Successive Immunization With Epitope-Decreasing Dengue Antigens Induced Conservative Anti-Dengue Immune Responses.

Repeated homologous antigen immunization has been hypothesized to hinder antibody diversification, whereas sequential immunization with heterologous immunogens can educate B cell differentiations towards conserved residues thereby facilitating the generation of cross-reactive immunity. In this study, we developed a sequential vaccination strategy that utilized epitope-decreasing antigens to reinforce the cross-reactivity of T and B cell immune responses against all four serotypes dengue virus. The epitope-decreasing immunization was implemented by sequentially inoculating mice with antigens of decreasing domain complexity that first immunized with DENV1 live-attenuated virus, following by the Envelope protein (Env), and then Env domain III (EDIII) subunit protein. When compared to mice immunized with DENV1 live-attenuated virus three times, epitope-decreasing immunization induced higher TNF-α CD8+ T cell immune response against consensus epitopes. Epitope-decreasing immunization also significantly improved neutralizing antibody response to heterologous serotypes. Moreover, this sequential approach promoted somatic hypermutations in the immunoglobulin gene of antigen-specific memory B cells in comparison to repeated immunization. This proof-of-concept work on epitope-decreasing sequential vaccination sheds light on how successively exposing the immune system to decreasing-epitope antigens can better induce cross-reactive antibodies.

Microfluidic label-free bioprocessing of human reticulocytes from erythroid culture.

In vitro erythroid cultures from human hematopoietic stem cells produce immature red blood cells (RBCs) called reticulocytes, which are important for RBCs production, and are widely used in scientific studies of malaria pathology, hematological diseases and protein translation. However, in vitro reticulocyte cultures contain expelled cell nuclei and erythroblasts as undesirable by-products and current purification methods such as density gradient centrifugation and fluorescence-activated cell sorting (FACS) are not optimal for integrated bioprocessing and downstream therapeutic applications. Developments in Dean flow fractionation (DFF) and deterministic lateral displacement (DLD) microfluidic sorting methods are ideal alternatives due to label-free size sorting, throughput scalability and low manufacturing cost. DFF sorting of reticulocytes from whole erythroid culture showed a 2.4-fold increase in cell recovery compared to FACS albeit with a lower purity; DLD sorting showed comparable cell recovery and purity with FACS using an inverse-L pillar structure to emphasize size and deformability sorting of reticulocytes. The viability and functional assurance of purified reticulocytes showed conserved cell deformability and supported the propagation of malaria parasites. Collectively, our study on label-free RBCs isolation represents a significant technical advancement towards developing in vitro generated viable human RBCs, opening opportunities for close-loop cell manufacturing, downstream therapeutic and research purposes.

Sequential immunization induces strong and broad immunity against all four dengue virus serotypes.

A major challenge in dengue vaccine development is the need to induce immunity against four dengue (DENV) serotypes. Dengvaxia®, the only licensed dengue vaccine, consists of four variant dengue antigens, one for each serotype. Three doses of immunization with the tetravalent vaccine induced only suboptimal protection against DENV1 and DENV2. Furthermore, vaccination paradoxically and adversely primes dengue naïve subjects to more severe dengue. Here, we have tested whether sequential immunization induces stronger and broader immunity against four DENV serotypes than tetravalent-formulated immunization. Mice were immunized with four DNA plasmids, each encoding the pre-membrane and envelope from one DENV serotype, either sequentially or simultaneously. The sequential immunization induced significantly higher levels of interferon (IFN)γ- or tumor necrosis factor (TNF)α-expressing CD4+ and CD8+ T cells to both serotype-specific and conserved epitopes than tetravalent immunization. Moreover, sequential immunization induced higher levels of neutralizing antibodies to all four DENV serotypes than tetravalent vaccination. Consistently, sequential immunization resulted in more diversified immunoglobulin repertoire, including increased complementarity determining region 3 (CDR3) length and more robust germinal center reactions. These results show that sequential immunization offers a simple approach to potentially overcome the current challenges encountered with tetravalent-formulated dengue vaccines.

Erratum: Author Correction: Mimicking immune signatures of flavivirus infection with targeted adjuvants improves dengue subunit vaccine immunogenicity.

[This corrects the article DOI: 10.1038/s41541-019-0119-3.].

Dengue Mosaic Vaccines Enhance Cellular Immunity and Expand the Breadth of Neutralizing Antibody Against All Four Serotypes of Dengue Viruses in Mice.

