The CD44+ ALDH+ population of human keratinocytes is enriched for epidermal stem cells with long-term repopulating ability.

Like for other somatic tissues, isolation of a pure population of stem cells has been a primary goal in epidermal biology. We isolated discrete populations of freshly obtained human neonatal keratinocytes (HNKs) using previously untested candidate stem cell markers aldehyde dehydrogenase (ALDH) and CD44 as well as the previously studied combination of integrin α6 and CD71. An in vivo transplantation assay combined with limiting dilution analysis was used to quantify enrichment for long-term repopulating cells in the isolated populations. The ALDH(+) CD44(+) population was enriched 12.6-fold for long-term repopulating epidermal stem cells (EpiSCs) and the integrin α6(hi) CD71(lo) population was enriched 5.6-fold, over unfractionated cells. In addition to long-term repopulation, CD44(+) ALDH(+) keratinocytes exhibited other stem cell properties. CD44(+) ALDH(+) keratinocytes had self-renewal ability, demonstrated by increased numbers of cells expressing nuclear Bmi-1, serial transplantation of CD44(+) ALDH(+) cells, and holoclone formation in vitro. CD44(+) ALDH(+) cells were multipotent, producing greater numbers of hair follicle-like structures than CD44(-) ALDH(-) cells. Furthermore, 58% ± 7% of CD44(+) ALDH(+) cells exhibited label-retention. In vitro, CD44(+) ALDH(+) cells showed enhanced colony formation, in both keratinocyte and embryonic stem cell growth media. In summary, the CD44(+) ALDH(+) population exhibits stem cell properties including long-term epidermal regeneration, multipotency, label retention, and holoclone formation. This study shows that it is possible to quantify the relative number of EpiSCs in human keratinocyte populations using long-term repopulation as a functional test of stem cell nature. Future studies will combine isolation strategies as dictated by the results of quantitative transplantation assays, in order to achieve a nearly pure population of EpiSCs.

Exercise for bone health: rationale and prescription.

PURPOSE OF REVIEW: Patients frequently inquire about exercise as a means to improve bone strength and reduce osteoporotic fracture. Understanding the biologic mechanisms and the available clinical evidence supporting the role of exercise in bone health is the key to an educated discussion. RECENT FINDINGS: Exercise downregulates sclerostin expression by the osteocyte favoring osteoblastogenesis. These changes are enhanced by dynamic cyclical load with rest periods and may be promoted by low-amplitude high-frequency stimuli. In the prepubertal years, exercise results in periosteal gains, whereas exercise later in life maintains bone mass, reduces falls and probably associated fractures, and improves quality-of-life measures. SUMMARY: Future studies should examine the effect of exercise on bone strength and determine the minimum quantity and frequency and the exercise type most effective to reduce osteoporotic fractures.

Selection of tumorigenic melanoma cells using ALDH.

Despite increasing knowledge regarding melanoma-initiating cells (MICs), questions persist regarding the number and phenotypic nature of cells with tumor-generating capability. Evidence for a phenotypically distinct human MIC has been found in NOD/SCID (non-obese diabetic/severe combined immunodeficiency) mice. However, a phenotypically distinct human MIC was not found in the NOD/SCIDIl2rg(-)/(-) (NSG) mouse model. The demonstration of a distinct population of human melanoma cells responsible for tumorigenesis and tumor cell self-renewal would provide an important target for new melanoma therapies. In this study, we show a 100-fold range in MIC frequency in human melanoma (1 in 18,000 to 1 in 1,851,000 cells) in the NOD/SCID mouse. In this model, human melanoma cells with high aldehyde dehydrogenase (ALDH) activity were enriched 16.8-fold in tumorigenic cells over unfractionated (UNF) cells, such that 1 in 21,000 cells was a MIC. In the NSG mouse, the ALDH expressing cell population was enriched 100-fold in tumorigenic cells over UNF cells, such that one in four cells was a MIC. Xenograft melanomas that developed from ALDH(+) cells displayed robust self-renewal, whereas those from ALDH(-) cells showed minimal self-renewal in vitro. Thus, ALDH(+) melanoma cells have enhanced tumorigenicity over ALDH(-) cells and superior self-renewal ability.

