Expression and targeted inhibition of the immunoregulatory carbohydrate-binding lectin, Galectin 1, in EBV-driven post-transplant lymphoproliferative disorders

JING OUYANG; PRZEMYSLAW JUSZCZYNSKI; EVAN O’DONNELL; MYRIAM ARMANT; SCOTT RODIG; KUNIHIKO TAKEYAMA; STEFANO MONTI; GABRIEL RABINOVICH,; JEFFERY KUTOK; JEROME RITZ; MARGARET SHIPP

New Orleans

Congreso; Annual Meeting American Hematology Society (ASH),; 2009

American Hematology Society

Post-transplant lymphoproliferative disorders (PTLD) are potentially fatal malignancies that develop in immunocompromised solid organ or bone marrow allograft recipients. These aggressive lymphomas are most commonly Epstein-Barr virus (EBV)-driven B-cell tumors. Proliferation of EBV-infected B cells in PTLD is maintained by expression of EBV latent genes such as latent membrane protein1 (LMP1) and LMP2A, viral immune evasion strategies and impaired host immune surveillance. PTLD management is currently based on reduction or withdrawal of immunosuppression which increases the risk of graft rejection. For these reasons, alternative treatments that specifically boost host anti-EBV immune responses are needed. To identify novel T-cell inhibitory molecules induced by EBV and expressed in PTLDs, we compared the transcription profiles of a series of EBV-transformed lymphoblastoid B-cell lines (LCLs) and diffuse large B-cell lymphoma (DLBCL) cell lines. The LCLs overexpressed galectin-1 (Gal-1), a carbohydrate-binding lectin that induces tolerogenic dendritic cells and triggers the selective apoptosis of CD4+ Th1 and CD8+ cytotoxic T cells. Gal-1 protein expression was also uniformly high in LCLs and low or undetectable in DLBCL lines by western blotting. Immunohistochemical staining of primary tumors confirmed abundant Gal-1 expression in PTLD B-cells, whereas DLBCLs were negative. To elucidate the mechanisms responsible for Gal-1 overexpression in EBV-associated PTLD, we cotransfected FLAG-tagged LMP1 and/or LMP2A with a luciferase reporter vector driven by Gal-1 promoter. LMP2A and LMP1 each increased Gal-1-driven luciferase expression 3- to 6-fold, respectively, and the combination of LMP2A and LMP1 was synergistic. In complementary experiments, siRNA-mediated depletion of LMP2A decreased Gal-1 abundance in EBV-transformed lymphoblastoid cells. The mechanism of LMP1 and LMP2A-induced Gal-1 expression in LCLs was both AP-1 and PI3K-dependent; the PI3K selective inhibitor, LY294002, markedly inhibited Gal-1 expression in these cells.  Given the tolerogenic and immunosuppressive function of Gal-1 and the EBV-driven overexpression of the lectin in LCLs and primary PTLDs, we postulated that Gal-1 might be a targetable immune escape mechanism in EBV-associated malignancies. For these reasons, we assessed the neutralizing activity of a recently developed series of anti-Gal1 monoclonal antibodies. After confirming that these reagents selectively identified both recombinant and native Gal1, we asked whether certain Gal-1 monoclonal antibodies neutralized recombinant Gal-1-mediated apoptosis of EBV-specific polyclonal, largely CD8+, T-cells. Preincubation of human recombinant Gal-1 (hrGal-1) with Gal-1 monoclonal antibodies, but not with isotype-matched controls, selectively inhibited hrGal-1 induced apoptosis of EBV-specific CD8+ T-cells. Taken together, these studies indicate that EBV-transformed LCLs and primary PTLDs express Gal-1 in LMP-1 and LMP2A-dependent manner. Given the acknowledged the role of Gal-1 in mediating an immunopriviledged tumor microenvironment, the lectin likely inhibits the host anti-tumor response in these tumors. Antibody-mediated neutralization of secreted Gal-1 may represent a novel immunotherapeutic strategy in PTLD and other Gal1-expressing tumors Post-transplant lymphoproliferative disorders (PTLD) are potentially fatal malignancies that develop in immunocompromised solid organ or bone marrow allograft recipients. These aggressive lymphomas are most commonly Epstein-Barr virus (EBV)-driven B-cell tumors. Proliferation of EBV-infected B cells in PTLD is maintained by expression of EBV latent genes such as latent membrane protein1 (LMP1) and LMP2A, viral immune evasion strategies and impaired host immune surveillance. PTLD management is currently based on reduction or withdrawal of immunosuppression which increases the risk of graft rejection. For these reasons, alternative treatments that specifically boost host anti-EBV immune responses are needed. To identify novel T-cell inhibitory molecules induced by EBV and expressed in PTLDs, we compared the transcription profiles of a series of EBV-transformed lymphoblastoid B-cell lines (LCLs) and diffuse large B-cell lymphoma (DLBCL) cell lines. The LCLs overexpressed galectin-1 (Gal-1), a carbohydrate-binding lectin that induces tolerogenic dendritic cells and triggers the selective apoptosis of CD4+ Th1 and CD8+ cytotoxic T cells. Gal-1 protein expression was also uniformly high in LCLs and low or undetectable in DLBCL lines by western blotting. Immunohistochemical staining of primary tumors confirmed abundant Gal-1 expression in PTLD B-cells, whereas DLBCLs were negative. To elucidate the mechanisms responsible for Gal-1 overexpression in EBV-associated PTLD, we cotransfected FLAG-tagged LMP1 and/or LMP2A with a luciferase reporter vector driven by Gal-1 promoter. LMP2A and LMP1 each increased Gal-1-driven luciferase expression 3- to 6-fold, respectively, and the combination of LMP2A and LMP1 was synergistic. In complementary experiments, siRNA-mediated depletion of LMP2A decreased Gal-1 abundance in EBV-transformed lymphoblastoid cells. The mechanism of LMP1 and LMP2A-induced Gal-1 expression in LCLs was both AP-1 and PI3K-dependent; the PI3K selective inhibitor, LY294002, markedly inhibited Gal-1 expression in these cells.  