Repeated Plasmodium falciparum infection in humans drives the clonal expansion of an adaptive γδ T cell repertoire

[Figure: see text].

Malian adults maintain serologic responses to virulent PfEMP1s amid seasonal patterns of fluctuation

Plasmodium falciparum erythrocyte membrane protein-1s (PfEMP1s), diverse malaria proteins expressed on the infected erythrocyte surface, play an important role in pathogenesis, mediating adhesion to host vascular endothelium. Antibodies to particular non-CD36-binding PfEMP1s are associated with protection against severe disease. We hypothesized that given lifelong P. falciparum exposure, Malian adults would have broad PfEMP1 serorecognition and high seroreactivity levels during follow-up, particularly to non-CD36-binding PfEMP1s such as those that attach to endothelial protein C receptor (EPCR) and intercellular adhesion molecule-1 (ICAM-1). Using a protein microarray, we determined serologic responses to 166 reference PfEMP1 fragments during a dry and subsequent malaria transmission season in Malian adults. Malian adult sera had PfEMP1 serologic responses throughout the year, with decreased reactivity to a small subset of PfEMP1 fragments during the dry season and increases in reactivity to a different subset of PfEMP1 fragments during the subsequent peak malaria transmission season, especially for intracellular PfEMP1 domains. For some individuals, PfEMP1 serologic responses increased after the dry season, suggesting antigenic switching during asymptomatic infection. Adults were more likely to experience variable serorecognition of CD36-binding PfEMP1s than non-CD36-binding PfEMP1s that bind EPCR or ICAM-1, which remained serorecognized throughout the year. Sustained seroreactivity to non-CD36-binding PfEMP1s throughout adulthood amid seasonal fluctuation patterns may reflect underlying protective severe malaria immunity and merits further investigation.

Atypical B cells are part of an alternative lineage of B cells that participates in responses to vaccination and infection in humans

The diversity of circulating human B cells is unknown. We use single-cell RNA sequencing (RNA-seq) to examine the diversity of both antigen-specific and total B cells in healthy subjects and malaria-exposed individuals. This reveals two B cell lineages: a classical lineage of activated and resting memory B cells and an alternative lineage, which includes previously described atypical B cells. Although atypical B cells have previously been associated with disease states, the alternative lineage is common in healthy controls, as well as malaria-exposed individuals. We further track Plasmodium-specific B cells after malaria vaccination in naive volunteers. We find that alternative lineage cells are primed after the initial immunization and respond to booster doses. However, alternative lineage cells develop an atypical phenotype with repeated boosts. The data highlight that atypical cells are part of a wider alternative lineage of B cells that are a normal component of healthy immune responses.

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Single-cell RNA-seq reveals two distinct B cell lineages

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An alternative lineage contains CXCR3⁺ and atypical B cells

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Alternative B cells are primed after primary vaccination and respond to boosters

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Alternative B cells adopt a more atypical phenotype following repeated antigen exposure

Low dose recombinant full-length circumsporozoite protein-based Plasmodium falciparum vaccine is well-tolerated and highly immunogenic in phase 1 first-in-human clinical testing

Plasmodium falciparum circumsporozoite protein (CSP) is a major sporozoite surface protein and a key target of pre-erythrocytic malaria subunit vaccines. A full-length recombinant CSP (rCSP) based strategy could be advantageous, as this antigen includes a region critical to sporozoite cell attachment and hepatocyte invasion. The adjuvant Glucopyranosyl Lipid A-liposome Quillaja saponaria 21 (GLA-LSQ) functions as a TLR4 agonist, promotes antigen-specific T_H1 responses and stimulates cytotoxic T cell production. To date, one study has reported the clinical acceptability of GLA-LSQ. We present interim results of a phase 1 first-in-human dose-escalation clinical trial of full-length rCSP vaccine given with or without GLA-LSQ adjuvant. Participants experienced only mild to moderate related solicited adverse events. The lowest adjuvanted vaccine dose achieved >90-fold rise in geometric mean anti-CSP IgG antibody titer. These favorable safety and immunogenicity results confirm the immunostimulatory capacity of this relatively new adjuvant and support next steps in clinical product development. Trial registration: ClinicalTrials.gov Identifier NCT03589794 (registered 18 July 2018).

