Intradermal fractional-dose inactivated polio vaccine (fIPV) adjuvanted with double mutant Enterotoxigenic Escherichia coli heat labile toxin (dmLT) is well-tolerated and augments a systemic immune response to all three poliovirus serotypes in a randomized placebo-controlled trial

Protective antibodies against enterotoxigenic Escherichia coli are generated from heat-labile toxoid vaccination and exhibit subject- and vaccine-specific diversity

Heat-labile toxin (LT) from enterotoxigenic Escherichia coli (ETEC) is an important pathogenic protein. Anti-LT antibodies (Abs) induced by vaccination can neutralize the toxin and potentially prevent diarrheal secretion from ~ 60% of ETEC strains expressing LT. However, only superficial investigation of the anti-toxin response is usually conducted in clinical trials. Here, we utilized human serum samples from two clinical trials performed to assess safety, immunogenicity and protection in a controlled human infection model with a LT + ST + CFA/I + H10407 ETEC strain. These Phase 1 and Phase 2b clinical trials explored a prototype ETEC adhesin (CfaE) and a chimeric adhesin-toxoid protein (dscCfaE-CTA2/LTB5) delivered intradermally or transcutaneously with a mutated form of LT (mLT) as an adjuvant. Serum samples were tested for antigen-specific IgG or IgA Abs by immunoblot, enzyme-linked immunosorbent assay (ELISA), or functional neutralizing Abs using LT holotoxin, LTA or LTB subunits. Abs to both LT subunits were present, but the response to each was altered by vaccine formulation, dose, and delivery routes as well as subject. The anti-LT IgG response correlated best to neutralizing antibodies and protection from H10407 controlled challenge when compared to other measures including serum IgA or anti-fimbriae (CfaE) Abs. In addition, our results helped to explain cohort attack rate differences in naïve unvaccinated participants and we found higher anti-LTA IgG post-challenge significantly related to ETEC severity score. Thus, strategies generating and measuring immunity to the complete AB5 structure of LT and subunits are better determinant of assessing protective immunity against LT + or LT + ST + ETEC diarrheal secretion in humans.

Safety and immunogenicity in humans of enterotoxigenic Escherichia coli double mutant heat-labile toxin administered intradermally

Enterotoxigenic Escherichia coli (ETEC) diarrhea is associated with a high burden of disease globally, for which no licensed vaccine is available. A Phase 1, double-blind, dose-escalation (0.1-2.0 µg) study was conducted to evaluate the safety and immunogenicity of double mutant heat-labile toxin LTR192G/L211A (dmLT) delivered intradermally (ID) to healthy adults. Subjects received up to three immunizations at three-week intervals. The vaccine was safe, although it induced mild local and some gastrointestinal adverse events, as well as frequent hyperpigmentation at the injection site. High levels of serum IgG and IgA, LT neutralizing antibodies, and IgG and IgA antibodies in lymphocyte supernatant were elicited post-vaccination, most prominently at the largest dose (2.0 μg). Rates of responses were the highest in subjects who received the largest dose (2.0 μg) and multiple immunizations. The ETEC dmLT vaccine was safe and highly immunogenic, inducing long-lasting systemic and mucosal responses when administered by the ID route. Trial registration Clinical Trials NCT02531685.

Inactivated Poliovirus Vaccine: Recent Developments and the Tortuous Path to Global Acceptance

