Preferential recognition of a microbial metabolite by human Vgamma2Vdelta2 T cells.

Human Vgamma2Vdelta2 T cells are stimulated by prenyl pyrophosphates, such as isopentenyl pyrophosphate (IPP), and play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) has been identified as a metabolite in the 2-C-methyl-D-erythritol-4 phosphate (MEP) pathway for isoprenoid biosynthesis that is used by many bacteria and protozoan parasites. We find that HMBPP is the major Vgamma2Vdelta2 T-cell antigen for many bacteria, including Mycobacterium tuberculosis, Yersinia enterocolitica and Escherichia coli. HMBPP was a 30 000-fold more potent antigen than IPP. Using mutant bacteria, we show that bacterial antigen levels for Vgamma2Vdelta2 T cells are controlled by MEP pathway enzymes and find no evidence for the production of 3-formyl-1-butyl pyrophosphate. Moreover, HMBPP reactivity required only germ line-encoded Vgamma2Vdelta2 TCR elements and is present at birth. Importantly, we show that bacterial HMBPP levels correlated with their ability to expand Vgamma2Vdelta2 T cells in vivo upon engraftment into severe combined immunodeficiency-beige mice. Thus, the production of HMBPP by a microbial-specific isoprenoid pathway plays a major role in determining whether bacteria will stimulate Vgamma2Vdelta2 T cells in vivo. This preferential stimulation by a common microbial isoprenoid metabolite allows Vgamma2Vdelta2 T cells to respond to a broad array of pathogens using this pathway.

Pyridinium-1-yl bisphosphonates are potent inhibitors of farnesyl diphosphate synthase and bone resorption.

We report the design, synthesis and testing of a series of novel bisphosphonates, pyridinium-1-yl-hydroxy-bisphosphonates, based on the results of comparative molecular similarity indices analysis and pharmacophore modeling studies of farnesyl diphosphate synthase (FPPS) inhibition, human Vgamma2Vdelta2 T cell activation and bone resorption inhibition. The most potent molecules have high activity against an expressed FPPS from Leishmania major, in Dictyostelium discoideum growth inhibition, in gammadelta T cell activation and in an in vitro bone resorption assay. As such, they represent useful new leads for the discovery of new bone resorption, antiinfective and anticancer drugs.

Synthesis of chiral phosphoantigens and their activity in gamma delta T cell stimulation.

Gammadelta T cells expressing Vgamma2Vdelta2 T cell receptors are activated by a broad range of phosphorus-containing small molecules, termed phosphoantigens, and are of interest in the context of the chemotherapy of B cell malignancies. Here, we report the synthesis of four pairs of chiral phosphoantigens: the bromohydrins of isopentenyl diphosphate (Phosphostim), the epoxides of isopentenyl diphosphate (EIPP); and the corresponding bromohydrin and epoxide analogs of but-3-enyl diphosphate. The ability of each compound to stimulate human Vgamma2Vdelta2 T cells was determined by TNF-alpha release and cell proliferation. In these assays, the (R)-bromohydrin diphosphates were, on average, about twice as active as the (S)-bromohydrin diphosphates. In contrast, the (S)-form of EIPP was about twice as active as (R)-EIPP. The activities of the epoxy but-3-enyl diphosphates were both very low. These results suggest that chiral phosphoantigens, as opposed to racemic mixtures, may have utility in immunotherapy.

Quantitative structure-activity relationships for gammadelta T cell activation by bisphosphonates.

gammadelta T cells are the first line of defense against many infectious organisms and are also involved in tumor cell surveillance and killing. They are stimulated by a broad range of small, phosphorus-containing antigens (phosphoantigens) as well as by the bisphosphonates commonly used in bone resorption therapy, such as pamidronate and risedronate. Here, we report the activation of gammadelta T cells by a broad range of bisphosphonates and develop a pharmacophore model for gammadelta T cell activation, in addition to using a comparative molecular similarity index analysis (CoMSIA) approach to make quantitative relationships between gammadelta T cell activation by bisphosphonates and their three-dimensional structures. The CoMSIA analyses yielded R(2) values of approximately 0.8-0.9 and q(2) values of approximately 0.5-0.6 for a training set of 45 compounds. Using an external test set, the activities (IC(50) values) of 16 compounds were predicted within a factor of 4.5, on average. The CoMSIA fields consisted of approximately 40% hydrophobic, approximately 40% electrostatic, and approximately 20% steric interactions. Since bisphosphonates are known to be potent, nanomolar inhibitors of the mevalonate/isoprene pathway enzyme farnesyl pyrophosphate synthase (FPPS), we also compared the pharmacophores for gammadelta T cell activation with those for FPPS inhibition, using the Catalyst program. The pharmacophores for gammadelta T cell activation and FPPS inhibition both consisted of two negative ionizable groups, a positive charge feature and an endocyclic carbon feature, all having very similar spatial dispositions. In addition, the CoMSIA fields were quite similar to those found for FPPS inhibition by bisphosphonates. The activities of the bisphosphonates in gammadelta T cell activation were highly correlated with their activities in FPPS inhibition: R = 0.88, p = 0.002, versus a human recombinant FPPS (N = 9 compounds); R = 0.82, p < 0.0001, for an expressed Leishmania major FPPS (N = 45 compounds). The bisphosphonate gammadelta T cell activation pharmacophore differs considerably, however, from that reported previously for gammadelta T cell activation by phosphoantigens (Gossman, W.; Oldfield, E. J. Med. Chem. 2002, 45, 4868-4874), suggesting different primary targets for the two classes of compounds. The ability to quite accurately predict the activity of bisphosphonates as gammadelta T cell activators by using 3D QSAR techniques can be expected to help facilitate the design of additional bisphosphonates for potential use in immunotherapy.