Hansenula polymorpha expressed heat shock protein gp96 exerts potent T cell activation activity as an adjuvant

Ogataea polymorpha as a next-generation chassis for industrial biotechnology

Ogataea (Hansenula) polymorpha is a nonconventional yeast with some unique characteristics, including fast growth, thermostability, and broad substrate spectrum. Other than common applications for protein production, O. polymorpha is attracting interest for chemical and protein production from methanol; a promising feedstock for the next-generation biomanufacturing due to its abundant sources and excellent characteristics. Benefiting from the development of synthetic biology, it has been engineered to produce value-added chemicals by extensively rewiring cellular metabolism. This Review discusses recently developed synthetic biology tools of O. polymorpha. The advances of chemicals production and systems biology were reviewed comprehensively. Finally, we look ahead to the developments of biomanufacturing in O. polymorpha to make an overall understanding of this chassis for academia and industry.

HBV Vaccines: Advances and Development

Hepatitis B virus (HBV) infection is a global public health problem that is closely related to liver cirrhosis and hepatocellular carcinoma (HCC). The prevalence of acute and chronic HBV infection, liver cirrhosis, and HCC has significantly decreased as a result of the introduction of universal HBV vaccination programs. The first hepatitis B vaccine approved was developed by purifying the hepatitis B surface antigen (HBsAg) from the plasma of asymptomatic HBsAg carriers. Subsequently, recombinant DNA technology led to the development of the recombinant hepatitis B vaccine. Although there are already several licensed vaccines available for HBV infection, continuous research is essential to develop even more effective vaccines. Prophylactic hepatitis B vaccination has been important in the prevention of hepatitis B because it has effectively produced protective immunity against hepatitis B viral infection. Prophylactic vaccines only need to provoke neutralizing antibodies directed against the HBV envelop proteins, whereas therapeutic vaccines are most likely needed to induce a comprehensive T cell response and thus, should include other HBV antigens, such as HBV core and polymerase. The existing vaccines have proven to be highly effective in preventing HBV infection, but ongoing research aims to improve their efficacy, duration of protection, and accessibility. The routine administration of the HBV vaccine is safe and well-tolerated worldwide. The purpose of this type of immunization is to trigger an immunological response in the host, which will halt HBV replication. The clinical efficacy and safety of the HBV vaccine are affected by a number of immunological and clinical factors. However, this success is now in jeopardy due to the breakthrough infections caused by HBV variants with mutations in the S gene, high viral loads, and virus-induced immunosuppression. In this review, we describe various types of available HBV vaccines, along with the recent progress in the ongoing battle to develop new vaccines against HBV.

Characterizing methanol metabolism-related promoters for metabolic engineering of Ogataea polymorpha

Promoters play an important role in regulating gene expression, and construction of microbial cell factories requires multiple promoters for balancing the metabolic pathways. However, there are only a limited number of characterized promoters for gene expression in the methylotrophic yeast Ogataea polymorpha, which hampers the extensive harnessing of this important yeast toward a cell factory. Here we characterized the promoters of methanol utilization pathway, precursor supply pathway, and reactive oxygen species (ROS) defense system, by using a green fluorescence protein variant (GFP_UV) as a quantification signal. Finally, the characterized promoters were used for tuning a fatty alcohol biosynthetic pathway in O. polymorpha and realized fatty alcohol production from methanol. This promoter box should be helpful for gene expression and pathway optimization in the methylotrophic yeast O. polymorpha. KEY POINTS : • 22 promoters related to methanol metabolism were characterized in O. polymorpha. • Promoter truncation resulted shorter and compact promoters. • Promoters with various strengths were used for regulating a fatty alcohol biosynthesis from methanol.