Inactivated poliovirus vaccine (IPV), available since 1955, became the first vaccine to be used to protect against poliomyelitis. While the immunogenicity of IPV to prevent paralytic poliomyelitis continues to be irrefutable, its requirement for strong containment (due to large quantities of live virus used in the manufacturing process), perceived lack of ability to induce intestinal mucosal immunity, high cost and increased complexity to administer compared to oral polio vaccine (OPV), have limited its use in the global efforts to eradicate poliomyelitis. In order to harvest the full potential of IPV, a program of work has been carried out by the Global Polio Eradication Initiative (GPEI) over the past two decades that has focused on: (1) increasing the scientific knowledge base of IPV; (2) translating new insights and evidence into programmatic action; (3) expanding the IPV manufacturing infrastructure for global demand; and (4) continuing to pursue an ambitious research program to develop more immunogenic and safer-to-produce vaccines. While the knowledge base of IPV continues to expand, further research and product development are necessary to ensure that the program priorities are met (e.g., non-infectious production through virus-like particles, non-transmissible vaccine inducing humoral and intestinal mucosal immunity and new methods for house-to-house administration through micro-needle patches and jet injectors), the discussions have largely moved from whether to how to use this vaccine most effectively. In this review, we summarize recent developments on expanding the science base of IPV and provide insight into policy development and the expansion of IPV manufacturing and production, and finally we provide an update on the current priorities.

Recent advances in enterotoxin vaccine adjuvants

Enterotoxin adjuvants have been researched for their ability to promote immunity to co-delivered antigens. Outside of cholera vaccines, however, these proteins have yet to be included in any currently licensed vaccines. They include molecules derived from the bacterial toxins of Vibrio cholerae, cholera toxin, or Escherichia coli, heat-labile toxin, such as detoxified mutants or subunits. This class of adjuvants is distinguished by their delivery possibilities, which include parenteral injection, skin applications, or direct mucosal administration by oral, sublingual, or nasal routes. In addition, inclusion of an enterotoxin adjuvant is associated with development of multifaceted cellular and humoral immune responses to vaccination. Here, we review exciting progress in the past few years in clinical trials for safety and efficacy, preclinical vaccines studies, and new mechanistic insights for enterotoxin adjuvants. This includes recent reports of their use in vaccines targeting microbial infections (bacterial, viral, parasitic) or substance abuse drugs.

Does IPV Boost Intestinal Immunity among Children under Five Years of Age? An Experience from Pakistan

The oral poliovirus vaccine (OPV) has been the mainstay of polio eradication, especially in low-income countries, and its use has eliminated wild poliovirus type 2. However, the inactivated poliovirus vaccine (IPV) is safer than OPV, as IPV protects against paralytic poliomyelitis without producing adverse reactions. The present study compared mucosal and humoral responses to poliovirus vaccines administered to previously OPV-immunized children to assess the immunity gap in children in areas of high poliovirus transmission. A cluster-randomized trial was implemented in three high-risk districts of Pakistan-Karachi, Kashmore, and Bajaur-from June 2013 to May 2014. This trial was community-oriented and included three arms, focusing on healthy children below five years of age. The study involved the randomization of 387 clusters, of which 360 were included in the final analysis. The control arm (A) received the routine polio program bivalent poliovirus vaccine (bOPV). The second arm (B) received additional interventions, including health camps providing routine vaccinations and preventive maternal and child health services. In addition to the interventions in arm B, the third arm (C) was also provided with IPV. Blood and stool samples were gathered from children to evaluate humoral and intestinal immunity. The highest levels of poliovirus type 1 serum antibodies were observed in Group C (IPV + OPV). The titers for poliovirus type 2 (P2) and poliovirus type 3 (P3) were noticeably higher in those who had received a routine OPV dose than in those who had not across all study groups and visits. Providing an IPV booster after at least two OPV doses could potentially fill immunity gaps in regions where OPV does not show high efficacy. However, IPV only marginally enhances humoral immunity and fails to offer intestinal immunity, which is critical to stop the infection and spread of live poliovirus in populations that have not been exposed before.

