HIV cut out: principle for a new therapy established
HIV introduces its genetic material permanently into the DNA of body cells. In particular, the white blood cells are important as permant source of dormant viral genetic information, decreasing in number by every reactivation of virus production. The teams of Joachim Hauber from the HPI and Frank Buchholz from the MPI-CBG, Hamburg, did sucessfully remove viral DNA from infected cells. “We got rid of the virus from the infected cells; nobody has done this before”, the scientists claimed.
To achieve this result they genetically engineered a recombinase, an enzyme that works like molecular scissors. Recombinases cut and paste DNA sequences at specific sites. “Naturally occurring recombinases do not recognize viral sequences and are therefore not useful for an anti-viral approach”, said Buchholz: “So we had to develop a recombinase that recognizes the viral sequence and removes the virus with precision.”
The molecular biologists started from a recombinase that naturally is found in a bacteriophage. This enzyme, termed “Cre”, does not recognize sequences from the HIV genome. Using the forces of evolution the scientists used more than 120 generation cycles to breed the enzyme “Tre”, which is now able to recognize HIV sequences.
“Although Tre has so far only been tested in tissue culture cells, this work lays the technical foundation for a novel therapeutic approach that one day might be used to eradicate the HIV from cells of infected patients” said Hauber. However, it is still a long way until this approach can be used in clinical practice. “We will first go back to the bench to further improve the enzyme and then test whether the recombinase can be delivered efficiently and safely to cells in the human body,” said Buchholz and Hauber.
Mind, if these results should be confirmed and developped successfully, an appropriate means of application of this principle in therapy would need some 10 years to reach the market, at least.
Science 29 June 2007: Vol. 316. no. 5833, pp. 1912 – 1915
HIV-1 integrates into the host chromosome and persists as a provirus flanked by long terminal repeats (LTRs). To date, treatment regimens primarily target the virus enzymes or virus-cell fusion, but not the integrated provirus. We report here the substrate-linked protein evolution of a tailored recombinase that recognizes an asymmetric sequence within an HIV-1 LTR. This evolved recombinase efficiently excised integrated HIV proviral DNA from the genome of infected cells. Although a long way from use in the clinic, we speculate that this type of technology might be adapted in future antiretroviral therapies, among other possible uses.
1 Max-Planck-Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany.
2 Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, D-20251 Hamburg, Germany.