The different forms of RSV protein expressed by the modified mRNA vaccines evaluated in this study are shown. wtRSV (mF) expresses the full length RSV F protein from the RSV A2 strain. The locations of the signal peptide (SP), p27 peptide (p27), fusion peptide (FP), heptad repeat A (HRA), heptad repeat B (HRB), and transmembrane peptide (TM) are shown. For each construct, arrows indicated proteolytic cleavage sites that remain in the expressed protein. Deleted amino acid sequences are indicated with a horizontal line replacing the bar. Point mutations added to stabilize the prefusion conformation of the antigen are indicated with a solid circle (•) and the identity of the amino acid change is indicated below the circle. The newly generated disulfide bonds formed in the DS-Cav1-based constructs is indicated with a bracket. Secreted constructs in which the transmembrane domain and cytoplasmic sequence are deleted and replaced with a foldon or GCN4 peptide sequence to support trimerization are indicated with a gray or black-filled bar, respectively.