Sae-Hae Kim

The M Cell-Targeting Ligand Promotes Antigen Delivery and Induces Antigen-Specific Immune Responses in Mucosal Vaccination

Oral mucosal immunization can induce protective immunity in both systemic compartments and the mucosa. Successful mucosal immunization depends on Ag delivery to the mucosal immune induction site. The high transcytotic activity of M cells within the mucosa makes these cells attractive targets for mucosal Ag delivery, although it remains unclear whether delivery of Ag to M cells only can guarantee the induction of effective immune responses. In this study, we evaluated the ability of an M cell-targeting ligand with adjuvant activity to induce immunity against ligand-fused Ag. We selected M cell-targeting ligands through biopanning of a phage display library against differentiated in vitro M-like cells and produced the recombinant Ags fused to the selected ligands using the model Ag. One of the selected peptide ligands, Co1, promoted the binding of ligand-fused Ag to mouse Peyer’s patch M cells and human M-like cells that had been defined by binding with the M cell-specific and anti-GP2 Abs. In addition, Co1 ligand enhanced the uptake of fused Ag by immunogenic tissue in an ex vivo loop assay and in vivo oral administration experiments. After oral administration, the ligand-fused Ag enhanced immune responses against the fused Ag compared with those of the control Ag without ligand. In addition, this use of the ligand supported a skewed Th2-type immune response against the fused Ag. Collectively, these results suggest that the ligand selected through biopanning against cultured M-like cells could be used as an adjuvant for targeted Ag delivery into the mucosal immune system to enhance immune induction.

Mucosal Immune System and M Cell-targeting Strategies for Oral Mucosal Vaccination.

Vaccination is one of the most effective methods available to prevent infectious diseases. Mucosa, which are exposed to heavy loads of commensal and pathogenic microorganisms, are one of the first areas where infections are established, and therefore have frontline status in immunity, making mucosa ideal sites for vaccine application. Moreover, vaccination through the mucosal immune system could induce effective systemic immune responses together with mucosal immunity in contrast to parenteral vaccination, which is a poor inducer of effective immunity at mucosal surfaces. Among mucosal vaccines, oral mucosal vaccines have the advantages of ease and low cost of vaccine administration. The oral mucosal immune system, however, is generally recognized as poorly immunogenic due to the frequent induction of tolerance against orally-introduced antigens. Consequently, a prerequisite for successful mucosal vaccination is that the orally introduced antigen should be transported across the mucosal surface into the mucosa-associated lymphoid tissue (MALT). In particular, M cells are responsible for antigen uptake into MALT, and the rapid and effective transcytotic activity of M cells makes them an attractive target for mucosal vaccine delivery, although simple transport of the antigen into M cells does not guarantee the induction of specific immune responses. Consequently, development of mucosal vaccine adjuvants based on an understanding of the biology of M cells has attracted much research interest. Here, we review the characteristics of the oral mucosal immune system and delineate strategies to design effective oral mucosal vaccines with an emphasis on mucosal vaccine adjuvants.

M cells expressing the complement C5a receptor are efficient targets for mucosal vaccine delivery

In the mucosal immune system, M cells are known as specialized epithelial cells that take up luminal antigens, although the receptors on M cells and the mechanism of antigen uptake into M cells are not well‐understood. Here, we report the expression of the complement C5a receptor (C5aR) on the apical surface of M cells. C5ar mRNA expression in co‐cultured Caco‐2 human M‐like cells was six‐fold higher than in mono‐cultured cells. C5aR expression was detected together with glycoprotein 2, an M‐cell‐specific protein, on the apical surface of M‐like cells and mouse Peyers patch M cells. Interestingly, after oral administration of Yersinia enterocolitica which expresses outer membrane protein H (OmpH) that is homologous to the Skp α1 domain of Escherichia coli, a ligand of C5aR, dense clustering and phosphorylation of C5aR were detected in M cells. Finally, targeted antigen delivery to M cells using C5aR as a receptor was achieved using the OmpH α1 of Y. enterocolitica such that the induction of ligand‐conjugated antigen‐specific immune responses was confirmed in mice after oral immunization of the OmpH β1α1‐conjugated antigen. Collectively, we identified C5aR expression on M cells and suggest that C5aR could be used as a target receptor for mucosal antigen delivery.

