npj Vaccines

Suboptimal rotavirus vaccine effectiveness in low- and middle-income countries (LMICs) highlights the need for next-generation vaccines, such as the neonatal RV3-BB vaccine. However, there is uncertainty in the duration of protection and future price of vaccines in development. We aim to identify the conditions under which switching to RV3-BB is optimal in Malawi and Ghana, where the current immunization programs use 2-dose Rotarix and 3-dose Rotavac schedules, respectively. A full incremental cost-effectiveness analysis was performed using a validated transmission model calibrated to country-specific rotavirus data. Over 2025-2034, introducing RV3-BB resulted in the largest rotavirus-related burden reduction compared with the current country-specific programs. At moderate willingness-to-pay (~0.5 time Gross Domestic Product per capita), RV3-BB was preferred over Rotavac if price per dose was <$1.2 in Malawi and <$2.5 in Ghana, and/or if the average duration of protection exceeded 40 weeks in Malawi. The RV3-BB vaccine is likely to be cost-effective in Malawi and Ghana, as well as other LMICs, based on expected pricing and duration of protection.

An efficacious blood-stage malaria vaccine would serve as a highly useful public health tool alongside licensed vaccines targeting the pre-erythrocytic life cycle stage of the Plasmodium falciparum parasite. RH5 is the leading blood-stage malaria vaccine candidate antigen due to its highly-conserved sequence and non-redundant role in merozoite invasion of red blood cells. Following encouraging immunogenicity data in UK and Tanzanian Phase Ia/b vaccine trials, RH5-based vaccines have progressed to Phase IIb evaluation in Burkina Faso in recent years. Here, we report a Phase Ia clinical trial in malaria-naive UK adults to assess the safety and immunogenicity of the malaria vaccine candidate RH5.1 soluble protein with Matrix-M(R) adjuvant using two different booster dosing regimens: 10-10-10 {micro}g versus 50-50-10 {micro}g RH5.1, both delivered in a 0-1-6-month schedule with 50{micro}g Matrix-M(R) adjuvant per dose (ClinicalTrials.gov NCT06141057). A total of n=24 participants were recruited to this study, with n=23 completing all follow-up visits through to 1 year following final vaccination. The RH5.1/Matrix-M(R) formulation was well-tolerated in this population, with injection site pain, myalgia and fatigue being the most commonly reported symptoms up to 7 days post-vaccination. There were no serious adverse events, adverse events of special interest, or suspected unexpected serious adverse reactions reported over the course of the trial. Both vaccination regimens were similarly immunogenic; no differences were observed in peak anti-RH5.1 serum IgG concentrations, in vitro functional anti-parasitic activity, avidity, or durability. Our findings build on other observations from clinical trials of adjuvanted RH5.1 indicating that humoral immunogenicity can be enhanced by delaying the final booster vaccination, but that there is limited impact of fractionation of the final dose. These insights can help to guide the next steps of multi-antigen, multi-stage malaria vaccine development in malaria-endemic settings.

Typhoid fever remains a significant public health challenge in low- and middle-income countries. In 2018, The World Health Organization recommended a single dose typhoid conjugate vaccine (TCV) for routine immunization in endemic settings; however, evidence guiding booster doses remains limited. Homologous TCV booster doses have demonstrated immune boosting. This study assessed the immunogenicity and safety of a heterologous booster using a Vi capsular polysaccharide-CRM197 TCV (Vi-CRM) administered 5-6 years after primary vaccination with a Vi capsular polysaccharide tetanus toxoid TCV (Vi-TT) in children. Children previously enrolled in a Phase 2 trial were recruited. Participants who had received TCV at 9-11 or 15-23 months were given a Vi-CRM booster at 6-7 years of age (Booster-TCV group), and controls received their first TCV dose at the same age (1st-TCV group). Serum anti-Vi IgG concentrations were measured at baseline and 28 days post-vaccination. Solicited and unsolicited adverse events (AEs) and serious adverse events (SAEs) were recorded. Among 147 children enrolled, 87 received a second and 60 received a first TCV dose. Baseline anti-Vi IgG geometric mean titers (GMT) were higher in the Booster-TCV group (21.5 EU/mL; 95% CI: 17.2-26.8) than in the 1st-TCV group (5.5 EU/mL; 95% CI: 4.5-6.7). At day 28, GMTs rose markedly in both groups: 5140.0 EU/mL (95% CI: 4302.0-6141.3) in the Booster-TCV group and 2084.8 EU/mL (95% CI: 1724.4-2520.5) in the 1st-TCV group. Local reactions and systemic AEs were mild. No SAEs were observed. Vi-TT-induced immunity persisted for at least 5-6 years, and a heterologous booster triggered a strong immune response with universal seroconversion. These findings support heterologous prime-boost strategies to maintain protection in school-age children and inform optimization of TCV schedules in endemic regions.

