In the field of vaccine development, there is a clear need for novel, effective platforms and adjuvants that can elicit robust, multifaceted adaptive immune responses to antigenic targets. Unfortunately, many methods investigated thus far are either too toxic or too weak to induce a substantial response against difficult targets, such as tumor-associated antigens (TAAs) or antigens from highly-mutagenic pathogens. In this dissertation, we explore the use of recombinant adenovirus serotype 5 (rAd5) platforms as vaccine vectors and the ability of innate immunostimulants to act as concurrently-administered adjuvants. First, we investigated how different variations of rAd5 vectors may promote altered innate immune signaling, and downstream, improved transgene memory responses. rAd5 vectors are strong vaccine candidates due to their intrinsic immunogenicity and potent transgene expression, however, widespread pre-existing Ad5 immunity has been considered a developmental barrier to the use of traditional, first-generation (Ad5[E1-]) vectors. Recently published studies have revealed that additionally E2b-deleted rAd5 (Ad5[E1-,E2b-]) vectors circumvent anti-Ad5 immunity to induce stronger transgene-specific memory responses than Ad5[E1-] vectors, yet it is unknown why these vector differences exist. Therefore, we decided to compare Ad5[E1-] and Ad5[E1-,E2b-] vector-induced innate immune responses by using human peripheral mononuclear cell (hPBMC) samples from multiple donors. We found that Ad5[E1-,E2b-] vectors trigger higher levels of pro-inflammatory cytokine secretion and Th1-dominant gene expression; yet lowered amounts of Ad viral-derived gene expression, independent of the donors' pre-existing anti-Ad5 adaptive responses. These results suggest that Ad5[E1-,E2b-], in contrast to Ad5[E1-], vaccines do not promote activities that suppress innate immune signaling, revealing a novel way they may produce superior efficacy and safety profiles, regardless of previous Ad5 immunity.Next, we investigated if and how a recombinant profilin-like immunostimulant derived from the Eimeria tenella protozoan (rEA) may promote innate immunity during rAd5-mediated vaccination. Upon finding that rEA could trigger activation of multiple types of hematopoietic immune cells in a MyD88-dependent, but TRIF-inhibitory, manner; we created a rAd5 vector expressing rEA to test its ability to enhance CMI responses against co-injected vaccine targets. rEA is an attractive vaccine candidate due to previous clinical investigations showing it to be a safe, immunogenic agent with the ability to trigger Th1-predominant responses in vivo. Subsequently, we investigated if an rEA-expressing rAd5 (rAd5-rEA) could promote and/or alter cytotoxic memory responses towards CEA, a colorectal cancer-related TAA. We found that the addition of rAd5-rEA to an Ad-based CEA vaccine (rAd5-CEA) induced a dose-dependent increase in the potency of anti-CEA T cell and B cell responses, elevated the number of CMI- and IgG-recognized CEA-specific epitopes, and enhanced in vivo CEA-targeted cell killing, suggesting that co-injection of rAd5-rEA with a TAA-directed vaccine can substantially boost and broaden the TAA-specific memory response. Finally, we briefly discuss the use of an rAd5 expressing endoplasmic reticulum aminopeptidase 1 (ERAP1) and how different polymorphisms of this gene may promote innate immune and cellular stress signaling. Overall, these dissertation findings address how best the features of rAd5-based vectors can be utilized as vaccine models and how modulation of innate immunity can be used to direct and foster vaccine-promoting long-term memory responses.
Read
