Tropism of Lentiviral Vectors in Skin Tissue

Hypoxia and Foxn1 alter the proteomic signature of dermal fibroblasts to redirect scarless wound healing to scar-forming skin wound healing in Foxn1-/- mice

BACKGROUND

Foxn1-/- deficient mice are a rare model of regenerative skin wound healing among mammals. In wounded skin, the transcription factor Foxn1 interacting with hypoxia-regulated factors affects re-epithelialization, epithelial-mesenchymal transition (EMT) and dermal white adipose tissue (dWAT) reestablishment and is thus a factor regulating scar-forming/reparative healing. Here, we hypothesized that transcriptional crosstalk between Foxn1 and Hif-1α controls the switch from scarless (regenerative) to scar-present (reparative) skin wound healing. To verify this hypothesis, we examined (i) the effect of hypoxia/normoxia and Foxn1 signalling on the proteomic signature of Foxn1-/- (regenerative) dermal fibroblasts (DFs) and then (ii) explored the effect of Hif-1α or Foxn1/Hif-1α introduced by a lentiviral (LV) delivery vector to injured skin of regenerative Foxn1-/- mice with particular attention to the remodelling phase of healing.

RESULTS

We showed that hypoxic conditions and Foxn1 stimulation modified the proteome of Foxn1-/- DFs. Hypoxic conditions upregulated DF protein profiles, particularly those related to extracellular matrix (ECM) composition: plasminogen activator inhibitor-1 (Pai-1), Sdc4, Plod2, Plod1, Lox, Loxl2, Itga2, Vldlr, Ftl1, Vegfa, Hmox1, Fth1, and F3. We found that Pai-1 was stimulated by hypoxic conditions in regenerative Foxn1-/- DFs but was released by DFs to the culture media exclusively upon hypoxia and Foxn1 stimulation. We also found higher levels of Pai-1 protein in DFs isolated from Foxn1+/+ mice (reparative/scar-forming) than in DFs isolated from Foxn1-/- (regenerative/scarless) mice and triggered by injury increase in Foxn1 and Pai-1 protein in the skin of mice with active Foxn1 (Foxn1+/+ mice). Then, we demonstrated that the introduction of Foxn1 and Hif-1α via lentiviral injection into the wounded skin of regenerative Foxn1-/- mice activates reparative/scar-forming healing by increasing the wounded skin area and decreasing hyaluronic acid deposition and the collagen type III to I ratio. We also identified a stimulatory effect of LV-Foxn1 + LV-Hif-1α injection in the wounded skin of Foxn1-/- mice on Pai-1 protein levels.

CONCLUSIONS

The present data highlight the effect of hypoxia and Foxn1 on the protein profile and functionality of regenerative Foxn1-/- DFs and demonstrate that the introduction of Foxn1 and Hif-1α into the wounded skin of regenerative Foxn1-/- mice activates reparative/scar-forming healing.

How have retrovirus pseudotypes contributed to our understanding of viral entry?

Study of virus entry into host cells is important for understanding viral tropism and pathogenesis. Studying the entry of in vitro cultured viruses is not always practicable. Study of highly pathogenic viruses, viruses that do not grow in culture, and viruses that rapidly change phenotype in vitro can all benefit from alternative models of entry. Retrovirus particles can be engineered to display the envelope proteins of heterologous enveloped viruses. This approach, broadly termed ‘pseudotyping’, is an important technique for interrogating virus entry. In this perspective we consider how retrovirus pseudotypes have addressed these challenges and improved our understanding of the entry pathways of diverse virus species, including Ebolavirus, human immunodeficiency virus and hepatitis C virus.

Innate defense mechanisms against HSV-1 infection in the target tissues, skin and brain

Herpes simplex virus type 1 (HSV-1) initiates productive infection in mucocutaneous tissues to cause cold sores and establishes latent infection in the trigeminal ganglia. Under certain circumstances, HSV-1 may cause encephalitis. Here, we compared host innate defenses against HSV-1 in the two clinically relevant tissues, skin and brain, using a unique ex vivo system of organ culture. Upon HSV-1 infection and spread, apoptosis induction was observed in the skin, but not in brain tissues. While the two tissues elicited interferon (IFN-β) response upon HSV1 infection, IFN induction was more robust in the skin compared to the brain. Moreover, antiviral response to exogenous IFNβ treatment was much stronger in the skin compared to brain tissues. This observation was not related to the availability of the IFN receptor on cells' surface. Taken together, our study demonstrates differential innate antiviral responses to HSV-1 infection that may be exploited in future development of selective and tissue-specific anti-viral treatments.

