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Exhaustion of virus-specific T cells may play an important role in the pathophysiology of chronic viral infections. Here, we analyzed telomere length and telomerase activity in HIV-1–specific CD8+T cells from progressors or controllers to determine underlying molecular pathways of T-cell exhaustion and senescence. Telomere lengths of HIV-1–specific CD8+T cells from progressors were significantly shorter compared with autologous cytomegalovirus (CMV)/Epstein-Barr virus (EBV)–specific CD8+T cells or bulk CD8+T cells, while telomere lengths from controllers significantly exceeded those of autologous bulk CD8+T cells and reached a similar level as HIV-1–specific CD8+T cells collected during primary HIV-1 infection. Telomere length stabilization in controllers corresponded to high levels of constitutive telomerase activity, which was associated with preservation of cytotoxic and proliferative properties. Conversely, limited constitutive telomerase activity was observed in HIV-1–specific CD8+T cells from progressors, although an increase in both telomere length and telomerase activity was achieved in antigenic-peptide–stimulated cells from progressors after blocking the PD-1/PD ligand 1 (PD-L1) pathway. Collectively, these data suggest a causal role of telomere shortening for the functional deficiencies of HIV-1–specific CD8+T cells in chronic progressive infection, while high constitutive telomerase activities appears to contribute to maintenance of polyfunctional HIV-1–specific CD8+T cells from HIV-1 controllers.

Quiescent T cells express Tob, an APRO gene family member, which functions as a transcriptional regulator. Subtractive hybridization identified Twisted gastrulation (Tsg) as one of the genes suppressed by Tob. Tsg is a secreted protein that interacts with Drosophila decapentaplegic (Dpp) and its vertebrate orthologs BMP2/4 and regulates morphogenetic effects in embryos. Here, we report the expression and function of Tsg in human T cells. Tsg mRNA was almost undetectable in unstimulated T cells and was up-regulated after activation by TCR/CD3 and either CD28, IL-2, or PMA. Tsg protein had no effect on responses of primary T cells to TCR/CD3 stimulation but had a potent inhibitory effect on proliferation and cytokine production of primed alloreactive CD4+ cells. Surprisingly, Tsg did not affect phosphorylation of the BMP-specific Smad1 but induced phosphorylation of the TGF-ß–specific Smad2 and mediated DNA binding on Smad3/4 consensus-binding sites, suggesting that it acted downstream of TGF-ß. In vitro association assays revealed a direct interaction of Tsg and TGF-ß proteins. Thus, Tsg functions as an agonist synergizing with TGF-ß to inhibit T-cell activation. Modulation of Tsg signaling may represent a novel target for molecular intervention toward control of aberrant T-cell responses during ongoing graft-versus-host disease (GVHD) and autoimmune diseases.

Quiescent T cells express Tob, an APRO gene family member, which functions as a transcriptional regulator. Subtractive hybridization identified Twisted gastrulation (Tsg) as one of the genes suppressed by Tob. Tsg is a secreted protein that interacts with Drosophiladecapentaplegic (Dpp) and its vertebrate orthologs BMP2/4 and regulates morphogenetic effects in embryos. Here, we report the expression and function of Tsg in human T cells. TsgmRNA was almost undetectable in unstimulated T cells and was up-regulated after activation by TCR/CD3 and either CD28, IL-2, or PMA. Tsg protein had no effect on responses of primary T cells to TCR/CD3 stimulation but had a potent inhibitory effect on proliferation and cytokine production of primed alloreactive CD4+cells. Surprisingly, Tsg did not affect phosphorylation of the BMP-specific Smad1 but induced phosphorylation of the TGF-β–specific Smad2 and mediated DNA binding on Smad3/4 consensus-binding sites, suggesting that it acted downstream of TGF-β. In vitro association assays revealed a direct interaction of Tsg and TGF-β proteins. Thus, Tsg functions as an agonist synergizing with TGF-β to inhibit T-cell activation. Modulation of Tsg signaling may represent a novel target for molecular intervention toward control of aberrant T-cell responses during ongoing graft-versus-host disease (GVHD) and autoimmune diseases.

Following T-cell receptor and CD28 signaling, CD8+T cells express a receptor for CD83, a molecule up-regulated on functionally mature dendritic cells. Although this expression pattern suggests that CD83 is involved in adaptive immunity, little is known about its function in the periphery, and the existence of its ligand on T cells is controversial. We demonstrate that the engagement of the CD83 ligand (CD83L) preferentially enriches and significantly amplifies the number of antigen-specific CD8+T cells. Coengagement of the T-cell receptor, CD28, and CD83L supports priming of naive CD8+T cells that retain antigen specificity and cytotoxic function for more than 6 months. Therefore, engagement of the CD83L provides a unique signal to activated CD8+T cells that could be exploited to generate long-lived antigen-specific cytotoxic T cells for the treatment of cancer and infection.

