Pooling Umbilical Cord-Mesenchymal Stromal Cells derived from selected multiple donors reduces donor-dependent variability and improves their immunomodulatory properties.

Background Umbilical Cord-derived Mesenchymal Stromal Cells (UC-MSCs) display high immunoregulatory properties, offering new perspectives to treat severe immune and inflammatory diseases. However, the heterogeneity of their biological properties remains a challenge to predict clinical response. The aim of our study is to evaluate a strategy based on the constitution of a pool of several pre-selected donors to reduce the biological variability of UC-MSCs and improve their immunomodulatory properties. Methods Umbilical cords were collected from 10 healthy donors. Isolated UC-MSCs were characterized in the basal state and after a pro-inflammatory priming in vitro by interferon-γ (IFNγ) and tumor necrosis factor-α (TNFα). Proliferation, immunophenotype, the expression of activation markers and the inhibition of T cell proliferation in vitro were assessed in UC-MSCs from selected single donors and from pools. Results Our study highlights the donor-dependent heterogeneity of UC-MSCs immunomodulatory functions. Based on their ability to suppress T-cell proliferation in vitro , we classified donors into three profiles: high, medium and low. Preparation of pools containing UC-MSCs derived from each profile in a 1:1:1 ratio reduced the donor-dependent variability and, most importantly, improved the lowest immunomodulatory functions. After priming with pro-inflammatory cytokines, the inhibition of T-cell expansion by the pooled UC-MSCs was significantly higher than the low donor and the theoretical mean of individual donors, and was associated with increased expression of the key immunoregulatory proteins. Interestingly, the pool did not induce a cumulative immunogenic effect: expression of HLA or costimulatory molecules between the high donor and the pool were similar. Finally, pooling UC-MSCs derived from high and low donors in a 1:2 ratio was sufficient to enhance the lowest immunomodulatory properties. Conclusion Overall, our results demonstrate that pooled UC-MSCs with selected high donor offers a new strategy to optimize the immunomodulatory functions of allogeneic UC-MSC-based medicinal products.