One Hundred Ten Years of Allergen Immunotherapy: A Broad Look Into the Future

Trained immunity-based vaccines for infections and allergic diseases

Trained immunity has emerged as a new concept in immunology that is associated with the memory of innate immune cells and linked to specific metabolic and epigenetic reprogramming of these cells. Trained immunity may confer nonspecific and sustained protection against a broad range of pathogens, and recent findings show that it might also be involved in allergy mechanisms. Some conventional vaccines have demonstrated trained immunity induction as the mechanism underlying their heterologous protection. The development of novel vaccines designed especially for this purpose (trained immunity-based vaccines) might be useful in the absence of conventional vaccines or in specific clinical settings. Under certain circumstances, trained immunity could lead to persistent inflammatory innate immune cell responses in subjects with allergy, which could be associated with the development and worsening of allergy by promoting and amplifying aberrant type 2 immune responses. In other cases, trained immunity may help promote healthy immune responses to allergens, such as type 1 responses that counterbalance the type 2 inflammation or regulatory T cells that induce tolerance. Trained immunity-based allergen vaccines could become the next generation of allergen-specific immunotherapy vaccines, harnessing the potential of trained immunity to induce allergen tolerance. The identification and characterization of proper training inducers might well pave the way for the development of novel immunotherapies.

Multifaceted roles of trained immunity in diverse pathological contexts

Trained immunity, an innate immune response characterized by enhanced cellular responsiveness, exhibits a profound memory akin to adaptive immunity. This phenomenon involves intricate metabolic and epigenetic reprogramming triggered by stimuli such as β-glucan and BCG, shaping innate immune memory. Following elucidation of the background on trained immunity, it is important to explore its multifaceted roles in various pathological contexts. In this review, we delve into the specific contributions of trained immunity in the intricate landscape of viral infections, tumorigenesis, and diverse inflammatory diseases, shedding light on its potential as a therapeutic target, and offering comprehensive understanding of its broader immunological implications. [BMB Reports 2024; 57(10): 431-440].

Clinical benefits with 300 IR HDM SLIT tablet in Europeans with house dust mite allergic rhinitis: Post hoc analysis of a large phase 3 trial

Background

House dust mite (HDM)-induced allergic rhinitis (AR) is a major cause of allergic respiratory disease. The efficacy and safety of the 300 IR HDM sublingual immunotherapy (SLIT) tablet in patients with moderate-to-severe HDM-AR was confirmed in a large, international, phase 3 randomized controlled trials (RCTs). Here, we analyzed the results in the European population.

Methods

Data from 91 European centers that participated in the international, double-blind, RCT (EudraCT 2014-004223-46, NCT02443805) with the 300 IR HDM SLIT tablet versus placebo over 12 months were analyzed post hoc. The treatment effect in European adults and adolescents was notably assessed through the European Academy of Allergy and Clinical Immunology (EAACI)-recommended combined symptom and medication score (CSMS0-6, pre-defined endpoint) and the total combined rhinitis score (TCRS0-24, post hoc endpoint, also balanced) during the primary evaluation period (4 weeks at the end of treatment period) using analysis of covariance (ANCOVA).

Results

There were 818 patients who comprised the modified full analysis set in Europe. Over the primary period, the differences in CSMS0-6 and TCRS0-24 between the 300 IR and placebo groups were statistically significant (p < 0.0001): -0.32 (95%CI [-0.46; -0.17]) and -1.28 (95%CI [-1.63; -0.94]), respectively, with relative differences of -20.9% and -21.2%. All post hoc and the rhinoconjunctivitis quality of life endpoints were significantly improved with 300 IR versus placebo. The 300 IR HDM tablet was generally well tolerated.

Conclusion

This RCT sub-analysis confirmed the 300 IR HDM SLIT tablet is an effective and safe treatment for European adults and adolescents with HDM-AR with clinically meaningful benefits from the patients' perspective.

Trial registration

NCT02443805. Registered on April 29, 2015./EudraCT 2014-004223-46. Registered on September 16, 2015.

Global, regional, and national incidence of six major immune-mediated inflammatory diseases: findings from the global burden of disease study 2019

Background

The causes for immune-mediated inflammatory diseases (IMIDs) are diverse and the incidence trends of IMIDs from specific causes are rarely studied. The study aims to investigate the pattern and trend of IMIDs from 1990 to 2019.

