Alvaro Meana

Large surface of cultured human epithelium obtained on a dermal matrix based on live fibroblast-containing fibrin gels

The aim of this study was to develop a new keratinocyte culture system on a dermal equivalent suitable for skin wound closure. Our dermal matrix is based on a fibrin gel from plasma cryoprecipitate containing live human fibroblast (from human foreskin). Keratinocytes obtained from primary culture according to the Rheinwald and Green method, were seeded on the gel at different seeding ratios. In all cases, the keratinocytes plated on the dermal equivalent grew to confluence and stratified epithelium was obtained within 10-15 days in culture. Early expression of basal membrane proteins was detected by immunostaining with laminin and type IV collagen antibodies. Cell proliferation was detected both in the epidermal layer and in the fibroblast embedded in the gel as assessed by BrdU incorporation. Detachment of composite cultures from dishes or flasks is a simple and quick procedure without the need for dispase treatment. Grafting of composite cultures to nude mice gave rise to an orderly stratified, orthokeratinized epithelium resembling human epidermis. A number of advantages including a large expansion factor without the need of 3T3 feeder layer, the availability of fibrin/plasma cryoprecipitate from blood banks and the versatile manipulation of composite cultures suggest that this system could be suitable for the definitive coverage of severely burned patients.

The Toll‐like receptor 4 (Asp299Gly) polymorphism is a risk factor for Gram‐negative and haematogenous osteomyelitis

Osteomyelitis is a bone infection caused mostly by Staphylococcus aureus but also by Gram‐negative bacteria. Toll‐like receptors (TLRs), after recognizing microbial products, induce a signal in neutrophils, leading to NF‐κB activation and transcription of pro‐inflammatory genes. Polymorphisms in TLR2 (Arg753Gln) and TLR4 (Asp299Gly, Thr399Ile) genes are associated with bacterial infections, we therefore studied these polymorphisms in osteomyelitis patients. Homozygotes for the TLR4 (Asp299Gly) polymorphism were significantly more frequent among the 80 osteomyelitis patients than in the 155 healthy controls (3/80, 3·8%versus 0/155, 0%; P = 0·038). Carriers of one or two G alleles of this tlr4 polymorphism were more likely to have Gram‐negative, haematogenous and/or chronic osteomyelitis than those without this mutation (P < 0·031). Patients with the TLR4 (Thr399Ile) mutant, which cosegregates with the TLR4 (Asp299Gly), were also carriers of this second polymorphism. No differences for the TLR2 (Arg753Gln) genotypes were found between patients and controls. Neutrophils of patients homozygous for the TLR4 (Asp299Gly) polymorphism showed lower LPS‐induced apoptosis reduction, phosphorylation of the inhibitor of NF‐κB, and lower IL‐6 and TNF‐α levels (P < 0·05). We report here for the first time an association between this TLR4 polymorphism and susceptibility to Gram‐negative bacteria and haematogenous osteomyelitis.

A Preclinical Model for the Analysis of Genetically Modified Human Skin In Vivo

Although skin is perhaps the most accessible of all somatic tissues for therapeutic gene transfer, it is a challenging site when attempting gene delivery. In addition to the transience of gene expression, important obstacles to cutaneous gene therapy have included the inability to sustain gene expression in a large proportion of keratinocytes within a given skin compartment. In this study, we have developed a novel experimental strategy that allows long-term regeneration of entirely genetically engineered human skin on the backs of NOD/SCID mice. Primary human keratinocytes were infected with a retroviral vector encoding the enhanced green fluorescent protein (EGFP) produced by transient transfection of 293T cells. EGFP expression allowed cell-sorting selection of a polyclonal population of productively transduced keratinocytes that were assembled in a live fibroblast-containing fibrin dermal matrix and orthotopically grafted onto mice. Epifluorescent illumination of the transplanted zone allowed in vivo monitoring of the genetically modified graft. EGFP-positive human skin was present on mice for 22 weeks after grafting. In addition, frozen sections prepared from the grafts displayed consistently strong EGFP-based fluorescence in all epidermal strata at every time point examined. Persistence of transgene expression was further confirmed through EGFP protein immunodetection. Purified EGFP-positive keratinocytes grafted as part of the fibrin-based artificial skin were capable of generating multilayer human epidermis on mice, with well-developed granulosum and corneum strata, and clearly defined rete ridges. Finally, the large proportion of transduced keratinocytes in our grafts allowed us to study, for the first time, the long-term in vivo clonal reconstitution pattern of the regenerated skin. Analysis of the provirus insertion sites indicates that a discrete number of epidermal stem cell clones was responsible for the maintenance of human skin regenerated in NOD/SCID recipients.

