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Assoc Prof

Toan Thang Phan

Research Associate Professor

Surgery

  • Research Associate Professor
    Surgery

PUBLICATIONS

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Showing page 1, publications 1 to 25 of 236
  • JOURNAL ARTICLE
    Red Deer Umbilical Cord Lining Mesenchymal Stem Cell-Conditioned Media Stimulates Fibroblast Elastin and Hyaluronic Acid Production to Improve Eyelid Aesthetics
    1 Sep 2025Dermatologic Surgery51(9):S25-S32
    Co-authors: Lim IJ, Ong CT, Jeyakumar M
    DOIDOI: 10.1097/DSS.0000000000004810
    BACKGROUND: Conditioned media (CM) from red deer umbilical cord lining mesenchymal stem cell (RD-CLMSC) culture comprises an exosomal suspension and is the active ingredient of a facial cream (CALECIM Professional Multi-Action Cream, CALECIM Cosmeceuticals, Singapore) shown to significantly improve skin tone after topical application. This effect appears to be related to increased human dermal fibroblast (HDF) proliferation, with increased HDF production of elastin and hyaluronic acid (HA). OBJECTIVE: The authors sought to investigate if RD-CLMSC-CM might increase elastin and HA to improve thin eyelid skin turgor and elasticity. MATERIALS AND METHODS: Upper eyelid skin HDF from 9 individuals were exposed in culture to RD-CLMSC-CM. Photocolorimetry after histochemical staining demonstrated increased expression of elastin by 68% and HA by 113% compared with exposure to Dulbecco's modified eagle medium/10% fetal calf serum. A topical eyelid skin formulation containing RD-CLMSC-CM was applied to the upper and lower eyelid skin of 4 preexisting users of RD-CLMSC-CM facial cream. Photographic comparison before and after application demonstrated subjective and objective cosmetic improvement. RESULTS AND CONCLUSIONS: Topical application of RD-CLMSC-CM increased eyelid HDF production of elastin and HA. This improved skin elasticity and turgor to heighten eyelid skin aesthetics.
  • JOURNAL ARTICLE
    Recent advances in smart hydrogels derived from polysaccharides and their applications for wound dressing and healing
    1 Jul 2025Biomaterials318
    Co-authors: Tian X, Wen Y, Zhang Z
    DOIDOI: 10.1016/j.biomaterials.2025.123134
    Owing to their inherent biocompatibility and biodegradability, hydrogels derived from polysaccharides have emerged as promising candidates for wound management. However, the complex nature of wound healing often requires the development of smart hydrogels---intelligent materials capable of responding dynamically to specific physical or chemical stimuli. Over the past decade, an increasing number of stimuli-responsive polysaccharide-based hydrogels have been developed to treat various types of wounds. While a range of hydrogel types and their versatile functions for wound management have been discussed in the literature, there is still a need for a review of the crosslinking strategies used to create smart hydrogels from polysaccharides. This review provides a comprehensive overview of how stimuli-responsive hydrogels can be designed and made using five key polysaccharides: chitosan, hyaluronic acid, alginate, dextran, and cellulose. Various methods, such as chemical crosslinking, dynamic crosslinking, and physical crosslinking, which are used to form networks within these hydrogels, ultimately determine their ability to respond to stimuli, have been explored. This article further looks at different polysaccharide-based hydrogel wound dressings that can respond to factors such as reactive oxygen species, temperature, pH, glucose, light, and ultrasound in the wound environment and discusses how these responses can enhance wound healing. Finally, this review provides insights into how stimuli-responsive polysaccharide-based hydrogels can be developed further as advanced wound dressings in the future.
  • JOURNAL ARTICLE
    Correction to: Intraperitoneally Delivered Umbilical Cord Lining Mesenchymal Stromal Cells Improve Survival and Kidney Function in Murine Lupus via Myeloid Pathway Targeting (International Journal of Molecular Sciences, (2022), 24, 1, (365), 10.3390/ijms24010365)
    1 Mar 2025International Journal of Molecular Sciences26(5)
    Co-authors: Chua AWC, Guo D, Tan JC
    DOIDOI: 10.3390/ijms26051997
    In the original publication, there was a mistake in Figure 2C as published [...].
  • JOURNAL ARTICLE
    Addressing the Peri-Wound Intact Skin of Hard-To-Heal Diabetic Foot Ulcers With Topical Red Deer Conditioned Media (PTT-6TM) Skin Conditioner: A Case Series on Clinical Efficacy
    1 Nov 2024Health Science Reports7(11)
    Co-authors: Leow K, Alvis LTC, Yuen BEC
    DOIDOI: 10.1002/hsr2.70211
    Background and Aim: The healing of diabetic foot ulcers (DFUs) can be hindered by the susceptibility of the surrounding intact skin to pro-inflammatory proteases. A conditioned media, known as PTT-6<sup>TM</sup>, derived from mesenchymal stem cells found in the lining of red deer umbilical cords, has been formulated to protect the intact peri-wound skin of DFUs. The aim is to evaluate the clinical effectiveness of PTT-6<sup>TM</sup> in managing peri-wound intact skin in hard-to-heal DFUs. Methods: Patients with DFUs that persisted for over 3 months were divided into two subgroups. The active wound group received standard-of-care treatment protocol followed by PTT-6<sup>TM</sup> application around the peri-wound area, while the maintenance wound group applied PTT-6<sup>TM</sup> media over the healed wound site. Results: Forty cases were recorded, of which 22 (55%) were included in the active wound group. The majority were male (75%, <i>n</i> = 30) and vast majority had cardiovascular risk factors, including diabetes mellitus (100%, <i>n</i> = 40), hyperlipidemia (82.5%, <i>n</i> = 33), and hypertension (77.5%, <i>n</i> = 31). Most patients had forefoot wounds (80%, <i>n</i> = 32) on the plantar aspect (82.5%, <i>n</i> = 33). The patients in the active wound group had chronic DFUs for a mean of 218 ± 201 days. Of those treated with PTT-6™ media, 68.4% (<i>n</i> = 13) achieved complete wound healing within a mean duration of 69 ± 50 days. Additionally, most patients in the maintenance wound group remained ulcer-free at 3 months (91.7%, <i>n</i> = 11) and 6 months (66.7%, <i>n</i> = 6). Conclusion: The study results suggest that PTT-6<sup>TM</sup> media may serve as an additional treatment modality for enhancing the microenvironment at the peri-wound intact skin site. This could indirectly facilitate wound healing by preserving the integrity of the peri-wound intact skin.
