Mark T. Orr

Key roles of adjuvants in modern vaccines

Vaccines containing novel adjuvant formulations are increasingly reaching advanced development and licensing stages, providing new tools to fill previously unmet clinical needs. However, many adjuvants fail during product development owing to factors such as manufacturability, stability, lack of effectiveness, unacceptable levels of tolerability or safety concerns. This Review outlines the potential benefits of adjuvants in current and future vaccines and describes the importance of formulation and mechanisms of action of adjuvants. Moreover, we emphasize safety considerations and other crucial aspects in the clinical development of effective adjuvants that will help facilitate effective next-generation vaccines against devastating infectious diseases.

Natural Killer Cell Education and Tolerance

Natural killer (NK) cells play a key role in the immune response to certain infections and malignancies by direct cytolysis of infected or transformed cells and by secretion of potent immune mediators. NK cells express an array of activating receptors that recognize self-molecules. If not restrained by inhibitory receptors recognizing major histocompatibility complex (MHC) class I proteins on the surface of self cells, NK cells are able to kill normal, healthy cells. Not all NK cells express inhibitory receptors for self-MHC class I; thus, other tolerance mechanisms are necessary to prevent NK cell-mediated autoimmunity. Here we review the major mechanisms of NK cell education and tolerance.

Biotechnology: Enzymatic production of biohydrogen

Although in theory the amount of hydrogen that could be generated from renewable sources of energy such as cellulose (a polymer of glucose) is vast, only 16–24% of the maximum stoichiometric yield of hydrogen from glucose (about 12 mol H2 per mol glucose) is typically achieved by biological methods. Here we show that the enzymes of the oxidative pentose phosphate cycle can be coupled to hydrogenase purified from the bacterium Pyrococcus furiosus, one of only a few hydrogenases that use NADP+ as the electron carrier, to generate 11.6 mol H2 per mol glucose-6-phosphate. Hydrogen produced by this pathway is the major product, unlike that produced by intermediate metabolic pathways of bacterial fermentation, and therefore has important practical implications for biohydrogen production.

Enzymatic production of biohydrogen.

Although in theory the amount of hydrogen that could be generated from renewable sources of energy such as cellulose (a polymer of glucose) is vast, only 16–24% of the maximum stoichiometric yield of hydrogen from glucose (about 12 mol H2 per mol glucose) is typically achieved by biological methods. Here we show that the enzymes of the oxidative pentose phosphate cycle can be coupled to hydrogenase purified from the bacterium Pyrococcus furiosus, one of only a few hydrogenases that use NADP+ as the electron carrier, to generate 11.6 mol H2 per mol glucose-6-phosphate. Hydrogen produced by this pathway is the major product, unlike that produced by intermediate metabolic pathways of bacterial fermentation, and therefore has important practical implications for biohydrogen production.

CD94 is essential for NK cell-mediated resistance to a lethal viral disease

It is well established that natural killer (NK) cells confer resistance to many viral diseases, but in only a few instances the molecular mechanisms whereby NK cells recognize virus-infected cells are known. Here we show that CD94, a molecule preferentially expressed by NK cells, is essential for the resistance of C57BL/6 mice to mousepox, a disease caused by the Orthopoxvirus ectromelia virus. Ectromelia virus-infected cells expressing the major histocompatibility complex (MHC) class Ib molecule Qa-1(b) are specifically recognized by the activating receptor formed by CD94 and NKG2E. Because CD94-NKG2 receptors and their ligands are highly conserved in rodents and humans, a similar mechanism may exist during human infections with the smallpox and monkeypox viruses, which are highly homologous to ectromelia virus.

Adjuvant formulation structure and composition are critical for the development of an effective vaccine against tuberculosis

One third of the world is infected with Mycobacterium tuberculosis (Mtb) with eight million new cases of active tuberculosis (TB) each year. Development of a new vaccine to augment or replace the only approved TB vaccine, BCG, is needed to control this disease. Mtb infection is primarily controlled by TH1 cells through the production of IFN-γ and TNF which activate infected macrophages to kill the bacterium. Here we examine an array of adjuvant formulations containing the TLR4 agonist GLA to identify candidate adjuvants to pair with ID93, a lead TB vaccine antigen, to elicit protective TH1 responses. We evaluate a variety of adjuvant formulations including alum, liposomes, and oil-in-water emulsions to determine how changes in formulation composition alter adjuvant activity. We find that alum and an aqueous nanosuspension of GLA synergize to enhance generation of ID93-specific TH1 responses, whereas neither on their own are effective adjuvants for generation of ID93-specific TH1 responses. For GLA containing oil-in-water emulsions, the selection of the oil component is critical for adjuvant activity, whereas a variety of lipid components may be used in liposomal formulations of GLA. The composition of the liposome formulation of ID93/GLA does alter the magnitude of the TH1 response. These results demonstrate that there are multiple solutions for an effective formulation of a novel TB vaccine candidate that enhances both TH1 generation and protective efficacy.

From mouse to man: safety, immunogenicity and efficacy of a candidate leishmaniasis vaccine LEISH-F3+GLA-SE.

