Immune cell “factories” work longer after mRNA vaccines like Pfizer

The tiny “factories” in lymph nodes that churn out antibody-producing B cells to fight infections, called germinal centers, were still functioning to hold COVID-19 at bay for months after people received the mRNA vaccine from BioNTech and Pfizer, according to a new study.

After most vaccines, germinal centers last only a few weeks. “Germinal centers are the key to a persistent, protective immune response,” said Ali Ellebedy of Washington University School of Medicine in St. Louis, who coauthored a report on Monday in Nature.

“Germinal centers are where our immune memories are formed. And the longer we have a germinal center, the stronger and more durable our immunity will be because there’s a fierce selection process happening there, and only the best immune cells survive.” Researchers studied cells from germinal centers in armpit lymph nodes of 14 recipients of the Pfizer/BioNTech vaccine.

Three weeks after the first dose, all 14 had germinal centers that were still generating B cells. B-cell production “expanded greatly” after the second shot and stayed high, they reported. Eight of 10 people biopsied 15 weeks after the first dose, still had functioning germinal centers.

“We’re still monitoring the germinal centers, and … in some people, they’re still ongoing,” Ellebedy said. “This is truly remarkable.”

The same effect is likely also true for Moderna’s mRNA vaccine, the researchers believe. Ultimately, immune cells called T cells are what sustains the germinal centers’ work after they disappear.

The researchers plan next to investigate the magnitude and durability of T cell responses after mRNA COVID-19 vaccines.