  • JOURNAL ARTICLE
    Results of the Phase 1 Open-Label Safety Study of Umbilical Cord Lining Mesenchymal Stromal/Stem Cells (Corlicyte®) to Heal Chronic Diabetic Foot Ulcers
    1 Jun 2024Biomedicines12(6)
    Co-authors: Low Wang CC, Chong T, Moore G
    DOIDOI: 10.3390/biomedicines12061375
    BACKGROUND: Mesenchymal stromal/stem cells (MSCs) play a critical role in wound healing. Corlicyte<sup>®</sup> is an MSC product derived from allogeneic umbilical cord tissue donated under an institutional review board-approved protocol and processed in accordance with section 501(a)(2)(B) of the Federal Food, Drug, and Cosmetic Act. This open-label phase 1 trial was performed under a United States Food and Drug Administration Investigational New Drug Application to establish the safety and tolerability of Corlicyte<sup>®</sup> in patients with diabetes and chronic diabetic foot ulcer (DFU). METHODS: Escalating doses were applied topically twice a week for up to 8 weeks after ulcer debridement, wound photography, and measurement. Subjects were followed for 4 weeks after the treatment phase. Adverse events were assessed at every visit. RESULTS: Nine subjects in 2 dosing cohorts completed the trial. No subjects experienced a serious adverse reaction to Corlicyte<sup>®</sup> or the development of anti-human leukocyte antigen (HLA) antibodies. Sixty percentage of subjects in the lower dose cohort experienced ulcer closure by Day 70 of follow-up, while the mean ulcer size was reduced by 54-67% in the other subjects. CONCLUSIONS: Topical administration of Corlicyte<sup>®</sup>, a novel biologic therapy consisting of allogeneic umbilical cord lining MSCs, appeared safe and tolerable and resulted in a significant decrease in ulcer area, demonstrating its potential as a therapy for healing of chronic DFU.
  • JOURNAL ARTICLE
    Improvement in Skin Elasticity Using Red Deer Umbilical Cord Lining Mesenchymal Stem Cell Conditioned Media
    1 Jan 2023Journal of Drugs in Dermatology Jdd22(1):82-89
    Co-authors: Ong C, Lim I, Goldman M
    DOIDOI: 10.36849/JDD.6906
    BACKGROUND: Significant improvement in skin tone was reported after topical application of a facial cream (CALECIM® Professional Multi-Action Cream, CALECIM Cosmeceuticals, Singapore) containing conditioned media (CM) derived from Red Deer Umbilical Cord Lining Mesenchymal Stem Cell (RD-CLMSC) culture. This study investigates the paracrine effects of RD-CLMSC-CM on human dermal fibroblasts (HDF) to understand how it may increase skin turgor and elasticity. Skin aging is associated with lower levels of extracellular matrix components such as hyaluronic acid (HA) and elastin, resulting in poor skin turgor and elasticity. Histochemical staining followed by photocolorimetry demonstrated that RD-CLMSC-CM upregulated HDF expression of elastin by 56% and HA by 83% compared with DMEM/10% Fetal Calf Serum (FCS).To further quantify the effects of CM, a proliferation assay was used to assess HDF response to RD-CLMSC-CM exposure. Exposure to RD-CLMSC-CM resulted in the highest increase in HDF proliferation over DMEM/10% FCS (113%) followed by Human (H)-CLMSC-CM (112%), then Human Foreskin Fibroblast (FSF)-CM (16%).These experimental results demonstrate both the cross-species efficacy and lack of toxicity of RD-CLMSC-CM on HDF. These pre-clinical studies also suggest the clinical effects of RD-CLMSC-CM on skin turgor may be related to increased HA and elastin production by HDF, as well as enhanced proliferation. J Drugs Dermatol. 2023;21(1):82-89. doi:10.36849/JDD.6906.
