Contact between dermal papilla cells and dermal sheath cells enhances the ability of DPCs to induce hair growth

The promising prospect of human hair follicle regeneration in the shadow of new tissue engineering strategies

Hair loss disorder (alopecia) affects numerous people around the world. The low effectiveness and numerous side effects of common treatments have prompted researchers to investigate alternative and effective solutions. Hair follicle (HF) bioengineering is the knowledge of using hair-inductive (trichogenic) cells. Most bioengineering-based approaches focus on regenerating folliculogenesis through manipulation of regulators of physical/molecular properties in the HF niche. Despite the high potential of cell therapy, no cell product has been produced for effective treatment in the field of hair regeneration. This problem shows the challenges in the functionality of cultured human hair cells. To achieve this goal, research and development of new and practical approaches, technologies and biomaterials are needed. Based on recent advances in the field, this review evaluates emerging HF bioengineering strategies and the future prospects for the field of tissue engineering and successful HF regeneration.

Combatting ageing in dermal papilla cells and promoting hair follicle regeneration using exosomes from human hair follicle dermal sheath cup cells

Dermal papilla cells (DPCs) undergo premature ageing in androgenetic alopecia and senescent alopecia. As critical components of hair follicle reconstruction, DPCs are also prone to senescence in vitro, resulting in a diminished hair follicle inductivity capacity. Dermal sheath cup cells (DSCCs), a specific subset of hair follicle mesenchymal stem cells, intimately linked to the function of DPCs. The primary objective of this research is to investigate the anti-ageing effect of exosomes derived from DSCCs (ExoDSCCs ) on DPCs. Exosomes were utilized to treat H2 O2 -induced DPCs or long-generation DPCs(P10). Our findings demonstrate that ExoDSCCs(P3) promote the proliferation, viability and migration of senescent DPCs while inhibiting cell apoptosis. The expression of senescence marker SA-β-Gal were significantly downregulated in senescent DPCs. When treated with ExoDSCCs(P3) , expression of inducibility related markers alkaline phosphatase and Versican were significantly upregulated. Additionally, ExoDSCCs(P3) activated the Wnt/β-catenin signalling in vitro. In patch assay, ExoDSCCs(P3) significantly promoted hair follicle reconstruction in senescent DPCs. In summary, our work highlights that ExoDSCCs(P3) may restore the biological functions and improve the hair follicle induction ability of senescent DPCs. Therefore, ExoDSCCs(P3) may represent a new strategy for intervening in the ageing process of DPCs, contributing to the prevention of senile alopecia.

Scalable and high-throughput production of an injectable platelet-rich plasma (PRP)/cell-laden microcarrier/hydrogel composite system for hair follicle tissue engineering

Background

Tissue engineering of hair follicles (HFs) has enormous potential for hair loss treatment. However, certain challenges remain, including weakening of the dermal papilla cell (DPC) viability, proliferation, and HF inducibility, as well as the associated inefficient and tedious preparation process required to generate extracellular matrix (ECM)-mimicking substrates for biomolecules or cells. Herein, we utilized gelatin methacryloyl (GelMA) and chitosan hydrogels to prepare scalable, monodispersed, and diameter-controllable interpenetrating network GelMA/chitosan-microcarriers (IGMs) loaded with platelet-rich plasma (PRP) and seeded with DPCs, on a high-throughput microfluidic chip.

Results

The ECM-mimicking hydrogels used for IGMs exhibited surface nano-topography and high porosity. Mass production of IGMs with distinct and precise diameters was achieved by adjusting the oil and aqueous phase flow rate ratio. Moreover, IGMs exhibited appropriate swelling and sustained growth factor release to facilitate a relatively long hair growth phase. DPCs seeded on PRP-loaded IGMs exhibited good viability (> 90%), adhesion, spreading, and proliferative properties (1.2-fold greater than control group). Importantly, PRP-loaded IGMs presented a higher hair inducibility of DPCs in vitro compared to the control and IGMs group (p < 0.05). Furthermore, DPC/PRP-laden IGMs were effectively mixed with epidermal cell (EPC)-laden GelMA to form a PRP-loaded DPC/EPC co-cultured hydrogel system (DECHS), which was subcutaneously injected into the hypodermis of nude mice. The PRP-loaded DECHS generated significantly more HFs (~ 35 per site) and novel vessels (~ 12 per site) than the other groups (p < 0.05 for each).

