registration: ClinicalTrials.gov - NCT02704533; 2018-004523-36.

Saliva and Plasma Antibody Levels in Children and Adolescents After Primary Infection With Omicron Variants of SARS-CoV-2 Infection in Germany.

This cross-sectional study evaluates IgG antibody levels in children and adolescents in Germany following SARS-CoV-2 infection.

First-in-human use of a modular capsid virus-like vaccine platform: an open-label, non-randomised, phase 1 clinical trial of the SARS-CoV-2 vaccine ABNCoV2.

BACKGROUND: Capsid virus-like particles (cVLP) have proven safe and immunogenic and can be a versatile platform to counter pandemics. We aimed to clinically test a modular cVLP COVID-19 vaccine in individuals who were naive to SARS-CoV-2. METHODS: In this phase 1, single-centre, dose-escalation, adjuvant-selection, open-label clinical trial, we recruited participants at the Radboud University Medical Center in Nijmegen, Netherlands, and sequentially assigned them to seven groups. Eligible participants were healthy, aged 18-55 years, and tested negative for SARS-CoV-2 and anti-SARS-CoV-2 antibodies. Participants were vaccinated intramuscularly on days 0 and 28 with 6 µg, 12 µg, 25 µg, 50 µg, or 70 µg of the cVLP-based COVID-19 vaccine (ABNCoV2). A subgroup received MF59-adjuvanted ABNCoV2. Follow-up was for 24 weeks after second vaccination. The primary objectives were to assess the safety and tolerability of ABNCoV2 and to identify a dose that optimises the tolerability-immunogenicity ratio 14 days after the first vaccination. The primary safety endpoint was the number of related grade 3 adverse events and serious adverse events in the intention-to-treat population. The primary immunogenicity endpoint was the concentration of ABNCoV2-specific antibodies. The trial is registered with ClinicalTrials.gov, NCT04839146. FINDINGS: 45 participants (six to nine per group) were enrolled between March 15 and July 15, 2021. Participants had a total of 249 at least possibly related solicited adverse events (185 grade 1, 63 grade 2, and one grade 3) within a week after vaccination. Two serious adverse events occurred; one was classified as a possible adverse reaction. Antibody titres were dose-dependent with levels plateauing at a vaccination dose of 25-70 µg ABNCoV2. After second vaccination, live virus neutralisation activity against major SARS-CoV-2 variants was high but was lower with an omicron (BA.1) variant. Vaccine-specific IFNγ+ CD4+ T cells were induced. INTERPRETATION: Immunisation with ABNCoV2 was well tolerated, safe, and resulted in a functional immune response. The data support the need for additional clinical development of ABNCoV2 as a second-generation SARS-CoV-2 vaccine. The modular cVLP platform will accelerate vaccine development, beyond SARS-CoV-2. FUNDING: EU, Carlsberg Foundation, and the Novo Nordisk Foundation.

Antibody Binding and Angiotensin-Converting Enzyme 2 Binding Inhibition Is Significantly Reduced for Both the BA.1 and BA.2 Omicron Variants.

BACKGROUND: The rapid emergence of the Omicron variant and its large number of mutations led to its classification as a variant of concern (VOC) by the World Health Organization. Subsequently, Omicron evolved into distinct sublineages (eg, BA.1 and BA.2), which currently represent the majority of global infections. Initial studies of the neutralizing response toward BA.1 in convalescent and vaccinated individuals showed a substantial reduction. METHODS: We assessed antibody (immunoglobulin G [IgG]) binding, ACE2 (angiotensin-converting enzyme 2) binding inhibition, and IgG binding dynamics for the Omicron BA.1 and BA.2 variants compared to a panel of VOCs/variants of interest, in a large cohort (N = 352) of convalescent, vaccinated, and infected and subsequently vaccinated individuals. RESULTS: While Omicron was capable of efficiently binding to ACE2, antibodies elicited by infection or immunization showed reduced binding capacities and ACE2 binding inhibition compared to wild type. Whereas BA.1 exhibited less IgG binding compared to BA.2, BA.2 showed reduced inhibition of ACE2 binding. Among vaccinated samples, antibody binding to Omicron only improved after administration of a third dose. CONCLUSIONS: Omicron BA.1 and BA.2 can still efficiently bind to ACE2, while vaccine/infection-derived antibodies can bind to Omicron. The extent of the mutations within both variants prevents a strong inhibitory binding response. As a result, both Omicron variants are able to evade control by preexisting antibodies.

A pharmacokinetic-pharmacodynamic model for chemoprotective agents against malaria.

