Yeast-expressed SARS-CoV recombinant receptor-binding domain (RBD219-N1) formulated with aluminum hydroxide induces protective immunity and reduces immune enhancement

Vaccine. 2020 Nov 3;38(47):7533-7541. doi: 10.1016/j.vaccine.2020.09.061. Epub 2020 Sep 22.


We developed a severe acute respiratory syndrome (SARS) subunit recombinant protein vaccine candidate based on a high-yielding, yeast-engineered, receptor-binding domain (RBD219-N1) of the SARS beta-coronavirus (SARS-CoV) spike (S) protein. When formulated with Alhydrogel®, RBD219-N1 induced high levels of neutralizing antibodies against both pseudotyped virus and a clinical (mouse-adapted) isolate of SARS-CoV. Here, we report that mice immunized with RBD219-N1/Alhydrogel® were fully protected from lethal SARS-CoV challenge (0% mortality), compared to ~30% mortality in mice immunized with the SARS S protein formulated with Alhydrogel®, and 100% mortality in negative controls. An RBD219-N1 formulation with Alhydrogel® was also superior to the S protein, unadjuvanted RBD, and AddaVax (MF59-like adjuvant)-formulated RBD in inducing specific antibodies and preventing cellular infiltrates in the lungs upon SARS-CoV challenge. Specifically, a formulation with a 1:25 ratio of RBD219-N1 to Alhydrogel® provided high neutralizing antibody titers, 100% protection with non-detectable viral loads with minimal or no eosinophilic pulmonary infiltrates. As a result, this vaccine formulation is under consideration for further development against SARS-CoV and potentially other emerging and re-emerging beta-CoVs such as SARS-CoV-2.

Keywords: Coronavirus; Eosinophil infiltration; Recombinant protein; Severe acute respiratory syndrome; Vaccine.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aluminum Hydroxide / administration & dosage
  • Animals
  • Antibodies, Neutralizing / immunology
  • Antibodies, Viral / immunology
  • Betacoronavirus / immunology*
  • COVID-19
  • COVID-19 Vaccines
  • Coronavirus Infections / immunology
  • Coronavirus Infections / prevention & control*
  • Female
  • Humans
  • Mice
  • Mice, Inbred BALB C
  • Pandemics / prevention & control*
  • Pneumonia, Viral / prevention & control*
  • Protein Domains / immunology
  • Recombinant Proteins / immunology
  • SARS-CoV-2
  • Severe Acute Respiratory Syndrome / prevention & control
  • Spike Glycoprotein, Coronavirus / genetics
  • Spike Glycoprotein, Coronavirus / immunology*
  • Vaccines, Subunit / immunology*
  • Vaccines, Synthetic / immunology*
  • Viral Load / immunology
  • Viral Vaccines / immunology*


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • COVID-19 Vaccines
  • Recombinant Proteins
  • Spike Glycoprotein, Coronavirus
  • Vaccines, Subunit
  • Vaccines, Synthetic
  • Viral Vaccines
  • Aluminum Hydroxide