Suppression of glomerulonephritis in NZB/NZW lupus prone mice by adoptive transfer of ex vivo expanded regulatory T cells.

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown cause characterized by expansion of autoreactive lymphocytes. Regulatory T cells (T(regs)) are a component of the normal immune system and contribute to the maintenance of peripheral tolerance. T(reg) abnormalities have been associated with several autoimmune diseases and there is interest in the role of T(regs) in SLE. We previously demonstrated that transfer of expanded CD4(+)CD25(+)CD62L(HI) T(regs) slows the development of lupus in (NZBxNZW)F(1) (B/W) mice. However in the absence of T(reg) specific surface antigens, cell purification remains a compromise between the breadth and purity of the population isolated. Importantly, purified populations always contain Foxp3(-) effector T cells (T(effs)) that theoretically could exacerbate autoimmunity in the recipient. Here we explore the impact of transferring the more comprehensive, but less pure T(reg) subset defined by CD4(+)CD25(+) expression on development of murine lupus. All cells were FACS sorted and expanded prior to adoptive transfer. Development of proteinuria and survival were measured. We found that exogenous expansion of CD4(+)CD25(+) cells produced a population containing 70-85% CD4(+)Foxp3(+)T(regs). Expanded T(regs) had higher CTLA-4 and Foxp3 expression, increased in vitro suppression capacity, and prolonged in vivo survival as compared to freshly isolated cells. Adoptive transfer of expanded CD4(+)CD25(+) T(regs) inhibited the onset of glomerulonephritis and prolonged survival in mice. Importantly the population of T(eff) contained within the adoptively transferred cells had reduced survival and proliferation capacity as compared to either co-transferred T(regs) or transferred T(effs) expanded in the absence of T(regs). These studies demonstrate that adoptive transfer of expanded CD4(+)CD25(+)Foxp3(+)T(regs) has the capacity to inhibit the onset of murine lupus and that this capacity is significant despite transfer of co-cultured T(eff) cells. These data indicate that when co-expanded with regulatory T cells, exogenously activated T(effs) from autoimmune patients may not pose a significant risk of promoting disease.

CTLA-4: a key regulatory point in the control of autoimmune disease.

SUMMARY: Chronic autoimmune disease in humans is the result of a failure to control autoreactive immune cells in the periphery. This control is largely achieved by inhibition of newly activated and memory cells. A number of negative immune regulatory pathways have been characterized. The cell surface coreceptor cytotoxic T-lymphocyte antigen-4 (CTLA-4) has emerged as a critical attenuator of T-cell activation and an essential component of the regulatory systems that serve to maintain peripheral tolerance. CTLA-4 expression is induced on the surface of T cells after they have received a costimulatory signal from antigen-presenting cells (APCs) via engagement of CD28 on the T-cell surface. CTLA-4 attenuates this costimulation by competing for CD28 ligands and through direct effects on APCs via the same ligands utilized by CD28. A large number of genetic association studies suggest that the CTLA-4 gene is a locus of susceptibility to autoimmune disease. However, specific functional defects in the CTLA-4 gene in patients have not been identified to date. Elucidating the role of CTLA-4 in immune tolerance has also led to a number of therapeutic applications, particularly in the treatment of malignancy and autoimmune disease.

Rapid adhesion to collagen isolates murine keratinocytes with limited long-term repopulating ability in vivo despite high clonogenicity in vitro.

