Among these cytokine-based gene therapies, an adenovirus that expresses both interleukin (IL)-12 and granulocyte-macrophage colony-stimulating-factor (GM-CSF) has been proven to be very effective in treating several tumors

[4, 5]. However, current adenoviruses deliver constitutive IL-12 gene expression, which causes serious normal tissue toxicity [6]. GM-CSF is a growth factor capable of enhancing antitumor activity by activating dendritic cells (DCs) to improve antigen presentation. GM-CSF can also activate macrophages and induce the release of tumor necrosis factor (TNF) [7] to achieve an antitumor effect. In addition, www.selleckchem.com/products/Acadesine.html GM-CSF can indirectly stimulate T-cell activation via interleukin-1 release [8]. However, increased cellular GM-CSF expression also leads to counter-regulatory immune responses to decrease the expansion of cytotoxic T cells (Tc), thereby limiting its antitumor activity [7]. In contrast, IL-12 has been shown to exert potent immunostimulatory effects on certain helper T cells as well as cytotoxic T lymphocytes (CTL) and natural killer (NK) cells [9]. Therefore, the combined use of GM-CSF and IL-12 can counteract the counter-regulatory role of GM-CSF on Tc and increase

the immune benefits of GM-CSF. Human IL-12 is a disulfide-linked heterodimer composed of 35 and 40 kDa subunits. Preclinical studies and clinical trials of IL-12 gene therapy showed that this treatment can induce remarkable anti-tumor response in various tumors, check details including melanoma, sarcoma, and adenocarcinoma [3]. However, both preclinical and clinical tests revealed that IL-12 gene therapy can induce highly toxic side effects [3]. This is because high constitutive

IL-12 expression increases IFN-γ production [10]. Thus, IL-12 expression in gene therapy requires regulation. However, the current adenovirus coexpressing GM-CSF and IL-12 genes does not account for the regulation of IL-12. Heat-based gene regulation is a ubiquitous stress response to heat shock IKBKE in mammalian cells. Based on this feature, heat shock protein 70 promoter (hsp70B) has been widely used in gene therapy to control gene expression [6]. The pharmacokinetics of GM-CSF and IL-12 production as well as possible interactions between constitutive GM-CSF expression and heat-induced IL-12 expression should be investigated before clinical use. However, there is the dilemma that IL-12 has a restrict species-specificity. For example, human IL-12 shows no activity in animal models and mouse IL-12 has no activity in human. Although the efficacy and toxicity of sustained human IL-12 expression cannot be evaluated in an animal model, the expression pattern of the adenoviral vector must be first tested in an animal model before entering clinical trials. Currently, gene therapy with combined GM-CSF and IL-12 has been established in several kinds of tumors using adenovirus to click here express constitutive GM-CSF and IL-12 levels.