Antigen targeting to M cells for enhancing the efficacy of mucosal vaccines

Vaccination is one of the most successful applications of immunology and for a long time has depended on parenteral administration protocols. However, recent studies have pointed to the promise of mucosal vaccination because of its ease, economy and efficiency in inducing an immune response not only systemically, but also in the mucosal compartment where many pathogenic infections are initiated. However, successful mucosal vaccination requires the help of an adjuvant for the efficient delivery of vaccine material into the mucosa and the breaking of the tolerogenic environment, especially in oral mucosal immunization. Given that M cells are the main gateway to take up luminal antigens and initiate antigen-specific immune responses, understanding the role and characteristics of M cells is crucial for the development of successful mucosal vaccines. Especially, particular interest has been focused on the regulation of the tolerogenic mucosal microenvironment and the introduction of the luminal antigen into the lymphoid organ by exploiting the molecules of M cells. Here, we review the characteristics of M cells and the immune regulatory factors in mucosa that can be exploited for mucosal vaccine delivery and mucosal immune regulation.

Suppression of TH2-Type Immune Response-Mediated Allergic Diarrhea Following Oral Administration of Traditional Korean Medicine: Atractylodes Macrocephala Koidz

Atractylodes macrocephala Koidz (AMK) is well-known as a digestive and tonic material and is widely used in traditional Korean herbal medicines. Previously, we found that protein samples obtained from the medicines could induce a preferential stimulation of type 1, rather than type 2, helper T lymphocytes (Th) immune responses in vitro. Since immune response induction is controlled by the balanced activation between Th1- and Th2-type immune responses, we tested to see whether or not the AMK protein sample could inhibit the ovalbumin (OVA)-mediated allergic diarrhea, whose induction has been known to be mediated by the Th2-type immune responses. The sample treatment markedly stimulated lymphocyte proliferation, antibody production, and cytokine secretion in vitro, showing a preferential stimulation of Th1-type immune responses. In particular, oral administration of the AMK sample suppressed the OVA-mediated allergic diarrhea in mice. The sample treatment also suppressed the OVA-mediated enhanced levels of total immunoglobulin (Ig) E, as well as OVA-specific IgE, which are closely associated with Th2 cell stimulation in mice. Furthermore, the oral treatment of the sample significantly increased gamma interferon (IFN-γ) production by lymphocytes, isolated from spleen and large intestine of the mice, that had been systematically challenged with OVA. Consequently, the oral administration of AMK protein sample suppressed the OVA-mediated allergic diarrhea by preferential stimulation of the Th1-type immune responses.

The development of mucosal vaccines for both mucosal and systemic immune induction and the roles played by adjuvants

Vaccination is the most successful immunological practice that improves the quality of human life and health. Vaccine materials include antigens of pathogens and adjuvants potentiating the effectiveness of vaccination. Vaccines are categorized using various criteria, including the vaccination material used and the method of administration. Traditionally, vaccines have been injected via needles. However, given that most pathogens first infect mucosal surfaces, there is increasing interest in the establishment of protective mucosal immunity, achieved by vaccination via mucosal routes. This review summarizes recent developments in mucosal vaccines and their associated adjuvants.

Application of an M-cell-targeting ligand for oral vaccination induces efficient systemic and mucosal immune responses against a viral antigen

Oral mucosal vaccination is an alternative method to overcome the pitfalls of current injection-based vaccines, such as pain and high cost of vaccination. It is a feasible and economic vaccine application, especially in developing countries. However, achieving effective antigen delivery into mucosal lymphoid organs and efficient immune stimulation are prerequisites to successful oral mucosal vaccination. One promising approach for oral mucosal vaccine development is exploring the potential of M cells via M-cell-targeting ligands that have the potential to deliver ligand-conjugated antigens into mucosal lymphoid organs and evoke conjugated-antigen-specific systemic and mucosal immune responses. Here, we investigated the M-cell-targeting ligand, Co1, in inducing specific immune responses against a pathogenic viral antigen, envelope domain III (EDIII) of dengue virus, to provide the foundation for oral mucosal vaccine development against the pathogen. After oral administration of Co1-conjugated EDIII antigens, we observed efficient antigen delivery into Peyers patches. We also report the elicitation of EDIII-specific immunity in systemic and mucosal compartments by Co1 ligand (located in the C-terminus of EDIII). Furthermore, the antibodies induced by the ligand-conjugated EDIII antigen showed effective virus-neutralizing activity. The results of this study suggest that the M-cell-targeting strategy using Co1 ligand as a mucosal adjuvant may be applicable for developing oral vaccine candidates against pathogenic viral antigen.