Methods

We collected detailed information on six major causes of IMIDs, including asthma, inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, psoriasis, and atopic dermatitis, between 1990 and 2019, derived from the Global Burden of Disease study in 2019. The average annual percent change (AAPC) in number of incidents and age standardized incidence rate (ASR) on IMIDs, by sex, age, region, and causes, were calculated to quantify the temporal trends.

Findings

In 2019, rheumatoid arthritis, atopic dermatitis, asthma, multiple sclerosis, psoriasis, inflammatory bowel disease accounted 1.59%, 36.17%, 54.71%, 0.09%, 6.84%, 0.60% of overall new IMIDs cases, respectively. The ASR of IMIDs showed substantial regional and global variation with the highest in High SDI region, High-income North America, and United States of America. Throughout human lifespan, the age distribution of incident cases from six IMIDs was quite different. Globally, incident cases of IMIDs increased with an AAPC of 0.68 and the ASR decreased with an AAPC of -0.34 from 1990 to 2019. The incident cases increased across six IMIDs, the ASR of rheumatoid arthritis increased (0.21, 95% CI 0.18, 0.25), while the ASR of asthma (AAPC = -0.41), inflammatory bowel disease (AAPC = -0.72), multiple sclerosis (AAPC = -0.26), psoriasis (AAPC = -0.77), and atopic dermatitis (AAPC = -0.15) decreased. The ASR of overall and six individual IMID increased with SDI at regional and global level. Countries with higher ASR in 1990 experienced a more rapid decrease in ASR.

Interpretation

The incidence patterns of IMIDs varied considerably across the world. Innovative prevention and integrative management strategy are urgently needed to mitigate the increasing ASR of rheumatoid arthritis and upsurging new cases of other five IMIDs, respectively.

Funding

The Global Burden of Disease Study is funded by the Bill and Melinda Gates Foundation. The project funded by Scientific Research Fund of Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital (2022QN38).

Advancing precision medicine in asthma: Evolution of treatment outcomes

The article discusses the historical evolution of asthma treatment and highlights recent advancements in personalized medicine, specifically the use of biologics in severe asthma therapy and its potential combination with allergen immunotherapy (AIT). One of the major breakthroughs of biologics is their potential effect on airway remodeling, a crucial aspect of asthma chronicity. The article introduces the concept of disease-modifying antiasthmatic drugs, which aim to modify the course of asthma and possibly modulate or prevent airway remodeling. Furthermore, the critical importance of patient-centered outcome measures to evaluate the efficacy and effectiveness of asthma treatments is emphasized, with the innovative concept of asthma remission introduced as a potential outcome. Recent studies suggest that AIT can be used as an additional therapy to biologic agents for the treatment of allergic asthma. The combination of these treatments has been shown to induce improved clinical outcomes. However, AIT is actually not recommended for use in patients with severe asthma, but encouraging results from studies investigating the combined use of AIT and biologics indicate a novel approach to exploring these treatment modalities. In conclusion, the introduction of biologics and AIT has changed the scenario of respiratory allergy treatment, from a "one size fits all" approach to embracing "individual treatments."

Why Current Therapy Does Not Cure Asthma. Is It Time to Move Towards a One Health Approach?

Asthma continues to be a disease for which there is no cure, even if it can be very well controlled with the appropriate therapies, which take into account the specific phenotype. The paradox of asthma is that asthma can heal spontaneously, albeit in a small percentage of cases. This observation is highly relevant, since understanding the mechanisms of spontaneous healing can pave the way for new strategies for treating asthma. It is likely that the lack of cure for asthma is due to the fact that current therapies target downstream mediators of the inflammatory response. Asthma can be considered a response of maladaptation of the airway epithelium to the environment, through the orientation of the innate immunity towards an inflammatory response. The important effect of the environment on asthma progress comes from interventions which help children who live in disadvantaged urban neighborhoods move to higher resourced neighborhoods. It is quite interesting that the magnitude of decrease of exacerbations associated with moving was larger than the effect of inhaled corticosteroids and similar to that observed for the effect of biologic agents. Alpine altitude climate treatment is a natural treatment that targets biological pathway, improving various outcomes such as asthma control and quality of life, exacerbation rate and hospitalizations. If as researchers we want to set ourselves the goal of achieving complete remission of asthma, without the need for ongoing maintenance treatment, we need to change the approach to finding new asthma treatment strategies. The One Health approach, an interdisciplinary strategy with focal point on human, animal, and environmental health interconnections, appears to be the right tool for researching asthma prevention and treatment.

