SUMMARY Perturbations in the transcriptional programs specifying epidermal differentiation cause diverse skin pathologies ranging from impaired barrier function to inflammatory skin disease. However, the global scope and organization of this complex cellular program remain undefined. Here we report single-cell RNA sequencing profiles of 92,889 human epidermal cells from 9 normal and 3 inflamed skin samples. Transcriptomics-derived keratinocyte subpopulations reflect classic epidermal strata but also sharply compartmentalize epithelial functions such as cell-cell communication, inflammation, and WNT pathway modulation. In keratinocytes, ~12% of assessed transcript expression varies in coordinate patterns, revealing undescribed gene expression programs governing epidermal homeostasis. We also identify molecular fingerprints of inflammatory skin states, including S100 activation in the interfollicular epidermis of normal scalp, enrichment of a CD1C+CD301A+ myeloid dendritic cell population in psoriatic epidermis, and IL1βhi CCL3hiCD14+ monocyte-derived macrophages enriched in foreskin. This compendium of RNA profiles provides a critical step toward elucidating epidermal diseases of development, differentiation, and inflammation.

Therapeutic, III.

Acellular dermis allowed for a greater initial fill of saline. This potentially improves cosmetic outcome, as it better capitalizes on preserved mastectomy skin for reconstruction. The authors conclude that acellular dermis-assisted implant breast reconstruction has a safety profile no worse than that of complete submuscular coverage but offers the benefit of fewer expansions and the potential for more predictable secondary revisions.

SummaryIdentification of human satellite cells that fulfill muscle stem cell criteria is an unmet need in regenerative medicine. This hurdle limits understanding how closely muscle stem cell properties are conserved among mice and humans and hampers translational efforts in muscle regeneration. Here, we report that PAX7 satellite cells exist at a consistent frequency of 2–4 cells/mm of fiber in muscles of the human trunk, limbs, and head. Xenotransplantation into mice of 50–70 fiber-associated, or 1,000–5,000 FACS-enriched CD56+/CD29+ human satellite cells led to stable engraftment and formation of human-derived myofibers. Human cells with characteristic PAX7, CD56, and CD29 expression patterns populated the satellite cell niche beneath the basal lamina on the periphery of regenerated fibers. After additional injury, transplanted satellite cells robustly regenerated to form hundreds of human-derived fibers. Together, these findings conclusively delineate a source of bona-fide endogenous human muscle stem cells that will aid development of clinical applications.

Prepectoral breast reconstruction has emerged as an excellent technique for postmastectomy reconstruction, as it allows for full preservation of a patient's pectoralis major muscle and chest wall function. This reduces pain, eliminates animation deformity, and results in high patient satisfaction. Safely performed prepectoral breast reconstruction requires a careful patient selection process before committing to the procedure, taking into account comorbidities, radiation status, and oncologic criteria such as tumor location and breast cancer stage. Furthermore, a thorough intraoperative assessment of mastectomy skin flaps is critical, with careful and precise confirmation that the skin is viable and well perfused, prior to proceeding with prepectoral breast reconstruction. This can be done both clinically and with perfusion assessment devices. The use of acellular dermal matrix (ADM) has enhanced outcomes and aesthetics of prepectoral reconstruction, by providing implant coverage and soft-tissue support. The ADM also adds the benefit of reducing capsular contracture rates and offers full control over the aesthetic definition of the newly reconstructed breast pocket. Aesthetic enhancement of results requires routine use of oversizing implants in the skin envelope, careful selection of full capacity or cohesive gel implants, and autologous fat grafting. In this way, patients in all clinical scenarios can benefit from the full muscle-sparing technique of prepectoral breast reconstruction, including those undergoing immediate reconstruction, delayed reconstruction, and delayed conversion from a subpectoral to prepectoral plane to correct animation deformity.

Background: Prepectoral breast reconstruction following mastectomy has become a more widely performed technique in recent years because of its numerous benefits for women. These include full pectoralis muscle preservation, reduced loss of strength, reduced pain, and elimination of animation deformity. As with any breast reconstruction technique, widespread adoption is dependent on a low morbidity profile in the setting of postmastectomy radiation therapy, as this adjuvant therapy is routine in breast cancer treatment. The authors assess the clinical outcomes of patients undergoing postmastectomy radiation therapy following prepectoral breast reconstruction, and compare these to outcomes of patients undergoing postmastectomy radiation therapy with submuscular reconstruction. Methods: A single surgeon’s experience with immediate prepectoral breast reconstruction, followed by postmastectomy radiation therapy, from 2015 to 2017 was reviewed. Patient demographics and incidence of complications during the tissue expander stage were assessed. In addition, the morbidity profile of these patients was compared to that of patients undergoing submuscular/dual-plane reconstruction and postmastectomy radiation therapy over the same period. Results: Over 3 years, 175 breasts underwent immediate prepectoral reconstruction, and 236 breasts underwent immediate submuscular/dual-plane reconstruction. Overall rates of adjuvant radiation therapy (postmastectomy radiation therapy) were similar between prepectoral [26 breasts (14.9 percent)] and submuscular [31 breasts (13.1 percent)] (p = 0.6180) reconstruction. There were no significant differences in complication rates between the two reconstructive cohorts, in the setting of postmastectomy radiation therapy, including rates of explantation (15.4 percent versus 19.3 percent; p = 0.695). Conclusions: Prepectoral breast reconstruction is a safe and effective option in the setting of postmastectomy radiation therapy. The morbidity profile is similar to that encountered with submuscular reconstruction in this setting. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Therapeutic, IV.

SummaryInvestigation of human muscle regeneration requires robust methods to purify and transplant muscle stem and progenitor cells that collectively constitute the human satellite cell (HuSC) pool. Existing approaches have yet to make HuSCs widely accessible for researchers, and as a result human muscle stem cell research has advanced slowly. Here, we describe a robust and predictable HuSC purification process that is effective for each human skeletal muscle tested and the development of storage protocols and transplantation models in dystrophin-deficient and wild-type recipients. Enzymatic digestion, magnetic column depletion, and 6-marker flow-cytometric purification enable separation of 104 highly enriched HuSCs per gram of muscle. Cryostorage of HuSCs preserves viability, phenotype, and transplantation potential. Development of enhanced and species-specific transplantation protocols enabled serial HuSC xenotransplantation and recovery. These protocols and models provide an accessible system for basic and translational investigation and clinical development of HuSCs.