1:Red Andaluza de diseño y traslación de Terapias Avanzadas. Fundación Progreso y Salud. 41092, Sevilla (España).; 2:Centro de transfusion, tejidos y células. 29009, Málaga (España).; 3:Instituto de Investigación Biosanitaria (IBS). 18012, Granada (España).

We demonstrated that clinical-grade human mesenchymal stromal cells derived from umbilical cord (MSC) and irradiated with 2 Gy (IR-MSC), display good viability and upregulate the expression of tumor suppressor genes 48 hours after irradiation (TRAIL, DKK3 and ANXA1), enhancing the effect of radiotherapy in tumor-bearing mice. To prove the safety of IR-MSC administrated systemically, we carried-out two subchronic toxicity studies (90 days, single and repeat doses) following Good Laboratory Practices (GLP). 18 NSG mice (n=6) were injected intravenously with a single dose of 5000 IR-MSC, MSC or transformed MSC (tMSC, positive control) / g, a similar dose to that intended to be administered in a clinical trial. tMSC-injected mice showed a significant weight reduction compared to the MSC mice. Two tMSC-mice showed nodules in spleen and lung. One of them, presented an increase in size and inflammation in the spleen. No significant alterations were detected in the organs of IR-MSC and MSC mice. Next, we carried-out PCR for Alu sequences to determine the presence of human DNA in selected organs. Human DNA was detected in the organs of 3 mice injected with tMSC, showing that tMSC may be present at 90 days post-injection. In addition, we performed a repeat dose assay (days 1 and 3) using IR-MSC and MSC. The histological analysis showed that the intravenous administration of IR-MSC and MSC does not produce morphological alterations. Besides, human DNA was not detected in any organ. In conclusion, the results indicated that systemic administration of IR-MSC and MSC is safe.