Search

Peptide and protein-based cancer vaccines usually fail to elicit efficient immune responses against tumors. However, delivery of these peptides and proteins as components within caged protein nanoparticles has shown promising improvements in vaccine efficacy. Advantages of protein nanoparticles over other vaccine platforms include their highly organized structures and symmetry, biodegradability, ability to specifically functionalize at three different interfaces (inside, outside, and between subunits in macromolecular assembly), and ideal size for vaccine delivery. In this review, we discuss different classes of virus-like particles and caged protein nanoparticles that have been used as vehicles to deliver and increase the interaction of cancer vaccine components with the immune system. We review the effectiveness of these protein nanoparticles towards inducing and elevating specific immune responses, which are needed to overcome the low immunogenicity of the tumor microenvironment. TEXT FOR GRAPHICAL ABSTRACT: In this review, we discuss several different protein-based nanoparticles as delivery vehicles to increase the interaction of cancer vaccine components (e.g., adjuvants, tumor-associated antigens) with the immune system. These important components can be efficiently internalized and processed by dendritic cells, which then present the antigen to the T cells for specific T cell responses that lead to specific tumor lysis and elimination. The elevated immune responses that are elicited by these nanoparticle vaccines are advantageous to overcome the low immunogenicity of the tumor microenvironment.

Immune checkpoint inhibition is a promising alternative treatment to standard chemotherapies; however, it fails to achieve long-term remission in a significant portion of patients. A previously developed protein nanoparticle-based platform (E2 nanoparticle) delivers cancer antigens to increase antigen-specific tumor responses. While prior work has focussed on prophylactic conditions, the objectives in this study are therapeutic. It is hypothesized that immune checkpoint inhibition, when augmented by antigen delivery using E2 nanoparticles containing CpG oligonucleotide 1826 (CpG) and a glycoprotein 100 (gp100) melanoma antigen epitope (CpG-gp-E2), would synergistically elicit antitumor responses. To identify a regimen primed for obtaining effective treatment results, immune benchmarks in the spleen and tumor are examined. Conditions that lead to significant immune activation, including increases in gp100-specific interferon gamma (IFN-𝜸), CD8 T cells in the spleen, tumor-infiltrating CD8 T cells, and survival time are identified. Based on the findings, the resulting combination of CpG-gp-E2 and anti-programmed cell death protein 1 (anti-PD-1) treatment in tumor-challenged mice yield significantly increased long-term survival; more than 50% of the mice treated with combination therapy were tumor-free, compared with 0% and ≈5% for CpG-gp-E2 and anti-PD-1 alone, respectively. Evidence of a durable antitumor response is also observed upon tumor rechallenge, pointing to long-lasting immune memory.

We have developed a novel, non-viral nanoparticle-based vaccine platform that has shown exciting promise for cancer antigen delivery to increase antigen-specific anti-tumor immune responses and significantly prolong survival in the aggressive B16-F10 melanoma model. Our non-viral protein nanoparticle has advantageous properties for antigen delivery and vaccine development. Nanoparticle studies have shown that there is an optimal size range for passive transport in the lymphatic system and uptake by antigen-presenting cells (approximately 20-45 nm); our particle is in this size range. Biodistribution studies of the nanoparticle have shown that they are effectively taken up by almost 50% of DCs within the draining lymph nodes. The structure of the nanoparticle allows for independent functionalization of its internal hollow cavity and external surface, enabling efficient and simultaneous adjuvant and antigen co-delivery. We, as have others, found that vaccine-elicited anti-tumor immune responses are insufficient to cure animals in this model.Immune checkpoint inhibition has provided significant clinical benefit and become an effective alternative treatment to standard chemotherapies in some tumor types. It is believed that immune checkpoint inhibition releases the brake on the existing anti-tumor immune response; however, even in the tumor types where there is clinical benefit, a significant proportion of patients fail to achieve long-term remission. We hypothesized that the combination of our anti-tumor protein nanoparticle vaccine ("E2"; to further prime the immune system to specific tumor-associated antigens) and immune checkpoint blockade will be synergistic and yield improved efficacy, even in the aggressive B16-F10 melanoma tumor model. Immunization with simultaneous delivery of CpG (adjuvant) and gp100 (melanoma MHC-I restricted antigen) within E2 nanoparticles results in significantly increased gp100-specific IFN-γ production by ELISpot, CD8 T cell count in the spleen, tumor-infiltrating CD8 T cell population, and survival time in the B16-F10 murine melanoma model. The combination of the CpG-gp-E2 nanoparticle with anti-PD-1 therapy significantly increased long-term survival; approximately 50% of the mice treated with combination therapy remained tumor-free for up to 60 days (cure) in mice that were inoculated with the poorly immunogenic B16-F10 syngeneic melanoma 24 hours prior to initiating treatment; this is compared with 0% and ≈5% for CpG-gp-E2 and anti-PD-1 treatments alone, respectively. The very limited efficacy of immune checkpoint inhibition in this model is well documented. Thus, this result is more significant. Evidence of a durable anti-tumor response was also observed upon tumor re-challenge. These investigations show that the combination of checkpoint inhibition with antigen delivery using a non-viral protein nanoparticle significantly improves the efficacy over vaccine or immune checkpoint blockade alone.To our knowledge, this is the first report demonstrating the synergistic effects of combination therapy of anti-PD-1 with protein-based nanoparticle vaccines. These data support the exceptional utility of our E2 nanoparticle-based vaccines, especially when combined with immune checkpoint blockade. Citation Format: Jo Anne Tucker, Medea Neek, Szu-Wen Wang, Edward L. Nelson. A novel protein nanoparticle antigen delivery platform combined with checkpoint inhibition has curative efficacy in the aggressive B16-F10 melanoma model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2223.

