Eph receptors and their ligands, ephrins, are known to play important roles in organ development (formation of tissue boundaries, neural crest cell migration, axon guidance) and angiogenesis. In particular, EphA2 has recently attracted interest in the field of cancer research. Many observations, including our own, have demonstrated that most cancers, such as renal cell carcinoma (RCC), overexpress the EphA2 protein. EphA2 overexpression/dysregulation is associated with carcinogenesis, metastasis, and poor clinical prognosis. Indeed EphA2 is not just a marker of metastatic potential, but its overexpression is directly linked to an aggressive tumor phenotype. As a consequence, EphA2 represents a potential target for therapeutic intervention in the setting of EphA2+ cancer histologies, with several agents being developed with clinical intent. Several strategies can be contemplated in this regard, including: (1) selected promotion of EphA2 degradation or to reduce EphA2 expression and signaling (via the application of agonistic antibody, ephrin-A1 Fc fusion protein, siRNA against EphA2, or protein tyrosine phosphatases (PTP) that regulate EphA2 expression or specific EphA2 kinase inhibitors); (2) antagonism of EphA2 receptor-ligand binding (by provision of mimetic peptides or EphA2 Fc fusion protein); and/or (3) vaccination against EphA2 (using specific peptide-, protein-, or gene-based methods) to elicit specific T-cell- or Ig-mediated immunity. In this chapter, we will discuss the basic immunobiology of tumor-associated EphA2 and potential therapeutic interventions directed against EphA2 that may yield clinical benefit in the setting of (renal cell) cancer.
Current immunotherapies designed to stimulate specific T cell-mediated immunity have thus far yielded modest objective clinical response rates, despite the increase of tumor-specific T cells have been observed in treated patient blood. Since the majority of tumor antigens being targeted in immunotherapies are non-mutated, self antigens, current clinical results may relate, in part, to the low-to-moderate avidity, negatively-selected T cell repertoire in patients that is being asked to regulate tumor progression. In the current thesis, I hypothesized that by conditionally enhancing the proteasomal degradation of tumor antigens, I could generate a synchronized pool of derivative peptides that could then be presented in a wave-like temporal fashion in MHC class I complexes on the tumor cell surface. For at least a transient period thereafter, I theorized that specific CD8+ T cell recognition and anti-tumor activities would be improved. I selected a family of tumor-associated antigens, receptor tyrosine kinases (RTK) for study, as their overexpression has been linked with poor clinical prognosis in many forms of cancer. In this thesis, I show that EphA2 agonists, as well as, HSP90 inhibitors effectively promote EphA2 degradation via a proteasome- dependent manner, providing the delivery of EphA2 peptides into the classical MHC class I presentation pathway. I also show that specific CD8+ T cell recognition of EphA2 peptides derived from both the extracellular and intracellular domains of this transmembrane protein was improved as a consequence of tumor cell treatment with these agents being in consistent with the use of TAP- and ER-associated degradation. Notably, the combination of both drugs further enhanced anti-EphA2 T cell recognition of tumor cells, suggesting these modalities work via complementary, but not identical mechanisms. Importantly, complete tumor eradication was achieved in vivo (in a Hu-SCID tumor model) using a combinational therapy consisting of agonist administration just prior to the adoptive transfer of human anti-EphA2 CD8+ T cells, where either single modality was minimally beneficial. Preliminary data from additional studies targeting the tumor cell-overexpressed RTKs, Her2/neu and EGFR, suggest that this core treatment paradigm may be generalizeable to many (if not all) RTKs.
Tumors represent an altered self cell type that can be recognized by both the host humoral (B cells, antibodies) and cellular (T cells) adaptive immune systems. Because most known tumor-associated antigens (TAA) recognized by T cells represent overexpressed or aberrantly expressed proteins, which are not mutated and to which tolerance has been developed, the anti−TAA T−cell repertoire available to the cancer patient is of moderate-to-low avidity. Specific vaccinations typically amplify the absolute number of such T cells, but may have little consequence on improving their functional avidity, which may fall below a critical threshold required for effective recognition of tumor cells in situ. This review will discuss methods to improve low-avidity T−cell recognition of cancer cells by manipulating the tumor cells themselves to conditionally express higher levels of TAA−derived peptide epitopes presented in major histocompatibility (MHC) complexes. This may facilitate the design and performance of novel combinational therapies for the effective treatment of a broad range of cancer types.