Epitope-Specific Antibody Responses to a Plasmodium falciparum Subunit Vaccine Target in a Malaria-Endemic Population

Circumsporozoite protein (CSP) coats the Plasmodium falciparum sporozoite surface and is a major malaria subunit vaccine target. We measured epitope-specific reactivity to field-derived CSP haplotypes in serum samples from Malian adults and children on a custom peptide microarray. Compared to children, adults showed greater antibody responses and responses to more variants in regions proximal to and within the central repeat region. Children acquired short-lived immunity to an epitope proximal to the central repeat region but not to the central repeat region itself. This approach has the potential to differentiate immunodominant from protective epitope-specific responses when combined with longitudinal infection data.

Multidose Priming and Delayed Boosting Improve Plasmodium falciparum Sporozoite Vaccine Efficacy Against Heterologous P. falciparum Controlled Human Malaria Infection

Background

A live-attenuated Plasmodium falciparum sporozoite (SPZ) vaccine (PfSPZ Vaccine) has shown up to 100% protection against controlled human malaria infection (CHMI) using homologous parasites (same P. falciparum strain as in the vaccine). Using a more stringent CHMI, with heterologous parasites (different P. falciparum strain), we assessed the impact of higher PfSPZ doses, a novel multi-dose prime regimen, and a delayed vaccine boost upon vaccine efficacy (VE).

Methods

We immunized 4 groups that each contained 15 healthy, malaria-naive adults. Group 1 received 5 doses of 4.5 x 105 PfSPZ (Days 1, 3, 5, and 7; Week 16). Groups 2, 3, and 4 received 3 doses (Weeks 0, 8, and 16), with Group 2 receiving 9.0 × 105/doses; Group 3 receiving 18.0 × 105/doses; and Group 4 receiving 27.0 × 105 for dose 1 and 9.0 × 105 for doses 2 and 3. VE was assessed by heterologous CHMI after 12 or 24 weeks. Volunteers not protected at 12 weeks were boosted prior to repeat CHMI at 24 weeks.

Results

At 12-week CHMI, 6/15 (40%) participants in Group 1 (P = .04) and 3/15 (20%) participants in Group 2 remained aparasitemic, as compared to 0/8 controls. At 24-week CHMI, 3/13 (23%) participants in Group 3 and 3/14 (21%) participants in Group 4 remained aparasitemic, versus 0/8 controls (Groups 2–4, VE not significant). Postboost, 9/14 (64%) participants versus 0/8 controls remained aparasitemic (3/6 in Group 1, P = .025; 6/8 in Group 2, P = .002).

Conclusions

Administering 4 stacked priming injections (multi-dose priming) resulted in 40% VE against heterologous CHMI, while dose escalation of PfSPZ using single-dose priming was not significantly protective. Boosting unprotected subjects improved VE at 24 weeks, to 64%.

Clinical Trials Registration

NCT02601716.

Microarray analyses reveal strain-specific antibody responses to Plasmodium falciparum apical membrane antigen 1 variants following natural infection and vaccination

Vaccines based on Plasmodium falciparum apical membrane antigen 1 (AMA1) have failed due to extensive polymorphism in AMA1. To assess the strain-specificity of antibody responses to malaria infection and AMA1 vaccination, we designed protein and peptide microarrays representing hundreds of unique AMA1 variants. Following clinical malaria episodes, children had short-lived, sequence-independent increases in average whole-protein seroreactivity, as well as strain-specific responses to peptides representing diverse epitopes. Vaccination resulted in dramatically increased seroreactivity to all 263 AMA1 whole-protein variants. High-density peptide analysis revealed that vaccinated children had increases in seroreactivity to four distinct epitopes that exceeded responses to natural infection. A single amino acid change was critical to seroreactivity to peptides in a region of AMA1 associated with strain-specific vaccine efficacy. Antibody measurements using whole antigens may be biased towards conserved, immunodominant epitopes. Peptide microarrays may help to identify immunogenic epitopes, define correlates of vaccine protection, and measure strain-specific vaccine-induced antibodies.

