Viruses are increasingly being used as delivery vectors in the pharmaceutical industry, for example to deliver genes to cells or DNA sequences that function as vaccines. But formulating them so that the virus' activity is retained presents considerable challenges.

One problem is that lyophilisation or freeze-drying - the most commonly used method for handling complex molecules - has been avoided with viruses because of the risk that small particles (aerosols) of virus could be released into the air, running the risk that production staff could be exposed to the vector.

One viral delivery system - adeno-associated virus (AAV) - has become a popular choice because it is stable enough to allow other formulation approaches to be used, in addition to the fact that it readily infects non-dividing cells (unlike retroviruses for example) and is not associated with any human disease.

However, despite its stability, AAV has proved difficult to formulate because it is surprisingly sensitive to a number of different factors, such as the nature of the container, the constituents of the formulation, the temperature of the formulation, as well as changes in temperature, and the concentration of the AAV particles (virions) stored.

Now, gene therapy specialist Avigen has been awarded a US patent on a new system that uses a variety of excipients to increase the stability of the virus particles even further. And the result of this should be a longer shelf-life, more active virions in the presentation and ultimately a higher rate of transduction - the successful delivery of actively-expressing genetic material into the patient.

The patent describes a number of compositions that provide protection against loss of recombinant AAV vector activity and transduceability under conditions such as exposure to cycles of freezing and thawing and storage in glass or polypropylene vials.

The compositions comprise recombinant AAV virions in combination with one or more dihydric or polyhydric alcohols, and, optionally, a detergent, such as a sorbitan ester.