Inflammatory conditions shape phenotypic and functional characteristics of lungresident memory T cells

Abstract Lung tissue-resident memory T cells (T RM) are critical for the local control of viral respiratory tract infections. However, the exact mechanisms of T RMstimulation and maintenance are not fully understood, rendering the induction of protective T RMresponses by vaccination an ambitious goal. Here, T RMpopulations induced by natural influenza A virus (IAV) infection or by mucosal immunization using adenoviral vector vaccines encoding the IAV antigens HA and NP as well as IL-1β as adjuvant were analyzed. Phenotypic and functional T RMresponses were assessed in mice over 200 days via flow cytometry. Interestingly, long-lasting T RMresponses with a less cytotoxic character were found scattered within the lung tissue after mucosal immunization. By contrast, T RMtriggered by prior IAV infection surrounded bronchus-associated B cell clusters and their quantity waned over time more rapidly. Furthermore, single cell RNA sequencing revealed different gene expression profiles of NP-specific T RMdepending on the priming condition. However, both T RMpopulations provided protection from heterologous challenge, resulting in an expansion of cognate antigen-specific T RM. Substantial differences in IAV-specific T-cell immunity after adenoviral vector immunization or prior infections could be confirmed in the Babraham pig model. Noticeably, increased T RMresponses did not correlate with protection against an infection with a heterologous IAV strain, indicating potentially different correlates of protection in pig and mice. In conclusion, mucosal immunization was associated with a prolonged tissue retention of functional T RM, opening up a promising line of enquiry for the design of future vaccines against respiratory viruses. Main parts of this work were supported by grants from IZKF (advanced project A90). The translational part into the pig model was carried out at the Pirbright Institute, supported by grants from VetBioNet (grant agreement No 731014, Ref: VBN_20_49) and BBSRC.