Purpose of review: Allogeneic hematopoietic cell transplantation (allogeneic HCT) is a highly effective therapy for a broad range of hematological diseases and its use is increasing worldwide. Despite advances in antiviral prophylaxis and treatment, viral infections are still one of the leading causes of post-HCT morbidity and mortality. In this patient population, metagenomic next-generation sequencing (mNGS) revealed a much larger diversity of viruses than previously suspected via the targeted screening approach. In the context of profound immunosuppression, these viral infections may cause transient viremia or protracted replication and potentially be associated with yet unrecognized or unspecific clinical manifestations. On the contrary, by constantly interacting with the immune system, viral infections may have a significant impact on posttransplant outcomes. Here, we review the latest advances in research assessing the role of the blood virome in the development of post-HCT complications.

Recent findings: Research efforts are under way to uncover the potential role of several previously undetected viruses in the development of allogeneic HCT complications and their impact on transplant outcomes.

Summary: The identification of viral actors impacting post-HCT morbidity and survival is key to optimize monitoring and infection prevention/treatment strategies.