Dose-Dependent Infectivity of Aseptic, Purified, Cryopreserved Plasmodium falciparum 7G8 Sporozoites in Malaria-Naive Adults

Direct venous inoculation of 3.2 × 103 aseptic, purified, cryopreserved, vialed Plasmodium falciparum (Pf) strain NF54 sporozoites, PfSPZ Challenge (NF54), has been used for controlled human malaria infection (CHMI) in the United States, 4 European countries, and 6 African countries. In nonimmune adults, this results in 100% infection rates. We conducted a double-blind, randomized, dose-escalation study to assess the infectivity of the 7G8 clone of Pf (PfSPZ Challenge [7G8]). Results showed dose-dependent infectivity from 43% for 8 × 102 PfSPZ to 100% for 4.8 × 103 PfSPZ. PfSPZ Challenge (7G8) will allow for more complete assessment by CHMI of antimalarial vaccines and drugs.

Safety and immunogenicity of unadjuvanted subvirion monovalent inactivated influenza H3N2 variant (H3N2v) vaccine in children and adolescents

OBJECTIVE

In response to the emergence of influenza viruses with pandemic potential, we evaluated a swine-origin influenza A/H3N2 variant (H3N2v) vaccine in children.

STUDY DESIGN

This multicenter phase II open-label study assessed the safety and immunogenicity of two doses, 21 days apart, of investigational unadjuvanted subvirion monovalent inactivated H3N2v vaccine administered via intramuscular injection. Children 6-35 months of age received 7.5mcg or 15mcg of hemagglutinin (HA)/dose; children 3-17 years of age received 15mcg HA/dose. Safety and reactogenicity were assessed by measuring the occurrence of solicited injection site and systemic reactions in the 7 days after each vaccination; adverse events were assessed for 42 days and serious adverse events for 7 months after the first vaccination. Immunogenicity was evaluated by measuring hemagglutination inhibition (HAI) and neutralizing (Neut) antibodies to H3N2v prior to and 21 days after each vaccination. Cross-reactivity against seasonal H3N2 strains was evaluated.

RESULTS

The H3N2v vaccine was well tolerated. Transient mild to moderate injection site tenderness, pain and erythema was observed, with the most commonly reported systemic reactogenicity being irritability in children 6-35 months, and headache and fatigue in children 9-17 years old. Children 6-35 months old, whether they received 7.5mcg or 15mcg/dose, had low HAI and Neut antibody responses after two doses compared to older children. Children under 9 years of age required two doses of vaccine to demonstrate a response, while 9-17 year olds responded well after one dose. Previous influenza vaccination and older age were associated with higher immune responses to H3N2v vaccine. Children 9-17 years of age also developed cross-reactive antibodies against recent seasonal H3N2 influenza viruses.

CONCLUSION

The H3N2v vaccine was safe and immunogenic in children and adolescents. Age-related increases in immunogenicity against H3N2v and seasonal H3N2 viruses were observed, suggesting prior priming via infection and/or immunization. Clinical trial registry: The trial is registered with clinicaltrial.gov: NCT02100436.

Serologic responses to the PfEMP1 DBL-CIDR head structure may be a better indicator of malaria exposure than those to the DBL-α tag

BACKGROUND

Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1) antigens play a critical role in host immune evasion. Serologic responses to these antigens have been associated with protection from clinical malaria, suggesting that antibodies to PfEMP1 antigens may contribute to natural immunity. The first N-terminal constitutive domain in a PfEMP1 is the Duffy binding-like alpha (DBL-α) domain, which contains a 300 to 400 base pair region unique to each particular protein (the DBL-α "tag"). This DBL-α tag has been used as a marker of PfEMP1 diversity and serologic responses in malaria-exposed populations. In this study, using sera from a malaria-endemic region, responses to DBL-α tags were compared to responses to the corresponding entire DBL-α domain (or "parent" domain) coupled with the succeeding cysteine-rich interdomain region (CIDR).

METHODS

A protein microarray populated with DBL-α tags, the parent DBL-CIDR head structures, and downstream PfEMP1 protein fragments was probed with sera from Malian children (aged 1 to 6 years) and adults from the control arms of apical membrane antigen 1 (AMA1) vaccine clinical trials before and during a malaria transmission season. Serological responses to the DBL-α tag and the DBL-CIDR head structure were measured and compared in children and adults, and throughout the season.

RESULTS

Malian serologic responses to a PfEMP1's DBL-α tag region did not correlate with seasonal malaria exposure, or with responses to the parent DBL-CIDR head structure in either children or adults. Parent DBL-CIDR head structures were better indicators of malaria exposure.

