Antiretroviral therapy (ART) quickly suppresses HIV-1 replication in patients, to nondetectable levels. However, even after years of effective ART, cessation of therapy results in the immediate rebound of viremia. This is attributed to a long-lived reservoir of latently HIV-1-infected memory CD4+ T cells (2-4). As a result of the long life span of memory T cells that serve as cellular hosts to latent HIV-1 infection, the latent HIV-1 reservoir is extremely stable. Natural eradication in the absence of any replenishment of the reservoir by de novo infection events is predicted to take about 70 years (26). Since natural depletion of the latent reservoir is unlikely to be achievable, HIV-1 latency is believed to represent the principal obstacle to curative AIDS therapy (2-9). Strategies to purge this viral reservoir will have to be included in any HIV-1 therapy with curative intent. Based on the molecular understanding of HIV-1 latency, several attempts to therapeutically deplete the latent HIV-1 reservoir by activating the integrated but transcriptionally silent viral promoter have previously been made. This was initially attempted using strategies that would increase NF-κB activity levels in latently infected T cells. With NF-κB being the major activating transcription factor for HIV-1, this was thought to promote HIV-1 reactivation (6, 18, 21). Patients on ART were thus treated with interleukin-2 (IL-2) or the anti-CD3 monoclonal antibody (MAb) OKT3, two known inducers of NF-κB activity in T cells (2-9). Later, histone deacetylase (HDAC) inhibitors (valproic acid) were applied therapeutically, as it had been proposed that similar to the case for inactive but inducible cellular genes, a restrictive histone code would govern HIV-1 latency. HDAC inhibitors were thought to trigger changes in the histone composition at the viral promoter to favor viral transcription in the absence of cellular activation. To date, all clinical HIV-1 reactivation protocols have failed to reduce the latent reservoir, or the clinical significance of reported reductions has been disputed (27, 28). This situation is further complicated by a recent report that latent HIV-1 infection events in vivo are found integrated predominantly into actively expressed host genes (12). While some have voiced concerns that the detected integration events were likely to be functionally inactive, we recently confirmed this idea in an unbiased cellular model of HIV-1 latency establishment (10). In this system, we found that all of the analyzed latently infected cell clones carried the HIV-1 genome in actively expressed host genes. However, actively expressed genes are an unlikely environment for the establishment of a restrictive histone code. In this setting, HIV-1 latency could be controlled by transcriptional interference of the host gene promoter by the integrated viral long terminal repeat (LTR) (10, 13, 22). These findings favor the development of reactivation strategies that would aim to directly transcriptionally activate the latent HIV-1 promoter by stimulating the host cell. However, if HIV-1 reactivation should be achieved by direct LTR activation, then in order to prevent the induction of a cytokine storm, therapeutics would have to be developed that, unlike anti-CD3 MAbs or IL-2, dissociate cellular gene activation from HIV-1 reactivation. Here we present proof-of-concept data showing that this can be achieved. In this study, we report that a protein activity secreted by the nonpathogenic bacterium Massilia timonae, termed HIV-1-reactivating factor (HRF), efficiently reactivated latent HIV-1 infection without inducing cellular gene expression. HRF produced a strong but short burst of NF-κB activity. This type of hit-and-run activation was sufficient to trigger initial HIV-1 Tat production, which then induced self-perpetuation of HIV-1 expression. Since cellular gene expression is not regulated by trans-acting positive feedback mechanisms, no sustainable gene expression was established, despite the strong initial trigger. These findings suggest that the control of both the amplitude and the duration of NF-κB activity can be used to selectively trigger latent HIV-1 expression without induction of cellular genes.