Expansion and characterization of human limbus-derived stromal/mesenchymal stem cells in xeno-free medium for therapeutic applications

BACKGROUND

Mesenchymal stem cells (MSCs) have been proven to prevent and clear corneal scarring and limbal stem cell deficiency. However, using animal-derived serum in a culture medium raises the ethical and regulatory bar. This study aims to expand and characterize human limbus-derived stromal/mesenchymal stem cells (hLMSCs) for the first time in vitro in the xeno-free medium.

METHODS

Limbal tissue was obtained from therapeutic grade corneoscleral rims and subjected to explant culture till tertiary passage in media with and without serum (STEM MACS XF; SM), to obtain pure hLMSCs. Population doubling time, cell proliferation, expression of phenotypic markers, tri-lineage differentiation, colony-forming potential and gene expression analysis were carried out to assess the retention of phenotypic and genotypic characteristics of hLMSCs.

RESULTS

The serum-free medium supported the growth of hLMSCs, retaining similar morphology but a significantly lower doubling time of 23 h (*p < 0.01) compared to the control medium. FACS analysis demonstrated ≥ 90% hLMSCs were positive for CD90⁺, CD73⁺, CD105⁺, and ≤ 6% were positive for CD45^-, CD34^- and HLA-DR^-. Immunofluorescence analysis confirmed similar expression of Pax6⁺, COL IV⁺, ABCG2⁺, ABCB5⁺, VIM⁺, CD90⁺, CD105⁺, CD73⁺, HLA-DR^- and CD45^-, αSMA^- in both the media. Tri-lineage differentiation potential and gene expression of hLMSCs were retained similarly to that of the control medium.

CONCLUSION

The findings of this study demonstrate successful isolation, characterization and culture optimization of hLMSCs for the first time in vitro in a serum-free environment. This will help in the future pre-clinical and clinical applications of MSCs in translational research.

Culturing Human Lung Adenocarcinoma Cells in a Serum-Free Environment

The human lung adenocarcinoma cell line A549 is commonly used in cancer research as a model of malignant alveolar type II epithelial cells. A549 cells are frequently cultured in Ham's F12K (Kaighn's) or Dulbecco's Modified Eagle's Medium (DMEM), supplemented with glutamine and 10% fetal bovine serum (FBS). However, the use of FBS presents significant scientific concerns, such as the presence of undefined components and batch-to-batch variation leading to possible reproducibility issues in experiments and readouts. This chapter describes how to transition A549 cells to FBS-free medium and gives some insights on the further characterizations and functionality assays that would be necessary to perform for the validation of the cultured cells.

Maximizing the relevance and reproducibility of A549 cell culture using FBS-free media

Scientists are using in vitro methods to answer important research questions and implementing strategies to maximize the reliability and human relevance of these methods. One strategy is to replace the use of fetal bovine serum (FBS)-an undefined and variable mixture of biomolecules-in cell culture media with chemically defined or xeno-free medium. In this study, A549 cells, a human lung alveolar-like cell line commonly used in respiratory research, were transitioned from a culture medium containing FBS to media without FBS. A successful transition was determined based on analysis of cell morphology and functionality. Following transition to commercially available CnT-Prime Airway (CELLnTEC) or X-VIVO™ 10 (Lonza) medium, the cells were characterized by microscopic evaluation and calculation of doubling time. Their genotype, morphology, and functionality were assessed by monitoring the expression of gene markers for lung cell types, surfactant production, cytokine release, the presence of multilamellar bodies, and cell viability following sodium dodecyl sulphate exposure. Our results showed that A549 cells successfully transitioned to FBS-free media under submerged and air-liquid-interface conditions. Cells grown in X-VIVO™ 10 medium mimicked cellular characteristics of FBS-supplemented media while those grown in CnT-Prime Airway medium demonstrated characteristics possibly more reflective of normal human alveolar epithelial cells.

Influences of Xeno-Free Media on Mesenchymal Stem Cell Expansion for Clinical Application

Mesenchymal stem/stromal cells (MSCs) are multipotent somatic stem/progenitor cells that can be isolated from various tissues and have attracted increasing attention from the scientific community. This is due to MSCs showing great potential for incurable disease treatment, and most applications of MSCs involve tissue degeneration and treatment of immune- and inflammation-mediated diseases. Conventional MSC cultures contain fetal bovine serum (FBS), which is a common supplement for cell development but is also a risk factor for exposure to animal-derived pathogens. To avoid the risks resulting from the xenogeneic origin and animal-derived pathogens of FBS, xeno-free media have been developed and commercialized to satisfy MSC expansion demands for human clinical applications. This review summarized and provided an overview of xeno-free media that are currently used for MSC expansion. Additionally, we discussed the influences of different xeno-free media on MSC biology with particular regard to cell morphology, surface marker expression, proliferation, differentiation and immunomodulation. The xeno-free media can be serum-free and xeno-free media or media supplemented with some human-originating substances, such as human serum, human platelet lysates, human umbilical cord serum/plasma, or human plasma-derived supplements for cell culture medium. These media have capacity to maintain a spindle-shaped morphology, the expression of typical surface markers, and the capacity of multipotent differentiation and immunomodulation of MSCs. Xeno-free media showed potential for safe use for human clinical treatment. However, the influences of these xeno-free media on MSCs are various and any xeno-free medium should be examined prior to being used for MSC cultures.

