Ageing SLOw: Modelling Ageing in Secondary Lymphoid Organs in vitro

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SummaryThe failure of animal models to predict therapeutic responses in humans is a major problem. However, non-animal technologies (NATs) are emerging as a viable solution. The current lack of human-relevant preclinical models leads to costly development of drugs destined to fail and fewer drugs reaching patients1. Infectious diseases have one of the highest attrition rates, vaccine candidates have an average market entry probability of 6%2, and development from the pre-clinical stage costs an estimated £374M-£1.5BN3. Animal models are used to test and study adaptive immune responses, yet they lack essential features of human immunity. What's more, we know from the COVID19 pandemic, that using vaccines to protect over 65s is less effective than in younger age groups4. Indeed, immune function declines with age, leading to increased susceptibility to infection and failure to generate long-lasting immunity after vaccination. For seasonal influenza, one of the best studied pathogens, vaccine efficacy in the elderly ranges from 0-50%5, resulting in £100Mpa in secondary healthcare costs to the NHS6, and 90% of mortalities result from infection in over 65s7. Yet animal models cannot account for age-associated immune variation8. Resulting in few vaccines aimed specifically at this high-risk age group. The development of NATs has the potential to drive human-relevant vaccine development, increasing the chance of developing vaccines efficacious in the elderly population. This would, in-turn, relieve financial burden and capacity pressures on the NHS.Secondary lymphoid organs (SLOs), lymph nodes and tonsils, are the sites where immune responses are mounted and where immune memory is stored. Making them the ideal organ to model vaccine responses. Recently, it was shown that poor response to vaccination in the elderly is dictated not by the age of circulating immune cells, but by the aged SLO microenvironment - i.e. stromal support cells and extracellular matrix (ECM)9. Current approaches to model SLOs rely on the ability of immune cells to self-aggregate in liquid culture and lack incorporation of these critical microenvironment components10. Hydrogels provide an ideal solution, they can incorporate ECM components and recapitulate 3D stroma. Yet there are limitations to using hydrogels to bioengineer relevant NATs. While synthetic hydrogels (e.g. poly (ethylene glycol); PEG) are highly reproducible and biomechanical properties, such as stiffness and viscosity, can be precisely controlled, they lack biological activity. Also, while natural materials (e.g. collagen) have excellent bioactivity, they lack the necessary reproducibility and tuning of biomechanics11. Synthetic-biological hybrid hydrogels (e.g. PEG-collagen) are emerging - these are reproducible materials, with high bioactivity and tuneability12,13. Hence, they provide a solution for NAT development.In this proposal, I will develop NAT models of SLOs using human cells and synthetic-biological hydrogels. I aim to: 1) Develop SLO organoids that mimic healthy and aged microenvironments; 2) Understand how biomechanical changes in the SLO microenvironment affect immune function, and 3) Investigate if mechano-immunological mechanisms can be targeted in aged SLOs to enhance immune responses in the elderly.Throughout this proposal I will use organoids and synthetic-biological hybrid hydrogels, with an extensive range of systems, such as live cell imaging and single cell nanoindentation. As well as new approaches, such as Brillouin microscopy, voted one of the top 10 game-changing technologies of 2022 due to its ability to non-invasively measure the biomechanics of 3D tissues14. With these, I will model SLOs and monitor ageing and vaccine-related mechano-immunological changes in SLO microenvironments.