Conclusion

Taken together, these results illustrate that, based on high-throughput microfluidics, we obtained scalable and controllable production of ECM-mimicking IGMs and DECHS, which simulate an effective micro- and macro-environment to promote DPC bioactivity and hair regeneration, thus representing a potential new strategy for HF tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01671-8.

Low-frequency electromagnetic fields promote hair follicles regeneration by injection a mixture of epidermal stem cells and dermal papilla cells

The bioeffects of low-frequency electromagnetic fields (EMF) on a bio-engineered hair follicle generation had not been fully elucidated. This present study was designed to evaluat the therapeutically effective of low frequency EMF on hair follicles regeneration. In this experiment, epidermal stem cells (ESCs) and dermal papilla (DP) cells were isolated and culture-expanded. Then the mixture containing of ESCs and DP cells was implanted into the epidermal layer or corium layer of nude mice. Those mice were  divided at random into the control group and EMF group, 7 days or 14 days later, the skin specimens were harvested to assess for hair regeneration or a bio-engineered skin formation using H&E staining. After injection of the mixture into the epidermal layer of nude mice for 14 days, H&E staining showed that the new hair formed the correct structure comprising hair matrix, hair shaft, and inner root sheath, outer root sheath, and DP. Comparing to the control, the hair follicles erupted at a higher density in the EMF group. When the mixture was implanted into the corium layer for 7 days, comparing with the characteristics of new hair follicles in the control group, H&E staining also showed the mixture induced to form 4 ~ 6 epidermal layers with a higher density of hair follicle like-structures in the bioengineered epithelial layers after EMF exposure. Our results suggested that the injection of a mixture of ESCs and DP cells in combination with EMF exposure facilitated the induction of hair follicle regeneration and a bioengineered skin formation with hair follicle-like structures.

Hair Regeneration Potential of Human Dermal Sheath Cells Cultured Under Physiological Oxygen

We investigated the effect of oxygen tension on the proliferation and hair-inductive capacity of human dermal papilla cells (DPCs) and dermal sheath cells (DSCs). DPCs and DSCs were separately obtained from human hair follicles and each cultured under atmospheric/hyperoxic (20% O₂), physiological/normoxic (6% O₂), or hypoxic (1% O₂) conditions. Proliferation of DPCs and DSCs was highest under normoxia. Compared with hyperoxia, hypoxia inhibited proliferation of DPCs, but enhanced that of DSCs. In DPCs, hypoxia downregulated the expression of hair-inductive capacity-related genes, including BMP4, LEF1, SOX2, and VCAN. In DSCs, both normoxia and hypoxia upregulated SOX2 expression, whereas hypoxia downregulated BMP4 expression. Microarray analysis revealed that normoxia increased the expression of pluripotency-related genes, including SPRY, NR0B1, MSX2, IFITM1, and DAZL, compared with hyperoxia. In an in vivo hair follicle reconstitution assay, cultured DPCs and DSCs were transplanted with newborn mouse epidermal keratinocytes into nude mice using a chamber method. In this experiment, normoxia resulted in the most efficient induction of DPC hair follicles, whereas hypoxia caused the most efficient induction and maturation of DSC hair follicles. These results suggest that application of physiological/hypoxic oxygen tension to cultured human DSCs enhances proliferation and maintenance of hair inductivity for skin engineering and clinical applications. Impact statement Dermal sheath cells (DSCs) and dermal papilla cells (DPCs) are useful cell sources for cell-based regenerative therapy. This is the first report to describe that low-oxygen conditions are better for DSCs. Normoxic and hypoxic culture of DSCs is beneficial for expanding these hair follicular cells and advancing development of cell-based therapy for both wound healing and hair regeneration. The current study supports that optimized oxygen tension can be applied to use expanded human DPCs and DSCs for skin engineering and clinical applications.

Establishment of dermal sheath cell line from Cashmere goat and characterizing cytokeratin 13 as its novel biomarker

OBJECTIVE

To establish a dermal sheath cell line, a dermal papilla cell line and a outer root sheath cell line from Cashmere goat and clarify the similarities and differences among them.

