Next generation designer virus-like particle vaccines for dengue

Endemic or regionally limited bacterial and viral infections in haematopoietic stem-cell transplantation recipients: a Worldwide Network for Blood and Marrow Transplantation (WBMT) Review

Literature discussing endemic and regionally limited infections in recipients of haematopoietic stem-cell transplantation (HSCT) outside western Europe and North America is scarce. This Worldwide Network for Blood and Marrow Transplantation (WBMT) article is part one of two papers aiming to provide guidance to transplantation centres around the globe regarding infection prevention and treatment, and considerations for transplantation based on current evidence and expert opinion. These recommendations were initially formulated by a core writing team from the WBMT and subsequently underwent multiple revisions by infectious disease experts and HSCT experts. In this paper, we summarise the data and provide recommendations on several endemic and regionally limited viral and bacterial infections, many of which are listed by WHO as neglected tropical diseases, including Dengue, Zika, yellow fever, chikungunya, rabies, brucellosis, melioidosis, and leptospirosis.

Cellular T-cell immune response profiling by tetravalent dengue subunit vaccine (DSV4) candidate in mice

While most vaccines aim to develop a solid humoral and neutralizing antibody response against the pathogen, an effective vaccine candidate should be able to stimulate both the B-cell mediated humoral immunity, and T-cell mediated cellular immunity. The focus of vaccinology is rapidly gaining to generate T cell responses, which can mediate pathogen clearance and help B cells leading to protective antibody responses. Here we evaluate the cellular immune response of the pre-clinical tetravalent dengue subunit vaccine candidate, DSV4, in mice. While we have shown previously that DSV4 induces type-specific neutralizing antibody responses in mice, in this study, we show that the vaccine candidate DSV4 well induces dengue-specific T- cell responses evaluated by their ability to produce IFN-γ. In addition to IFN-γ secretion by both CD4+ and CD8+ T-cells in immunized mice, we observed that DSV4 also induces a higher frequency and cytokine functions of follicular CD4+ helper T-cells (T_FH). These cytokines lead to an efficient germinal center reaction and potent B cell antibody response. Apart from T_FH response, DSV4 stimulated Type 1 T helper cells (T_H1) which is characteristic of a viral infection leading to secretion of pro-inflammatory cytokines and phagocyte-dependent protective immune responses. Our study highlights that DSV4 can mediate both arms of adaptive immunity-humoral and cell-mediated immunity in mice. By elucidating vaccine-specific T cell response, our work has implications in showing DSV4 as an effective, type-specific and safe dengue vaccine candidate.

Subdominance in Antibody Responses: Implications for Vaccine Development

Vaccines work primarily by eliciting antibodies, even when recovery from natural infection depends on cellular immunity. Large efforts have therefore been made to identify microbial antigens that elicit protective antibodies, but these endeavors have encountered major difficulties, as witnessed by the lack of vaccines against many pathogens. This review summarizes accumulating evidence that subdominant protein regions, i.e., surface-exposed regions that elicit relatively weak antibody responses, are of particular interest for vaccine development. This concept may seem counterintuitive, but subdominance may represent an immune evasion mechanism, implying that the corresponding region potentially is a key target for protective immunity. Following a presentation of the concepts of immunodominance and subdominance, the review will present work on subdominant regions in several major human pathogens: the protozoan Plasmodium falciparum, two species of pathogenic streptococci, and the dengue and influenza viruses. Later sections are devoted to the molecular basis of subdominance, its potential role in immune evasion, and general implications for vaccine development. Special emphasis will be placed on the fact that a whole surface-exposed protein domain can be subdominant, as demonstrated for all of the pathogens described here. Overall, the available data indicate that subdominant protein regions are of much interest for vaccine development, not least in bacterial and protozoal systems, for which antibody subdominance remains largely unexplored.

Antibody-Dependent Enhancement: A Challenge for Developing a Safe Dengue Vaccine

In 2019, the United States Food and Drug Administration accorded restricted approval to Sanofi Pasteur's Dengvaxia, a live attenuated vaccine (LAV) for dengue fever, a mosquito-borne viral disease, caused by four antigenically distinct dengue virus serotypes (DENV 1-4). The reason for this limited approval is the concern that this vaccine sensitized some of the dengue-naïve recipients to severe dengue fever. Recent knowledge about the nature of the immune response elicited by DENV viruses suggests that all LAVs have inherent capacity to predominantly elicit antibodies (Abs) against the pre-membrane (prM) and fusion loop epitope (FLE) of DENV. These antibodies are generally cross-reactive among DENV serotypes carrying a higher risk of promoting Antibody-Dependent Enhancement (ADE). ADE is a phenomenon in which suboptimal neutralizing or non-neutralizing cross-reactive antibodies bind to virus and facilitate Fcγ receptor mediated enhanced entry into host cells, followed by its replication, and thus increasing the cellular viral load. On the other hand, antibody responses directed against the host-cell receptor binding domain of DENV envelope domain-III (EDIII), exhibit a higher degree of type-specificity with lower potential of ADE. The challenges associated with whole DENV-based vaccine strategies necessitate re-focusing our attention toward the designed dengue vaccine candidates, capable of inducing predominantly type-specific immune responses. If the designed vaccines elicited predominantly EDIII-directed serotype specific antibodies in the absence of prM and FLE antibodies, this could avoid the ADE phenomenon largely associated with the prM and FLE antibodies. The generation of type-specific antibodies to each of the four DENV serotypes by the designed vaccines could avoid the immune evasion mechanisms of DENVs. For the enhanced vaccine safety, all dengue vaccine candidates should be assessed for the extent of type-specific (minimal ADE) vs. cross-reactive (ADE promoting) neutralizing antibodies. The type-specific EDIII antibodies may be more directly related to protection from disease in the absence of ADE promoted by the cross-reactive antibodies.

Recent Advances in the Development of Virus-Like Particle-Based Flavivirus Vaccines

Flaviviruses include several medically important viruses, such as Zika virus (ZIKV), Dengue virus (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV). They have expanded in geographic distribution and refocused international attention in recent years. Vaccination is one of the most effective public health strategies for combating flavivirus infections. In this review, we summarized virus-like particle (VLP)-based vaccines against the above four mentioned flaviviruses. Potential strategies to improve the efficacy of VLP-based flavivirus vaccines were also illustrated. The applications of flavivirus VLPs as tools for viral detection and antiviral drug screening were finally proposed.

The Interplay between Dengue Virus and the Human Innate Immune System: A Game of Hide and Seek

With 40% of the world population at risk, infections with dengue virus (DENV) constitute a serious threat to public health. While there is no antiviral therapy available against this potentially lethal disease, the efficacy of the only approved vaccine is not optimal and its safety has been recently questioned. In order to develop better vaccines based on attenuated and/or chimeric viruses, one must consider how the human immune system is engaged during DENV infection. The activation of the innate immunity through the detection of viruses by cellular sensors is the first line of defence against those pathogens. This triggers a cascade of events which establishes an antiviral state at the cell level and leads to a global immunological response. However, DENV has evolved to interfere with the innate immune signalling at multiple levels, hence dampening antiviral responses and favouring viral replication and dissemination. This review elaborates on the interplay between DENV and the innate immune system. A special focus is given on the viral countermeasure mechanisms reported over the last decade which should be taken into consideration during vaccine development.