Mesenchymal stromal cells: a novel and effective strategy for facilitating engraftment and accelerating hematopoietic recovery after transplantation?

MSCs are multipotent cells that can be isolated from several human tissues and expanded ex vivo for clinical use. They comprise a heterogeneous population of cells, which, through production of growth factors, cell-to-cell interactions and secretion of matrix proteins, has a role in the regulation of hematopoiesis. In recent years, several experimental studies have shown that MSCs are endowed with immunomodulatory properties and with the capacity to promote graft survival in animal models. In view of these properties, MSCs have been tested in pilot studies aimed at preventing/treating graft rejection and at accelerating recovery after hematopoietic cell transplantation (HCT). The available clinical evidence deriving from these studies indicates that MSC infusion is safe and promising in terms of capacity of preventing graft failure. More debated is the effect of MSCs for what concerns their capacity of accelerating hematopoietic reconstitution after HCT. Whether the favorable effect of MSCs largely depends on the type of transplantation remains also a field of future investigation. Moreover, future researches should be oriented to gain more insights on MSC biological and functional mechanisms relevant for exploiting their use in the modulation of alloreactivity and in the promotion of hematopoietic reconstitution.

Automated washing of human progenitor cells: evaluation of apoptosis and cell necrosis.

BACKGROUND: High-dose chemotherapy followed by reinfusion of autologous stem cells harvested from peripheral blood has been increasingly applied for a variety of disorders. The critical importance of cell dose in the clinical outcome, after transplant, has motivated the need to develop techniques aimed at reducing cell losses and increasing reproducibility. OBJECTIVES: The aim of this study is to evaluate the efficacy of the Sepax S-100 device to process thawed HPC-A products in comparison with manual procedure. METHODS/MATERIALS: We have analysed viability, total nucleated cells (TNC), haematopoietic progenitors and CD34+ cells recovery. RESULTS: The TNC and CD34+ cells recovery in the automatic procedure was of 91.9% (73-100; SD ± 12.60) and 86.7% (69-100; SD ± 10.21), respectively. Instead the recovery of TNC and CD34+ cells using the manual method was of 84.7% (47-100; SD ± 22.9) and 80.29% (23-100; SD ± 25.96). The results, obtained from the assessment of viability of CD34+ both 7-AAD)+ and AnnV+ showed a high percentage of necrosis and apoptosis in this cell subset by using the manual procedure in respect to the Sepax automated system. CONCLUSION: Overall, our data suggest that the automated washing procedure is safe and suitable for processing of thawed HPC-A products and can be daily used in clinical routine.

Co-infusion of ex vivo-expanded, parental MSCs prevents life-threatening acute GVHD, but does not reduce the risk of graft failure in pediatric patients undergoing allogeneic umbilical cord blood transplantation.

When compared with BMT, umbilical cord blood transplantation (UCBT) is associated with a lower rate of engraftment and delayed hematological/immunological recovery. This leads to increased risk of TRM in the early post transplantation period due to infection. Acute GVHD, although occurring less frequently in UCBT compared with BMT, is also significantly associated with increased rate of early TRM. BM MSCs are known to support normal in vivo hematopoiesis, and co-transplantation of MSCs has been shown to enhance engraftment of human cord blood hematopoietic cells in nonobese diabetic/SCID mice. In 13 children with hematological disorders (median age 2 years) undergoing UCBT, we co-transplanted paternal, HLA-disparate MSCs with the aim of improving hematological recovery and reducing rejection. We observed no differences in hematological recovery or rejection rates compared with 39 matched historical controls, most of whom received G-CSF after UCBT. However, the rate of grade III and IV acute GVHD was significantly decreased in the study cohort when compared with controls (P=0.05), thus resulting in reduced early TRM. Although these data do not support the use of MSCs in UCBT to support hematopoietic engraftment, they suggest that MSCs, possibly because of their immunosuppressive effect, may abrogate life-threatening acute GVHD and reduce early TRM.

Assessment of human herpesvirus-6 infection in mesenchymal stromal cells ex vivo expanded for clinical use.

Infection or reactivation of human herpesvirus (HHV)-6 represents a potentially serious complication (often involving the central nervous system) in patients receiving either solid organ or hematopoietic stem cell transplantation. The objective of this study was to assess the risk of HHV-6 infection/reactivation in mesenchymal stromal cells (MSCs). MSCs are multipotent cells displaying immunomodulatory properties that have been already successfully used in the clinical setting to enhance hematopoietic stem cell engraftment and to treat steroid-refractory acute graft-versus-host disease. We analyzed 20 samples of ex vivo expanded MSCs, at different passages of culture, isolated both from bone marrow and from umbilical cord blood. Through Western blotting and immunocytochemistry techniques, we investigated the presence of the HHV-6 receptor (CD46) on cell surface, whereas the presence of HHV-6 DNA was evaluated by nested polymerase chain reaction assay. All of the MSC samples tested were positive for the virus receptor (CD46), suggesting their potential susceptibility to HHV-6. However, none of the MSC samples derived from cultures, performed in the perspective of clinical use, was found to harbor HHV-6. This preliminary observation on a consistent number of MSC samples, some of them tested at late in vitro passages, indicates a good safety profile of the product in terms of HHV-6 contamination. Nevertheless, it remains important to set up in vitro experimental models to study MSCs' susceptibility to HHV-6 (and HHV-7) infection, to verify their capacity to integrate the virus into cellular DNA, and to investigate which experimental conditions are able to induce virus reactivation.

Optimization of in vitro expansion of human multipotent mesenchymal stromal cells for cell-therapy approaches: further insights in the search for a fetal calf serum substitute.

There is great interest in mesenchymal stromal cells (MSCs) for cell-therapy and tissue engineering approaches. MSCs are currently expanded in vitro in the presence of fetal calf serum (FCS); however, FCS raises concerns when used in clinical grade preparations. The aim of this study was to evaluate whether MSCs expanded in medium supplemented with platelet-lysate (PL), already shown to promote MSC growth, are endowed with biological properties appropriate for cell-therapy approaches. We confirm previously published data showing that MSCs expanded in either FCS or PL display comparable morphology, phenotype, and differentiation capacity, while PL-MSCs were superior in terms of clonogenic efficiency and proliferative capacity. We further extended these data by investigating the immune-regulatory effect of MSCs on the alloantigen-specific immune response in mixed lymphocyte culture (MLC). We found that MSCs-PL are comparable to MSCs-FCS in their capacity to: (i) decrease alloantigen-induced cytotoxic activity; (ii) favor differentiation of CD4+ T-cell subsets expressing a Treg phenotype; (iii) increase early secretion of IL-10 in MLC supernatant, as well as induce a striking augmentation of IL-6 production. As compared with MSCs-PL, MSCs-FCS were more efficient in suppressing alloantigen-induced lymphocyte subset proliferation and reducing early IFNgamma-secretion. Resistance to spontaneous transformation into tumor cells of expanded MSCs was demonstrated by molecular karyotyping and maintenance of normal morphology/phenotype after prolonged in vitro culture. Our data support the immunological functional plasticity of MSCs and suggest that MSCs-PL can be used as an alternative to MSCs-FCS, although these latter cells might be more suitable for preventing/treating alloreactivity-related immune complications.