Peptide immunotherapy for aeroallergens

Background: Allergen specific immunotherapy (SIT) has been used for more than a century. Researchers have been working to improve efficacy and reduce the side effects. Objective: We have reviewed the literature about peptides immunotherapy for inhaled allergens. The mechanism of SIT is to induce regulatory T (Treg) cells and to reduce T helper (Th)2 cells to induce class switching from IgE to IgG and induce blocking antibodies to inhibit allergen binding of IgE. Methods: The relevant published literatures on the peptide SIT for aeroallergens have been searched on the medline. Results: Modification of allergens and routes of treatment has been performed. Among them, many researchers were interested in peptide immunotherapy. T-cell epitope peptide has no IgE epitope, that is able to bind IgE, but rather induces Treg and reduces Th2 cells, which was considered an ideal therapy. Results from cellular and animal model studies have been successful. However, in clinical studies, T-cell peptide immunotherapy has failed to show efficacy and caused side effects, because of the high effective rate of placebo and the development of IgE against T-cell epitope peptides. Currently, the modifications of IgE-allergen binding by blocking antibodies are considered for successful allergen immunotherapy. Conclusion: Newly developed hypoallergenic B cell epitope peptides and computational identification methods hold great potential to develop new peptide immunotherapies.

Clinical and experimental treatment of allergic asthma with an emphasis on allergen immunotherapy and its mechanisms

Allergen immunotherapy (AIT) is currently the only form of treatment that modifies allergic asthma. Pharmacotherapy alone seeks to control the symptoms of allergic asthma, allergic rhinitis, and other atopic conditions. In contrast, AIT can induce long-term physiological modifications through the immune system. AIT enables individuals to live improved lives many years after treatment ends, where they are desensitized to the allergen(s) used or no longer have significant allergic reactions upon allergen provocation. The leading forms of treatment with AIT involve injections of allergen extracts with increasing doses via the subcutaneous route or drops/tablets via the sublingual route for several years. Since the initial attempts at this treatment as early as 1911 by Leonard Noon, the mechanisms by which AIT operates remain unclear. This literature-based review provides the primary care practitioner with a current understanding of the mechanisms of AIT, including its treatment safety, protocols, and long-term efficacy. The primary mechanisms underlying AIT include changes in immunoglobulin classes (IgA, IgE, and IgG), immunosuppressive regulatory T-cell induction, helper T cell type 2 to helper T cell type 1 cell/cytokine profile shifts, decreased early-phase reaction activity and mediators, and increased production of IL-10, IL-35, TGF-β, and IFN-γ. Using the databases PubMed and Embase, a selective literature search was conducted searching for English, full-text, reviews published between 2015 and 2022 using the keywords (with wildcards) "allerg*," "immunotherap*," "mechanis*," and "asthma." Among the cited references, additional references were identified using a manual search.

Allergenicity of peanut allergens and its dependence on the structure

Food allergies are a global food safety problem. Peanut allergies are common due, in part, to their popular utilization in the food industry. Peanut allergy is typically an immunoglobulin E-mediated reaction, and peanuts contain 17 allergens belonging to different families in peanut. In this review, we first introduce the mechanisms and management of peanut allergy, followed by the basic structures of associated allergens. Subsequently, we summarize methods of epitope localization for peanut allergens. These methods can be instrumental in speeding up the discovery of allergenicity-dependent structures. Many attempts have been made to decrease the allergenicity of peanuts. The structures of hypoallergens, which are manufactured during processing, were analyzed to strengthen the desensitization process and allergen immunotherapy. The identification of conformational epitopes is the bottleneck in both peanut and food allergies. Further, the identification and modification of such epitopes will lead to improved strategies for managing and preventing peanut allergy. Combining traditional wet chemistry research with structure simulation studies will help in the epitopes' localization.