Abstract The receptor tyrosine kinase EphA2 is over-expressed in numerous carcinomas in association with poor clinical prognosis. While pharmacologic agents that antagonize EphA2-mediated signaling could be contemplated as a therapy, a more preferred result would be to decrease tumor cell EphA2 expression while coordinately enhancing specific immune reactivity to tumor cells. We show that specific mAb triggers the internalization of EphA2, resulting in increased processing of EphA2 protein and presentation of EphA2-derived epitopes in tumor cell HLA class I complexes to CD8+ T cells (detected by IFN-γ production and CD107b translocation). Ab-enhanced CTL recognition is blocked by tumor cell co-treatment with Pseudomonas Exotoxin-A and proteasome inhibitors, but not by chloroquine, suggesting that internalized EphA2 complexes are rapidly translocated into the cytoplasm for delivery of peptides into the class I biosynthetic route. When combined with vaccines designed to augment the frequency of circulating anti-EphA2 CD8+ T cells, this agonist strategy may define an effective therapy for patients harboring EphA2+ cancers.
Abstract Many receptor tyrosine kinases (RTK) are overexpressed/dysregulated in advanced cancers, serving as negative prognostic indicators. We evaluated the immunogenicity of dendritic cell (DC)/RTK(EphA2, EGFR, Her2/neu)-based vaccines in HLA-A2 (HHD) Tg mice. To enhance the stimulatory capacity of BM-derived DCs, these cells were infected with a recombinant adenovirus encoding mIL-12p70 (Ad.IL12), prior to being pulsed with RTK-derived peptides. We also evaluated a cohort of DC co-infected with both Ad.IL12 and Ad.EphA2. Each of these DC preparations (vs. control DCs) were injected three times s.c. into HHD mice on a weekly schedule. DTH reactions were monitored 48–72h after each vaccination and splenocytes were harvested on d28 and d60 to assess specific CD8+ T cell reactivity (IFN-γ ELISA). Autoimmunity pathology in RTK+ normal tissues (i.e. kidney, liver, lung) were also evaluated for immune infiltration and tissue destruction by (immuno)histochemistry. Vaccines induced specific DTH responses and Tc1 responses in HHD mice, in association with an increased accumulation of CD8+ T cells around proximal endothelial cells (PEC) in the kidney and in the interstitial lung at d28, in the absence of tissue pathology. DC/RTK-based vaccines may promote specific Type-1 immunity that has the potential to eradicate RTK+ tumors, while sparing normal RTK+ tissues. This work was supported by NIH R01 grant CA114071 (W.J.S.)
Ineffective recognition of tumor cells by CD8+ T cells is a limitation of cancer immunotherapy. Therefore, treatment regimens that coordinately promote enhanced antitumor CD8+ T-cell activation, delivery, and target cell recognition should yield greater clinical benefit. Using an MCA205 sarcoma model, we show that in vitro treatment of tumor cells with the HSP90 inhibitor 17-DMAG results in the transient (proteasome-dependent) degradation of the HSP90 client protein EphA2 and the subsequent increased recognition of tumor cells by Type-1 anti-EphA2 CD8+ T cells. In vivo administration of 17-DMAG to tumor-bearing mice led to slowed tumor growth, enhanced/prolonged recognition of tumor cells by anti-EphA2 CD8+ T cells, reduced levels of myeloid-derived suppressor cells and regulatory T cells in the tumor microenvironment, and activation of tumor-associated vascular endothelial cells in association with elevated levels of Type-1 tumor-infiltrating lymphocytes. When combined with EphA2-specific active vaccination or the adoptive transfer of EphA2-specific CD8+ T cells, 17-DMAG cotreatment yielded a superior tumor therapeutic regimen that was capable of rendering animals free of disease. Taken together, our findings indicate that 17-DMAG functions as an immune adjuvant in the context of vaccines targeting EphA2.