Broadly Protective CD8+ T Cell Immunity to Highly Conserved Epitopes Elicited by Heat Shock Protein gp96-Adjuvanted Influenza Monovalent Split Vaccine

Currently, immunization with inactivated influenza virus vaccines is the most prevalent method to prevent infections. However, licensed influenza vaccines provide only strain-specific protection and need to be updated and administered yearly; thus, new vaccines that provide broad protection against multiple influenza virus subtypes are required. In this study, we demonstrated that intradermal immunization with gp96-adjuvanted seasonal influenza monovalent H1N1 split vaccine could induce cross-protection against both group 1 and group 2 influenza A viruses in BALB/c mouse models. Vaccination in the presence of gp96 induced an apparently stronger antigen-specific T cell response than split vaccine alone. Immunization with the gp96-adjuvanted vaccine also elicited an apparent cross-reactive CD8⁺ T cell response that targeted the conserved epitopes across different influenza virus strains. These cross-reactive CD8⁺ T cells might be recalled from a pool of memory cells established after vaccination and recruited from extrapulmonary sites to facilitate viral clearance. Of note, six highly conserved CD8⁺ T epitopes from the viral structural proteins hemagglutinin (HA), M1, nucleoprotein (NP), and PB1 were identified to play a synergistic role in gp96-mediated cross-protection. Comparative analysis showed that most of conservative epitope-specific cytotoxic T lymphocytes (CTLs) apparently induced by heterologous virus infection were also activated by gp96-adjuvanted vaccine, thus resulting in broader protective CD8⁺ T cell responses. Our results demonstrated the advantage of adding gp96 to an existing seasonal influenza vaccine to improve its ability to provide better cross-protection.IMPORTANCE Owing to continuous mutations in hemagglutinin (HA) or neuraminidase (NA) or recombination of the gene segments between different strains, influenza viruses can escape the immune responses developed by vaccination. Thus, new strategies aimed to efficiently activate immune response that targets to conserved regions among different influenza viruses are urgently needed in designing broad-spectrum influenza vaccine. Heat shock protein gp96 is currently the only natural T cell adjuvant with special ability to cross-present coupled antigen to major histocompatibility complex class I (MHC-I) molecule and activate the downstream antigen-specific CTL response. In this study, we demonstrated the advantages of adding gp96 to monovalent split influenza virus vaccine to improve its ability to provide cross-protection in the BALB/c mouse model and proved that a gp96-activated cross-reactive CTL response is indispensable in our vaccine strategy. Due to its unique adjuvant properties, gp96 might be a promising adjuvant for designing new broad-spectrum influenza vaccines.

Heat Shock Proteins 90 kDa: Immunomodulators and Adjuvants in Vaccine Design Against Infectious Diseases

Heat shock proteins 90 kDa (Hsp90s) were originally identified as stress-responsive proteins and described to participate in several homeostatic processes. Additionally, extracellular Hsp90s have the ability to bind to surface receptors and activate cellular functions related to immune response (cytokine secretion, cell maturation, and antigen presentation), making them very attractive to be studied as immunomodulators. In this context, Hsp90s are proposed as new adjuvants in the design of novel vaccine formulations that require the induction of a cell-mediated immune response to prevent infectious diseases. In this review, we summarized the adjuvant properties of Hsp90s when they are either alone, complexed, or fused to a peptide to add light to the knowledge of Hsp90s as carriers and adjuvants in the design of vaccines against infectious diseases. Besides, we also discuss the mechanisms by which Hsp90s activate and modulate professional antigen-presenting cells.

Yeast-based vaccines: New perspective in vaccine development and application

In presently licensed vaccines, killed or attenuated organisms act as a source of immunogens except for peptide-based vaccines. These conventional vaccines required a mass culture of associated or related organisms and long incubation periods. Special requirements during storage and transportation further adds to the cost of vaccine preparations. Availability of complete genome sequence, well-established genetic, inherent natural adjuvant and non-pathogenic nature of yeast species viz. Saccharomyces cerevisiae, Pichia pastoris makes them an ideal model system for the development of vaccines both for public health and for on-farm consumption. In this review, we compile the work in this emerging field during last two decades with major emphases on S. cerevisiae and P. pastoris which are routinely used worldwide for expression of heterologous proteins with therapeutic value against infectious diseases along with possible use in cancer therapy. We also pointed towards the developments in use of whole recombinant yeast, yeast surface display and virus-like particles as a novel strategy in the fight against infectious diseases and cancer along with other aspects including suitability of yeast in vaccines preparations, yeast cell wall component as an immune stimulator or modulator and present status of yeast-based vaccines in clinical trials.

