Chitosan-based delivery systems for mucosal vaccines

Introduction: Mucosal vaccine development faces several challenges and opportunities. Critical issues for effective mucosal vaccination include the antigen-retention period that enables interaction with the lymphatic system, choice of adjuvant that is nontoxic and induces the required immune response and possibly an ability to mimic mucosal pathogens. Chitosan-based delivery systems are reviewed here as they address these issues and hence represent the most promising candidates for the delivery of mucosal vaccines.

Areas covered: A comprehensive literature search was conducted, to locate relevant studies published within the last 5 years. Mucosal delivery via nasal and oral routes is evaluated with respect to chitosan type, dosage forms, co-adjuvanting with novel adjuvants and modulation of the immune system.

Expert opinion: It is concluded that chitosan derivatives offer advantageous opportunities such as nanoparticle and surface charge manipulation that facilitate vaccine targeting. Nevertheless, these technologies represent a longer-term goal. By contrast, chitosan (unmodified form) with or without a co-adjuvant has significant toxicology and human data to support safe mucosal administration, and thus has the potential for earlier product introduction into the market.     

Chitosan for mucosal vaccination.

The striking advantage of mucosal vaccination is the production of local antibodies at the sites where pathogens enter the body. Because vaccines alone are not sufficiently taken up after mucosal administration, they need to be co-administered with penetration enhancers, adjuvants or encapsulated in particles. Chitosan easily forms microparticles and nanoparticles which encapsulate large amounts of antigens such as ovalbumin, diphtheria toxoid or tetanus toxoid. It has been shown that ovalbumin loaded chitosan microparticles are taken up by the Peyer's patches of the gut associated lymphoid tissue (GALT). This unique uptake demonstrates that chitosan particulate drug carrier systems are promising candidates for oral vaccination. Additionally, after co-administering chitosan with antigens in nasal vaccination studies, a strong enhancement of both mucosal and systemic immune responses is observed. This makes chitosan very suitable for nasal vaccine delivery. In conclusion, chitosan particles, powders and solutions are promising candidates for mucosal vaccine delivery. Mucosal vaccination not only reduces costs and increases patient compliance, but also complicates the invasion of pathogens through mucosal sites.     

黏膜疫苗传递系统的研究进展

黏膜疫苗能同时诱导系统和局部黏膜免疫应答,是预防感染性疾病最理想的一类疫苗.但黏膜疫苗存在两大障碍:抗原无效摄取和难以引发有效免疫反应.因此,研发新型黏膜疫苗传递系统必须要克服这些障碍.本文综述了黏膜免疫的作用机制、黏膜疫苗的特点及其传递系统的研究现状.     

Bioadhesive delivery systems for mucosal vaccine delivery

Mucosal vaccine delivery potentially induces mucosal as well as systemic immune responses and may have advantages particularly for optimal protection against pathogens that infect the host through mucosal surfaces. However, the delivery of antigens through mucosal membranes remains a major challenge due to unfavorable physiological conditions (pH and enzymes) and significant biological barriers, which restrict the uptake of antigens. To improve mucosal vaccine delivery, the use of bioadhesive delivery systems offers numerous advantages, including protection from degradation, increasing concentration of antigen in the vicinity of mucosal tissue for better absorption, extending their residence time, and/or targeting them to sites of antigen uptake. Although some bioadhesives have direct immune stimulating properties, it appears most likely that successful mucosal vaccination will require the addition of vaccine adjuvants for optimal immune responses, particularly if they are to be used in an unprimed population. Thus, complex vaccine formulations and delivery strategies have to be carefully designed to appropriately stimulate immune response for the target pathogen. In addition, careful consideration is needed to define the “best” route for mucosal immunization for each individual pathogen.     

Chitosan and its derivatives in mucosal drug and vaccine delivery.