CONCLUSIONS

Larger PfEMP1 domains may be better indicators of malaria exposure than short, variable PfEMP1 fragments such as DBL-α tags. PfEMP1 head structures that include conserved sequences appear particularly well suited for study as serologic predictors of malaria exposure.

The Controlled Human Malaria Infection Experience at the University of Maryland

Controlled human malaria infection (CHMI) is a powerful tool to evaluate the efficacy of malaria vaccines and pharmacologics. Investigators at the University of Maryland, Baltimore, Center for Vaccine Development (UMB-CVD) pioneered the technique in the 1970s and continue to advance the frontiers of CHMI research. We reviewed the records of 338 malaria-naive volunteers who underwent CHMI at UMB-CVD with Plasmodium falciparum from 1971 until 2017. These 338 volunteers underwent 387 CHMI events, including 60 via intradermal injection or direct venous inoculation (DVI) of purified, cryopreserved sporozoites. No volunteer suffered an unplanned hospitalization or required intravenous therapy related to CHMI. Median prepatency period was longer in challenges using NF54 (9 days) than in those using 7G8 (8 days), P = 0.0006 by the log-rank test. With dose optimization of DVI, the prepatent period did not differ between DVI and mosquito bite challenge (log-rank test, P = 0.66). Polymerase chain reaction (PCR) detected P. falciparum infection 3 days earlier than thick smears (P < 0.001), and diagnosis by ultrasensitive PCR was associated with less severe symptoms than smear-based diagnosis (39% versus 0%, P = 0.0003). Historical studies with NF54 showed a shorter median prepatency period of 10.3 days than more recent studies (median 11.0 days, P = 0.02) despite significantly lower salivary gland scores in earlier studies, P = 0.0001. The 47-year experience of CHMI at UMB-CVD has led to advancements in sporozoite delivery, diagnostics, and use of heterologous challenge. Additional studies on new challenge strains and genomic data to reflect regional heterogeneity will help advance the use of CHMI as supporting data for vaccine licensure.

Immunoglobulin G subclass and antibody avidity responses in Malian children immunized with Plasmodium falciparum apical membrane antigen 1 vaccine candidate FMP2.1/AS02A

BACKGROUND

A malaria vaccine based on Plasmodium falciparum apical membrane antigen 1 (AMA1) elicited strain specific efficacy in Malian children that waned in the second season after vaccination despite sustained AMA1 antibody titers. With the goal of identifying a humoral correlate of vaccine-induced protection, pre- and post-vaccination sera from children vaccinated with the AMA1 vaccine and from a control group that received a rabies vaccine were tested for AMA1-specific immunoglobulin G (IgG) subclasses (IgG1, IgG2, IgG3, and IgG4) and for antibody avidity.

METHODS

Samples from a previously completed Phase 2 AMA1 vaccine trial in children residing in Mali, West Africa were used to determine AMA1-specific IgG subclass antibody titers and avidity by ELISA. Cox proportional hazards models were used to assess correlation between IgG subclass antibody titers and risk of time to first or only clinical malaria episode and risk of multiple episodes. Asexual P. falciparum parasite density measured for each child as area under the curve were used to assess correlation between IgG subclass antibody titers and parasite burden.

RESULTS

AMA1 vaccination did not elicit a change in antibody avidity; however, AMA1 vaccinees had a robust IgG subclass response that persisted over the malaria transmission season. AMA1-specific IgG subclass responses were not associated with decreased risk of subsequent clinical malaria. For the AMA1 vaccine group, IgG3 levels at study day 90 correlated with high parasite burden during days 90-240. In the control group, AMA1-specific IgG subclass rise and persistence over the malaria season was modest and correlated with age. In the control group, titers of several IgG subclasses at days 90 and 240 correlated with parasite burden over the first 90 study days, and IgG3 at day 240 correlated with parasite burden during days 90-240.

CONCLUSIONS

Neither IgG subclass nor avidity was associated with the modest, strain-specific efficacy elicited by this blood stage malaria vaccine. Although a correlate of protection was not identified, correlations between subclass titers and age, and correlations between IgG subclass titers and parasite burden, defined by area under the curve parasitaemia levels, were observed, which expand knowledge about IgG subclass responses. IgG3, known to have the shortest half-life of the IgG subclasses, might be the most temporally relevant indicator of ongoing malaria exposure when examining antibody responses to AMA1.

