Laser delivers DNA

PHILIP BALL

DNA-injected cells glowed green. source: Nature

Lasers can open a temporary doorway into cells so that DNA can get inside, researchers in Germany report. This technique might hasten gene therapy by making it easier to get new genes into living cells without harming them.

It could also be useful for DNA vaccination. This new method for fighting viral, bacterial and parasitic infection provides cells with the genes to produce an immune response.

Uday Tirlapur and Karsten Konig of the Friedrich Schiller University in Jena used an infrared laser to cut a hole in mammal cells, letting in a loop of DNA. The DNA encoded a protein that glows green, so they were able to track the DNA because it turned the cells green¹. The cells went on to grow and divide normally.

The researchers transferred DNA into every one of the cells they hit using a series of ultrashort laser pulses. Cells that did not receive this laser surgery did not produce the glowing protein.

This efficiency and selectivity is a dramatic improvement over existing methods for getting DNA into cells. One of the most common techniques, electroporation, uses electricity pulses to render cell membranes temporarily permeable. It can't target individual cells, and the transfer isn't perfect.

Another approach involves hitching the gene to something that can attach to and breach the cell membrane - a virus modified to be harmless, for example. Viruses naturally invade this way, injecting their genetic material into cells and appropriating their replication machinery. But again, it is very hard to make viruses selective or 100% efficient.

Gene therapy - the addition of certain genes to cells that lack them, or that have faulty versions - relies on getting DNA across the cell membrane. If methods for doing this can be perfected, many genetically based diseases could become far easier to treat.

Lasers have been used before to usher DNA, even sperm, into cells. Previous studies used pulses of ultraviolet laser light lasting a few billionths of a second. These damaged cells irreparably.

Tirlapur and Konig use mild pulses a million times shorter. Their high-power beam has a wavelength in the near-infrared part of the spectrum, just beyond red light. Cells exposed to this laser take up DNA without suffering any apparent damage.

1. Tirlapur, U. K. & Konig, K.. Targeted transfection by femtosecond laser. Nature, 418, 290 - 291, (2002).

© Nature News Service / Macmillan Magazines Ltd 2002