Key antigens of Leishmania species identified in the context of host responses in Leishmania‐exposed individuals from disease‐endemic areas were prioritized for the development of a subunit vaccine against visceral leishmaniasis (VL), the most deadly form of leishmaniasis. Two Leishmania proteins—nucleoside hydrolase and a sterol 24‐c‐methyltransferase, each of which are protective in animal models of VL when properly adjuvanted— were produced as a single recombinant fusion protein NS (LEISH‐F3) for ease of antigen production and broad coverage of a heterogeneous major histocompatibility complex population. When formulated with glucopyranosyl lipid A‐stable oil‐in‐water nanoemulsion (GLA‐SE), a Toll‐like receptor 4 TH1 (T helper 1) promoting nanoemulsion adjuvant, the LEISH‐F3 polyprotein induced potent protection against both L. donovani and L. infantum in mice, measured as significant reductions in liver parasite burdens. A robust immune response to each component of the vaccine with polyfunctional CD4 TH1 cell responses characterized by production of antigen‐specific interferon‐γ, tumor necrosis factor and interleukin‐2 (IL‐2), and low levels of IL‐5 and IL‐10 was induced in immunized mice. We also demonstrate that CD4 T cells, but not CD8 T cells, are sufficient for protection against L. donovani infection in immunized mice. Based on the sum of preclinical data, we prepared GMP materials and performed a phase 1 clinical study with LEISH‐F3+GLA‐SE in healthy, uninfected adults in the United States. The vaccine candidate was shown to be safe and induced a strong antigen‐specific immune response, as evidenced by cytokine and immunoglobulin subclass data. These data provide a strong rationale for additional trials in Leishmania‐endemic countries in populations vulnerable to VL.

Ly49H signaling through DAP10 is essential for optimal natural killer cell responses to mouse cytomegalovirus infection

The activating natural killer (NK) cell receptor Ly49H recognizes the mouse cytomegalovirus (MCMV) m157 glycoprotein expressed on the surface of infected cells and is required for protection against MCMV. Although Ly49H has previously been shown to signal via DAP12, we now show that Ly49H must also associate with and signal via DAP10 for optimal function. In the absence of DAP12, DAP10 enables Ly49H-mediated killing of m157-bearing target cells, proliferation in response to MCMV infection, and partial protection against MCMV. DAP10-deficient Ly49H+ NK cells, expressing only Ly49H–DAP12 receptor complexes, are partially impaired in their ability to proliferate during MCMV infection, display diminished ERK1/2 activation, produce less IFN-γ upon Ly49H engagement, and demonstrate reduced control of MCMV infection. Deletion of both DAP10 and DAP12 completely abrogates Ly49H surface expression and control of MCMV infection. Thus, optimal NK cell–mediated immunity to MCMV depends on Ly49H signaling through both DAP10 and DAP12.

Therapeutic immunization against Mycobacterium tuberculosis is an effective adjunct to antibiotic treatment.

BACKGROUND Recent advances in rational adjuvant design and antigen selection have enabled a new generation of vaccines with potential to treat and prevent infectious disease. The aim of this study was to assess whether therapeutic immunization could impact the course of Mycobacterium tuberculosis infection with use of a candidate tuberculosis vaccine antigen, ID93, formulated in a synthetic nanoemulsion adjuvant, GLA-SE, administered in combination with existing first-line chemotherapeutics rifampicin and isoniazid. METHODS We used a mouse model of fatal tuberculosis and the established cynomolgus monkey model to design an immuno-chemotherapeutic strategy to increase long-term survival and reduce bacterial burden, compared with standard antibiotic chemotherapy alone. RESULTS This combined approach induced robust and durable pluripotent antigen-specific T helper-1-type immune responses, decreased bacterial burden, reduced the duration of conventional chemotherapy required for survival, and decreased M. tuberculosis-induced lung pathology, compared with chemotherapy alone. CONCLUSIONS These results demonstrate the ability of therapeutic immunization to significantly enhance the efficacy of chemotherapy against tuberculosis and other infectious diseases, with implications for treatment duration, patient compliance, and more optimal resource allocation.

Cutting Edge: Recombinant Listeria monocytogenes Expressing a Single Immune-Dominant Peptide Confers Protective Immunity to Herpes Simplex Virus-1 Infection

The vast majority of the world’s population is infected with HSV. Although antiviral therapy can reduce the incidence of reactivation and asymptomatic viral shedding, and limit morbidity and mortality from active disease, it cannot cure infection. Therefore, the development of an effective vaccine is an important global health priority. In this study, we demonstrate that recombinant Listeria monocytogenes (Lm) expressing the H-2Kb glycoprotein B (gB)498–505 peptide from HSV-1 triggers a robust CD8 T cell response to this Ag resulting in protective immunity to HSV infection. Following challenge with HSV-1, immune-competent mice primed with recombinant Lm-expressing gB498–505 Ag were protected from HSV-induced paralysis. Protection was associated with dramatic reductions in recoverable virus, and early expansion of HSV-1-specific CD8 T cells in the regional lymph nodes. Thus, recombinant Lm-expressing Ag from HSV represents a promising new class of vaccines against HSV infection.