Vaccine-induced systemic and mucosal T cell immunity to SARS-CoV-2 viral variants.

The first-generation COVID-19 vaccines have been effective in mitigating severe illness and hospitalization, but recurring waves of infections are associated with the emergence of SARS-CoV-2 variants that display progressive abilities to evade antibodies, leading to diminished vaccine effectiveness. The lack of clarity on the extent to which vaccine-elicited mucosal or systemic memory T cells protect against such antibody-evasive SARS-CoV-2 variants remains a critical knowledge gap in our quest for broadly protective vaccines. Using adjuvanted spike protein­based vaccines that elicit potent T cell responses, we assessed whether systemic or lung-resident CD4 and CD8 T cells protected against SARS-CoV-2 variants in the presence or absence of virus-neutralizing antibodies. We found that 1) mucosal or parenteral immunization led to effective viral control and protected against lung pathology with or without neutralizing antibodies, 2) protection afforded by mucosal memory CD8 T cells was largely redundant in the presence of antibodies that effectively neutralized the challenge virus, and 3) "unhelped" mucosal memory CD8 T cells provided no protection against the homologous SARS-CoV-2 without CD4 T cells and neutralizing antibodies. Significantly, however, in the absence of detectable virus-neutralizing antibodies, systemic or lung-resident memory CD4 and "helped" CD8 T cells provided effective protection against the relatively antibody-resistant B1.351 (ß) variant, without lung immunopathology. Thus, induction of systemic and mucosal memory T cells directed against conserved epitopes might be an effective strategy to protect against SARS-CoV-2 variants that evade neutralizing antibodies. Mechanistic insights from this work have significant implications in the development of T cell­targeted immunomodulation or broadly protective SARS-CoV-2 vaccines.

Immunogenicity and protective activity of mRNA vaccine candidates against yellow fever virus in animal models.

Despite the success of the widely used attenuated yellow fever (YF) vaccine, its global supply remains a substantial barrier to implementing vaccination campaigns in endemic regions and combating emerging epidemics. In A129 mice and rhesus macaques, we evaluated the immunogenicity and protective activity of messenger RNA (mRNA) vaccine candidates encapsulated in lipid nanoparticles, expressing the pre-membrane and envelope proteins or the non-structural protein 1 of YF virus. Vaccine constructs induced humoral and cell-mediated immune responses in mice, resulting in protection against lethal YF virus infection after passive administration of serum or splenocytes from vaccinated mice. Vaccination of macaques induced sustained high humoral and cellular immune responses for at least 5 months after the second dose. Our data demonstrate that these mRNA vaccine candidates can be considered an attractive addition to the licensed YF vaccine supply based on the induction of functional antibodies correlating with protection and T-cell responses; they could alleviate the limited supply of current YF vaccines, mitigating future YF epidemics.

Immunogenicity of poxvirus-based vaccines against Nipah virus.

Nipah virus (NiV), an emerging zoonotic pathogen in Southeast Asia, is transmitted from Pteropus species of fruit bats to a wide range of species, including humans, pigs, horses, dogs, and cats. NiV has killed millions of animals and caused highly fatal human outbreaks since no vaccine is commercially available. This study characterized the immunogenicity and safety of poxvirus-based Nipah vaccines that can be used in humans and species responsible for NiV transmission. Mice were vaccinated with modified vaccinia Ankara (MVA) and raccoon pox (RCN) viral vectors expressing the NiV fusion (F) and glycoprotein (G) proteins subcutaneously (SC) and intranasally (IN). Importantly, both vaccines did not induce significant weight loss or clinical signs of disease while generating high circulating neutralizing antibodies and lung-specific IgG and IgA responses. The MVA vaccine saw high phenotypic expression of effector and tissue resident memory CD8ɑ+ T cells in lungs and splenocytes along with the expression of central memory CD8ɑ+ T cells in lungs. The RCN vaccine generated effector memory (SC) and tissue resident (IN) CD8ɑ+ T cells in splenocytes and tissue resident (IN) CD8ɑ+ T cells in lung cells. These findings support MVA-FG and RCN-FG viral vectors as promising vaccine candidates to protect humans, domestic animals, and wildlife from fatal disease outcomes and to reduce the global threat of NiV.

mRNA Vaccine Protects against Zika Virus.

