Three-dimensional culture models for human viral diseases and antiviral drug development

A scientific career from the early 1960s till 2023: A tale of the various protagonists

In this era spanning more than 60 years (from the early 1960s till today (2023), a broad variety of actors played a decisive role: Piet De Somer, Tom C. Merigan, Paul A. Janssen, Maurice Hilleman, and Georges Smets. Two protagonists (Antonín Holý and John C. Martin) formed with me a unique triangle (the Holý Trinity). Walter Fiers' group (with the help of Jean Content) contributed to the cloning of human β-interferon, and Piet Herdewijn accomplished the chemical synthesis of an array of anti-HIV 2',3'-dideoxynucleoside analogues. Rudi Pauwels, Masanori Baba, Dominique Schols, Johan Neyts, Lieve Naesens, Anita Van Lierde, Graciela Andrei, Robert Snoeck and Dirk Daelemans, as members of my team, helped me in achieving the intended goal, the development of a selective therapy for virus infections. The collaboration with "Lowie" (Guangdi Li) generated a new dimension for the future.

Transcriptome reprogramming of Epstein-Barr virus infected epithelial and B cells reveals distinct host-virus interaction profiles

Epstein-Barr virus (EBV) is an opportunistic pathogen that can manifest itself as a potential contributor to human diseases years after primary infection, specifically in lymphoid and epithelial cell malignancies in immune-competent and immune-compromised hosts. The virus shuttles between B cells and epithelial cells during its infection cycle, facilitating its persistence and transmission in humans. While EBV efficiently infects and transforms B-lymphocytes, epithelial cells are not as susceptible to transformation in vitro. We utilized a 3D platform for culturing normal oral keratinocyte cells (NOKs) using Matrigel for greater insights into the molecular interactions between EBV and infected cells. We determined the transcriptome of EBV infected NOKs and peripheral blood mononuclear cells (PBMCs) for 7 and 15 days. LMPs (-1, -2A, and -2B) and EBNAs (-1, -2, -3A, -3B and -3C) were detected in all samples, and lytic gene expression was significantly higher in NOKs than PBMCs. We identified over 2000 cellular genes that were differentially expressed (P-value<0.05). Gene ontology (GO) and pathway analyses significantly identified pathways related to collagen-activation, chemokine signaling, immune response, metabolism, and antiviral responses. We also identified significant changes in metalloproteases and genes encoding chemotactic ligands and cell surface molecules. C-X-C chemokine receptor type 4 (CXCR4) was dramatically downregulated in PBMCs and upregulated in NOKs. However, MMP1 was significantly downregulated in NOKs and upregulated in PBMCs. Therefore, multiple pathways contribute to distinct pathologies associated with EBV infection in epithelial and B cells, and MMP1 and CXCR4 are critical molecules involved in regulation of latent and lytic states linked to viral associated diseases.

3D Cell Culture Models in COVID-19 Times: A Review of 3D Technologies to Understand and Accelerate Therapeutic Drug Discovery

In the last decades, emerging viruses have become a worldwide concern. The fast and extensive spread of the disease caused by SARS-CoV-2 (COVID-19) has impacted the economy and human activity worldwide, highlighting the human vulnerability to infectious diseases and the need to develop and optimize technologies to tackle them. The three-dimensional (3D) cell culture models emulate major tissue characteristics such as the in vivo virus-host interactions. These systems may help to generate a quick response to confront new viruses, establish a reliable evaluation of the pathophysiology, and contribute to therapeutic drug evaluation in pandemic situations such as the one that humanity is living through today. This review describes different types of 3D cell culture models, such as spheroids, scaffolds, organoids, and organs-on-a-chip, that are used in virus research, including those used to understand the new severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2).

Immunocytochemistry Analysis of HepG2 Cell 3D Culture Encapsulated as Spheroids in Alginate Beads

3D Cell culture is an alternative to animal use in many drug development and toxicity studies. The 3D cell culture can mimic and reproduce the original tissue microenvironment, morphology, and mechanical and physiological characteristics, to provide a more realistic and reliable response as compared to two-dimensional cultures. 3D cell culture encapsulated in alginate beads is a very simple and relatively inexpensive tool that is easy to handle and to maintain. The alginate beads function as a scaffold that imprisons cells and allows 3D cell growth, to generate spheroids that can have greater genic expression and cell-cell communication as a nano or microtissue. The HepG2 cell line is a human hepatocellular carcinoma cell derivative. HepG2 cells preserve several of the characteristics of hepatocytes and are therefore often used in toxicity studies. Here, we describe HepG2 cell encapsulation in alginate beads and analyze the resulting spheroids formed within the alginate beads by immunocytochemistry, by staining a certain structure with a specific antibody coupled with a fluorophore. This method preserves the beads and enables cell analysis by confocal microscopy.