Conventional vaccines have so far failed to elicit the types of antibodies needed for protection against HIV. As an alternative, we evaluated adeno-associated virus (AAV) delivery of rhesus macaque antibodies to the SIV envelope glycoprotein for protection against SIV challenge. AAV vectors encoding a broadly neutralizing antibody (bnAb) and an antibody that only mediates antibody-dependent cellular cytotoxicity (ADCC) were administered individually or together to separate groups of rhesus macaques. Antibody expression was sustained for more than a year with minimal anti-drug antibody responses. All animals that received a control antibody or the ADCC-only antibody became infected after five low-dose, intrarectal challenges with SIVmac239. In contrast, 14 of 16 animals that received the bnAb resisted two rounds of twelve SIVmac239 challenges more than a year apart. Thus, AAV delivery of a single bnAb can afford durable protection against a pathogenic SIV strain that is notoriously difficult to protect against by vaccination.

IntroductionMalaria is a leading health problem with high disease burden and mortality rates worldwide. Currently approved vaccines target the sporozoite form of Plasmodium falciparum that initially infects the liver, but only provide modest protection against malaria in young children. There is an urgent need to develop next-generation malaria vaccines that target multiple parasite developmental stages for greater efficacy. Antibodies to merozoites, which are involved in blood-stage replication, and are associated with clinical illness, have multiple functional activities and can protect against malaria. A promising merozoite vaccine candidate is Merozoite Surface Protein 2 (PfMSP2). Antibodies to PfMSP2 can promote multiple antibody Fc-mediated functional activities to clear merozoites. MethodsWe developed and evaluated monovalent and bivalent (3D7 and FC27 variants) PfMSP2-based mRNA vaccines. We designed and codon-optimised mRNA, which was validated for in vitro expression in mammalian cells, and subsequently formulated as lipid nanoparticles for vaccination of mice in a 3-dose regimen. Vaccination with recombinant PfMSP2 protein with adjuvant was performed for comparison. We evaluated the induction of antibodies and functional activities relevant to protective immunity. ResultsmRNA vaccines induced prominent IgG responses using monovalent (3D7 allele) and bivalent (3D7 and FC27 alleles) vaccines encoding near full-length PfMSP2, and antibodies recognised the surface of whole merozoites. Vaccine responses were equivalent to, or superior than, a recombinant protein-based PfMSP2 vaccine. The bivalent vaccine induced equivalent antibodies to the two PfMSP2 alleles. Vaccination induced cytophilic IgG subclasses with multiple functional activities, including complement fixation, binding of human Fc{gamma}-receptors I and IIa, and opsonic phagocytosis. ConclusionsPfMSP2 is highly immunogenic using the mRNA vaccine platform and induces antibodies with multiple functional activities associated with protective immunity in humans. Combining PfMSP2 with other merozoite and sporozoite antigens is a promising strategy to develop highly efficacious vaccines to achieve malaria control and elimination goals.

Herpes simplex virus 2 (HSV-2) is associated with genital ulcers, neonatal encephalitis, increased risk of HIV infection, and dementia. There is no licensed HSV-2 vaccine. We developed nanoparticles displaying the HSV-2 attachment protein gD and fusion mediation protein complex gH/gL. Immunization of mice and non-human primates elicited high levels of neutralizing antibodies. Vaccination conferred robust protection in mice, preventing disease and nearly eliminating infection and shedding following HSV-2 challenge. While gD induced high neutralizing antibody titers, gH/gL contributed substantially to protection despite lower neutralization titers. Instead, gH/gL immunization generated strong fusion-blocking responses which were an important correlate of protection, showing that standard neutralization assays incompletely capture the importance of fusion-blocking activity. These findings demonstrate that targeting both HSV-2 attachment and fusion elicit complementary mechanisms for protection from infection and that neutralizing antibody alone may be insufficient for protection. Overall, these results present an innovative strategy for an HSV-2 vaccine.