RESULTS

We established a dermal sheath cell line, a dermal papilla cell line and a outer root sheath cell line from the pelage skin hair follicles of Cashmere goat. The growth rate of dermal sheath cells was intermediate between that of dermal papilla cells and outer root sheath cells. Immunofluorescence experiments and reverse transcription-polymerase chain reaction analysis showed that at both the transcriptional and translational levels, the dermal sheath cells were alpha-smooth muscle actin (α-SMA)⁺/cytokeratin 13⁺, while the dermal papilla cells were α-SMA⁺/cytokeratin 13^- and the outer root sheath cells were α-SMA^-/cytokeratin 13⁺. Patterns of cytokeratin 13 expression could distinguish the dermal sheath cells from the dermal papilla cells.

CONCLUSIONS

These results suggest that cytokeratin 13 could serve as a novel biomarker for dermal sheath cells of Cashmere goat, and should prove useful for researchers investigating dermal stem cells or interaction of different types of cells during hair cycle.

Spontaneous hair follicle germ (HFG) formation in vitro, enabling the large-scale production of HFGs for regenerative medicine

Hair follicle morphogenesis is triggered by reciprocal interactions between hair follicle germ (HFG) epithelial and mesenchymal layers. Here, we developed a method for large-scale preparation of HFGs in vitro via self-organization of cells. We mixed mouse epidermal and mouse/human mesenchymal cells in suspension and seeded them in microwells of a custom-designed array plate. Over a 3-day culture period, cells initially formed a randomly distributed single cell aggregate and then spatially separated from each other, exhibiting typical HFG morphological features. These self-sorted hair follicle germs (ssHFGs) were shown to be capable of efficient hair-follicle and shaft generation upon intracutaneous transplantation into the backs of nude mice. This finding facilitated the large-scale preparation of approximately 5000 ssHFGs in a microwell-array chip made of oxygen-permeable silicone. We demonstrated that the integrity of the oxygen supply through the bottom of the silicone chip was crucial to enabling both ssHFG formation and subsequent hair shaft generation. Finally, spatially aligned ssHFGs on the chip were encapsulated into a hydrogel and simultaneously transplanted into the back skin of nude mice to preserve their intervening spaces, resulting in spatially aligned hair follicle generation. This simple ssHFG preparation approach is a promising strategy for improving current hair-regenerative medicine techniques.

Human Hair Reconstruction: Close, But Yet So Far

Billions of dollars are annually invested in pharmaceutical industry and cosmetic sector with intent to develop new drugs and treatment strategies for alopecia. Because the hair looks an important characteristic of humans-an effective appendage in perception, expression of beauty, and preservation of self-esteem-the global market for hair loss treatment products is exponentially increasing. However, current methods to treat hair loss endure yet multiple challenges, such as unfavorable outcomes, nonpermanent and patient-dependent results, as well as unpredictable impacts, which limit their application. Over recent years, remarkable advances in the fields of regenerative medicine and hair tissue engineering have raised new hopes for introducing novel cell-based approaches to treat hair loss. Through cell-based approaches, it is possible to produce hair-like structures in the laboratory setting or manipulate cells in their native niche (in vivo lineage reprogramming) to reconstruct the hair follicle. However, challenging issues still exist with the functionality of cultured human hair cells, the proper selection of nonhair cell sources in cases of shortage of donor hair, and the development of defined culture conditions. Moreover, in the case of in vivo lineage reprogramming, selecting appropriate induction factors and their efficient delivery to guide resident cells into a hair fate-with the aim of reconstructing functional hair-still needs further explorations. In this study, we highlight recent advances and current challenges in hair loss treatment using cell-based approaches and provide novel insights for crucial steps, which must be taken into account to develop reproducible, safe, and efficient cell-based treatment.

