Suzanne Ostrand-Rosenberg

Cutting Edge: STAT6-Deficient Mice Have Enhanced Tumor Immunity to Primary and Metastatic Mammary Carcinoma

STAT4 and STAT6 are essential for the development of CD4+ Th1 and Th2 development, respectively. Tumor immunologists have hypothesized that Th1 cells are critical in tumor immunity because they facilitate differentiation of CD8+ T cells, which are potent anti-tumor effectors. We have used STAT4−/− and STAT6−/− mice to test this hypothesis. BALB/c and knockout mice were challenged in the mammary gland with the highly malignant and spontaneously metastatic BALB/c-derived 4T1 mammary carcinoma. Primary tumor growth and metastatic disease are reduced in STAT6−/− mice relative to BALB/c and STAT4−/− mice. Ab depletions demonstrate that the effect is mediated by CD8+ T cells, and immunized STAT6−/− mice have higher levels of 4T1-specific CTL than BALB/c or STAT4−/− mice. Surprisingly, Th1 or Th2 cells are not involved, because CD4 depletion does not diminish the anti-tumor effect. Therefore, deletion of the STAT6 gene facilitates development of potent anti-tumor immunity via a CD4+-independent pathway.

Tumor immunotherapy: the tumor cell as an antigen-presenting cell

Increased knowledge in basic immunology has led to a variety of innovative and imaginative approaches for tumor-specific immunotherapy. One of these approaches is based on the premise that tumor cells do not normally stimulate an effective tumor-specific immune response, because they do not efficiently present tumor antigens to the relevant lymphocytes. To overcome inadequate antigen presentation, it has been hypothesized that tumor cells can be genetically engineered to present tumor peptides directly to T lymphocytes.

Resistance to Metastatic Disease in STAT6-Deficient Mice Requires Hemopoietic and Nonhemopoietic Cells and Is IFN-γ Dependent

Mice deficient for the STAT6 gene (STAT6−/− mice) have enhanced immunosurveillance against primary and metastatic tumors. Because STAT6 is a downstream effector of the IL-4R, and IL-13 binds to the type 2 IL-4R, IL-13 has been proposed as an inhibitor that blocks differentiation of tumor-specific CD8+ T cells. Immunity in STAT6−/− mice is unusually effective in that 45–80% of STAT6−/− mice with established, spontaneous metastatic 4T1 mammary carcinoma, whose primary tumors are surgically excised, survive indefinitely, as compared with <10% of STAT+/+ (BALB/c) mice. Surprisingly, STAT6−/− and BALB/c reciprocal bone marrow chimeras do not have increased immunosurveillance, demonstrating that immunity requires STAT6−/− hemopoietic and nonhemopoietic components. Likewise, CD1−/− mice that are NKT deficient and therefore IL-13 deficient also have heightened tumor immunity. However, STAT6−/− and CD1−/− reciprocal bone marrow chimeras do not have increased survival, suggesting that immunity in STAT6−/− and CD1−/− mice is via noncomplementing mechanisms. Metastatic disease is not reduced in BALB/c mice treated with an IL-13 inhibitor, indicating that IL-13 alone is insufficient for negative regulation of 4T1 immunity. Likewise, in vivo depletion of CD4+CD25+ T cells in BALB/c mice does not increase survival, demonstrating that CD4+CD25+ cells do not regulate immunity. Cytokine production and tumor challenges into STAT6−/−IFN-γ−/− mice indicate that IFN-γ is essential for immunity. Therefore, immunosurveillance in STAT6−/− mice facilitates survival against metastatic cancer via an IFN-γ-dependent mechanism involving hemopoietic and nonhemopoietic derived cells, and is not exclusively dependent on counteracting IL-13 or CD4+CD25+ T cells.