Abstract EphA2, a member of receptor tyrosine kinases (RTK), is commonly expressed by a broad range of cancer types, where its level of (over)expression correlates with poor clinical outcome. Since tumor cell expressed EphA2 is a non-mutated "self" protein, specific CD8+ T cells are subject to self-tolerance mechanisms and typically exhibit only moderate-to-low functional avidity, rendering them marginally competent to recognize EphA2+ tumor cells in vitro or in vivo. We have recently reported that the ability of specific CD8+ T cells to recognize EphA2+ tumor cells can be augmented after the cancer cells are pretreated with EphA2 agonists that promote proteasomal degradation (Wesa et al., J. Immunol., in press, 2008). In the current study we show that treatment of EphA2+ tumor cells with the HSP90 inhibitor, 17-DMAG, similarly enhances EphA2 degradation by the proteasome, minimally impairs MHC class I antigen presentign machinery, and increases tumor cell recognition by specific CD8+ T cell lines and clones in vitro. These studies suggest that EphA2 represents a novel HSP90 client protein and that the treatment of cancer patients with 17-DMAG-based "pulse" therapy may improve the anti-tumor efficacy of CD8+ T effector cells reactive against EphA2-derived epitopes.
HLA-A2 transgenic mice bearing established HLA-A2neg B16 melanomas were effectively treated by intratumoral (i.t.) injection of syngeneic dendritic cells (DCs) transduced to express high levels of interleukin (IL)-12, resulting in CD8+ T cell-dependent antitumor protection. In this model, HLA-A2-restricted CD8+ T cells do not directly recognize tumor cells and therapeutic benefit was associated with the crosspriming of HLA-A2-restricted type-1 CD8+ T cells reactive against antigens expressed by stromal cells [i.e., pericytes and vascular endothelial cells (VEC)]. IL-12 gene therapy-induced CD8+ T cells directly recognized HLA-A2+ pericytes and VEC flow-sorted from B16 tumor lesions based on interferon (IFN)-γ secretion and translocation of the lytic granule-associated molecule CD107 to the T cell surface after coculture with these target cells. In contrast, these CD8+ T effector cells failed to recognize pericytes/VEC isolated from the kidneys of tumor-bearing HHD mice. The tumor-associated stromal antigen (TASA)-derived peptides studied are evolutionarily conserved and could be recognized by CD8+ T cells harvested from the blood of HLA-A2+ normal donors or melanoma patients after in vitro stimulation. These TASA and their derivative peptides may prove useful in vaccine formulations against solid cancers, as well as, in the immune monitoring of HLA-A2+ cancer patients receiving therapeutic interventions, such as IL-12 gene therapy. HLA-A2 transgenic mice bearing established HLA-A2neg B16 melanomas were effectively treated by intratumoral (i.t.) injection of syngeneic dendritic cells (DCs) transduced to express high levels of interleukin (IL)-12, resulting in CD8+ T cell-dependent antitumor protection. In this model, HLA-A2-restricted CD8+ T cells do not directly recognize tumor cells and therapeutic benefit was associated with the crosspriming of HLA-A2-restricted type-1 CD8+ T cells reactive against antigens expressed by stromal cells [i.e., pericytes and vascular endothelial cells (VEC)]. IL-12 gene therapy-induced CD8+ T cells directly recognized HLA-A2+ pericytes and VEC flow-sorted from B16 tumor lesions based on interferon (IFN)-γ secretion and translocation of the lytic granule-associated molecule CD107 to the T cell surface after coculture with these target cells. In contrast, these CD8+ T effector cells failed to recognize pericytes/VEC isolated from the kidneys of tumor-bearing HHD mice. The tumor-associated stromal antigen (TASA)-derived peptides studied are evolutionarily conserved and could be recognized by CD8+ T cells harvested from the blood of HLA-A2+ normal donors or melanoma patients after in vitro stimulation. These TASA and their derivative peptides may prove useful in vaccine formulations against solid cancers, as well as, in the immune monitoring of HLA-A2+ cancer patients receiving therapeutic interventions, such as IL-12 gene therapy.
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