Learning antibody sequence constraints from allelic inclusion

Although antibody sequences are highly diverse, they are constrained by requirements for expression and limited off-target reactivity. Describing which sequences violate such constraints has proven to be difficult. Here, we introduce a machine-learning framework to leverage a previously underutilized source of data for this problem. We use human single-cell sequencing data to find instances of allelic inclusion, a rare event where B cells express two different antibody light chains as mRNA. Previous studies suggest that one of these chains is either autoreactive or non-expressing as protein. We train machine-learning models to identify abnormal sequences associated with allelic inclusion. The resulting models generalize to predict antibody properties including polyreactivity, surface expression, and mutation usage, outperforming methods that do not use allelic inclusion data. We also investigate similar selection forces on the heavy chain in mice and observe that surrogate light-chain pairing has a large impact on heavy-chain diversity.