Gr-1+ CD11b+ Myeloid-derived Suppressor Cells Suppress Inflammation and Promote Insulin Sensitivity in Obesity

Activation of immune cells, including macrophages and CD8+ T cells, contributes significantly to the advancement of obesity and its associated medical complications, such as atherosclerosis, insulin resistance, and type 2 diabetes. However, how the activation of these immune cells is regulated in vivo remains largely unexplored. Here we show that a group of immature myeloid cells with cell surface markers of Gr-1+ CD11b+ are highly enriched in peripheral tissues (i.e. liver and adipose tissues) during obesity. Down-regulation of these cells in obese animals significantly increases inflammation and impairs insulin sensitivity and glucose tolerance, whereas elevation of these cells via adoptive transfer has the opposite effects. Mechanistically, we show that under obese conditions, the Gr-1+ cells suppress proliferation and induce apoptosis of CD8+ T cells and are capable of skewing differentiation of macrophages into insulin-sensitizing, alternatively activated M2 macrophages. Taken together, our study demonstrates that immature myeloid cells provide a checks-and-balances platform to counter proinflammatory immune cells in the liver and adipose tissue during obesity to prevent overt immune responses.

Tumor Cells Present MHC Class II-Restricted Nuclear and Mitochondrial Antigens and Are the Predominant Antigen Presenting Cells In Vivo

MHC class II-restricted tumor Ags presented by class II+ tumor cells identified to date are derived from proteins expressed in the cytoplasm or plasma membrane of tumor cells. It is unclear whether MHC class II+ tumor cells present class II-restricted epitopes derived from other intracellular compartments, such as nuclei and/or mitochondria, and whether class II+ tumor cells directly present Ag in vivo. To address these questions, a model Ag, hen egg lysozyme, was targeted to various subcellular compartments of mouse sarcoma cells, and the resulting cells were tested for presentation of three lysozyme epitopes in vitro and for presentation of nuclear Ag in vivo. In in vitro studies, Ags localized to all tested compartments (nuclei, cytoplasm, mitochondria, and endoplasmic reticulum) are presented in the absence invariant chain and H-2M. Coexpression of invariant chain and H-2M inhibit presentation of some, but not all, of the epitopes. In vivo studies demonstrate that class II+ tumor cells, and not host-derived cells, are the predominant APC for class II-restricted nuclear Ags. Because class II+ tumor cells are effective APC in vivo and probably present novel tumor Ag epitopes not presented by host-derived APC, their inclusion in cancer vaccines may enhance activation of tumor-reactive CD4+ T cells.

Cell-based vaccines for the stimulation of immunity to metastatic cancers

Summary: We are developing vaccines for inducing immunity lo metastatic cancers. Although primary tumors are frequently cured by surgery, chemotherapy, or radiation therapy, metastatic lesions often do not respond lo these treatments or proliferate after conventional therapy is terminated. Vaccine therapy for established metastases as well as prophylactic vaccine treatment to prevent outgrowth of latent metastatic tumor cells would therefore be beneficial. Our goal is to activate CD4+ and CDS+ T lymphocytes; however, we have focused on activating tumor‐specific CD4+ T‐helper lymphocytes because of their pivotal role as regulatory cells and in the generation of long‐term immunological memory. The vaccines are based on the premise that tumor cells express potentially immunogenic antigens that could be targeted for T‐cell activation, and that if appropriately genetically modified, tumor cells could be antigen presenting cells for these antigens. To facihtate direct antigen presentation to CD4+ T cells, tumor cells have been transfected with syngeneic major histocompatibility complex class II, co‐stimulatory molecule, and/or superantigen genes. In vivo studies in three mouse tumor models demonstrate that vaccination protects against future challenge with wild‐type tumor, cures some solid primary tumors, reduces established metastatic disease, and extends mean survival time. Antigen presentation studies demonstrate that m vivo vaccine efficacy is directly related to in vitro antigen presentation activity. The relevance of antigen presentation activity of the vaccines is further confirmed by in vivo studies demonstrating that during the immunization process, the vaccines directly present tumor‐encoded antigens to CD4+ T lymphocytes. Adaptation of these vaccines for the treatment of human metastatic cancers is discussed.

Tumor antigen presentation: changing the rules

Abstractu2003Cell-based tumor vaccines have been developed on the basis of the hypothesis that tumor cells can be genetically modified to present antigen to T lymphocytes directly. Contrary to expectations, cross-priming is the predominant pathway for activation of tumor-specific CD8+ T cells, while direct presentation of antigen dominates activation of tumor-specific CD4+ T cells. These results pose interesting paradoxes for the generation of immune responses, and have definite implications for the development of anti-cancer vaccines.

