Melanocyte stem cells in the skin: Origin, biological characteristics, homeostatic maintenance and therapeutic potential

Melanocyte stem cells (MSCs), melanocyte lineage-specific skin stem cells derived from the neural crest, are observed in the mammalian hair follicle, the epidermis or the sweat gland. MSCs differentiate into mature melanin-producing melanocytes, which confer skin and hair pigmentation and uphold vital skin functions. In controlling and coordinating the homeostasis, repair and regeneration of skin tissue, MSCs play a vital role. Decreased numbers or impaired functions of MSCs are closely associated with the development and therapy of many skin conditions, such as hair graying, vitiligo, wound healing and melanoma. With the advancement of stem cell technology, the relevant features of MSCs have been further elaborated. In this review, we provide an exhaustive overview of cutaneous MSCs and highlight the latest advances in MSC research. A better understanding of the biological characteristics and micro-environmental regulatory mechanisms of MSCs will help to improve clinical applications in regenerative medicine, skin pigmentation disorders and cancer therapy. KEY POINTS: This review provides a concise summary of the origin, biological characteristics, homeostatic maintenance and therapeutic potential of cutaneous MSCs. The role and potential application value of MSCs in skin pigmentation disorders are discussed. The significance of single-cell RNA sequencing, CRISPR-Cas9 technology and practical models in MSCs research is highlighted.

Management of the refractory vitiligo patient: current therapeutic strategies and future options

Vitiligo is an autoimmune disease that leads to disfiguring depigmented lesions of skin and mucosa. Although effective treatments are available for vitiligo, there are still some patients with poor responses to conventional treatment. Refractory vitiligo lesions are mostly located on exposed sites such as acral sites and lips, leading to significant life stress. Understanding the causes of refractory vitiligo and developing targeted treatments are essential to enhance vitiligo outcomes. In this review, we summarized recent treatment approaches and some potential methods for refractory vitiligo. Janus kinase inhibitors have shown efficacy in refractory vitiligo. A variety of surgical interventions and fractional carbon dioxide laser have been widely applied to combination therapies. Furthermore, melanocyte regeneration and activation therapies are potentially effective strategies. Patients with refractory vitiligo should be referred to psychological monitoring and interventions to reduce the potential pathogenic effects of chronic stress. Finally, methods for depigmentation and camouflage may be beneficial in achieving uniform skin color and improved quality of life. Our ultimate focus is to provide alternative options for refractory vitiligo and to bring inspiration to future research.

Clinical effect of stem cell transplantation combined with 308-nm excimer laser therapy for 56 cases of vitiligo

OBJECTIVE

To probe the clinical effect of stem cell transplantation in combination with 308-nm excimer laser therapy for vitiligo and to analyze its value in clinical application.

METHODS

A total of 56 patients with stable non-segmental vitiligo in different parts who were not cured by other therapies visiting our hospital from March 2019 to December 2021 were enrolled as study subjects. They were treated by stem cell transplantation combined with 308-nm excimer laser therapy. The treatment efficacy was observed and analyzed.

RESULTS

Among the 56 patients, 38 (67.85%) and 49 (87.5%) patients were cured at 6 and 12 months after treatment, respectively.

CONCLUSION

Stem cell transplantation combined with 308-nm excimer laser therapy for vitiligo achieves significant efficacy, with the cure rate far superior to that of other therapies for vitiligo. The therapy is worthy of popularization in the clinic.

Current Status of Cell-Based Therapies for Vitiligo

Vitiligo is a chronic pigmentary disease with complex etiology, the signs of which are caused by the destruction of melanocytes in the epidermis, leading to the lack of melanin pigment responsible for skin coloration. The treatment of vitiligo, which aims at repigmentation, depends both on the clinical characteristics of the disease as well as on molecular markers that may predict the response to treatment. The aim of this review is to provide an overview of the clinical evidence for vitiligo cell-based therapies taking into account the required procedures and equipment necessary to carry them out as well as their effectiveness in repigmentation, assessed using the percentage of repigmentation of the treated area. This review was conducted by assessing 55 primary clinical studies published in PubMed and ClinicalTrails.gov between 2000 and 2022. This review concludes that the extent of repigmentation, regardless of the treatment method, is highest in stable localized vitiligo patients. Moreover, therapies that combine more than one cell type, such as melanocytes and keratinocytes, or more than one method of treatment, such as the addition of NV-UVB to another treatment, increase the chances of >90% repigmentation. Lastly, this review concludes that various body parts respond differently to all treatments.