Targeting IL-11 in the treatment of BK virus-associated haemorrhagic cystitis-A promising new approach

The BK polyomavirus (BKPyV) has pathogenic relevance especially in immunocompromised patients. No causal therapy has been established yet. Therefore, new therapeutic targets need to be identified in experimental studies. A 3D organotypic cell culture model with primary urothelial cells and fibroblasts was used as infection model. The detection of virus replication was performed with quantitative polymerase chain reaction (qPCR), and immunohistochemistry (IHC) was also used for analysis. Interleukin levels were measured by enzyme‐linked immunosorbent assay (ELISA). Interestingly, the signal transducer and activator of transcription 3 (STAT3) pathway seems to be activated during infection with BKPyV, for example phosphorylated STAT3 is significantly (P < 0.0001) elevated on day 6 following infection. Therefore, we performed ELISAs for involved interleukins in STAT3 pathway. Interleukin 11 (IL‐11) was significantly (P = 0.026) elevated at day 9. Subsequently, 3D cultures were treated with IL‐11 neutralizing antibody. At day 9 following infection, the median virus replication rate is 4.4 × 10⁶ copies/ml. The difference to replication rate without treatment was significantly lower at day 6 (P < 0.0001) and at day 9 (P < 0.0001), respectively. STAT3 pathways seem to be involved during BKPyV infection and need further investigation in experimental studies. A very promising target for treatment might be IL‐11.

Novel 3D organotypic urothelial cell culture model for identification of new therapeutic approaches in urological infections

PURPOSE

3D organotypic cell cultures offer the possibility to study cell growth in a more in vivo like situation. To our knowledge no 3D culture of primary urothelial cells has been established yet. BK Polyomavirus (BKPyV), replicating in urothelial cells, may cause haemorrhagic cystitis in immunocompromised patients.

PRIMARY ENDPOINTS OF THIS STUDY

Establishment of a 3D organotypic cell culture of primary urothelial cells and fibroblasts; use of this model as infection model for archetype BKPyV; description of first parts of viral life cycle with identification of therapeutic targets.

METHODS

This is an experimental study. Primary urothelial cells were purchased from CellnTec, Bern, Switzerland; fibroblasts were isolated from the ureter of patients with no urothelial malignancy in their medical history. As main methods we used quantitative real-time PCR and immunohistochemistry. Outcomes were analysed using SPSS 23.0.

RESULTS

We were able to develop a 3D organotypic culture for primary urothelium. An infection with archetype BKPyV was established in this model with virus replication rates up to 6.41 × 108 copies/ml on day 9 following Infection. Interestingly, proliferation rate of the urothelial cells is significantly (p = 0.049 at day 6 following infection) elevated while cells are losing differentiation under infection. Phosphorylated STAT3 is also significantly elevated (p < 0.0001) during infection.

CONCLUSIONS

The established of urothelial 3D cultures is a new method to study several urothelial diseases. The archetype BKPyV infection model is novel and the first method to study archetype viral life cycle. The STAT3 pathway might be an interesting target for the development of a causal therapy.

Antineoplastic effect of 1α,25(OH)2D3 in spheroids from endothelial cells transformed by Kaposi's sarcoma-associated herpesvirus G protein coupled receptor