Intracytoplasmic domains of MHC class II molecules are essential for lipid-raft-dependent signaling

In addition to their role in antigen presentation, major histocompatibility complex (MHC) class II molecules have been widely described as signaling proteins in diverse antigen-presenting cells (APCs) including B cells and dendritic cells. By contrast, little is known of the signaling function of MHC class II molecules expressed in solid tumors. We describe the functional organization and signaling ability of I-Ak expressed in a sarcoma, and report the recruitment of I-Ak to lipid rafts after MHC class II engagement. Lipid raft integrity was required for I-Ak-mediated reorganization of the actin cytoskeleton and translocation of protein kinase C-α(PKC-α) to the precise site of stimulation via I-Ak. Truncation of the intracytoplasmic domains of I-Ak did not perturb I-Ak recruitment to lipid rafts but abrogated PKC-αtranslocation and actin rearrangement. PKC-αwas detected in lipid microdomains and enrichment of activated PKC-αin lipid rafts was induced by I-Ak signaling. Ordering of the molecular events following engagement of the MHC class II molecules revealed that I-Ak recruitment to lipid rafts precedes signaling. This is consistent with the absence of a requirement for the intracytoplasmic tails for localization to lipid rafts. These data reveal that lipid-rich microdomains play a key role in MHC class II-mediated signaling in a solid tumor.

Class II-transfected tumor cells directly present endogenous antigen to CD4+ T cells in vitro and are APCs for tumor-encoded antigens in vivo

We have previously demonstrated that class II-transfected tumor cells are very effective immunogens that protect against wild-type primary and metastatic tumor and, if supertransfected with genes encoding co-stimulatory molecules, are immunotherapeutic agents that successfully treat mice with established solid tumor. These results are consistent with our hypothesis that the class II-transfected tumor cells act as antigen-presenting cells (APCs) that directly activate tumor-specific CD4+ T cells; however, direct data supporting this hypothesis are lacking. In the present study, we test this hypothesis using class II-transfected tumor cells supertransfected with the hen egg lysozyme gene as a surrogate tumor antigen. In vitro antigen presentation assays demonstrate that class II-transfected tumor cells present to CD4+ T cells endogenously encoded tumor antigen, provided they do not co-express the class II-associated invariant chain. In vivo experiments using genetically marked tumor cells and host APCs demonstrate that both class II-transfected tumor cells and host cells are APCs for tumor-encoded antigens, although tumor cells appear to dominate the response. These results support the hypothesis that the immunogenicity and therapeutic value of class II-transfected tumor cells stem from their ability to function as APCs for tumor-encoded antigens and directly activate tumor-specific CD4+ T lymphocytes.

TLR5 ligand-secreting T cells reshape the tumor microenvironment and enhance antitumor activity

The tumor microenvironment counters antitumor T-cell responses, in part, by blunting their activation and infiltration. Ligands that engage Toll-like receptors (TLR) on T cells and antigen-presenting cells can act as potent immune adjuvants. In this study, we show how tumor-reactive T cells engineered to secrete bacterial flagellin, a TLR5 ligand (TLR5L), can engender a costimulatory signal that augments antitumor activity. Human T cells engineered to express TLR5L along with DMF5, a T-cell receptor that recognizes the melanoma antigen MART-127-35 (DMF5(TLR5L) T cells), displayed increased proliferation, cytokine production, and cytolytic activity against melanoma cells. In a xenogenetic model, adoptive transfer of DMF5(TLR5L) T cells reduced tumor growth kinetics and prolonged mouse survival. In a syngeneic model, similarly engineered melanoma-reactive T cells (pmel(TLR5L)) displayed a relative increase in antitumor activity against established tumors, compared with unmodified T cells. In this model, we documented increased T-cell infiltration associated with increased levels of CCR1 and CXCR3 levels on T cells, a reduction in PD-1(+)Lag3(+) T cells and CD11(+)Gr1(+) myeloid-derived suppressor cells, and changes in the chemokine/cytokine profile of tumors. Our findings show how T cell-mediated delivery of a TLR agonist to the tumor site can contribute to antitumor efficacy, in the context of adoptive T-cell immunotherapy.