Graft-versus-host disease (GVHD) is initiated by adoptively transferred donor T cells that recognize host alloantigens. Whereas the absence of donor T-cell proliferation to host alloantigens in a mixed-leukocyte reaction does not predict freedom from GVHD, the frequency of alloreactive precursor helper T lymphocytes (pHTL) is predictive. Complete blockade of B7 family-mediated costimulation, but not of major histocompatibility complex recognition or adhesion, induces host alloantigen-specific anergy by reducing cytokine production below threshold levels necessary for common γ-chain signaling. The associated reduction of alloreactive pHTL frequency below that predictive for GVHD, without depletion of either nonallospecific T cells or hematopoietic progenitors, has led us to embark upon human clinical trials of haplomismatched allogeneic bone marrow transplantation.

Previous studies have suggested that interleukin-6 (IL-6) may mediate growth of multiple myeloma (MM) in either an autocrine or paracrine growth mechanism. However, those molecules which can trigger IL-6 secretion either by tumor cells or non-MM marrow cells are not well characterized. In the present study, we have examined the expression and functional significance of CD40 on MM and plasma cell leukemia (PCL) cells and derived cell lines, as well as long-term bone marrow stromal cells (BMSCs) and derived cell lines. CD40 was expressed on the majority of MM cells (≫90%) and BMSCs (≫70%). Triggering via CD40 using NIH3T3 CD40 ligand transfectant (CD40LT) cells increased (≫30%) cell surface CD80, CD18, CD11a, CD11b, and CD11c expression on MM cell lines. Culture with either fresh or paraformaldehyde fixed NIH3T3 CD40LT cells upregulates IL-6 secretion in MM cells and MM-derived cell lines, as well as normal and MM bone marrow mononuclear cells (BMMCs), BMSCs, and BMSC lines; this effect can be specifically blocked by anti- CD40 monoclonal antibody (MoAb). BMMCs and BMSCs from patients with MM secreted significantly more IL-6 than those from healthy donors (n = 3, P ≪.001); moreover, after stimulation using CD40L, IL-6 secretion was fourfold greater (n = 3, P ≪.001) from MM BMMCs and BMSCs than from normal BMMCs and BMSCs. Myeloma (CD38+CD45RA-) cells and non-MM (CD38+CD45RA+, CD38-CD45RA+. and CD38-CD45RA-) BMMCs were separated by dual fluorescence cell sorting. The latter secreted fourfold more IL-6 than the former (n = 2, P≪ .001). Increased IL-6 secretion (up to 28-fold) and proliferation (Stimulation Index 10) by CD38+CD45RA-MM cells was triggered by culture with NIH3T3 CD40LT cells. Finally, anti-CD40 MoAb partially (30%) blocked tumor cell to BMSC adhesion-induced IL-6 secretion. These studies support the view that CD40L may trigger IL- 6 secretion by both MM cells and BMSCs and that IL-6— mediated autocrine and paracrine growth mechanisms may be possible in MM.

B7 is an activation antigen expressed on activated B cells and γ-interferon-stimulated monocytes. The B7 antigen is the natural ligand for CD28 on T cells. After engagement of T-cell receptor with antigen in association with major histocompatibility complex class II, a second signal mediated through the binding of B7 to CD28 greatly upregulates the production of multiple lymphokines. We have now mapped the B7 gene to human chromosome 3 using the technique of polymerase chain reaction on a panel of hamster x human somatic cell hybrid DNAs. We have further localized the gene to 3q13.3-3q21 using in situ hybridization on human metaphase chromosomes. Trisomy of chromosome 3 is a recurrent chromosome change seen in various lymphomas and lymphoproliferative diseases, particularly diffuse, mixed, small, and large cell lymphomas, human T-cell lymphotropic virus type l-induced adult T-cell leukemia, and angioimmunoblastic lymphadenopathy. A number of chromosomal defects involving 3q21 have been described in acute myeloid leukemia and also in myelo-dysplastic and myeloproliferative syndromes. The mapping of B7 may permit further insight into disease states associated with aberrant lymphocyte activation and lymphokine synthesis.© 1992 by The American Society of Hematology. 0006-4971/92/7902-0015$3.00/0

T-cell activation is initiated after T-cell receptor binding to antigen, but also requires interactions between costimulatory molecules expressed on antigen-presenting cells. An important costimulatory molecule expressed by monocytes and activated B lymphocytes has been recently identified and termed B7-2 or B70. Independently, a new Cluster of Differentiation was defined in the Fifth International Leukocyte Differentiation Antigen Workshop as CD86, a molecule predominantly expressed by monocytes and activated B lymphocytes. In this study, the two monoclonal antibodies that defined CD86, FUN-1 and BU-63, were shown to bind to cDNA transfected cells expressing B7-2/B70. The FUN-1 monoclonal antibody also completely blocked the costimulatory activity of B7-2/B70 in functional assays. Therefore, the serologically defined CD86 differentiation antigen is the B7-2/B70 molecule.

Abstract 916