Enhanced restoration of in situ-damaged hairs by intradermal transplantation of trichogenous dermal cells

We developed a nude rat model for determining the capacity of trichogenous cells to restore in vivo-damaged hair follicles (HFs). A surgical scalpel was inserted into the rat's dermis to generate the in vivo-damaged pelage HFs, the HFs whose lower parts were lost, but the upper parts containing sebaceous and bulge regions remained intact. Dermal papilla cells (DPCs) and dermal sheath cells (DSCs) from EGFP transgenic rat vibrissae were propagated in culture, and each alone (DPC or DSC) or a mixture (DPC/DSC) was transplanted into the intradermal path made by a scalpel. It was found that the in vivo-damaged HFs had hair self-restoration ability, and the transplanted trichogenic dermal cells prominently enhanced this ability, DPC/DSC transplants being more effective in enhancement than DPC or DSC alone. The restored bulbs contained EGFP-positive cells, shed their original straight shafts, generated new shafts, and further developed into hairs with a sebaceous gland and bulge structures by ~6 weeks post-transplantation. Compared to the preceding animal models, this model is less invasive, requires fewer donor cells and allows repeated operations with higher reproducibility and accuracy. The present study suggests that conditions causing in situ-damaged HFs, such as androgenic alopecia, in which HFs are damaged and miniaturized, can be restored by functional trichogenous dermal cell transplantation therapy. Copyright © 2015 John Wiley & Sons, Ltd.

A review of adipocyte lineage cells and dermal papilla cells in hair follicle regeneration

Alopecia is an exceedingly prevalent problem effecting men and women of all ages. The standard of care for alopecia involves either transplanting existing hair follicles to bald areas or attempting to stimulate existing follicles with topical and/or oral medication. Yet, these treatment options are fraught with problems of cost, side effects, and, most importantly, inadequate long-term hair coverage. Innovative cell-based therapies have focused on the dermal papilla cell as a way to grow new hair in previously bald areas. However, despite this attention, many obstacles exist, including retention of dermal papilla inducing ability and maintenance of dermal papilla productivity after several passages of culture. The use of adipocyte lineage cells, including adipose-derived stem cells, has shown promise as a cell-based solution to regulate hair regeneration and may help in maintaining or increasing dermal papilla cells inducing hair ability. In this review, we highlight recent advances in the understanding of the cellular contribution and regulation of dermal papilla cells and summarize adipocyte lineage cells in hair regeneration.

Exogenous connective tissue growth factor preserves the hair-inductive ability of human dermal papilla cells

Connective tissue growth factor influences human dermal papilla cells' hair inductive ability through several signaling pathways.

Treatment of MSCs with Wnt1a-conditioned medium activates DP cells and promotes hair follicle regrowth

Hair loss (alopecia) is a common problem for people. The dermal papilla is the key signaling center that regulates hair growth and it engage in crosstalk with the microenvironment, including Wnt signaling and stem cells. In this study, we explored the effects of bone marrow mesenchymal stem cell overexpression of Wnt1a on mouse hair follicle regeneration. Wnt-CM accelerated hair follicle progression from telogen to anagen and enhanced the ALP expression in the DP area. Moreover, the hair induction-related genes were upregulated, as demonstrated by qRT-PCR. Wnt-CM treatment restored and increased DP cell expression of genes downregulated by dihydrotestosterone treatment, as demonstrated by qRT-PCR assays. Our study reveals that BM-MSC-generated Wnt1a promotes the DP's ability to induce hair cycling and regeneration.

Development and prospects of organ replacement regenerative therapy

Current approaches for the development of regenerative therapies have been influenced by our understanding of embryonic development, stem cell biology, and tissue engineering technology. The ultimate goal of regenerative therapy is to develop fully functioning bioengineered organs to replace lost or damaged organs that result from disease, injury, or aging. Almost all organs including ectodermal organs, such as teeth, hair, salivary glands, and lacrimal glands, arise from organ germs induced by reciprocal epithelial-mesenchymal interactions in the developing embryo. A novel concept to generate a bioengineered organ is to recreate organogenesis and thereby develop fully functioning bioengineered organs from the resulting bioengineered organ germ generated via 3-dimensional cell manipulation using immature stem cells in vitro. We have previously developed a bioengineering method for forming a 3-dimensional organ germ in the early developmental stages, termed the "bioengineered organ germ method." Recently, we reported fully functioning bioengineered tooth replacements after transplantation of a bioengineered tooth germ or a mature tooth unit comprising the bioengineered tooth and periodontal tissues. This concept could be adopted to generate not only teeth but also bioengineered hair follicles, salivary glands, and lacrimal glands. These studies emphasize the potential for bioengineered organ replacement in future regenerative therapies. In this review, we will summarize the strategies and the recent progress of research and development for the establishment of organ replacement regenerative therapies.