Biomimetic Melanosomes Promote Orientation-Selective Delivery and Melanocyte Pigmentation in the H2O2-Induced Vitiligo Mouse Model

Extremely limited drug retention and depigmentation represent the greatest barriers against vitiligo treatment advancement. Here, inspired by biological melanosomes, the primary melanin transporter, we developed biomimetic melanosomes to combat reactive oxygen species (ROS)-mediated melanocyte damage and depigmentation. Briefly, methylprednisolone (MPS) and melanin-mimicking polydopamine (PDA) were encapsulated inside lysine-proline-valine (KPV)-modified deformable liposomes (KPV-Lipos). Owing to their phospholipid bilayer flexibility and the specific affinity for melanocortin 1 receptor (MC1R), KPV-Lipos exhibited 1.43-fold greater skin deposition than traditional liposomes. The binding of KPV and its receptor also contributed to activating the cAMP-tyrosinase (TYR) signaling pathway, improving the endogenous melanin content. In addition, PDA mimicked melanosomes as it effectively increased the exogenous melanin content and scavenged ROS. Meanwhile, MPS inhibited inflammatory cytokine secretion, limiting the depigmented area. Ultimately, the biomimetic melanosomes affected the skin color of mice with H₂O₂-induced vitiligo. These melanosomes show potential as a universal platform for the self-supply of melanin by self-driven melanin synthesis with exogenous supplementation. Furthermore, this study offers ideas for the production of artificial packed melanosome substitutes for melanocyte-related diseases.

Surgical Interventions for Patients With Vitiligo: A Systematic Review and Meta-analysis

Importance

Surgical interventions are a key part of the therapeutic arsenal, especially in refractory and stable vitiligo. Comparison of treatment outcomes between the different surgical procedures and their respective adverse effects has not been adequately studied.

Objective

To investigate the reported treatment response following different surgical modalities in patients with vitiligo.

Data Sources

A comprehensive search of the MEDLINE, Embase, Web of Science, and Cochrane Library databases from the date of database inception to April 18, 2020, was conducted. The key search terms used were vitiligo, surgery, autologous, transplantation, punch, suction blister, and graft.

Study Selection

Of 1365 studies initially identified, the full texts of 358 articles were assessed for eligibility. A total of 117 studies were identified in which punch grafting (n = 19), thin skin grafting (n = 10), suction blister grafting (n = 29), noncultured epidermal cell suspension (n = 45), follicular cell suspension (n = 9), and cultured epidermal cell suspension (n = 17) were used.

Data Extraction and Synthesis

Three reviewers independently extracted data on study design, patients, intervention characteristics, and outcomes. Random effects meta-analyses using generic inverse-variance weighting were performed.

Main Outcomes and Measures

The primary outcomes were the rates of greater than 90%, 75%, and 50% repigmentation response. These rates were calculated by dividing the number of participants in an individual study who showed the corresponding repigmentation by the total number of participants who completed the study. The secondary outcomes were the factors associated with treatment response to the surgical intervention.

Results

Among the 117 unique studies and 8776 unique patients included in the analysis, rate of repigmentation of greater than 90% for surgical interventions was 52.69% (95% CI, 46.87%-58.50%) and 45.76% (95% CI, 30.67%-60.85%) for punch grafting, 72.08% (95% CI, 54.26%-89.89%) for thin skin grafting, 61.68% (95% CI, 47.44%-75.92%) for suction blister grafting, 47.51% (95% CI, 37.00%-58.03%) for noncultured epidermal cell suspension, 36.24% (95% CI, 18.92%-53.57%) for noncultured follicular cell suspension, and 56.82% (95% CI, 48.93%-64.71%) for cultured epidermal cell suspension. The rate of repigmentation of greater than 50% after any surgical intervention was 81.01% (95% CI, 78.18%-83.84%). In meta-regression analyses, the treatment response was associated with patient age (estimated slope, -1.1418), subtype of vitiligo (estimated slope, 0.3047), and anatomical sites (estimated slope, -0.4050).

