Improved Method for DNA Payloads Delivered into Cells

Dr. Chang Lu and his research group from Virginia Polytechnic Institute and State University (Virginia Tech; Blacksburg, USA) have published their findings in the July 8, 2010, issue of the journal Nature and in an upcoming issue of Lab on a Chip. Dr. Lu's ultimate goal is to apply this technique to generate genetically modified cells for cancer immunotherapy, stem cell therapy and tissue regeneration.

One of the most widely used physical techniques to deliver genes into cells "is incredibly inefficient because only a small fraction of a cell's total membrane surface can be permeated,” stated Dr. Lu, an associate professor of chemical engineering at Virginia Tech. The method Lu is referring to is called electroporation, a phenomenon known for years that increases the permeability of a cell by applying an electric field to generate tiny pores in the membrane of cells.

Dr. Lu called the process "a new spin on DNA delivery.” He clarified the process: "Conventional electroporation methods deliver DNA only within a very small portion of the cell surface, determined by the physics governing the interaction between an electric field and a cell. Our method enables uniform DNA delivery over the entire cell surface, which is the first time we are aware that this has been demonstrated. The result is a greatly enhanced transfer of the genetic material.”

Dr. Lu reported that his new approach harnesses "hydrodynamic effects that uniquely occur when fluids flow along curved paths. Flow under these conditions is known to generate vortices. Cells carried by such flow experience rotation and spinning that help expose the majority area of its surface to the electric field.” Having the gene delivery done by flows in curved paths is critical in the gene delivery process as opposed to the traditionally used electroporation in static solution or in straight channels. "A spiral-shaped channel design yields a two-fold increase than a straight channel and an even larger factor compared to in static solution,” he added.

By using fluorescence microscopy, the engineers were able to map the area on the cell surface that was subjected to electroporation, and determine the extent of the DNA entry into the cell. Dr. Lu explained the conventional delivery using a cuvette-type of device with static cell suspension produces DNA delivery restricted to a narrow zone on the cell surface. However, when electroporation is applied to flowing cells in a spiral or curved channel, the images "appear dramatically different with the DNA delivery uniformly distributed over the entire cell surface.”

Dr. Lu's group plans to make larger devices to exploit this phenomenon and apply them to large volume gene delivery in the near future.

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Virginia Polytechnic Institute and State University