A cutaneous gene therapy approach to human leptin deficiencies: correction of the murine ob/ob phenotype using leptin-targeted keratinocyte grafts

Leptin deficiency produces a phenotype of obesity, diabetes, and infertility in the ob/ob mouse. In humans, leptin deficiency occurs in some cases of congenital obesity and in lipodystrophic disorders characterized by reduced adipose tissue and insulin resistance. Cutaneous gene therapy is considered an attractive potential method to correct circulating protein deficiencies, since gene‐transferred human keratinocytes can produce and secrete gene products with systemic action. However, no studies showing correction of a systemic defect have been reported. We report the successful correction of leptin deficiency using cutaneous gene therapy in the ob/ob mouse model. As a feasibility approach, skin explants from transgenic mice overexpressing leptin were grafted on immunodeficient ob/ob mice. One month later, recipient mice reached body weight values of lean animals. Other biochemical and clinical parameters were also normalized. In a second human gene therapy approach, a retroviral vector encoding both leptin and EGFP cDNAs was used to transduce HK and, epithelial grafts enriched in high leptin‐producing HK were transplanted to immunosuppressed ob/ob mice. HK‐derived leptin induced body weight reduction after a drop in blood glucose and food intake. Leptin replacement through genetically engineered HK grafts provides a valuable therapeutic alternative for permanent treatment of human leptin deficiency conditions.—Larcher, F., Del Rio, M., Serrano, F., Segovia, J. C., Ramírez, A., Meana, A., Page, A., Abad, J. L., González, M. A., Bueren, J., Bernad, A., Jorcano, J. L. A cutaneous gene therapy approach to human leptin deficiencies: correction of the murine ob/ob phenotype using leptin‐tar‐geted keratinocyte grafts. FASEB J. 15, 1529–1538 (2001)

Nonviral transfer of genes to pig primary keratinocytes. Induction of angiogenesis by composite grafts of modified keratinocytes overexpressing VEGF driven by a keratin promoter.

Cultured epithelial grafts have proven to be life-saving in the treatment of large skin losses. It has become apparent that one of the main difficulties of this technology is the overall poor take of the grafts as a consequence of severely damaged dermal beds. Skin substitutes providing both cultured keratinocytes, as an epidermal layer, and a dermal analogous offer a more suitable material for skin repair. Ex vivo transfer of stroma regeneration-promoting genes to keratinocytes appears to be an attractive strategy for improving the therapeutic action of these grafts. The use of epidermal-specific promoters as expression drivers of exogenous genes results in both high expression levels and stratum specificity, as shown in transgenic mice studies. Most current gene transfer protocols to primary keratinocytes involve transduction of epidermal cells with retroviral vectors. However, transfer of gene constructs harboring these long DNA fragment promoters cannot be achieved through viral transduction. In this paper, we describe a protocol consisting of lipid-mediated transfection, G418 selection and an enhanced green fluorescence protein (EGFP)-based enrichment step for obtaining high levels of transgene-expressing primary keratinocytes. Using this protocol, the cDNA for vascular endothelial growth factor (VEGF), a potent endothelial cell mitogen driven by the 5.2 kb bovine keratin K5 promoter, was stably transfected into pig primary keratinocytes. Genetically modified keratinocytes, expanded on live fibroblast-containing fibrin gels and transplanted to nude mice as a composite material, elicited a strong angiogenic response in the host stroma as determined by fresh tissue examination and CD31 immunostaining. Since the formation of a well-vascularized wound bed is a crucial step for permanent wound closure, the use of an ‘angiogenic’ composite material may improve wound bed preparation and coverage with cultured keratinocyte grafts.

Development of a Bioengineered Skin-Humanized Mouse Model for Psoriasis: Dissecting Epidermal-Lymphocyte Interacting Pathways

Over the past few years, whole skin xenotransplantation models that mimic different aspects of psoriasis have become available. However, these models are strongly constrained by the lack of skin donor availability and homogeneity. We present in this study a bioengineering-based skin-humanized mouse model for psoriasis, either in an autologous version using samples derived from psoriatic patients or, more importantly, in an allogeneic context, starting from skin biopsies and blood samples from unrelated healthy donors. After engraftment, the regenerated human skin presents the typical architecture of normal human skin but, in both cases, immunological reconstitution through intradermal injection in the regenerated skin using in vitro-differentiated T1 subpopulations as well as recombinant IL-17 and IL-22 Th17 cytokines, together with removal of the stratum corneum barrier by a mild abrasive treatment, leads to the rapid conversion of the skin into a bona fide psoriatic phenotype. Major hallmarks of psoriasis were confirmed by the evaluation of specific epidermal differentiation and proliferation markers as well as the mesenchymal milieu, including angiogenesis and infiltrate. Our bioengineered skin-based system represents a robust platform to reliably assess the molecular and cellular mechanisms underlying the complex interdependence between epidermal cells and the immune system. The system may also prove suitable to assess preclinical studies that test the efficacy of novel therapeutic treatments and to predict individual patient response to therapy.

The first COL7A1 mutation survey in a large Spanish dystrophic epidermolysis bullosa cohort: c.6527insC disclosed as an unusually recurrent mutation

Background  Dystrophic epidermolysis bullosa (DEB) is a genodermatosis caused by mutations in COL7A1. The clinical manifestations are highly variable from nail dystrophy to life‐threatening blistering, making early molecular diagnosis and prognosis of utmost importance for the affected families. Mutation identification is mandatory for prenatal testing.

