Engineering Vaccines for Tissue-Resident Memory T Cells.

In recent years, tissue-resident memory T cells (TRM) have attracted significant attention in the field of vaccine development. Distinct from central and effector memory T cells, TRM cells take up residence in home tissues such as the lung or urogenital tract and are ideally positioned to respond quickly to pathogen encounter. TRM have been found to play a role in the immune response against many globally important infectious diseases for which new or improved vaccines are needed, including influenza and tuberculosis. It is also increasingly clear that TRM play a pivotal role in cancer immunity. Thus, vaccines that can generate this memory T cell population are highly desirable. The field of immunoengineering-that is, the application of engineering principles to study the immune system and design new and improved therapies that harness or modulate immune responses-is ideally poised to provide solutions to this need for next-generation TRM vaccines. This review covers recent developments in vaccine technologies for generating TRM and protecting against infection and cancer, including viral vectors, virus-like particles, and synthetic and natural biomaterials. In addition, it offers critical insights on the future of engineering vaccines for tissue-resident memory T cells.

Co-delivery of Peptide Neoantigens and Stimulator of Interferon Genes Agonists Enhances Response to Cancer Vaccines.

Cancer vaccines targeting patient-specific neoantigens have emerged as a promising strategy for improving responses to immune checkpoint blockade. However, neoantigenic peptides are poorly immunogenic and inept at stimulating CD8+ T cell responses, motivating a need for new vaccine technologies that enhance their immunogenicity. The stimulator of interferon genes (STING) pathway is an endogenous mechanism by which the innate immune system generates an immunological context for priming and mobilizing neoantigen-specific T cells. Owing to this critical role in tumor immune surveillance, a synthetic cancer nanovaccine platform (nanoSTING-vax) was developed that mimics immunogenic cancer cells in its capacity to efficiently promote co-delivery of peptide antigens and the STING agonist, cGAMP. The co-loading of cGAMP and peptides into pH-responsive, endosomolytic polymersomes promoted the coordinated delivery of both cGAMP and peptide antigens to the cytosol, thereby eliciting inflammatory cytokine production, co-stimulatory marker expression, and antigen cross-presentation. Consequently, nanoSTING-vax significantly enhanced CD8+ T cell responses to a range of peptide antigens. Therapeutic immunization with nanoSTING-vax, in combination with immune checkpoint blockade, inhibited tumor growth in multiple murine tumor models, even leading to complete tumor rejection and generation of durable antitumor immune memory. Collectively, this work establishes nanoSTING-vax as a versatile platform for enhancing immune responses to neoantigen-targeted cancer vaccines.

Mucosal Immunization with a pH-Responsive Nanoparticle Vaccine Induces Protective CD8+ Lung-Resident Memory T Cells.

Tissue-resident memory T cells (TRM) patrol nonlymphoid organs and provide superior protection against pathogens that commonly infect mucosal and barrier tissues, such as the lungs, intestine, liver, and skin. Thus, there is a need for vaccine technologies that can induce a robust, protective TRM response in these tissues. Nanoparticle (NP) vaccines offer important advantages over conventional vaccines; however, there has been minimal investigation into the design of NP-based vaccines for eliciting TRM responses. Here, we describe a pH-responsive polymeric nanoparticle vaccine for generating antigen-specific CD8+ TRM cells in the lungs. With a single intranasal dose, the NP vaccine elicited airway- and lung-resident CD8+ TRM cells and protected against respiratory virus challenge in both sublethal (vaccinia) and lethal (influenza) infection models for up to 9 weeks after immunization. In elucidating the contribution of material properties to the resulting TRM response, we found that the pH-responsive activity of the carrier was important, as a structurally analogous non-pH-responsive control carrier elicited significantly fewer lung-resident CD8+ T cells. We also demonstrated that dual-delivery of protein antigen and nucleic acid adjuvant on the same NP substantially enhanced the magnitude, functionality, and longevity of the antigen-specific CD8+ TRM response in the lungs. Compared to administration of soluble antigen and adjuvant, the NP also mediated retention of vaccine cargo in pulmonary antigen-presenting cells (APCs), enhanced APC activation, and increased production of TRM-related cytokines. Overall, these data suggest a promising vaccine platform technology for rapid generation of protective CD8+ TRM cells in the lungs.

Poly(propylacrylic acid)-peptide nanoplexes as a platform for enhancing the immunogenicity of neoantigen cancer vaccines.

