Abstract LB-132: The potential role of the multienzyme aminoacyl-tRNA synthetase complex in Th-1 immunity: implications for cancer immunotherapy
Authors: Halpert Matthew M. , Spencer David , Bhardwaj Ratan , Berens Michael E. , Decker William K. 
Published: August 2012

Abstract
Recent advances in dendritic cell (DC)-based cancer vaccines have highlighted the potential utility of arming the immune system to target neoplastic self. A strong, yet controlled, TH1 response has typically been the goal of DC-based protocols, as it is cell-based adaptive immunity that possesses the ability to most-efficiently destroy the nascent tumor or occult micrometastases. Nonetheless, many DC-intrinsic factors have impeded the development of a vaccine strong enough to impart meaningful clinical results, and there remains a need for further study of the parameters required for maximal, targeted DC activity. Previously, we have shown that contemporaneous loading of DC with overlapping MHC class I and MHC class II peptide antigens leads to an enhanced TH1 response when compared to canonical DC stimulation as assayed by release of IL-12, sCTLA-4, proliferation of CD8+ CD25+, INF-γ release, and specific killing of target both in vitro and in vivo. These and other data have lead to the hypothesis that DC possess a sensor mechanism capable of discerning amino acid sequence similarities between peptides bound by MHC class I and class II and that tRNA synthetases may serve as critical components of the putative recognition machinery due to their inherent ability to recognize and distinguish between individual amino acid side chains. Here we report that the aminoacyl-tRNA synthetase complex (MACS), a large molecular complex comprised of at least nine aminoacyl-tRNA synthetases, possess interesting characteristics that might link it to this phenomenon. Components of the MACS complex, including the p43 structural subunit, were found in DC exosomes, the contents of which mimic those of the late endosome, a known cross-presentation compartment. MARS (methionyl-tRNA synthetase), a component of the MACS, as well as non-MACS components VARS (valyl-tRNA synthetase) and GARS (glycyl-tRNA synthetase) were found within exosomes as well. UVC cross-linking of exosomal extracts resulted in the incorporation of individual tRNA-synthetase isoforms into a very large complex of indeterminate size. p43 was differentially released from the MACS in response to the loading of DC only with matched class I (GFP mRNA) and class II (recombinant GFP protein) determinants. siRNA knockdown of MACS structural component p38 was able to ablate the ability of doubly-loaded DC to enhance the generation of CD8+CD25+ cells as well as the ability of these cells to secrete IFN-γ. Further, siRNA knockdown of p38 abrogated the release of p43 from DC loaded with matched class I and II determinants. With an enhanced understanding of these regulatory phenomena, the development of small molecule TH1 agonists and/or immunotherapeutic protocols with enhanced clinical efficacy become realistic and achievable goals.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-132. doi:1538-7445.AM2012-LB-132