Conclusions and Relevance

The findings of this systematic review and meta-analysis suggest that surgical intervention can be an effective option for refractory stable vitiligo. An appropriate procedure should be recommended based on patient age, site and size of the lesion, and costs.

Stem cell therapy in dermatology

Stem cells are precursor cells present in many tissues with ability to differentiate into various types of cells. This interesting property of plasticity can have therapeutic implications and there has been substantial research in this field in last few decades. As a result, stem cell therapy is now used as a therapeutic modality in many conditions, and has made its way in dermatology too. Stem cells can be classified on the basis of their source and differentiating capacity. In skin, they are present in the inter-follicular epidermis, hair follicle, dermis and adipose tissue, which help in maintaining normal skin homeostasis and repair and regeneration during injury. In view of their unique properties, they have been employed in treatment of several dermatoses including systemic sclerosis, systemic lupus erythematosus, scleromyxedema, alopecia, Merkel cell carcinoma, pemphigus vulgaris, psoriasis, wound healing, epidermolysis bullosa and even aesthetic medicine, with variable success. The advent of stem cell therapy has undoubtedly brought us closer to curative treatment of disorders previously considered untreatable. Nevertheless, there are multiple lacunae which need to be addressed including ideal patient selection, timing of intervention, appropriate conditioning regimens, post-intervention care and cost effectiveness. Further research in these aspects would help optimize the results of stem cell therapy.

Electrofulguration-assisted dermabrasion is comparable to manual dermabrasion in patients undergoing autologous non-cultured epidermal cell suspension for treatment of stable vitiligo: A randomized controlled trial

BACKGROUND

Recipient site preparation is a crucial step in non-cultured epidermal cell suspension (NCES) as it facilitates proper uptake of the grafted melanocytes.

OBJECTIVES

To compare the repigmentation rate of recipient sites prepared with manual dermabrasion (MD) versus electrofulguration-assisted dermabrasion (EF) in patients undergoing NCES for treatment of stable vitiligo.

METHODS

This was a prospective randomized study including 26 patients of stable vitiligo (VIDA 0 or -1), each having two patches of size greater than 3 × 3 cm located symmetrically or at the same site or a single patch of 6 × 6 cm or larger. After randomization of patches in the given patient, MD and EF were performed on recipient areas followed by NCES. The patients were followed up at 4 weekly intervals up to 24 weeks and assessed for extent of repigmentation and adverse effects if any.

RESULTS

Greater than 75% repigmentation was observed in 69.3% of the patches prepared by MD as compared to 73.1% patches prepared by EF at the end of 24 weeks (p = 0.791). The mean improvement in target VASI was 64.0% in the MD group as compared to 68.8% in the EF group (p = 0.21). Patches prepared by EF achieved successful repigmentation earlier as compared to patches prepared by MD (9.4 weeks vs 11.4 weeks, p = 0.12).

CONCLUSION

Both MD and EF have comparable outcomes with respect to all parameters.

A retrospective study of long term follow-up of 2283 vitiligo patients treated by autologous, non-cultured melanocyte-keratinocyte transplantation

Background: Autologous non-cultured melanocyte-keratinocyte transplantation (MKTP) can be used to treat stable vitiligo cases, but there were insufficient clinical data to evaluate its safety and efficacy.

Objective: To assess the influence of various factors on the therapeutic outcome of MKTP.

Method: The single-center retrospective study included stable vitiligo patients who underwent MKTP between June 2009 and June 2018. Univariate and/or multivariable analysis were used to determine the factors affecting the outcome of repigmentation.

Result: The study comprised 2283 patients who had long-term follow-up data (12-108months). Excellent repigmentation was achieved in 400/606 (66%),788/1341 (58.8%),437/684 (63.9%),18/24 (75%) patients with segmental vitiligo, pre-MKTP phototherapy, younger than 24 years, the lesion on the perineum and scrotum, respectively. However, the patients with a positive family history, Koebner phenomenon responded worse(χ²=29.417, P<0.001; χ²=107.397, P<0.001; respectively). Overall, a significant positive correlation between duration of stability and percentage of repigmentation was found (χ²=42.053, P<0. 001).