  • JOURNAL ARTICLE
    Intraperitoneally Delivered Umbilical Cord Lining Mesenchymal Stromal Cells Improve Survival and Kidney Function in Murine Lupus via Myeloid Pathway Targeting
    1 Jan 2023International Journal of Molecular Sciences24(1)
    Co-authors: Chua AWC, Guo D, Tan JC
    DOIDOI: 10.3390/ijms24010365
    To determine the therapeutic efficacy of human umbilical cord lining mesenchymal stromal cells (CL-MSCs) (US Patent number 9,737,568) in lupus-prone MRL/lpr (Fas<sup>lpr</sup>) mice and elucidate its working mechanisms. A total of 4 doses of (20-25) × 10<sup>6</sup> cells/kg of CL-MSCs was given to 16-week-old female Fas<sup>lpr</sup> mice by intraperitoneal injection. Three subsequent doses were given on 17 weeks, 18 weeks, and 22 weeks, respectively. Six-week-old Fas<sup>lpr</sup> mice were used as disease pre-onset controls. Mice were monitored for 10 weeks. Mouse kidney function was evaluated by examining complement component 3 (C3) deposition, urinary albumin-to-creatinine ratio (ACR), and lupus nephritis (LN) activity and chronicity. Working mechanisms were elucidated by flow cytometry, Luminex/ELISA (detection of anti-dsDNA and isotype antibodies), and RNA sequencing. CL-MSCs improved mice survival and kidney function by reducing LN activity and chronicity and lymphocyte infiltration over 10 weeks. CL-MSCs also reduced urinary ACR, renal complement C3 deposition, anti-dsDNA, and isotype antibodies that include IgA, IgG1, IgG2a, IgG2b, and IgM. Immune and cytokine profiling demonstrated that CL-MSCs dampened inflammation by suppressing splenic neutrophils and monocytes/macrophages, reducing plasma IL-6, IL-12, and CXCL1 and stabilizing plasma interferon-γ and TNF-α. RNA sequencing further showed that CL-MSCs mediated immunomodulation via concerted action of pro-proinflammatory cytokine-induced chemokines and production of nitric oxide in macrophages. CL-MSCs may provide a novel myeloid (neutrophils and monocytes/macrophages)-targeting therapy for SLE.
  • JOURNAL ARTICLE
    Sensitive ex vivo human skin transdermal assay testing method with mass spectrometric analysis for cosmetics application
    1 Nov 2022Journal of Cosmetic Dermatology21(11):6124-6128
    Co-authors: Tan TY, Wee HN, Lee LS
    DOIDOI: 10.1111/jocd.15154
    BACKGROUND: Cosmetics manufacturers are focused on cosmetic delivery systems into the skin, but the level of diffusion of the systems in the skin tissues is not well understood. The current methods, such as Franz diffusion, assess analyte diffusion in the whole skin or artificial membranes, which has limitations for understanding skin delivery systems. AIMS: Our study aimed to create a transdermal delivery method which is based on dermal-epidermal separation of human skin, allowing us to assess each layer of skin separately for its efficacy. MATERIALS AND METHODS: During the experiment, resveratrol was used as the target analyte by applying it to the skin and then separating it into dermis and epidermis. Each layer is treated individually and subjected to a high-resolution mass spectrometry analysis to detect resveratrol levels. As a result, the efficiency of resveratrol diffusion in the dermal and epidermal layers of the skin can be evaluated. RESULTS: We found that resveratrol was detected in both the dermal and epidermal layers using our method. CONCLUSIONS: Hence, we developed a sensitive method for transdermal delivery testing that can be used to evaluate skin delivery systems for cosmetic or pharmaceutical purposes.
  • JOURNAL ARTICLE
    Human Umbilical Cord Lining-Derived Epithelial Cells: A Potential Source of Non-Native Epithelial Cells That Accelerate Healing in a Porcine Cutaneous Wound Model
    1 Aug 2022International Journal of Molecular Sciences23(16)
    Co-authors: Kua JEH, Siow CW, Lim WK
    DOIDOI: 10.3390/ijms23168918
    Human umbilical cord lining epithelial cells [CLECs) are naïve in nature and can be ethically recovered from cords that are routinely discarded. The success of using oral mucosal epithelial cells for cornea defects hints at the feasibility of treating cutaneous wounds using non-native CLECs. Herein, we characterized CLECs using flow cytometry (FC) and skin organotypic cultures in direct comparison with skin keratinocytes (KCs). This was followed by wound healing study to compare the effects of CLEC application and the traditional use of human skin allografts (HSGs) in a porcine wound model. While CLECs were found to express all the epidermal cell markers probed, the major difference between CLECs and KCs lies in the level of expression (in FC analysis) as well as in the location of expression (of the epithelium in organotypic cultures) of some of the basal cell markers probed. On the pig wounds, CLEC application promoted accelerated healing with no adverse reaction compared to HSG use. Though CLECs, like HSGs, elicited high levels of local and systemic immune responses in the animals during the first week, these effects were tapered off more quickly in the CLEC-treated group. Overall, the in vivo porcine data point to the potential of CLECs as a non-native and safe source of cells to treat cutaneous wounds.
