Comparisons of Antibody Populations in Different Pre-Fusion F VLP-Immunized Cotton Rat Dams and Their Offspring

Abstract

Respiratory syncytial virus (RSV) infection poses a significant risk for infants. Since the direct vaccination of infants is problematic, maternal vaccination may provide a safer, more effective approach to their protection. In the cotton rat (CR) model, we have compared the immunization of pregnant CR dams with virus-like particles assembled with the prototype mutation stabilized pre-fusion F protein, DS-Cav1, as well two alternative mutation stabilized pre-fusion proteins (UC-2 F, UC-3 F) and showed that the alternative pre-fusion F VLPs protected the offspring of immunized dams significantly better than DS-Cav1 F VLPs (Blanco, et al. J. Virol. 93: e00914). Here, we have addressed the reasons for this increased protection by characterizing the specificities of antibodies in the sera of both immunized dams and their offspring. The approach was to measure the levels of total anti-pre-F IgG serum antibodies that would block the binding of representative pre-fusion specific monoclonal antibodies to soluble pre-fusion F protein targets. Strikingly, we found that the sera in most offspring of DS-Cav1 F VLP-immunized dams had no mAb D25-blocking antibodies, although their dams had robust levels. In contrast, all offspring of UC-3 F VLP-immunized dams had robust levels of these D25-blocking antibodies. Both sets of pup sera had significant levels of mAb AM14-blocking antibodies, indicating that all pups received maternal antibodies. A lack of mAb D25-blocking antibodies in the offspring of DS-Cav1 F VLP-immunized dams may account for the lower protection of their pups from challenge compared to the offspring of UC-3 F VLP-immunized dams.Vaccines 2020, 8, 133 2 of 15 to infectious, attenuated, or vector viruses, since they do not contain a genome and do not produce a spreading infection. Our VLPs are based on the core proteins of Newcastle disease virus (NDV), NP and M proteins, and they are assembled with the RSV F and G protein ectodomains fused to the transmembane and cytoplasmic domains of the NDV F and HN proteins, respectively.There has been a resurgence of interest and activity in RSV vaccine development due to the ground-breaking studies of McLellan, et al. who succeeded in solving the crystal structure of the RSV pre-fusion F protein and identifying a set of mutations in the F protein, termed DS-Cav1, which stabilized the pre-fusion form of the F protein [20,21]. We have reported that VLPs assembled with the DS-Cav1 mutant F protein stimulate, in mice and in cotton rats, neutralizing antibody titers much higher than those induced by VLPs assembled with the post-fusion F protein or wild-type F protein [16,22]. Furthermore, the immunization of cotton rat dams with DS-Cav1 F VLPs protected their offspring from RSV challenge [14].Since the description of DS-Cav1 F protein, a number of other laboratories and companies have identified different sets of mutations that reportedly stabilize the pre-fusion F protein [23][24][25][26][27][28][29]. A very important question for vaccine development is whether the different m...

Evolution of protection after maternal immunization for respiratory syncytial virus in cotton rats

“…In these studies, we have used RSV-primed animals since most if not all normal human populations have been previously infected with RSV. We have reported that immunization of RSVprimed dams during pregnancy with pre-F VLPs resulted in robust protection of offspring from RSV challenge with no evidence of pathology [29][30][31]. Here we describe the durability of these protective responses in dams after a single immunization and compare the degree of protection these dams can transfer to their offspring in two consecutive litters.…”

“…McLellan et al identified mutations in the RSV F protein (DS-Cav1 mutant) that stabilize the pre-fusion conformation, and this prototype pre-fusion F protein is now widely used in many vaccine candidates in different stages of development [5]. Subsequently, others have reported different F protein mutations that are stabilizing [28], one of which, UC-3 F, induces higher neutralizing antibody (NAb) titers than the widely-used form, DS-Cav1 F [28,29]. We have assembled VLPs containing the DS-Cav1 or the UC-3 F pre-fusion RSV F proteins along with the RSV G attachment protein and have established UC-3 F VLP superiority over DS-Cav1 F as well as post-F protein, or wildtype F protein containing VLPs in inducing NAbs in both mice and cotton rats [28,30].…”

The Respiratory Syncytial Virus G Protein Enhances the Immune Responses to the RSV F Protein in an Enveloped Virus-like Particle Vaccine Candidate

“…The copyright holder for this preprint this version posted September 13, 2022. ; https://doi.org/10.1101/2022.09.12.507712 doi: bioRxiv preprint and G protein ectodomains fused to the transmembrane and cytoplasmic domains of the NDV F and HN, respectively, for efficient assembly into the VLPs (19)(20)(21)(22). We have shown that these VLPs induce both anti-RSV F and anti-RSV G antibodies and good protective responses in the cotton rat model commonly used in RSV studies (19)(20)(21)(22)(23).…”

Evolution of protection after maternal immunization for respiratory syncytial virus in cotton rats

“…In these studies, we have used RSV-primed animals in order to mimic normal human populations, most of which have been previously infected with RSV. We have reported that immunization of RSV-primed dams during pregnancy with pre-F VLPs resulted in robust protection of offspring from RSV challenge with no evidence of pathology (29)(30)(31). Here we describe the durability of these protective responses in dams after a single immunization and compare the degree of protection these dams can transfer to their offspring in two consecutive litters.…”