Conclusion: MKTP is efficient and well tolerated for stable vitiligo treatment. Various factors such as duration of disease stability, vitiligo type, family history, site of lesion should be carefully assessed before using MKTP, as it would further improve the post-operative repigmentation.

Effect of platelet-rich plasma on the outcome of mini-punch grafting procedure in localized stable vitiligo: Clinical evaluation and relation to lesional basic fibroblast growth factor

Surgical methods are favorably used for treatment of stable vitiligo, and platelet-rich plasma (PRP) can be added to augment the effect. The additive value of PRP, however, remains elusive. Basic fibroblast growth factor (bFGF) is released from activated platelets with a capacity for stimulating melanocyte proliferation and migration. The treatment outcomes for the mini-punch grafting (MPG)/phototherapy treatment with and without PRP were assessed and the relation between bFGF and the obtained results were evaluated. Thirty-four vitiliginous patches, two per each patient with stable vitiligo, were enrolled in this intrapatient-controlled study and treated with autologous MPG and subsequent exposure to phototherapy with and without enhancement via PRP procedure at the time of the procedure, and monthly for the subsequent 3 months. Re-pigmentation assessment via vitiligo scores as well as measurement of lesional bFGF were done. PRP assistance to MPG/phototherapy treatment resulted in earlier re-pigmentation at week 8. However, this enhancement effect vanished at the study end (week 20) as ideal re-pigmentation (>75% re-pigmentation) was encountered in 10 patches (58.8%) treated with MPG/phototherapy modality, and in 12 patches (70.6%) treated with PRP-assisted method without significant difference between them. Lesional bFGF increased after both treatments with a higher expression with PRP assistance but without clinical reflection on the final outcome. PRP can speed the re-pigmentation response for MPG/phototherapy procedure without any significant effect on the final outcome.

A prospective, randomized clinical study to compare the efficacy of recipient site preparation using dermabrasion, cryoblister, and dermaroller in autologous noncultured epidermal cell suspension in stable vitiligo

Noncultured epidermal cell suspension (NCES) is a well-established surgical treatment modality for stable vitiligo. The outcome of this procedure significantly depends on the method of recipient site preparation, a critical step to achieve cosmetically acceptable repigmentation. To compare the efficacy of recipient site preparation using three methods namely, dermabrasion, cryoblister, and dermaroller followed by NCES in stable vitiligo. In this single-center, prospective, intra-patient, randomized clinical trial; 36 participants having at least three vitiligo patches in same anatomic region with minimum lesional stability of 1 year were randomized 1:1:1 for recipient site preparation using manual dermabrasion, cryoblister, and dermaroller followed by NCES. Patients were followed up at 4, 8, and 12 weeks and assessment of extent and pattern of repigmentation, color match and patient satisfaction were done. Among 36 patients, 22 (61.1%) were females; mean (SD) age was 28.33 (9.4) years. Dermabrasion and cryoblister techniques showed equal efficacy with respect to extent of repigmentation (>75% repigmentation; 55.6% vs 47.2%; P = .63) and patient satisfaction score (20.2 ± 9.6 vs 19.9 ± 7.9, P = .194). However, dermabrasion was superior to cryoblister in terms of rapidity (65% vs 32.5% at 4 weeks, P = .04) and color match (47.2% vs 19.4%, P = .004). Dermaroller had poor repigmentation outcomes compared to both dermabrasion and cryoblister. Cryoblister as a method of recipient site preparation is equally effective as manual dermabrasion in NCES for attaining good to excellent repigmentation, but with risk of hyperpigmentation. However, dermaroller is inferior to both dermabrasion and cryoblister.

Hair Follicle as a Source of Pigment-Producing Cells for Treatment of Vitiligo: An Alternative to Epidermis?

