Discovery and engineering of the antibody response to a prominent skin commensal.

Abstract

The ubiquitous skin colonist Staphylococcus epidermidis elicits a CD8⁺ T cell response pre-emptively, in the absence of an infection¹. However, the scope and purpose of this anticommensal immune programme are not well defined, limiting our ability to harness it therapeutically. Here, we show that this colonist also induces a potent, durable and specific antibody response that is conserved in humans and non-human primates. A series of S. epidermidis cell-wall mutants revealed that the cell surface protein Aap is a predominant target. By colonizing mice with a strain of S. epidermidis in which the parallel β-helix domain of Aap is replaced by tetanus toxin fragment C, we elicit a potent neutralizing antibody response that protects mice against a lethal challenge. A similar strain of S. epidermidis expressing an Aap-SpyCatcher chimera can be conjugated with recombinant immunogens; the resulting labelled commensal elicits high antibody titres under conditions of physiologic colonization, including a robust IgA response in the nasal and pulmonary mucosa. Thus, immunity to a common skin colonist involves a coordinated T and B cell response, the latter of which can be redirected against pathogens as a new form of topical vaccination.