Secretory IgA and T cells targeting SARS-CoV-2 spike protein are transferred to the breastmilk upon mRNA vaccination

Cell Rep Med. 2021 Dec 21;2(12):100468. doi: 10.1016/j.xcrm.2021.100468. Epub 2021 Dec 2.


In view of the scarcity of data to guide decision making, we evaluated how BNT162b2 and mRNA-1273 vaccines affect the immune response in lactating women and the protective profile of breastmilk. Compared with controls, lactating women had a higher frequency of circulating RBD memory B cells and higher anti-RBD antibody titers but similar neutralizing capacity. We show that upon vaccination, immune transfer to breastmilk occurs through a combination of anti-spike secretory IgA (SIgA) antibodies and spike-reactive T cells. Although we found that the concentration of anti-spike IgA in breastmilk might not be sufficient to directly neutralize SARS-CoV-2, our data suggest that cumulative transfer of IgA might provide the infant with effective neutralization capacity. Our findings put forward the possibility that breastmilk might convey both immediate (through anti-spike SIgA) and long-lived (via spike-reactive T cells) immune protection to the infant. Further studies are needed to address this possibility and to determine the functional profile of spike T cells.

Keywords: COVID-19; breastmilk T cells; lactating women; mRNA vaccine; maternal vaccination; memory B cells; milk-transferred SARS-CoV-2 protection; milk-transferred spike-reactive T cells; plasmablasts; spike SIgA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Viral / blood
  • Antibodies, Viral / immunology
  • COVID-19 / immunology
  • COVID-19 / prevention & control
  • COVID-19 Vaccines / immunology*
  • Female
  • Humans
  • Immunity, Maternally-Acquired
  • Immunoglobulin A, Secretory / immunology*
  • Lactation / immunology
  • Memory B Cells / immunology
  • Milk, Human / immunology*
  • SARS-CoV-2 / immunology*
  • Spike Glycoprotein, Coronavirus / immunology*
  • T-Lymphocytes / immunology*
  • Vaccination
  • mRNA Vaccines / immunology


  • Antibodies, Viral
  • COVID-19 Vaccines
  • Immunoglobulin A, Secretory
  • Spike Glycoprotein, Coronavirus
  • mRNA Vaccines
  • spike protein, SARS-CoV-2