Nasal immunization with major epitope-containing ApxIIA toxin fragment induces protective immunity against challenge infection with Actinobacillus pleuropneumoniae in a murine model

Actinobacillus pleuropneumoniae is an infective agent that leads to porcine pleuropneumonia, a disease that causes severe economic losses in the swine industry. Based on the fact that the respiratory tract is the primary site for bacterial infection, it has been suggested that bacterial exclusion in the respiratory tract through mucosal immune induction is the most effective disease prevention strategy. ApxIIA is a vaccine candidate against A. pleuropneumoniae infection, and fragment #5 (aa. 439-801) of ApxIIA contains the major epitopes for effective vaccination. In this study, we used mice to verify the efficacy of intranasal immunization with fragment #5 in the induction of protective immunity against nasal challenge with A. pleuropneumoniae and compared its efficacy with that of subcutaneous immunization. Intranasal immunization of the fragment induced significantly higher systemic and mucosal immune responses measured at the levels of antigen-specific antibodies, cytokine-secreting cells after antigen exposure, and antigen-specific lymphocyte proliferation. Intranasal immunization not only efficiently inhibited the bacterial colonization in respiratory organs, but also prevented alveolar tissue damage in infectious condition similar to that of a contaminated pig. Moreover, intranasal immunization with fragment #5 provided acquired protective immunity against intranasal challenge with A. pleuropneumoniae serotype 2. In addition, it conferred cross-protection against serotype 5, a heterologous pathogen that causes severe disease by ApxI and ApxII secretion. Collectively, intranasal immunization with fragment #5 of ApxIIA can be considered an efficient protective immunization procedure against A. pleuropneumoniae infection.

C5a receptor-targeting ligand-mediated delivery of dengue virus antigen to M cells evokes antigen-specific systemic and mucosal immune responses in oral immunization

Oral mucosal immunization is a feasible and economic vaccination strategy. In order to achieve a successful oral mucosal vaccination, antigen delivery to gut immune inductive site and avoidance of oral tolerance induction should be secured. One promising approach is exploring the specific molecules expressed on the apical surfaces of M cells that have potential for antigen uptake and immune stimulation. We previously identified complement 5a receptor (C5aR) expression on human M-like cells and mouse M cells and confirmed its non-redundant role as a target receptor for antigen delivery to M cells using a model antigen. Here, we applied the OmpH ligand, which is capable of targeting the ligand-conjugated antigen to M cells to induce specific mucosal and systemic immunities against the EDIII of dengue virus (DENV). Oral immunization with the EDIII-OmpH efficiently targeted the EDIII to M cells and induced EDIII-specific immune responses comparable to those induced by co-administration of EDIII with cholera toxin (CT). Also, the enhanced responses by OmpH were characterized as Th2-skewed responses. Moreover, oral immunization using EDIII-OmpH did not induce systemic tolerance against EDIII. Collectively, we suggest that OmpH-mediated targeting of antigens to M cells could be used for an efficient oral vaccination against DENV infection.

Nasal immunization with M cell-targeting ligand-conjugated ApxIIA toxin fragment induces protective immunity against Actinobacillus pleuropneumoniae infection in a murine model

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia and severe economic loss in the swine industry has been caused by the infection. Therefore, the development of an effective vaccine against the bacteria is necessary. ApxII toxin, among several virulence factors expressed by the bacteria, is considered to be a promising vaccine candidate because ApxII toxin not only accompanies cytotoxic and hemolytic activities, but is also expressed in all 15 serotypes of bacteria except serotypes 10 and 14. In this study, we identified the peptide ligand capable of targeting the ligand-conjugated ApxIIA #5 fragment antigen to nasopharynx-associated lymphoid tissue. It was found that nasal immunization with ligand-conjugated ApxIIA #5 induced efficient mucosal and systemic immune responses measured at the levels of antigen-specific antibodies, cytokine-secreting cells after antigen exposure, and antigen-specific lymphocyte proliferation. More importantly, the nasal immunization induced protective immunity against nasal challenge infection of the bacteria, which was confirmed by histopathological studies and bacterial clearance after challenge infection. Collectively, we confirmed that the ligand capable of targeting the ligand-conjugated antigen to nasopharynx-associated lymphoid tissue can be used as an effective nasal vaccine adjuvant to induce protective immunity against A. pleuropneumoniae infection.