Chen, Lieping

Abstract Contemporary approaches for vaccination and immunotherapy are often capable of eliciting strong T-cell responses against tumor antigens. However, such responses are not parallel to clinical tumor regression. The development of evasion mechanisms within tumor microenvironment may be responsible for poor therapeutic responses. We report here that constitutive or inducible expression of B7-H1, a B7 family molecule widely expressed by cancers, confers resistance to therapeutic anti-CD137 antibody in mice with established tumors. The resistance is accompanied with failure of antigen-specific CD8+ CTLs to destroy tumor cells without impairment of CTL function. Blockade of B7-H1 or PD-1 by specific monoclonal antibodies could reverse this resistance and profoundly enhance therapeutic efficacy. Our findings support that B7-H1/PD-1 forms a molecular shield to prevent destruction by CTLs and implicate new approaches for immunotherapy of human cancers.

ABSTRACTC57BL/6 mice mount a cytotoxic T-lymphocyte (CTL) response against the Daniel’s strain of Theiler’s murine encephalomyelitis virus (TMEV) 7 days after infection and do not develop persistent infection or the demyelinating syndrome similar to multiple sclerosis seen in susceptible mice. The TMEV capsid peptide VP2121–130sensitizesH-2Db+target cells for killing by central-nervous-system-infiltrating lymphocytes (CNS-ILs) isolated from C57BL/6 mice infected intracranially. Db:VP2121–130peptide tetramers were used to stain CD8+CNS-ILs, revealing that 50 to 63% of these cells bear receptors specific for VP2121–130presented in the context of Db. No T cells bearing this specificity were found in the cervical lymph nodes or spleens of TMEV-infected mice.H-2bmice lacking CD4, class II, gamma interferon, or CD28 expression are susceptible to persistent virus infection but surprisingly still generate high frequencies of CD8+, Db:VP2121–130-specific T cells. However, CD4-negative mice generate a lower frequency of Db:VP2121–130-specific T cells than do class II negative or normalH-2banimals. Resistant tumor necrosis factor alpha receptor I knockout mice also generate a high frequency of CD8+CNS-ILs specific for Db:VP2121–130. Furthermore, normally susceptible FVB mice that express a Dbtransgene generate Db:VP2121–130-specific CD8+CNS-ILs at a frequency similar to that of C57BL/6 mice. These results demonstrate that VP2121–130presented in the context of Dbis an immunodominant epitope in TMEV infection and that the frequency of the VP2121–130-specific CTLs appears to be independent of several key inflammatory mediators and genetic background but is regulated in part by the expression of CD4.

AbstractDendritic cells (DCs) are critical subsets of leukocytes providing antigen presentation for initiation of humoral and cellular immune responses. Their role as effector cells in tumor resistance, however, is less known. We report here that human DCs generated by culturing plastic-adherent peripheral blood monocytes in the presence of granulocyte-monocyte colony–stimulating factor (GM-CSF) and interleukin-4 have potent growth-inhibition activity in vitro on a wide spectrum of human tumor lines of different tissue origin. Proinflammatory stimuli lipopolysaccharide (LPS) and interferon-γ, but not tumor necrosis factor– and CD40 signaling, can further enhance DC-mediated inhibition of tumor growth. The growth inhibition requires contact between DCs and tumor cells while LPS treatment enhances the antitumor activity in DC culture supernatants. Our results suggest that in addition to their predominant role as regulatory cells, activated DCs are also potential effector cells in tumor immunity.

Abstract This report describes a new human B7-like gene designatedB7-H2. Cell surface expression of B7-H2 protein is detected in monocyte-derived immature dendritic cells. Soluble B7-H2 and immunoglobulin (Ig) fusion protein, B7-H2Ig, binds activated but not resting T cells and the binding is abrogated by inducible costimulator Ig (ICOSIg), but not CTLA4Ig. In addition, ICOSIg stains Chinese hamster ovary cells transfected with B7-H2 gene. By suboptimal cross-linking of CD3, costimulation of T-cell proliferation by B7-H2Ig is dose-dependent and correlates with secretion of interleukin (IL)-2, whereas optimal CD3 ligation preferentially stimulates IL-10 production. The results indicate that B7-H2 is a putative ligand for the ICOS T-cell molecule.

Dendritic cells (DCs) are critical subsets of leukocytes providing antigen presentation for initiation of humoral and cellular immune responses. Their role as effector cells in tumor resistance, however, is less known. We report here that human DCs generated by culturing plastic-adherent peripheral blood monocytes in the presence of granulocyte-monocyte colony–stimulating factor (GM-CSF) and interleukin-4 have potent growth-inhibition activity in vitro on a wide spectrum of human tumor lines of different tissue origin. Proinflammatory stimuli lipopolysaccharide (LPS) and interferon-γ, but not tumor necrosis factor– and CD40 signaling, can further enhance DC-mediated inhibition of tumor growth. The growth inhibition requires contact between DCs and tumor cells while LPS treatment enhances the antitumor activity in DC culture supernatants. Our results suggest that in addition to their predominant role as regulatory cells, activated DCs are also potential effector cells in tumor immunity.