The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor (KSHV/vGPCR) is a key molecule in the pathogenesis of Kaposi's sarcoma. In endothelial cells, tumor maintenance and NF-κB activation depends on vGPCR constitutive expression and activity. We have previously demonstrated that 1α,25(OH)₂D₃ induces apoptosis in a VDR dependent manner, inhibits vGPCR cell growth and NF-κB activity. In this study, we developed a method to obtain multicellular spheroids (MCS) from endothelial cells expressing vGPCR in order to test whether MCS have a similar response to 2D-cultures after 1α,25(OH)₂D₃ treatment. Firstly, we found that vGPCR MCS started to form at 2^nd day-growth, reaching a diameter up to 300 μm at 7^th day-growth, whereas cells without vGPCR expression (SVEC) developed spheroids earlier and remained smaller throughout the period monitored. Secondly, vGPCR MCS size and architecture were analyzed during 1α,25(OH)₂D₃ (0.1-100 nM, 48 h) treatment. We found that once treated with 10 nM of 1α,25(OH)₂D₃ the initials MCS began a slight disaggregation with no changes in size; whereas at the higher dose (100 nM) the architecture of MCS was found completely broken. Furthermore, VDR mRNA expression increased significantly and this change was accompanied by a reduction of HIF-1α, an increase of VEGF, p21 and Bim mRNA expression. Finally, results from Western blot analysis showed that 1α,25(OH)₂D₃ decreased Akt and ERK1/2 protein phosphorylation. In conclusion, these data have revealed that 1α,25(OH)₂D₃ inhibits vGPCR MCS proliferation and induces apoptosis similar to vGPCR cells growing in 2D-cultures.

High density Huh7.5 cell hollow fiber bioreactor culture for high-yield production of hepatitis C virus and studies of antivirals

Chronic hepatitis C virus (HCV) infection poses a serious global public health burden. Despite the recent development of effective treatments there is a large unmet need for a prophylactic vaccine. Further, antiviral resistance might compromise treatment efficiency in the future. HCV cell culture systems are typically based on Huh7 and derived hepatoma cell lines cultured in monolayers. However, efficient high cell density culture systems for high-yield HCV production and studies of antivirals are lacking. We established a system based on Huh7.5 cells cultured in a hollow fiber bioreactor in the presence or absence of bovine serum. Using an adapted chimeric genotype 5a virus, we achieved peak HCV infectivity and RNA titers of 7.6 log₁₀ FFU/mL and 10.4 log₁₀ IU/mL, respectively. Bioreactor derived HCV showed high genetic stability, as well as buoyant density, sensitivity to neutralizing antibodies AR3A and AR4A, and dependency on HCV co-receptors CD81 and SR-BI comparable to that of HCV produced in monolayer cell cultures. Using the bioreactor platform, treatment with the NS5A inhibitor daclatasvir resulted in HCV escape mediated by the NS5A resistance substitution Y93H. In conclusion, we established an efficient high cell density HCV culture system with implications for studies of antivirals and vaccine development.

In vitro models for deciphering the mechanisms underlying the sexual transmission of viruses at the mucosal level

Sexually transmitted viruses infect the genital and colorectal mucosa of the partner exposed to contaminated genital secretions through a wide range of mechanisms, dictated in part by the organization of the mucosa. Because understanding the modes of entry into the organism of viruses transmitted through sexual intercourse is a necessary prerequisite to the design of treatments to block those infections, in vitro modeling of the transmission is essential. The aim of this review is to present the models and methodologies available for the in vitro study of the interactions between viruses and mucosal tissue and for the preclinical evaluation of antiviral compounds, and to point out their advantages and limitations according to the question being studied.

Three-dimensional cell culture models for investigating human viruses

Three-dimensional (3D) culture models are physiologically relevant, as they provide reproducible results, experimental flexibility and can be adapted for high-throughput experiments. Moreover, these models bridge the gap between traditional two-dimensional (2D) monolayer cultures and animal models. 3D culture systems have significantly advanced basic cell science and tissue engineering, especially in the fields of cell biology and physiology, stem cell research, regenerative medicine, cancer research, drug discovery, and gene and protein expression studies. In addition, 3D models can provide unique insight into bacteriology, virology, parasitology and host-pathogen interactions. This review summarizes and analyzes recent progress in human virological research with 3D cell culture models. We discuss viral growth, replication, proliferation, infection, virus-host interactions and antiviral drugs in 3D culture models.

3D rotating wall vessel and 2D cell culture of four veterinary virus pathogens: A comparison of virus yields, portions of infectious particles and virus growth curves

Only very few comparative studies have been performed that evaluate general trends of virus growth under 3D in comparison with 2D cell culture conditions. The aim of this study was to investigate differences when four animal viruses are cultured in 2D and 3D. Suid herpesvirus 1 (SuHV-1), Vesicular stomatitis virus (VSIV), Bovine adenovirus (BAdV) and Bovine parainfluenza 3 virus (BPIV-3) were cultivated in 3D rotating wall vessels (RWVs) and conventional 2D cultures. The production of virus particles, the portion of infectious particles, and the infectious growth curves were compared. For all viruses, the production of virus particles (related to cell density), including the non-infectious ones, was lower in 3D than in 2D culture. The production of only infectious particles was significantly lower in BAdV and BPIV-3 in 3D cultures in relation to cell density. The two cultivation approaches resulted in significantly different virus particle-to-TCID50 ratios in three of the four viruses: lower in SuHV-1 and BPIV-3 and higher in BAdV in 3D culture. The infectious virus growth rates were not significantly different in all viruses. Although 3D RWV culture resulted in lower production of virus particles compared to 2D systems, the portion of infectious particles was higher for some viruses.

