Project description:Memory B cells represent one of the pillar of humoral protection and are found in the circulation and secondary lymphoid organs several decades after initial pathogen or vaccine encounter. The exact cellular and biological mechanisms allowing long-term survival of quiescent cells in such a fluctuating microenvironment remain poorly understood. Assessing the true longevity of human memory B cells against common pathogens is, in most settings, hindered by the possibility for any given individual to re-encounter them during his lifetime. Smallpox, officially declared eradicated in 1980 (Fenner WHO 1988), represents one notable exception. Alongside smallpox eradication, anti-smallpox vaccination, based on the live Vaccinia virus, was progressively discontinued during the 1970s. As such, any detectable anti-vaccinia memory B cell in an individual post 2010 would likely have been generated more than 40 years ago, without any re-stimulation with the immunizing antigen during that timeframe. Anti-vaccinia antibodies serum titers remain stable in human for more than 80 years after first vaccination (Amanna NEJM 2007, PMID: 17989383), with several identified immunodominant epitopes including the envelope glycoprotein B5R (Lantto J Virol 2011, PMID: 21147924). Anti-vaccinia memory B cells have similarly been followed longitudinally in the blood for up to 65 years post vaccination (Amanna NEJM 2007, PMID: 17989383 ; Crotty JI 2003, PMID : 14607890) and, following a contraction phase taking place in the first couple of years after immunization, reach a remarkably stable plateau that last for decades at around 0.1% of total circulating IgG+ memory B cells. Functional analysis of such long-lived memory B cells, however, is still lacking. As a proxy to study long-lived memory B cells, IgG+ switched memory B cells specific for the immunodominant Vaccinia antigen B5R (B5R+ IgG+ memory B cells) were sorted and analyzed by scRNAseq from the spleen of six organ donors, collected between 2015 and 2018. For all donors, B5R+ IgG+ memory B cells were sorted alongside total IgG+ memory B cells (live IgD-CD27+IgG+CD20+CD3-CD14-CD16-) and naïve B cells (live IgD+CD27-CD38-CD24-CD20+CD3-CD14-CD16-). Single-cell mRNA sequencing was performed according to an adapted version of the SORT-seq protocol (Muraro et al., 2016, PMID: 27693023), with cDNA libraries generation, sequencing and reads alignment performed at Single Cell Discoveries (Utrecht, Netherlands).

Project description:Inducing the long-term protection via effector memory CD8+ T cells residing in the peripheral tissues is the ultimate goal of T cell-based vaccination strategies. CD8+ T cell reacting against a particular set of antigenic peptides show propensity to generate stable pools of memory inflating cells with profound protective capacity. While the epitopes that induce memory inflation have been thoroughly characterized and used as excellent constituents of vaccines such as recombinant adenoviruses, the identity of the tissue factors responsible for maintaining memory inflating CD8+ T cells remains elusive. Here, we have used a Cre recombinase-dependent, -galactosidase (gal)–recombinant adenovirus vector that allowed for cell-specific expression of gal epitopes and identification of cell types involved in generation of inflationary responses. While targeting antigen expression to classical hematopoietic antigen presenting cells was insufficient to activate gal-specific CD8+ T cells, expressing the antigen exclusively in CCL19-producing fibroblastic stromal cells (FSCs) induced robust anti-gal CD8+ T cell response. Using bone marrow chimera mice to abolish the expression of major histocompatibility complex I (MHC-I) and Basic Leucine Zipper ATF-Like Transcription Factor 3 (BATF3) in hematopoietic cells we demonstrated that CCL19-expressing FCS function as antigen libraries, gradually releasing the antigen to CD103+ DCs to maintain gal-specific memory inflating population. Moreover, targeted ablation of CCL19-producing cells revealed that pulmonary fibroblastic stromal cells act as the principal organizer of the nurturing niches that support the metabolic conversion in CD8+ T cells necessary for the generation of long-lasting protective inflationary responses. Overall, our data reveal a hitherto unknown function of CCL19-expressiong fibroblastic stromal in supporting the metabolic fitness of CD8+ T cells, thereby promoting the generation of tissue-specific and long-lasting protective CD8+ T cell responses.

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Metabolic quiescence of naïve-like memory T cells precedes and maintains antigen-specific T-cell memory

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