Numerous studies have demonstrated that chitosan and their derivatives (N-trimethyl chitosan, mono-N-carboxymethyl chitosan) are effective and safe absorption enhancers to improve mucosal (nasal, peroral) delivery of hydrophylic macromolecules such as peptide and protein drugs and heparins. This absorption enhancing effect of chitosans is caused by opening of the intercellular tight junctions, thereby favouring the paracellular transport of macromolecular drugs. Chitosan nano- and microparticles are also suitable for controlled drug release. Association of vaccines to some of these particulate systems has shown to enhance the antigen uptake by mucosal lymphoid tissues, thereby inducing strong systemtic and mucosal immune responses against the antigens. The aspecific adjuvant activity of chitosans seems to be dependent on the degree of deacetylation and the type of formulation. From the studies reviewed it is concluded that chitosan and chitosan derivatives are promising polymeric excipients for mucosal drug and vaccine delivery.     

Needle-free vaccine delivery

The search for methods of vaccine delivery not requiring a needle and syringe has been accelerated by recent concerns regarding pandemic disease, bioterrorism, and disease eradication campaigns. Needle-free vaccine delivery could aid in these mass vaccinations by increasing ease and speed of delivery, and by offering improved safety and compliance, decreasing costs, and reducing pain associated with vaccinations. In this article, we summarize the rationale for delivery of needle-free vaccines and discuss several methods currently in use and under development, focusing on needle-free injection devices, transcutaneous immunization, and mucosal immunization. Jet injectors are needle-free devices that deliver liquid vaccine through a nozzle orifice and penetrate the skin with a high-speed narrow stream. They generate improved or equivalent immune responses compared with needle and syringe. Powder injection, a form of jet injection using vaccines in powder form, may obviate the need for the "cold chain." Transcutaneous immunization involves applying vaccine antigen and adjuvant to the skin, using a patch or "microneedles," and can induce both systemic and mucosal immunity. Mucosal immunization has thus far been focused on oral, nasal, and aerosol vaccines. Promising newer technologies in oral vaccination include using attenuated bacteria as vectors and transgenic plant "edible" vaccines. Improved knowledge regarding the immune system and its responses to vaccination continues to inform vaccine technologies for needle-free vaccine delivery.     

Novel approaches for the induction of T helper 1 (Th1)- or Th2-type mucosal and parenteral immune responses

Mucosal surfaces are constantly challenged by micro-organisms and are protected by an integrated component of the immune system called mucosa-associated lymphoreticular tissue (MALT). The immune responses elicited at the mucosal level are regulated by T-helper (Th) cells and involve secretory IgA (S-IgA) antibodies (Abs) and cytotoxic T-lymphocytes (CTLs). Mucosal immunisation has the advantage over parenteral immunisation, of inducing S-IgA Abs and of conferring protection at both the mucosal and parenteral levels; however, administration of soluble antigens through a mucosal route very seldom results in significant mucosal and systemic immune responses. Therefore, appropriate mucosal adjuvants, recombinant bacterial and viral vectors and delivery systems have been developed to increase the immunogenicity of vaccine antigens and to preferentially induce antigen-specific T-helper (Th)1- or Th2-type responses, which in turn result in polarised effector immune responses. Understanding the mechanisms underlying Th1- and Th2-type developmental pathways and the ability of novel mucosal adjuvants and delivery systems to target the desired Th1- or Th2-type immune response would help to design effective mucosal vaccines, inducing predominant cell-mediated or humoral responses.     

Novel approaches for the induction of T helper 1 (Th1)- or Th2-type mucosal and parenteral immune responses

Mucosal surfaces are constantly challenged by micro-organisms and are protected by an integrated component of the immune system called mucosa-associated lymphoreticular tissue (MALT). The immune responses elicited at the mucosal level are regulated by T-helper (Th) cells and involve secretory IgA (S-IgA) antibodies (Abs) and cytotoxic T-lymphocytes (CTLs). Mucosal immunisation has the advantage over parenteral immunisation, of inducing S-IgA Abs and of conferring protection at both the mucosal and parenteral levels; however, administration of soluble antigens through a mucosal route very seldom results in significant mucosal and systemic immune responses. Therefore, appropriate mucosal adjuvants, recombinant bacterial and viral vectors and delivery systems have been developed to increase the immunogenicity of vaccine antigens and to preferentially induce antigen-specific T-helper (Th)1- or Th2-type responses, which in turn result in polarised effector immune responses. Understanding the mechanisms underlying Th1- and Th2-type developmental pathways and the ability of novel mucosal adjuvants and delivery systems to target the desired Th1- or Th2-type immune response would help to design effective mucosal vaccines, inducing predominant cell-mediated or humoral responses.     