From trained immunity in allergy to trained immunity-based allergen vaccines

Innate immune cells experience long lasting metabolic and epigenetic changes after an encounter with specific stimuli. This facilitates enhanced immune responses upon secondary exposition to both the same and unrelated pathogens, a process termed trained immunity. Trained immunity-based vaccines (TIbV) are vaccines able to induce innate immune memory, thus conferring heterologous protection against a broad range of pathogens. While trained immunity has been well documented in the context of infections and multiple immune-mediated diseases, the role of innate immune memory and its contribution to the initiation and maintenance of chronic allergic diseases remains poorly understood. Over the last years, different studies attempting to uncover the role of trained immunity in allergy have emerged. Exposition to environmental factors impacting allergy development such as allergens or viruses induces the reprogramming of innate immune cells to acquire a more pro-inflammatory phenotype in the context of asthma or food allergy. Several studies have convincingly demonstrated that prevention of viral infections using TIbV contributes to reduce wheezing attacks in children, which represent a high-risk factor for asthma development later in life. Innate immune cells trained with specific stimuli might also acquire anti-inflammatory features and promote tolerance, which may have important implications for chronic inflammatory diseases such as allergies. Recent findings showed that allergoid-mannan conjugates, which are next generation vaccines for allergen-specific immunotherapy (AIT), are able to reprogram monocytes into tolerogenic dendritic cells by mechanisms depending on metabolic and epigenetic rewiring. A better understanding of the underlying mechanisms of trained immunity in allergy will pave the way for the design of novel trained immunity-based allergen vaccines as potential alternative strategies for the prevention and treatment of allergic diseases.

Omalizumab may protect allergic patients against COVID-19: A systematic review

Omalizumab, which downregulates the immunoglobulin E (IgE) receptor site on plasmacytoid dendritic cells and thereby increases interferon-α (INF-α) production, may shorten the duration of viral infections by enhancing the antiviral immunity. A systematic review was conducted to investigate whether previous anti-IgE treatment with omalizumab could protect against SARS-CoV-2 disease ("COVID-19") (infection, disease duration, and severity), and whether IFN-α upregulation could be involved. The research included articles published from March 2020 to January 2022. An accurate search was performed on bibliographic biomedical database (MEDLINE - Pubmed, SCOPUS, EMBASE, BIOMED CENTRAL, Google scholar, COCHRANE LIBRARY, ClinicalTrial.gov) including cohorts, case reports and reviews. Different methods were used, based on the study design, to assess the quality of eligible studies. Several authors link omalizumab to a possible protection against viruses, but they often refer to studies carried out before the pandemic and with viruses other than SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) (eg, rhinoviruses -RV). Few cases of COVID-19 patients treated with omalizumab have been recorded, and, in most of them, no increased susceptibility to severe disease was observed. According to these data, the current indication is to continue omalizumab therapy during the pandemic. Moreover, although omalizumab may enhance the antiviral immune response even for SARS-CoV-2, further studies are needed to confirm this hypothesis. It would be helpful to establish a registry of omalizumab-treated (or in treatment) patients who have developed COVID-19. Finally, randomized controlled trials could be able to demonstrate the effect of omalizumab in protecting against severe SARS-CoV-2, through IFN-α upregulation or other immunological pathways.

Subcutaneous birch pollen allergen immunotherapy with a depigmented polymerized extract shows only sustained and long-term efficacy in a subgroup of monosensitized adults and adolescents with allergic rhinitis

Background

Allergen immunotherapy (AIT) is an approved treatment for seasonal respiratory allergic diseases. A depigmented polymerized birch pollen extract for subcutaneous allergen immunotherapy (SCIT) has been demonstrated to be efficacious and safe in patients allergic to birch pollen and its homologous group.

Objective

To determine whether SCIT with a birch pollen formulation (5000 depigmented polymerized (DPP) units/mL) shows sustained and long-term efficacy in adults and adolescents with birch-pollen induced allergic rhinitis with or without intermittent asthma.

Methods

A multicentre (n = 66), double-blind, placebo-controlled Phase III clinical trial was performed in the Czech Republic, Finland, Germany, Latvia, Lithuania, Poland and Russia. Participants were randomized 2:1 to active treatment (birch 5000 DPP/ml) or placebo for three years of SCIT and followed up for two treatment-free years. The primary efficacy endpoint was the EAACI's combined symptom and medication score for rhinoconjunctivitis (CSMSEAACI).

