Purpose: We performed a phase I trial to investigate the safety, clinical responses, and Wilms' tumor 1 (WT1)-specific immune responses following treatment with dendritic cells (DC) pulsed with a mixture of three types of WT1 peptides, including both MHC class I and II-restricted epitopes, in combination with chemotherapy.
HLA-A2 transgenic mice bearing established HLA-A2(neg) 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.
We have recently shown that effective cytokine gene therapy of solid tumors in HLA-A2 Tg (HHD) mice lacking murine MHC class I molecule expression results in the generation of HLA-A2-restricted CD8+ T effector cells selectively recognizing tumor blood vessel-associated pericytes and/or vascular endothelial cells (VEC). Using an HHD model in which HLA-A2neg tumor (MC38 colon carcinoma or B16 melanoma) cells are not recognized by the CD8+ T cell repertoire, we now show that vaccines based on tumor-associated blood vessel antigens (TBVA) elicit protective Tc1-dependent immunity capable of mediating tumor regression or extending overall survival. Vaccine efficacy was not observed if (HLA-A2neg) wild-type C57BL/6 mice were instead used as recipient animals. In the HHD model, effective vaccination resulted in profound infiltration of tumor lesions by CD8+ (but not CD4+) T cells, in a coordinate reduction of CD31+ blood vessels in the tumor microenvironment (TME) and in the “spreading” of CD8+ T cell responses to alternate TBVA that were not intrinsic to the vaccine. Protective Tc1-mediated immunity was durable and directly recognized pericytes and/or VEC flow-sorted from tumor tissue, but not from tumor-uninvolved normal kidneys harvested from these same animals. Strikingly, the depletion of CD8+, but not CD4+, T cells at late time points after effective therapy frequently resulted in the recurrence of disease at the site of the regressed primary lesion. This suggests that the vaccine-induced anti-TBVA T cell repertoire can mediate the clinically-preferred outcomes of either effectively eradicating tumors or policing a state of (occult) tumor dormancy.
Pancreatic cancer is a highly aggressive and notoriously difficult to treat. As the vast majority of patients are diagnosed at advanced stage of the disease, only a small population is curative by surgical resection. Although gemcitabine-based chemotherapy is typically offered as standard of care, most patients do not survive longer than 6 months. Thus, new therapeutic approaches are needed. Pancreatic cancer cells that develop gemcitabine resistance would still be suitable targets for immunotherapy. Therefore, one promising treatment approach may be immunotherapy that is designed to target pancreatic-cancer-associated antigens. In this paper, we detail recent work in immunotherapy and the advances in concept of combination therapy of immunotherapy and chemotherapy. We offer our perspective on how to increase the clinical efficacy of immunotherapies for pancreatic cancer.
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