Prospects for a human Toxoplasma vaccine

Human toxoplasmosis is usually benign, but may occasionally lead to severe or lethal damages when combined with immunosuppressive states or when transmitted to the fetus during pregnancy. Only a vaccine could prevent these harmful effects. The oral route is the natural portal of entry of T. gondii. A protective immune response at the mucosal level is required to kill the parasite as soon as it penetrates the intestinal barrier thus preventing toxoplasma from invading the host and settling into tissues. The probable major roles played by both CD8 T cells and antibodies, specially IgA, suggest that the best strategy would be to stimulate both the cellular and humoral arms of the mucosal immune system. Mucosal dendritic cells have been shown to induce good protection against oral toxoplasma challenge. Our hypothesis is that an acceptable and effective human vaccine would have to carry the optimized synthetic vaccine (subunit, DNA or replicon) plus an appropriate adjuvant and to target the mucosal dendritic cells by means of an inert delivery system such as polymer microparticles, which can be endocytosed by M cells of the gut or nasal-associated lymphoid tissues.     

Mucosal vaccine delivery

Vaccine development and vaccination is a major growth area of the pharmaceutical industry. As new vaccine products become available, potential will be given to physicians to provide prophylaxis for diseases that were previously not preventable, or to improve immunisation for some diseases that are currently suboptimally covered. Many factors influence vaccine effectiveness but one of the most important is the route of delivery of the product. Mucosal delivery of vaccines allows primary immunisation at the sites of the body where many of mankind’s mortality- and morbidity-causing diseases are initiated. Effective mucosal immunity is best induced by mucosal delivery of vaccines, due to the specialised and interlinked nature of the mucosal lymphoid tissues. As well as the potential for enhanced immunity, mucosal vaccine delivery is expected to increase patient compliance, make vaccines easier to use and reduce the pain, side-effects and fear of parenteral injection. However, mucosal delivery of vaccines is not straightforward and several strategies have been developed to allow for administration by the oral, nasal, rectal, genito-urinary and even pulmonary routes. These strategies include the use of live attenuated micro-organisms, attenuated toxins, bioadhesive polymers and emulsions, liposomes and proteosomes, biodegradable microparticles and immune stimulatory complexes (ISCOMS) as mucosal vaccine delivery systems/adjuvants. Details of some of the recent advances utilising these systems for mucosal antigen delivery are included in the article with a brief discussion on some of the strengths and weaknesses of the various strategies.     

Nanoparticles for nasal vaccination

The great interest in mucosal vaccine delivery arises from the fact that mucosal surfaces represent the major site of entry for many pathogens. Among other mucosal sites, nasal delivery is especially attractive for immunization, as the nasal epithelium is characterized by relatively high permeability, low enzymatic activity and by the presence of an important number of immunocompetent cells. In addition to these advantageous characteristics, the nasal route could offer simplified and more cost-effective protocols for vaccination with improved patient compliance.The use of nanocarriers provides a suitable way for the nasal delivery of antigenic molecules. Besides improved protection and facilitated transport of the antigen, nanoparticulate delivery systems could also provide more effective antigen recognition by immune cells. These represent key factors in the optimal processing and presentation of the antigen, and therefore in the subsequent development of a suitable immune response. In this sense, the design of optimized vaccine nanocarriers offers a promising way for nasal mucosal vaccination.     

Delivery strategies to enhance oral vaccination against enteric infections

While the majority of human pathogens infect the body through mucosal sites, most licensed vaccines are injectable. In fact the only mucosal vaccine that has been widely used globally for infant and childhood vaccination programs is the oral polio vaccine (OPV) developed by Albert Sabin in the 1950s. While oral vaccines against Cholera, rotavirus and Salmonella typhi have also been licensed, the development of additional non-living oral vaccines against these and other enteric pathogens has been slow and challenging. Mucosal vaccines can elicit protective immunity at the gut mucosa, in part via antigen-specific secretory immunoglobulin A (SIgA). However, despite their advantages over the injectable route, oral vaccines face many hurdles. A key challenge lies in design of delivery strategies that can protect antigens from degradation in the stomach and intestine, incorporate appropriate immune-stimulatory adjuvants and control release at the appropriate gastrointestinal site. A number of systems including micro and nanoparticles, lipid-based strategies and enteric capsules have significant potential either alone or in advanced combined formulations to enhance intestinal immune responses. In this review we will outline the opportunities, challenges and potential delivery solutions to facilitate the development of improved oral vaccines for infectious enteric diseases.     