A prevalent belief in epidermal biology is that stem cells are highly clonogenic; that is, they have the ability to produce many large colonies in vitro. However, it has been well-established in hematology, and recently suggested in epithelial biology, that short-term in vitro clonogenic assays may not be reliable predictors of long-term in vivo repopulating ability. Numerous groups have shown that rapid adhesion to collagen selects for highly clonogenic keratinocytes, but it has not been demonstrated whether this subpopulation is enriched in stem cells as defined by long-term repopulating ability in vivo. We found that although rapid adhesion to collagen (within 5 minutes) selected for cells with increased short-term colony forming ability in vitro, these cells were not enriched in long-term proliferative ability in vitro or in repopulating ability in vivo after 9 weeks. Conversely, keratinocytes that did not adhere to collagen (after 20 minutes) were less clonogenic in short-term assays but possessed equivalent long-term proliferative ability in vitro and superior long-term repopulating ability in vivo. Both the rapidly adherent cell and not rapidly adherent cell populations contained small, noncomplex basaloid cells, expressed integrin alpha2 (a collagen IV receptor), and expressed the putative epidermal stem cell phenotype integrin alpha6(hi)CD71(lo). Our results indicate that the superior short-term colony forming ability of collagen-adherent murine keratinocytes does not correlate with long-term repopulating ability in vitro or in vivo and that proliferation in vitro is not a reliable surrogate for stem cell behavior in vivo.

Suppression of disease in New Zealand Black/New Zealand White lupus-prone mice by adoptive transfer of ex vivo expanded regulatory T cells.

An increasing number of studies indicate that a subset of CD4(+) T cells with regulatory capacity (regulatory T cells; T(regs)) can function to control organ-specific autoimmune disease. To determine whether abnormalities of thymic-derived T(regs) play a role in systemic lupus erythematosus, we evaluated T(reg) prevalence and function in (New Zealand Black x New Zealand White)F(1) (B/W) lupus-prone mice. To explore the potential of T(regs) to suppress disease, we evaluated the effect of adoptive transfer of purified, ex vivo expanded thymic-derived T(regs) on the progression of renal disease. We found that although the prevalence of T(regs) is reduced in regional lymph nodes and spleen of prediseased B/W mice compared with age-matched non-autoimmune mice, these cells increase in number in older diseased mice. In addition, the ability of these cells to proliferate in vitro was comparable to those purified from non-autoimmune control animals. Purified CD4(+)CD25(+)CD62L(high) B/W T(regs) were expanded ex vivo 80-fold, resulting in cells with a stable suppressor phenotype. Adoptive transfer of these exogenously expanded cells reduced the rate at which mice developed renal disease; a second transfer after treated animals had developed proteinuria further slowed the progression of renal disease and significantly improved survival. These studies indicate that thymic-derived T(regs) may have a significant role in the control of autoimmunity in lupus-prone B/W mice, and augmentation of these cells may constitute a novel therapeutic approach for systemic lupus erythematosus.

Childhood onset systemic sclerosis: classification, clinical and serologic features, and survival in comparison with adult onset disease.

OBJECTIVE: To describe the differences between patients with systemic sclerosis (SSc) having childhood versus adult onset evaluated at a single medical center. METHODS: Patients were divided into those with childhood onset (first SSc symptom or finding before age 16 yrs) and those with early adult and late adult onset. The 3 groups were compared with respect to disease classification, clinical, laboratory and serologic data, and survival. RESULTS: One hundred eleven childhood onset SSc cases seen between 1960 and 2003 were compared with 2559 adult onset SSc cases (1087 with onset age 16-40 and 1472 with onset after age 40 yrs) first evaluated between 1972 and 2001. Age distribution at onset was unimodal, suggesting that childhood disease is part of the spectrum of adult onset SSc. A significantly greater proportion of childhood onset patients had overlap syndromes, most frequently with polymyositis-dermatomyositis (PM-DM), and skeletal muscle involvement. Children with diffuse cutaneous (dc) SSc had significantly lower maximum mean total skin thickness scores than adult patients with dcSSc. Renal involvement was uncommon in childhood onset cases, and the frequency increased with age of onset. Serum anti-PM-Scl and anti-U1RNP antibodies were detected significantly more frequently in childhood than in adult onset cases. In contrast, anti-RNA polymerase III and anticentromere antibodies were found significantly more frequently in adults. Survival was significantly better among childhood than all adult onset cases combined, but similar to survival in young adult onset SSc cases. Scleroderma heart disease was a frequent cause of death among children with SSc. CONCLUSION: Patients with juvenile onset SSc more frequently have an overlap syndrome with PM-DM, higher frequency of skeletal muscle involvement, serum anti-PM-Scl and anti-U1RNP antibody, fatal cardiac disease, and improved survival compared with adult onset SSc cases.