Skin-on-Chip for Preclinical Herpes Disease Modeling
Blog post by Nina Culum, MSc
Despite the high global prevalence of herpes simplex virus (HSV) infection, a cure remains elusive. Approximately 67% of the global population has HSV type 1 (HSV-1), which is transmitted through oral contact, while 13% has HSV type 2 (HSV-2), a sexually-transmitted infection that increases the risk of acquiring and transmitting human immunodeficiency virus (HIV) . Effective HSV vaccines are urgently needed to help decrease HIV incidence, as well as prevent neonatal herpes, which, although rare, can lead to neurological disability or death .
The development of effective HSV vaccines is largely hindered by our poor understanding of the host and viral determinants of HSV manifestation in humans, as well as the early kinetics of the immune response [2, 3]. Although murine HSV models are useful for studies of basic immunology, they do not mimic primary or recurrent infection in humans; as a result, vaccine candidates that have shown promising results in animal studies have failed in clinical trials . Skin biopsies from HSV-infected individuals have also provided valuable immunological insights, but it is difficult to access HSV-affected skin on a large scale . Therefore, alternative preclinical platforms for understanding HSV pathogenesis in humans are needed, such as organs-on-a-chip.
What are organs-on-a-chip?
Organs-on-a-chip are miniature tissues grown in vitro that can model human physiology and disease, and further drug development by addressing the limitations of cell and animal models . These platforms combine the benefits of both models by culturing human cells in tissue-specific settings that recapitulate the molecular, structural, and physical cues that are found in vivo for an organ system . Consequently, organs-on-a-chip are attractive alternatives for bridging the translational gap between preclinical and clinical stages in vaccine development, particularly for HSV. Sun et al. recently published an article in Nature Communications describing the development of a skin-on-chip platform for modeling HSV infection, as well as evaluating immune responses and antiviral drug efficacy, which we review in this blog post .
Modeling HSV infection with skin-on-chip
The design and fabrication of this microfluidic-based, full-thickness skin-on-chip platform were extensively detailed by Sun et al. in this paper. Briefly, the authors employed skin-specific primary human cells and lithography-based vascular engineering to create a biomimetic microfluidic device composed of a stratified epidermis and an underlying dermis with a functional microvascular network. Viral infectivity was monitored at different stages of keratinocyte differentiation, which diminished rapidly with increasing differentiation, indicating the importance of intact skin barrier function in protecting against HSV infection. The authors also mechanically disrupted the epidermis with a biopsy punch to simulate tissue micro-injury, thereby facilitating viral access to cells in fully differentiated epidermis, and demonstrated that the skin-on-chip platform could mimic native HSV infection in human skin (Figure 1).
Figure 1: HSV infection in skin-on-chip epidermis, with arrows indicating chromatin margination, cell nucleus enlargement, and multi-nucleation (scale bar = 20 μm). © 2022 Sun et al., licensed under CC BY 4.0.
Evaluating inflammatory responses and drug efficacy
To evaluate the inflammatory responses of the device to HSV infection, Sun et al. perfused neutrophils through its microvascular network and observed rapid attraction and adhesion to the vessel wall. In contrast, minimal neutrophil adhesion was found in a mock infection model. Additionally, HSV infection resulted in proinflammatory cytokine and chemokine secretion in the skin-on-chip system, particularly IL-8, which is absent in rodent genomes. When perfused with neutralizing antibodies specific to IL-8, neutrophil trans-endothelial migration in the device was effectively inhibited. The authors noted that these findings are consistent with in vivo evidence that neutrophils are the first responders to HSV infection in humans.
Since a major application of this research is in drug development, the authors monitored the effects of antiviral drug perfusion in the skin-on-chip device. Acyclovir (ACV), an effective HSV treatment, was perfused through the microvascular network, which was shown to inhibit HSV-2 infection in a dose-dependent manner (Figure 2, top row). Drug efficacy was also shown to be impacted by time of treatment administration; ACV perfusion 24 hours prior to or at the time of HSV-1 infection significantly improved antiviral activity compared to treatment 24 hours after infection (Figure 2, bottom row). The authors concluded that this platform could be useful for preclinical drug efficacy testing and for evaluating pharmacokinetics/pharmacodynamics.
Figure 2: HSV infection in skin-on-chip epidermis following ACV perfusion at varying concentrations (top row) and times (bottom row) (scale bars = 500 μm). © 2022 Sun et al., licensed under CC BY 4.0.
Limitations and future perspectives
Despite the potential for this platform in disease modeling, some limitations exist. At this early stage, only structural components were incorporated in the device, resulting in low expression of the cytokine TNFα. The authors noted that tissue-resident immune cells should be considered for inclusion in the future since they are likely important in initial pathogen sensing and cytokine/chemokine induction. Furthermore, future skin-on-chips should contain autologous cellular components to delineate complex human immune responses to HSV infection. Nevertheless, this skin-on-chip platform holds promise in mimicking human HSV infection and enables greater understanding of disease pathology and potential therapies.
About the Author
About the Author
Nina Culum graduated from the University of Western Ontario with a Master of Science in physical and analytical chemistry. During her graduate studies, she fabricated plasmonic nanohole arrays to capture extracellular vesicles and detect cancer by surface-enhanced Raman spectroscopy. Prior to attending UWO, Nina completed her Bachelor of Science in chemistry at the University of Waterloo.
- World Health Organization [Internet]. Herpes simplex virus; 2022 Mar 10 [cited 2022 Sep 23]. Available from: https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus.
- Johnston C, Koelle DM, Wald A. Current status and prospects for development of an HSV vaccine. Vaccine. 2014;32(14):1553-60. DOI: 10.1016/j.vaccine.2013.08.066.
- Sun S, Jin L, Zheng Y, Zhu J. Modeling human HSV infection via a vascularized immune-competent skin-on-chip platform. Nat Commun. 2022;13:5481. DOI: 10.1038/s41467-022-33114-1.
- Ronaldson-Bouchard K, Vunjak-Novakovic G. Organs-on-a-chip: a fast track for engineered human tissues in drug development. Cell Stem Cell. 2018;22(3):310-24. DOI: 10.1016/j.stem.2018.02.011.