Expression of the SLAM Family of Receptors Adapter EAT-2 as a Novel Strategy for Enhancing Beneficial Immune Responses to Vaccine Antigens

Abstract

Recent studies have shown that activation of the signaling lymphocytic activation molecule (SLAM) family of receptors plays an important role in several aspects of immune regulation. However, translation of this knowledge into a useful clinical application has not been undertaken. One important area where SLAM-mediated immune regulation may have keen importance is in the field of vaccinology. Because SLAM signaling plays such a critical role in the innate and adaptive immunity, we endeavored to develop a strategy to improve the efficacy of vaccines by incorporation of proteins known to be important in SLAM-mediated signaling. In this study, we hypothesized that coexpression of the SLAM adapter EWS-FLI1–activated transcript 2 (EAT-2) along with a pathogen-derived Ag would facilitate induction of beneficial innate immune responses, resulting in improved induction of Ag-specific adaptive immune responses. To test this hypothesis, we used rAd5 vector-based vaccines expressing murine EAT-2, or the HIV-1–derived Ag Gag. Compared with appropriate controls, rAd5 vectors expressing EAT-2 facilitated bystander activation of NK, NKT, B, and T cells early after their administration into animals. EAT-2 overexpression also augments the expression of APC (macrophages and dendritic cells) surface markers. Indeed, this multitiered activation of the innate immune system by vaccine-mediated EAT-2 expression enhanced the induction of Ag-specific cellular immune responses. Because both mice and humans express highly conserved EAT-2 adapters, our results suggest that human vaccination strategies that specifically facilitate SLAM signaling may improve vaccine potency when targeting HIV Ags specifically, as well as numerous other vaccine targets in general.

Merck Ad5/HIV induces broad innate immune activation that predicts CD8 + T-cell responses but is attenuated by preexisting Ad5 immunity

“…5 A and B). Consistent with this association between EAT-2 expression and CD8 + T-cell responses, it was recently reported that adenoviral expression of EAT-2 as part of a vaccine strategy enhanced vaccine-induced T-cell responses (30). Because interaction network analysis of the overall CD8 + T-cell response gene set itself was found to be uninformative, we investigated whether any the gene set members are protein-protein interaction neighbors of genes belonging to MRKAd5 regulated functional modules (Fig.…”

“…One compelling component of the gene signature was EAT-2 ( Fig. 5B), which was recently reported to enhance the frequency of vaccine induced T cells when encoded in an Ad5 vector (30). Despite the striking differences in innate response kinetics between the vaccines, we also tested whether the CD8 + signature for MRKAd5/HIV was associated with CD8 + T-cell response magnitudes for YF-17D.…”

Vaccines Expressing the Innate Immune Modulator EAT-2 Elicit Potent Effector Memory T Lymphocyte Responses despite Pre-Existing Vaccine Immunity

“…Because EAT-2 is the only known SLAM-associated adaptor protein expressed in DCs and macrophages, it has been proposed that EAT-2 facilitates SLAM-dependent immunoregulatory function (such as proinflammatory cytokine expression) in these cell types (22). Based on these facts, we demonstrated that expression of EAT-2 from a vaccine platform triggers early activation of innate immune cells in vivo and consequently improved the induction of Ag-specific adaptive immune responses (19,20). Specifically, Ad vaccine-mediated EAT-2 expression improved elaboration of beneficial cytokine and chemokine responses, enhanced the early activation of NK and NKT cells, and improved APC function by upregulating the expression of maturation markers, including CD40, CD80, CD86, MHC class II, and CCR7 (19).…”

“…Specifically, Ad vaccine-mediated EAT-2 expression improved elaboration of beneficial cytokine and chemokine responses, enhanced the early activation of NK and NKT cells, and improved APC function by upregulating the expression of maturation markers, including CD40, CD80, CD86, MHC class II, and CCR7 (19). Improvements in innate immune system recruitment correlated with induction of superior cytolytic CD8 + T cell-mediated immune responses to several Ags, including HIV-1/Gag (19) and the malaria circumsporozoite protein (20).…”

“…We have previously reported that an rAd5-based vaccine platform that expresses the signaling lymphocyte activation molecule (SLAM) family of receptors adaptor molecule, EAT-2, have superior qualities relative to current generation rAd5-based vaccines (19,20). In recent years, there has been accumulating evidence implicating a critical role for SLAM family of receptors and signaling lymphocyte activation molecule-associated protein (SAP) family of adaptors in regulating both innate and adaptive immunity (21).…”