hy

ST

genetic stability of ex vivo-expanded human MSCs.

expanded in a bioreactor (Quantum Cell ExpansionSystem; Terumo BCT, Lakewood, CO, USA), and

the addition of conditioned medium for CV MSCs.Finally, a wide range of techniques were used to assess

and RNA sequencing could be used.

has never happened? To study the potential trans-formation steps of expanded MSCs, we need trans-

MSCs and help dene relevant controls.Transformation is only one side of the coin. The

S/EFS/UPS-INSERM U1031, bat L1, 1 avenue Jean Poulhes 31400, Toulouse,

Cytotherapy, 2013; 15: 1307e1308Correspondence: Luc Sensebe, MD, PhD, UMR5273 STROMALab CNRgenetic stability, including conventional karyotyping, other side, senescence, should be avoided too.ASCs and CV MSCs were expanded in asks. Themedia were similar, including fetal bovine serum, with

formed human MSC clones. Such studies couldreveal mechanisms of transformation of humanMSCs used in these studies came from threedifferent sources: two from adult tissue [bonemarrow(BMMSCs) (10) and adipose tissue (ASCs) (11)] andone from a fetal source [chorionic villi (CV MSCs)(12)]. The culture processes differed. BMMSCswere

Despite the availability of numerous tools, are welooking in the right direction? Have we dened thereal target? Transformation is an extremely rare eventand has never been reported after >15 years ofclinical use, so how can we predict something thatCOMMENTARY

Beyond genetic stability of mesenc

LUC SENSEBE

Etablissement Franais du Sang, France, and UMR5273Toulouse, France

Mesenchymal stromal cells (MSCs) have been usedin the clinic for more than a decade. However, thisrapidly emerging area of research (352 clinical trialsregistered at ClinicalTrials.gov) is associated withmuch debate and controversy. A major issue is thesafety and risk of transformation of MSCs during exvivo expansion. Previous articles (1,2), now retracted(3,4), or analyses (5) reported the transformation orrisk of transformation of MSCs from different sour-ces during expansion. Although such transformationis likely a rare event (6,7), some genetic abnormal-ities, mainly aneuploidy, can appear during culturebut are not related to the transformation per se (8).Consequently, from a regulatory point of view, weneed to develop processes avoiding such trans-formation that use relevant controls to avoid therisk of transformation. A recent review, following ameeting of the European Medicines Agency inLondon to ensure the safety of MSC production, atleast in pre-clinical settings, determined that cyto-genetic abnormalities should be assessed (9). In thisissue of Cytotherapy, three teams report on theFrance. E-mail: luc.sensebe@efs.sante.fr

ISSN 1465-3249 Copyright 2013, International Society for Cellular Therapy. Phttp://dx.doi.org/10.1016/j.jcyt.2013.09.001mal stromal cells

ROMALab CNRS/EFS/UPS-INSERM U1031,

spectral karyotyping, uorescent in situ hybridization,genome-wide array comparative genomic hybridiza-tion, microsatellite genotyping and micronucleusformation. Whatever the source of cells and processused, the studies found no (BM MSCs) or only rare(ASCs and CV MSCs) clonal cytogenetic abnormal-ities increasing with time during culture. Injection ofBMMSCs and ASCs into immunodecient mice didnot produce tumors. These reports reinforce previousresults (8,13) showing that human MSCs do nottransform during ex vivo expansion, and aneuploidy isnot related to transformation but rather to senescence.Microsatellite genotyping did not reveal any alleleexpansion or loss of heterozygosity. However, sensi-tivity of karyotyping with conventional techniques orspectral karyotyping was poor. Fluorescent in situ hy-bridization, requiring a knowledge of the target, hasslightly increased sensitivity, and array comparativegenomic hybridization detects small genomic abnor-malities but only in a large percentage of cells(>20e30%). If sensitivity is the problem, existingtechniques such as single nucleotide polymorphismublished by Elsevier Inc. All rights reserved.

Senescence is related not only to risk of trans-formation but also to the risk of inefciency and in-crease in side effects. As recommended by theEuropean Medicines Agency and other experts,population doublings should be kept to a minimum(9). Although these three reports reinforce that hu-man MSCs that are not overly expanded can besafely used, we look forward to studies giving deeperinsight into transformation mechanisms of humanMSCs to help establish better relevant controls.

References

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10. Jones M, Varella-Garcia M, Skokan M, Bryce S,Schowinsky J, Peters R, et al. Genetic stability of bonemarrow-derived human mesenchymal stromal cells in theQuantum System. Cytotherapy. 2013;15:1323e39.

11. Roemeling-van Rhijn M, de Klein A, Douben H, Pan Q, vander Laan LJW, Ijzermans JN, et al. Culture expansion inducesnon-tumorigenic aneuploidy in adipose tissue-derivedmesenchymal stromal cells. Cytotherapy. 2013;15:1352e61.

12. Roselli EA, Lazzati S, Iseppon F, Manganini M, Marcato L,Gariboldi MB, et al. Fetal mesenchymal stromal cells fromcryopreserved human chorionic villi: cytogenetic and molec-ular analysis of genome stability in long-term cultures. Cyto-therapy. 2013;15:1340e51.

13. Bernardo ME, Zaffaroni N, Novara F, Cometta AM,Avanzini MA, Moretta A, et al. Human bone marrow-

1308 L. SensebeCancer Res. 2010;70:6393e6.5. Ben-David U, Mayshar Y, Benvenisty N. Large-scale analysis

reveals acquisition of lineage-specic chromosomal aberrationsin human adult stem cells. Cell Stem Cell. 2011;9:97e102.derived mesenchymal stem cells do not undergo trans-formation after long-term in vitro culture and do not exhibittelomere maintenance mechanisms. Cancer Res. 2007;67:9142e9.

Beyond genetic stability of mesenchymal stromal cellsReferences