Treating chronic wound infections with genetically modified free flaps

CXCL12-Targeted Immunomodulatory Gene Therapy Reduces Radiation-Induced Fibrosis in Healthy Tissues

Radiation-induced fibrosis (RIF) is a progressive pathology deleteriously impacting cancer survivorship. CXCL12 is an immune-stromal signal implicated in fibrosis and innate response. We hypothesized that modulation of CXCL12 would phenotypically mitigate RIF. CXCL12 expression was characterized in a rodent model of RIF and its expression modulated by the intravascular delivery of lentiviral vectors encoding small hairpin RNA to silence (LVShCXCL12) or overexpress (LVOeCXCL12) CXCL12. Multimodal fibrotic outcomes were quantified, and flow cytometry and Y-chromosome lineage-tracking studies performed to examine cellular recruitment and activation after radiotherapy. Whole-tissue RNA sequencing was used to examine matrisomal response. MATBIII tumors were engrafted within tissues with differing levels of CXCL12 expression, and tumoral response to RT was evaluated. CXCL12 was upregulated in irradiated fibroblasts demonstrating DNA damage after radiotherapy, which led to the recruitment of CD68+ macrophages. Silencing CXCL12 with LVShCXCL12 demonstrated reduced RIF phenotype as a result of decreased macrophage recruitment. Transcriptomic profiling identified osteopontin (OPN; SPP1) as being highly differentially expressed in LVShCXCL12-treated tissues. Tumors growing in tissues devoid of CXCL12 expression responded better after RT because of reductions in peritumoral fibrosis as a result of decreased CXCL12 and OPN expression at the tumor/normal tissue interface. This was also associated with greater CD8+ T-cell infiltration in tumors with less fibrosis. Antibody-mediated OPN blockade slowed tumor growth by increased intratumoral CD8+ T-cell activation. The CXCL12/OPN axis is an important node of immune/matrisomal cross-talk in the development of fibrosis. Therapeutic manipulation of this axis may offer greater antitumor efficacy while also reducing adverse effects.

Biologic Brachytherapy: Genetically Modified Surgical Flap as a Therapeutic Tool-A Systematic Review of Animal Studies

Surgical flaps are rudimentary tools in reconstructive surgery, especially following extensive solid tumour resections. They cover skin and soft tissue defects but are prone to ischaemia and necrosis. Since their primary aim is reconstruction, they rarely exhibit a therapeutic activity against the treated disease. Attempts have been made to develop a new therapeutic strategy-biologic brachytherapy, which uses genetically engineered surgical flaps as a drug delivery vehicle, allowing the flap tissue to act as a "biologic pump". This systematic review summarizes the preclinical evidence on using genetically modified surgical flaps. A literature search was conducted in PubMed, EMBASE, Scopus and Web of Science. The initial literature search yielded 714 papers, and, eventually, seventy-seven studies were included in qualitative analysis. The results show that genetic enhancement of flaps has been used as a local or systemic therapy for numerous disease models. Frequently, it has been used to increase flap survival and limit ischaemia or promote flap survival in a non-ischemic context, with some studies focusing on optimizing the technique of such gene therapy. The results show that genetically modified flaps can be successfully used in a variety of contexts, but we need more studies to implement this research into specific clinical scenarios.

Innovations in Skin and Soft Tissue Aging-A Systematic Literature Review and Market Analysis of Therapeutics and Associated Outcomes

PURPOSE

Skin and soft tissue aging has been an important topic of discussion among plastic surgeons and their patients. While botulinum toxin, facial fillers, chemical peels, and surgical lifts preside as the mainstay of treatment to restore appearance of youth, emergent technologies, such as CRISPR-Cas9, proteostasis, flap biology, and stem cell therapies, have gained traction in addressing the aging process of skin and soft tissue. Several studies have introduced these advancements, but it remains unclear how safe and effective these therapeutics are in facial rejuvenation, and how they may fit in the existent treatment workflow for soft tissue aging.

MATERIALS/METHODS

A systematic literature review was conducted to identify and assess therapeutics utilized in addressing skin and soft tissue aging. Variables collected included year of publication, journal, article title, organization of study, patient sample, treatment modality, associated outcomes. In addition, we performed a market analysis of companies involved in promoting technologies and therapeutics within this space. PitchBook (Seattle, WA), a public market database, was utilized to classify companies, and record the amount of venture capital funding allocated to these categories.