An estimated 400 million people in the world are infected with any of the four types of dengue virus (DENV) annually. The only licensed dengue vaccine cannot effectively prevent infection with all of the four DENVs, especially in those immunologically naïve at baseline. In this study, we explored a mosaic vaccine approach, which utilizes an artificial recombinant sequence for each serotype to achieve maximum coverage of variant epitopes in the four DENVs. We determined the immunogenicity and cross-reactivity of DNA plasmids encoding individual mosaic sequences or the natural sequences in mice. We show that the mosaic vaccines, particularly those targeting DENV serotype 1 and 2, improved vaccine immunogenicity by increasing the percentage of antigen-specific IFNγ- or TNFα-secreting CD4 and CD8 T cells, and titers of neutralizing antibodies. The mosaic vaccine diversified and broadened anti-dengue T cell responses and cross-reactive neutralizing antibodies against all four serotypes. The mosaic vaccines also induced higher level of antigen-specific B cell responses. These results suggest that mosaic vaccines comprising of DENV serotype 1 and 2 variant epitopes could stimulate strong and broad immune responses against all four serotypes.

Mimicking immune signatures of flavivirus infection with targeted adjuvants improves dengue subunit vaccine immunogenicity.

Neutralizing antibodies (nAbs) are a critical component for protection against dengue virus (DENV) infection, but little is known about the immune mechanisms governing their induction and whether such mechanisms can be harnessed for vaccine development. In this study, we profiled the early immune responses to flaviviruses in human peripheral blood mononuclear cells and screened a panel of toll-like receptor (TLR) agonists that stimulate the same immune signatures. Monocyte/macrophage-driven inflammatory responses and interferon responses were characteristics of flavivirus infection and associated with induction of nAbs in humans immunized with the yellow fever vaccine YF-17D. The signatures were best reproduced by the combination of TLR agonists Pam3CSK4 and PolyI:C (PP). Immunization of both mice and macaques with a poorly immunogenic recombinant DENV-2 envelope domain III (EDIII) induced more consistent nAb and CD4+ T-cell responses with PP compared to alum plus monophosphoryl lipid A. Induction of nAbs by PP required interferon-mediated signals in macrophages in mice. However, EDIII + PP vaccination only provided partial protection against viral challenge. These results provide insights into mechanisms underlying nAb induction and a basis for further improving antigen/adjuvant combinations for dengue vaccine development.

Serum Metabolomics Investigation of Humanized Mouse Model of Dengue Virus Infection.

Dengue is an acute febrile illness caused by dengue virus (DENV) and a major cause of morbidity and mortality in tropical and subtropical regions of the world. The lack of an appropriate small-animal model of dengue infection has greatly hindered the study of dengue pathogenesis and the development of therapeutics. In this study, we conducted mass spectrometry-based serum metabolic profiling from a model using humanized mice (humice) with DENV serotype 2 infection at 0, 3, 7, 14, and 28 days postinfection (dpi). Forty-eight differential metabolites were identified, including fatty acids, purines and pyrimidines, acylcarnitines, acylglycines, phospholipids, sphingolipids, amino acids and derivatives, free fatty acids, and bile acid. These metabolites showed a reversible-change trend-most were significantly perturbed at 3 or 7 dpi and returned to control levels at 14 or 28 dpi, indicating that the metabolites might serve as prognostic markers of the disease in humice. The major perturbed metabolic pathways included purine and pyrimidine metabolism, fatty acid ß-oxidation, phospholipid catabolism, arachidonic acid and linoleic acid metabolism, sphingolipid metabolism, tryptophan metabolism, phenylalanine metabolism, lysine biosynthesis and degradation, and bile acid biosynthesis. Most of these disturbed pathways are similar to our previous metabolomics findings in a longitudinal cohort of adult human dengue patients across different infection stages. Our analyses revealed the commonalities of host responses to DENV infection between humice and humans and suggested that humice could be a useful small-animal model for the study of dengue pathogenesis and the development of dengue therapeutics.IMPORTANCE Dengue virus is the most widespread arbovirus, causing an estimated 390 million dengue infections worldwide every year. There is currently no effective treatment for the disease, and the lack of an appropriate small-animal model of dengue infection has greatly increased the challenges in the study of dengue pathogenesis and the development of therapeutics. Metabolomics provides global views of small-molecule metabolites and is a useful tool for finding metabolic pathways related to disease processes. Here, we conducted a serum metabolomics study on a model using humanized mice with dengue infection that had significant levels of human platelets, monocytes/macrophages, and hepatocytes. Forty-eight differential metabolites were identified, and the underlying perturbed metabolic pathways are quite similar to the pathways found to be altered in dengue patients in previous metabolomics studies, indicating that humanized mice could be a highly relevant small-animal model for the study of dengue pathogenesis and the development of dengue therapeutics.

Targeting Epstein-Barr virus-transformed B lymphoblastoid cells using antibodies with T-cell receptor-like specificities.