This report describes a new human B7-like gene designatedB7-H2. Cell surface expression of B7-H2 protein is detected in monocyte-derived immature dendritic cells. Soluble B7-H2 and immunoglobulin (Ig) fusion protein, B7-H2Ig, binds activated but not resting T cells and the binding is abrogated by inducible costimulator Ig (ICOSIg), but not CTLA4Ig. In addition, ICOSIg stains Chinese hamster ovary cells transfected with B7-H2 gene. By suboptimal cross-linking of CD3, costimulation of T-cell proliferation by B7-H2Ig is dose-dependent and correlates with secretion of interleukin (IL)-2, whereas optimal CD3 ligation preferentially stimulates IL-10 production. The results indicate that B7-H2 is a putative ligand for the ICOS T-cell molecule.

Abstract LIGHT is a recently identified member of the TNF superfamily and its receptors, herpesvirus entry mediator and lymphotoxin β receptor, are found in T cells and stromal cells. In this study, we demonstrate that LIGHT is selectively expressed on immature dendritic cells (DCs) generated from human PBMCs. In contrast, LIGHT is not detectable in DCs either freshly isolated from PBMCs or rendered mature in vitro by LPS treatment. Blockade of LIGHT by its soluble receptors, lymphotoxin β receptor-Ig or HVEM-Ig, inhibits the induction of DC-mediated primary allogeneic T cell response. Furthermore, engagement of LIGHT costimulates human T cell proliferation, amplifies the NF-κB signaling pathway, and preferentially induces the production of IFN-γ, but not IL-4, in the presence of an antigenic signal. Our results suggest that LIGHT is a costimulatory molecule involved in DC-mediated cellular immune responses.

Abstract A human IgM Ab, serum-derived human IgM 12 (sHIgM12), is identified that binds mouse and human dendritic cells (DC), inducing dramatic immunopotentiation following treatment of the mouse DC in vitro. Competition, transfection, and knockout studies identified the ligand on mouse DC as the costimulatory molecule family member B7-DC. Potent T cell responses are stimulated by Ag-pulsed DC treated with the sHIgM12 Ab in vitro and upon adoptive transfer of Ab-treated Ag-pulsed DC into animals. The multivalent structure of pentameric IgM provides the potential for cross-linking cell surface targets, endowing the soluble Abs with biological potential not normally associated with immune function. The ability of the sHIgM12 Ab to potentiate the immune response is dependent on the multimeric structure of IgM, as bivalent monomers do not retain this property. Furthermore, pretreatment of DC with IgM monomers blocks subsequent potentiation by intact IgM pentamers, an indication that cross-linking of B7-DC on the cell surface is critical for potentiation of Ag presentation. These findings imply that, in addition to known costimulatory roles, B7-DC can function as a receptor for signals delivered by cells expressing B7-DC ligands.

Abstract Islet allografts are subject to rapid rejection through host cellular immune responses involving mononuclear cell recruitment and tissue injury. Interruption of leukocyte recruitment through chemokine receptor targeting is of therapeutic benefit in various experimental models, but little is known about the contribution of chemokine pathways to islet allograft rejection. We found that murine islets produce monocyte chemoattractant protein-1 (MCP-1; CCL2) in vitro and that islet allograft rejection was associated with intragraft expression of MCP-1 and its receptor, CCR2. We therefore investigated whether MCP-1 and CCR2 are required for the rejection of fully MHC-disparate islet allografts. Wild-type mice treated with blocking anti-MCP-1 mAb plus a brief, subtherapeutic course of rapamycin had long-term islet allograft survival, in contrast to the effect of treatment with either mAb or rapamycin alone. CCR2−/− mice treated with rapamycin also maintained islet allografts long-term. Both MCP/CCR2- and rapamycin-sensitive signals were required for maximal proliferation of alloreactive T cells, suggesting that MCP-1/CCR2 induce rejection by promoting alloreactive T cell clonal expansion and homing and migration. Prolonged islet allograft survival achieved by blockade of the MCP-1/CCR2 pathway plus rapamycin therapy was accompanied by a mononuclear cell infiltrate expressing the inhibitory receptor, programmed death-1 (PD-1), and its ligand (PD-L1, B7-H1), and prolongation of islet allograft survival was abrogated by anti-PD-L1 mAb therapy. These data show that the blockade of MCP-1 binding to CCR2 in conjunction with subtherapeutic immunosuppression can have profound effects on islet allograft survival and implicate the expression of the PD-1/PD-L1 pathway in the regulation of physiologic responses in vivo.