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

Abstract

Summary: 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.

Keywords

• SARS-CoV-2
• Human milk
• Antibody subclasses
• Neutralizing antibodies
• Phagocytic activity