Caregiver and adolescent factors associated with delayed completion of the three-dose human papillomavirus vaccination series

BACKGROUND

Delayed completion of human papillomavirus vaccination (4vHPV) series is common. We sought to identify factors associated with delay.

METHODS

This substudy was part of a large prospective, multi-site study recruiting 9-17 year old girls at the time of their third 4vHPV dose to assess immunogenicity associated with prolonged dosing intervals. At participating sites, parents/legal guardians (caregivers) of all enrolled girls (9-17 years old) and enrolled girls aged 14-17 years were approached for participation. Caregivers completed a questionnaire measuring adolescent and caregiver sociodemographic characteristics, caregiver attitudes and beliefs about on-schedule HPV vaccination and HPV vaccine safety, adolescent's health behaviors, barriers to accessing health care, provider office vaccination practices and a Rapid Estimate of Adult Literacy in Medicine (REALM). Participating girls completed a separate questionnaire measuring their attitudes and beliefs about on-schedule HPV vaccination and HPV vaccine safety. Delay was defined as receiving the third 4vHPV dose >12 months after the first. Bivariate, multinomial logistic regression and multivariate logistic regression analyses were used to identify factors predicting delayed completion.

RESULTS

Questionnaires were completed by 482 caregivers and 386 adolescents; 422 caregivers completed a REALM. Delayed 4vHPV dosing occurred in most adolescents (67%). In multivariate analyses, predictors of delayed completion included caregiver demographic factors (self-reported black vs. white race and high school or less education vs. college or more) and an interaction between caregiver's inability to get an immunization appointment as soon as needed and adolescent's type of insurance.

CONCLUSIONS

Caregiver's race and educational level, accessibility of immunization appointments, and adolescent's insurance type were found to be related to delays in completion of 4vHPV, but caregiver or adolescent attitudes and beliefs about on-schedule HPV vaccination or HPV vaccine safety were not. Therefore, interventions to improve adherence to recommended vaccination schedules could benefit from a focus on improving access to immunizations. ClinicalTrials.gov (NCT01030562).

Antibody responses among adolescent females receiving two or three quadrivalent human papillomavirus vaccine doses at standard and prolonged intervals

BACKGROUND

The originally recommended dosing schedule, 0, 2, 6 months, for the 3-dose quadrivalent human papillomavirus vaccine (4vHPV) was often not followed, resulting in longer than recommended intervals between doses and interest in the effect of prolonged intervals. Recent two-dose recommendations require investigations into the effect of delaying dose 2.

METHODS

This multi-site, prospective study enrolled healthy 9-17 year old girls (n = 1321) on the day of or within 28 days following a third dose of 4vHPV vaccination. Antibody titers to 4vHPV types were measured at one and six months post-dose 3 from all participants and post-dose 2 from participants who were on time for dose 3. To compare antibody responses, participants were categorized into groups: second and third doses on time (control group); on-time dose 2, substantially late dose 3 (group 2); substantially late dose 2, on-time dose 3 (group 3); both doses substantially late (group 4). Analyses compared age-adjusted geometric mean titers (GMTs) at one-month and six-months post-dose 3, effect of delaying the second dose, and two versus three doses as well as post-dose 2 GMTs, stratified by age.

RESULTS

Compared to on-time dosing, one-month post-dose 3 GMTs were non-inferior in groups 2, 3, and 4 and were superior in group 2. Six month post-dose 3 GMTs were superior in groups 2, 3, and 4 for each genotype, except HPV 18 in group 3. Age-adjusted post does 2 titers were significantly lower than post-dose 3 titers when dose 2 was on time but were significantly higher when dose 2 was substantially late. Participants ≥15 years old had no difference in post-dose 2 titers compared to <15 year olds when dose 2 was substantially delayed.

CONCLUSIONS

Prolonged intervals between doses do not appear to diminish and may enhance antibody response to 4vHPV. ClinicalTrials.gov (NCT00524745).

