Long-term complications, immunologic effects, and role of passage for outcome in mesenchymal stromal cell therapy.

Thirty-one patients treated with mesenchymal stromal cells (MSCs) for acute graft-versus-host disease (aGVHD) or hemorrhagic cystitis between 2002 and 2007 were followed to investigate predictors of outcome, immunologic effects in vivo, and long-term survival. There was no correlation between in vitro suppression by MSCs in mixed lymphocyte cultures and outcome. Soluble IL-2 receptors were measured in blood before and after MSC infusion and declined significantly during the first week after MSC infusion (P = .03). Levels of interleukin-6 and HLA-G were unaffected. Infectious complications occurred several years after recovery from aGVHD. Cytomegalovirus viral load was high, and cytomegalovirus disease was common. Among patients recovering from aGVHD, 54% died of late infections, between 4 months and 2 years after MSC treatment. No increase in leukemia relapse or graft rejection was found. Children had a better survival rate than adults (P = .005). In GVHD patients, 1-year survival was 75% in patients who received early-passage MSCs (from passages 1-2) in contrast to 21% using later passage MSCs (from passages 3-4) (P < .01). We conclude that treatment with early-passage MSCs improved survival in patients with therapy-resistant GVHD. Death from infection was common in MSC-treated patients, but there was no increase in leukemia relapse.