RESULTS

Initial review yielded four hundred and two papers. Of these, thirty-five were extracted after applying inclusion and exclusion criteria. Though previous literature regards CRISPR-Cas9 technology as the most favorable anti-aging innovation, after reviewing the current literature, stem cell therapies utilizing recipient chimerism appeared to be the superior skin anti-aging technique when accounting for possible disadvantages of various techniques. The psychosocial and cosmetic outcomes from using cell therapy to modulate allograft survival and tolerance may confer more long-term proposed benefits than the technologies in CRISPR-Cas9, flap biology innovations, and autologous platelet-rich plasma use. Market analysis yielded a total of 87 companies, which promoted innovations in technology, biotechnology, biopharmaceuticals, cell-based therapies, and genetic therapy.

CONCLUSION

This review provides physicians and patients with relevant, usable information regarding how therapeutics can impact treatment regimen for facial aesthetics and skin rejuvenation. Furthermore, the goal of this research is to elucidate the varying therapeutics to restore appearance of youth, present associated outcomes, and in doing so, present plastic surgeons and their colleagues with greater insight on the role of these therapeutics and technologies in clinical practice. Future studies can further assess the safety and efficacy of these innovations and discuss how these may fit within surgical plans among patients seeking rejuvenation procedures.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Selective Microvascular Tissue Transfection Using Minicircle DNA for Systemic Delivery of Human Coagulation Factor IX in a Rat Model Using a Therapeutic Flap

BACKGROUND

Gene therapy is a promising treatment for protein deficiency disorders such as hemophilia B. However, low tissue selectivity and efficacy are limitations of systemic vector delivery. The authors hypothesized that selective transfection of rat superficial inferior epigastric artery flaps could provide systemic delivery of coagulation factor IX, preventing the need for systemic vector administration.

METHODS

Minicircle DNA containing green fluorescent protein, firefly luciferase, and human coagulation factor IX was created. Vector constructs were validated by transfecting adipose-derived stromal cells isolated from Wistar rat superficial inferior epigastric artery flaps and evaluating transgene expression by fluorescence microscopy, bioluminescence, and enzyme-linked immunosorbent assay. Minicircle DNA luciferase (10 and 30 μg) was injected into murine (wild-type, C57/BL/6) inguinal fat pads (n = 3) and followed by in vivo bioluminescence imaging for 60 days. Wistar rat superficial inferior epigastric artery flaps were transfected with minicircle DNA human coagulation factor IX (n = 9) with plasma and tissue transgene expression measured by enzyme-linked immunosorbent assay at 2 and 4 weeks.

RESULTS

Transfected adipose-derived stromal cells expressed green fluorescent protein for 30 days, luciferase for 43 days, and human coagulation factor IX (21.9 ± 1.2 ng/ml) for 28 days in vitro. In vivo murine studies demonstrated dose-dependence between minicircle DNA delivery and protein expression. Ex vivo rat superficial inferior epigastric artery flap transfection with minicircle DNA human coagulation factor IX showed systemic transgene expression at 2 (266.6 ± 23.4 ng/ml) and 4 weeks (290.1 ± 17.1 ng/ml) compared to control tissue (p < 0.0001).

CONCLUSIONS

Rat superficial inferior epigastric artery flap transfection using minicircle DNA human coagulation factor IX resulted in systemic transgene detection, suggesting that selective flap or angiosome-based tissue transfection may be explored as a treatment for systemic protein deficiency disorders such as hemophilia B.

Use of the Keystone Perforator Island Flap in the treatment of chronic lower extremity wounds complicated by osteomyelitis

INTRODUCTION

Reconstruction of chronic lower extremity wounds can be especially challenging when these wounds are complicated by osteomyelitis. They require the joint expertise of plastic and orthopaedic surgeons.

METHODS

We report our experience using the Keystone Perforator Island Flap following wound and bone debridement as a valuable surgical tool for coverage of complex wounds with bone infection.

RESULTS

Twelve patients underwent similar procedures with overall good outcomes, although two patients experienced a complication, specifically partial flap necrosis and wound dehiscence subsequent to recurrent osteomyelitis. We also reviewed the underlying physiological mechanisms of employing the Keystone flap in order to demonstrate its advantages and efficacy.

CONCLUSION

Our results confirm that the Keystone flap can be a safe, reliable and effective method for coverage of soft tissue defects and the preservation of bone integrity in the management of patients with chronic osteomyelitis.