To discuss the advantages and limitations of hair follicle-derived cell transplantation (FCT) in vitiligo, compared to the epidermal cell transplantation (ECT), and the knowledge gap which is required to be bridged. The papers relevant to the purpose was reviewed. Surgical approaches for treating vitiligo are based on the idea of replenishing lost melanocytes. Skin and hair follicles as the main sources of melanocytes have been applied for this purpose transferring the whole tissue or tissue-derived cell suspension to the vitiligo lesions. Considering the differences between hair follicle and epidermis in terms of the constituting cell populations, phenotype and function of melanocytes, and micro-environmental factors, different response of vitiligo patients to treatment with FCT or ECT would be expected theoretically. However, there is currently a lack of evidence on such a difference. However, ECT appears to be a more feasible, less time-consuming, and more comfortable treatment for both physicians and patients. Although the current evidence has not shown a significant difference between ECT and FCT in terms of efficacy, ECT appears to be more feasible specifically in the treatment of large lesions. However, further randomized controlled clinical trials with larger sample sizes and longer follow-up durations are required to be conducted to draw a definite conclusion on comparing FCT with ECT in terms of the safety, efficacy, durability of the therapeutic effects, and indications in vitiligo patients.

Vitiligo: A Review

Vitiligo, a common depigmenting skin disorder, has an estimated prevalence of 0.5–2% of the population worldwide. The disease is characterized by the selective loss of melanocytes which results in typical nonscaly, chalky-white macules. In recent years, considerable progress has been made in our understanding of the pathogenesis of vitiligo which is now clearly classified as an autoimmune disease. Vitiligo is often dismissed as a cosmetic problem, although its effects can be psychologically devastating, often with a considerable burden on daily life. In 2011, an international consensus classified segmental vitiligo separately from all other forms of vitiligo, and the term vitiligo was defined to designate all forms of nonsegmental vitiligo. This review summarizes the current knowledge on vitiligo and attempts to give an overview of the future in vitiligo treatment.

Combination of Follicular and Epidermal Cell Suspension as a Novel Surgical Approach in Difficult-to-Treat Vitiligo: A Randomized Clinical Trial

Importance

Epidermal cell suspension (ECS) and follicular cell suspension (FCS) are successful surgical modalities for the treatment of stable vitiligo. However, repigmentation in generalized and acrofacial vitiligo and over acral or bony sites (eg, elbows, knees, iliac crests, and malleoli), which are difficult to treat, is challenging.

Objective

To study the efficacy of transplanting a combination of autologous, noncultured ECS and FCS (ECS + FCS) compared with ECS alone in stable vitiligo.

Design, Setting, and Participants

A prospective, observer-blinded, active-controlled, randomized clinical trial was conducted at a tertiary care hospital, with treatment administered as an outpatient procedure. Thirty participants who had stable vitiligo with symmetrical lesions were recruited between October 18, 2013, and October 28, 2016. All of the lesions were resistant to medical modalities with minimum lesional stability of 1 year. Intent-to-treat analysis was used.

Interventions

ECS + FCS was prepared by mixing equal amounts (in cell number) of FCS with ECS. After manual dermabrasion, ECS was applied to 1 lesion and ECS + FCS was applied to the anatomically based paired lesion of the same patient. No adjuvant treatment was given.

Main Outcomes and Measures

Patients were followed up at 4, 8, and 16 weeks by a blinded observer and extent of repigmentation, color match, pattern of repigmentation, patient satisfaction and complications were noted. Both the visual and the computerized image analysis methods were used for outcome assessment. Cell suspensions were assessed post hoc for OCT4+ stem cell counts using flow cytometry; expression of stem cell factor and basic fibroblast growth factor was evaluated using quantitative relative messenger RNA expression.

Results

Of the 30 patients included in the study, 18 (60%) were women; mean (SD) age was 23.4 (6.4) years. Seventy-four percent of the lesions (62 of 84) were difficult-to-treat vitiligo. ECS + FCS showed superior repigmentation outcomes compared with ECS: extent (76% vs 57%, P < .001), rapidity (48% vs 31%, P = .001), color match (73% vs 61%, P < .001), and patient satisfaction (mean [SD] patient global assessment score, 23.30 [6.89] vs 20.81 [6.61], P = .047). Melanocyte stem cell counts (2% in ECS + FCS vs 0.5% in ECS) as well as expression of basic fibroblast growth factor (11.8-fold) and stem cell factor (6.0-fold) were higher in ECS + FCS suspension (P<.05 for both).

