Small phosphorylated metabolites from mycobacteria stimulate human ␥␦ T lymphocytes. Although such phosphoantigens could prove useful in the composition of vaccines involving ␥␦ T cell-mediated immunity, their very low abundance in natural sources limits such applications. Here, we describe the chemical production, purification, and bioactivity of a phosphorylated bromohydrin (BrHPP) analogue that mimics the biological properties of natural phosphoantigens. This compound can be obtained in gram amounts, is easy to detect, and is of high stability in aqueous solutions. Whereas unspecific binding of BrHPP to a wide panel of cell surface receptors is not detected even at micromolar concentrations, nanomolar concentrations specifically trigger effector responses of human ␥␦ T lymphocytes. Thus, BrHPP is a novel molecule enabling potent immunostimulation of human ␥␦ T lymphocytes.Stimulating ligands for ␣␤ T lymphocytes are usually composed of single peptides complexed at the surface of major histocompatibility complex molecules. Some small non-peptidic structures, however, may also constitute specific agonist ligands for T cells, particularly ␥␦ T lymphocytes. In human blood, about 3% of T cells initiate their physiological function upon recognition of small phosphorylated non-peptide antigens (phosphoantigens). This cognate interaction involves on the one hand phosphoantigens in the absence of major histocompatibility complex-presenting molecules, and on the other hand, highly selective receptors (TCR) 1 of ␥␦ subtype. In nature, phosphoantigens that can activate human ␥␦ T cells at nanomolar concentrations are produced by Gram-positive and Gram-negative bacteria and also by some eukaryotic parasites and plants. Synthetic analogues of natural phosphoantigens are also known, but their stimulating concentrations for the reactive cells never go below the micromolar range. Mycobacterium tuberculosis, the agent of human tuberculosis, produces four distinct phosphoantigens. These molecules share a moiety that is responsible for the potent stimulation of ␥␦ cells seen in tuberculosis patients (1). The structure of this common core is 3-formyl-1-butyl-pyrophosphate, a recently described phosphoester (2). Its metabolic production might be related to the non-mevalonate (or so-called Rohmer's) pathway for isoprenoid precursor biosynthesis (3). 3-formyl-1-butyl-pyrophosphate is produced in very small amounts in slow-growing mycobacteria such as Mycobacterium tuberculosis and only accumulates to submicromolar concentrations in culture media from fast-growing mycobacterial species (4). Getting large amounts of highly bioactive phosphoantigens by purification routes from such natural sources is therefore hard to conceive.Such molecules could prove therapeutically useful for immunotherapeutic approaches involving ␥␦ T cell-mediated immunity, such as elicitation of anti-infectious protection or antitumor immunity (5, 6). To address the need for readily available highly bioactive phosphoantigens, we have developed a synthetic reagen...

Soluble human interleukin-6 receptor (sIL-6R) was measured in the serum of 30 healthy individuals, 32 individuals with monoclonal gammopathy of undetermined significance (MGUS), 20 patients with early multiple myeloma (MM) and 54 patients with overt MM. The serum activity recognized by an immunoradiometric assay was determined to be sIL-6R, because of its binding capacity to IL-6 and its molecular mass of 55 kDa. All sera of healthy individuals contained sIL-6R (mean value: 89 ng/ml, range 17-300 ng/ml). Serum sIL-6R levels were increased by 51% in patients with MGUS (mean value: 135 ng/ml, p < 0.005), by 44% in patients with early myeloma (mean value: 128 ng/ml, p < 0.001) and by 116% in patients with overt MM (mean value: 193 ng/ml, p < 0.001). In patients with MM, a complete lack of correlation (p > 0.7) was found between serum sIL-6R levels and other previously recognized prognostic factors in this disease, particularly serum IL-6 levels and those factors related to tumor cell mass. The independence of serum sIL-6R levels on tumor cell mass was directly demonstrated by studying four patients with MM treated with autologous bone marrow transplantation for periods of between 320 and 760 days. These levels were found to be remarkably stable and constant, independent of whether patients relapsed or achieved complete remission. Finally, physiological concentrations of sIL-6R were found to increase by tenfold the sensitivity of human myeloma cell lines to IL-6. These observations suggest a high control of the sIL-6R level in vivo, and, possibly, an important functional role of this circulating protein in patients with monoclonal gammopathies.

A patient with plasma cell leukemia was treated with anti-interleukin (IL)-6 monoclonal antibodies (mAb) for 2 months. Using chromatography on protein A-Sepharose, anti-murine-IgG-Sepharose, anti-IL-6-mAb-Sepharose and gel filtration at pH 2.3, we have demonstrated that the anti-IL-6 mAb, by preventing the binding of IL-6 to its cell membrane receptor and its renal elimination, has induced huge amounts of IL-6 to circulate in the form of monomeric immune complexes. By using this observation, we have developed a mathematical modelling that allows the determination of the overall daily production of IL-6 in this patient, which was in the range of 15 micrograms per day. Overall in vivo production of cytokines has never been evaluated in animals or in humans before.

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Interleukin 6 and C-reactive protein (CRP) were determined prior to IL-2 therapy in sera from metastatic melanoma patients. Patients with elevated serum IL-6 (> 20 pg ml-1) and/or CRP (> 10 mg l-1) levels were associated with resistance to IL-2 therapy. A correlation between high serum IL-6 levels and a shorter median survival was also observed.