  • JOURNAL ARTICLE
    8 Mar 2021Frontiers in Cell and Developmental Biology8
    Co-authors: Chua K, Lim FP, Lee VKM
    DOIDOI: 10.3389/fcell.2020.596170
    <b>Purpose:</b> We investigated the use of human Cord Lining Mesenchymal Stem Cells (CL-MSCs) (US Patent number 9,737,568), in a rabbit hindlimb ischemia model, and evaluated their potential in stimulating neovascularization. Allogenic human CL- MSCs could potentially be used to treat patients with lower limb ischemia and non-healing wounds. <b>Methods:</b> Twenty rabbits were divided into two separate groups. We created a hindlimb ischemia model surgically. At 21 and 49 days post-operatively, animals in the treatment group were injected with CL-MSCs (500,000 cells per 0.2 ml on each site) at 10 different sites (Quadriceps- 4 sites, Hamstrings- 4 sites and Calf--2 sites) in the hindlimb muscles. The control group received only saline injection to the corresponding sites at the same time point as the treatment group. We then evaluated the effects of treatment on neovascularization by angiography, laser doppler perfusion imaging, as well as by histology. We evaluated the tissue samples for any signs of local immune reaction to the cell implantation. We also observed the rabbit clinically for any adverse effects after treatment. <b>Results:</b> We found a higher number of CD31 positive cells in the treatment group, with a greater number of capillaries found in the treated muscles. The Rectus Femoris demonstrated a median vessel count/muscle fiber of 0.121 for the treatment group, compared to 0.076 in the control group (median difference 0.04; 95% CI 0.001-0.11; <i>p</i> = 0.041). The Gastrocnemius demonstrated a median vessel count/muscle fiber of 0.175 for the treatment group, compared to 0.089 in the control group (median difference 0.087; 95% CI -0.006 to 0.234; <i>p</i> = 0.07). Blood perfusion quantification through Laser Doppler Perfusion Imaging (LDPI) also demonstrated a non-statistically significant increase in perfusion in favor of the treatment group. CL-MSCs demonstrated no toxicity associated morbidity and minimal local immune reaction to implantation. <b>Conclusion:</b> CL-MSCs have a positive effect on angiogenesis in a rabbit hindlimb ischemia model. This preliminary data is encouraging and paves the way for future large animal studies or for clinical trials.
  • JOURNAL ARTICLE
    1 Jan 2020Cell Transplantation29
    Co-authors: Lim RHG, Liew JXK, Wee A
    DOIDOI: 10.1177/0963689719896559
    We investigated the safety of using umbilical cord-lining stem cells for liver regeneration and tested a novel method for stem cell delivery. Stem cells are known by their ability to repair damaged tissues and have the potential to be used as regenerative therapies. The umbilical cord's outer lining membrane is known to be a promising source of multipotent stem cells and can be cultivated in an epithelial cell growth medium to produce cell populations which possess the properties of both epithelial cells and embryonic stem cells-termed cord-lining epithelial cells (CLEC). Hepatocytes are epithelial cells of the liver and their proliferation upon injury is the main mechanism in restoring the liver. Earlier studies conducted showed CLEC can be differentiated into functioning hepatocyte-like cells (HLC) and can survive in immunologically competent specimens. In this study, we chose a porcine model to investigate CLEC as a treatment modality for liver failure. We selected 16 immune competent Yorkshire-Dutch Landrace pigs, with a mean weight of 40.5 kg, for this study. We performed a 50% hepatectomy to simulate the liver insufficient disease model. After the surgery, four pigs were transplanted with a saline scaffold while seven pigs were transplanted with a HLC scaffold. Five pigs died on the surgical table and were omitted from the study analysis. This study addressed the safety of transplanting human CLEC in a large animal model. The transplant interfaces were evaluated and no signs of cellular rejection were observed in both groups.
  • JOURNAL ARTICLE
    30 Dec 2019Open Access Macedonian Journal of Medical Sciences7(24):4266-4271
    Co-authors: Ngan ND, Chau HM, Dong PN
    DOIDOI: 10.3889/oamjms.2019.372
    BACKGROUND: Persistent corneal epithelial defect (PED) is a consequence of many ocular surface disorders. Although many therapies have been suggested, the treatment of this disease have faced a lot of difficulties up to now. The transplatation of cultivated amniotic epithelial cells sheets is the new promised method for PED. Cord lining epithelial cells (CLECs) are epithelial cells of amniotic membrane of umbilical cord, so these cultivated cells sheet may be good for treating PED. AIM: To evaluate the efficacy of the transplantation of cultivated CLECs sheets in treatment of PED and analyze some influential factors of this therapy. METHODS: A prospective interventional case series with transplantation of tissue-cultured human CLECs in 37 PED eyes in Vietnam National Institute of Ophthalmology. RESULTS: Thirty four of 37 eyes were healed with the cells transplantation and 22 eyes of them healed within a week postoperatively. There were normal corneal scars and normal corneal epithelial cell (by impression cytology detection) on transplantation site in all 31 successful cases. The other successful eyes were done lamellar keratoplasty (respectively in 1 month, 3 months, 6 months and 27 months postoperatively) to investigate the histopathology of the CLECs transplant site. The histopathological images showed normal corneal scar and there was no appearance of CLECs in transplant site. CONCLUSION: tissue-cultured human CLECs transplantation is a quite safe and effective treatment for persistent corneal epithelial defect. The CLECs may help the epithelial healing at early stage but do not exist at transplant site for a long time.