Epstein-Barr virus (EBV) is an oncovirus associated with several human malignancies including posttransplant lymphoproliferative disease in immunosuppressed patients. We show here that anti-EBV T-cell receptor-like monoclonal antibodies (TCR-like mAbs) E1, L1, and L2 bound to their respective HLA-A*0201-restricted EBV peptides EBNA1562-570, LMP1125-133, and LMP2A426-434 with high affinities and specificities. These mAbs recognized endogenously presented targets on EBV B lymphoblastoid cell lines (BLCLs), but not peripheral blood mononuclear cells, from which they were derived. Furthermore, these mAbs displayed similar binding activities on several BLCLs, despite inherent heterogeneity between different donor samples. A single weekly administration of the naked mAbs reduced splenomegaly, liver tumor spots, and tumor burden in BLCL-engrafted immunodeficient NOD-SCID/Il2rg(-/-) mice. In particular, mice that were treated with the E1 mAb displayed a delayed weight loss and significantly prolonged survival. In vitro, these TCR-like mAbs induced early apoptosis of BLCLs, thereby enhancing their Fc-dependent phagocytic uptake by macrophages. These data provide evidence for TCR-like mAbs as potential therapeutic modalities to target EBV-associated diseases.

Human natural killer cells control Plasmodium falciparum infection by eliminating infected red blood cells.

Immunodeficient mouse-human chimeras provide a powerful approach to study host-specific pathogens, such as Plasmodium falciparum that causes human malaria. Supplementation of immunodeficient mice with human RBCs supports infection by human Plasmodium parasites, but these mice lack the human immune system. By combining human RBC supplementation and humanized mice that are optimized for human immune cell reconstitution, we have developed RBC-supplemented, immune cell-optimized humanized (RICH) mice that support multiple cycles of P. falciparum infection. Depletion of human natural killer (NK) cells, but not macrophages, in RICH mice results in a significant increase in parasitemia. Further studies in vitro show that NK cells preferentially interact with infected RBCs (iRBCs), resulting in the activation of NK cells and the elimination of iRBCs in a contact-dependent manner. We show that the adhesion molecule lymphocyte-associated antigen 1 is required for NK cell interaction with and elimination of iRBCs. Development of RICH mice and validation of P. falciparum infection should facilitate the dissection of human immune responses to malaria parasite infection and the evaluation of therapeutics and vaccines.

Induction of functional human macrophages from bone marrow promonocytes by M-CSF in humanized mice.

Engraftment of human CD34⁺ hematopoietic stem/progenitor cells into immunodeficient mice leads to robust reconstitution of human T and B cells but not monocytes and macrophages. To identify the cause underlying the poor monocyte and macrophage reconstitution, we analyzed human myeloid cell development in humanized mice and found that it was blocked at the promonocyte stage in the bone marrow. Expression of human M-CSF or GM-CSF by hydrodynamic injection of cytokine-encoding plasmid completely abolished the accumulation of promonocytes in the bone marrow. M-CSF promoted the development of mature monocytes and tissue-resident macrophages whereas GM-CSF did not. Moreover, correlating with an increased human macrophages at the sites of infection, M-CSF-treated humanized mice exhibited an enhanced protection against influenza virus and Mycobacterium infection. Our study identifies the precise stage at which human monocyte/macrophage development is blocked in humanized mice and reveals overlapping and distinct functions of M-CSF and GM-CSF in human monocyte and macrophage development. The improved reconstitution and functionality of monocytes/macrophages in the humanized mice following M-CSF expression provide a superior in vivo system to investigate the role of macrophages in physiological and pathological processes.

CD166(pos) subpopulation from differentiated human ES and iPS cells support repair of acute lung injury.

Previous efforts to derive lung progenitor cells from human embryonic stem (hES) cells using embryoid body formation or stromal feeder cocultures had been limited by low efficiencies. Here, we report a step-wise differentiation method to drive both hES and induced pluripotent stem (iPS) cells toward the lung lineage. Our data demonstrated a 30% efficiency in generating lung epithelial cells (LECs) that expresses various distal lung markers. Further enrichment of lung progenitor cells using a stem cell marker, CD166 before transplantation into bleomycin-injured NOD/SCID mice resulted in enhanced survivability of mice and improved lung pulmonary functions. Immunohistochemistry of lung sections from surviving mice further confirmed the specific engraftment of transplanted cells in the damaged lung. These cells were shown to express surfactant protein C, a specific marker for distal lung progenitor in the alveoli. Our study has therefore demonstrated the proof-of-concept of using iPS cells for the repair of acute lung injury, demonstrating the potential usefulness of using patient's own iPS cells to prevent immune rejection which arise from allogenic transplantation.