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Journal of Virology, July 2003, p. 7174-7181, Vol. 77, No. 13
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.13.7174-7181.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Sustained Small Interfering RNA-Mediated Human Immunodeficiency Virus Type 1 Inhibition in Primary Macrophages

Erwei Song,1 Sang-Kyung Lee,1 Derek M. Dykxhoorn,2 Carl Novina,2 Dong Zhang,1 Keith Crawford,1 Jan Cerny,1 Phillip A. Sharp,2,3 Judy Lieberman,1 N Manjunath,1 and Premlata Shankar1*

Center for Blood Research, Harvard Medical School, Boston, Massachusetts 02115,1 Center for Cancer Research,2 Department of Biology and McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 021393

Received 21 January 2003/ Accepted 4 April 2003

Small interfering RNAs (siRNAs) can induce potent gene silencing by degradation of cognate mRNA. However, in dividing cells, the silencing lasts only 3 to 7 days, presumably because of siRNA dilution with cell division. Here, we investigated if sustained siRNA-mediated silencing of human immunodeficiency virus type 1 (HIV-1) is possible in terminally differentiated macrophages, which constitute an important reservoir of HIV in vivo. CCR5, the major HIV-1 coreceptor in macrophages, and the viral structural gene for p24 were targeted either singly or in combination. When transfected 2 days prior to infection, both CCR5 and p24 siRNAs effectively reduced HIV-1 infection for the entire 15-day period of observation, and combined targeting of both genes abolished infection. To investigate whether exogenously introduced siRNA is maintained stably in macrophages, we tested the kinetics of siRNA-mediated viral inhibition by initiating infections at various times (2 to 15 days) after transfection with CCR5 and p24 siRNAs. HIV suppression mediated by viral p24 siRNA progressively decreased and was lost by day 7 posttransfection. In contrast, viral inhibition by cellular CCR5 knockdown was sustained even when transfection preceded infection by 15 days, suggesting that the continued presence of target RNA may be needed for persistence of siRNA. The longer sustenance of CCR5 relative to p24 siRNA in uninfected macrophages was also confirmed by detection of internalized siRNA by modified Northern blot analysis. We also tested the potential of p24 siRNA to stably silence HIV in the setting of an established infection where the viral target gene is actively transcribed. Under these circumstances, long-term suppression of HIV replication could be achieved with p24 siRNA. Thus, siRNAs can induce potent and long-lasting HIV inhibition in nondividing cells such as macrophages.

* Corresponding author. Mailing address: Center for Blood Research, 800 Huntington Ave., Boston, MA 02115. Phone: (617) 278-3476. Fax: (617) 278-3493. E-mail: shankar{at}cbr.med.harvard.edu.

Journal of Virology, July 2003, p. 7174-7181, Vol. 77, No. 13
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.13.7174-7181.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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