Trispecific SEED antibodies engineered for neutrophil-mediated cell killing.

Immunoglobulin (Ig) A has attracted interest as a proposed therapeutic agent due to its ability to engage cell groups differently compared to an IgG scaffold and elicit tumor eradication. Further, its multimeric forms enable increased flexibility in the design of available paratopes. The latter is particularly advantageous for bi- and multispecific antibody formats, which are unparalleled in their enhanced selectivity and unique biological functions. We engineered bispecific heterodimeric IgA-based antibodies using the strand-exchanged engineered domain (SEED) technology, which relies on intertwined segments of IgA and IgG in the C_H3 domain, and applied mutagenesis to introduce two additional binding sites to enable the interaction of IgA-Fc with the myeloid cell-activating receptor CD89 (FcαR). These antibodies exhibited good biophysical properties and thermostability similar to the parental SEED molecule. Binding capacity to both antigens recognized by variable domains, epidermal growth factor receptor (EGFR) and receptor tyrosine kinase like orphan receptor 1 (ROR1), was not impaired, and in contrast to the original SEED-IgA, trispecific mutants could bind to CD89-expressing cells, mediate tumor cell-effector cell clustering, and induce neutrophil-mediated specific lysis of tumor cells. Trispecific design was applicable to both SEED-IgA1 and -IgA2 scaffolds. Interestingly, HEK-expressed mutants featured a CH2-linked N-glycan pattern more similar to wild-type IgA, with reduced core fucosylation in comparison with IgA-SEED. Collectively, the presented format combines the mobilization of CD89-positive effector cells with the flexibility of incorporating antigen specificities of choice into the variable domains, and thus is a promising basis for biochemically stable multispecific IgA with high therapeutic potential.