Chemoprophylactics are a vital tool in the fight against malaria. They can be used to protect populations at risk, such as children younger than the age of 5 in areas of seasonal malaria transmission or pregnant women. Currently approved chemoprophylactics all present challenges. There are either concerns about unacceptable adverse effects such as neuropsychiatric sequalae (mefloquine), risks of hemolysis in patients with G6PD deficiency (8-aminoquinolines such as tafenoquine), or cost and daily dosing (atovaquone-proguanil). Therefore, there is a need to develop new chemoprophylactic agents to provide more affordable therapies with better compliance through improving properties such as pharmacokinetics to allow weekly, preferably monthly, dosing. Here we present a pharmacokinetic-pharmacodynamic (PKPD) model constructed using DSM265 (a dihydroorotate dehydrogenase inhibitor with activity against the liver schizonts of malaria, therefore, a prophylaxis candidate). The PKPD model mimics the parasite lifecycle by describing parasite dynamics and drug activity during the liver and blood stages. A major challenge is the estimation of model parameters, as only blood-stage parasites can be observed once they have reached a threshold. By combining qualitative and quantitative knowledge about the parasite from various sources, it has been shown that it is possible to infer information about liver-stage growth and its initial infection level. Furthermore, by integrating clinical data, the killing effect of the drug on liver- and blood-stage parasites can be included in the PKPD model, and a clinical outcome can be predicted. Despite multiple challenges, the presented model has the potential to help translation from preclinical to late development for new chemoprophylactic candidates.

The IgG glycome of SARS-CoV-2 infected individuals reflects disease course and severity.

Immunoglobulin G (IgG) antibodies play an important role in the immune response against viruses such as SARS-CoV-2. As the effector functions of IgG are modulated by N-glycosylation of the Fc region, the structure and possible function of the IgG N-glycome has been under investigation in relation to divergent COVID-19 disease courses. Through LC-MS analysis we studied both total IgG1 and spike protein-specific IgG1 Fc glycosylation of 129 German and 163 Brazilian COVID-19 patients representing diverse patient populations. We found that hospitalized COVID-19 patients displayed decreased levels of total IgG1 bisection and galactosylation and lowered anti-S IgG1 fucosylation and bisection as compared to mild outpatients. Anti-S IgG1 glycosylation was dynamic over the disease course and both anti-S and total IgG1 glycosylation were correlated to inflammatory markers. Further research is needed to dissect the possible role of altered IgG glycosylation profiles in (dys)regulating the immune response in COVID-19.

Stabilized recombinant SARS-CoV-2 spike antigen enhances vaccine immunogenicity and protective capacity.

The SARS-CoV-2 spike (S) glycoprotein is synthesized as a large precursor protein and must be activated by proteolytic cleavage into S1 and S2. A recombinant modified vaccinia virus Ankara (MVA) expressing native, full-length S protein (MVA-SARS-2-S) is currently under investigation as a candidate vaccine in phase I clinical studies. Initial results from immunogenicity monitoring revealed induction of S-specific antibodies binding to S2, but low-level antibody responses to the S1 domain. Follow-up investigations of native S antigen synthesis in MVA-SARS-2-S-infected cells revealed limited levels of S1 protein on the cell surface. In contrast, we found superior S1 cell surface presentation upon infection with a recombinant MVA expressing a stabilized version of SARS-CoV-2 S protein with an inactivated S1/S2 cleavage site and K986P and V987P mutations (MVA-SARS-2-ST). When comparing immunogenicity of MVA vector vaccines, mice vaccinated with MVA-SARS-2-ST mounted substantial levels of broadly reactive anti-S antibodies that effectively neutralized different SARS-CoV-2 variants. Importantly, intramuscular MVA-SARS-2-ST immunization of hamsters and mice resulted in potent immune responses upon challenge infection and protected from disease and severe lung pathology. Our results suggest that MVA-SARS-2-ST represents an improved clinical candidate vaccine and that the presence of plasma membrane-bound S1 is highly beneficial to induce protective antibody levels.

A PfSPZ vaccine immunization regimen equally protective against homologous and heterologous controlled human malaria infection.

Immunization with radiation-attenuated Plasmodium falciparum (Pf) sporozoites (SPZ) in PfSPZ Vaccine, has provided better vaccine efficacy (VE) against controlled human malaria infection (CHMI) with the same parasites as in the vaccine (homologous) than with genetically distant parasites (heterologous). We sought to identify an immunization regimen that provided similar VE against CHMI with homologous and heterologous Pf for at least 9 weeks in malaria-naïve adults. Such a regimen was identified in part 1 (optimization), an open label study, and confirmed in part 2 (verification), a randomized, double-blind, placebo-controlled study in which VE was assessed by cross-over repeat CHMI with homologous (PfNF54) and heterologous (Pf7G8) PfSPZ at 3 and 9-10 weeks. VE was calculated using Bayesian generalized linear regression. In part 1, vaccination with 9 × 105 PfSPZ on days 1, 8, and 29 protected 5/5 (100%) subjects against homologous CHMI at 3 weeks after the last immunization. In part 2, the same 3-dose regimen protected 5/6 subjects (83%) against heterologous CHMI at both 3 and 9-10 weeks after the last immunization. Overall VE was 78% (95% predictive interval: 57-92%), and against heterologous and homologous was 79% (95% PI: 54-95%) and 77% (95% PI: 50-95%) respectively. PfSPZ Vaccine was safe and well tolerated. A 4-week, 3-dose regimen of PfSPZ Vaccine provided similar VE for 9-10 weeks against homologous and heterologous CHMI. The trial is registered with ClinicalTrials.gov, NCT02704533.

