Learnings on Immunosenescence from the COVID-19 Pandemic

Abstract

Background Age related diseases represent a major concern within the global population due to an increasing proportion of older to younger adults. With ageing, individuals experience a decline in their immunological function, which leads to a reduced ability to respond to viral infections and vaccinations, such as SARS-CoV-2. Age-related senescent immune cells have been well characterised in the adaptive immune repertoire, however, the impact of immunosenescence on response to viral infection is less known – particularly in context of the COVID-19 pandemic. This thesis aims to understand the degree to which age and senescence is associated with poor viral response and clearance, whilst also providing pilot understanding for the impact that T2D plays in exacerbating an immunosenescent phenotype. Senotherapeutic drugs have effectively ameliorated senescence in various cell and tissue types. As such, they represent a novel drug development opportunity for ageing immunity, which is piloted here too. Methods Data chapter 3 of this thesis involved collection of PBMC blood sampling from a cohort of 49 individuals, split into groups of 18-35 years old and 60+ years old. PBMCs were evaluated for T cell senescence using flow cytometry, RT-qPCR, microsatellite sequencing and ELISAs. Data chapter 4 studied a cohort of 265 SARS-CoV-2 positive individuals, where RNA was tested using RT-qPCR assays for sub-genomic RNA – an element of active SARS-CoV-2 infections to understand viral load dynamics. Data chapter 5 is a pilot study which assesses the impact of senotherapeutic intervention on the antibody production, senescence markers and TCR clonality in older PBMCs both with and without the presence of SARS-CoV-2spike protein. These are assessed using RT-qPCR, microsatellite sequencing and ELISAs. Results I identified that aged individuals demonstrated higher immune ageing metrics from flow cytometry relative to younger counterparts (Median respective IMMAX scores: 0.75 vs 0.48, P<0.0001). This correlated with IgG production in individuals reporting a COVID infection within 6 months of sampling, where lower scores correlated with improved antibody response (p=0.048). This is further linked to higher immune age metrics correlated to reduced TCR delta diversity both without and with spike treatment (p<0.0001 and p=0.0001 respectively). Whilst no associations were found between viral load and age, higher viral loads were associated with worsened COVID-19 outcomes using existing and novel sgRNA targeted testing for infectious virus (p=0.006 and p=0.03 respectively). This data also demonstrated that individuals can remain infectious beyond 10 days, without predictive clinical characteristics. Average IgG production in trametinib treated cells is 21.7 ng/mL higher within older adult samples when treated with SARS-CoV-2 Omicron spike protein (p<0.0001), however may largely be due to and adjuvant effect of trametinib. Evaluation of typical molecular markers of senescence demonstrated younger and older adult spike challenged PBMCs have statistically significant differences in P53, P21 and P16 markers of senescence when metabolically challenge (p=0.0008/p=0.0009/p=0.0107 respectively). Conclusions This thesis contributes to knowledge of SARS-CoV-2 viral kinetics. Work here also assesses mechanisms for how immunosenescence causes declining immune function in older adults and individuals with metabolic disease. Finally, pilot data evaluates the potential for senotherapeutic drug interventions as a method of vaccine adjuvant and improvement of ageing immunity.