The human cytomegalovirus chemokine binding protein UL22A is necessary for efficient reactivation from latency in CD34 ⁺ hematopoietic progenitor cells and humanized mice

Herpesviruses and poxviruses encode secreted chemokine binding proteins that prevent the interaction between chemokines and their cognate G protein-coupled receptors to alter chemotactic gradients and intracellular signaling pathways. Human cytomegalovirus (HCMV) encodes the secreted protein UL22A (formerly UL21.5), which is described as a CCL5 (RANTES) binding protein and requires sulfation at two tyrosine residues (Y65 and Y69) for efficient RANTES interaction. In this report, we show that the UL22A protein and the UL22A Y65 and Y69 residues are necessary for efficient HCMV reactivation from latency in CD34 + hematopoietic progenitor cells and that UL22A expression is essential for reactivation in a humanized mouse model of latency. However, RANTES neutralization is not sufficient to complement the in vitro reactivation defect of UL22A mutant viruses. These data suggest that UL22A plays an important role in latency, possibly through interactions with additional chemokines or other types of ligands via its tyrosine residues in order to mediate efficient HCMV reactivation. IMPORTANCE Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that infects 60%–90% of the population worldwide. In immunocompetent individuals, primary infection is asymptomatic and results in lifelong latent infection in CD34 + hematopoietic progenitor cells. Viral reactivation remains a major complication for immunosuppressed individuals, but current therapeutics targeting HCMV replication show significant toxicity. Thus, a better understanding of the mechanisms controlling latency and reactivation is necessary to develop new therapeutics targeting these stages of the HCMV lifecycle. UL22A is a chemokine-binding protein encoded by HCMV. Viral chemokine-binding proteins help regulate the host immune response and promote virus replication. We show that UL22A and its Y65 and Y69 residues are necessary for reactivation from latency in CD34 + hematopoietic progenitor cells and in a humanized mouse model. Additionally, we show that UL22A binding to its only known chemokine partner, RANTES (regulated on activation, normal T cell expressed and secreted), is not necessary for this reactivation phenotype. These findings suggest other novel functions for UL22A that we do not yet understand.