Eosinophils and severe forms of graft-versus-host disease

Basara et al1 recently reported interesting data on the predictive value of eosinophilia in the evolution to acute graft-versus-host disease (GVHD) in a systematic prospective study of bone marrow smears and biopsies (n = 237). This is in accordance with our previous findings in patients with upper gastrointestinal tract GVHD. In a series of 93 patients, eosinophils were present only when there were histologic signs of GVHD and eosinophil density correlated with GVHD severity.2 Since few data are available on eosinophils and GVHD, it is therefore important to have a validation of similar results by 2 independent teams on 2 different organs in patients with GVHD.

The fact that eosinophils show signs of activation both in blood3 and target organs2,4 of patients with acute flares of GVHD raises the question of their deleterious effect on target organs in GVHD. Signs of eosinophil activation, both in blood and target organs, were also found in patients with severe eosinophilic syndromes.5 Experimental studies to assess the role of eosinophils in target organ damage cannot be performed in humans for ethical reasons. However, there is an increasing amount of clinicopathologic data that links eosinophils to severity of target organ damage. To remain in the field of GVHD, eosinophils are linked to severe forms of GVHD when detected in bone marrow, gut, and conjunctiva, but they are also associated with a striking resistance to conventional therapy in fasciitis. This rare form of GVHD6shares many clinicopathologic features with eosinophilic fasciitis7 except for the dramatic response to steroid therapy.

Therefore, systematic study of eosinophils in biopsies of patients with GVHD could contribute to assess GVHD severity and thus may help to modulate immunosuppression therapy.