Author Affiliationis: Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida (firstname.lastname@example.org).
In Reply: We agree with Dr Zhang and colleagues that the issue of donor characteristics for allogeneic MSC donation is important. We chose male donors aged 21 to 35 years. Donors were carefully screened medically and documented to be free of a panel of viral infections. The age cutoff was selected to optimize the chances of culture expanding sufficient quantities of MSCs for use in several recipients.
Second, regarding the tumor complication rate, we are pleased to report that no patient in the trial exhibited neoplasia or ectopic tissue formation. This is a crucial issue,1 and one suggested by rodent studies. This potential complication has not materialized in the POSEIDON population or in other studies testing MSCs2,3 in humans. Possible reasons for the apparent safety of MSCs in this regard include their limited differentiation capacity compared with pluripotent embryonic stem cells, the relatively low level of sustained engraftment, and the lower rate of cellular transformation in human cells than in rodents.1
Hare JM, Difede D, Heldman AW. Use of Stem Cells for Ischemic Cardiomyopathy—Reply. JAMA. 2013;309(14):1458-1459. doi:10.1001/jama.2013.2893