Advances in Using Hansenula polymorpha as Chassis for Recombinant Protein Production

The methylotrophic yeast Hansenula polymorpha, known as a non-conventional yeast, is used for the last 30 years for the production of recombinant proteins, including enzymes, vaccines, and biopharmaceuticals. Although a large number of reviews have been published elucidating the applications of this yeast as a cell factory, the latest was released about 10 years ago. Therefore, this review aimed at summarizing available information on the use of H. polymorpha as a host for recombinant protein production in the last decade. Examples of chemicals and virus-like particles produced using this yeast also are discussed. Firstly, the aspects that feature this yeast as a host for recombinant protein production are highlighted including the techniques available for its genetic manipulation as well as strategies for cultivation in bioreactors. Special attention is given to the novel genomic editing tools, mainly CRISPR/Cas9 that was recently established in this yeast. Finally, recent examples of using H. polymorpha as an expression platform are presented and discussed. The production of human Parathyroid Hormone (PTH) and Staphylokinase (SAK) in H. polymorpha are described as case studies for process establishment in this yeast. Altogether, this review is a guideline for this yeast utilization as an expression platform bringing a thorough analysis of the genetic aspects and fermentation protocols used up to date, thus encouraging the production of novel biomolecules in H. polymorpha.

Immunogenic Effect of Hyperthermia on Enhancing Radiotherapeutic Efficacy

Hyperthermia is a cancer treatment where tumor tissue is heated to around 40 °C. Hyperthermia shows both cancer cell cytotoxicity and immune response stimulation via immune cell activation. Immunogenic responses encompass the innate and adaptive immune systems, involving the activation of macrophages, natural killer cells, dendritic cells, and T cells. Moreover, hyperthermia is commonly used in combination with different treatment modalities, such as radiotherapy and chemotherapy, for better clinical outcomes. In this review, we will focus on hyperthermia-induced immunogenic effects and molecular events to improve radiotherapy efficacy. The beneficial potential of integrating radiotherapy with hyperthermia is also discussed.

CD8+ T-Cell Response-Associated Evolution of Hepatitis B Virus Core Protein and Disease Progress

Under the immune pressure of cytotoxic T cells (CTLs), hepatitis B virus (HBV) evolves to accumulate mutations more likely within epitopes to evade immune detection. However, little is known about the specific patterns of the immune pressure-associated HBV mutation of T-cell epitopes and their link to disease progression. Here, we observed a correlation of the accumulated variants on HBV core protein (HBc) with the disease severity of HBV infection. Further analysis indicated that these substitutions were mostly located within CD8⁺ T-cell epitopes of HBc protein, which were systematically screened and identified in an unbiased manner in our study. From individual peptide level to the human leukocyte antigen I (HLA-I)-restricted population level, we elucidated that the mutations in these well-defined HLA-I-restricted T-cell epitopes significantly decreased antiviral activity-specific CTLs and were positively associated with clinical parameters and disease progression in HBV-infected patients. The molecular pattern for viral epitope variations based on the sequencing of 105 HBV virus genomes indicated that the C-terminal portion (Pc), especially the Pc-1 and Pc-2 positions, have the highest mutation rates. Further structural analysis of HLA-A*02 complexed to diverse CD8⁺ T-cell epitopes revealed that the highly variable C-terminal bulged peak of M-shaped HBc-derived epitopes are solvent exposed, and most of the CDR3βs of the T-cell receptor hover over them. These data shed light on the molecular and immunological mechanisms of T-cell immunity-associated viral evolution in hepatitis B progression, which is beneficial for designing immunotherapies and vaccines.IMPORTANCE The specific patterns of sequence polymorphisms of T-cell epitopes and the immune mechanisms of the HBV epitope mutation-linked disease progression are largely unclear. In this study, we systematically evaluated the contribution of CD8⁺ T cells to the disease progress-associated evolution of HBV. By evaluation of patient T-cell responses based on the peptide repertoire, we comprehensively characterized the association of clinical parameters in chronic hepatitis B with the antiviral T-cell response-associated mutations of the viruses from the single-epitope level to the overall HLA-I-restricted peptide levels. Furthermore, we investigated the molecular basis of the HLA-A2-restricted peptide immune escape and found that the solvent-exposed C-terminal portion of the epitopes is highly variable under CDR3β recognition. Our work may provide a comprehensive evaluation of viral mutations impacted by the host CTL response in HBV disease progression in the context of the full repertoire of HBc-derived epitopes.

