Editing B cells at the IGHA2 gene position provides alternative route to therapeutic IgA production

As professional and long-lived immunoglobulin (Ig) producers, B cells represent attractive candidates for adoptive immunotherapy and their highly expressed Ig heavy (IgH) chain locus is ideal for editing. Each of its constant genes, expressed after class switch recombination (CSR), affords an attractive platform where an adoptive Ig variable domain would acquire IgM, IgG, IgE or IgA class-specific functions. In particular, IgA plays a unique role in mucosal immunity but has remained excluded from therapeutic applicability due to unfavorable chemistry, manufacturing, and control (CMC) issues. To test whether these barriers could be overcome by producing IgA in vivo rather than in vitro, we edited the human B cell-specific IGHA2 gene and found it to be a suitable platform for inserting gene cassettes for expression in B cells. Targeted deletions can also induce CSR to IgA2, while, by combining IgA2 CSR with the insertion of a linked VH and a complete light chain, we have replaced the endogenous Ig chains with a customized full-size but single-chain IgA carrying an adoptive antigen specificity. Taken together, we show that IGHA2-editing of B cells could provide a novel avenue to B-cell targeted delivery of therapeutic IgA, overcoming the problems that have so far excluded IgA from clinical use.