Zika virus (ZIKV), a mosquito-borne flavivirus, has recently triggered global concern due to severe health complications. In 2015, a large ZIKV outbreak occurred in the Americas and established a link between ZIKV and microcephaly in newborn babies, spontaneous abortion, persistent viremia, and Guillain-Barré syndrome. While antivirals are being developed and prevention strategies focus on vector control, a safe and effective Zika vaccine remains unavailable. Messenger RNA (mRNA) vaccine technology has arisen as a flexible, simplified, and fast vaccine production platform. Here, we report on an mRNA vaccine candidate that encodes the pre-membrane and envelope (prM-E) glycoproteins of ZIKV strain Brazil SPH2015 and is encapsulated in lipid nanoparticles (LNPs). Our ZIKV prM-E mRNA-LNP vaccine candidate induced antibody responses that protected in AG129 mice deficient in interferon (IFN) alpha/beta/gamma (IFN-α/ß/γ) receptors. Notably, a single administration of ZIKV prM-E mRNA-LNP protected against a lethal dose of ZIKV, while a two-dose strategy induced strong protective immunity. E-specific double-positive IFN-γ and TNF-α T-cells were induced in BALB/c mice after immunizations with a two-dose strategy. With the success of mRNA vaccine technology in facing the coronavirus (COVID-19) pandemic, our data support the development of prM-E RNActive® as a promising mRNA vaccine against Zika to counter future epidemics.

Neonatal Development in Prenatally Zika Virus-Exposed Infant Macaques with Dengue Immunity.

Infants exposed to Zika virus (ZIKV) prenatally may develop birth defects, developmental deficits, or remain asymptomatic. It is unclear why some infants are more affected than others, although enhancement of maternal ZIKV infection via immunity to an antigenically similar virus, dengue virus (DENV), may play a role. We hypothesized that DENV immunity may worsen prenatal ZIKV infection and developmental deficits in offspring. We utilized a translational macaque model to examine how maternal DENV immunity influences ZIKV-exposed infant macaque neurodevelopment in the first month of life. We inoculated eight macaques with prior DENV infection with ZIKV, five macaques with ZIKV, and four macaques with saline. DENV/ZIKV-exposed infants had significantly worse visual orientation skills than ZIKV-exposed infants whose mothers were DENV-naive, with no differences in motor, sensory or state control development. ZIKV infection characteristics and pregnancy outcomes did not individually differ between dams with and without DENV immunity, but when multiple factors were combined in a multivariate model, maternal DENV immunity combined with ZIKV infection characteristics and pregnancy parameters predicted select developmental outcomes. We demonstrate that maternal DENV immunity exacerbates visual orientation and tracking deficits in ZIKV-exposed infant macaques, suggesting that human studies should evaluate how maternal DENV immunity impacts long-term neurodevelopment.

Zika virus like particles elicit protective antibodies in mice.

Mosquito-borne Zika virus (ZIKV) typically causes a mild and self-limiting illness known as Zika fever. Since its recent emergence in 2014 in the American continent, ZIKV infection during pregnancy has been closely associated with a wide range of congenital abnormalities. To date, no vaccines or antivirals are publicly available. We developed Zika virus-like particles (VLPs) and evaluated their immunogenicity and protective efficacy in mouse models. ZIKV VLPs (ZIKVLPs) formulated with alum were injected into 6-8-week-old interferon deficient AG129 mice as well as wild type BALB/c mice. Control mice received PBS/alum. Animals were challenged with 200 PFU (>1000 AG129 LD50s) of ZIKV strain H/PF/2013. All vaccinated mice survived with no morbidity or weight loss while control animals either died at 9 days post challenge (AG129) or had increased viremia (BALB/c). Neutralizing antibodies were observed in all ZIKVLP vaccinated mice. The role of neutralizing antibodies in protecting mice was demonstrated by passive transfer. Our findings demonstrate the protective efficacy of the ZIKVLP vaccine and highlight the important role that neutralizing antibodies play in protection against ZIKV infection.