In Vivo Assessment of Acute UVB Responses in Normal and Xeroderma Pigmentosum (XP-C) Skin-Humanized Mouse Models

In vivo studies of UVB effects on human skin are precluded by ethical and technical arguments on volunteers and inconceivable in cancer-prone patients such as those affected with Xeroderma Pigmentosum (XP). Establishing reliable models to address mechanistic and therapeutic matters thus remains a challenge. Here we have used the skin-humanized mouse system that circumvents most current model constraints. We assessed the UVB radiation effects including the sequential changes after acute exposure with respect to timing, dosage, and the relationship between dose and degree-sort of epidermal alteration. On Caucasian-derived regenerated skins, UVB irradiation (800 J/m(2)) induced DNA damage (cyclobutane pyrimidine dimers) and p53 expression in exposed keratinocytes. Epidermal disorganization was observed at higher doses. In contrast, in African descent-derived regenerated skins, physiological hyperpigmentation prevented tissue alterations and DNA photolesions. The acute UVB effects seen in Caucasian-derived engrafted skins were also blocked by a physical sunscreen, demonstrating the suitability of the system for photoprotection studies. We also report the establishment of a photosensitive model through the transplantation of XP-C patient cells as part of a bioengineered skin. The inability of XP-C engrafted skin to remove DNA damaged cells was confirmed in vivo. Both the normal and XP-C versions of the skin-humanized mice proved proficient models to assess UVB-mediated DNA repair responses and provide a strong platform to test novel therapeutic strategies.

IL‐1α (− 889) promoter polymorphism is a risk factor for osteomyelitis

As osteomyelitis (OM) induces the synthesis of inflammatory cytokines and IL‐1 mediates bone resorption by osteoclasts we determined if there is an association between certain common polymorphisms of the genes encoding proinflammatory cytokines (IL‐1α and β, IL‐6, TNF‐α) and OM in adults. The IL‐1α (− 889) TT genotype was significantly more frequent among 52 OM patients than in 109 healthy controls (13/52, [25.0%] vs. 9/109, [8.3%], P = 0.0081, χ2 = 7.01, OR = 3.7, 95% CI, 1.35–10.34). Patients who were homozygous for the T allele were younger than the rest of the OM patients (mean age 35.7 ± 11.5 vs. 58.1 ± 18.6 years, P = 0.001). IL‐1β TT (+ 3953) polymorphism was also more frequent in OM patients (P = 0.014, χ2 = 5.12, OR = 5.1, 95% CI, 1.21–52.14), but IL‐1β is in linkage disequilibrium with the IL‐1α *T (P < 0.001). Route of infection, chronicity of the infection, type of microorganism isolated, and frequency of relapses were similar in patients with and without the IL‐1α TT genotype. There were no associations between OM and polymorphisms of other cytokines genes. IL‐1α serum levels were significantly increased in all the OM patients independently of their IL‐1 genotype compared to the controls (P = 0.021). Although IL‐1α serum levels were not significantly higher in patients with the IL‐1α (− 889) polymorphism, this does not exclude a difference in production of IL‐1α by osteoclasts or other inflammatory cells at the site of infection.

A Comparison of Targeting Performance of Oncoretroviral Versus Lentiviral Vectors on Human Keratinocytes

The epidermis, like other rapidly renewing tissues, relies on a stem cell compartment to undergo constant regeneration. In order to develop realistic and long-lasting therapeutic approaches for some skin disorders, gene transfer to these critical cells must be obtained. While efficient retroviral ex vivo targeting and transgene integration in human keratinocytes is tightly dependent on proliferation, transferring genetic information to quiescent cells in culture also presents advantages, including the possibility of targeting putative dormant epidermal stem cells. In the present study we compared the efficiency of transduction achieved with a third-generation of human immunodeficiency virus (HIV)-based lentiviral vector to that obtained with a Moloney murine leukemia oncoretroviral vector (MLV) on proliferating and quiescent human keratinocytes growing in vitro in standard Rheinwald and Green cultures as well as in confluent organotypic cultures. Each viral vector contained the enhanced green fluorescent protein (EGFP) as a reporter gene. The lentiviral vector, but not the MLV vector, led to EGFP expression both in nondividing and proliferating epidermal cell populations in vitro. This feature was clearly evident when direct targeting of human keratinocytes, forming part of the epidermal component of an organotypic skin culture, was attempted. Keratinocytes modified by both MLV and the lentiviral vector allowed long-term regeneration of genetically engineered human skin on the backs of immunodeficient nonobese diabetic/severe combined immunodeficiency disorders (NOD/SCID) mice. However, EGFP transgene expression in the context of the MLV (long-terminal repeat [LTR]-driven) or lentiviral vector (cytomegalovirus [CMV]-driven) demonstrated clear differences both in quantitative terms and in the in vivo localization pattern.