壳聚糖衍生物在口鼻黏膜疫苗中的应用

壳聚糖是一种有效的黏膜疫苗佐剂和递送载体,但因其水溶性差,应用受到一定限制.通过对壳聚糖进行不同的化学修饰可得到各类壳聚糖衍生物,这些衍生物不仅溶解性较好,而且保持了壳聚糖良好的生物相容性、生物降解性、免疫刺激活性等优势,为黏膜疫苗,尤其是经口、鼻途径递送的疫苗提供了新型候选佐剂和递送载体.此文对修饰壳聚糖的主要方法以及其衍生物在口鼻黏膜疫苗中的应用做一综述.     

Immunoadjuvant potential of cross-linked dextran microspheres mixed with chitosan nanospheres encapsulated with tetanus toxoid

Context: Nasal mucosa is a desirable route for mucosal vaccine delivery. Mucosal co-administration of chitosan nanoparticles with absorption enhancers such as cross-linked dextran microspheres (CDM, Sephadex^®) is a promising antigen delivery system.

Objective: In the current study, the chitosan nanospheres loaded with tetanus toxoid (CHT:TT NPs) was prepared and characterized. The immune responses against tetanus toxoid after nasal administration of CHT:TT NPs alone or mixed with CDM were also determined.

Materials and methods: Chitosan nanospheres were prepared by ionic gelation method. Particle size, releasing profile and antigen stability were evaluated by dynamic light scattering, diffusion chamber and SDS-PAGE methods, respectively. Rabbits were nasally immunized with different formulations loaded with 40 Lf TT. After three times immunizations with 2 weeks intervals, sera IgG titres and nasal lavage sIgA titres were determined.

Results: Mean size of CHT NPs and CHT:TT NPs were 205?±?42?nm and 432?±?85?nm, respectively. The release profile showed that 42.4?±?10.5% of TT was released after 30?min and reached to a steady state after 1.5?h. Stability of encapsulated TT in nanospheres was confirmed by SDS-PAGE. The antibody titres showed that CHT:TT NPs-induced antibody titres were higher than TT solution. CHT NPs mixed with CDM induced the systemic IgG and nasal lavage sIgA titres higher than intranasal administration of TT solution (p?Discussion and conclusion: As the results indicated, these CHT:TT NPs when co-administered with CDM were able to induce more immune responses and have the potential to be used in mucosal immunization.     

Novel approaches to pediatric vaccine delivery

Although currently available vaccines represent an outstanding success story in modern medicine and have had a dramatic effect on morbidity and mortality worldwide, it is clear that improvements in vaccine delivery are required. Vaccine delivery improvements may include the addition of novel injectable adjuvants, or the use of novel routes of delivery, including mucosal immunization. Mucosal delivery may be required to provide protection against pathogens that infect at mucosal sites, including sexually transmitted diseases. Alternatively, novel approaches to delivery, including mucosal administration, may be used to improve compliance for existing vaccines. Of particular interest for safer mass immunization are needle-free delivery devices, which would avoid problems due to needle re-use in many parts of the world, or needle-stick injuries.     

Mucosal vaccine delivery:A focus on the breakthrough of specific barriersOA

Mucosal vaccines can effectively induce an immune response at the mucosal site and form the first line of defense against microbial invasion.The induced mucosal immunity includes the proliferation of effector T cells and the production of IgG and IgA antibodies,thereby effectively blocking microbial infection and transmis sion.However,after a long period of development,the transformation of mucosal vaccines into clinical use is still relatively slow.To date,fewer than ten mucosal vaccines have b...     