Cancer vaccines targeting patient-specific tumor neoantigens have recently emerged as a promising component of the rapidly expanding immunotherapeutic armamentarium. However, neoantigenic peptides typically elicit weak CD8+ T cell responses, and so there is a need for universally applicable vaccine delivery strategies to enhance the immunogenicity of these peptides. Ideally, such vaccines could also be rapidly fabricated using chemically synthesized peptide antigens customized to an individual patient. Here, we describe a strategy for simple and rapid packaging of peptide antigens into pH-responsive nanoparticles with endosomal escape activity. Electrostatically-stabilized polyplex nanoparticles (nanoplexes) can be assembled instantaneously by mixing decalysine-modified antigenic peptides and poly(propylacrylic acid) (pPAA), a polyanion with pH-dependent, membrane destabilizing activity. These nanoplexes increase and prolong antigen uptake and presentation on MHC-I (major histocompatibility complex class I) molecules expressed by dendritic cells, resulting in enhanced activation of CD8+ T cells. Using an intranasal immunization route, nanoplex vaccines inhibit formation of lung metastases in a murine melanoma model. Additionally, nanoplex vaccines strongly synergize with the adjuvant α-galactosylceramide (α-GalCer) in stimulating robust CD8+ T cell responses, significantly increasing survival time in mice with established melanoma tumors. Collectively, these findings demonstrate that peptide/pPAA nanoplexes offer a facile and versatile platform for enhancing CD8+ T cell responses to peptide antigens, with potential to complement ongoing advancements in the development of neoantigen-targeted cancer vaccines.

Fatty Acid-Mimetic Micelles for Dual Delivery of Antigens and Imidazoquinoline Adjuvants.

Vaccine design has undergone a shift towards the use of purified protein subunit vaccines, which offer increased safety and greater control over antigen specificity, but at the expense of immunogenicity. Here we report the development of a new polymer-based vaccine delivery platform engineered to enhance immunity through the co-delivery of protein antigens and the Toll-like receptor 7 (TLR7) agonist imiquimod (IMQ). Owing to the preferential solubility of IMQ in fatty acids, a series of block copolymer micelles with a fatty acid-mimetic core comprising lauryl methacrylate (LMA) and methacrylic acid (MAA), and a poly(ethylene glycol) methyl ether methacrylate (PEGMA) corona decorated with pyridyl disulfide ethyl methacrylate (PDSM) moieties for antigen conjugation were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Carriers composed of 50 mole% LMA (LMA50) demonstrated the highest IMQ loading (2.2 w/w%) and significantly enhanced the immunostimulatory capacity of IMQ to induce dendritic cell maturation and proinflammatory cytokine production. Conjugation of a model antigen, ovalbumin (OVA), to the corona of IMQ-loaded LMA50 micelles enhanced in vitro antigen uptake and cross-presentation on MHC class I (MHC-I). A single intranasal (IN) immunization of mice with carriers co-loaded with IMQ and OVA elicited significantly higher pulmonary and systemic CD8+ T cell responses and increased serum IgG titer relative to a soluble formulation of antigen and adjuvant. Collectively, these data demonstrate that rationally designed fatty acid-mimetic micelles enhance intracellular antigen and IMQ delivery and have potential as synthetic vectors for enhancing the immunogenicity of subunit vaccines.

Eliciting Epitope-Specific CD8+ T Cell Response by Immunization with Microbial Protein Antigens Formulated with α-Galactosylceramide: Theory, Practice, and Protocols.

CD8+ cytotoxic T lymphocytes confer protection against infectious diseases caused by viruses, bacteria, and parasites. Hence, significant efforts have been invested into devising ways to generate CD8+ T cell-targeted vaccines. Generation of microbe-free protein subunit vaccines requires a thorough knowledge of protective target antigens. Such antigens are proteolytically processed peptides presented by MHC class I molecules. To induce a robust antigen-specific CD8+ T cell response through vaccination, it is essential to formulate the antigen with an effective adjuvant. Here, we describe a versatile method for generating high-frequency antigen-specific CD8+ T cells through immunization of mice using the invariant natural killer T cell agonist α-galactosylceramide as the adjuvant.

Synthesis and characterization of a poly(lactic-co-glycolic acid) core + poly(N-isopropylacrylamide) shell nanoparticle system.

Poly(lactic-co-glycolic acid) (PLGA) is a popular material used to prepare nanoparticles for drug delivery. However, PLGA nanoparticles lack desirable attributes including active targeting abilities, resistance to aggregation during lyophilization, and the ability to respond to dynamic environmental stimuli. To overcome these issues, we fabricated a nanoparticle consisting of a PLGA core encapsulated within a shell of poly(N-isopropylacrylamide). Dynamic light scattering and transmission electron microscope imaging were used to characterize the nanoparticles, while an MTT assay and ELISA suggested biocompatibility in THP1 cells. Finally, a collagen type II binding assay showed successful modification of these nanoparticles with an active targeting moiety.