Background: Induction of HIV envelope (Env)-specific broadly neutralizing antibodies (bnAbs) is considered a key objective for HIV-1 vaccine development. One approach is to vaccinate with HIV Env immunogens that initially target the naive B cell receptors of a bnAb type and boost with a series of HIV Env variants. We chose a priming immunogen, the CH505 transmitted/founder Env with high affinity for the naive B cell receptor of the prototype CD4 binding site (bs) bnAb lineage, CH103, as a candidate priming immunogen to induce the initial critical step in CD4bs bnAb development. Methods: HVTN 300 is a first-in-human, open-label Phase 1 study evaluating the safety and immunogenicity of a CH505 TF chimeric (ch) Trimer adjuvanted with 3M-052-AF (a TLR7/8 agonist) + Alum. The immunogen is a recombinant, stabilized chimeric Env trimer protein with the N-terminal sequence of CH505 TF gp120 Env transplanted into the BG505 SOSIP sequence. Participants received the adjuvanted protein administered in both deltoid muscles at months 0, 2, 4, 8, and 12. Results: Adults (n=18) aged 18 to 55 were screened at a single site in Boston, USA, and 13 were enrolled. Local and systemic reactogenicity was typically mild to moderate. One participant had severe pain/tenderness, and five participants reported transient severe systemic symptoms at least once. Five participants chose to stop further vaccination due to reactogenicity. No vaccine-related SAEs occurred. Vaccine-specific B-cell response rates reached 100% two weeks post third and fifth vaccinations. Antibody blocking experiments with monoclonal antibodies demonstrated that most participants had antibodies directed to the CD4bs. Four out of 11 participants had serum neutralization signatures for CD4bs bnAb precursors. Conclusions: No safety concerns were identified. The adjuvanted CH505 TF chTrimer elicited serum antibodies capable of CD4bs-mediated neutralization against strains designed to detect early precursors of the CD4bs B-cell lineages. Trial Registration: NCT04915768 Disclosure: Presented in part at HIVR4P 2024, Lima, Peru, October 6-10, 2024

Adenoviruses (Ads) are widely used as vaccine vectors. However, pre-existing immunity to commonly used serotypes, like Ad5, can reduce vaccine immunogenicity, with neutralizing antibody titers >200 previously shown to impact vaccine efficacy. Gorilla adenovirus (GRAd) vectors have been developed to evade pre-existing anti-vector responses, but their seroprevalence in southern Africa is poorly defined. Here, we assessed seroprevalence to GRAd32, Ad26 and Ad5 before (baseline) and after COVID-19 vaccination, in cohorts from South Africa and Zimbabwe. Sera from South African participants enrolled in the Sisonke sub-study (n=100, prior to Ad26.COV2.S vaccination) and the follow-up "Booster after Sisonke" (BaSiS) study (n=226) were tested for neutralizing antibodies to Ad5, Ad26, and GRAd32. These samples included paired pre/post boost samples for 27 donors. We also tested sera from the Zimbabwean Mutala cohort (n=131, of which 44 were unvaccinated, and 87 vaccinated with inactivated vaccines). Participants living with HIV (PLWH) comprised 30-50% of each cohort. In the pre-vaccination samples from the Sisonke cohort, geometric mean titers (GMT) for anti-GRAd32, Ad26, and Ad5 antibodies were 78, 142, and 459, with neutralization titers >200 observed in 14%, 32%, and 68% of participants, respectively. Similarly, in the unvaccinated participants in the Mutala cohort, GMTs for GRAd32, Ad26, and Ad5 were 117, 245, and 536, with neutralizing titers >200 in 22%, 42%, and 69% of participants. We observed no significant difference in Ad antibody titers between PLWH and those living without HIV. We next assessed the impact of COVID-19 vaccination on titers. Vaccination with inactivated COVID-19 vaccines (Sinopharm/Sinovac) did not significantly affect Ad5, Ad26 or GRAd32 titers in an unpaired analysis. In contrast, [~]9 months after Ad26.COV2.S vaccination, anti-Ad26 titers for longitudinally sampled participants (n=27) increased 10-fold from a GMT of 141 to 1,426. By comparison, GRAd32 responses were not significantly altered by Ad26.COV2.S vaccination, while anti-Ad5 responses showed a modest <2-fold increase. Our data support previous findings that, whereas anti-Ad5 neutralizing antibody responses are commonly detected globally, GRAd32 responses are less frequent. Importantly, GRAd32 neutralizing responses remained unchanged after Ad26.COV2.S vaccination. HIV status had no significant effect on antibody titers. These results support the use of the GRAd32 vector in upcoming HIV vaccine trials, including in regions where Ad26-based COVID-19 vaccines were widely deployed.

