One direct route for the discovery of therapeutic human monoclonal antibodies (mAbs) involves the isolation of peripheral B cells from survivors/sero-positive individuals after exposure to an infectious reagent or disease etiology followed by single-cell sequencing or hybridoma generation. Peripheral B cells, however, are not always easy to obtain and only represent a small percentage of the total B cell population across all bodily tissues. Although it has been demonstrated that tandem mass

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... ctrometry (MS/MS) techniques can interrogate the full polyclonal antibody (pAb) response to an antigen in vivo, all current approaches identify MS/MS spectra against databases derived from genetic sequencing of B cells from the same patient. In this proof-of-concept study, we demonstrate the feasibility of a novel MS/MS antibody discovery approach in which only serum antibodies are required, without the need for sequencing of genetic material. Peripheral pAbs from a CMV exposed individual were purified by glycoprotein B antigen-affinity and de novo sequenced from MS/MS data. Purely MS-derived mAbs were then manufactured in mammalian cells to validate potency via antigen-binding ELISA. Interestingly, we found that these mAbs accounted for 1-2% of total donor IgG but were not detected in parallel sequencing of memory B cells from the same patient.