Conclusions and Relevance

The findings from this study establish ECS + FCS as a novel approach in vitiligo surgery for attaining good to excellent repigmentation in a short period with good color match, even in difficult-to-treat vitiligo.

Trial Registration

ctri.nic.in Identifier: CTRI/2017/05/008692.

Vitiligo surgery: A journey from tissues via cells to the stems!

Depigmented patches in vitiligo, a common dermatosis, cause a great psychological distress to the patients. Hence, apart from halting the disease process, the strategies to impart normal skin colour to these white patches carry an important role in the management of vitiligo. Surgical procedures are often required for stable vitiligo lesions not responding to medical therapies. It involves "shuffling" of melanocytes from the pigmented skin to the depigmented areas. During the last fifty years, the vitiligo surgery has evolved from tissue transplantation via cellular transplantation to reach a stage where the use of stem cells or immunomodulatory cells is contemplating. We would like to depict this wonderful journey of vitiligo surgery through this viewpoint.

Autologous non-cultured melanocyte-keratinocyte transplantation in the treatment of vitiligo: patient selection and perspectives

Autologous non-cultured melanocyte–keratinocyte transplantation procedure (MKTP) is one of the simplest cellular grafting techniques. Various modifications were done over the years to make the technique easier and more economical which led to its great popularity among dermatologists. Proper patient selection and good technical skills are essential for achieving success with this technique. In this review, different patient-related and procedure-related factors that affect the outcome are discussed. This review may guide dermatologists to select suitable candidates, and explains what to expect in each case and indicates different techniques which can be used. The expected complications and stability of acquired pigmentation, which are an essential part of the pretreatment patient counseling, are also discussed.

Restoration of skin pigmentation after deep partial or full-thickness burn injury

Significant skin pigmentation changes occur when patients suffer deep burn injuries. These pigmentation disorders may cause not only cosmetic and psychological issues, but more importantly it increases the risk of skin cancer or photoaging. Severe burns significantly effect on the process of repigmentation as the pigmentation is tightly regulated by cell proliferation and differentiation of melanocytes and melanocyte stem cells which are housing in the epidermis and hair follicles of the skin. In the present review, we discuss the possible mechanisms to replenish the melanocytes from the healthy epidermis and hair follicles surrounding burn wounds. The molecular mechanisms of skin repigmentation following healing of burn injuries includes the differentiation of melanoblasts into melanocytes, the distribution and responses of melanocytes and melanocyte stem cells after burn injury, and the regulation of melanin production. We also reviewed advanced therapeutic strategies to treat pigmentation disorders, such as convectional surgery, laser, UV treatment and emerging concepts in skin tissue-engineering.

Study of efficacy and safety of noncultured, extracted follicular outer root sheath cell suspension transplantation in the management of stable vitiligo

BACKGROUND

Noncultured, extracted follicular outer root sheath suspension (NC-EHF-ORS-CS) is a recently introduced technique for the treatment of stable vitiligo.

OBJECTIVE

To study the clinical efficacy of this technique and to determine the viability and cell composition of the suspension.

METHODS

Twenty-five patients with stable vitiligo were included in this prospective study. Fifty follicles were extracted from occipital scalp and were incubated with trypsin-ethylenediaminetetraacetic acid to separate outer root sheath cells. The cell suspension was filtered and centrifuged to obtain a cell pellet, which was resuspended and applied to the dermabraded recipient area. Cell viability of the suspension was assessed using trypan blue staining, and markers of keratinocyte stem cells (CD200) and melanocytes (S100) were evaluated using flow cytometry and immunocytochemistry, respectively.

RESULTS

At 6 months, the mean (±SD) repigmentation was 52 ± 25.1%, and >75% repigmentation was seen in 8/25 (32%) patients. Mean percentage cell viability of the suspension was 80 ± 17.2% with a mean concentration of CD200 + and S100 + cells being 7.91 ± 8.68% and 9.93 ± 1.22% (n = 3), respectively. Recipient site infection was seen in 4 of 25 (16%) patients and a color mismatch in 11 of 25 (44%) patients.

CONCLUSION

NC-EHF-ORS-CS is a useful minimally invasive therapy for vitiligo.