Blocking transmission of Borrelia burgdorferi (Bb), the causative agent of Lyme disease (LD), from reservoir hosts to humans via Ixodes scapularis ticks represents an alternative strategy to reduce LD incidence. Here, we evaluated Purified Borrelial Lipoproteins (PBL) with a combination of adjuvants, for their ability to limit Bb transmission using C3H/HeN mice and Peromyscus leucopus reservoir models. Immunization with PBL as oral gavage, either alone or nanoparticle-encapsulated, elicited increased antibody responses and reduced pathogen burden in fed larvae and select host tissues. A formulation combining PBL with a recombinant fusion protein adjuvant consisting of Cholera Toxin B subunit, Outer surface protein A, and two-tandem repeats of an M-cell-targeting peptide (rCOM) induced durable protective immunity for up to 10 months in C3H/HeN mice. This oral regimen significantly reduced Bb burden in host tissues, in fed larvae from vaccinated hosts, molted nymphs, and nymph-challenged naive mice. Immunization with PBL+rCOM elevated peripheral levels of Bb-specific IgG isotypes and increased antigen-specific T cell responses producing IFN-{gamma} and IL-4 at days 28 and 65 post-immunization. Significant protective responses were observed in P. leucopus, including strong antibody responses, reduced Bb burden in tissues and reduced Bb transmission to naive larvae, independent of sex but influenced by challenge dose. Sodium chloride content in oral formulation modulated vaccine induced protective responses. Notably, Bb burden in infected nymphs was reduced during the bloodmeal on vaccinated hosts with decreased pathogen transmission to both vertebrate hosts. These findings support PBL+rCOM as a promising oral, reservoir-targeted, transmission-blocking biologic for controlling Lyme disease. Lay AbstractNumerous vertebrate hosts serve as reservoirs of pathogens that are transmitted to humans via the bite of blood feeding vectors such as ticks. Lyme disease, caused by Borrelia burgdorferi (Bb), is the most common tick-borne disease in the US. Bb is transmitted to humans following the bite of infected Ixodes scapularis ticks. In nature, ticks acquire Bb and other pathogens from a variety of reservoir hosts, notably Peromyscus leucopus. Therefore, strategies that limit pathogen burden in reservoir hosts or block their transmission via ticks are options to prevent human infectious diseases, circumventing need for human vaccines and therapeutics. An oral, reservoir host-targeted, pathogen-derived, biologic prepared by extracting immunogenic lipoproteins (Purified Borrelial Lipoproteins) from Bb and combining them with a mucosal adjuvant derived by fusing Cholera-Toxin B subunit, Outer surface protein A of Bb and 2 repeats of an M-cell targeting peptide was tested in C3H/HeN mice and Peromyscus leucopus hosts. Single or two dose regimens via the oral route resulted in significant increases in peripheral Bb specific antibody responses, select T cell responses, blocking the transmission of Bb to naive Is larvae, reducing pathogen burden in vaccinated hosts, and interfering with the infectious cycle of the agent of Lyme disease.

Neonatal sepsis caused by Klebsiella pneumoniae is a major cause of under-five mortality in sub-Saharan Africa, and the rapid increase of infections caused by bacteria resistant to most or all available antimicrobials severely limits treatment options. An effective, maternally-administered vaccine could make a substantial reduction in neonatal sepsis and associated negative outcomes, as well as reduce the overall need for antimicrobials, a key driver of antimicrobial resistance. This study explored the potential for a maternally administered protein-based vaccine to provide neonatal protection via antibodies transferred transplacentally and through breastfeeding. A case-control study of mother and baby dyads was designed with 20 neonates developing K. pneumoniae sepsis and 80 uninfected control neonates to analyse breastmilk IgA, cord blood IgG and maternal serum IgA and IgG antibodies on a protein microarray with 161 selected K. pneumoniae proteins representing 152 unique genes. This analysis identified a set of proteins eliciting antibody responses, some associated with lack of K. pneumoniae sepsis, that indicate the presence of potentially protective antibodies. This is an essential first step in exploring surface protein accessibility, despite the large capsule. We highlight fimbrial structures, conjugative pili, and small lipoproteins associated with large outer membrane complexes as potential protein vaccine targets.

