SARS-CoV-2 infection induces human milk antibodies capable of mediating multiple functional activities

Background and Aims

Passive transfer of antibodies through breastfeeding is a potential mode of protection for newborns and infants following maternal SARS-CoV-2 infection. The primary goal of this study was to evaluate and characterize SARS-CoV-2 Spike (S)-specific antibodies in human milk samples collected longitudinally from a cohort of convalescent mothers.

Methods

SARS-CoV-2 infected participants enrolled in this study were lactating women aged 29–36 years with a confirmed COVID-19 diagnosis who donated milk samples at intervals over the six-month study period. Samples were evaluated for antibody subclass SARS-Cov-2 S glycoprotein binding activity by ELISA, and for the capacity of antibodies purified from these samples to mediate neutralizing antibody (nAb) activity in S pseudovirus inhibition assays and phagocytic activity in an antibody-dependent phagocytosis assay.

Results

Robust S-reactive IgM, IgG and IgA ELISA titers were found at day 7 after enrollment, with IgG and IgA levels persisting through 6 months. The majority of S-reactive IgA in milk was secretory in nature. Strong IgG (mean IC₅₀ value 29.19μg/ml) and IgA (mean IC₅₀ value 10.17μg/ml) nAb activity was found in all convalescent samples at 14 days with a decline by 3 months after the onset of symptoms but was not seen in pre-pandemic controls. Both IgG and IgA antibodies mediated phagocytic activity in samples from all subjects by day 14 after the onset of symptoms.

Conclusions

Our findings indicate that human milk from SARS-CoV-2 infected mothers have the capacity to transfer SARS-CoV-2-specific antibodies capable of mediating multiple functional activities to newborns via breastfeeding.