Mechanistic adaptability of cancer cells strongly affects anti-migratory drug efficacy

Cancer metastasis involves the dissemination of cancer cells from the primary tumour site and is responsible for the majority of solid tumour-related mortality. Screening of anti-metastasis drugs often includes functional assays that examine cancer cell invasion inside a three-dimensional hydrogel that mimics the extracellular matrix (ECM). Here, we built a mechanically tuneable collagen hydrogel model to recapitulate cancer spreading into heterogeneous tumour stroma and monitored the three-dimensional invasion of highly malignant breast cancer cells, MDA-MB-231. Migration assays were carried out in the presence and the absence of drugs affecting four typical molecular mechanisms involved in cell migration, as well as under five ECMs with different biophysical properties. Strikingly, the effects of the drugs were observed to vary strongly with matrix mechanics and microarchitecture, despite the little dependence of the inherent cancer cell migration on the ECM condition. Specifically, cytoskeletal contractility-targeting drugs reduced migration speed in sparse gels, whereas migration in dense gels was retarded effectively by inhibiting proteolysis. The results corroborate the ability of cancer cells to switch their multiple invasion mechanisms depending on ECM condition, thus suggesting the importance of factoring in the biophysical properties of the ECM in anti-metastasis drug screenings.

Adding new dimensions: towards an integrative understanding of HIV-1 spread

In vitro studies in primary or immortalized cells continue to be used to elucidate the essential principles that govern the interactions between HIV-1 and isolated target cells. However, until recently, substantial technical barriers prevented this information from being efficiently translated to the more complex scenario of HIV-1 spread in the host in vivo, which has limited our understanding of the impact of host physiological parameters on the spread of HIV-1. In this Review, we discuss the recent development of imaging approaches to visualize HIV-1 spread and the adaptation of these approaches to organotypic ex vivo models and animal models. We focus on new concepts, including the mechanisms and in vivo relevance of cell-cell transmission for HIV-1 spread and the function of the HIV-1 pathogenesis factor Nef, which have emerged from the application of these integrative approaches in complex cell systems.

Multicellular self-assembled spheroidal model of the blood brain barrier

The blood brain barrier (BBB) has evolved unique characteristics such as dense coverage of the endothelial cells by pericytes and interactions with astrocytes through perivascular endfeet. We study BBB formation in a 3-dimensional multicellular spheroid system of human primary brain endothelial cells (hpBECs), primary pericytes (hpPs) and primary astrocytes (hpAs). We show for the first time that hpBECs, hpPs and hpAs spontaneously self-organize into a defined multicellular structure which recapitulates the complex arrangement of the individual cell types in the BBB structure. Pericytes play a crucial role mediating the interaction between hpBECs and hpAs. This process is not dependent on a scaffold support demonstrating that formation and cellular architecture of the BBB is intrinsically programmed within each specific cell type. In a matrigel setup the hpBECs, hpPs and hpAs also undergo self-arrangement to form endothelial tube-like structures tightly covered by hpPs and loosely attached hpAs mainly at the junctions.

Three-dimensional normal human neural progenitor tissue-like assemblies: a model of persistent varicella-zoster virus infection

Varicella-zoster virus (VZV) is a neurotropic human alphaherpesvirus that causes varicella upon primary infection, establishes latency in multiple ganglionic neurons, and can reactivate to cause zoster. Live attenuated VZV vaccines are available; however, they can also establish latent infections and reactivate. Studies of VZV latency have been limited to the analyses of human ganglia removed at autopsy, as the virus is strictly a human pathogen. Recently, terminally differentiated human neurons have received much attention as a means to study the interaction between VZV and human neurons; however, the short life-span of these cells in culture has limited their application. Herein, we describe the construction of a model of normal human neural progenitor cells (NHNP) in tissue-like assemblies (TLAs), which can be successfully maintained for at least 180 days in three-dimensional (3D) culture, and exhibit an expression profile similar to that of human trigeminal ganglia. Infection of NHNP TLAs with cell-free VZV resulted in a persistent infection that was maintained for three months, during which the virus genome remained stable. Immediate-early, early and late VZV genes were transcribed, and low-levels of infectious VZV were recurrently detected in the culture supernatant. Our data suggest that NHNP TLAs are an effective system to investigate long-term interactions of VZV with complex assemblies of human neuronal cells.

