Tamada, Koji

53BP1 participates early in the DNA damage response and is involved in cell cycle checkpoint control. Moreover, the phenotype of mice and cells deficient in 53BP1 suggests a defect in DNA repair (Ward et al., 2003b). Therefore, we asked whether or not 53BP1 would be required for the efficient repair of DNA double strand breaks. Our data indicate that homologous recombination by gene conversion does not depend on 53BP1. Moreover, 53BP1-deficient mice support normal V(D)J recombination, indicating that 53BP1 is not required for “classic” nonhomologous end joining. However, class switch recombination is severely impaired in the absence of 53BP1, suggesting that 53BP1 facilitates DNA end joining in a way that is not required or redundant for the efficient closing of RAG-induced strand breaks. These findings are similar to those observed in mice or cells deficient in the tumor suppressors ATM and H2AX, further suggesting that the functions of ATM, H2AX, and 53BP1 are closely linked.

AbstractT-cell anergy is a tolerance mechanism defined as a hyporesponsive status of antigen-specific T cells upon prior antigen encounter and is believed to play a critical role in the evasion of tumor immunity and the amelioration of allogeneic transplant rejection. Molecular mechanisms in controlling T-cell anergy are less known. We show here that administration of an agonistic monoclonal antibody (mAb) to CD137, a member of the tumor necrosis factor receptor superfamily, prevents the induction of CD8+ cytolytic T-lymphocyte (CTL) anergy by soluble antigens. More importantly, CD137 mAb restores the functions of established anergic CTLs upon reencountering their cognate antigen. As a result, infusion of CD137 mAb inhibits progressive tumor growth that is caused by soluble tumor antigen-induced tolerance in a P815R model. CD137 mAb also restores proliferation and effector functions of anergic alloreactive 2C T cells in a bone marrow transplantation model. Our results indicate that ligation of CD137 receptor delivers a regulatory signal for T-cell anergy and implicate manipulation of the CD137 pathway as a new approach to break T-cell tolerance.

OBJECTIVESCD62L was evaluated as a determinant of human pre‐effector T cells.STUDY DESIGN AND SETTINGPhenotype and cytokine secretion profiles of CD62L cells were determined based on activation status.RESULTSCD62LLow T cells demonstrated significantly higher secretion of interleukin (IL)‐10 and interferon (IFN)‐Γ than did CD62LHigh T cells. After activation, the majority of cells expressed high levels of the CD62L surface marker. Postactivation levels of IL‐10 production remained elevated or unchanged. In a murine B16 melanoma model, freshly isolated CD62LLow tumor draining lymph nodes (TDLN) T cells showed increased secretion of IL‐2 and IL‐4 but not of IL‐10 or IFN‐γ. The surface expression of CD62L and cytokine secretion patterns were maintained after activation with concomitant increases in IL‐10.CONCLUSIONOur results provide evidence that CD62LLow T cells in TDLNs of progressively growing squamous cell carcinoma of the head and neck differ phenotypically and functionally from those of mouse origin.SIGNIFICANCECharacterization of this human CD62LLow T cell population provides initial insight regarding novel surface markers in TDLN T cells that might correlate with antitumor reactivity.

B7-DC molecules are known to function as ligands on antigen-presenting cells (APCs), enhancing T cell activation. In this study, cross-linking B7-DC with the monoclonal antibody sHIgM12 directly potentiates dendritic cell (DC) function by enhancing DC presentation of major histocompatibility complex–peptide complexes, promoting DC survival; and increasing secretion of interleukin (IL)-12p70, a key T helper cell type 1 promoting cytokine. Furthermore, ex vivo treatment of DCs or systemic treatment of mice with sHIgM12 increases the number of transplanted DCs that reach draining lymph nodes and increases the ability of lymph node APCs to activate naive T cells. Systemic administration of the antibody has an equivalent effect on DCs transferred at a distant site. These findings implicate B7-DC expressed on DCs in bidirectional communication. In addition to the established costimulatory and inhibitory functions associated with B7-DC, this molecule can also function as a conduit for extracellular signals to DCs modifying DC functions.

AbstractThe members of tumor necrosis factor receptor (TNFR) superfamily have been designated as the “guardians of the immune system” due to their roles in immune cell proliferation, differentiation, activation, and death (apoptosis). This study reports the cloning of a new member of the TNFR superfamily, RELT (ReceptorExpressed in Lymphoid Tissues). RELT is a type I transmembrane glycoprotein with a cysteine-rich extracellular domain, possessing significant homology to other members of the TNFR superfamily, especially TNFRSF19, DR3, OX40, and LTβ receptor. The messenger RNA of RELT is especially abundant in hematologic tissues such as spleen, lymph node, and peripheral blood leukocytes as well as in leukemias and lymphomas. RELT is able to activate the NF-κB pathway and selectively binds tumor necrosis factor receptor-associated factor 1. Although the soluble form of RELT fusion protein does not inhibit the one-way mixed lymphocyte reaction, immobilized RELT is capable of costimulating T-cell proliferation in the presence of CD3 signaling. These results define a new member of the TNFR superfamily that may be a potential regulator of immune responses.

B7-H1 is a recently described B7-like molecule that costimulates T-cell growth and cytokine secretion without binding to CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4), and inducible costimulator (ICOS). In this report, a mouse homologue of human B7-H1 is identified, and its immunologic functions are studied in vitro and in vivo. Mouse B7-H1 shares 69% amino acid homology to the human counterpart. Similar to human B7-H1, mouse B7-H1 can be induced to express on macrophages, T cells, and B cells and to enhance T-cell proliferation and secretion of interleukin-10 (IL-10), interferon-γ, and granulocyte-macrophage colony-stimulating factor but not IL-2 and IL-4. Furthermore, B7-H1 preferentially costimulates CD4+ T cells independently of CD28 and enhances mixed lymphocyte responses to allogeneic antigens. In contrast to B7-1, expression of B7-H1 on murine P815 tumor cells by transfection fails to increase allogeneic and syngeneic cytolytic T-cell responses in vitro and in vivo. Administration of B7-H1Ig fusion protein, however, enhances keyhole limpet hemocyanin– specific T-cell proliferation and 2,4,6-trinitrophenyl–specific immunoglobulin G2a antibody production. The study thus identifies a unique costimulatory pathway that preferentially affects T-helper cell functions.

Interaction between inducible costimulator (ICOS) and its ligand is implicated in the induction of cell-mediated and humoral immune responses. However, the molecular details of this interaction are unknown. We report here a mutagenesis analysis of residues in ICOS that are critical for ligand binding. A three-dimensional model of the extracellular immunoglobulin-like domain of ICOS was used to map the residues conserved within the CD28 family. This analysis identified a surface patch containing the characteristic “PPP” sequence and is conserved in human and mouse ICOS. Mutations in this region of human ICOS reduce or abolish ligand binding. Our results suggest that the ligand binding site in ICOS maps to a region overlapping yet distinct from the CD80/CD86 binding sites in CD28 and cytotoxic T lymphocyte antigen (CTLA)-4. Thus, the analysis suggests that differences in ligand binding specificity between these related costimulatory molecules have evolved by utilization of overlapping regions with different patterns of conserved and nonconserved residues. Two site-specific mutants generated in the course of our studies bound ICOS ligand with higher avidity than wild-type ICOS. An S76E mutant protein of ICOS blocked T cell costimulatory function of ICOS ligand and inhibited T cell response to allogeneic antigens superior to wild-type ICOS. Our studies thus identified critical residues involving in ICOS receptor–ligand interaction and provide new modulators for immune responses.