  • CONFERENCE PAPER
    COMPARISON OF EXTRACTION METHODS AND CULTURE MEDIUM FOR UMBILICAL CORD LINING- AND WHARTON'S JELLY-DERIVED MESENCHYMAL STROMAL CELLS
    May 2019CYTOTHERAPY21(5):S80 (1 page)ELSEVIER SCI LTD
    Co-authors: Boey KP, Lim DS, Ong C
    DOIDOI: 10.1016/j.jcyt.2019.03.489
    Background & Aim The umbilical cord (UC) is a rich source of mesenchymal stromal cells (MSC). The function of UC-MSC extracted by enzymatic digestion and long-term culture in bovine serum-supplemented medium may be adversely affected. Using a higher proportion of animal-based supplements may introduce variability in manufactured MSC. We investigated if a cGMP-compliant method would overcome these challenges. This study compared the yield, purity, differentiation potential and chromosomal stability of MSC derived from cryopreserved UC lining and Wharton's Jelly, under the influence of different extraction methods (enzymatic digest versus explant) and culture media (PTT-6 versus DMEM:F12 with 10% FBS). Methods, Results & Conclusion Six donated UC samples were disinfected, cut into discs and frozen in cryopreservant containing 10% DMSO. Samples were thawed at 37°C, then incubated in either media for 3 - 4 days at 37°C in 5% CO2. MSC were extracted from the incubated tissues and differentially treated to generate every permutation of cell source, extraction method and culture media (total conditions: 8). At every passage, cell doubling rate was calculated and morphology was captured. At Passage 6 (P6), trilineage differentiation and karyotype were evaluated by StemPro® differentiation kits and G-banding. MSC extracted from all conditions displayed fibroblastic, spindle-shaped morphology and plastic-adherence. Only P6 MSC cultured in DMEM:F12 but not PPT-6 displayed enlarged and polygonal morphology. Overall doubling rate of PTT-6 cultured MSC was significantly faster than its DMEM:F12 counterpart (50.1 ± 9.7 h versus 98.4 ± 37.5 h, P < 0.05). Cell doubling rate was independent of either extraction method or tissue source. Tissue source and extraction method did not influence trilineage differentiation. PTT-6 favoured adipogenesis while MSC from DMEM:F12 were inclined towards osteogenesis. Both media allowed for chondrogenesis. No gross chromosomal abnormalities were observed after at least 10 population doublings. The patented PTT-6 medium maintained MSC stemness and significantly hastened UC-MSC expansion without detriment to trilineage differentiation or chromosomal stability. Further work is warranted to determine whether replicative senescence was averted.
  • JOURNAL ARTICLE
    Functional cationic derivatives of starch as antimicrobial agents
    21 Jan 2019Polymer Chemistry10(3):412-423
    Co-authors: Venkataraman S, Lee ALZ, Tan JPK
    DOIDOI: 10.1039/c8py00740c
    <p> Antimicrobial polymers with a broad spectrum of action and high selectivity towards pathogens ( versus mammalian cells) provide the opportunity to combat infections with only a limited chance of resistance development. </p> <p> Antimicrobial polymers with a broad spectrum of action and high selectivity towards pathogens ( versus mammalian cells) provide the opportunity to combat infections with only a limited chance of resistance development. To this end, functional antimicrobial biodegradable materials derived from inexpensive renewable resources such as polysaccharides would pave the way for broader applications. Here we report a facile one-pot approach to access potent functional antimicrobial polymers from soluble starch, a renewable plant-based starting material and other readily available reagents. In solution-state, these polymers with optimal composition demonstrate excellent antibacterial activity, but limited antifungal properties. The reactive allyl groups installed onto this polymeric platform enabled seamless translation of these polymers into antimicrobial hydrogels and coatings via photo-mediated thiol–ene reactions. Both the hydrogels and hydrogel-coated cotton-pads exhibited high killing efficiencies across multiple strains of pathogens (∼100% for S. aureus , E. coli and P. aeruginosa ). Installation of reactive groups onto antimicrobial platforms allows for rapid development of formulations and prototypes in different forms such as solutions, gels and surface coatings by minimizing or completely eliminating the need to optimize the polymer to suit different applications. These results demonstrate the potential utility of cationic starch-based biodegradable polymers as antimicrobial materials and coatings for the prevention of infections. </p>
  • JOURNAL ARTICLE
    Integrated multimodal evaluation of genotoxicity in ZFN-modified primary human cells
    1 Jan 2018Methods in Molecular Biology1867:141-164
    Co-authors: Sivalingam J, Kenanov D, Ng WH
    DOIDOI: 10.1007/978-1-4939-8799-3_11
    Iatrogenic adverse events in clinical trials of retroviral vector-mediated gene-corrected cells have prioritized the urgent need for more comprehensive and stringent assessment of potentially genotoxic off-target alterations and the biosafety of cells intended for therapeutic applications. Genome editing tools such as zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced palindromic repeats (CRISPR)-Cas9 nuclease systems are being investigated as safer and efficient alternatives for site-directed genome modification. Using site-specific integration into the AAVS1 locus of primary human cells as an example, we present an integrated approach to multimodal investigation of off-target alterations and an evaluation of potential genotoxicity induced by ZFN-mediated integration of a therapeutic transgene.
  • JOURNAL ARTICLE
    1 Dec 2017Scientific Reports7(1)
    Co-authors: Prasad A, Teh DBL, Blasiak A
    DOIDOI: 10.1038/s41598-017-06331-8
    The cellular-level effects of low/high frequency oscillating magnetic field on excitable cells such as neurons are well established. In contrast, the effects of a homogeneous, static magnetic field (SMF) on Central Nervous System (CNS) glial cells are less investigated. Here, we have developed an in vitro SMF stimulation set-up to investigate the genomic effects of SMF exposure on oligodendrocyte differentiation and neurotrophic factors secretion. Human oligodendrocytes precursor cells (OPCs) were stimulated with moderate intensity SMF (0.3 T) for a period of two weeks (two hours/day). The differential gene expression of cell activity marker (c-fos), early OPC (Olig1, Olig2. Sox10), and mature oligodendrocyte markers (CNP, MBP) were quantified. The enhanced myelination capacity of the SMF stimulated oligodendrocytes was validated in a dorsal root ganglion microfluidics chamber platform. Additionally, the effects of SMF on the gene expression and secretion of neurotrophic factors- BDNF and NT3 was quantified. We also report that SMF stimulation increases the intracellular calcium influx in OPCs as well as the gene expression of L-type channel subunits-CaV1.2 and CaV1.3. Our findings emphasize the ability of glial cells such as OPCs to positively respond to moderate intensity SMF stimulation by exhibiting enhanced differentiation, functionality as well as neurotrophic factor release.
