Dermal papilla cells of the adult hair follicle have the capacity to induce the formation of hair follicles when combined with keratinocytes in vivo. This remarkable regenerative ability forms the basis of a cell therapy, Follicular Cell Implantation (FCI), in which cells from a few dermal papillae are expanded in culture to produce cells from which many new follicles can form. Proof of principle for this therapy comes from research demonstating hair growth using culture dermal papilla cells combined with a variety of different keratinocyte sources to generate new follicles in different experimental models. A major challenge in the development of FCI is the ability to generate thousands of new follicles after a single therapy session. In order to accomplish this, the efficiency of hair growth must be high and the implants must be easy to perform. We have developed a method to generate immature hair-like structures or “proto-hairs” in culture. Proto-hairs form after the incubation of mixed aggregates, which consist of dermal papilla cells and keratinocytes that combine spontaneously under appropriate conditions. Initially, the mixed aggregrates have no structure and the dermal papilla cells and keratinocytes are randomly mixed within them. After 5-7 days in culture, proto-hairs form that have hair-like features including a dermal papilla, hair matrix, and a rudimentary hair shaft. When proto-hairs are implanted in an animal model, visible hairs emerge within 10-14 days. Proto-hairs represent a convenient form in which cultured follicular cells can be inplanted to produce new follicles with high efficiency.
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