The Evolving Landscape of Gene Therapy in Plastic Surgery

With the rapid rise of personalized genomic sequencing and clustered regularly interspaced short palindromic repeat (CRISPR) technology, previous gaps in gene therapy are beginning to be bridged, paving the way for increasing clinical applicability. This article aims to provide an overview of the fundamentals of gene therapy and discuss future potential interventions relevant to plastic surgeons. These interventions include enhancing tissue regeneration and healing, as well as modifying disease processes in congenital anomalies. Though clinical applications are still on the horizon, a deeper understanding of these new advances will help plastic surgeons understand the current landscape of gene therapy and stay abreast of future opportunities.

BD-2 and BD-3 increase skin flap survival in a model of ischemia and Pseudomonas aeruginosa infection

The main aim of this work was to study the usefulness of human β-defensins 2 (BD-2) and 3 (BD-3), which are part of the innate immune system, in the treatment of infected ischemic skin flaps. We investigated the effect of transducing rat ischemic skin flaps with lentiviral vectors encoding human BD-2, BD-3, or both BD-2 and BD-3, to increase flap survival in the context of a P. aeruginosa infection associated with a foreign body. The secondary endpoints assessed were: bacterial counts, and biofilm formation on the surface of the foreign body. A local ischemic environment was created by producing arterialized venous flaps in the left epigastric region of rats. Flaps were intentionally infected by placing underneath them two catheters with 105 CFU of P. aeruginosa before the surgical wounds were hermetically closed. Flap biopsies were performed 3 and 7 days post-operatively, and the specimens submitted to immunohistochemical analysis for BD-2 and BD-3, as well as to bacterial quantification. Subsequently, the catheter segments were analyzed with scanning electron microscopy (SEM). Flaps transduced with BD-2 and BD-3 showed expression of these defensins and presented increased flap survival. Rats transduced with BD-3 presented a net reduction in the number of P. aeruginosa on the surface of the foreign body and lesser biofilm formation.

Engineering in-vitro stem cell-based vascularized bone models for drug screening and predictive toxicology

The production of veritable in-vitro models of bone tissue is essential to understand the biology of bone and its surrounding environment, to analyze the pathogenesis of bone diseases (e.g., osteoporosis, osteoarthritis, osteomyelitis, etc.), to develop effective therapeutic drug screening, and to test potential therapeutic strategies. Dysregulated interactions between vasculature and bone cells are often related to the aforementioned pathologies, underscoring the need for a bone model that contains engineered vasculature. Due to ethical restraints and limited prediction power of animal models, human stem cell-based tissue engineering has gained increasing relevance as a candidate approach to overcome the limitations of animals and to serve as preclinical models for drug testing. Since bone is a highly vascularized tissue, the concomitant development of vasculature and mineralized matrix requires a synergistic interaction between osteogenic and endothelial precursors. A number of experimental approaches have been used to achieve this goal, such as the combination of angiogenic factors and three-dimensional scaffolds, prevascularization strategies, and coculture systems. In this review, we present an overview of the current models and approaches to generate in-vitro stem cell-based vascularized bone, with emphasis on the main challenges of vasculature engineering. These challenges are related to the choice of biomaterials, scaffold fabrication techniques, and cells, as well as the type of culturing conditions required, and specifically the application of dynamic culture systems using bioreactors.

A Model of Free Tissue Transfer: The Rat Epigastric Free Flap

Free tissue transfer has been increasingly used in clinical practice since the 1970s, allowing reconstruction of complex and otherwise untreatable defects resulting from tumor extirpation, trauma, infections, malformations or burns. Free flaps are particularly useful for reconstructing highly complex anatomical regions, like those of the head and neck, the hand, the foot and the perineum. Moreover, basic and translational research in the area of free tissue transfer is of great clinical potential. Notwithstanding, surgical trainees and researchers are frequently deterred from using microsurgical models of tissue transfer, due to lack of information regarding the technical aspects involved in the operative procedures. The aim of this paper is to present the steps required to transfer a fasciocutaneous epigastric free flap to the neck in the rat.

This flap is based on the superficial epigastric artery and vein, which originates from and drain into the femoral artery and vein, respectively. On average the caliber of the superficial epigastric vein is 0.6 to 0.8 mm, contrasting with the 0.3 to 0.5 mm of the superficial epigastric artery. Histologically, the flap is a composite block of tissues, containing skin (epidermis and dermis), a layer of fat tissue (panniculus adiposus), a layer of striated muscle (panniculus carnosus), and a layer of loose areolar tissue.

Succinctly, the epigastric flap is raised on its pedicle vessels that are then anastomosed to the external jugular vein and to the carotid artery on the ventral surface of the rat's neck. According to our experience, this model guarantees the complete survival of approximately 70 to 80% of epigastric flaps transferred to the neck region. The flap can be evaluated whenever needed by visual inspection. Hence, the authors believe this is a good experimental model for microsurgical research and training.