Results

A total of 973 participants were screened and 649 were randomized (active treatment: n = 434; placebo: n = 215). The intention-to-treat analysis of the CSMSEAACI in the overall study population did not demonstrate statistically significant differences in years 1, 2 and 3. In a post-hoc analysis, among the subgroup of patients monosensitized to birch pollen allergen only (n = 200), we observed a statistically significant difference (active treatment vs. placebo) in the CSMSEAACI in year 2, 3 and 5. The AIT's safety profile was good.

Conclusions

SCIT with a depigmented polymerized birch pollen extract was safe. Sustained and long-term efficacy in years 2, 3 and 5 in monosensitized patients, but not in polysensitized patients was demonstrated.(EudraCT 2012-000414-11).

LNIT-Local nasal immunotherapy in allergic rhinitis: revisited evidence and perspectives

PURPOSE OF REVIEW

Allergen immunotherapy (AIT) is a personalized treatment approach for the allergic airway disease. The most common routes of administration are subcutaneous and sublingual. Local nasal immunotherapy (LNIT) presents another alternative route for allergen desensitization. Nasal mucosa is the first entry site of pathogens and numerous lymphoid organs are located in this area, making LNIT a favorable method for triggering immune tolerance. LNIT has shown promising results in reducing symptoms and medication use in allergic rhinitis patients. Over time, difficulties in dosing adjustments have made this method less popular. Recent advances in intranasal drug delivery systems warrant re-examination of LNIT as a viable option for the treatment of the allergic airway disease.

RECENT FINDINGS

The scope of the review includes evidences of LNIT in human trials including comparison with placebo and conventional method of immunotherapy. Recent articles regarding the mechanism of LNIT and the challenges of intranasal drug delivery are reviewed. Advances in the LNIT delivery system which have overcome previous limitations demonstrate promising effects.

SUMMARY

LNIT presents a judicious alternative for noninjection AIT. The evidences from previous clinical trials and the novel improvement of drug delivery system will lead into the future allergen vaccine production.

Subcutaneous allergen immunotherapy in the treatment of allergic respiratory disease

Subcutaneous immunotherapy is recognized as a cornerstone in the management of allergic respiratory disease in patients who are properly characterized with allergy and with allergic rhinoconjunctivis and/or well-controlled asthma, and who are willing to adhere to the rigorous treatment program. A key tenet is that it affords the opportunity to effect long-term clinical remission through its disease-modifying properties. Furthermore, it has the potential to prevent the progression of allergic rhinitis to asthma, prevent new allergen sensitivities, and improve a patient's quality of life.

Local nasal immunotherapy for allergic rhinitis: A systematic review and meta-analysis

INTRODUCTION

Local nasal immunotherapy (LNIT), an alternative noninjection immunotherapy method, is theoretically an efficient method for inducing immunotolerance directly in the affected organ. LNIT is more convenient and less invasive than injection immunotherapy, with fewer systemic reactions. The development of adjuvants to overcome LNIT's limitations raises the possibility of it being an alternative allergen immunotherapy.

OBJECTIVES

To evaluate the clinical and immunological efficacy and safety of LNIT for patients with allergic rhinitis.

METHODS

A systematic search for randomized controlled trials comparing LNIT and placebo was performed using OVID Medline and Embase. Outcomes were total nasal symptom score (TNSS), symptom-medication score (SMS), medication score, immunological assessment, and nasal provocation threshold. Data were pooled for meta-analysis.

RESULTS

A total of 20 studies with 698 participants were included. The LNIT group had greater posttreatment improvement in TNSS, SMS, and medication score than control (TNSS: standardized mean difference [SMD], -1.37 [95% confidence interval [CI], -2.04 to -0.69]; SMS: SMD, -1.55 [95% CI, -2.83 to -0.28]; and medication score: SMD, -1.09 [95% CI, -1.35 to -0.83]). Immunological assessments showed no significant differences in serum-specific IgE (mean difference [MD], 6.35; 95% CI, -4.62 to 17.31), nasal IgE (MD, -0.59; 95% CI, -1.99 to 0.81), or nasal eosinophil cationic protein (MD, 7.63; 95% CI, -18.65 to 33.91). Only serum IgG significantly increased with LNIT (MD, 0.45; 95% CI, 0.20, 0.70). Posttreatment, nasal provocation threshold was higher with LNIT (MD, 27.30; 95% CI, 10.13-44.46). No significant adverse events were reported.

