Sequential immunization of llamas with SARS-CoV and MERS-CoV S proteins resulted in identification of VHH-72, VHH-1, and VHH-6, all of which show high binding affinity for the SARS-CoV S protein; VHH-72 and another nanobody, VHH-44, show neutralizing activity against pseudotyped SARS-CoV infection (IC50: 9 and 355 nM, respectively) [114]. This evidence concerns the gene PROS1 and severe acute respiratory syndrome.