CD123 is a useful immunohistochemical marker to facilitate diagnosis of acute graft-versus-host disease in colon.

The efficacy of hematopoietic stem cell transplantation (HSCT) is greatly hampered by graft-versus-host disease (GVHD) and opportunistic infection; the gastrointestinal tract is one of the main target organs involved by GVHD and opportunistic infectious agents. The presence of crypt apoptosis is the major criterion for the histologic diagnosis of GVHD; however, it can also be seen in infection, especially cytomegalovirus (CMV) colitis. Therefore, the definitive histopathologic diagnosis of GVHD in gastrointestinal tract can be challenging or impossible without reliable ancillary markers. We studied the expression of CD123 and C4d in 38 colonic biopsies from patients with HSCT with acute GVHD and 14 colon biopsies from patients with CMV colitis without history of HSCT. CD123 expression was significantly increased in the acute GVHD group compared with the CMV group (65.8% versus 14.3%; P < .05) with increasing sensitivity in higher-grade GVHD (grades 1-2, 60%; grades 3-4, 72.2%). However, there was no significant difference in C4d deposition between the acute GVHD and CMV groups (68.4% versus 42.9%; P > .05). We further applied CD123 immunostaining to upper gastrointestinal (n = 23) and colonic biopsies (n = 24) in patients with HSCT without evidence of acute GVHD or infection and 11 biopsies from patients who had used mycophenolate. The negative staining of CD123 in all these cases further supports the specificity of CD123 in acute GVHD. In summary, CD123 might be a useful ancillary marker to aid in separating infection from GVHD in patients with HSCT.