There is accelerating interest in the use of nonspecific immunostimulants or adjuvants as a means of enhancing or inducing
nonspecific immunity. A further requirement for the development of successful therapeutic vaccines is the upregulation or
induction of intrinsic innate immune defenses that have the capacity to destroy the infectious agent or tumor cell directly,
or to synergize with existing cytotoxic or immunologic treatment regimens. This article discusses the potential of MIS416
adjuvant, a novel vaccine adjuvant and immunogen co-delivery system, to fulfill this requirement.
( IMAGE SOURCE/GETTY IMAGES)
There is a great need for the development of therapeutic vaccines for patients with cancer or acquired chronic infections,
such as HIV, hepatitis, tuberculosis, and malaria. Therapeutic vaccines aim to enhance the inherent capability of the patient's
immune system to fight the disease, leading to a reduction in severity or complete elimination of the disease. To date, developments
have fallen short of expectations. This is caused, in part, by the failure of chronically infected or immunosuppressed patients
to respond adequately to the vaccine adjuvant component, which itself may not have the appropriate breadth of immunostimulatory
A requirement underpinning the successful development of prophylactic and therapeutic vaccines lies in the ability to target
adjuvant or antigen complexes to dendritic cells with the simultaneous induction of a coordinated and targeted inflammatory
response in the secondary lymphoid tissues. In addition to providing adequate immunostimulation to overcome host factors that
may limit the success of therapeutic vaccines, we believe a further requirement for the development of successful therapeutic
vaccines is the upregulation or induction of intrinsic innate immune defenses that have the capacity to destroy the infectious
agent or tumor cell directly, or to synergize with existing cytotoxic or immunologic treatment regimens.
MIS416 adjuvant, a novel vaccine adjuvant and immunogen co-delivery system designed by Virionyx Corporation, is well positioned
to fulfill this requirement, acting to induce anti-infective mechanisms such as the production of anti-viral IFN-α, and activation
of oxidative microbiocidal pathways, in addition to the activation of broad spectrum anti-tumor responses. MIS416 adjuvant-mediated
co-stimulation of dendritic and accessory cell immune crosstalk, concomitant with MIS416-enhanced anti-infective or anticancer
cytotoxic activity is likely to facilitate uptake and presentation of autologous viral, bacterial, or tumor antigens, enhancing
the generation of vaccine induced immunity. The additional activation of broad spectrum host immune defenses by MIS416 vaccine
adjuvant therefore presents an exciting strategy for developing a broad range of therapeutic vaccines.
MIS416 comprises multiple immunostimulatory TLR9 and NOD-2 ligands that are cross linked in a manner that also permits the
covalent attachment of a broad range of immunogens (Figure 1). MIS416 vaccine candidates incorporating a broad range of immunogens
have been shown to act in a well-defined manner and have demonstrated significant potency for induction of protective, long-lived
humoral immunity, and cellular adaptive immunity with no adverse events noted, even following multiple immunizations.
Figure 1. Graphical representation of MIS416. MIS416 is a semi-synthetic, nontoxic, nonimmunogenic, cage structured microparticle
(2 microns) composed of muramyl dipeptide repeats covalently attached to a poly amino acid backbone principally composed of
lysine and glycine amino acid repeats. N-acetyl glucosamine is incorporated as an oxidizable carbohydrate for use in linking
amino containing ligands. Bacterial DNA is incorporated through amino linkages covalently attached to the poly amino backbone.
Microparticle components are isolated from the cell wall of Propionibacterium acnes and ligands or immunogens are produced
synthetically with recombinant technology or isolated from natural sources to produce the desired vaccine formulation or activate
the desired immune pathway. Insertion and covalent linkage of ligands or immunogens is achieved using bifunctional cross linkers,
which link through primary and secondary amino groups present in the microparticle or through carbohydrate moieties following
oxidation. (IMAGE CREDIT: RUSSELL KIGHTLEY MEDIA)
Activating Host Antimicrobial Defense Mechanisms
The release of inflammatory mediators by first-line immune cells is followed by cell activation. These mediators act, in part,
through autocrine and paracrine signaling loops to enhance innate immune activities, such as phagocytosis and intracellular
killing. A key example of this is the ability of MIS416 to induce reactive oxygen species (ROS) and nitrogen monoxide (NO)
production by monocytes and granulocytes (Figure 2).
Figure 2. MIS416 is a potent activator of reactive oxygen species and nitric monoxide in granulocytes and monocytes. (A)
Human blood was cultured with 10, 5, or 1 µg/mL MIS416 for three hours at 37°C. Cells were loaded with 1 µM of cell permeant
fluorescent ROS indicator 3´-(p-aminophenyl) fluorescein (APF) for the last 30 minutes. Reactions were quenched by the addition
of excess ice-cold 1.5 mM EDTA and cells were labelled with anti-CD14-PerCP for identification of monocytes and PI viability
dye (1 µg/mL). Cells were analyzed by flow cytometry of gated viable monocytes and granulocytes and the percent of cells expressing
upregulated APF fluorescence was determined. (B) Whole diluted blood was incubated for two hours with 10, 5, or 1 µg/mL MIS416.
5 µM nitric oxide (NO) cell permeant indicator dye (4-amino-5-methylamino-2, 7-difluorofluorescein diacetate; DAF-FM) was
added and cells incubated for a further 30 minutes to allow for dye loading. Cells were then washed and re-incubated for 20
minutes at 37°C to allow for de-esterification fo the dye, then samples were analyzed by flow cytometry. The percent of cells
showing DAF-FM positive fluorescence are indicated.
The functional potential of MIS416 microbiocidal activity has been demonstrated in a mouse therapeutic vaccine model studying
the ability of MIS416 and Titermax adjuvant to induce adaptive immunity against drug resistant Mycobacterium tuberculosis
(MTb) and reduce the infectious bioburden (Figure 3). Immunization of mice three times over a period of 14 days led to a significant
reduction of infectious MTb in the MIS416-treated group, which was greater than that observed in the Titermax treated group.
Figure 3. MIS416 enhances the immunogenicity of ESAT-6 and clearance of drug-resistant M. tuberculosis in mice. C57Bl/6 mice
were intravenously infected with drug-resistant strain of MTb at 105 CFU per mouse and infection allowed to progress for 14
days. Mice were then treated with 25 µg per mouse of recombinant MTb ESAT-6 protein in either Titermax adjuvant, MIS416 adjuvant,
or no adjuvant, given on days 14, 18, and 21 (3 doses per mouse). Mice were sacrificed on day 28 and lung CFU counts performed
by plating organ homogenates on 7H11 agar. 3-mice per time point were analyzed (* denotes significance by t test).