Work

Suicide Caspase 9 Gene For Improved Safety Of Therapies Using Mesenchymal Stromal Cells

Year: 2010

Type: article

Abstract: Although MSC have been administered to hundreds of patients so far with minimal reported side effects, little is known about their long term effects. Recent reports of osteosarcoma formation in culture and interference with major organ function due to ectopic ossification raise safety concerns. In light of these, we sought to develop a system allowing control over the growth and survival of MSCs administered therapeutically, using an inducible caspase-9 (iCasp9) protein that can be activated by a specific chemical inducer of dimerization (CID) leading to cell death. MSCs from healthy donors were retrovirally transduced with iCasp9 linked to a truncated form of CD19, allowing selection of transduced cells: 47±6% of the cells were iCasp9+, a percentage stable over more than two weeks in culture, suggesting no deleterious or growth advantageous effects of the construct on MSCs. iCasp9+ cells were easily immunomagnetically selected. Phenotype (>99% CD73+CD90+CD105+, and negative for hematopoietic markers) and differential potential of iCasp9+ cells was identical to that of untransduced cells, proving the genetic manipulation of MSCs did not modify their basic characteristics. Non-transduced MSCs had a spontaneous rate of apoptosis in culture ∼18% (±7%), similar to iCasp9+ cells at baseline (15±6%, P=0.47). Addition of CID to cultures after transduction resulted in apoptotic death of >90% of iCasp9+ cells (93±1%, P<0.0001), while iCasp9– cells retained an apoptosis index similar to that of non-transduced controls (20±7%, P=0.99 and P=0.69 vs. non-transduced controls with or without CID respectively), demonstrating that iCasp9+ MSCs can be selectively killed. Addition of CID to cultures of differentiated MSCs resulted in widespread apopotosis as assessed by TUNEL assay. Furthermore, using an in vivo imaging system, we saw that iCasp9+ MSCs injected subcutaneously in SCID mice were selectively eliminated after administration of CID, without toxic effects. In summary, MSCs are easily transduced with our iCasp9 system, the transduced cells can be selected with clinical grade procedures and maintain their basic physiology, and their differentiated progeny can be selectively eliminated by exposure to a CID, analogues of which have been safely tested in a phase I study. This directed MSC killing provides a necessary safety mechanism for therapies using progenitor cells. This approach will become of increasing value as clinical applications for MSCs develop further.

Source: Transplantation and Cellular Therapy

DOI: 10.1016/j.bbmt.2009.12.182