Understanding plasma cell longevity and their roles beyond antibody production - Project Summary Secretion of antibodies is a specialized cellular function of plasma cells, which differentiate from naïve, germinal center, or memory B cells upon antigen exposure during infection or vaccination. Vaccines against infectious diseases, such as measles, mumps, and yellow fever, work by inducing high-affinity plasma cells that live for years or even decades, even in the absence of further exposure to antigens. These are the so-called long-lived plasma cells (LLPCs), which, in most cases, are not sufficiently generated upon many vaccinations attempts against different infectious agents. While vaccinologists and immunologists are making substantial advancements in vaccines and adjuvant formulations capable of significantly engaging plasma cell differentiation and antibody production, we still do not understand the rules and mechanisms that dictate how plasma cells live or die - the basic biology behind the decision to become long-lived. This topic lies at the core of the research in this proposal, which focuses on the utilization of innovative mouse tools specifically engineered to track LLPCs over time and understand how they evolve during their path toward longevity. The “double fate-mapper” (DFM) mouse was intentionally designed to follow cohorts of plasma cells induced by the germinal center reaction and understand how they over compete each other for survival, determining where they reside and become bona fide LLPCs. In combination with high-throughput technologies (single-cell RNA and BCR sequencing, ATAC- seq, and 10X-sequencing), the DFM allows precise monitoring of the molecular, cellular, and clonal properties that plasma cells undergo over time, pinpointing essential molecules and cellular traits to be targeted for further mechanistic studies. Interestingly, the DFM mouse enables LLPC fate-mapping in different tissues, further exploring their properties not only for infectious diseases and vaccinology but also in homeostasis and inflammatory conditions, given LLPC presence in the skin, lungs, thymus, and especially in the gut’s lamina propria. To understand their functional properties in the steady state and under inflammatory conditions, we will use another mouse model recently developed by us (Prdm1CreERT2) to conditionally delete genes in plasma cells in a timely manner, allowing proper understanding of the individual importance of certain genes for plasma cell maintenance and differentiation into LLPCs. Through a combination of fate-mapping with the DFM and conditional knockout of genes in the LLPC compartment, we will advance our understanding of important factors affecting plasma cell longevity and how they are ultimately instructed to join the LLPC pool in different tissues. Understanding the basic biology of this “decision” will be strongly informative for translational approaches to humans, potentially improving vaccination strategies, especially for diseases where engagement of LLPC- derived broadly neutralizing antibodies is extremely challenging, such as HIV, Plasmodium, and dengue. Additionally, we expect this knowledge to be highly informative in conditions where plasma cells play a pathological role, such as multiple myeloma and autoimmune disease (lupus, multiple sclerosis).
