Soluble human lymphocyte activation gene-3 modulates allospecific T cell responses.

Lymphocyte activation gene (LAG)-3, a member of the Ig superfamily, has been characterized as an activation antigen of T cells and NK cells. LAG-3 has been proposed as an alternate ligand for HLA class II due to some sequence homology and similarities in exon-intron organization with CD4. Here, we report the functional evaluation of a soluble Ig fusion molecule of human LAG-3 (LAG-3-Ig) in T cell activation assays. Cytofluorimetry studies revealed LAG-3-Ig binding predominantly to class II-expressing cells. In functional assays, inhibition of primary allogeneic mixed lymphocyte response (MLR) and murine-human xenogeneic MLR was observed in the presence of LAG-3-Ig. Effects of LAG-3-Ig addition were not observed on mitogen-, recall antigen- or superantigen-mediated stimulation. Cytotoxic T lymphocyte effector functions were also not affected by LAG-3-Ig. Inhibition of alloresponses by LAG-3-Ig occurred within the first 24 h of activation, resulting in a strong inhibition of IL-2 production. Unlike blockade of the CD28 receptor, however, LAG-3-Ig-mediated inhibition could not be reversed by exogenous IL-2 supplementation. Cytofluorimetric analysis of the phenotype of cells exposed to LAG-3-Ig in MLR cultures revealed a decrease in IL-2 receptor expression (CD25) on CD4+ cells in all donors tested. Based on the results from these studies, we conclude that LAG-3-Ig inhibits alloresponses of naive peripheral blood lymphocytes, by blocking the activation of a subpopulation of allo reactive cells.

Genetic immunization with the free human chorionic gonadotropin beta subunit elicits cytotoxic T lymphocyte responses and protects against tumor formation in mice.

The free beta subunit of human chorionic gonadotropin (hCG beta) is produced and secreted by human lung, bladder, and pancreatic tumors. We attempted to generate cytotoxic T lymphocytes (CTL) with activity against free hCG beta-producing tumors by genetic immunization using a construct containing a beta subunit expressing cDNA. To assess CTL activity in vivo, a cloned syngeneic SP2/O myeloma call line was established that constitutively expresses the free hCG beta protein. Inoculation of this cell line into BALB/c mice produced large tumors within 2 weeks. However, mice immunized with the free hCG beta expression construct demonstrated a marked reduction of tumor size and weight compared with animals immunized with mock DNA ("empty" plasmid). Indeed, 30% of immunized mice were tumor-free after 3 months and thus considered long-term survivors. Inhibition of tumor growth was strongly associated with the level of CTL activity present in CD8+ cells derived from the spleen. In addition, immunized mice developed high titer anti-hCG beta antibodies that neutralized the biologic effects of the intact hCG glycoprotein hormone on its cellular receptor as well. These results illustrate that substantial cellular and humoral immune responses to the free hCG beta subunit may be generated by DNA immunization. This study thus presents a potential approach to inhibiting growth of human tumor cells that produce and secrete the free hCG beta protein.

The cloning of the human follicle stimulating hormone receptor and its expression in COS-7, CHO, and Y-1 cells.

Follicle stimulating hormone (FSH) receptor clones were isolated from a human testis cDNA library. Characterization of the cDNA clones showed that the DNA and predicted amino acid sequences of the long open reading frame differed from a previously published human ovarian FSH receptor sequence (Minegish et al. (1991) Biochem. Biophys. Res. Commun. 175, 1125-1130) by seven nucleotides and five amino acids. A human FSH receptor splice variant was also identified and characterized. A full-length human FSH receptor cDNA was engineered for expression in COS-7, CHO, and Y-1 cells. In transient transfections of COS-7 cells and stable transfections of Y-1 cells, efficient FSH receptor mRNA accumulation and isolation of FSH-responsive cell lines occurred only when an intron was included in the 5' untranslated region of the FSH receptor transcription unit. Y-1 cells stably transfected with the FSH receptor responded to FSH treatment by rounding up and by synthesizing increased amounts of progesterone. Stably transfected CHO cell lines, which responded to FSH by synthesizing increased amounts of cAMP, were isolated irrespective of the presence of the heterologous intron. The FSH-responsive CHO and Y-1 cell lines may be suitable for the development of better in vitro FSH bioassays. These cells also constitute a convenient source of human FSH receptor protein for use in radioreceptor assays and in studies of receptor-ligand interactions.