  • JOURNAL ARTICLE
    Comparison of international normalized ratio audit parameters in patients enrolled in GARFIELD-AF and treated with vitamin K antagonists
    1 Aug 2016British Journal of Haematology174(4):610-623
    Co-authors: Fitzmaurice DA, Accetta G, Haas S
    DOIDOI: 10.1111/bjh.14084
    Vitamin K antagonist (VKA) therapy for stroke prevention in atrial fibrillation (AF) requires monitoring of the international normalized ratio (INR). We evaluated the agreement between two INR audit parameters, frequency in range (FIR) and proportion of time in the therapeutic range (TTR), using data from a global population of patients with newly diagnosed non-valvular AF, the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF). Among 17 168 patients with 1-year follow-up data available at the time of the analysis, 8445 received VKA therapy (±antiplatelet therapy) at enrolment, and of these patients, 5066 with ≥3 INR readings and for whom both FIR and TTR could be calculated were included in the analysis. In total, 70 905 INRs were analysed. At the patient level, TTR showed higher values than FIR (mean, 56·0% vs 49·8%; median, 59·7% vs 50·0%). Although patient-level FIR and TTR values were highly correlated (Pearson correlation coefficient [95% confidence interval; CI], 0·860 [0·852-0·867]), estimates from individuals showed widespread disagreement and variability (Lin's concordance coefficient [95% CI], 0·829 [0·821-0·837]). The difference between FIR and TTR explained 17·4% of the total variability of measurements. These results suggest that FIR and TTR are not equivalent and cannot be used interchangeably.
  • JOURNAL ARTICLE
    1 Mar 2016Molecular Therapy24(3):607-619
    Co-authors: Sivalingam J, Kenanov D, Han H
    DOIDOI: 10.1038/mt.2015.223
    Costly coagulation factor VIII (FVIII) replacement therapy is a barrier to optimal clinical management of hemophilia A. Therapy using FVIII-secreting autologous primary cells is potentially efficacious and more affordable. Zinc finger nucleases (ZFN) mediate transgene integration into the AAVS1 locus but comprehensive evaluation of off-target genome effects is currently lacking. In light of serious adverse effects in clinical trials which employed genome-integrating viral vectors, this study evaluated potential genotoxicity of ZFN-mediated transgenesis using different techniques. We employed deep sequencing of predicted off-target sites, copy number analysis, whole-genome sequencing, and RNA-seq in primary human umbilical cord-lining epithelial cells (CLECs) with AAVS1 ZFN-mediated FVIII transgene integration. We combined molecular features to enhance the accuracy and activity of ZFN-mediated transgenesis. Our data showed a low frequency of ZFN-associated indels, no detectable off-target transgene integrations or chromosomal rearrangements. ZFN-modified CLECs had very few dysregulated transcripts and no evidence of activated oncogenic pathways. We also showed AAVS1 ZFN activity and durable FVIII transgene secretion in primary human dermal fibroblasts, bone marrow- and adipose tissue-derived stromal cells. Our study suggests that, with close attention to the molecular design of genome-modifying constructs, AAVS1 ZFN-mediated FVIII integration in several primary human cell types may be safe and efficacious.
  • CONFERENCE PAPER
    Immuno-privileged cord lining epithelial cells for advanced wound repair - a pilot in vivo study
    2016International Society for Stem Cell Research Annual Meeting
    Co-authors: THANG PT
  • JOURNAL ARTICLE
    Preclinical Evaluation of Tegaderm™ Supported Nanofibrous Wound Matrix Dressing on Porcine Wound Healing Model
    Feb 2015ADVANCES IN WOUND CARE4(2):110-118 (9 pages)MARY ANN LIEBERT, INC
    Co-authors: Ong CT, Zhang Y, Lim R
    DOIDOI: 10.1089/wound.2014.0527
    <b>Objective:</b> Nanofibers for tissue scaffolding and wound dressings hold great potential in realizing enhanced healing of wounds in comparison with conventional counterparts. Previously, we demonstrated good fibroblast adherence and growth on a newly developed scaffold, Tegaderm™-Nanofiber (TG-NF), made from poly ɛ-caprolactone (PCL)/gelatin nanofibers electrospun onto Tegaderm (TG). The purpose of this study is to evaluate the performance and safety of TG-NF dressings in partial-thickness wound in a pig healing model. <b>Approach:</b> To evaluate the rate of reepithelialization, control TG, human dermal fibroblast-seeded TG-NF(+) and -unseeded TG-NF(-) were randomly dressed onto 80 partial-thickness burns created on four female and four male pigs. Wound inspections and dressings were done after burns on day 7, 14, 21, and 28. On day 28, full-thickness biopsies were taken for histopathological evaluation by Masson-Trichrome staining for collagen and hematoxylin-eosin staining for cell counting. <b>Results:</b> No infection and severe inflammation were recorded. Wounds treated with TG-NF(+) reepithelialized significantly faster than TG-NF(-) and control. Wound site inflammatory responses to study groups were similar as total cell counts on granulation tissues show no significant differences. Most of the wounds completely reepithelialized by day 28, except for two wounds in control and TG-NF(-). A higher collagen coverage was also recorded in the granulation tissues treated with TG-NF(+). <b>Innovation and Conclusion:</b> With better reepithelialization achieved by TG-NF(+) and similar rates of wound closure by TG-NF(-) and control, and the absence of elevated inflammatory responses to TG-NF constructs, TG-NF constructs are safe and demonstrated good healing potentials that are comparable to Tegaderm.
