Human Cytomegalovirus Latency: Targeting Differences in the Latently Infected Cell with a View to Clearing Latent Infection

Figure 4

Establishment of experimental latency in primary progenitor CD34+ cells and reactivation in the myeloid lineage. Following infection of CD34+ progenitor cells with the TB40E strain of HCMV, latency is established, demonstrated by the hallmark of chromatin repressor HP1 association with the MIEP in chromatin immunoprecipitation assays (ChIP): Inp = input, IgG = immunoglobulin control, AcH3 = acetylated histone H3 (marker of active chromatin), and HP1 = heterochromatin protein 1 (marker of repressed chromatin). Coculture of these cells with fibroblasts (HFFs) does not result in IE gene expression. Untreated cells remain in a state of latency shown here for 20 days (top). Alternatively, if after 10 days cells are differentiated and matured into DCs, ChIP analysis shows that the MIEP becomes associated with markers of active chromatin (AcH4) and coculture with fibroblasts shows immediate early 72-protein (IE72) gene expression. Consistent with these observations, transcripts can be detected for the viral latent gene transcript UL138, the viral lytic gene transcript IE72, and the cellular gene transcript GAPDH following reactivation by RT-PCR.