Hair curvature: a natural dialectic and review

Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways, and others, can explain many alternatives and specific variations of hair bending phenotypes. Mechanisms for hair papilla budding or its division by bisection or fission can explain MPC formation. Epithelial-to-mesenchymal (EMT) and mesenchymal-to-epithelial (MET) transitions, acting in collaboration with epithelial-mesenchymal communications are also considered as mechanisms affecting hair growth and its bending and twisting. These may be treated as sub-mechanisms of an overall development from neural-crest stem cell (NCSC) lineages to differentiated hair follicle (HF) cell types, thus providing a unified framework for hair growth and development.

Strategies to enhance epithelial-mesenchymal interactions for human hair follicle bioengineering

Hair follicle morphogenesis and regeneration depend on intensive but well-orchestrated interactions between epithelial and mesenchymal components. Accordingly, the enhancement of this crosstalk represents a promising approach to achieve successful bioengineering of human hair follicles. The present article summarizes the techniques, both currently available and potentially feasible, to promote epithelial-mesenchymal interactions (EMIs) necessary for human hair follicle regeneration. The strategies include the preparation of epithelial components with high receptivity to trichogenic dermal signals and/or mesenchymal cell populations with potent hair inductive capacity. In this regard, bulge epithelial stem cells, keratinocytes predisposed to hair follicle fate or keratinocyte precursor cells with plasticity may provide favorable epithelial cell populations. Dermal papilla cells sustaining intrinsic hair inductive capacity, putative dermal papilla precursor cells in the dermal sheath/neonatal dermis or trichogenic dermal cells derived from undifferentiated stem/progenitor cells are promising candidates as hair inductive dermal cells. The most established protocol for in vivo hair follicle reconstitution is co-grafting of epithelial and mesenchymal components into immunodeficient mice. In theory, combination of individually optimized cellular components of respective lineages should elicit most intensive EMIs to form hair follicles. Still, EMIs can be further ameliorated by the modulation of non-cell autonomous conditions, including cell compartmentalization to replicate the positional relationship in vivo and humanization of host environment by preparing human stromal bed. These approaches may not always synergistically intensify EMIs, however, step-by-step investigation probing optimal combinations should maximally enhance EMIs to achieve successful human hair follicle bioengineering.

Participation of CD34-enriched mouse adipose cells in hair morphogenesis

Adipose-derived stromal vascular fraction (SVF) cells are heterogeneous in nature, containing a number of different cell types. Recent studies indicate that CD34 may be a specific marker for adipose-derived mesenchymal stem cells (ADMSCs). Using their participation in hair morphogenesis as a model, the multi-differentiation potential of adult stem cells was investigated. In addition, adipose tissue or adipogenic lineage cells appear to be associated with the hair follicle cycle. The purpose of this study was to test the potential of CD34+ cells enriched from fat tissue in hair morphogenesis. To investigate this, unsorted SVF, CD34+ and CD34- cells sorted from the SVF of green fluorescence protein (GFP) transgenic mice were mixed with fetal mouse keratinocytes and dermal fibroblasts of gestational day 17.5 (E17.5) and then subcutaneously injected into nude mice. The results showed that in the reconstituted skin tissue, larger tissue blocks with more developed hair follicles were observed in the CD34+ cell group compared with the other two groups. Histological and immunofluorescent staining analyses revealed that only CD34+ cells may participate in hair morphogenesis by their integration into dermal sheath structures. However, no involvement in other skin appendages was observed. In addition, differentiation into endothelial cells and participation in blood vessel formation were also observed in both CD34+ and SVF cells, but not in CD34- cells. As expected, participation in adipogenesis was observed in all groups. Our results suggest that CD34+ cells may represent the ADMSCs which possess stronger multiple differentiation potential during reconstituted skin development.