  • JOURNAL ARTICLE
    1 Jan 2015Journal of the American Heart Association5(3)
    Co-authors: Pokorney SD, Piccini JP, Stevens SR
    DOIDOI: 10.1161/JAHA.115.002197
    BACKGROUND: Atrial fibrillation is associated with higher mortality. Identification of causes of death and contemporary risk factors for all-cause mortality may guide interventions. METHODS AND RESULTS: In the Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF) study, patients with nonvalvular atrial fibrillation were randomized to rivaroxaban or dose-adjusted warfarin. Cox proportional hazards regression with backward elimination identified factors at randomization that were independently associated with all-cause mortality in the 14 171 participants in the intention-to-treat population. The median age was 73 years, and the mean CHADS2 score was 3.5. Over 1.9 years of median follow-up, 1214 (8.6%) patients died. Kaplan-Meier mortality rates were 4.2% at 1 year and 8.9% at 2 years. The majority of classified deaths (1081) were cardiovascular (72%), whereas only 6% were nonhemorrhagic stroke or systemic embolism. No significant difference in all-cause mortality was observed between the rivaroxaban and warfarin arms (P=0.15). Heart failure (hazard ratio 1.51, 95% CI 1.33-1.70, P<0.0001) and age ≥75 years (hazard ratio 1.69, 95% CI 1.51-1.90, P<0.0001) were associated with higher all-cause mortality. Multiple additional characteristics were independently associated with higher mortality, with decreasing creatinine clearance, chronic obstructive pulmonary disease, male sex, peripheral vascular disease, and diabetes being among the most strongly associated (model C-index 0.677). CONCLUSIONS: In a large population of patients anticoagulated for nonvalvular atrial fibrillation, ≈7 in 10 deaths were cardiovascular, whereas <1 in 10 deaths were caused by nonhemorrhagic stroke or systemic embolism. Optimal prevention and treatment of heart failure, renal impairment, chronic obstructive pulmonary disease, and diabetes may improve survival. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov/. Unique identifier: NCT00403767.
  • JOURNAL ARTICLE
    Human umbilical cord lining cells as novel feeder layer for ex vivo cultivation of limbal epithelial cells
    1 Jan 2015Investigative Ophthalmology and Visual Science56(8):4697-4704
    Co-authors: Ang LPK, Jain P, Phan TT
    DOIDOI: 10.1167/iovs.14-15965
    PURPOSE: To determine the effectiveness of human umbilical cord-derived mucin-expressing cord lining epithelial cells (CLEC-muc) as feeder cells in a coculture system for the cultivation of human limbal stem cells. METHODS: Human CLEC-muc were cultured in PTTe-1 medium and treated with mitomycin C to arrest their growth to make the feeder layer. Single-cell suspension of limbal cells was prepared from corneal rim collected from the Singapore Eye Bank. Limbal cells were cultured in a coculture system with CLEC-muc as well as 3T3 cells as feeder layer. We compared the colony-forming efficiency and cell morphology of the limbal cells cultured in the two different feeder layers. We also compared the expression level of several putative limbal stem cell markers, such as HES1, ABCG2, ΔNP63, and BMI1, in the cultured limbal cells by immunostaining and quantitative (q)RT-PCR. Expression of cytokeratins CK14, CK15, CK19, CK3, and CK4 was further compared. RESULTS: Human limbal epithelial cells cultured in both types of feeder layers showed comparable cell morphology and colony-forming efficiency. These cells exhibited a similar expression pattern of HES1, ABCG2, ΔNP63, BMI1, CK14, CK15, CK19, and CK3 as detected by immunostaining and PCR. CONCLUSIONS: Human CLEC-muc may be a suitable alternative to conventional mouse 3T3 feeder cells, which may reduce the risk of zoonotic infection.