Immunological profiles associated with distinct parasitemic states in volunteers undergoing malaria challenge in Gabon.

Controlled human malaria infection (CHMI) using cryopreserved non-attenuated Plasmodium falciparum sporozoites (PfSPZ) offers a unique opportunity to investigate naturally acquired immunity (NAI). By analyzing blood samples from 5 malaria-naïve European and 20 African adults with lifelong exposure to malaria, before, 5, and 11 days after direct venous inoculation (DVI) with SanariaR PfSPZ Challenge, we assessed the immunological patterns associated with control of microscopic and submicroscopic parasitemia. All (5/5) European individuals developed parasitemia as defined by thick blood smear (TBS), but 40% (8/20) of the African individuals controlled their parasitemia, and therefore remained thick blood smear-negative (TBS- Africans). In the TBS- Africans, we observed higher baseline frequencies of CD4+ T cells producing interferon-gamma (IFNγ) that significantly decreased 5 days after PfSPZ DVI. The TBS- Africans, which represent individuals with either very strong and rapid blood-stage immunity or with immunity to liver stages, were stratified into subjects with sub-microscopic parasitemia (TBS-PCR+) or those with possibly sterilizing immunity (TBS-PCR-). Higher frequencies of IFNγ+TNF+CD8+ γδ T cells at baseline, which later decreased within five days after PfSPZ DVI, were associated with those who remained TBS-PCR-. These findings suggest that naturally acquired immunity is characterized by different cell types that show varying strengths of malaria parasite control. While the high frequencies of antigen responsive IFNγ+CD4+ T cells in peripheral blood keep the blood-stage parasites to a sub-microscopic level, it is the IFNγ+TNF+CD8+ γδ T cells that are associated with either immunity to the liver-stage, or rapid elimination of blood-stage parasites.

Cellular and antibody response in GMZ2-vaccinated Gabonese volunteers in a controlled human malaria infection trial.

BACKGROUND: Antibody and cellular memory responses following vaccination are important measures of immunogenicity. These immune markers were quantified in the framework of a vaccine trial investigating the malaria vaccine candidate GMZ2. METHODS: Fifty Gabonese adults were vaccinated with two formulations (aluminum Alhydrogel and CAF01) of GMZ2 or a control vaccine (Verorab). Vaccine efficacy was assessed using controlled human malaria infection (CHMI) by direct venous inoculation of 3200 live Plasmodium falciparum sporozoites (PfSPZ Challenge). GMZ2-stimulated T and specific B-cell responses were estimated by flow cytometry before and after vaccination. Additionally, the antibody response against 212 P. falciparum antigens was estimated before CHMI by protein microarray. RESULTS: Frequencies of pro- and anti-inflammatory CD4+ T cells stimulated with the vaccine antigen GMZ2 as well as B cell profiles did not change after vaccination. IL-10-producing CD4+ T cells and CD20+ IgG+ B cells were increased post-vaccination regardless of the intervention, thus could not be specifically attributed to any malaria vaccine regimen. In contrast, GMZ2-specific antibody response increased after the vaccination, but was not correlated to protection. Antibody responses to several P. falciparum blood and liver stage antigens (MSP1, MSP4, MSP8, PfEMP1, STARP) as well as the breadth of the malaria-specific antibody response were significantly higher in protected study participants. CONCLUSIONS: In lifelong malaria exposed adults, the main marker of protection against CHMI is a broad antibody pattern recognizing multiple stages of the plasmodial life cycle. Despite vaccination with GMZ2 using a novel formulation, expansion of the GMZ2-stimulated T cells or the GMZ2-specific B cell response was limited, and the vaccine response could not be identified as a marker of protection against malaria. Trial registration PACTR; PACTR201503001038304; Registered 17 February 2015; https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=1038.

Host genetic loci LZTFL1 and CCL2 associated with SARS-CoV-2 infection and severity of COVID-19.