Nanoparticles have attracted considerable interest as cancer vaccine delivery vehicles for inducing sufficient CD8+ T cell-mediated immune responses to overcome the low immunogenicity of the tumor microenvironment. Our studies described here are the first to examine the effects of clinically-tested human cancer-testis (CT) peptide epitopes within a synthetic nanoparticle. Specifically, we focused on two significant clinical CT targets, the HLA-A2 restricted epitopes of NY-ESO-1 and MAGE-A3, using a viral-mimetic packaging strategy. Our data shows that simultaneous delivery of a NY-ESO-1 epitope (SLLMWITQV) and CpG using the E2 subunit assembly of pyruvate dehydrogenase (E2 nanoparticle), resulted in a 25-fold increase in specific IFN-γ secretion in HLA-A2 transgenic mice. This translated to a 15-fold increase in lytic activity toward target cancer cells expressing the antigen. Immunization with a MAGE-A3 epitope (FLWGPRALV) delivered with CpG in E2 nanoparticles yielded an increase in specific IFN-γ secretion and cell lysis by 6-fold and 9-fold, respectively. Furthermore, combined delivery of NY-ESO-1 and MAGE-A3 antigens in E2 nanoparticles yielded an additive effect that increased lytic activity towards cells bearing NY-ESO-1+ and MAGE-A3+. Our investigations demonstrate that formulation of CT antigens within a nanoparticle can significantly enhance antigen-specific cell-mediated responses, and the combination of the two antigens in a vaccine can preserve the increased individual responses that are observed for each antigen alone.

Efficient delivery of antigens is of paramount concern in immunotherapies. We aimed to target antigen presenting cells (APCs) by conjugating CpG oligonucleotides to an E2 protein nanoparticle surface (CpG-PEG-E2). Compared to E2 alone, we observed ~4-fold increase of in vitro APC uptake of both CpG-PEG-E2 and E2 conjugated to non-CpG DNA. Furthermore, compared to E2-alone or E2 functionalized solely with polyethylene glycol (PEG), the CpG-PEG-E2 showed enhanced lymph node retention up to at least 48 hr and 2-fold increase in APC uptake in vivo, parameters which are advantageous for vaccine success. This suggests that enhanced APC uptake of nanoparticles mediated by oligonucleotide display may help overcome delivery barriers in vaccine development.

The immune system is a powerful resource for the eradication of cancer, but to overcome the low immunogenicity of tumor cells, a sufficiently strong CD8(+) T cell-mediated adaptive immune response is required. Nanoparticulate biomaterials represent a potentially effective delivery system for cancer vaccines, as they can be designed to mimic viruses, which are potent inducers of cellular immunity. We have been exploring the non-viral pyruvate dehydrogenase E2 protein nanoparticle as a biomimetic platform for cancer vaccine delivery. Simultaneous conjugation of a melanoma-associated gp100 epitope and CpG to the E2 nanoparticle (CpG-gp-E2) yielded an antigen-specific increase in the CD8(+) T cell proliferation index and IFN-γ secretion by 1.5-fold and 5-fold, respectively, compared to an unbound peptide and CpG formulation. Remarkably, a single nanoparticle immunization resulted in a 120-fold increase in the frequency of melanoma epitope-specific CD8(+) T cells in draining lymph nodes and a 30-fold increase in the spleen, relative to free peptide with free CpG. Furthermore, in the very aggressive B16 melanoma murine tumor model, prophylactic immunization with CpG-gp-E2 delayed the onset of tumor growth by approximately 5.5 days and increased animal survival time by approximately 40%, compared to PBS-treated animals. These results show that by combining optimal particle size and simultaneous co-delivery of molecular vaccine components, antigen-specific anti-tumor immune responses can be significantly increased.