Development and function of inflammatory dendritic cells

The vaccination method relies on the activation and expansion of cells called T lymphocytes that can recognise the antigens of pathogens. After vaccination, these T cells react quicker and better to pathogen encounter and can mediate immune protection.

The activation of T lymphocytes is controlled by a family of cells called dendritic cells that capture pathogens and present pathogen derived antigens to T cells on presenter molecules called MHC (major histocompatibility complex).

Several populations of dendritic cells have been described. They harbour distinct immune function important for the establishment of protective immunity. However, some members of the dendritic cell family are ill described and their specific contribution to the protective T cell responses not yet defined. In particular, during the small inflammation caused by vaccination (or infection), a new type of cells is produced in large quantities by the immune system called inflammatory DCs (iDCs). How iDCs are produced and to what extent they contribute to the development of protective immune responses has still to be understood.

This proposal intends to :
- better characterise these cells,
- understand how the immune system produces them and
- determine how they impact the development of adaptive immunity induced by vaccination

This research is important for human and animal health because it will enable to produce better vaccines. Indeed understanding iDCs biology is key to tailor vaccine adjuvants that will maximise the induction of protective immune responses required for the success of vaccination.

Inflammatory dendritic cells (iDCs) are monocyte-derived antigen presenting cells arising during inflammation.

Ly6ChiCD115+ inflammatory monocytes give rise to inflammatory DCs (iDCs) and iNOS-producing microbicidal phagocytes (iMPs) through CCR2-dependent mobilization. This proposal addresses a) the mechanisms underlying the generation of iDCs from Ly6ChiCD115+, b) the contribution of iDCs to T cell responses. We aim at:

1- Characterising monocytes subsets acting as progenitors for iDCs (pre-iDCs).

The applicant laboratory has recently evidenced that Ly6Chigh blood monocytes are heterogeneous and contain CCR2-dependent progenitors (Ly6ChighFlt3+CD11c-MHCII+ and Ly6ChighFlt3+CD11c+MHCII+) poised to iDCs differentiation and poorly able to generate iMPs. This proposal intends to fully assess the pre-iDCs progeny in various inflammatory settings.

2- Identifying transcriptional networks controlling iDCs development.

We have acquired preliminary evidence that IRF4, CIITA and MHCII expression is heterogeneous within naive Ly6Chigh monocytes subsets. We hypothesise the existence of regulatory network integrating positive master regulators (SFPI1) or negative master regulators (NFIL3) regulators of monocyte fate and iDCs lineage commitment. These hypotheses will be tested in vitro and in vivo by genetic experiments.

3- Producing a cre recombinase knock in mouse model targeting specifically iDCs.

To this end, we will use the CD209a gene that is highly expressed in iDC-committed monocytes subsets.

4- Visualising iDCs lineage by fate-mapping.

The CD209acre line will be crossed to ROSAloxSTOPloxTomato reporter to assess the dynamic of iDCs populations.

5- Assessing iDCs contribution to T cell responses.

We will perform inducible, conditional iDC ablation (CD209acre x Csf1rloxSTOPloxDTR) and conditional gene inactivation in iDCs (CD209acre x Ablox/lox) to define their contribution to CD4+ T cell responses in models of vaccination.

Industrial development
This research may generate commercially-exploitable research tools and possibly intellectual property as well. Indeed, understanding the generation of inflammatory cells should improve the ability to screen for the most effective adjuvant relevant for vaccine design.
Also, in-depth analysis of inflammatory dendritic cells (an their transcriptional underpinnings) might lead to the identification of pharmacologically targetable pathways susceptible to provide a level of manipulation of inflammatory immune responses. This might serve the rational design of new anti-inflammatory therapies.
We will take advantage of industrial outreach structures dedicated to foster industrialization projects at King's College London. We will try also to develop industrial interactions that may lead to the application for a CASE studentship attached to this project.

Outreach, education, training and capacity-building
To publicise our research findings, we will attend national and international conferences. All research findings funded by this grant will be published using open-access mechanisms (such as PMC) to facilitate access of the findings to a wide public.
In addition, insertion of the PI into the teaching faculty at King's College London might facilitate the diffusion of new findings to a wide public of new scientist and health professional in training.

Societal beneficiaries
The research in this proposal has both medical and societal impact since it is expected to improve health status through the rational design of vaccines by a better understanding of the cells mediating the immune responses triggered by vaccines.
Indirectly, this might have a broad impact on the health status of the human and animal population as well. Indeed, mechanisms unravelled by our research might benefit to the rationale design of new vaccines against old (malaria) or emerging (Ebola virus) pathogens.