Adenovirally delivered enzyme prodrug therapy with herpes simplex virus-thymidine kinase in composite tissue free flaps shows therapeutic efficacy in rat models of glioma

INTRODUCTION

Free flap gene therapy exploits a novel therapeutic window when viral vectors can be delivered into a flap ex vivo. The authors investigated the therapeutic potential of an adenovirally-delivered thymidine kinase/ganciclovir prodrug system expressed following vector delivery into a free flap.

METHODS

The authors demonstrated direct in vitro cytotoxicity by treating a panel of malignant cell lines with the thymidine kinase/ganciclovir system and demonstrated significant cell kill proportional to the multiplicity of infection of adenoviral vector expressing thymidine kinase. Bystander cytotoxicity was demonstrated using conditioned media from producer cells (expressing adenovirally-delivered thymidine kinase and treated with ganciclovir) to demonstrate cytotoxicity in naive tumor cells. The authors investigated the effect of adenoviral vector expressing thymidine kinase/ganciclovir therapy in vivo, using models of microscopic and macroscopic residual disease in a rodent superficial inferior epigastric artery flap model.

RESULTS

The authors observed retardation of tumor volume growth in both microscopic (p = 0.0004) and macroscopic (p = 0.0005) residual disease models and prolongation of animal survival. Gene expression studies demonstrated that viral genomic material was found predominantly in flap tissues but declined over time.

CONCLUSIONS

The authors describe the utility of virally delivered enzyme/prodrug therapy, using a free flap as a vehicle for delivery. They discuss the merits and limitations of this approach and the unique role of therapeutic free flaps among reconstructive techniques available to the plastic surgeon.

Gene-directed enzyme prodrug therapy for localized chemotherapeutics in allograft and xenograft tumor models

Most chemotherapy regimens rely on systemic administration of drugs leading to a wide array of toxicities. Using viral-vector-mediated gene modification of muscle tissues, we have developed a method for gene-directed enzyme prodrug therapy that allows for localized drug administration. An inactive prodrug of geldanamycin was activated locally for inhibition of tumor growth without systemic toxicities. A recombinant adeno-associated virus (rAAV) was used to deliver β-galactosidase (LacZ) to the treatment group and green fluorescent protein to the control group. After 1 week, both groups received adenocarcinoma cells in the same location as the previous rAAV injection. The geldanamycin prodrug was administered 1 h later via intraperitoneal injection. Tumor growth was significantly suppressed in animals whose muscles were gene modified to express β-galactosidase compared with the control. Serum assay to access hepatotoxicity resulted in no significant differences between the animals treated with the inactive or activated form of geldanamycin, indicating minimal damage to non-target organs. Using gene-directed enzyme prodrug therapy, in combination with novel recombinant AAV vectors, we have developed a method for localized activation of chemotherapeutic agents that limits the toxicities seen with traditional systemic administration of these potent drugs.

Fat grafting as a vehicle for the delivery of recombinant adenoassociated viral vectors to achieve gene modification of muscle flaps

BACKGROUND

The combination of gene therapy and plastic surgery may have the potential to improve the specificity that is needed to achieve clinically applicable treatment regimens. Our goal was to develop a method for gene modification that would yield sustainable production of gene products but would be less time consuming than existing protocols.

METHODS

An adenoassociated virus was used to deliver gene products to pectoralis muscle flaps. Gene modification was accomplished via either direct injection or novel fat grafting techniques.

RESULTS

The production of gene product was observable by both in vivo imaging and immunohistochemical staining. Gene products were not detected in tissues that were not in contact with the fat grafts that were incubated with the viral vector, indicating that the transduction stayed local to the flap.

CONCLUSIONS

Using novel recombinant adenoassociated virus vectors, we have developed a method for gene delivery that is highly efficient and applicable to muscle flaps.

Vascular surgery, microsurgery and supramicrosurgery for treatment of chronic diabetic foot ulcers to prevent amputations

INTRODUCTION

Diabetic foot ulcers occur in approximately 2,5% of patients suffering from diabetes and may lead to major infections and amputation. Such ulcers are responsible for a prolonged period of hospitalization and co- morbidities caused by infected diabetic foot ulcers. Small, superficial ulcers can be treated by special conservative means. However, exposed bones or tendons require surgical intervention in order to prevent osteomyelitis. In many cases reconstructive surgery is necessary, sometimes in combination with revascularization of the foot. There are studies on non surgical treatment of the diabetic foot ulcer. Most of them include patients, classified Wagner 1-2 without infection. Patients presenting Wagner 3D and 4D however are at a higher risk of amputation. The evolution of microsurgery has extended the possibilities of limb salvage. Perforator based flaps can minimize the donorsite morbidity.

