Studies in our laboratory have established that the route of vaccination, viral vector and the cytokine milieu, specifically IL-13 can critically impact the vaccine-specific adaptive immune outcomes. Recent efforts in understanding which cells at the vaccination site produced IL-13 revealed that innate lymphoid cells (ILC)2 were the major source of this cytokine at the vaccination site 24h post delivery. Knowing that manipulating IL-13 levels at the vaccination site also significantly altered resident lung dendritic cell (DC) recruitment, this study focused on dissecting the underlying mechanisms by which ILCs and DCs regulated vaccine-specific immunity at the lung mucosae following intranasal vaccination.
Poxviral and non-poxviral vaccine vectors induced uniquely different ILC-derived cytokine and DC profiles at the lung mucosae, 24 h post vaccination. For example, rFPV priming known to induce high avidity T cells, exhibited low ILC2-derived IL-13, high ILC1/ILC3-derived IFN-g and enhanced recruitment of CD11b+ CD103- conventional DCs (cDC). Whereas, rMVA, rVV and Influenza A vector priming, linked to low avidity T cells, induced opposing ILC-derived cytokine profiles, together with enhanced CD11b- CD103+ cross-presenting DCs and reduced cDCs. Interestingly, Rhinovirus (RV) and Adenovius type 5 (Ad5) vectors, also showed different ILC-derived cytokine profiles and predominant recruitment of CD11b- B220+ plasmacytoid DCs (pDC). Knowing that cDCs are associated with high avidity CD8 T cell priming and pDCs are involved in antibody differentiation, these findings showed that vaccine derived early ILC/DC profiles directly impact the downstream adaptive immune outcomes.
When trying to unravel how IL-13 signalling modulated these vaccine-specific adaptive immune outcomes, unlike IL-13Ra1, IL-13Ra2 was found to be the major sensor and regulator of early IL-13 mediated DC activity. For the first time a dual role of IL-13Ra2 was unraveled on lung cDC, where low IL-13 was associated with IL-13Ra2 signalling via STAT3 activating TGF-b1, whilst, high IL-13 triggered sequestration by the same receptor. Interestingly, in this study differential IL-13 receptor mediated STAT3/STAT6 paradigms were observed, regulated collaboratively or independently by TGF-b1 and IFN-g. Low IL-13 driven early IL-13Ra2/STAT3 responses were regulated primarily by TGF-b1, whereas, high IL-13 driven IL-13Ra1/STAT6 responses were associated with IFN-gR expression bias. Moreover, inherent properties of viral vaccine vectors (host tropism, replication status and presence or absence of immunomodulatory genes), were also found to significantly alter the IL-4/IL-13 receptor regulation on lung DCs, in a time dependent manner. Specifically, the generation of a balanced adaptive immune outcome was associated with early regulation of IL-13Ra2, succeeded by IL-13Ra1/ IL-4Ra on lung DCs, as observed with rFPV vaccination unlike the other poxviral vectors tested.
Collectively, findings of this thesis for the first time demonstrated the importance of understanding the mechanisms of IL-13 mediated DC regulation, at the vaccination site. Therefore, knowing these innate mechanisms associated with ILC/DC regulation may help design more efficacious vaccines and therapeutics against IL-13 related disease conditions
