B and Tfh cell dynamics underlying durable antibody responses to flu vaccine in children - Abstract Seasonal influenza infection is a major health issue in the United States with children facing increased susceptibility to illness and death. Quadrivalent inactivated influenza vaccine (IIV4) is recommended for the prevention of influenza in children. However, influenza vaccine protection is currently insufficient with vaccine effectiveness from 2019-2020 estimated to be 39%. The primary driver of protection provided by influenza vaccines are serum antibodies (Abs). T Follicular helper cells (TFH) are a subset of CD4+ T cells that interact with activated B cells in germinal centers (GCs) to promote selection of higher affinity B cell clones, generated by somatic hypermutation. Such clones give rise to memory B cells as well as precursors of long-lived plasma cells (LLPCs), the latter account for durable Ab titers. Our preliminary results in a mouse model suggest that that LLPC precursors, with a distinctive genomic profile, are preferentially generated at late phases of a sustained GC response. We hypothesize that sustained TFH dependent GC B cell responses are required for generation of human LLPC precursors and therefore durable Ab responses after vaccination. We propose to utilize PBMC and serum samples, from a unique cohort of children and young adults that were administered cell-based IIV4, for high dimensional and multi-omic analyses, so as to predict and infer latent factors and gene networks that may underlie the generation of long-lived PCs and therefore durable Ab responses. We will use samples from selected vaccinees in the clinical trial who mounted significant responses by d28 which were either durable (d365 titers of Abs dropped less than 2-fold when compared with d28 titers) or waned substantially (returned to near baseline). We will perform multi-parameter FACS based immune profiling of PBMCs with an emphasis on activated cTFH and HA-specific B cells, cytokine profiling using MSD multiplex platform and single cell genomic profiling using 10X multiome (scRNA-seq+scATAC-seq) of cTFH, and PC precursors at d28. These datasets will be analyzed using state of the art and novel machine learning and computational genomics algorithms, to delineate latent factors and gene networks, that are predictive of and may control, respectively, the generation of LLPC precursors. Additionally, the genomic datasets are anticipated to provide the first single cell genomic snapshots of human LLPC precursors.