Varicella-zoster virus (VZV), the alphaherpesvirus that typically causes childhood chickenpox and shingles in adults, becomes latent in neurons, thus remaining in the body for a lifetime. Unfortunately, few models are available to study the establishment of VZV latency since the virus infects only humans and establishes persistent infections and latency only in neurons, a slowly proliferating, short-lived cell in culture. We have successfully maintained normal human neural progenitor cells (NHNP) in tissue-like assemblies (TLAs) in 3-dimensional (3D) cultures for up to 6 months. The 3D NHNP TLAs show some characteristics as those found in the human trigeminal ganglia, the site of VZV latency. NHNP TLAs infected with VZV remain viable for 3 months during which time VZV DNA replicates and remains genetically stable, virus genes are transcribed, and infectious VZV is sporadically released. The ability to maintain VZV infected NHNP cells in culture for extended times provides the unique opportunity to study the molecular interactions between this important human pathogen and neuronal tissue to an extent previously unattainable.

Rapid and automated multidimensional fluorescence microscopy profiling of 3D human breast cultures

Three-dimensional (3D) tissue culture provides a physiologically relevant microenvironment for distinguishing malignant from non-malignant breast cell phenotypes. 3D culture assays can also be used to test novel cancer therapies and predict a differential response to radiation between normal and malignant cells in vivo. However, biological measurements in such complex models are difficult to quantify and current approaches do not allow for in-depth multifaceted assessment of individual colonies or unique sub-populations within the entire culture. This is in part due to the limitations of imaging at a range of depths in 3D culture resulting from optical aberrations and intensity attenuation. Here, we address these limitations by combining sample smearing techniques with high-throughput 2D imaging algorithms to accurately and rapidly quantify imaging features acquired from 3D cultures. Multiple high resolution imaging features especially designed to characterize 3D cultures show that non-malignant human breast cells surviving large doses of ionizing radiation acquire a "swelled acinar" phenotype with fewer and larger nuclei, loss of cell connectivity and diffused basement membrane. When integrating these imaging features into hierarchical clustering classification, we could also identify subpopulations of phenotypes from individual human tumor colonies treated with ionizing radiation or/and integrin inhibitors. Such tools have therefore the potential to further characterize cell culture populations after cancer treatment and identify novel phenotypes of resistance.

Long-term viability of transplanted hybrid cellular spheroids within chondrocyte sheets

Encapsulation of transplanted cells within an immunoisolating membrane may provide a new strategy for protecting these cells from recipient immune responses without the use of immunosuppressive drugs. We have previously reported a novel concept of immunoisolation and immunodelusion using recipient cells instead of traditional artificial materials. We developed a chondrocyte sheeting immunodelusive immunoisolated bioartificial pancreas (CSI-BAP) that would enable transplantation of cells across allogeneic and xenogeneic barriers without the cells being recognized as donor cells and without the need for immunosuppression. Recently, we have constructed hybrid cellular spheroids (HCSs) containing cells from two different cell lines (RIN-5F, an insulin-secreting cell line, and Hep-G2, a hepatocellular carcinoma cell line) to enhance the function and biocompatibility of the HCSs. These HCSs were then encapsulated with multiple layers of chondrocyte sheets obtained from the auricular cartilage of Sprague-Dawley (SD) rats. The in vitro ability of the CSI-BAP to secrete insulin was tested before transplantation. Histological evaluation of CSI-BAP chondrocyte microencapsulated immunoisolated islet morphology and viability of allogeneic or xenogeneic cell lines was performed 100 days after the CSI-BAP was transplanted into SD rats. Morphological evaluations revealed good viability of the islets and progression of islet encapsulation. In vitro insulin secretion from the CSI-BAP was well maintained. Additionally, insulin and albumin secretion from the CSI-BAP was confirmed by in vivo immunohistochemical examination. Moreover, the cell lines transplanted into the subcutaneous space in the form of HCSs within the chondrocyte sheets showed good viability of more than 100 days and sustained insulin and albumin secreting ability.

