DNA tattoo vaccination: effect on plasmid purity and transfection efficiency of different topoisoforms

Recently, DNA tattooing was introduced as novel intradermal administration technique for plasmid DNA (pDNA) vaccines. The aim of this study was to determine if tattooing affects the integrity of pDNA (reduction in supercoiled (SC) content) and whether a change in pDNA topology would affect antigen expression and immune response. We show that 1.) in vitro tattooing of pDNA solutions results in minor damage to pDNA (<or=3% SC pDNA reduction) and only open circular (OC) pDNA formation, 2.) antigen expression and T-cell responses upon tattoo administration of SC and OC pDNA are equal in a murine model, 3.) SC pDNA gives a significantly higher antigen expression than OC and linear pDNA in ex vivo human skin, 4.) pDNA topology does not influence antigen expression when formulated as PEGylated polyplexes. We conclude that a 3% reduction in SC purity most likely will have little or no effect on clinical antigen expression and T-cell responses. For intradermal tattoo administration the ex vivo skin model might be more suitable than the standard murine model for distinguishing subtle alterations in antigen expression of clinical pDNA formulations. The results from this study enable justification of release and shelf-life specifications of pDNA products applied by this specific route of administration, as requested by the regulatory authorities (>or=80% SC).

GMP production of pDERMATT for vaccination against melanoma in a phase I clinical trial

For the treatment of melanoma DNA vaccines are a promising therapeutic approach. In our institute a plasmid encoding a melanoma-associated epitope (MART-1) and an immunostimulatory sequence (tetanus toxin fragment-c) termed pDERMATT was developed. In a phase I study the plasmid will be administered intradermally using a newly developed tattoo strategy to assess the toxicity and efficacy of inducing tumor-specific T-cell immunity. To facilitate this study a Good Manufacturing Practice (GMP)-compliant plasmid manufacturing process was set up and a pharmaceutical dosage form was developed. Each batch resulted in approximately 200mg plasmid DNA of a high purity >90% supercoiled DNA, an A260/280 ratio 1.80-1.95, undetectable or extremely low residual endotoxins, Escherichia coli host cell protein, RNA, and DNA. In the manufacturing process no animal derived enzymes like RNase or potentially harmful organic solvents are used. After sterile filtration the concentration of the plasmid solution is approximately 1.1mg/mL. For the scheduled phase I study a concentration of 5mg/mL is desired, and further concentration of the solution is achieved by lyophilisation. The formulation solution is composed of 1mg/mL pDERMATT and 20mg/mL sucrose in Water for Injections. Upon reconstitution with a five times smaller volume an isotonic sucrose solution containing 5mg/mL pDERMATT is obtained. Lyophilised pDERMATT is sterile with >90% supercoiled DNA, an A260-280 ratio 1.80-1.95, content 90-110% of labeled, and residual water content <2% (w/w). The product yields the predicted profile upon restriction-enzyme digestion, is highly immunogenic as confirmed in an in vivo mouse model, and stable for at least six months at 5 degrees C. We have not only developed a reproducible process to manufacture pharmaceutical grade plasmid DNA but also a stable dosage form for the use in clinical trials.