Dexamethasone Promotes Transgene Expression and Supresses the Early Immune /Inflammatory Response in Adenovirus- Mediated Gene Delivery to Hemophilic Mice.
Authors: Othman Maha , Mazzetti Ian , Labelle Andrea , Lillicrap David 
Published: April 2020

Abstract
The major limitation of adenovirus-mediated gene therapy is the generation of immune/inflammatory responses that result in host toxicity and impair gene transfer efficiency. Adenovirus vectors (Ad) activate the innate arm of the immune response resulting in systemic inflammation and cytotoxicity to transduced tissues. In addition to these systemic effects, endothelial cell interactions play a critical role in the host response to Ad vectors. Dexamethasone (DEX) is one of the long acting corticosteroid preparations that acts as a potent anti-inflammatory and immune suppression agent with a wide variety of clinical applications. We investigated the effects of Dexamethasone as an anti-inflammatory agent on the outcome of adenoviral gene delivery of FVIII to a group of Balb/C hemophilic mice. We have used an E1/E3 deleted Ad vector expressing B domain deleted version of the canine FVIII gene under the transcriptional control of a liver-restricted promoter. All mice received 1 x 10 11 viral particles/ mouse. Dexamethasone at 1.5 mg/Kg was administered SC, 24h before adenovirus injection and the treatment regimen was continued twice a week for 4 weeks post virus administration. We compared the outcome of gene therapy in mice treated with dexamethasone (DEX+Ad group) to a group of mice that received adenovirus only (Ad only group) as well as saline and DEX only controls. We assessed the outcome of the gene therapy by measuring FVIII levels, acute liver injury by means of Alanine aminotransferase enzyme (ALT), the principal cytokine TNF alpha, platelet count and Hb levels. Compared to the Ad only group, the DEX+ Ad group showed significant elevation of FVIII expression levels at day 2, 1w, 2w and 4w post Adenovirus administration (n=3, p= 0.05, 0.002, 0.0002 and 0.005 respectively). DEX resulted in 2.7, 1.6, 2.7and 2.5 fold increase in transgene expression in these time points over the Ad only group. There was a significant reduction of TNF alpha levels 5 hours post Ad administration in the DEX+Ad group (n=3, p&lt; 0.002) when compared to the Ad only group. This corresponded to 4-fold reduction in cytokine release. With regards acute hepatotoxicity, ALT levels were significantly reduced at 1w post administration in the DEX+ Ad group Vs Ad only group. The average ALT levels represented a 5.3 fold elevation and only 1.4 fold elevation relative to the pre vector administration levels in the Ad only group Vs DEX+Ad. Dexamathasone did not appear to have a significant effect on the acute transient thrombocytopenia. In each of the DEX+Ad group and Ad only group, the reduction in platelet count at 24 h post Ad injection was significant when compared to the pre injection level (n=3, p&lt;0.01, p&lt; 0.003 respectively). Monitoring HB level over 4 weeks did not show any significant alteration with respect to the use of DEX when compared the Ad only treated mice (n=3, p: 0.09–0.4 throughout).Our results indicate a beneficial effect of coverage with Dexamethasone to prevent some of the early adverse host effects that are associated with adenovirus gene therapy. This study provides a rationale for the further assessment of this anti-inflammatory agent as a useful tool in adenovirus- based gene transfer protocols.