Different modes of herpes simplex virus type 1 spread in brain and skin tissues

Herpes simplex virus type 1 (HSV-1) initially infects the skin and subsequently spreads to the nervous system. To investigate and compare HSV-1 mode of propagation in the two clinically relevant tissues, we have established ex vivo infection models, using native tissues of mouse and human skin, as well as mouse brain, maintained in organ cultures. HSV-1, which is naturally restricted to the human, infects and spreads in the mouse and human skin tissues in a similar fashion, thus validating the mouse model. The spread of HSV-1 in the skin was concentric to form typical plaques of limited size, predominantly of cytopathic cells. By contrast, HSV-1 spread in the brain tissue was directed along specific neuronal networks with no apparent cytopathic effect. Two additional differences were noted following infection of the skin and brain tissues. First, only a negligible amount of extracellular progeny virus was produced of the infected brain tissues, while substantial quantity of infectious progeny virus was released to the media of the infected skin. Second, antibodies against HSV-1, added following the infection, effectively restricted viral spread in the skin but have no effect on viral spread in the brain tissue. Taken together, these results reveal that HSV-1 spread within the brain tissue mostly by direct transfer from cell to cell, while in the skin the progeny extracellular virus predominates, thus facilitating the infection to new individuals.

Lentiviral vectors for cutaneous RNA managing

Post-transcriptional managing of RNA plays a key role in the intricate network of cellular pathways that regulate our genes. Numerous small RNA species have emerged as crucial regulators of RNA processing and translation. Among these, microRNAs (miRNAs) regulate protein synthesis through specific interactions with target RNAs and are believed to play a role in almost any cellular process and tissue. Skin is no exception, and miRNAs are intensively studied for their role in skin homoeostasis and as potential triggers of disease. For use in skin and many other tissues, therapeutic RNA managing by small RNA technologies is now widely explored. Despite the easy accessibility of skin, the natural barrier properties of skin have challenged genetic intervention studies, and unique tools for studying gene expression and the regulatory role of small RNAs, including miRNAs, in human skin are urgently needed. Human immunodeficiency virus (HIV)-derived lentiviral vectors (LVs) have been established as prominent carriers of foreign genetic cargo. In this review, we describe the use of HIV-derived LVs for efficient gene transfer to skin and establishment of long-term transgene expression in xenotransplanted skin. We outline the status of engineered LVs for delivery of small RNAs and their in vivo applicability for expression of genes and small RNA effectors including small hairpin RNAs, miRNAs and miRNA inhibitors. Current findings suggest that LVs may become key tools in experimental dermatology with particular significance for cutaneous RNA managing and in vivo genetic intervention.

Biopump: Autologous skin-derived micro-organ genetically engineered to provide sustained continuous secretion of therapeutic proteins

A novel approach for sustained production of therapeutic proteins is described, using genetic modification of intact autologous micro-organ tissue explants from the subject's own skin. The skin-derived micro-organ can be maintained viable ex vivo for extended periods and is transduced with a transgene encoding a desired therapeutic protein, resulting in protein-secreting micro-organ (biopump (BP)). The daily protein production from each BP is quantified, enabling drug dosing by subcutaneous implantation of the requisite number of BPs into the patient to provide continuous production to the circulation of a known amount of the therapeutic protein. Each implanted BP remains localized and is accessible, to enable removal or ablation if needed. Examples from preclinical and clinical studies are presented, including use of associated virus vector 1 and helper-dependent adenoviral vectors producing BPs to provide long-term sustained secretion of recombinant interferon-α and erythropoietin.

Extracellular matrix constituents interfere with Newcastle disease virus spread in solid tissue and diminish its potential oncolytic activity

Advanced melanoma cells, characterized by resistance to chemotherapy, have been shown to be highly sensitive to oncolysis by Newcastle disease virus (NDV). In the present study, we investigated the capacity of NDV to specifically infect and spread into solid tissues of human melanoma and lung carcinoma, in vivo and ex vivo. For this purpose a new model of SCID-beige mice implanted with human melanoma was developed. Surprisingly, the replication competent NDV-MTH and the attenuated, single-cycle replication NDV-HUJ strains, demonstrated a similar oncolytic activity in the melanoma-implanted mice. Further, ex vivo analysis, using organ cultures derived from the melanoma tissues indicated a limited spread of the two NDV strains in the tissue. Extracellular matrix (ECM) molecules, notably heparin sulfate and collagen, were found to limit viral spread in the tissue. This observation was validated with yet another solid tumour of human lung carcinoma. Taken together, the results indicate that the ECM acts as a barrier to virus spread within solid tumour tissues and that this restriction must be overcome to achieve effective oncolysis with NDV.

