Per-Oral Immunization with Antigen-Conjugated Nanoparticles followed by Sub-Cutaneous Boosting Immunization Induces Long-Lasting Mucosal and Systemic Antibody Responses in Mice

Abstract

Food or water-borne enteric pathogens invade their hosts via intestinal mucosal surfaces, thus developing effective oral vaccines would greatly reduce the burden of infectious diseases. The nature of the antigen, as well as the mode of its internalization in the intestinal mucosa affects the ensuing immune response. We show that model protein antigen ovalbumin (Ova) given per-orally (p.o.) induces oral tolerance (OT), characterized by systemic IgG1—dominated antibody response, which cannot be boosted by sub-cutaneous (s.c.) immunization with Ova in complete Freund’s adjuvant (CFA). Intestinal IgA generated in response to Ova feeding diminished over time and was abrogated by s.c. immunization with Ova+CFA. Humoral response to Ova was altered by administering Ova conjugated to 20 nm nanoparticles (NP-Ova). P.o. administration of NP-Ova induced systemic IgG1/IgG2c, and primed the intestinal mucosa for secretion of IgA. These responses were boosted by secondary s.c. immunization with Ova+CFA or p.o. immunization with NP-Ova. However, only in s.c.-boosted mice serum and mucosal antibody titers remained elevated for 6 months after priming. In contrast, s.c. priming with NP-Ova induced IgG1-dominated serum antibodies, but did not prime the intestinal mucosa for secretion of IgA, even after secondary p.o. immunization with NP-Ova. These results indicate that Ova conjugated to NPs reaches the internal milieu in an immunogenic form and that mucosal immunization with NP-Ova is necessary for induction of a polarized Th1/Th2 immune response, as well as intestinal IgA response. In addition, mucosal priming with NP-Ova, followed by s.c. boosting induces superior systemic and mucosal memory responses. These findings are important for the development of efficacious mucosal vaccines.

Immunogenicity of antigen‐conjugated biodegradable polydiacetylene liposomes administered mucosally

“…priming and p.o. boosting immunization . These findings highlight the fact that in addition to the NP size, antigen administration route and prime‐boost immunization strategy are critical determinants of NP immunogenicity.…”

“…NPs larger than 200 nm have been mostly used for antigen and drug delivery because they can carry a large amount of cargo. In regard to antigen delivery, studies showing superior immunogenicity of both large and small NPs have been published, however, due to the varying properties of NPs used in these studies (such as NP chemistry, charge, antigen encapsulation, NP rigidity, and so forth), it is difficult to draw a definitive conclusion that NP size alone determines their immunogenicity. Moreover, NPs have been used in various prime‐boost immunization schemes, and are administered with (or without) adjuvants, thus additionally affecting their immunogenicity and making comparisons between studies even more challenging.…”

“…Ova‐conjugated NPs (∼40 nm) administered intradermally induce superior cellular and humoral immune responses compared to larger particles . Using Ova‐conjugated polystyrene NPs (NP‐Ova), it was shown that s.c. NP‐Ova administration without adjuvants induces high serum IgG1 antibody titers, while mucosal NP‐Ova administration induces mixed serum IgG1/IgG2c titers and primes the intestinal mucosa for secretion of IgA . Most importantly, mucosal priming followed by s.c. boosting induced superior systemic and mucosal memory compared to p.o.…”

“…These findings highlight the fact that in addition to the NP size, antigen administration route and prime‐boost immunization strategy are critical determinants of NP immunogenicity. Although polystyrene NPs were shown to be very immunogenic and exhibited no obvious detrimental or toxic effects in immunized mice, polystyrene NPs are not suitable for vaccine development due to potential toxic effects of styrenes which may be released in vaccinated animals . In addition, non‐biodegradable NPs may exert long‐term detrimental effects by accumulating in tissues of immunized animals, or by blocking blood and lymphatic flow.…”

What Makes A Bacterial Oral Vaccine a Strong Inducer of High-Affinity IgA Responses?

“…Howe et al [70] recently demonstrated that while high doses of soluble OVA administered orally induced oral tolerance, OVA-coated nanoparticles (NP-OVA) induced systemic IgG1/IgG2c as well as high-affinity sIgA responses. These responses were boosted by subcutaneous injections of OVA + CFA or oral NP-OVA.…”