Simultaneous approach using systemic, mucosal and transcutaneous routes of immunization for development of protective HIV-1 vaccines

Mucosal tissues are major sites of HIV entry and initial infection. Induction of a local mucosal cytotoxic T lymphocyte response is considered an important goal in developing an effective HIV vaccine. In addition, activation and recruitment of memory CD4(+) and CD8(+) T cells in systemic lymphoid circulation to mucosal effector sites might provide the firewall needed to prevent virus spread. Therefore a vaccine that generates CD4(+) and CD8(+) responses in both mucosal and systemic tissues might be required for protection against HIV. However, optimal routes and number of vaccinations required for the generation of long lasting CD4(+) and CD8(+) CTL effector and memory responses are not well understood especially for mucosal T cells. A number of studies looking at protective immune responses against diverse mucosal pathogens have shown that mucosal vaccination is necessary to induce a compartmentalized immune response including maximum levels of mucosal high-avidity CD8(+) CTL, antigen specific mucosal antibodies titers (especially sIgA), as well as induction of innate anti-viral factors in mucosa tissue. Immune responses are detectable at mucosal sites after systemic delivery of vaccine, and prime boost regimens can amplify the magnitude of immune responses in mucosal sites and in systemic lymphoid tissues. We believe that the most optimal mucosal and systemic HIV/SIV specific protective immune responses and innate factors might best be achieved by simultaneous mucosal and systemic prime and boost vaccinations. Similar principals of vaccination may be applied for vaccine development against cancer and highly invasive pathogens that lead to chronic infection.     

Lessons from nature: “Pathogen-Mimetic” systems for mucosal Nano-medicines

Mucosal surfaces establish an interface with external environments that provide a protective barrier with the capacity to selectively absorb and secrete materials important for homeostasis of the organism. In man, mucosal surfaces such as those in the gastrointestinal tract, respiratory tree and genitourinary system also represent significant barrier to the successful administration of certain pharmaceutical agents and the delivery of newly designed nano-scale therapeutic systems. This review examines morphological, physiological and biochemical aspects of these mucosal barriers and presents currently understood mechanisms used by a variety of virulence factors used by pathogenic bacteria to overcome various aspects of these mucosal barriers. Such information emphasizes the impediments that biologically active materials must overcome for absorption across these mucosal surfaces and provides a template for strategies to overcome these barriers for the successful delivery of nano-scale bioactive materials, also known as nano-medicines.     

New patents on mucosal delivery of vaccines

Background: Noninvasive mucosal immune responses have been shown to be important in controlling various infections through the mucosal route. Therefore, the appropriate induction of humoral, mucosal and cellular immune response should be elicited after immunization. Objective: The objective of this review is to give an overview of novel strategies and patents for the delivery of vaccines through the mucosal route. Method: Different strategies have been developed and patented to facilitate and enhance the mucosal immunity, including the use of lipid-based delivery systems (i.e., liposomes, virosomes, archaeosomes, chochleated, immune stimulating complexes), entrapment/encapsulation of immunogens into polymeric matrix (poly(lactide-co-glycolide), chitosan, alginates, carbopol, gelatin etc.), admixing of immunogens with mucosal adjuvants (cholera toxin or CT, enterotoxin, lipid A, tetanus toxin or lymphotactin), use of live attenuated bacterial and viral vector encoding antigen of interest and ingestible plant-based mucosal vaccines. Conclusion: Lipid- and polymer-based novel delivery systems have been widely investigated in mucosal vaccine delivery systems. Recent advancement in the molecular technology has also shown great potential of genetic immunization for the delivery of wide range of infectious molecular targets. Effective and selective delivery of vaccines through the mucosal route could provide new therapeutic conduit in the treatment of mucous-associated disease.     

Novel Approaches to Vaccine Delivery

Although the currently available vaccines represent an outstanding success story in modern medicine and have had a dramatic effect on morbidity and mortality worldwide, it is clear that improvements are required in the current vaccine delivery technologies. Improvements are required to enable the successful development of vaccines against infectious diseases that have so far proven difficult to control with conventional approaches. Improvements may include the addition of novel injectable adjuvants or the use of novel routes of delivery, including mucosal immunization. Mucosal delivery may be required to provide protection against pathogens that infect at mucosal sites, including sexually transmitted diseases. Alternatively, novel approaches to delivery, including mucosal administration, may be used to improve compliance for existing vaccines. Of particular interest for safer mass immunization campaigns are needle-free delivery devices, which would avoid problems due to needle re-use in many parts of the world and would avoid needle-stick injuries.