CONCLUSIONS

LNIT is a safe alternative allergen immunotherapy route without significant adverse events. It improves clinical symptoms, reduces medication usage, and increases the nasal provocation threshold.

One hundred and ten years of Allergen Immunotherapy: A journey from empiric observation to evidence

One hundred and ten years after Noon's first clinical report of the subcutaneous application of allergen extracts, allergen immunotherapy (AIT) has evolved as the most important pillar of the treatment of allergic patients. It is the only disease-modifying treatment option available and the evidence for its clinical efficacy and safety is broad and undisputed. Throughout recent decades, more insights into the underlying mechanisms, in particular the modulation of innate and adaptive immune responses, have been described. AIT is acknowledged by worldwide regulatory authorities, and following the regulatory guidelines for product development, AIT products are subject to a rigorous evaluation before obtaining market authorization. Knowledge and practice are anchored in international guidelines, such as the recently published series of the European Academy of Allergy and Clinical Immunology (EAACI). Innovative approaches continue to be further developed with the focus on clinical improvement by, for example, the usage of adjuvants, peptides, recombinants, modification of allergens, new routes of administration, and the concomitant use of biologicals. In addition, real-life data provide complementary and valuable information on the effectiveness and tolerability of this treatment option in the clinical routine. New mobile health technologies and big-data approaches will improve daily treatment convenience, adherence, and efficacy of AIT. However, the current coronavirus disease 2019 (COVID-19) pandemic has also had some implications for the feasibility and practicability of AIT. Taken together, AIT as the only disease-modifying therapy in allergic diseases has been broadly investigated over the past 110 years laying the path for innovations and further improvement.

New insights in mite immunotherapy - sublingual tablets

PURPOSE OF REVIEW

Sublingual tablet immunotherapy has been demonstrated to be effective for allergies induced by exposure to grass, ragweed, specific trees (Japanese Cedar; birch homologous tree mix), and house dust mites (HDM). This review provides both an overview of the evidence-based clinical studies that address the use of the HDM SLIT-tablet for the treatment of HDM-induced allergic rhinitis/conjunctivitis and its appropriate use in carefully selected asthmatic patients and provides the clinician with practical management considerations.

RECENT FINDINGS

Solid evidence-based clinical studies have shown that the HDM SLIT-tablet is both well tolerated in patients with mild-to-moderate asthma and has demonstrated a meaningful improvement in exacerbations, need for rescue medication, quality of life, and asthma control.

SUMMARY

The HDM SLIT-tablet provides the allergy specialist with a well-tolerated treatment that has established superior safety to subcutaneous injection therapy, which can be administered easily as a sublingual dissolvable tablet, and which provides the opportunity to address one of the more difficult aspects in the management of an inducer of perennial allergic disease - that of persistent airway inflammation and allergic asthma.

Demystifying particle-based oral vaccines

Introduction: The oral route of vaccination is pain- and needle-free and can induce systemic and mucosal immunity. However, gastrointestinal barriers and antigen degradation impose significant hurdles in the development of oral vaccines. Live attenuated viruses and bacteria can overcome these barriers but at the risk of introducing safety concerns. As an alternative, particles have been investigated for antigen protection and delivery, yet there are no FDA-approved oral vaccines based on particle-based delivery systems. Our objective was to discover underlying determinants that can explain the current inadequacies and identify paradigms that can be implemented in future for successful development of oral vaccines relying on particle-based delivery systems.Areas covered: We reviewed literature related to the use of particles for oral vaccination and placed special emphasis on formulation characteristics and administration schedules to gain an insight into how these parameters impact production of antigen-specific antibodies in systemic and mucosal compartments.Expert opinion: Despite the long history of vaccines, particle-based oral vaccination is a relative new field with the first study published in 1989. Substantial variability exists between different studies with respect to dosing schedules, number of doses, and the amount of vaccine per dose. Most studies have not used adjuvants in the formulations. Better standardization in vaccination parameters is required to improve comparison between experiments, and adjuvants should be used to enhance the systemic and mucosal immune responses and to reduce the number of doses, which will make oral vaccines more attractive.