Imprinting of serum neutralizing antibodies by Wuhan-1 mRNA vaccines.

Immune imprinting is a phenomenon in which prior antigenic experiences influence responses to subsequent infection or vaccination1,2. The effects of immune imprinting on serum antibody responses after boosting with variant-matched SARS-CoV-2 vaccines remain uncertain. Here we characterized the serum antibody responses after mRNA vaccine boosting of mice and human clinical trial participants. In mice, a single dose of a preclinical version of mRNA-1273 vaccine encoding Wuhan-1 spike protein minimally imprinted serum responses elicited by Omicron boosters, enabling generation of type-specific antibodies. However, imprinting was observed in mice receiving an Omicron booster after two priming doses of mRNA-1273, an effect that was mitigated by a second booster dose of Omicron vaccine. In both SARS-CoV-2-infected and uninfected humans who received two Omicron-matched boosters after two or more doses of the prototype mRNA-1273 vaccine, spike-binding and neutralizing serum antibodies cross-reacted with Omicron variants as well as more distantly related sarbecoviruses. Because serum neutralizing responses against Omicron strains and other sarbecoviruses were abrogated after pre-clearing with Wuhan-1 spike protein, antibodies induced by XBB.1.5 boosting in humans focus on conserved epitopes targeted by the antecedent mRNA-1273 primary series. Thus, the antibody response to Omicron-based boosters in humans is imprinted by immunizations with historical mRNA-1273 vaccines, but this outcome may be beneficial as it drives expansion of cross-neutralizing antibodies that inhibit infection of emerging SARS-CoV-2 variants and distantly related sarbecoviruses.

Vaccination with prefusion-stabilized respiratory syncytial virus fusion protein elicits antibodies targeting a membrane-proximal epitope.

IMPORTANCE: Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in infants, infecting all children by age 5. RSV also causes substantial morbidity and mortality in older adults, and a vaccine for older adults based on a prefusion-stabilized form of the viral F glycoprotein was recently approved by the FDA. Here, we investigate a set of antibodies that belong to the same public clonotype and were isolated from individuals vaccinated with a prefusion-stabilized RSV F protein. Our results reveal that these antibodies are highly potent and recognize a previously uncharacterized antigenic site on the prefusion F protein. Vaccination with prefusion RSV F proteins appears to boost the elicitation of these neutralizing antibodies, which are not commonly elicited by natural infection.