Robust and Specific Secretory IgA Against SARS-CoV-2 Detected in Human Milk

Highlights

• All milk from recovered donors contained significant SARS-CoV-2-specific IgA

• Most IgA could bind the Receptor-Binding Domain (important neutralization epitope)

• Most Receptor-Binding Domain-specific IgA was in secretory (s) form

• sIgA is durable in the mucosa, and thus potentially as a respiratory therapeutic

Summary

The SARS-CoV-2 immune response in human milk has not yet been examined, although protecting infants and young children from COVID-19 is critical for limiting community transmission and preventing serious illness and death. Here, milk samples from eight COVID-19-recovered and seven COVID-19-suspected donors were tested for antibody (Ab) binding to the SARS-CoV-2 Spike protein. All samples exhibited significant specific IgA reactivity to the full Spike, whereas 80% exhibited significant IgA and secretory (s)Ab binding to the Receptor-Binding Domain (RBD). Additionally, 67% samples exhibited IgG and/or IgM binding to RBD. IgA and sAb titers were highly correlated, indicating most IgA to be sIgA. Overall, these data indicate that a robust sIgA-dominant SARS-CoV-2 Ab response in human milk after infection should be expected in a significant majority of individuals. Further research is highly warranted to determine Ab functionality and the potential for exploiting extracted milk sIgA for therapeutic use.