Synthesis and biological activity of phosphonate analogues and geometric isomers of the highly potent phosphoantigen (E)-1-hydroxy-2-methylbut-2-enyl 4-diphosphate

Specific requirements for Vgamma9Vdelta2 T cell stimulation by a natural adenylated phosphoantigen

Human Vgamma9Vdelta2 T lymphocytes recognize phosphorylated alkyl Ags. Isopentenyl pyrophosphate (IPP) was previously proposed as the main Ag responsible for Vgamma9Vdelta2 T cell activation by cancer cells. However, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), a metabolite in which the isopentenyl moiety is linked to ATP, was reported in cells activated with aminobisphosphonates. The contribution of this compound to tumor-stimulatory activity was thus examined. ApppI induces selective expansion of Vgamma9Vdelta2 T cells from PBMCs. In the absence of APCs, however, ApppI has little stimulatory activity on Vgamma9Vdelta2 T cells, and optimal activation with ApppI requires addition of a nucleotide pyrophosphatase releasing IPP plus AMP. Thus, ApppI has no intrinsic stimulatory activity. Nevertheless, stimulation by ApppI is strengthened by the presence of APCs. Moreover, in contrast to IPP, ApppI can be efficiently pulsed on dendritic cells as well as on nonprofessional APCs. Pulsed APCs display stable and phosphatase-resistant stimulatory activity, indicative of Ag modification. HPLC analysis of tumor cell extracts indicates that latent phosphoantigenic activity is stored intracellularly in the Vgamma9Vdelta2 cell-sensitive tumor Daudi and can be activated by a nucleotide pyrophosphatase activity. The presence of ApppI in Daudi cell extracts was demonstrated by mass spectrometry. Nucleotidic Ags such as ApppI are thus a storage form of phosphoantigen which may represent a major source of phosphoantigenic activity in tumor cells. The unique properties of ApppI may be important for the design of Ags used in anticancer immunotherapeutic protocols using Vgamma9Vdelta2 cells.

Thiopyrophosphoantigens: solid-phase synthesis and in vitro characterization of a new class of Vgamma9 Vdelta2 T cells activators

The Vgamma9 Vdelta2 T cells mediate rapid, innate-like immune responses to pathogens and are important in several key immunoregulatory pathways, including those involved in infections and tumor development. Vgamma9 Vdelta2 T cells respond to low molecular weight isoprenoid phosphoantigens; the prototypic stimulatory compound is isopentenylpyrophosphate (IPP), an alkylphosphate intermediate of mevalonate metabolism that elicits proliferative, cytotoxic, and cytokine secretion responses. We studied the replacement of the pyrophosphate moiety with the thiopyrophosphate bioisostere, synthesizing thioanalogues of IPP and 4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP, the most potent natural antigen known to date). Once their in vitro efficacy and stability had been demonstrated, we synthesized a small library of compounds through the development of an innovative solid-phase strategy. Biological results confirmed thioHMBPP to be the best compound of this first series. Future aims are (i) the exploitation of the parallel solid-phase strategy to further explore structure-activity relationships of this new class of synthetic antigens and (ii) the determination of the PK/PD profile of thioHMBPP.

IL-21-mediated potentiation of antitumor cytolytic and proinflammatory responses of human V gamma 9V delta 2 T cells for adoptive immunotherapy

Vgamma9Vdelta2 T lymphocytes are a major human gammadelta T cell subset that react against a wide array of tumor cells, through recognition of phosphorylated isoprenoid pathway metabolites called phosphoantigens. Immunotherapeutic protocols targeting Vgamma9Vdelta2 T cells have yielded promising, yet limited, signs of antitumor efficacy. To improve these approaches, we analyzed the effects on gammadelta T cells of IL-21, a cytokine known to enhance proliferation and effector functions of CD8(+) T cells and NK cells. IL-21 induced limited division of phosphoantigen-stimulated Vgamma9Vdelta2 T cells, but did not modulate their sustained expansion induced by exogenous IL-2. Vgamma9Vdelta2 T cells expanded in the presence of IL-21 and IL-2 showed enhanced antitumor cytolytic responses, associated with increased expression of CD56 and several lytic molecules, and increased tumor-induced degranulation capacity. IL-21 plus IL-2-expanded Vgamma9Vdelta2 T cells expressed higher levels of inhibitory receptors (e.g., ILT2 and NKG2A) and lower levels of the costimulatory molecule NKG2D. Importantly, these changes were rapidly and reversibly induced after short-term culture with IL-21. Finally, IL-21 irreversibly enhanced the proinflammatory Th1 polarization of expanded Vgamma9Vdelta2 T cells when added at the beginning of the culture. These data suggest a new role played by IL-21 in the cytotoxic and Th1 programming of precommitted Ag-stimulated gammadelta T cells. On a more applied standpoint, IL-21 could be combined to IL-2 to enhance gammadelta T cell-mediated antitumor responses, and thus represents a promising way to optimize immunotherapies targeting this cell subset.

Photoaffinity antigens for human gammadelta T cells

Vgamma2Vdelta2 T cells comprise the major subset of peripheral blood gammadelta T cells in humans and expand during infections by recognizing small nonpeptide prenyl pyrophosphates. These molecules include (E)-4-hydroxy-3-methyl-but-2-enyl-pyrophosphate (HMBPP), a microbial isoprenoid intermediate, and isopentenyl pyrophosphate, an endogenous isoprenoid intermediate. Recognition of these nonpeptide Ags is mediated by the Vgamma2Vdelta2 T cell Ag receptor. Several findings suggest that prenyl pyrophosphates are presented by an Ag-presenting molecule: contact between T cells and APC is required, the Ags do not bind the Vgamma2Vdelta2 TCR directly, and Ag recognition is abrogated by TCR mutations in CDRs distant from the putative Ag recognition site. Identification of the putative Ag-presenting molecule, however, has been hindered by the inability to achieve stable association of nonpeptide prenyl pyrophosphate Ags with the presenting molecule. In this study, we show that photoaffinity analogues of HMBPP, meta/para-benzophenone-(methylene)-prenyl pyrophosphates (m/p-BZ-(C)-C(5)-OPP), can crosslink to the surface of tumor cell lines and be presented as Ags to gammadelta T cells. Mutant tumor cell lines lacking MHC class I, MHC class II, beta(2)-microglobulin, and CD1, as well as tumor cell lines from a variety of tissues and individuals, will all crosslink to and present m-BZ-C(5)-OPP. Finally, pulsing of BZ-(C)-C(5)-OPP is inhibited by isopentenyl pyrophosphate and an inactive analog, suggesting that they bind to the same molecule. Taken together, these results suggest that nonpeptide Ags are presented by a novel-Ag-presenting molecule that is widely distributed and nonpolymorphic, but not classical MHC class I, MHC class II, or CD1.