Human Mesenchymal Stroma Cells (hMSCs) Expanded with Human Platelets Lysate Are Safe and Effective For the Treatment of Graft Versus Host Disease

Background Very recently, encouraging results indicate that third party human mesenchymal stromal cells (hMSCs) are a rapidly available therapeutic tool for the treatment of severe (grade III–IV), steroid resistant, acute graft versus host disease (aGVHD). In the clinical experience published so far, hMSCs have been expanded in Fetal Bovine Serum (FBS), which may constitute a problem for its antigenicity and as a possible vehicle of animal pathogens. We have established a highly efficient protocol for the in vitro expansion, under strict GMP compliance, of bone marrow derived hMSCs using human platelets lysate (PL) in place of FBS (Capelli C. et al.: BMT, 2007). In this study, upon Ethical Committee approval and patient’s informed consent, hMSCs were administered on a compassionate basis for the treatment of refractory GVHD.

Methods hMSCs were prepared from washouts of bags and filters, left over at the end of the standard filtration procedures of the bone marrow harvests from third party HLA mismatched healthy donors. Cells were grown in the presence of DMEM with 5% PL obtained from the Blood Bank of our Hospitals. In a short period of time (10–33 days), low density seeding of unmanipulated cells (100–200/cm²), obtained from 7 bone marrow harvests allowed to prepare large quantities of hMSCs (median 115×10⁶, range: 67–375), with only one in vitro passage. Twenty-three frozen bags of hMSCs (each containing approximately 1×10⁶/kg of recipient body weight) have been quarantined until the completion of quality tests, including viability, phenotype, absence of detectable bacteria, fungi, mycoplasma or endotoxin, according to European Pharmacopea guidelines. Differentiation to osteogenic and chondrogenic cells as well as the immunosuppressive potential of these cells was confirmed when tested in mixed lymphocyte reaction (MLR). Q banding and clonogenic assays were performed for each batch and never showed abnormalities of karyotype or autonomous growth in vitro.

Results Two adult and 4 pediatric patients were treated for aGVHD (grade II–IV) and 2 adults for extensive chronic GVHD (cGVHD) between January and July 2008, using 12 hMSCs bags that had completed quarantine. Before hMSCs, second or third line treatments had been given to patients with aGVHD, including Etanercept (n= 5), Mycophenolate Mofetil (MMF, n= 4) and Extracorporeal Photopheresis (ECP, n= 3), Rituximab (1 patient). Patients with cGVHD were previously treated with ECP and MMF (n= 2), Imatinib (n= 1) and Etanercept (n= 1). Each infusion contained a median dose of 1×10⁶/kg (range, 0.7–1.2×10⁶) hMSCs. For patients with aGVHD, a single infusion was performed in 4 pediatric patients while 1 and 3 infusions were performed in 2 adult patients. The 2 patients with cGVHD received 1 and 4 infusions, respectively. All infusions were very well tolerated with no immediate or late adverse events according to WHO common criteria. Among pediatric patients with aGVHD, 3 complete and 1 partial responses were registered and all patients are alive and in complete hematologic remission. A complete response was observed in 1 adult with grade III cutaneous aGVHD although the patient rapidly relapsed and died of leukemia progression. No response was observed in the other adult patient who died of progressive grade IV gut and liver aGVHD. The 2 adult patients with cGVHD had both a partial response and are alive.

Conclusions These data show that large numbers of third party hMSCs can be expanded in vitro with PL containing medium and stored for immediate use in patients with GVHD. Moreover, the clinical results and the toxicity profile confirm those reported with hMSCs expanded in FBS containing media.