Abstract
Therapeutic DNA-based vaccines aim to prime an adaptive host immune response against tumor-associated antigens, eliminating cancer cells primarily through CD8+ cytotoxic T cell-mediated destruction. To be optimally effective, immunological adjuvants are required for the activation of tumor-specific CD8+ T cells responses by DNA vaccination. Here, we describe enhanced anti-tumor efficacy of an in vivo electroporation-delivered DNA vaccine by inclusion of a genetically encoded chimeric MyD88/CD40 (MC) adjuvant, which integrates both innate and adaptive immune signaling pathways. When incorporated into a DNA vaccine, signaling by the MC adjuvant increased antigen-specific CD8+ T cells and promoted elimination of pre-established tumors. Interestingly, MC-enhanced vaccine efficacy did not require direct-expression of either antigen or adjuvant by local antigen-presenting cells, but rather our data supports a key role for MC function in “atypical” antigen-presenting cells of skin. In particular, MC adjuvant-modified keratinocytes increased inflammatory cytokine secretion, upregulated surface MHC class I, and were able to increase in vitro and in vivo priming of antigen-specific CD8+ T cells. Furthermore, in the absence of critical CD8α+/CD103+ cross-priming dendritic cells, MC was still able to promote immune priming in vivo, albeit at a reduced level. Altogether, our data support a mechanism by which MC signaling activates an inflammatory phenotype in atypical antigen-presenting cells within the cutaneous vaccination site, leading to an enhanced CD8+ T cell response against DNA vaccine-encoded antigens, through both CD8α+/CD103+ dendritic cell-dependent and independent pathways.
Highlights
Though once nothing more than background noise, immunotherapies have jumped to the forefront of cutting-edge medicine in recent years, treating a variety of diseases including autoimmunity, atopic disorders, and malignancies
We describe the in vivo action of MC adjuvant when expressed in cutaneous nonhematopoietic cell types present at the site of vaccine administration, revealing both a CD8α+/ CD103+ dendritic cells (DCs)-dependent and independent mechanism, overall demonstrating an important immunological contribution of MC signaling in atypical Ag-presenting cell (APC) to the vaccine-mediated augmentation of anti-TAg cytotoxic T cell responses
Since the membrane-localized MyD88/CD40 (MC) fusion protein is capable of propagating both toll-like receptor (TLR)/IL1 Receptor-α and CD40 signaling pathways, we hypothesized that MC could function as an effective adjuvant in EP-mediate DNA vaccines
Summary
Though once nothing more than background noise, immunotherapies have jumped to the forefront of cutting-edge medicine in recent years, treating a variety of diseases including autoimmunity, atopic disorders, and malignancies. Therapeutic cancer vaccines have garnered much attention, theorizing that the generation of de novo immune responses to tumor-specific targets could exploit the full and complex breadth of cell types and secreted factors of the immune system to combat malignant disease [1]. Recent clinical trials of cancer vaccines have supported their potential; the results have been modest in most cases and key questions remain to be answered at both the bench and bedside [1,2]. Due to its versatility and relatively low cost, DNA-based vaccine approaches were introduced in the early 1990s, to modulate humoral and cellular immunity, and extensive research to increase efficacy has followed, in particular through the design of novel immunological adjuvants [4,5]. In addition to co-injection of soluble adjuvants, DNA vaccines can substitute genetically encoded, immune modulatory components into the vaccine cocktail, such as cytokines (e.g., GM-CSF), chemokines, and immune stimulatory signaling molecules (e.g., CD80), allowing for extended production of adjuvant in situ, typically in the skin or muscle [6,7,8,9]
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