Early Immune Cell and Antibody Kinetics Following SARS-CoV-2 Vaccination in Healthy Adults and Low-Count Monoclonal B-Cell Lymphocytosis.

The early immune kinetics after SARS-CoV-2 vaccination remain poorly understood, particularly among individuals with low-count monoclonal B-cell lymphocytosis (MBLlo). We investigated the cellular and humoral kinetics in the blood of 50 non-MBL healthy donors (HD) vs. 16 MBLlo subjects after SARS-CoV-2 vaccination, who were subclassified according to their history of previous exposure to SARS-CoV-2 into SARS-CoV-2 naïve and previously infected subjects. Overall, we found decreased neutrophil and lymphocyte counts at day +4 following each dose in non-MBL HD, together with an earlier and higher increase in plasma cell (PC) counts and SARS-CoV-2-specific antibody levels after the first vaccine in previously infected non-MBL HD. MBLlo subjects showed a similar profile, except for lower B-cell and higher PC counts after vaccination, and a trend towards a higher (but delayed) antibody response. In summary, we found different cell-kinetic profiles following vaccination in SARS-CoV-2 naïve vs. previously infected non-MBL HD (earlier PC and antibody responses in the latter group); additionally, MBLlo subjects had significantly lower B-cell and higher PC counts after vaccination, and a delayed SARS-CoV-2-specific antibody response.