Project Details
Projekt
Suppression of human T cells by 5'-methylthioadenosine
Applicants
Dr. Michael Aigner; Professor Dr. Andreas Mackensen
Subject Area
Hematology, Oncology
Term
from 2011 to 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 190230491
Malignant cells develop diverse mechanisms to escape T cell-mediated immune recognition, including a dysregulated metabolism. Studies in melanoma and renal cell carcinoma have revealed loss of 5-methylthioadenosine phosphorylase (MTAP) expression in vitro and in vivo. The enzyme MTAP is responsible for the catalytic degradation of its substrate 5-methythioadenosine (MTA). As a direct consequence, MTAP-deficient tumors secrete high amounts of MTA. In the first funding period we could demonstrate that MTA suppresses human CD8+ cytotoxic T cells in vitro by inhibiting proliferation and cytokine secretion. To study the role of endogenously secreted MTA on antitumor immune responses, a human MTAP-deficient, high MTA secreting melanoma cell line was stably transfected with MTAP resulting in a significant reduction of MTA secretion. Comparative mixed tumor/lymphocyte cultures revealed a reduced proliferative capacity in T cells stimulated with allogeneic mock-transfected melanoma cells (high MTA secretors) compared to T cells stimulated with MTAP-transfected melanoma cells (low MTA secretors). In addition, we were able to identify two distinct effects of MTA on human T cell subpopulations. When resting CD8+ T cells were exposed to MTA upon antigen-specific stimulation with peptide-pulsed APCs, MTA KFO 262 Project 3 strongly inhibited activation, proliferation, and differentiation of antigen-specific T cells. In contrast, exposure of already activated antigen-specific CD8+ T cells with low doses of MTA resulted in apoptotic death of T cells. Next, we analyzed signaling pathways in CD8+ T cells after MTA exposure and found that MTA leads to downregulation of phosphorylated (p)Akt but not ERK or p38. As pAkt is part of the CD28 co-receptor pathway we postulate that MTA inhibits signal II of T cell activation. To reconstitute tumor-specific T cell responses in vitro and in vivo we aim to overcome the inhibitory effects of MTA by overexpression of MTAP in human CD8+ T cells. Antigen specific CD8+ T cells will be stably transfected with MTAP, characterized and adoptively transferred into tumor bearing, immunodeficient mice to study the antitumor efficacy in vivo. Our previous results have shown that MTA can affect Akt-mediated signaling which is crucial for T cell activation. Therefore we aim to overcome this blockade by using a natural Akt activating cytokine (IL-7) or a small molecule (SC-79) which acts as an Akt activator. To further understand the molecular mechanism of MTA induced T cell suppression in more detail, we aim to characterize the effects of MTA on asymmetric protein methylation after T cell activation. MTA could also interfere with the metabolic potential of T cells and tumor cells thereby exerting in part its immunoregulatory effects. To test this hypothesis the aerobic and/or anaerobic metabolic potential of T cells in relation to tumor cells will be analyzed in short-term or long-term cultures. In a first series of experiments we could
DFG Programme
Clinical Research Units
