STAT5 is an additional transcription factor activated in response to a variety of cytokines and growth factors and is also involved in the activation of DC and macrophages (Hennighausen and Robinson, 2008). the induction of the MAP kinase pathway, the phosphorylation of STAT1, STAT5 and AKT and with transcription factor NF-B activationin vitroandin vivo. These results thus provide important insights into the mechanisms by which CRCL-based vaccines exert their adjuvant effects on antigen presenting cells. Keywords:Tumor vaccines, Dendritic cells, Macrophages, Cell signaling == Introduction == Heat shock proteins (HSP), also known as stress proteins or chaperone proteins, are the most abundant intracellular proteins present in all living organisms (Smith et al., 1998). They display a multitude of housekeeping functions, including the folding of nascent polypeptides, refolding of denatured proteins and stabilizing proteins against aggregation and intracellular transport. Chaperone proteins are essential for cellular survival and for protecting cells from a variety of damaging environments. Purified individual tumor-derived chaperone proteins such CDDO-EA as HSP 70, HSP 90, GRP94/gp96, and calreticulin (CRT) have also shown promise as vaccines which are capable of generating tumor-specific T cell responses leading to protective anti-cancer immunity (Heike et al., 1999;Li, 1997;Srivastava and Amato, 2001;Srivastava et al., 1998;Wells and Malkovsky, 2000). The underlying principle for the use of chaperone proteins as vaccines is based on their intrinsic function as intracellular carriers of antigenic peptides. The capture of chaperone proteins and their associated antigenic peptides by antigen presenting cells (APC) may foster the delivery of these peptides into the antigen-processing pathways and may lead to their MHC-dependent presentation to T cells (Li et al., 2002;Srivastava, 2002a;Srivastava, 2002b). Some groups have reported that chaperone proteins may also act as natural adjuvants or danger signals that are capable of activating antigen-presenting cells (Segal et al., 2006;Srivastava et al., 1998). This effect has however been disputed by other studies suggesting that endotoxin contamination or LPS binding to chaperone proteins purified from tissues may play a major role in APC activation (Gao and Tsan, 2003;Nicchitta, 2003;Radsak et al., 2003;Reed et al., 2003;Wallin et al., 2002). A cancer cell-based vaccine has been developed in our laboratory which consists of CDDO-EA tumor lysates enriched for the major immunogenic chaperone proteins using a free solution-isoelectric focusing technique (FS-IEF) (Graner et al., 2000a;Graner et al., 2004;Zeng et al., 2006). The enriched, tumor-derived chaperone proteins form large, multi-chaperone complexes termed Chaperone Rich Cell Lysate(s) (CRCL) that contain the HSP90 and HSP70 family members, the endoplasmic reticulum chaperones glucose regulated protein (GRP)94/glycoprotein (gp)96, and calreticulin (Graner et al., 2000a;Graner et al., 2000b;Graner et al., 2003;Zeng et al., 2006). CRCL is thus different from conventional individually purified chaperone preparation used as vaccine. In numerous animal models, CRCL demonstrated a more pronounced anti-tumor effect per unit material of protein than the individual purified chaperone protein alone (Graner et al., 2000a;Graner et al., 2000b;Graner et al., 2003;Zeng et al., 2003). CRCL elicited specific T cell responses resulting in tumor regression (Graner et al., 2000a;Graner et al., 2000b;Graner et al., 2003). Previous results have indicated that the efficacy of this vaccine stems in part from its ability to induce dendritic CDDO-EA cell (DC) activation through upregulation of CD40 expression and IL-12 production (Zeng et al., 2003). The objective of this study was to identify the main signaling events and modifications associated with CRCL-induced activation of APC. We herein demonstrate that tumor-derived CRCL, in addition to triggering DC pro-inflammatory Rabbit Polyclonal to ARMX1 cytokine secretion also promotes the upregulation of the recently described co-stimulatory molecule, CD70. In addition, CRCL stimulates the direct tumor killing activity of macrophages, which is associated with inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production. The CDDO-EA molecular CDDO-EA signaling events associated with CRCL-mediated activation of APC involve the induction of the MAP kinase pathway evidenced by increased phosphorylation of ERK1/2 and p38, the activation of the transcription factor NF-B and the phosphorylation.