Given the tolerogenic and immunosuppressive function of Gal-1 and the EBV-driven overexpression of the lectin in LCLs and primary PTLDs, we postulated that Gal-1 might be a targetable immune escape mechanism in EBV-associated malignancies. For these reasons, we assessed the neutralizing activity of a recently developed series of anti-Gal1 monoclonal antibodies. After confirming that these reagents selectively identified both recombinant and native Gal1, we asked whether certain Gal-1 monoclonal antibodies neutralized recombinant Gal-1-mediated apoptosis of EBV-specific polyclonal, largely CD8+, T-cells. Preincubation of human recombinant Gal-1 (hrGal-1) with Gal-1 monoclonal antibodies, but not with isotype-matched controls, selectively inhibited hrGal-1 induced apoptosis of EBV-specific CD8+ T-cells. Taken together, these studies indicate that EBV-transformed LCLs and primary PTLDs express Gal-1 in LMP-1 and LMP2A-dependent manner. Given the acknowledged the role of Gal-1 in mediating an immunopriviledged tumor microenvironment, the lectin likely inhibits the host anti-tumor response in these tumors. Antibody-mediated neutralization of secreted Gal-1 may represent a novel immunotherapeutic strategy in PTLD and other Gal1-expressing tumors Post-transplant lymphoproliferative disorders (PTLD) are potentially fatal malignancies that develop in immunocompromised solid organ or bone marrow allograft recipients. These aggressive lymphomas are most commonly Epstein-Barr virus (EBV)-driven B-cell tumors. Proliferation of EBV-infected B cells in PTLD is maintained by expression of EBV latent genes such as latent membrane protein1 (LMP1) and LMP2A, viral immune evasion strategies and impaired host immune surveillance. PTLD management is currently based on reduction or withdrawal of immunosuppression which increases the risk of graft rejection. For these reasons, alternative treatments that specifically boost host anti-EBV immune responses are needed. To identify novel T-cell inhibitory molecules induced by EBV and expressed in PTLDs, we compared the transcription profiles of a series of EBV-transformed lymphoblastoid B-cell lines (LCLs) and diffuse large B-cell lymphoma (DLBCL) cell lines. The LCLs overexpressed galectin-1 (Gal-1), a carbohydrate-binding lectin that induces tolerogenic dendritic cells and triggers the selective apoptosis of CD4+ Th1 and CD8+ cytotoxic T cells. Gal-1 protein expression was also uniformly high in LCLs and low or undetectable in DLBCL lines by western blotting. Immunohistochemical staining of primary tumors confirmed abundant Gal-1 expression in PTLD B-cells, whereas DLBCLs were negative. To elucidate the mechanisms responsible for Gal-1 overexpression in EBV-associated PTLD, we cotransfected FLAG-tagged LMP1 and/or LMP2A with a luciferase reporter vector driven by Gal-1 promoter. LMP2A and LMP1 each increased Gal-1-driven luciferase expression 3- to 6-fold, respectively, and the combination of LMP2A and LMP1 was synergistic. In complementary experiments, siRNA-mediated depletion of LMP2A decreased Gal-1 abundance in EBV-transformed lymphoblastoid cells. The mechanism of LMP1 and LMP2A-induced Gal-1 expression in LCLs was both AP-1 and PI3K-dependent; the PI3K selective inhibitor, LY294002, markedly inhibited Gal-1 expression in these cells.  Given the tolerogenic and immunosuppressive function of Gal-1 and the EBV-driven overexpression of the lectin in LCLs and primary PTLDs, we postulated that Gal-1 might be a targetable immune escape mechanism in EBV-associated malignancies. For these reasons, we assessed the neutralizing activity of a recently developed series of anti-Gal1 monoclonal antibodies. After confirming that these reagents selectively identified both recombinant and native Gal1, we asked whether certain Gal-1 monoclonal antibodies neutralized recombinant Gal-1-mediated apoptosis of EBV-specific polyclonal, largely CD8+, T-cells. Preincubation of human recombinant Gal-1 (hrGal-1) with Gal-1 monoclonal antibodies, but not with isotype-matched controls, selectively inhibited hrGal-1 induced apoptosis of EBV-specific CD8+ T-cells. Taken together, these studies indicate that EBV-transformed LCLs and primary PTLDs express Gal-1 in LMP-1 and LMP2A-dependent manner. Given the acknowledged the role of Gal-1 in mediating an immunopriviledged tumor microenvironment, the lectin likely inhibits the host anti-tumor response in these tumors. Antibody-mediated neutralization of secreted Gal-1 may represent a novel immunotherapeutic strategy in PTLD and other Gal1-expressing tumors