Heat-Shock Protein gp96 Enhances T Cell Responses and Protective Potential to Bacillus Calmette-Guérin Vaccine

The commonly used Bacillus Calmette-Guérin (BCG) vaccine only induces moderate T cell responses and is less effective in protecting against pulmonary tuberculosis (TB) in adults and ageing populations. Thus, developing new TB vaccine candidates is an important strategy against the spread of Mycobacterium tuberculosis. Here, we demonstrated that immunization with heat-shock protein gp96 as an adjuvant led to a significantly increased CD4(+) and CD8(+) T cell response to a BCG vaccine. Secretion of the Th1-type cytokines was increased by splenocytes from gp96-immunized mice. In addition, adding gp96 as an adjuvant effectively improved the protection against intravenous challenge with Mycobacterium bovis BCG in mice. Our study reveals the novel property of gp96 in boosting the vaccine-specific T cell response and its potential use as an adjuvant for BCG vaccines against mycobacterial infection.

Interaction of Toll-Like Receptors with the Molecular Chaperone Gp96 Is Essential for Its Activation of Cytotoxic T Lymphocyte Response

The heat shock protein gp96 elicits specific T cell responses to its chaperoned peptides against cancer and infectious diseases in both rodent models and clinical trials. Although gp96-induced innate immunity, via a subset of Toll like receptors (TLRs), and adaptive immunity, through antigen presentation, are both believed to be important for priming potent T cell responses, direct evidence for the role of gp96-mediated TLR activation related to its functional T cell activation is lacking. Here, we report that gp96 containing mutations in its TLR-binding domain failed to activate macrophages, but peptide presentation was unaffected. Moreover, we found that peptide-specific T cell responses, as well as antitumor T cell immunity induced by gp96, are severely impaired when the TLR-binding domain is mutated. These data demonstrate the essential role of the gp96-TLR interaction in priming T cell immunity and provide further molecular basis for the coupling of gp96-mediated innate with adaptive immunity.

Immunogenicity of multi-epitope-based vaccine candidates administered with the adjuvant Gp96 against rabies

Rabies, a zoonotic disease, causes > 55,000 human deaths globally and results in at least 500 million dollars in losses every year. The currently available rabies vaccines are mainly inactivated and attenuated vaccines, which have been linked with clinical diseases in animals. Thus, a rabies vaccine with high safety and efficacy is urgently needed. Peptide vaccines are known for their low cost, simple production procedures and high safety. Therefore, in this study, we examined the efficacy of multi-epitope-based vaccine candidates against rabies virus. The ability of various peptides to induce epitope-specific responses was examined, and the two peptides that possessed the highest antigenicity and conservation, i.e., AR16 and hPAB, were coated with adjuvant canine-Gp96 and used to prepare vaccines. The peptides were prepared as an emulsion of oil in water (O/W) to create three batches of bivalent vaccine products. The vaccine candidates possessed high safety. Virus neutralizing antibodies were detected on the day 14 after the first immunization in mice and beagles, reaching 5-6 IU/mL in mice and 7-9 IU/mL in beagles by day 28. The protective efficacy of the vaccine candidates was about 70%-80% in mice challenged by a virulent strain of rabies virus. Thus, a novel multi-epitope-based rabies vaccine with Gp96 as an adjuvant was developed and validated in mice and dogs. Our results suggest that synthetic peptides hold promise for the development of novel vaccines against rabies.