The Immunogenicity and Properties of a Whole-Cell ETEC Vaccine Inactivated with Psoralen and UVA Light in Comparison to Formalin

Inactivated whole-cell vaccines present a full repertoire of antigens to the immune system. Formalin treatment, a standard method for microbial inactivation, can modify or destroy protein antigenic epitopes. We tested the hypothesis that photochemical inactivation with psoralen and UVA light (PUVA), which targets nucleic acid, would improve the immunogenicity of an Enterotoxigenic E. coli (ETEC) vaccine relative to a formalin-inactivated counterpart. Exposure of ETEC H10407 to PUVA using the psoralen drug 4'-Aminomethyltrioxsalen hydrochloride (AMT) yielded replication-incompetent bacteria that retained their metabolic activity. CFA/I-mediated mannose-resistant hemagglutination (MRHA) was equivalent for PUVA-inactivated and live ETEC, but was severely reduced for formalin-ETEC, indicating that PUVA preserved fimbrial protein functional integrity. The immunogenicity of PUVA-ETEC and formalin-ETEC was compared in mice ± double mutant heat-labile enterotoxin (dmLT) adjuvant. Two weeks after an intramuscular prime/boost, serum anti-ETEC IgG titers were similar for the two vaccines and were increased by dmLT. However, the IgG responses raised against several conserved ETEC proteins were greater after vaccination with PUVA-ETEC. In addition, PUVA-ETEC generated IgG specific for heat-labile toxin (LT) in the absence of dmLT, which was not a property of formalin-ETEC. These data are consistent with PUVA preserving ETEC protein antigens in their native-like form and justify the further testing of PUVA as a vaccine platform for ETEC using murine challenge models.

Threat of resurgence or hope for global eradication of poliovirus?

PURPOSE OF REVIEW

Recent outbreaks of poliomyelitis in countries that have been free of cases for decades highlight the challenges of eradicating polio in a globalized interconnected world beset with a novel viral pandemic. We provide an epidemiological update, advancements in vaccines, and amendments in public health strategy of poliomyelitis in this review.

RECENT FINDINGS

Last year, new cases of wild poliovirus type 1 (WPV1) were documented in regions previously documented to have eradicated WPV1 and reports of circulating vaccine-derived poliovirus type 2 (cVDPV2) and 3 (cVDPV3) in New York and Jerusalem made international headlines. Sequencing of wastewater samples from environmental surveillance revealed that the WPV1 strains were related to WPV1 lineages from endemic countries and the cVDPV2 strains from New York and Jerusalem were not only related to each other but also to environmental isolates found in London. The evidence of importation of WPV1 cases from endemic countries, and global transmission of cVDPVs justifies renewed efforts in routine vaccination programs and outbreak control measures that were interrupted by the COVID-19 pandemic. After the novel oral poliovirus vaccine type 2 (nOPV2) received emergency authorization for containment of cVDPV2 outbreaks in 2021, subsequent reduced incidence, transmission rates, and vaccine adverse events, alongside increased genetic stability of viral isolates substantiates the safety and efficacy of nOPV2. The nOPV1 and nOPV3 vaccines, against type 1 and 3 cVDPVs, and measures to increase accessibility and efficacy of inactivated poliovirus vaccine (IPV) are in development.

SUMMARY

A revised strategy utilizing more genetically stable vaccine formulations, with uninterrupted vaccination programs and continued active surveillance optimizes the prospect of global poliomyelitis eradication.

The Fight against Poliovirus Is Not Over

Poliovirus (PV), the virus that causes both acute poliomyelitis and post-polio syndrome, is classified within the Enterovirus C species, and there are three wild PV serotypes: WPV1, WPV2 and WPV3. The launch of the Global Polio Eradication Initiative (GPEI) in 1988 eradicated two of the three serotypes of WPV (WPV2 and WPV3). However, the endemic transmission of WPV1 persists in Afghanistan and Pakistan in 2022. There are cases of paralytic polio due to the loss of viral attenuation in the oral poliovirus vaccine (OPV), known as vaccine-derived poliovirus (VDPV). Between January 2021 and May 2023, a total of 2141 circulating VDPV (cVDPV) cases were reported in 36 countries worldwide. Because of this risk, inactivated poliovirus (IPV) is being used more widely, and attenuated PV2 has been removed from OPV formulations to obtain bivalent OPV (containing only types 1 and 3). In order to avoid the reversion of attenuated OPV strains, the new OPV, which is more stable due to genome-wide modifications, as well as sabin IPV and virus-like particle (VLP) vaccines, is being developed and offers promising solutions for eradicating WP1 and VDPV.

