Nano-multilamellar lipid vesicles promote the induction of SARS-CoV-2 immune responses by a protein-based vaccine formulation.

The development of safe and effective vaccine formulations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents a hallmark in the history of vaccines. Here we report a COVID-19 subunit vaccine based on a SARS-CoV-2 Spike protein receptor binding domain (RBD) incorporated into nano-multilamellar vesicles (NMV) associated with monophosphoryl lipid A (MPLA). The results based on immunization of C57BL/6 mice demonstrated that recombinant antigen incorporation into NMVs improved antibody and T-cell responses without inducing toxic effects under both in vitro and in vivo conditions. Administration of RBD-NMV-MPLA formulations modulated antigen avidity and IgG subclass responses, whereas MPLA incorporation improved the activation of CD4+/CD8+ T-cell responses. In addition, immunization with the complete vaccine formulation reduced the number of doses required to achieve enhanced serum virus-neutralizing antibody titers. Overall, this study highlights NMV/MPLA technology, displaying the performance improvement of subunit vaccines against SARS-CoV-2, as well as other infectious diseases.

Reactivity of DENV-positive sera against recombinant envelope proteins produced in bacteria and eukaryotic cells.

Dengue is a mosquito-borne disease endemic in many tropical and subtropical countries. It is caused by the dengue virus (DENV) that can be classified into 4 different serotypes (DENV-1-4). Early diagnosis and management can reduce morbidity and mortality rates of severe forms of the disease, as well as decrease the risk of larger outbreaks. Hiperendemicity in some regions of the world and the possibility that some people develop a more severe form of disease after a secondary infection caused by antibody-dependent enhancement justify the need to understand more thoroughly the antibody response induced against the virus. Here, we successfully produced a recombinant DENV-2 envelope (E) protein and its domains (EDI/II and EDIII) in two distinct expression systems: the Drosophila S2 insect cell system and the BL21 (DE3) pLySs bacterial system. We then evaluated the reactivity of sera from patients previously infected with DENV to each recombinant protein and to each domain separately. Our results show that the E protein produced in Drosophila S2 cells is recognized more frequently than the protein produced in bacteria. However, the recognition of E protein produced in bacteria correlates better with the DENV-2 sera neutralization capacity. The results described here emphasize the differences observed when antigens produced in bacteria or eukaryotic cells are used and may be useful to gain more insight into the humoral immune responses induced by dengue infection.

STAT6 signaling pathway controls germinal center responses promoted after antigen targeting to conventional type 2 dendritic cells.

Conventional dendritic cells (cDCs) are antigen-presenting cells specialized in naïve T cell priming. Mice splenic cDCs are classified as cDC1s and cDC2s, and their main functions have been elucidated in the last decade. While cDC1s are specialized in priming type 1 helper T cells (TH1) and in cross presentation, cDC2s prime T follicular helper (TFH) cells that stimulate germinal center (GC) formation, plasma cell differentiation and antibody production. However, less is known about the molecular mechanisms used by cDCs to prime those responses. Here, using WT and STAT6-deficient mice (STAT6 KO), we targeted a model antigen to cDC1s and cDC2s via DEC205 and DCIR2 receptors, respectively, in an attempt to study whether the STAT6 signaling pathway would modulate cDCs' ability to prime helper T cells. We show that the differentiation and maturation of cDCs, after stimulation with an adjuvant, were comparable between WT and STAT6 KO mice. Besides, our results indicate that, in STAT6 KO mice, antigen targeting to cDC2s induced reduced TFH and GC responses, but did not alter plasma cells numbers and antibody titers. Thus, we conclude that the STAT6 signaling pathway modulates the immune response after antigen targeting to cDC2s via the DCIR2 receptor: while STAT6 stimulates the development of TFH cells and GC formation, plasma cell differentiation occurs in a STAT6 independent manner.

Early dengue virus interactions: the role of dendritic cells during infection.

Dengue is an acute infectious disease caused by dengue virus (DENV) that affects approximately 400 million people annually, being the most prevalent human arthropod-borne disease. DENV infection causes a wide variety of clinical manifestations that range from asymptomatic to dengue fever, and in some cases may evolve to the more severe dengue hemorrhagic fever and dengue shock syndrome. The exact reasons why some patients do not have symptoms while others develop the severe forms of disease are still elusive, but gathered evidence showed correlation between a secondary infection with a heterologous DENV serotype and the occurrence of severe symptoms. Despite several advances, the mechanisms of DENV infection are still not completely elucidated, and efforts have been made to understand the development of immunity and/or pathology to DENV. When a mosquito transmits DENV, the virus is initially deposited in the skin, where mononuclear phagocytic cells, such as dendritic cells (DCs), become infected. DCs play a critical role in the induction of immune responses, as they are able to rapidly detect pathogen-associated molecular patterns, endocytose and process antigens, and efficiently activate naïve-T and B cells. Recent findings have shown that DCs serve as DENV targets, but they are also important mediators of immunity against the virus. In this review, we will briefly discuss DENV infection pathogenesis, and introduce DCs as central players in the induction of anti-DENV immune responses. Then, we will review in more detail how DENV interacts with and is sensed by DCs, with particular emphasis in two classes of receptors implicated in viral entry.