Background: The isolation of many HIV broadly neutralizing antibodies (bnAbs) from people living with HIV (PLWH) and rigorous characterization of their ontogeny has promoted the goal of reverse engineering their natural development as a strategy for achieving an effective preventive HIV vaccine. We previously described the developmental process of CH103, a CD4-binding site (CD4bs)-specific monoclonal antibody, and the associated evolution of HIV Envelopes (Envs) within the person (CH505) from whom it was isolated. A series of monomeric gp120 protein subunit immunogens representing the transmitted founder (TF) and Envs that evolved during infection and optimally reacted with lineage members at each step of the CH103 clone maturation path were evaluated in this placebo controlled randomized vaccine trial to test for the first time in humans the concept of whether sequential immunization with gp120 monomeric proteins can recapitulate the development of CD4bs B-cell clonal lineages, including CH103. Methods: HIV Vaccine Trials Network 115 (HVTN 115) was a randomized placebo-controlled vaccine trial at US clinical research sites. We tested the safety and immunogenicity of CH505TF gp120 + GLA-SE (Part A), and then the ability of sequential CH505 gp120 proteins (corresponding to CH505s weeks 53 and 78 Envs) + GLA-SE immunizations to induce CD4bs-specific neutralizing antibodies (Part B). We assessed binding and neutralizing antibody responses, antibody dependent cellular cytotoxicity, antibody dependent cellular phagocytosis, T-cell responses and B-cell phenotyping. Results: We enrolled 42 participants between October 2017 and May 2018 for Part A, and 65 participants from December 2020 to October 2022 for Part B. Immunization with the CH505 gp120 proteins adjuvanted with GLA-SE was well tolerated and induced CD4bs-specific B cells and Env-specific plasma antibodies. The plasma neutralizing antibody response was limited to primarily tier 1 autologous and heterologous HIV-1 strains. Blood-derived B-cell repertoire analyses identified CD4bs antibodies that preferentially bound to open-occluded trimeric Envs that exist in an intermediate state between prefusion-closed to CD4-bound open confirmations, consistent with tier 1 HIV neutralizing activity. Conclusions: Together, these results suggest that the low-affinity CH505TF gp120 monomer elicited CD4bs antibodies in the sera and B-cell repertoires of humans. However, our findings also indicate that gp120 monomers are insufficient to induce detectable bnAb precursors to epitopes on native Env trimers. Nonetheless, our data provide a benchmark for comparison with ongoing clinical trials testing high-affinity CH505 Env trimers for induction of CD4bs bnAb precursors.

The emergence of new SARS-CoV-2 variants and breakthrough infections underscores the need for next-generation vaccines capable of protecting from natural infection and/or preventing virus transmission to others. Intranasal vaccination offers a promising approach by eliciting local immune responses in the nasal mucosa, the primary site of infection and reservoir for transmissible virus. We evaluated two live-attenuated, respiratory syncytial virus vectored vaccines in which the RSV F and G surface glycoproteins were replaced with a chimeric SARS-CoV-2 Spike protein from either the ancestral USA/WA-1/2020 strain (MV-014-212) or the Delta variant (MV-014-212-delta). A single intranasal dose of either vaccine elicited systemic and mucosal immunity in K18-hACE2 mice, including serum neutralizing antibodies, Spike-specific memory B cells and plasmablasts, and Spike-specific CD8 lung-resident memory T cells. Although MV-014-212-delta vaccination provided the best protection against Delta variant virus challenge, both vaccines decreased viral loads in nasal discharge, lung and brain, and reduced weight loss and mortality. In naturally acquired infection studies, vaccinated hamsters exposed to infected cagemates exhibited minimal weight loss, limited viral replication within the nasal mucosa, and attenuated lung pathology. Therefore, intranasal RSV-vectored vaccines can elicit broad protective respiratory immunity, suggesting that this platform could be leveraged for other respiratory pathogens.