Two-year antibody persistence in children vaccinated at 12-15 months with a measles-mumps-rubella virus vaccine without human serum albumin

One combined measles-mumps-rubella (MMR) vaccine without Human Serum Albumin (HSA) is currently licensed in the USA (M-M-R II; Merck, USA) and another has been developed (Priorix™ [MMR-RIT, GSK, Belgium]). In this follow-up study, children from USA or Puerto Rico, who had received one dose of M-M-R II or MMR-RIT at 12-15 months of age in the primary study (NCT00861744), were followed-up for 2 y post-vaccination. Anti-measles and anti-rubella antibodies were measured using Enzyme-Linked Immunosorbent Assay (ELISA), and anti-mumps antibodies using ELISA and plaque reduction neutralization (PRN) assays. Serious adverse events (SAEs) were recorded during the entire follow-up. The according-to-protocol (ATP) persistence cohort included 752 children (M-M-R II = 186, MMR-RIT = 566), who received primary vaccination at a mean age of 12.3 ( ± 0.67) months. 104 children were revaccinated with MMR-containing vaccines; therefore, serology results for timepoints after revaccination were excluded from the analysis. Seropositivity for measles (Year 1≥ 98.3%; Year 2≥ 99.4%) and rubella (Year 1≥ 98.9%; Year 2 = 100%) remained as high at Year 2 as at Day 42. Similarly, seropositivity for mumps determined by ELISA (Year 1≥ 90.1%; Year 2≥ 94.1%) and PRN assays (Year 1≥ 87.5%; Year 2≥ 91.7%) persisted. Thirty-three SAEs were recorded in 23 children; 2 SAEs (inguinal adenitis and idiopathic thrombocytopenic purpura) and one SAE (febrile convulsion) were considered as potentially related to MMR-RIT and M-M-R II, respectively. This study showed that antibodies against measles, mumps and rubella persisted for up to 2 y post-vaccination with either MMR vaccine in children aged 12-15 months, and that both vaccines were well-tolerated during the follow-up period.

Protection against malaria at 1 year and immune correlates following PfSPZ vaccination

An attenuated Plasmodium falciparum (Pf) sporozoite (SPZ) vaccine, PfSPZ Vaccine, is highly protective against controlled human malaria infection (CHMI) 3 weeks after immunization, but the durability of protection is unknown. We assessed how vaccine dosage, regimen, and route of administration affected durable protection in malaria-naive adults. After four intravenous immunizations with 2.7 × 10(5) PfSPZ, 6/11 (55%) vaccinated subjects remained without parasitemia following CHMI 21 weeks after immunization. Five non-parasitemic subjects from this dosage group underwent repeat CHMI at 59 weeks, and none developed parasitemia. Although Pf-specific serum antibody levels correlated with protection up to 21-25 weeks after immunization, antibody levels waned substantially by 59 weeks. Pf-specific T cell responses also declined in blood by 59 weeks. To determine whether T cell responses in blood reflected responses in liver, we vaccinated nonhuman primates with PfSPZ Vaccine. Pf-specific interferon-γ-producing CD8 T cells were present at ∼100-fold higher frequencies in liver than in blood. Our findings suggest that PfSPZ Vaccine conferred durable protection to malaria through long-lived tissue-resident T cells and that administration of higher doses may further enhance protection.

Safety and Immunogenicity of Sequential Rotavirus Vaccine Schedules

BACKGROUND AND OBJECTIVES

Although both licensed rotavirus vaccines are safe and effective, it is often not possible to complete the schedule by using the same vaccine formulation. The goal of this study was to investigate the noninferiority of the immune responses to the 2 licensed rotavirus vaccines when administered as a mixed schedule compared with administering a single vaccine formulation alone.

METHODS

Randomized, multicenter, open-label study. Healthy infants (6-14 weeks of age) were randomized to receive rotavirus vaccines in 1 of 5 different schedules (2 using a single vaccine for all doses, and 3 using mixed schedules). The group receiving only the monovalent rotavirus vaccine received 2 doses of vaccine and the other 4 groups received 3 doses of vaccine. Serum for immunogenicity testing was obtained 1 month after the last vaccine dose and the proportion of seropositive children (rotavirus immunoglobulin A ≥20 U/mL) were compared in all the vaccine groups.