Establishment and characterization of a differentiated epithelial cell culture model derived from the porcine cervix uteri

Background

Cervical uterine epithelial cells maintain a physiological and pathogen-free milieu in the female mammalian reproductive tract and are involved in sperm-epithelium interaction. Easily accessible, differentiated model systems of the cervical epithelium are not yet available to elucidate the underlying molecular mechanisms within these highly specialized cells. Therefore, the aim of the study was to establish a cell culture of the porcine cervical epithelium representing in vivo-like properties of the tissue.

Results

We tested different isolation methods and culture conditions and validated purity of the cultured cells by immunohistochemistry against keratins. We could reproducibly culture pure epithelial cells from cervical tissue explants. Based on a morphology score and the WST-1 Proliferation Assay, we optimized the growth medium composition. Primary porcine cervical cells performed best in conditioned Ham's F-12, containing 10% FCS, EGF and insulin. After cultivation in an air-liquid interface for three weeks, the cells showed a discontinuously multilayered phenotype. Finally, differentiation was validated via immunohistochemistry against beta catenin. Mucopolysaccharide production could be shown via alcian blue staining.

Conclusions

We provide the first suitable protocol to establish a differentiated porcine epithelial model of the cervix uteri, based on easily accessible cells using slaughterhouse material.

Herpes simplex virus-induced epithelial damage and susceptibility to human immunodeficiency virus type 1 infection in human cervical organ culture

Normal human premenopausal cervical tissue has been used to derive primary cell populations and to establish ex vivo organ culture systems to study infections with herpes simplex virus (HSV-1 or HSV-2) and human immunodeficiency virus type 1 (HIV-1). Infection with either HSV-1 or HSV-2 rapidly induced multinuclear giant cell formation and widespread damage in mucosal epithelial cells. Subsequent exposure of the damaged mucosal surfaces to HIV-1 revealed frequent co-localization of HSV and HIV-1 antigens. The short-term organ culture system provides direct experimental support for the epidemiological findings that pre-existing sexually transmitted infections, including primary and recurrent herpes virus infections at mucosal surfaces, represent major risk factors for acquisition of primary HIV-1 infection. Epithelial damage in combination with pre-existing inflammation, as described here for overtly normal human premenopausal cervix, creates a highly susceptible environment for the initiation and establishment of primary HIV-1 infection in the sub-mucosa of the cervical transformation zone.

Coming of age: reconstruction of heterosexual HIV-1 transmission in human ex vivo organ culture systems

Heterosexual transmission of human immunodeficiency virus-1 (HIV-1), from men to women, involves exposure to infectious HIV-1 in semen. Therefore, the cellular and molecular processes that underlie HIV-1 transmission are closely interconnected with fundamental principles of human reproductive biology. Human ex vivo organ culture systems allow experimental reconstruction of HIV-1 transmission, using human semen and premenopausal cervicovaginal mucosal tissue, with specific emphasis on the progression from exposure to development of primary HIV-1 infection. Clearly, an isolated piece of human tissue cannot duplicate the full complexity of events in natural infections, but with correct observation of conventional medical and ethical standards, there is no opportunity to study HIV-1 exposure and primary infection in young women. Human mucosal organ cultures allow direct study of HIV-1 infection in a reproducible format while retaining major elements of complexity and variability that typify community-based HIV-1 transmission. Experimental manipulation of human mucosal tissue both allows and requires acquisition of new insights into basic processes of human mucosal immunology. Expanding from the current foundations, we believe that human organ cultures will become increasingly prominent in experimental studies of HIV-1 transmission and continuing efforts to prevent HIV-1 infection at human mucosal surfaces.

Virus inactivation by salt (NaCl) and phosphate supplemented salt in a 3D collagen matrix model for natural sausage casings