Serum-free media for the growth of primary bovine myoblasts

The demand for meat is expected to exceed production capacity by livestock in the coming decennia. Therefore, cultured beef might be a viable alternative to traditional livestock-derived beef. One of the problems however is the sustainability of cultured beef through the use of fetal bovine serum. We aimed to identify a serum-free medium or a serum-replacement that is as effective as the current method used for culturing bovine myoblasts. Cells were harvested from a female Blanc Bleu Belge cow and myoblasts were subsequently isolated. Cells were cultured in either Advanced DMEM containing 20% FBS and 10% HS or one of the chemically-defined, serum-free media for 6 days. MTS was used as a measure of cell proliferation at day 1, 4 or 6 and microscopic pictures were taken to assess cell morphology. FBM™, TesR™ and Essential 8™ are commercially available xeno-free media developed for human PSCs and fibroblasts, with the highest potential to sustain bovine myoblast proliferation. Of the supplements tested, XenoFree™ and a custom-prepared growth factor mix failed to stimulate cell proliferation. LipoGro™ stimulated cell proliferation in some cases but also changed the phenotype of myoblasts to an adipocyte-like phenotype. We conclude that serum-free media stimulate exponential cell expansion, albeit not to the extent of the current growth medium containing up to 30% serum. Further research is needed to investigate whether prolonged cell culture or an adaptation period could further increase cell proliferation.

Effect of allogeneic platelet lysate on equine bone marrow derived mesenchymal stem cell characteristics, including immunogenic and immunomodulatory gene expression profile

Propagation ex vivo of mesenchymal stem cells (MSCs) requires culture medium supplementation. Fetal bovine serum (FBS) has long been the gold standard supplement, but its use is being questioned mainly due to ethical and safety issues. The use of platelet lysate (PL) as substitute of FBS has been proposed but little is known about its effects on equine MSCs characteristics including their immune profile. The aim of this work was to investigate for the first time the effect of allogenic PL on the immunogenic and immunomodulatory gene expression profile of equine bone marrow derived MSCs (eBM-MSCs) as well as on their proliferation ability, phenotype markers, and viability post-cryopreservation. The eBM-MSCs (n = 3) cultures were supplemented with 20% of allogeneic pooled concentrated PL (CPL; 591 × 10³ platelets/μL) or basal PL (BPL; 177 × 10³ platelets/μL) from three donors, using 10% FBS supplementation as control. The proliferative ability of eBM-MSCs under the three conditions was evaluated by calculating the cell doubling times (DT) up to passage 3 (P₃) and by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay at P₃. Viability of eBM-MSCs post-cryopreserved with CPL or FBS was assessed at 15, 30 and 60 days. The gene expression profile of eBM-MSCs was evaluated in P₃ by RT-qPCR for characterization, immunogenic and immunomodulatory markers. The cells cultured in CPL had significantly higher ability to proliferate than with FBS or BPL (P < 0.001) in the MTT assay. Post-cryopreserved viability was similar between cells cultured and preserved in FBS and CPL at all time-points. Gene expression of MSC characterization markers was similar among the three conditions. The gene expression of the immunogenic markers MHC-I, MHC-II and CD40 was slightly (non-significant) increased in CPL condition compared to FBS and BPL. The CPL condition showed higher expression of the genes coding for the immunomodulatory molecules VCAM-1 (non-significant) and IL-6 (P < 0.05), and similar for COX-2; whereas iNOS and IDO were not expressed under any condition. In conclusion, the replacement of FBS by allogeneic CPL as a supplement for ex vivo propagation of eBM-MSCs provides appropriate proliferation and cryopreservation, and mildly upregulates the gene expression of immunomodulatory markers, thus constituting a potentially suitable alternative to the use of FBS. Further studies are needed to clarify the composition and effects of CPL supplementation on equine MSCs immunological profile.

Optimal Xeno-free Culture Condition for Clinical Grade Stem Cells from Human Exfoliated Deciduous Teeth

Background and Objectives

Stem cells from human exfoliated deciduous teeth (SHED) are a promising clinical resource for various tissue defects, including lumbar spondylosis, neural compression, and cleft palate. Use of media containing animal-derived serum carries potential risk of infectious diseases and unwanted immunogenicity. To increase the potential utility of SHED for clinical application, SHED was adapted to xeno-free conditions.

Methods

Define xeno-free culture media were compared with the conventional serum containing media in the culture of SHED. Cultured SHED in different media were further characterized through proliferative capacities, cellular phenotype, and differentiation potential.

Results

Selected xeno-free media were capable of supporting the growth of SHED. MSCGM-CD Bulletkit medium greatly increased the number and proliferate capacity of colony-forming unit-fibroblast than SHED cultured in other media. In addition, the characteristic surface markers expression and multipotent differentiation potential of SHED in the MSCGM-CD Bulletkit medium were comparable to those observed with serum-containing medium.

Conclusions

The xeno-free medium described herein has the potential to be further used for the safe expansion and to determine efficient way to produce clinical grade dental stem cells for therapeutic applications.