RESULTS

Between March 2011 and September 2013, 1393 children were enrolled and randomized. Immune responses to all the sequential mixed vaccine schedules were shown to be noninferior when compared with the 2 single vaccine reference groups. The proportion of children seropositive to at least 1 vaccine antigen at 1 month after vaccination ranged from 77% to 96%, and was not significantly different among all the study groups. All schedules were well tolerated.

CONCLUSIONS

Mixed schedules are safe and induced comparable immune responses when compared with the licensed rotavirus vaccines given alone.

Safety and Immunogenicity of Full-Dose Trivalent Inactivated Influenza Vaccine (TIV) Compared With Half-Dose TIV Administered to Children 6 Through 35 Months of Age

BACKGROUND

Children 6 through 35 months of age are recommended to receive half the dose of influenza vaccine compared with older children and adults.

METHODS

This was a 6-site, randomized 2:1, double-blind study comparing full-dose (0.5 mL) trivalent inactivated influenza vaccine (TIV) with half-dose (0.25 mL) TIV in children 6 through 35 months of age. Children previously immunized with influenza vaccine (primed cohort) received 1 dose, and those with no previous influenza immunizations (naive cohort) received 2 doses of TIV. Local and systemic adverse events were recorded. Sera were collected before immunization and 1 month after last dose of TIV. Hemagglutination inhibition antibody testing was performed.

RESULTS

Of the 243 subjects enrolled (32 primed, 211 naive), data for 232 were available for complete analysis. No significant differences in local or systemic reactions were observed. Few significant differences in immunogenicity to the 3 vaccine antigens were noted. The immune response to H1N1 was significantly higher in the full-dose group among primed subjects. In the naive cohort, the geometric mean titer for all 3 antigens after 2 doses of TIV were significantly higher in the 12 through 35 months compared with the 6 through 11 months age group.

CONCLUSIONS

Our study confirms the safety of full-dose TIV given to children 6 through 35 months of age. An increase in antibody responses after full- versus half-dose TIV was not observed, except for H1N1 in the primed group. Larger studies are needed to clarify the potential for improved immunogenicity with higher vaccine doses. Recommending the same dose could simplify the production, storage, and administration of influenza vaccines.

Effect of Varying Doses of a Monovalent H7N9 Influenza Vaccine With and Without AS03 and MF59 Adjuvants on Immune Response: A Randomized Clinical Trial

IMPORTANCE

Human infections with the avian influenza A(H7N9) virus were first reported in China in 2013 and continue to occur. Hemagglutinin H7 administered alone is a poor immunogen necessitating evaluation of adjuvanted H7N9 vaccines.

OBJECTIVE

To evaluate the immunogenicity and safety of an inactivated H7N9 vaccine with and without AS03 adjuvant, as well as mixed vaccine schedules that included sequential administration of AS03- and MF59-containing formulations and of adjuvanted and unadjuvanted formulations.

DESIGN, SETTING, AND PARTICIPANTS

Double-blind, phase 2 trial at 5 US sites enrolled 980 adults aged 19 through 64 years from September 2013 through November 2013; safety follow-up was completed in January 2015.

INTERVENTIONS

The H7N9 vaccine was given on days 0 and 21 at nominal doses of 3.75 µg, 7.5 µg, 15 µg, and 45 µg of hemagglutinin with or without AS03 or MF59 adjuvant mixed on site.

MAIN OUTCOMES AND MEASURES

Proportions achieving a hemagglutination inhibition antibody (HIA) titer of 40 or higher at 21 days after the second vaccination; vaccine-related serious adverse events through 12 months after the first vaccination; and solicited signs and symptoms after vaccination through day 7.

RESULTS

Two doses of vaccine were required to induce detectable antibody titers in most participants. After 2 doses of an H7N9 formulation containing 15 µg of hemagglutinin given without adjuvant, with AS03 adjuvant, or with MF59 adjuvant, the proportion achieving an HIA titer of 40 or higher was 2% (95% CI, 0%-7%) without adjuvant (n = 94), 84% (95% CI, 76%-91%) with AS03 adjuvant (n = 96), and 57% (95% CI, 47%-68%) with MF59 adjuvant (n = 92) (P < .001 for comparison of the AS03 and MF59 schedules). The 2 schedules alternating AS03-and MF59-adjuvanted formulations led to lower geometric mean titers (GMTs) of (41.5 [95% CI, 31.7-54.4]; n = 92) and (58.6 [95% CI, 44.3-77.6]; n = 96) than the group induced by 2 AS03-adjuvanted formulations (n = 96) (103.4 [95% CI, 78.7-135.9]; P < .001) but higher GMTs than 2 doses of MF59-adjuvanted formulation (n = 94) (29.0 [95% CI, 22.4-37.6]; P < .001).