Due to possible presence and spread of contagious animal viruses via natural sausage casings the international trade in these food products is subject to veterinary and public health requirements. In order to manage these restrictions we determined the effect of casing preservation on four highly contagious viruses for livestock: foot-and-mouth-disease virus (FMDV), classical swine fever virus (CSFV), swine vesicular disease virus (SVDV) and African swine fever virus (ASFV). We used an in vitro 3D collagen matrix model in which cells, infected with the four different viruses were embedded in a bovine collagen type I gel matrix and treated with either saturated salt (NaCl) or phosphate supplemented saturated salt at four different temperatures (4, 12, 20 and 25 °C) during a period of 30 days. The results showed that all viruses were faster inactivated at higher temperatures, but that stability of the various viruses at 4 °C differed. Inactivation of FMDV in the 3D collagen matrix model showed a clear temperature and treatment effect on the reduction of FMDV titres. At 4 and 12 °C phosphate supplemented salt showed a very strong FMDV inactivation during the first hour of incubation. Salt (NaCl) only had a minor effect on FMDV inactivation. Phosphate supplemented salt treatment increased the effect temperature had on inactivation of CSFV. In contrast, the salt (NaCl) treatment only increased CSFV inactivation at the higher temperatures (20 °C and 25 °C). Also SVDV inactivation was increased by phosphate supplemented salt, but salt (NaCl) treatment only resulted in a significant decrease of SVDV titre at a few time points. The ASFV results showed that both salt (NaCl) and phosphate supplemented salt were capable to inactivate ASFV within 48 h. In contrast to the other viruses (FMDV, CSFV and SVDV), ASFV was the most stable virus even at higher temperatures. The results obtained in this in vitro model underline the efficacy of a combined treatment using phosphate supplemented salt and storage at 20 °C or higher for a period of 30 days. This treatment may therefore be useful in reducing the animal health risks posed by spread of contagious animal viruses by international trade of natural sausage casings.

Epithelial raft cultures for investigations of virus growth, pathogenesis and efficacy of antiviral agents

The organotypic epithelial raft cultures, originally developed to study keratinocytes differentiation, represent a novel approach to the study of viruses able to infect epithelial cells. Organotypic epithelial raft cultures accurately reproduce the process of epithelial differentiation in vitro and can be prepared from normal keratinocytes, explanted epithelial tissue, or established cell lines. This culture system permits cells to proliferate and fully differentiate at the air-liquid interface on a dermal-equivalent support. Normal primary human keratinocytes (PHKs) stratify and fully differentiate in a manner similar to the normal squamous epithelial tissues, while transformed cell lines exhibit dysplastic morphologies similar to the (pre)neoplastic lesions seen in vivo. This three-dimensional (3D) culture system provides an essential tool for investigations of virus growth, virus-host cell interactions, for the genetic analysis of viral proteins and regulatory sequences, and for the evaluation of antiviral agents. The 3D epithelial cultures have proven a breakthrough in the research on papillomaviruses, since their life cycle is strictly linked to the differentiation of the host epithelium. In the last years, several reports have shown the usefulness of the 3D epithelial cultures for the study of other viruses that target at least during a part of their life cycles epithelial cells. The 3D epithelial cultures allow the analysis of virus-host cell interactions in stratified epithelia that more closely resemble the in vivo situation. In this review we describe the advances on research on 3D epithelial cultures for the study of virus growth and pathogenesis of different families of viruses, including papilloma-, herpes-, pox-, adeno-, and parvoviruses.

Strain-dependent viral dynamics and virus-cell interactions in a novel in vitro system supporting the life cycle of blood-borne hepatitis C virus

We developed an in vitro system that can be used for the study of the life cycle of a wide variety of blood-borne hepatitis C viruses (HCV) from various patients using a three-dimensional hollow fiber culture system and an immortalized primary human hepatocyte (HuS-E/2) cell line. Unlike the conventional two-dimensional culture, this system not only enhanced the infectivity of blood-borne HCV but also supported its long-term proliferation and the production of infectious virus particles. Both sucrose gradient fractionation and electron microscopy examination showed that the produced virus-like particles are within a similar fraction and size range to those previously reported. Infection with different HCV strains showed strain-dependent different patterns of HCV proliferation and particle production. Fluctuation of virus proliferation and particle production was found during prolonged culture and was found to be associated with change in the major replicating virus strain. Induction of cellular apoptosis was only found when strains of HCV-2a genotype were used for infection. Interferon-alpha stimulation also varied among different strains of HCV-1b genotypes tested in this study.

CONCLUSION

These results suggest that this in vitro infection system can reproduce strain-dependent events reflecting viral dynamics and virus-cell interactions at the early phase of blood-borne HCV infection, and that this system can allow the development of new anti-HCV strategies specific to various HCV strains.