  • JOURNAL ARTICLE
    Epithelial and mesenchymal stem cells from the umbilical cord lining membrane
    1 Jan 2014Cell Transplantation23(4-5):497-503
    Co-authors: Lim IJ, Phan TT
    DOIDOI: 10.3727/096368914X678346
    Intense scientific research over the past two decades has yielded much knowledge about embryonic stem cells, mesenchymal stem cells from bone marrow, as well as epithelial stem cells from the skin and cornea. However, the billions of dollars spent in this research have not overcome the fundamental difficulties intrinsic to these stem cell strains related to ethics (embryonic stem cells), as well as to technical issues such as accessibility, ease of cell selection and cultivation, and expansion/mass production, while maintaining consistency of cell stemness (all of the stem cell strains already mentioned). Overcoming these technical hurdles has made stem cell technology expensive and any potential translational products unaffordable for most patients. Commercialization efforts have been rendered unfeasible by this high cost. Advanced biomedical research is on the rise in Asia, and new innovations have started to overcome these challenges. The Nobel Prize-winning Japanese development of iPSCs has effectively introduced a possible replacement for embryonic stem cells. For non-embryonic stem cells, cord lining stem cells (CLSCs) have overcome the preexisting difficulties inherent to mesenchymal stem cells from the bone marrow as well as epithelial stem cells from the skin and cornea, offering a realistic, practical, and affordable alternative for tissue repair and regeneration. This novel CLSC technology was developed in Singapore in 2004 and has 22 international patents granted to date, including those from the US and UK. CLSCs are derived from the umbilical cord outer lining membrane (usually regarded as medical waste) and is therefore free from ethical dilemmas related to its collection. The large quantity of umbilical cord lining membrane that can be collected translates to billions of stem cells that can be grown in primary stem cell culture and therefore very rapid and inexpensive cell cultivation and expansion for clinical translational therapies. Both mesenchymal and epithelial stem cells can be isolated from the umbilical cord lining membrane, usefully regenerating not only mesenchymal tissue, such as bone, cartilage, and cardiac and striated muscle, but also epithelial tissue, such as skin, cornea, and liver. Both mesenchymal and epithelial CLSCs are immune privileged and resist rejection. Clinically, CLSCs have proved effective in the treatment of difficult-to-heal human wounds, such as diabetic ulcers, recalcitrant chronic wounds, and even persistent epithelial defects of the cornea. Heart and liver regeneration has been shown to be successful in animal studies and await human trials. CLSCs have also been shown to be an effective feeder layer for cord blood hematopoietic stem cells and, more recently, has been recognized as an abundant and high-quality source of cells for iPSC production. Banking of CLSCs by cord blood banks in both private and public settings is now available in many countries, so that individuals may have their personal stores of CLSCs for future translational applications for both themselves and their families. Cord lining stem cells are strongly positioned to be the future of cell therapy and regenerative medicine.
  • JOURNAL ARTICLE
    Intragenic integration in DLC1 sustains factor VIII expression in primary human cells without insertional oncogenicity
    1 Jan 2014Gene Therapy21(4):402-412
    Co-authors: Sivalingam J, Phan TT, Kon OL
    DOIDOI: 10.1038/gt.2014.11
    Techniques enabling precise genome modifications enhance the safety of gene-based therapy. DLC1 is a hot spot for phiC31 integrase-mediated transgene integration in vitro and in vivo. Here we show that integration of a coagulation factor VIII transgene into intron 7 of DLC1 supports durable expression of factor VIII in primary human umbilical cord-lining epithelial cells. Oligoclonal cells with factor VIII transgene integrated in DLC1 did not have altered expression of DLC1 or neighbouring genes within a 1-Mb interval. Only 1.9% of all expressed genes were transcriptionally altered; most were downregulated and mapped to cell cycle and DNA repair pathways. DLC1-integrated cells were not tumourigenic in vivo and were normal by high-resolution genomic DNA copy number analysis. Our data identify DLC1 as a locus for durable transgene expression that does not incur features of insertional oncogenesis, thus expanding options for developing ex vivo cell therapy mediated by site-specific integration methods.
  • JOURNAL ARTICLE
    Grafts enriched with subamnion-cord-lining mesenchymal stem cell angiogenic spheroids induce post-ischemic myocardial revascularization and preserve cardiac function in failing rat hearts
    1 Dec 2013Stem Cells and Development22(23):3087-3099
    Co-authors: Martinez EC, Vu DT, Wang J
    DOIDOI: 10.1089/scd.2013.0119
    A crucial question in post-ischemic cell therapy refers to the ideal method of cell delivery to the heart. We hypothesized that epicardial implantation of subamnion-cord-lining mesenchymal stem cells (CL-MSC) angiogenic spheroids embedded within fibrin grafts (SASG) facilitates donor cell survival and enhances cardiac function in failing rat hearts. Furthermore, we compared the efficacy of this approach applied through two delivery methods. Spheroids made of 1.5×10(4) human CL-MSC coated with 2×10(3) human umbilical vein endothelial cells were self-assembled in hanging drops. SASG were constructed by embedding 150 spheroids in fibrin matrix. Except for untreated rats (MI, n=8), grafts were implanted 2 weeks after myocardial infarction upon confirmation of ensued heart failure through thoracotomy: SASG (n=8) and fibrin graft (FG, n=8); or video-assisted thoracoscopic surgery (VATS): SASG-VATS (n=8) and FG-VATS (n=7). In vivo CL-MSC survival was comparable between both SASG-treated groups throughout the study. SASG and SASG-VATS animals had decreased left ventricular end-diastolic pressure relative to untreated animals, and increased fractional shortening compared to MI and FG controls, 4 weeks after treatment. A 14.1% and 6.2% enhancement in ejection fraction from week 2 to 6 after injury was observed in SASG/SASG-VATS, paralleled by improvement in cardiac output. Treated hearts had smaller scar size, and more blood vessels than MI, while donor CL-MSC contributed to arteriogenesis within the graft and infarct areas. Taken together, our data suggest that SASG treatment has the potential to restore failing hearts by preserving cardiac function and inducing myocardial revascularization, while attenuating cardiac fibrosis. Furthermore, we introduce a method for minimally invasive in situ graft assembly.