Investigating the Site of Innate Lymphoid Cell Division Following BCG Vaccination

Tuberculosis (TB) is the most deadly infectious disease worldwide, killing 1.4 million people each year. Efforts to control the spread of this disease through antibiotic treatments and a century-old preventative vaccine, BCG, have proved to be ineffective. Therefore, development of an improved vaccine against TB is vital. The recent discovery of a new subset of immune cells, the innate lymphoid cells (ILCs) have provided a new possible target for vaccine development. However, little is known about the role of ILCs in the immune response against TB, so therefore we aimed to determine whether ILC populations were altered in response to BCG. Previous work from our lab found that the number of ILCs in the lung increased four weeks after intranasal vaccination with BCG. Therefore the aim of this study was to determine whether this increase in ILCs was due to local proliferation in the lungs, or due to migration of ILCs from other sites in the body. For these experiments, a novel in vivo labelling system was adapted. This used the intranasal administration of the fluorescent dye CFSE to label all the cells in the lungs, and the intranasal and intraperitoneal administration of BrdU to identify all proliferating cells in the body. Using flow cytometry, ILCs could be analysed for the presence of CFSE and BrdU, indicating whether they had proliferated within the lung. It was hypothesised that the majority of the ILCs would proliferate in the lung, as there is a lung-resident ILC population, and ILCs are relatively rare in lymphoid tissues. Two research questions were generated to address the aim: when after BCG vaccination were ILCs proliferating, and whether this proliferation was occurring within the lungs. It was found that proliferating ILCs of interest, ILC1s, ILC3s an Natural Killer cells could be detected between three and four weeks after vaccination with BCG. In addition, all of the ILCs appeared to be dividing within the lung. These results suggest that ILCs proliferate in the lung following vaccination with BCG, and that further investigation may identify protective effects of these cells that can be manipulated for future vaccine development