Zika purified inactivated virus (ZPIV) vaccine reduced vertical transmission in pregnant immunocompetent mice.

Zika virus (ZIKV) is a significant threat to pregnant women and their fetuses as it can cause severe birth defects and congenital neurodevelopmental disorders, referred to as congenital Zika syndrome (CZS). Thus, a safe and effective ZIKV vaccine for pregnant women to prevent in utero ZIKV infection is of utmost importance. Murine models of ZIKV infection are limited by the fact that immunocompetent mice are resistant to ZIKV infection. As such, interferon-deficient mice have been used in some preclinical studies to test the efficacy of ZIKV vaccine candidates against lethal virus challenge. However, interferon-deficient mouse models have limitations in assessing the immunogenicity of vaccines, necessitating the use of immunocompetent mouse pregnancy models. Using the human stat2 knock-in (hSTAT2KI) mouse pregnancy model, we show that vaccination with a purified formalin-inactivated Zika virus (ZPIV) vaccine prior to pregnancy successfully prevented vertical transmission. In addition, maternal immunity protected offspring against postnatal challenge for up to 28 days. Furthermore, passive transfer of human IgG purified from hyper-immune sera of ZPIV vaccinees prevented maternal and fetal ZIKV infection, providing strong evidence that the neutralizing antibody response may serve as a meaningful correlate of protection.

Protective efficacy of a Zika purified inactivated virus vaccine candidate during pregnancy in marmosets.

Zika virus (ZIKV) infection during pregnancy poses significant threats to maternal and fetal health, leading to intrauterine fetal demise and severe developmental malformations that constitute congenital Zika syndrome (CZS). As such, the development of a safe and effective ZIKV vaccine is a critical public health priority. However, the safety and efficacy of such a vaccine during pregnancy remain uncertain. Historically, the conduct of clinical trials in pregnant women has been challenging. Therefore, clinically relevant animal pregnancy models are in high demand for testing vaccine efficacy. We previously reported that a marmoset pregnancy model of ZIKV infection consistently demonstrated vertical transmission from mother to fetus during pregnancy. Using this marmoset model, we also showed that vertical transmission could be prevented by pre-pregnancy vaccination with Zika purified inactivated virus (ZPIV) vaccine. Here, we further examined the efficacy of ZPIV vaccination during pregnancy. Vaccination during pregnancy elicited virus neutralizing antibody responses that were comparable to those elicited by pre-pregnancy vaccination. Vaccination also reduced placental pathology, viral burden and vertical transmission of ZIKV during pregnancy, without causing adverse effects. These results provide key insights into the safety and efficacy of ZPIV vaccination during pregnancy and demonstrate positive effects of vaccination on the reduction of ZIKV infection, an important advance in preparedness for future ZIKV outbreaks.

Impact of prior dengue virus infection on Zika virus infection during pregnancy in marmosets.

Zika virus (ZIKV) infection during pregnancy causes severe developmental defects in newborns, termed congenital Zika syndrome (CZS). Factors contributing to a surge in ZIKV-associated CZS are poorly understood. One possibility is that ZIKV may exploit the antibody-dependent enhancement of infection mechanism, mediated by cross-reactive antibodies from prior dengue virus (DENV) infection, which may exacerbate ZIKV infection during pregnancy. In this study, we investigated the impact of prior DENV infection or no DENV infection on ZIKV pathogenesis during pregnancy in a total of four female common marmosets with five or six fetuses per group. The results showed that negative-sense viral RNA copies increased in the placental and fetal tissues of DENV-immune dams but not in DENV-naïve dams. In addition, viral proteins were prevalent in endothelial cells, macrophages, and neonatal Fc receptor-expressing cells in the placental trabeculae and in neuronal cells in the brains of fetuses from DENV-immune dams. DENV-immune marmosets maintained high titers of cross-reactive ZIKV-binding antibodies that were poorly neutralizing, raising the possibility that these antibodies might be involved in the exacerbation of ZIKV infection. These findings need to be verified in a larger study, and the mechanism involved in the exacerbation of ZIKV infection in DENV-immune marmosets needs further investigation. However, the results suggest a potential negative impact of preexisting DENV immunity on subsequent ZIKV infection during pregnancy in vivo.

Efficacy of an inactivated Zika vaccine against virus infection during pregnancy in mice and marmosets.