Safety, tolerability, and immunogenicity of inactivated poliovirus vaccine with or without E.coli double mutant heat-labile toxin (dmLT) adjuvant in healthy adults; a phase 1 randomized study

BACKGROUND

Inactivated trivalent poliovirus vaccine (IPV) induces humoral immunity, which protects against paralytic poliomyelitis but does not induce sufficient mucosal immunity to block intestinal infection. We assessed the intestinal immunity in healthy adults in Belgium conferred by a co-formulation of IPV with the mucosal adjuvant double mutant Labile Toxin (dmLT) derived from Escherichia coli.

METHODS

Healthy fully IPV-vaccinated 18-45-year-olds were randomly allocated to three groups: on Day 1 two groups received one full dose of IPV (n = 30) or IPV + dmLT (n = 30) in a blinded manner, and the third received an open-label dose of bivalent live oral polio vaccine (bOPV types 1 and 3, n = 20). All groups received a challenge dose of bOPV on Day 29. Participants reported solicited and unsolicited adverse events (AE) using study diaries. Mucosal immune responses were measured by fecal neutralization and IgA on Days 29 and 43, with fecal shedding of challenge viruses measured for 28 days. Humoral responses were measured by serum neutralizing antibody (NAb).

RESULTS

Solicited and unsolicited AEs were mainly mild-to-moderate and transient in all groups, with no meaningful differences in rates between groups. Fecal shedding of challenge viruses in both IPV groups exceeded that of the bOPV group but was not different between IPV and IPV + dmLT groups. High serum NAb responses were observed in both IPV groups, alongside modest levels of fecal neutralization and IgA.

CONCLUSIONS

Addition of dmLT to IPV administered intramuscularly neither affected humoral nor intestinal immunity nor decreased fecal virus shedding following bOPV challenge. The tolerability of the dose of dmLT used in this study may allow higher doses to be investigated for impact on mucosal immunity. Registered on ClinicalTrials.gov - NCT04232943.

Route and antigen shape immunity to dmLT-adjuvanted vaccines to a greater extent than biochemical stress or formulation excipients

A key aspect to vaccine efficacy is formulation stability. Biochemical evaluations provide information on optimal compositions or thermal stability but are routinely validated by ex vivo analysis and not efficacy in animal models. Here we assessed formulations identified to improve or reduce stability of the mucosal adjuvant dmLT being investigated in polio and enterotoxigenic E. coli (ETEC) clinical vaccines. We observed biochemical changes to dmLT protein with formulation or thermal stress, including aggregation or subunit dissociation or alternatively resistance against these changes with specific buffer compositions. However, upon injection or mucosal vaccination with ETEC fimbriae adhesin proteins or inactivated polio virus, experimental findings indicated immunization route and co-administered antigen impacted vaccine immunogenicity more so than dmLT formulation stability (or instability). These results indicate the importance of both biochemical and vaccine-derived immunity assessment in formulation optimization. In addition, these studies have implications for use of dmLT in clinical settings and for delivery in resource poor settings.

Identifying a stable bulk dmLT adjuvant formulation at a clinically relevant concentration

Double mutant heat-labile toxin (dmLT) is a novel vaccine adjuvant under development with several different vaccine candidates. Studies using existing dmLT adjuvant stocks require significant dilution to achieve a clinically relevant dose. This dilution leads to wastage of the adjuvant. This manuscript describes a limited formulation study to improve the stability of bulk dmLT at a more clinically relevant concentration (20 µg/mL) with minimal changes to the existing bulk dmLT formulation. In vitro methods were used to evaluate dmLT stability after lyophilization and short-term accelerated stability studies. The addition of the excipient polysorbate 80 (PS80) at 0.05 % to the existing dmLT formulation was identified as the lead modification that provided improved stability of the lyophilized dmLT at 20 µg/mL through 4 weeks at 40 °C.