Modeling of human cytomegalovirus maternal-fetal transmission in a novel decidual organ culture

Human cytomegalovirus (HCMV) is the leading cause of congenital infection, associated with severe birth defects and intrauterine growth retardation. The mechanism of HCMV transmission via the maternal-fetal interface is largely unknown, and there are no animal models for HCMV. The initial stages of infection are believed to occur in the maternal decidua. Here we employed a novel decidual organ culture, using both clinically derived and laboratory-derived viral strains, for the ex vivo modeling of HCMV transmission in the maternal-fetal interface. Viral spread in the tissue was demonstrated by the progression of infected-cell foci, with a 1.3- to 2-log increase in HCMV DNA and RNA levels between days 2 and 9 postinfection, the expression of immediate-early and late proteins, the appearance of typical histopathological features of natural infection, and dose-dependent inhibition of infection by ganciclovir and acyclovir. HCMV infected a wide range of cells in the decidua, including invasive cytotrophoblasts, macrophages, and endothelial, decidual, and dendritic cells. Cell-to-cell viral spread was revealed by focal extension of infected-cell clusters, inability to recover infectious extracellular virus, and high relative proportions (88 to 93%) of cell-associated viral DNA. Intriguingly, neutralizing HCMV hyperimmune globulins exhibited inhibitory activity against viral spread in the decidua even when added at 24 h postinfection-providing a mechanistic basis for their clinical use in prenatal prevention. The ex vivo-infected decidual cultures offer unique insight into patterns of viral tropism and spread, defining initial stages of congenital HCMV transmission, and can facilitate evaluation of the effects of new antiviral interventions within the maternal-fetal interface milieu.

Integrated strategy for the production of therapeutic retroviral vectors

The broad application of retroviral vectors for gene delivery is still hampered by the difficulty to reproducibly establish high vector producer cell lines generating sufficient amounts of highly concentrated virus vector preparations of high quality. To enhance the process for producing clinically relevant retroviral vector preparations for therapeutic applications, we have integrated novel and state-of-the-art technologies in a process that allows rapid access to high-efficiency vector-producing cells and consistent production, purification, and storage of retroviral vectors. The process has been designed for various types of retroviral vectors for clinical application and to support a high-throughput process. New modular helper cell lines that permit rapid insertion of DNA encoding the therapeutic vector of interest at predetermined, optimal chromosomal loci were developed to facilitate stable and high vector production levels. Packaging cell lines, cultivation methods, and improved medium composition were coupled with vector purification and storage process strategies that yield maximal vector infectivity and stability. To facilitate GMP-grade vector production, standard of operation protocols were established. These processes were validated by production of retroviral vector lots that drive the expression of type VII collagen (Col7) for the treatment of a skin genetic disease, dystrophic epidermolysis bullosa. The potential efficacy of the Col7-expressing vectors was finally proven with newly developed systems, in particular in target primary keratinocyte cultures and three-dimensional skin tissues in organ culture.

The oncolytic activity of Newcastle disease virus NDV-HUJ on chemoresistant primary melanoma cells is dependent on the proapoptotic activity of the inhibitor of apoptosis protein Livin

Patients with advanced melanoma usually do not benefit from conventional chemotherapy treatment. There is therefore a true need for a new kind of therapy for melanoma. One factor responsible for the poor prognosis of melanoma is the inhibitor of apoptosis protein (IAP) family member Livin. In this study, we applied a novel approach for the treatment of melanoma, using a unique strain of the oncolytic Newcastle disease virus (NDV-HUJ). We found that, unlike chemotherapeutic drugs, NDV-HUJ, a one-cycle replicating virus, overcomes the resistance to apoptosis of melanoma primary cultures that over express the Livin protein. In contrast, melanoma tumor cells that do not express Livin are relatively resistant to NDV-HUJ treatment. Furthermore, we show that NDV-HUJ-induced oncolysis is attributed to the dual function of Livin: although Livin inhibits apoptosis through the inhibition of caspases, under the robust apoptotic stimulation of NDV-HUJ, caspases can cleave Livin to create a truncated protein with a paradoxical proapoptotic activity. Thus, NDV-HUJ is a potent inducer of apoptosis that can overcome the antiapoptotic effect of Livin and allow cleavage of Livin into the proapoptotic tLivin protein. Moreover, the results indicate that the interferon system, which is functional in melanoma, is not involved in NDV-induced oncolysis. Taken together, our data offer the possibility of a new viral oncolytic treatment for chemoresistant melanoma.