Immunocastration, a non-surgical strategy based on active immunization against gonadotropin-releasing hormone (GnRH), effectively suppresses steroidogenesis and spermatogenesis. However, peptide vaccines targeting poorly immunogenic antigens such as GnRH often fail to elicit robust adaptive immune responses, requiring adjuvants or carrier proteins. Previously, we introduced Coated Bacterial Vaccines (CBVs), a platform that uses chemically inactivated Gram-positive bacteria to display recombinant antigens fused to the SlpA carboxy-terminal domain (dSLPA) on their surface. This system leverages natural pathogen-associated molecular patterns (PAMPs) to enhance immunogenicity without additional adjuvants. In this work, we extended the application of the CBVs platform to enhance the immune response against a poorly immunogenic GnRH-based peptide vaccine. GnRH-CBVs were formulated using inactivated Bacillus subtilis var. natto coated with a recombinant GnRH tandem-repeat-dSLPA fusion protein and administered to male BALB/c mice. A chitosan-adjuvanted GnRH-dSLPA formulation served as a positive control. GnRH-CBVs induced a strong Th2-biased humoral response, characterized by predominant IgG1 levels comparable to those achieved with chitosan. The resulting antibodies effectively neutralized endogenous GnRH, reducing steroidogenesis and spermatogenesis and inducing marked testicular histological alterations. These findings support CBVs as a promising strategy to enhance peptide vaccine immunogenicity for veterinary immunocastration.

West Nile virus (WNV) is the causative agent of fatal West Nile encephalitis. To date, no human vaccine against WNV has been approved. Adjuvants are important for developing effective and affordable vaccines that enhance the immunogenicity and decrease the required antigen doses. In this study, we assessed the efficacy of AddaS03, a synthetic adjuvant analogous to AS03, in a WNV subunit vaccine composed of soluble recombinant envelope protein (sEnv). Using a passive immunization mouse model, we defined the neutralizing antibody titer threshold required for protection against lethal WNV infections and applied this threshold as a surrogate marker to evaluate adjuvant efficacy. AddaS03-adjuvanted formulations elicited markedly higher neutralizing antibody titers compared to Alhydrogel adjuvant 2% (Alhydrogel), even at suboptimal antigen doses, and consistently exceeded the defined protective threshold titer. Moreover, in a sequential challenge mouse model, AddaS03-adjuvanted vaccines completely protected mice from symptomatic WNV infections, whereas Alhydrogel-adjuvanted vaccines failed to confer full protection. Collectively, these findings demonstrate that AddaS03 is a promising adjuvant for WNV subunit vaccine development and highlights the utility of a passive immunization model for defining protective antibody thresholds as a surrogate marker for vaccine evaluation.

IntroductionNext-generation malaria vaccines are urgently needed to provide greater efficacy and longevity. Antibodies targeting blood-stage merozoites can confer protection against clinical malaria through multiple Fc-mediated functions. In particular, merozoite surface protein 2 (PfMSP2), is a known target of protective antibodies that can clear merozoites via multiple antibody Fc-mediated functions, making is a highly promising vaccine candidate. MethodsWe developed PfMSP2 as a self-amplifying RNA (saRNA) vaccine, which was successfully validated for in vitro expression in mammalian cells. Subsequently, the PfMSP2-saRNA was formulated as lipid nanoparticles (LNP) and evaluated for immunogenicity in mice in a 3-dose regimen comparing 1 g and 10 g doses. We evaluated the induction of antibodies with functional activities relevant to protective immunity. ResultsOur PfMSP2-saRNA vaccine induced antigen-specific IgG responses that recognised the surface of whole merozoites. Both 1 g and 10 g dosing induced comparable antibodies to PfMSP2, and responses were predominantly murine cytophilic IgG subclasses. These vaccine-induced antibodies demonstrated potent Fc-mediated functions, including complement fixation and binding of human Fc{gamma}-receptor I (Fc{gamma}RI), after only two doses, which remained consistent after the third dose. ConclusionsPfMSP2 is highly immunogenic using the saRNA vaccine platform in a dose-sparing regimen, and induces antibodies with multiple Fc-mediated functions associated with protective immunity in humans. This saRNA platform is a promising strategy to develop highly efficacious vaccines requiring lower and fewer doses.

