Frequent detection of herpes simplex virus antigen in skin and peripheral blood CD34+ mononuclear cells from patients with graft-versus-host disease.

Viruses are implicated in the initiation or flare of graft-versus-host disease (GVHD) by virtue of their ability to activate antigen-presenting dendritic cells (DC). Herpes simplex virus (HSV) infects circulating CD34+ stem cell progenitors, favoring their differentiation into skin homing DC (CD1a+ Langerhans cells) that contribute to the development of an inflammatory skin rash known as HSV-associated erythema multiforme (HAEM). Following on these findings, we conducted a prospective study to examine whether HSV is also associated with GVHD. Skin biopsies and peripheral blood mononuclear cells (PBMC) were collected from 37 consecutive patients on admission before and after allogeneic hematopoietic stem cell transplantation (HSCT) and examined for HSV antigen (Pol) expression and the presence of Pol+CD34+ and Pol+CD1a+ cells. Sixteen patients developed a skin rash that was histopathologically consistent with GVHD (group I), 3 patients had a rash that was not GVHD (group II, EM-like) and 18 patients did not develop any rash after HSCT (group III). Skin biopsies from the group I patients were Pol negative pre-HSCT (baseline) but became Pol+ after the diagnosis of GVHD. The GVHD biopsies also contained Pol+CD34+ and Pol+CD1a+ cells, and these patients had a significant percentage of circulating Pol+CD34+ and Pol+CD1a+ PBMC. By contrast, the group II patients had Pol+ skin cells and Pol+CD34+ circulating PBMC at baseline that decreased post-HSCT. The group III patients had Pol negative skin and very few circulating Pol+CD34+ and Pol+CD1a+ PBMC at baseline that were not significantly changed post-HSCT. The data associate skin GVHD with HSV reactivation during conditioning and its propensity for nonreplicative infection of CD34+ PBMC that induces DC activation. Further studies are needed to better elucidate this association.