The release of inflammatory Cytokines from human peripheral blood mononuclear cells in vitro following exposure to adenovirus variants and capsid

Preclinical and clinical studies with adenoviral vectors have clearly illustrated the potential advantages of this gene transfer system. However, many studies have also demonstrated potent immune responses directed at both vector and transduced cells. We examined in vitro responses of human peripheral blood mononuclear cells (PBMC) to virus exposure as a model for this host response. PBMC were isolated from normal donors and incubated with wild-type adenovirus (Ad5), Ad5 variants deleted for segments of E1 and/or E3, and empty viral capsids. Proinflammatory cytokine release was monitored for 96 hr. Induction of TNF-alpha by intact virions was low although stimulation by empty capsid gave a significant and sustained response. Induction of IL-6, GM-CSF, and a panel alpha- and beta-chemokines by intact virions was prominent, often approaching results obtained with 2.5 mg/ml of lipopolysaccharide (LPS). Responses were generally independent of virion genetic composition and were only partially blunted when UV-inactivated virus was used. Dose-response data showed 100-fold increases in virion concentration produced a maximum 3-fold increase in cytokine release, suggesting saturation. Surprisingly, prominent stimulation occurred after addition of empty capsid, which typically provoked responses equivalent to those seen with LPS stimulation. We present arguments that cellular signal transduction mechanisms activated by binding of virions/capsids stimulate transcription of proinflammatory cytokine genes.