Placental malaria, due to the sequestration of Plasmodium falciparum-infected erythrocytes (IE), causes adverse pregnancy outcomes. The sequestration is mediated by VAR2CSA, a protein that binds to placental chondroitin sulfate A (CSA). VAR2CSA antibodies protect against adverse pregnancy outcomes; however, no licensed VAR2CSA-based vaccine or therapeutic exists to date. We identified and expressed VAR2CSA-specific IgG1 monoclonal antibodies (mAbs) using B cells of malaria-exposed Papua New Guinean women. VAR2CSA mAbs were characterised by their ability to recognise eight heterologous CSA-binding P. falciparum strains, to neutralise CSA binding and/or to induce phagocytosis of IEs by THP-1 monocytes. We identified 16 mAbs, all of which targeted just two of the six domains of VAR2CSA, DBL3X and DBL5{varepsilon}. Cross-reactivity varied between mAbs, but was highest among mAbs to DBL5{varepsilon}, with four of eight of these mAbs binding to all eight strains. Although individual mAbs did not promote phagocytosis, combinations of mAbs recognising distinct epitopes either on the same domain or over different domains did. None of the mAbs inhibited IEs from binding to CSA. Our findings suggest that a combination of mAbs recognising more than one epitope would be needed for a therapeutic aiming to promote parasite clearance by phagocytosis; that DBL5{varepsilon} could be considered for a VAR2CSA vaccine that aims to elicit cross-reactive antibodies that promote phagocytosis; and that identification of binding-inhibitory mAbs requires thoughtful B-cell bait design.

Human adenovirus serotype 4 (Ad4) is used as a replication-competent oral vaccine that safely and effectively prevents Ad4 respiratory illness in US military personnel. Recombinant Ad4 vaccine candidates elicit mucosal and systemic immune responses against respiratory viruses in hamsters, nonhuman primates, and humans. Although evaluation of Ad4 vaccine candidates in mice would be extremely useful given the large number of immunologic tools available, this has been limited by concerns about a lack of viral replication in these animals. Here we generated recombinant Ad4 vectors that express either luciferase (Ad4-Luc) or herpes simplex virus type 2 (HSV-2) glycoprotein D (Ad4-gD2) to identify transgene expression kinetics, the presence of Ad4 vector replication, and HSV-2 immune responses and protection against HSV-2 infection. Local luciferase activity was observed from 7 hours to 20 days after intranasal inoculation of BALB/c and humanized mice. Subsequent inoculations with Ad4-Luc showed reduced luciferase expression in BALB/c mice, but robust expression in humanized mice, suggesting an immune response to the vector in wild-type mice. Ad4 DNA, but not luciferase activity, was reduced in the lungs of BALB/c mice treated with cidofovir before inoculation with Ad4, implying that Ad4 replicated, albeit at a low level, in the lungs. Intranasal vaccination of mice with Ad4-gD2 resulted in HSV-2 neutralizing antibody in the serum, and after HSV-2 intravaginal challenge reduced disease scores, increased survival, and reduced shedding. Overall, the BALB/c mouse model is semi-permissive to Ad4 mucosal infection, but transgene expression is sufficient for the study of Ad4-based vaccine candidates. ImportanceMucosal surfaces serve as the primary site of infection and shedding for many viral pathogens. Immune responses at mucosal sites provide protection, but few mucosal vaccines are licensed. The oral replication-competent adenovirus serotype 4 (Ad4) vaccine is used to prevent respiratory illness in military recruits, has an extraordinary record of safety and efficacy and has been tested as a recombinant platform for other viruses. Further development of this vaccine platform has been partially hindered by the perceived inability to evaluate vaccine candidates in mice. Here we characterize recombinant Ad4 transgene expression kinetics and viral replication after inoculation at various sites and show protection against herpes simplex virus type 2 (HSV-2) genital disease in mice after intranasal vaccination. We show that Ad4 can induce protective efficacy, even in a semi-permissive mouse model, suggesting this is a promising vector for HSV-2 and potentially other viral pathogens.