OBJECTIVES: Host genetic factors contribute to the variable severity of COVID-19. We examined genetic variants from genome-wide association studies and candidate gene association studies in a cohort of patients with COVID-19 and investigated the role of early SARS-CoV-2 strains in COVID-19 severity. METHODS: This case-control study included 123 COVID-19 cases (hospitalized or ambulatory) and healthy controls from the state of Baden-Wuerttemberg, Germany. We genotyped 30 single nucleotide polymorphisms, using a custom-designed panel. Cases were also compared with the 1000 genomes project. Polygenic risk scores were constructed. SARS-CoV-2 genomes from 26 patients with COVID-19 were sequenced and compared between ambulatory and hospitalized cases, and phylogeny was reconstructed. RESULTS: Eight variants reached nominal significance and two were significantly associated with at least one of the phenotypes "susceptibility to infection", "hospitalization", or "severity": rs73064425 in LZTFL1 (hospitalization and severity, P <0.001) and rs1024611 near CCL2 (susceptibility, including 1000 genomes project, P = 0.001). The polygenic risk score could predict hospitalization. Most (23/26, 89%) of the SARS-CoV-2 genomes were classified as B.1 lineage. No associations of SARS-CoV-2 mutations or lineages with severity were observed. CONCLUSION: These host genetic markers provide insights into pathogenesis and enable risk classification. Variants which reached nominal significance should be included in larger studies.

Efficacy, T cell activation and antibody responses in accelerated Plasmodium falciparum sporozoite chemoprophylaxis vaccine regimens.

Repeated direct venous inoculation of Plasmodium falciparum sporozoites (PfSPZ) together with antimalarial chemoprophylaxis (PfSPZ-CVac) is the most potent way to induce sterile immunity against P. falciparum infection in malaria-naive volunteers. However, established schedules are complex and long. Here, we tested two accelerated three-dose schedules (28- and 10-day regimen) assessing efficacy by controlled human malaria infection (CHMI) against placebo, comparing vaccine-specific T cell and antibody responses by antigen-reactive T cell enrichment (ARTE) and protein microarray, respectively. Both regimens were similarly efficacious (67 and 63% vaccine efficacy) but different in the induction of vaccine-specific T cells and antibodies. The 10-day regimen resulted in higher numbers of antigen-specific CD4+ effector memory pro-inflammatory T cells and a broader antibody response compared with the 28-day regimen. Usually in nature, P. falciparum liver stage lasts about 6.5 days. The short vaccination-interval of the 10-day regimen prolongs the time of continuous exposure to liver-stage parasites, which may explain the stronger response. Besides dose and number of vaccinations, duration of liver-stage exposure is a factor to optimize PfSPZ-CVac immunogenicity.

SARS-CoV-2 Antibodies Are Persisting in Saliva for More Than 15 Months After Infection and Become Strongly Boosted After Vaccination.

SARS-CoV-2 antibodies in saliva serve as first line of defense against the virus. They are present in the mucosa, more precisely in saliva, after a recovered infection and also following vaccination. We report here the antibody persistence in plasma and in saliva up to 15 months after mild COVID-19. The IgG antibody response was measured every two months in 72 participants using an established and validated in-house ELISA assay. In addition, the virus inhibitory activity of plasma antibodies was assessed in a surrogate virus neutralization test before and after vaccination. SARS-CoV-2-specific antibody concentrations remained stable in plasma and saliva and the response was strongly boosted after one dose COVID-19 vaccination.

Non-Invasive Antibody Assessment in Saliva to Determine SARS-CoV-2 Exposure in Young Children.

Saliva is a body fluid with hitherto unused potential for the assessment of SARS-CoV-2 antibodies. Specific antibodies can indicate a past SARS-CoV-2 infection and allow to estimate the proportion of individuals with a potential protective immunity. First, we carefully characterized plasma samples obtained from adult control groups with and without prior SARS-CoV-2 infection using certified reference ELISAs. Simultaneously collected saliva samples of confirmed convalescent and negative individuals where then used to validate the herein newly developed ELISA for the detection of SARS-CoV-2 IgG antibodies in saliva. The saliva ELISA was applied to assess SARS-CoV-2 exposure in young children (N = 837) in the age between 1 and 10 years in Tübingen, Germany, towards the end of the first pandemic year 2020. Sensitivity and specificity of the new saliva ELISA was 87% and 100%, respectively. With 12% of all Tübingen children sampled via their respective educational institutions, estimates of SARS-CoV-2 antibody prevalence was 1.6%. Interestingly, only 0.4% preschool kids were positive compared to 3.0% of primary school children. Less than 20% of positive children self-reported symptoms within two months prior to saliva sampling that could be associated - but not exclusively - with a SARS-CoV-2 infection. The saliva ELISA is a valid and suitable protocol to enable population-based surveys for SARS-CoV-2 antibodies. Using non-invasive sampling and saliva ELISA testing, we found that prevalence of SARS-CoV-2 antibodies was significantly lower in young children than in primary school children.