Baculovirus expression of the N-terminus of porcine heat shock protein Gp96 improves the immunogenicity of recombinant PCV2 capsid protein

Porcine circovirus type 2 (PCV2) causes significant economic losses to the swine industry worldwide. Heat shock proteins (Hsps) can be used as modulators to enhance both innate and adaptive immune responses. In the present study, recombinant baculoviruses expressing the PCV2Cap protein and the N-terminal 22-370 amino acids of porcine Gp96 (Gp96N), Hsp90, and Hsp70 (rBac-cap/Gp96N, rBac-cap/Hsp90 and rBac-cap/Hsp70, respectively) were constructed and the immune responses were examined in mice and piglets. The mouse experiments showed that rBac-cap/Gp96N increased the titers of specific anti-PCV2 neutralizing antibodies, proliferative responses of peripheral blood mononuclear cells (PBMCs) and IFN-γ levels compared to rBac-cap/Hsp90, rBac-cap/Hsp70, or rBac-cap. The pig experiments showed that the levels of anti-PCV2 antibody, proliferative responses of PBMCs, and IFN-γ in the rBac-cap/Gp96N groups were increased compared to those in rBac-cap group. There were no clear clinical signs of infection following PCV2 challenge in pigs inoculated with recombinant rBac-cap/Gp96N and rBac-cap, and the relative daily weight gains were higher than those in the challenge control (CC) group. The pathological lesions, extent of viremia, and viral loads of the vaccinated groups were milder than those in the CC group. Meanwhile, the extent of viremia and viral load present in the rBac-cap/Gp96N group were significantly lower than those in the rBac-cap group. These results indicated that porcine Gp96N effectively increased the humoral and cell-mediated immune responses of PCV2Cap. Gp96N presents an attractive adjuvant or immunotargeting strategy to enhance the protective efficacy of PCV2 subunit vaccines in swine.

Production of Protein Complexes in Non-methylotrophic and Methylotrophic Yeasts : Nonmethylotrophic and Methylotrophic Yeasts

Protein complexes can be produced in multimilligram quantities using nonmethylotrophic and methylotrophic yeasts such as Saccharomyces cerevisiae and Komagataella (Pichia) pastoris. Yeasts have distinct advantages as hosts for recombinant protein production owing to their cost efficiency, ease of cultivation and genetic manipulation, fast growth rates, capacity to introduce post-translational modifications, and high protein productivity (yield) of correctly folded protein products. Despite those advantages, yeasts have surprisingly lagged behind other eukaryotic hosts in their use for the production of multisubunit complexes. As our knowledge of the metabolic and genomic bottlenecks that yeast microorganisms face when overexpressing foreign proteins expands, new possibilities emerge for successfully engineering yeasts as superb expression hosts. In this chapter, we describe the current state of the art and discuss future possibilities for the development of yeast-based systems for the production of protein complexes.

A new unconventional HLA-A2-restricted epitope from HBV core protein elicits antiviral cytotoxic T lymphocytes

Cytotoxic T cells (CTLs) play a key role in the control of Hepatitis B virus (HBV) infection and viral clearance. However, most of identified CTL epitopes are derived from HBV of genotypes A and D, and few have been defined in virus of genotypes B and C which are more prevalent in Asia. As HBV core protein (HBc) is the most conservative and immunogenic component, in this study we used an overlapping 9-mer peptide pool covering HBc to screen and identify specific CTL epitopes. An unconventional HLA-A2-restricted epitope HBc141-149 was discovered and structurally characterized by crystallization analysis. The immunogenicity and anti-HBV activity were further determined in HBV and HLA-A2 transgenic mice. Finally, we show that mutations in HBc141-149 epitope are associated with viral parameters and disease progression in HBV infected patients. Our data therefore provide insights into the structure characteristics of this unconventional epitope binding to MHC-I molecules, as well as epitope specific CTL activity that orchestrate T cell response and immune evasion in HBV infected patients.