Zika virus (ZIKV) is a mosquito-borne arbovirus that can cause severe congenital birth defects. The utmost goal of ZIKV vaccines is to prevent both maternal-fetal infection and congenital Zika syndrome. A Zika purified inactivated virus (ZPIV) was previously shown to be protective in non-pregnant mice and rhesus macaques. In this study, we further examined the efficacy of ZPIV against ZIKV infection during pregnancy in immunocompetent C57BL6 mice and common marmoset monkeys (Callithrix jacchus). We showed that, in C57BL/6 mice, ZPIV significantly reduced ZIKV-induced fetal malformations. Protection of fetuses was positively correlated with virus-neutralizing antibody levels. In marmosets, the vaccine prevented vertical transmission of ZIKV and elicited neutralizing antibodies that remained above a previously determined threshold of protection for up to 18 months. These proof-of-concept studies demonstrate ZPIV's protective efficacy is both potent and durable and has the potential to prevent the harmful consequence of ZIKV infection during pregnancy.

Adoptive transfer of tumor-specific Tc17 effector T cells controls the growth of B16 melanoma in mice.

In vitro generated OVA-specific IL-17-producing CD8 T effector cells (Tc17) from OT-1 mice, adoptively transferred into B16-OVA tumor-bearing mice, controlled tumor growth in early and late stage melanoma. IL-17, TNF, and IFN-gamma from the Tc17 effectors all played a role in an enhanced recruitment of T cells, neutrophils, and macrophages to the tumor. In addition, Tc17 cells and recently recruited, activated neutrophils produced further chemokines, including CCL3, CCL4, CCL5, CXCL9, and CXCL10, responsible for the attraction of type 1 lymphocytes (Th1 and Tc1) and additional neutrophils. Neutrophils were rapidly attracted to the tumor site by an IL-17 dependent mechanism, but at later stages the induction of the chemokine CXCL2 by Tc17-derived TNF and IFN-gamma contributed to sustain neutrophil recruitment. Approximately 10-50 times as many Tc17 effectors were required compared with Tc1 effectors to exert the same level of control over tumor growth. The recruitment of neutrophils was more prominent when Tc17 rather than Tc1 were used to control tumor and depletion of neutrophils resulted in a diminished capacity to control tumor growth.

Persistence and responsiveness of immunologic memory in the absence of secondary lymphoid organs.

Secondary lymphoid organs (SLOs) promote primary immune responses by recruiting naive lymphocytes and activated APCs. However, their role in the persistence or responsiveness of memory lymphocytes is unclear. We tested whether memory cells were maintained and could respond to challenge in the absence of SLOs. We found that influenza-specific CD8 cells in the lung acquired a memory phenotype, underwent homeostatic proliferation, recirculated through nonlymphoid tissues, and responded to and cleared a challenge infection in the complete absence of SLOs. Similarly, influenza-specific virus-neutralizing antibody was generated and maintained in the absence of SLOs. Inducible bronchus-associated lymphoid tissue (iBALT) was also formed in the lungs of previously infected mice and may provide a niche for the maintenance of memory cells at the local level. These data show that SLOs are dispensable for the maintenance of immunologic memory and directly demonstrate the utility of local tissues, such as iBALT, in secondary immune responses.

Upper respiratory tract resistance to influenza infection is not prevented by the absence of either nasal-associated lymphoid tissue or cervical lymph nodes.

The murine nasal-associated lymphoid tissue (NALT) and cervical lymph nodes (CLN) are involved in the generation of local immune responses within the upper respiratory tract (URT). However, their involvement in these responses does not imply the necessity for resistance to URT infections. We surgically removed NALT or CLN to address the necessity of these lymphatic tissues for the development of a local protective immune response after a URT influenza infection. No histological evidence of the re-establishment of either tissue was detected after surgery and the subsequent infection. Removal of NALT did not elicit changes in serum or nasal mucosa-associated influenza-specific Ig levels. However, increases in PR8-specific serum IgG and nasal mucosa-associated IgA were detected after removal of CLN. Recruitment of influenza-specific CD4 T cells into the nasal mucosa was not altered by removal of NALT. The removal of NALT or CLN did not alter the recruitment of influenza-specific CD8 T cells into the URT. However, increased levels of influenza-specific CD8 T cells were observed in the tracheal-bronchial lymph nodes after CLN surgery. The rate of viral clearance from nasal mucosa and lungs was not altered by removal of NALT or CLN. These studies demonstrate that despite the participation of NALT and CLN in the generation of local immunity to influenza infections, neither tissue is essential for the development of protective immunity and viral clearance in URT.