Synthesis and biological evaluation of a new class of vaccine adjuvants: aminoalkyl glucosaminide 4-phosphates (AGPs)

A single vaccination with protein-microspheres elicits a strong CD8 T-cell-mediated immune response against Mycobacterium tuberculosis antigen Mtb8.4

Efficient protein-based vaccine delivery systems are needed to achieve a persistent memory immune response capable of detecting and eliminating intracellular pathogens such as Mycobacterium tuberculosis (TB). We have developed a novel protein-microsphere formulation using the recently discovered TB antigen Mtb8.4. Immunization of mice with a single dose of this Mtb8.4-microsphere formulation resulted in both humoral and cellular responses against Mtb8.4. The Mtb8.4-specific CD8 T-cell responses following a single administration of Mtb8.4-microspheres exceeded that elicited by protein plus adjuvant following multiple immunizations. These results demonstrate the efficacy of a single dose protein-microsphere vaccine for the induction of strong cell-mediated and humoral immune responses against M. tuberculosis antigens.

Structure-Activity Relationship of Synthetic Toll-like Receptor 4 Agonists

Important questions remain regarding the impact of variations in the structure of the lipid A portion of lipopolysaccharide on activation of cells via the Toll-like receptor 4 complex. We have studied a series of synthetic lipid A mimetic compounds known as aminoalkyl glucosaminide phosphates in which the length of the secondary acyl chain has been systematically varied. Using transcriptional profiling of human monocytes and responses of Toll-like receptor 4 complex cell transfectants, we demonstrate a clear dependence of length on secondary acyl chain on Toll-like receptor 4 activation. Compounds with secondary acyl chains less than eight carbons in length have dramatically reduced activity, and substitutions of the left-sided secondary acyl chain had the most important effect on the Toll-like receptor 4 agonist activity of these molecules. The structure-function relationships of these compounds assessed via the induction of chemokines and cytokines following in vivo administration closely mirrored those seen with cell-based studies. This novel set of synthetic lipid A mimetics will be useful for Toll-like receptor 4-based investigations and may have clinical utility as stand-alone immunomodulators.

Taking toll: lipid A mimetics as adjuvants and immunomodulators

Vaccine adjuvants based on the structure of lipid A, such as monophosphoryl lipid A (MLA), have proven to be safe and effective in inducing immune responses to heterologous proteins in animal and human vaccines. Recent work on the development of a recombinant vaccine for leishmaniasis has demonstrated that a clinical grade MLA formulation - MPL(R) adjuvant - is essential in the development of a protective response. Preliminary evidence suggests that MLA and a chemically distinct family of lipid A mimetics - the aminoalkyl glucosaminide 4-phosphates - act on Toll-like receptor 4 (TLR4). As TLR4 agonists, they have potent immunomodulatory effects when used both as vaccine adjuvants and as stand-alone products. Novel approaches to vaccine development could benefit from taking full advantage of the effects of these compounds on innate and adaptive responses.