Direct measurement of B lymphocyte gene expression biomarkers in peripheral blood enables early prediction of seroconversion after vaccination
Vaccination is a common and efficient means to reduce the mortality and morbidity of emerging infectious diseases. Among responders, injected antigen induces acquired immunity pathways and leads to the final production of antigen-specific antibodies. The whole process may take weeks to months, depending on the antigen. Typically, seroconversion to influenza vaccine is expected after one month with a responder rate of ~50%. An early biomarker to predict response is desirable. Peripheral blood gene expression (or transcript abundance, TA) datasets in the public domain were analyzed for early biomarkers among responders. As peripheral blood samples (such as peripheral blood mononuclear cells, PBMC) are cell mixture samples containing various blood cell-types (leukocyte subpopulations, LS). We first develop a model that enables the determination of TA in B lymphocytes of certain genes directly in PBMC samples without the need of prior cell isolation. These genes are called B cell informative genes. Then a ratio of two B cell informative genes (a target gene and a stably expressed reference gene) measured in PBMC was used as a new biomarker to gauge the target gene expression in B lymphocytes. This method having an obvious advantage over conventional methods by eliminating the tedious procedure of cell sorting and enables directly determining TA of a leukocyte subpopulation in cell mixture samples is called Direct LS-TA method. By using a B lymphocyte-specific gene such as TNFRSF17 or TXNDC5 as target genes with either TNFRSF13C or FCRLA as reference genes, the B cell biomarkers were determined directly in PBMC which was highly correlated with TA of target genes in purified B lymphocytes. These Direct LS-TA biomarkers in PBMC increased significantly early after vaccination in both the discovery dataset and a meta-analysis of 7 datasets. Responders had almost a 2-fold higher Direct LS-TA biomarker level of TNFRSF17 (SMD=0.84, 95% CI=0.47-1.21 after log2). And Direct LS-TA biomarkers of TNFRSF17 and TXNDC5 measured at day 7 predict responder with sensitivity values of higher than 0.7. The Area-under curves (AUC) in receiver operation curve (ROC) analysis were over 0.8. Here, we report a straightforward approach to directly analyses B lymphocyte gene expression in PBMC, which could be used in a routine clinical setting as it avoids the labor-intensive procedures of B lymphocyte isolation. And the method allows the practice of precision medicine in the prediction of vaccination response. Furthermore, response to vaccination could be predicted as early as on day 7. As vaccination response is based on the similar acquired immunology pathway in the upcoming worldwide vaccination campaign against COVID-19, these biomarkers could also be useful to predict seroconversion for individuals.