Do ABO blood group antigens hamper the therapeutic efficacy of mesenchymal stromal cells?

Bottlenecks in the Efficient Use of Advanced Therapy Medicinal Products Based on Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) have been established as promising candidate sources of universal donor cells for cell therapy due to their contributions to tissue and organ homeostasis, repair, and support by self-renewal and multidifferentiation, as well as by their anti-inflammatory, antiproliferative, immunomodulatory, trophic, and proangiogenic properties. Various diseases have been treated by MSCs in animal models. Additionally, hundreds of clinical trials related to the potential benefits of MSCs are in progress. However, although all MSCs are considered suitable to exert these functions, dissimilarities have been found among MSCs derived from different tissues. The same levels of efficacy and desired outcomes have not always been achieved in the diverse studies that have been performed thus far. Moreover, autologous MSCs can be affected by the disease status of patients, compromising their use. Therefore, collecting information regarding the characteristics of MSCs obtained from different sources and the influence of the host (patient) medical conditions on MSCs is important for assuring the safety and efficacy of cell-based therapies. This review provides relevant information regarding factors to consider for the clinical application of MSCs.

Human adipose tissue-derived stem cells cultured in xeno-free culture condition enhance c-MYC expression increasing proliferation but bypassing spontaneous cell transformation

Introduction

Human adipose tissue-derived stem cells (hASCs) are attractive cells for therapeutic applications and are currently being evaluated in multiple clinical trials. Prior to their clinical application, hASCs must be expanded ex vivo to obtain the required number of cells for transplantation. Fetal bovine serum is the supplement most widely used for cell culture, but it has disadvantages and it is not safe for cell therapy due to the risks of pathogen transmission and immune reaction. Furthermore, the cell expansion poses a risk of accumulating genetic abnormalities that could lead to malignant cell transformation. In this study, our aim was to evaluate the proliferation pattern as well as the resistance to spontaneous transformation of hASCs during expansion in a xeno-free culture condition.

Methods

hASCs were expanded in Dulbecco’s modified Eagle’s medium supplemented with pooled allogeneic human serum or fetal bovine serum to enable a side-by-side comparison. Cell viability and differentiation capacity toward the mesenchymal lineages were assessed, along with immunophenotype. Ki-67 expression and the proliferation kinetics were investigated. The expression of the transcription factors c-FOS and c-MYC was examined with Western blot, and MYC, CDKN2A, ERBB2 and TERT gene expression was assessed with quantitative PCR. Senescence was evaluated by β-gal staining. Karyotype analysis was performed and tumorigenesis assay in vivo was also evaluated.

Results

The hASCs expanded in medium with pooled allogeneic human serum did not show remarkable differences in morphology, viability, differentiation capacity or immunophenotype. The main difference observed was a significantly higher proliferative effect on hASCs cultured in pooled allogeneic human serum. There was no significant difference in C-FOS expression; however, C-MYC protein expression was enhanced in pooled allogeneic human serum cultures compared to fetal bovine serum cultures. No difference was observed in MYC and TERT mRNA levels. Moreover, the hASCs presented normal karyotype undergoing senescence, and did not form in vivo tumors, eliminating the possibility that spontaneous immortalization of hASCs had occurred with pooled allogeneic human serum.

Conclusions

This complete characterization of hASCs cultivated in pooled allogeneic human serum, a suitable xeno-free approach, shows that pooled allogeneic human serum provides a high proliferation rate, which can be attributed for the first time to C-MYC protein expression, and showed cell stability for safe clinical applications in compliance with good manufacturing practice.

Caveats of mesenchymal stem cell therapy in solid organ transplantation

In the past decade, therapeutic use of mesenchymal stem cells (MSCs) has increased dramatically. The weight of existing evidence supports that the short-term application of MSCs is safe and feasible; however, concerns remain over the possibility of unwanted long-term effects. One fundamental difference between MSCs and pharmacotherapy is that, once applied, the effects of cell products cannot be easily reversed. Therefore, a carefully considered decision process is indispensable before cell infusion. In addition to unwanted interactions of MSCs with the host immune system, there are concerns that MSCs may promote tumor progression or even give rise to cancer themselves. As animal models and first-in-man clinical studies have provided conflicting results, it is challenging to estimate the long-term risk of individual patients. In addition, most animal models, especially rodents, are ill-suited to adequately address questions over long-term side effects. Based on the available evidence, we address the potential pitfalls for the use of MSCs as a therapeutic agent to control alloimmune effects. The aim of this review was not to discourage investigators from clinical studies, but to raise awareness of the intrinsic risks of MSC therapy.

Actin cytoskeletal disruption following cryopreservation alters the biodistribution of human mesenchymal stromal cells in vivo

Mesenchymal stromal cells have shown clinical promise; however, variations in treatment responses are an ongoing concern. We previously demonstrated that MSCs are functionally stunned after thawing. Here, we investigated whether this cryopreservation/thawing defect also impacts the postinfusion biodistribution properties of MSCs. Under both static and physiologic flow, compared with live MSCs in active culture, MSCs thawed from cryopreservation bound poorly to fibronectin (40% reduction) and human endothelial cells (80% reduction), respectively. This reduction correlated with a reduced cytoskeletal F-actin content in post-thaw MSCs (60% reduction). In vivo, live human MSCs could be detected in murine lung tissues for up to 24 hr, whereas thawed MSCs were undetectable. Similarly, live MSCs whose actin cytoskeleton was chemically disrupted were undetectable at 24 hr postinfusion. Our data suggest that post-thaw cryopreserved MSCs are distinct from live MSCs. This distinction could significantly affect the utility of MSCs as a cellular therapeutic.

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Immediately after thawing, MSCs display attenuated binding and engraftment potential

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Immediately after thawing, MSCs display defective actin polymerization

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Disrupting actin cytoskeleton in MSCs replicates post-thaw MSC engraftment defect

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A 48 hr culture recovery of MSCs post-thaw restores in vivo engraftment potential