Activation of innate immunity enhances adaptive immune responses and underlies the mechanism of action of vaccine adjuvants. First-generation mRNA vaccines lack a dedicated adjuvant, relying instead on the self-adjuvanting properties of lipid nanoparticles (LNPs), and are thus expected to benefit from additional engagement of innate immune pathways not activated by LNPs. Among innate immune modulators, TLR5 agonists are particularly promising adjuvants due to their ability to induce a balanced Th1/Th2 immune response and their relatively favorable safety profile. Here we tested whether supplementing mRNA vaccines with mRNA encoding a TLR5 agonist could enhance immunization efficacy by induction of TLR5 signaling coordinated with vaccine antigen expression. We designed FL711, an mRNA encoding a derivative of Salmonella flagellin optimized for mammalian expression, functionally active in TLR5 signaling, deimmunized for pre-existing human T and B cell epitopes, and engineered for secretion to stimulate the TLR5 pathway in the local tissue microenvironment. We characterized FL711 in vitro and in vivo for functional and pharmacological parameters and assessed its adjuvant effect as a component of experimental anti-influenza and anti-SARS-CoV-2 mRNA vaccines. Supplementation with small amounts of FL711 mRNA (up to 30-fold less than antigen-encoding mRNA) significantly enhanced vaccine immunogenicity and protective efficacy, stimulating local NF-{kappa}B induction, boosting antibody production and T cell activation, and prolonging the durability of the response -- while enabling a marked reduction in mRNA dose per vaccine. These findings support the potential of FL711 as a broadly applicable mRNA-encoded adjuvant to improve the potency, durability, and dose efficiency of next-generation mRNA vaccines.

Background Despite the significant impact of longstanding paediatric pneumococcal conjugate vaccine (PCV) use in the United Kingdom (UK), pneumococcal disease burden remains substantial and is primarily driven by nonPCV13 serotypes. Higher valent vaccines such as the 20 valent PCV (PCV20) may provide additional public health and economic benefits, yet their value in the contemporary UK setting has not been fully assessed using recent data. Methods We updated an age structured dynamic transmission model using post COVID 19 UK epidemiology (2001 to 2023) to compare pediatric PCV20 with PCV13 and PCV15. Over a 10 year horizon, we assessed cost effectiveness and number needed to vaccinate (NNV), capturing invasive and non invasive disease cases, deaths, costs, quality adjusted life years, and incremental cost effectiveness ratios. PCV20 was evaluated under 1+1 and 2+1 schedules; PCV13 and PCV15 were assessed under 1+1. Scenario analyses examined key uncertainties. Results PCV20 was estimated to avert more cases and deaths than PCV13 or PCV15, driven by broader serotype coverage and indirect effects. Both PCV20 schedules were dominant or cost saving versus lower valent comparators, with lower NNVs. PCV20s higher vaccination costs were offset by reductions in downstream healthcare expenditures. Conclusion Paediatric PCV20 implementation in the UK could deliver substantial health gains while improving economic efficiency, supporting timely adoption.

In a confirmatory study, we evaluated the immunogenicity and protective efficacy of a heterologous prime-boost vaccination strategy against respiratory syncytial virus (RSV) in non-human primates. Building on prior evidence of protective mucosal immunity induced by intramuscular DNA priming followed by an oropharyngeal adenoviral boost, we conducted a randomized, blinded, dual-centre study across two European primate research facilities. Rhesus macaques received a codon-optimized RSV-F DNA vaccine via electroporation, followed by two mucosal administrations of a recombinant adenovirus serotype 5 vector encoding the same antigen. Control groups included animals vaccinated with irrelevant influenza antigens and a comparator group mimicking natural immunity induced by primary RSV infection. Systemic and mucosal immune responses, including RSV-F-specific antibodies and tissue-resident memory T cells, were monitored longitudinally. Here, we detected robust immune responses, but with some variability between the two centres. However, following experimental RSV challenge performed 22 weeks after the final immunization, RSV-vaccinated animals demonstrated markedly reduced viral replication in both upper and lower respiratory tracts. However, unexpected RSV-specific immunity in the control group at one single study site prevented confirmation of the predefined primary endpoint. Overall, these results support the potential of mucosal adenoviral boosting following DNA priming to induce protective immunity against RSV, while highlighting challenges associated with multi-centre preclinical vaccine studies.