Matrix-M adjuvant enhances antibody, cellular and protective immune responses of a Zaire Ebola/Makona virus glycoprotein (GP) nanoparticle vaccine in mice

Abstract

Ebola virus (EBOV) causes severe hemorrhagic fever for which there is no approved treatment or preventive vaccine. Immunological correlates of protective immunity against EBOV disease are not well understood. However, non-human primate studies have associated protection of experimental vaccines with binding and neutralizing antibodies to the EBOV glycoprotein (GP) as well as EBOV GP-specific CD4(+) and CD8(+) T cells. In this report a full length, unmodified Zaire EBOV GP gene from the 2014 EBOV Makona strain (EBOV/Mak) was cloned into a baculovirus vector. Recombinant EBOV/Mak GP was produced in Sf9 insect cells as glycosylated trimers and, when purified, formed spherical 30-40 nm particles. In mice, EBOV/Mak GP co-administered with the saponin adjuvant Matrix-M was significantly more immunogenic, as measured by virus neutralization titers and anti-EBOV/Mak GP IgG as compared to immunization with AlPO4 adjuvanted or non-adjuvanted EBOV/Mak GP. Similarly, antigen specific T cells secreting IFN-γ were induced most prominently by EBOV/Mak GP with Matrix-M. Matrix-M also enhanced the frequency of antigen-specific germinal center B cells and follicular helper T (TFH) cells in the spleen in a dose-dependent manner. Immunization with EBOV/Mak GP with Matrix-M was 100% protective in a lethal viral challenge murine model; whereas no protection was observed with the AlPO4 adjuvant and only 10% (1/10) mice were protected in the EBOV/Mak GP antigen alone group. Matrix-M adjuvanted vaccine induced a rapid onset of specific IgG and neutralizing antibodies, increased frequency of multifunctional CD4+ and CD8(+) T cells, specific TFH cells, germinal center B cells, and persistence of EBOV GP-specific plasma B cells in the bone marrow. Taken together, the addition of Matrix-M adjuvant to the EBOV/Mak GP nanoparticles enhanced both B and T-cell immune stimulation which may be critical for an Ebola subunit vaccine with broad and long lasting protective immunity.

Safety and immunogenicity of GamEvac-Combi, a heterologous VSV- and Ad5-vectored Ebola vaccine: An open phase I/II trial in healthy adults in Russia

“…Notably, clinical trials of VSV-based vaccine 16-17 showed that immunization with GP Kikwit led to production not only Kikwit GP-specific antibodies, but also Mayinga GP and Makona/Gueckedou GP (2014). Animal studies of EBOV-GP nanoparticles showed that mice immunized with GP Makona produced NtAb to ZEBOV Mayinga and were protected from lethal dose of ZEBOV Mayinga 18 . All these data suggest that there is cross-protection from the immune responses to Makona/Gueckedou, Mayinga, and Kikwit.…”

T-cell-dependent mechanisms promote Ebola VLP-induced antibody responses, but are dispensable for vaccine-mediated protection

“…19, 20 The production of high-affinity class-switched antibodies is dependent on germinal center (GC) formation; 26, 33 however, limited characterization of this B-cell compartment has been reported for vaccine platforms that were developed against EBOV. 28 Therefore, we examined if VLP vaccination resulted in the generation of GC reactions and if poly-ICLC would impact these responses. Mice were vaccinated with VLP (intramuscularly) in the presence or absence of poly-ICLC using a prime-boost schedule at three-week intervals (day 0, day 21).…”

“…23, 24, 45 However, little is known about the early EBOV B-cell initiating events that are required for the establishment of these responses. 28 …”

“…26, 27 However, in vivo studies that define how EBOV B-cell immunity is established, the relative contributions of TI and TD B-cell mechanisms and the direct requirement for B-cell responses to protect against EBOV infection have been limited to date. 17, 28 …”

Innate immune responses induced by the saponin adjuvant Matrix-M in specific pathogen free pigs

“…Immunization experiments using Matrix-M as adjuvant reveal an antigen specific immune response characterized by long-lasting antibody production, a balanced T H 1/T H 2 cytokine profile and induction of cytotoxic T cells [7–9]. These adjuvant properties of Matrix-M also seem to increase the otherwise poor immunogenicity of Ebola virus glycoproteins [10]. …”