Heat shock protein gp96 adjuvant induces T cell responses and cross-protection to a split influenza vaccine

The commonly used inactivated or split influenza vaccines induce only induce minimal T cell responses and are less effective in preventing heterologous virus infection. Thus, developing cross-protective influenza vaccines against the spread of a new influenza virus is an important strategy against pandemic emergence. Here we demonstrated that immunization with heat shock protein gp96 as adjuvant led to a dramatic increased antigen-specific T cell response to a pandemic H1N1 split vaccine. Notably, gp96 elicited a cross-protective CD8(+) T cell response to the internal conserved viral protein NP. Although the split pH1N1vaccine alone has low cross-protective efficiency, adding gp96 as an adjuvant effectively improved the cross-protection against challenge with a heterologous virus in mice. Our study reveals the novel property of gp96 in boosting the T cell response against conserved epitopes of influenza virus and its potential use as an adjuvant for human pre-pandemic inactivated influenza vaccines against different viral subtypes.

TAT-mediated gp96 transduction to APCs enhances gp96-induced antiviral and antitumor T cell responses

The heat shock protein gp96 is an adjuvant that can elicit T cell responses against cancer and infectious diseases, via antigen presentation, in both rodent models and clinical trials. Its uptake and internalization into antigen presenting cells (APCs) is a critical step in gp96-mediated immune responses. This study examined strategies to improve the cell internalization and T cell activation of gp96. It was found that recombinant fusion with the cell-penetrating peptide TAT (trans-activator of transcription) slightly decreased the aggregation level of gp96 and significantly increased its internalization into macrophages. Furthermore, immunization with the TAT-gp96 fusion dramatically enhanced gp96-mediated hepatitis B virus (HBV)-specific T cell responses and its antiviral efficiency in HBV transgenic mice compared to rgp96. In addition, the inclusion of TAT significantly improved the antitumor T cell immune response to a gp96 vaccine in the B16 melanoma model. These results provide evidence that the efficient transduction of gp96 into APCs can significantly enhance the outcome of gp96-based immunotherapy, and therefore provide a basis for more efficient approaches to improving the immunoregulatory and adjuvant functions of this unique T cell adjuvant.

Gp96 enhances the immunogenicity of subunit vaccine of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses in the pig industry worldwide. Currently available commercial vaccines provide limited protection due to delayed and weak cell-mediated immunity and neutralizing antibody production, thus the immunomodulators should be considered in order to improve the efficacy of PRRSV vaccines. Heat shock protein gp96 may be used as a modulator to enhance both innate and adaptive immune responses. In the present study, two multi-epitope subunit vaccines, named as Cp1 and Cp2, were designed based on the conserved B cell epitopes of viral proteins with the N-terminal 22-370 amino acids (aa) of porcine gp96 (Gp96N) chosen as the adjuvant. Immune responses elicited by the different combinations of Cp1/Cp2 and Gp96N were examined in mice and piglets. The results indicated that the group of Cp1/Cp2-Gp96N (CG) combination induced 3-4-fold higher titers of Cp1/Cp2-ELISA antibodies and neutralizing antibodies (NAs) in mice than the groups which received Cp1/Cp2 immunization alone or with Freund's adjuvant. Additionally, Gp96N significantly enhanced the levels of lymphocyte proliferative responses of splenocytes or peripheral blood mononuclear cells from vaccinated mice or piglets. The production of IFN-γ in mice splenocytes, TNF-α, IFN-γ, and IL-12 in sera of piglets were also remarkably increased with the treatment of Gp96N, while IL-4 was reduced by half and IL-10 was decreased to an undetectable level. These results suggest that the porcine Gp96N could effectively enhance the innate and adaptive immune responses of Cp1/Cp2 with a Th1-type bias. Therefore, the multi-epitope subunit vaccine Cp1/Cp2 co-administered with porcine Gp96N might potentially be a promising candidate vaccine for the prevention and control of PRRSV in pigs.