Evaluate Glycoprotein Complexes-Elicited Antibody Responses to Inform Congenital Cytomegalovirus Vaccine Design.

Abstract

Human CMV (HCMV), a ubiquitous β-herpesvirus, remains the most common congenital infection and infectious complication in immunocompromised patients. Despite the severe clinical impacts, there is no current approved HCMV vaccine or immunotherapy. Two major hurdles have been identified for the HCMV vaccine development. First, the HCMV genome is highly diverse and variable, i.e., a HCMV vaccine design that only includes immunogens from a single strain might not provide effective protection against other HCMV strains. Second, a large gap remains to understand what virologic determinants are essential for congenital CMV transmission.HCMV glycoprotein B (gB) and pentameric glycoprotein complex (PC) are currently the most promising vaccine targets. gB is essential for viral entry into all host cells and was shown to elicit both neutralizing and non-nAb responses. The most successful HCMV vaccine to-date, a gB subunit vaccine adjuvanted with MF59, achieved 50% efficacy against primary HCMV infection. The gB/MF59 vaccinees were less frequently infected with HCMV gB genotype strains most similar to the vaccine strain than strains encoding genetically distinct gB genotypes, suggests that the strain-specific immunity might account for the limited efficacy. Applying the lipid nanoparticles-encapsulated nucleoside-modified mRNA (mRNA-LNP) vaccine platform, we hypothesized that vaccination with multiple HCMV gB genotypes could increase the breadth of gB-specific humoral and cellular responses, leading to broader protection.To test our hypothesis, we intradermally immunized female rabbits with three doses of the monovalent or multivalent gB mRNA-LNP vaccines and measured the vaccine-elicited humoral and cellular responses. Compared to the monovalent vaccine, the multivalent vaccines did not demonstrate a higher magnitude or breadth of gB-specific IgG binding or functional antibody responses against multiple gB genotype. In addition, the multivalent vaccines did not elicit a stronger T cell response against variable regions among gB genotypes. Our data suggests that inclusion of multivalent gB antigens is not an effective strategy to increase the breadth of anti-HCMV gB antibody and T cell responses. PC, composed of the subunits gH/gL/UL128/UL130/UL131A, has been demonstrated to be essential for CMV entry into non-fibroblast cells in vitro. The PC was also identified as the major target of neutralizing antibodies. As HCMV infection of most cell types found near the maternal-fetal interface depends on the PC-mediated entry in vitro, it is conceivable that this complex could be required for cross-placental CMV transmission in vivo. These findings link the PC to broad cell tropism and virus dissemination in vivo, denoting all subunits as potential targets for intervention strategies and vaccine development.To determine the importance of the PC for congenital transmission in a translational non-human primate (NHP) model, we engineered a rhesus CMV (RhCMV) mutant lacking the homologues of UL128 and UL130 which demonstrated diminished infection of epithelial cell in vitro. Nevertheless, intravenous inoculation of immunocompetent and CD4+ T cell-depleted, RhCMV-seronegative, pregnant rhesus macaques with the PC-deficient mutant resulted in similar maternal RhCMV peak plasma viremia levels to that of PC-intact RhCMV, while virus shedding in saliva and urine was limited. Infections with the PC-intact virus induced strong IgG responses that were able to neutralize RhCMV entry into epithelial cells. These responses were reduced, but not absent, from animals infected with the PC-deficient mutant, which also induced IgG responses against gH. Most importantly, congenital infection rates determined by the viral DNA detection in amniotic fluid was identical between the PC-deficient and PC-intact RhCMV. Our data indicates that the PC is dispensable for transplacental transmission in non-human primates.