3D cultured immortalized human hepatocytes useful to develop drugs for blood-borne HCV

Due to the high polymorphism of natural hepatitis C virus (HCV) variants, existing recombinant HCV replication models have failed to be effective in developing effective anti-HCV agents. In the current study, we describe an in vitro system that supports the infection and replication of natural HCV from patient blood using an immortalized primary human hepatocyte cell line cultured in a three-dimensional (3D) culture system. Comparison of the gene expression profile of cells cultured in the 3D system to those cultured in the existing 2D system demonstrated an up-regulation of several genes activated by peroxisome proliferator-activated receptor alpha (PPARalpha) signaling. Furthermore, using PPARalpha agonists and antagonists, we also analyzed the effect of PPARalpha signaling on the modulation of HCV replication using this system. The 3D in vitro system described in this study provides significant insight into the search for novel anti-HCV strategies that are specific to various strains of HCV.

Modelling tissues in 3D: the next future of pharmaco-toxicology and food research?

The development and validation of reliable in vitro methods alternative to conventional in vivo studies in experimental animals is a well-recognised priority in the fields of pharmaco-toxicology and food research. Conventional studies based on two-dimensional (2-D) cell monolayers have demonstrated their significant limitations: the chemically and spatially defined three-dimensional (3-D) network of extracellular matrix components, cell-to-cell and cell-to-matrix interactions that governs differentiation, proliferation and function of cells in vivo is, in fact, lost under the simplified 2-D condition. Being able to reproduce specific tissue-like structures and to mimic functions and responses of real tissues in a way that is more physiologically relevant than what can be achieved through traditional 2-D cell monolayers, 3-D cell culture represents a potential bridge to cover the gap between animal models and human studies. This article addresses the significance and the potential of 3-D in vitro systems to improve the predictive value of cell-based assays for safety and risk assessment studies and for new drugs development and testing. The crucial role of tissue engineering and of the new microscale technologies for improving and optimising these models, as well as the necessity of developing new protocols and analytical methods for their full exploitation, will be also discussed.

C. albicans colonization of human mucosal surfaces

BACKGROUND

Candida albicans is a low level commensal organism in normal human populations with the continuous potential to expand and cause a spectrum of clinical conditions.

METHODOLOGY/PRINCIPAL FINDINGS

Using ex vivo human organ cultures and populations of primary human cells, we have developed several related experimental systems to examine early-stage interactions between C. albicans and mucosal surfaces. Experiments have been conducted both with exogenously added C. albicans and with overtly normal human mucosal surfaces supporting pre-existing infections with natural isolates of Candida. Under different culture conditions, we have demonstrated the formation of C. albicans colonies on human target cells and filament formation, equivalent to tissue invasion.

CONCLUSIONS/SIGNIFICANCE

These organ culture systems provide a valuable new resource to examine the molecular and cellular basis for Candida colonization of human mucosal surfaces.

Activities of several classes of acyclic nucleoside phosphonates against camelpox virus replication in different cell culture models

Camelpox virus (CMLV) is the closest known virus to variola virus. Here we report on the anti-CMLV activities of several acyclic nucleoside phosphonates (ANPs) related to cidofovir [(S)-1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC; Vistide)] against two CMLV strains, CML1 and CML14. Cytopathic effect (CPE) reduction assays performed with human embryonic lung fibroblast monolayers revealed the selectivities of the first two classes of ANPs (cHPMPA, HPMPDAP, and HPMPO-DAPy) and of the hexadecyloxyethyl ester of 1-{[(5S)-2-hydroxy-2-oxido-1,4,2-dioxaphosphinan-5-yl]methyl}-5-azacytosine (HDE-cHPMP-5-azaC), belonging to the newly synthesized ANPs, which are HPMP derivatives containing a 5-azacytosine moiety. The inhibitory activities of ANPs against both strains were also confirmed with primary human keratinocyte (PHK) monolayers, despite the higher toxicity of those molecules on growing PHKs. Virus yield assays confirmed the anti-CML1 and anti-CML14 efficacies of the compounds selected for the highest potencies in CPE reduction experiments. Ex vivo studies were performed with a 3-dimensional model of human skin, i.e., organotypic epithelial raft cultures of PHKs. It was ascertained by histological evaluation, as well as by virus yield assays, that CMLV replicated in the human skin equivalent. HPMPC and the newly synthesized ANPs proved to be effective at protecting the epithelial cells against CMLV-induced CPE. Moreover, in contrast to the toxicity on PHK monolayers, signs of toxicity in the differentiated epithelium were seen only at high ANP concentrations. Our results demonstrate that compounds belonging to the newly synthesized ANPs, in addition to cidofovir, represent promising candidates for the treatment of poxvirus infections.