PATIENTS AND METHODS

41 patients were treated with free tissue transfer for diabetic foot syndrome and chronic defects. 44 microvascular flaps were needed. The average age of patients was 64.3 years. 18 patients needed revascularization. 3 patients needed 2 microvascular flaps. In 6 cases supramicrosurgical technique was used.

RESULTS

There were 2 flap losses leading to amputation. 4 other patients required amputation within 6 months postoperatively due to severe infection or bypass failure. Another 4 patients died within one year after reconstruction. The remaining patients were ambulated.

DISCUSSION

Large defects of the foot can be treated by free microvascular myocutaneous or fasciocutaneous tissue transfer. If however, small defects, exposing bones or tendons, are not eligible for local flaps, small free microvascular flaps can be applied. These flaps cause a very low donor site morbidity. Arterialized venous flaps are another option for defect closure. Amputation means reduction of quality of life and can lead to an increased mortality postoperatively.

Cellular and Molecular Bioengineering: A Tipping Point

In January of 2011, the Biomedical Engineering Society (BMES) and the Society for Physical Regulation in Biology and Medicine (SPRBM) held its inaugural Cellular and Molecular Bioengineering (CMBE) conference. The CMBE conference assembled worldwide leaders in the field of CMBE and held a very successful Round Table discussion among leaders. One of the action items was to collectively construct a white paper regarding the future of CMBE. Thus, the goal of this report is to emphasize the impact of CMBE as an emerging field, identify critical gaps in research that may be answered by the expertise of CMBE, and provide perspectives on enabling CMBE to address challenges in improving human health. Our goal is to provide constructive guidelines in shaping the future of CMBE.

A Bioengineered Human Skin Tissue for the Treatment of Infected Wounds

BACKGROUND

Complex skin defects resulting from acute skin trauma and chronic, nonhealing wounds are life-threatening injuries. Infection is one of the most common obstacles to the healing of these types of wounds. Host defense peptides (HDPs) possessing a broad spectrum of activity against microorganisms and serving as innate immune modulators have emerged as potential treatment strategies for infected wounds.

THE PROBLEM

The increase in multidrug-resistant clinical bacterial isolates highlights the need for new and innovative anti-infective therapies for the treatment of both acute and chronic skin wounds.

BASIC/CLINICAL SCIENCE

To address the critical need for new therapeutic options to reduce infection and improve wound healing, a bioengineered skin substitute (BSS) tissue has been created to act as an anti-infective living human skin tissue that provides enhanced expression of the endogenous HDP, cathelicidin. To generate a BSS exhibiting these antimicrobial properties, the clinically tested NIKS progenitor cells were employed to provide a source of genetically uniform, nontumorigenic, pathogen-free human keratinocytes that are amenable to genetic engineering using nonviral means.

CLINICAL CARE RELEVANCE

Pathogenic bacterial strains are increasingly developing antibiotic resistance, thereby forcing the clinician to use potent antibiotics with deleterious effects on keratinocyte viability and migration. Therefore, an urgent need exists for new wound therapies that can circumvent many of the problems associated with current antibiotic treatments.

CONCLUSION

Enhanced expression of cathelicidin in a genetically engineered human BSS has been shown to inhibit the bacterial growth of a multidrug-resistant clinical strain of Acinetobacter baumannii in vivo, creating a new and innovative therapeutic option for combating these debilitating wound infections while also promoting healing.

Biological roles of host defense peptides: lessons from transgenic animals and bioengineered tissues

Host defense peptides (HDPs) have long been recognized as microbicidal agents, but their roles as modulators of innate and adaptive immunity have only more recently been appreciated. The study of transgenic animal and tissue models has provided platforms to improve our understanding of the immune modulatory functions of HDPs. Here, the characterization of transgenic animals or tissue models that over-express and/or are deficient for specific HDPs is reviewed. We also attempt to reconcile this data with evidence from human studies monitoring HDP expression at constitutive levels and/or in conjunction with inflammation, infection models, or disease states. We have excluded activities ascribed to HDPs derived exclusively from in vitro experiments. An appreciation of the way that HDPs promote innate immunity or influence the adaptive immune response is necessary in order to exploit their therapeutic or adjuvant potential and to open new perspectives in understanding the basis of immunity. The potential applications for HDPs are discussed.