Assessing human B cell responses to influenza virus vaccines and adjuvants in a PBMC-derived in vitro culture system

In vitro systems based on human peripheral blood mononuclear cells (PBMCs) can bridge the gap between preclinical and clinical vaccine evaluation but have so far mainly been exploited to assess vaccine effects on antigen-presenting cells and T cells. Our study aimed to assess whether B cells present in PBMCs also respond to vaccines and reflect the effects of different vaccine formulations and adjuvants. We stimulated PBMCs with whole inactivated virus (WIV) or split virus (SIV) H5N1 influenza vaccine, with or without the addition of the adjuvant cytosine phosphoguanine (CpG) ODN 2395, and collected the cells and supernatants at different timepoints. B cell subsets were measured by flow cytometry, immunoglobulin (IgG) levels by ELISA, B cell-related genes by qPCR, and cytokine levels by intracellular staining. B cells differentiated more readily to plasmablasts and plasma cells and produced more IgG when PBMC cultures were stimulated with WIV than when stimulated with SIV. In line, PRDM1, XBP1, and AICDA, genes associated with the differentiation of B cells to antibody-secreting cells, were expressed at higher levels in WIV- than in SIV-stimulated PBMCs. The combination of WIV and CpG consistently induced the highest levels of antibody-secreting cell differentiation, IgG production, and B-cells secreting IL-6 and IL-10. Taken together, B cells in human PBMC cultures show distinct responses to different types of vaccines and vaccine/CpG combinations. This underlines the suitability of unfractionated PBMCs for evaluating vaccine effects on different types of human immune cells before running costly clinical trials.