Mucosal vaccines constitute an advantageous immunization approach to achieve broad immunization against widespread diseases; however, improvements in this field are still required to expand their exploitation. As gold nanoparticles are biocompatible and can be easily functionalized with antigens, they have been proposed as carriers for the delivery of vaccines. The study of gold nanoparticles (AuNPs) in vaccinology has been of interest for a number of research groups in recent years and important advances have been made. This review provides a summary of the AuNPs synthesis methodologies and an updated overview of the current AuNPs-based vaccines under development. The implications of these advances for the development of new mucosal vaccines as well as future prospects for the field are discussed.

During the last 25 years, the technology to produce recombinant vaccines in plant cells has evolved from modest proofs of the concept to viable technologies adopted by some companies due to significant improvements in the field. Viral-based expression strategies have importantly contributed to this success owing to high yields, short production time (which is in most cases free of tissue culture steps), and the implementation of confined processes for production under GMPs. Herein the distinct expression systems based on viral elements are analyzed. This review also presents the outlook on how these technologies have been successfully applied to the development of plant-based vaccines, some of them being in advanced stages of development. Perspectives on how viral expression systems could allow for the development of innovative oral vaccines constituted by minimally-processed plant biomass are discussed.

Genetically engineered plants can be used for the biomanufacture and delivery of oral vaccines. Although a myriad of antigens have been produced using this approach, improving our knowledge of their oral immunogenic properties is a priority as this aspect has not been well researched. Some studies have provided evidence of a higher immunogenic activity for antigens that were orally administered in the form of plant-based vaccines in comparison with conventional pure antigens. The characteristics of the plant-derived vaccines that may influence oral immunogenicity are identified and discussed in this review. Among the hypotheses explaining these immunogenic properties are the following: bioencapsulation favors antigen uptake and displays a resistance to degradation; plant metabolites exert adjuvant activity; plant compounds, such as polysaccharides, exert mucoadhesive properties; differential glycosylation conferred by the plant cell machinery enhances immunogenicity. Perspectives on how these hypotheses may be assessed are examined.

Plant glycans play a central role in vaccinology: they can serve as adjuvants and/or delivery vehicles or backbones for the synthesis of conjugated vaccines. In addition, genetic engineering is leading to the development of platforms for the production of novel polysaccharides in plant cells, an approach with relevant implications for the design of new types of vaccines. This review contains an updated outlook on this topic and provides key perspectives including a discussion on how the molecular pharming field can be linked to the production of innovative glycan-based and conjugate vaccines.

Multi-HIV, a multiepitopic protein derived from both gp120 and gp41 envelope proteins of the human immunodeficiency virus (HIV), has been proposed as a vaccine prototype capable of inducing broad immune responses, as it carries various B and T cell epitopes from several HIV strains. In this study, the immunogenic properties of a Multi-HIV expressed in tobacco chloroplasts are evaluated in test mice. BALB/c mice orally immunized with tobacco-derived Multi-HIV have elicited antibody responses, including both the V3 loop of gp120 and the ELDKWA epitope of gp41. Based on splenocyte proliferation assays, stimulation with epitopes of the C4, V3 domain of gp120, and the ELDKWA domain of gp41 elicits positive cellular responses. Furthermore, specific interferon gamma production is observed in both CD4+ and CD8+ T cells stimulated with HIV peptides. These results demonstrate that plant-derived Multi-HIV induces T helper-specific responses. Altogether, these findings illustrate the immunogenic potential of plant-derived Multi-HIV in an oral immunization scheme. The potential of this low-cost immunization approach and its implications on HIV/AIDS vaccine development are discussed.