CONCLUSIONS AND RELEVANCE

The AS03 and MF59 adjuvants augmented the immune responses to 2 doses of an inactivated H7N9 influenza vaccine, with AS03-adjuvanted formulations inducing the highest titers. This study of 2 adjuvants used in influenza vaccine formulations with adjuvant mixed on site provides immunogenicity information that may be informative to influenza pandemic preparedness programs.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01942265.

Hemoglobin C Trait Provides Protection From Clinical Falciparum Malaria in Malian Children

Background. Hemoglobin C trait, like hemoglobin S trait, protects against severe malaria in children, but it is unclear whether hemoglobin C trait also protects against uncomplicated malaria. We hypothesized that Malian children with hemoglobin C trait would have a lower risk of clinical malaria than children with hemoglobin AA.

Methods. Three hundred children aged 0–6 years were enrolled in a cohort study of malaria incidence in Bandiagara, Mali, with continuous passive and monthly active follow-up from June 2009 to June 2010.

Results. Compared to hemoglobin AA children (n = 242), hemoglobin AC children (n = 39) had a longer time to first clinical malaria episode (hazard ratio [HR], 0.19; P = .001; 364 median malaria-free days vs 181 days), fewer episodes of clinical malaria, and a lower cumulative parasite burden. Similarly, hemoglobin AS children (n = 14) had a longer time to first clinical malaria episode than hemoglobin AA children (HR, 0.15; P = .015; 364 median malaria-free days vs 181 days), but experienced the most asymptomatic malaria infections of any group.

Conclusions. Both hemoglobin C and S traits exerted a protective effect against clinical malaria episodes, but appeared to do so by mechanisms that differentially affect the response to infecting malaria parasites.

Differential recognition of terminal extracellular Plasmodium falciparum VAR2CSA domains by sera from multigravid, malaria-exposed Malian women

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family mediates parasite sequestration in small capillaries through tissue-specific cytoadherence. The best characterized of these proteins is VAR2CSA, which is expressed on the surface of infected erythrocytes that bind to chondroitin sulfate in the placental matrix. Antibodies to VAR2CSA prevent placental cytoadherence and protect against placental malaria. The size and complexity of the VAR2CSA protein pose challenges for vaccine development, but smaller constitutive domains may be suitable for subunit vaccine development. A protein microarray was printed to include five overlapping fragments of the 3D7 VAR2CSA extracellular region. Malian women with a history of at least one pregnancy had antibody recognition of four of these fragments and had stronger reactivity against the two distal fragments than did nulliparous women, children, and men from Mali, suggesting that the C-terminal extracellular VAR2CSA domains are a potential focus of protective immunity. With carefully chosen sera from longitudinal studies of pregnant women, this approach has the potential to identify seroreactive VAR2CSA domains associated with protective immunity against pregnancy-associated malaria.

Seroreactivity to a large panel of field-derived Plasmodium falciparum apical membrane antigen 1 and merozoite surface protein 1 variants reflects seasonal and lifetime acquired responses to malaria

Parasite antigen diversity poses an obstacle to developing an effective malaria vaccine. A protein microarray containing Plasmodium falciparum apical membrane antigen 1 (AMA1, n = 57) and merozoite surface protein 1 19-kD (MSP119, n = 10) variants prevalent at a malaria vaccine testing site in Bandiagara, Mali, was used to assess changes in seroreactivity caused by seasonal and lifetime exposure to malaria. Malian adults had significantly higher magnitude and breadth of seroreactivity to variants of both antigens than did Malian children. Seroreactivity increased over the course of the malaria season in children and adults, but the difference was more dramatic in children. These results help to validate diversity-covering protein microarrays as a promising tool for measuring the breadth of antibody responses to highly variant proteins, and demonstrate the potential of this new tool to help guide the development of malaria vaccines with strain-transcending efficacy.