Robust and specific secretory IgA against SARS-CoV-2 detected in human milk

Abstract

The SARS-CoV-2 immune response in human milk has not yet been examined, though protecting infants and young children from COVID-19 is critical for limiting community transmission, and preventing serious illness and death. Here, milk samples from 8 COVID-19-recovered and 7 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, while 80% exhibited significant IgA and secretory (s)Ab binding to the receptor binding domain (RBD). Additionally, 67% of 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.