Profiling the blood compartment of Hematopoietic Stem Cell Transplant patients during Human Cytomegalovirus reactivation

Human cytomegalovirus (HCMV) reactivation is a leading infectious cause of morbidity and mortality in hematopoietic stem cell transplantation (HSCT) patients. HCMV reactivation is characterized by detection of viral DNA in the blood (DNAemia), however, the role of the blood compartment during HCMV reactivation is not well characterized. Using powerful molecular tools, we characterized HCMV infection in Peripheral Blood Mononuclear Cells (PBMCs) during DNAemia in HCMV reactivating HSCT patients. Surprisingly we found that all PBMC populations harbored extremely low levels of viral DNA and extremely low levels of viral transcripts. Remarkably, the viral transcripts detected in these samples were mainly immediate early genes indicating that these cells do not go through a full productive cycle. Analysis of the cellular transcriptome revealed characteristic transcriptional changes in high DNAemic samples implying the development of HCMV-specific T cells and inhibition of regulatory T cell function. Overall, our data indicate that DNAemia in HCMV reactivating HSCT patients is associated with distinct immune signatures but is not necessarily accompanied by substantial infection of PBMCs, and that PBMCs are not productively infected. These findings are important for understanding the role of the blood compartment in progression and control of HCMV during reactivation. MARS-Seq bulk protocol was used for PBMC from HSCT recipients with HSCT reactivation and for monocytes infected with HCMV ex-vivo