Hair organ regeneration via the bioengineered hair follicular unit transplantation

Organ regenerative therapy aims to reproduce fully functional organs to replace organs that have been lost or damaged as a result of disease, injury, or aging. For the fully functional regeneration of ectodermal organs, a concept has been proposed in which a bioengineered organ is developed by reproducing the embryonic processes of organogenesis. Here, we show that a bioengineered hair follicle germ, which was reconstituted with embryonic skin-derived epithelial and mesenchymal cells and ectopically transplanted, was able to develop histologically correct hair follicles. The bioengineered hair follicles properly connected to the host skin epithelium by intracutaneous transplantation and reproduced the stem cell niche and hair cycles. The bioengineered hair follicles also autonomously connected with nerves and the arrector pili muscle at the permanent region and exhibited piloerection ability. Our findings indicate that the bioengineered hair follicles could restore physiological hair functions and could be applicable to surgical treatments for alopecia.

Fully functional hair follicle regeneration through the rearrangement of stem cells and their niches

Organ replacement regenerative therapy is purported to enable the replacement of organs damaged by disease, injury or aging in the foreseeable future. Here we demonstrate fully functional hair organ regeneration via the intracutaneous transplantation of a bioengineered pelage and vibrissa follicle germ. The pelage and vibrissae are reconstituted with embryonic skin-derived cells and adult vibrissa stem cell region-derived cells, respectively. The bioengineered hair follicle develops the correct structures and forms proper connections with surrounding host tissues such as the epidermis, arrector pili muscle and nerve fibres. The bioengineered follicles also show restored hair cycles and piloerection through the rearrangement of follicular stem cells and their niches. This study thus reveals the potential applications of adult tissue-derived follicular stem cells as a bioengineered organ replacement therapy.

Bioengineered hair follicles can be produced from embryonic follicle germ cells, but whether these follicles can interact with the surrounding tissue and function normally is unknown. Here, bioengineered hair follicles transplanted into mouse dermis make connections with the surrounding tissue and show normal hair cycles.

Polyclonal origin and hair induction ability of dermal papillae in neonatal and adult mouse back skin

Hair follicle development and growth are regulated by Wnt signalling and depend on interactions between epidermal cells and a population of fibroblasts at the base of the follicle, known as the dermal papilla (DP). DP cells have a distinct gene expression signature from non-DP dermal fibroblasts. However, their origins are largely unknown. By generating chimeric mice and performing skin reconstitution assays we show that, irrespective of whether DP form during development, are induced by epidermal Wnt activation in adult skin or assemble from disaggregated cells, they are polyclonal in origin. While fibroblast proliferation is necessary for hair follicle formation in skin reconstitution assays, mitotically inhibited cells readily contribute to DP. Although new hair follicles do not usually develop in adult skin, adult dermal fibroblasts are competent to contribute to DP during hair follicle neogenesis, irrespective of whether they originate from skin in the resting or growth phase of the hair cycle or skin with β-catenin-induced ectopic follicles. We propose that during skin reconstitution fibroblasts may be induced to become DP cells by interactions with hair follicle epidermal cells, rather than being derived from a distinct subpopulation of cells.

Clinically applicable transplantation procedure of dermal papilla cells for hair follicle regeneration

Dermal papilla cells (DPCs) interact with epithelial stem cells and induce hair folliculogenesis. Cell-based therapies using expanded DPCs for hair regeneration have been unsuccessful in humans. Two major challenges remain: first, expanded DPCs obtained from adult hair follicles have functional limitations; second, a clinically applicable method is needed for transplanting DPCs. This study aimed to identify an efficient, minimally invasive and economical DPC transplantation procedure for use in clinical settings. Five clinically applicable transplantation procedures were tested, termed the Pinhole, Laser, Slit, Non-vascularized sandwich (NVS) and Hemi-vascularized sandwich (HVS) methods. Labelled rat dermal papilla tissue was transplanted into rat sole skin, and hair follicle regeneration was evaluated histologically. Regenerated follicles and labelled DPCs were detected for all methods, although some follicles showed abnormal growth, i.e. a cystic or inverted appearance. The HVS method, pioneered here, resulted in significantly larger number of regenerated follicles that were more mature and regular than those observed using the other methods. Moreover, hair growth was detected after expanded adult-derived DPC transplantation using the HVS method. These results suggest that direct contact of epithelial and dermal components and better vascularization/oxygenation of the recipient site are critical for hair regeneration in cell-based therapies.