Naturally occurring T-cell response against mutated p21 ras oncoprotein in pancreatic cancer.

Abstract

Mutated p21 ras proteins (muRas) are present in f90% of pancreatic adenocarcinomas and express mutants which can function as cancer-specific antigens. To evaluate the frequency and magnitude of the natural T-cell response against muRas in 19 HLA-A2-positive patients with muRas-positive pancreatic carcinomas, antigen-experienced T lymphocytes in fresh peripheral blood mononuclear cells were shown by IFN-g enzyme-linked immunospot using muRas peptides (5-21) that encompass both HLA class I (HLA-A2)^and class II^restricted (HLA-DRB1) epitopes. Six of 19 patients (32%) were found to have a specific T-cell response against individual mutation-specific ras 5-21 but not against other ras mutations or wild-type ras. In contrast, none of 19 healthy subjects had T cells specifically secreting IFN-g (P = 0.004). The T-cell response consisted of both CD8 + and CD4 + T cells but was dominated by CD8 T cells in three of four patients. MuRas 5-14 and muRas 6-14 were shown to specifically induce CD8 + T-cell mediated cytotoxicity against HLA-A2-positive, muRas-bearing pancreatic carcinoma cells. The T-cell response was not correlated with prognostic or clinical variables such as tumor-node-metastasis status, stage, or survival. In conclusion, a natural T-cell response against muRas proteins that could be exploited for immunostimulatory therapeutic approaches has been shown in a significant proportion of patients with pancreatic cancer.The ras proto-oncogenes (H-ras, K-ras, and N-ras) encode 21-kDa proteins with intrinsic GTPase activity that are involved in cell proliferation and differentiation. Point mutations in the ras proto-oncogenes have been identified in a wide range of human solid tumors, in particular carcinomas of the pancreas, colon, lung, and thyroid as well as myeloid malignancies. The majority of point mutations of the ras gene reside at codons 12, 13, and 61 (1). These mutations result in the production of aberrant proteins, which are structurally and functionally distinct from normal endogenous ras and, due to their strict tumor specificity, can function as targets for cellular and humoral immune responses in cancer patients (1-5) and healthy donors (6-8).In pancreatic adenocarcinomas where ras point mutations occur in 80% to 90% of cases, it is the K-ras gene at codon 12 that is found frequently mutated. Replacement of the normal glycine (Gly) residue by an aspartatic acid (Asp), valine (Val), cysteine (Cys), or arginine (Arg) residue accounts for f98% of all ras mutations in pancreatic carcinomas, rendering pancreatic cancer an ideal model for the investigations of T-cell responses against ras mutations at position 12. Previous studies have shown that CD4 + T-cell immunity to position 12 mutated Ras (muRas) can be detected in the majority of patients with pancreatic cancer (3, 5). The proof of this T-cell response and the early presence of muRas in the tumoral process have prompted the implementation of clinical trials aimed at inducing CTL responses against defined muRas antigens (9-11). In these st...

Carcinoembryonic Antigen-Specific but Not Antiviral CD4+ T Cell Immunity Is Impaired in Pancreatic Carcinoma Patients

“…ϩ and CD4 ϩ T cells specific for SART1-3 and ART4 (7), wild-type and mutated ras (6,8,10), MUC-1 (9), and the autologous tumors (9) were found in variable percentages. In most cases, effectors were shown to produce IFN-␥ in response to their cognate Ags, suggesting a Th1 polarization.…”

Nras in melanoma: Targeting the undruggable target

“…Second, by overcoming host-protecting adaptive immune responses [31]. Upon oncogenic RAS expression, the recruitment of immunosuppressive regulatory T cells and myeloid-derived suppressor cells at tumor site may lead to a compromised antitumor immune response [32].…”

Characterization of Preexisting MAGE-A3-Specific CD4+ T Cells in Cancer Patients and Healthy Individuals and Their Activation by Protein Vaccination

“…Ag-expressing tumors but not in patients with Ag-negative tumors or healthy individuals (1)(2)(3)(4). In addition, vaccination with various forms of tumor Ags successfully induced humoral and cellular immune responses, even in patients who had no spontaneous immunity against the Ag (5-7).…”

“…In contrast, detection of tumor Ag-specific T cells in patients without spontaneous immunity before vaccination or in healthy individuals is difficult because of low frequency and/or suppression by regulatory T cells (8 -11). In general, multiple stimulations of T cells from healthy donors with tumor Ag-loaded dendritic cells (DC) 3 are required to induce tumor Ag-specific T cells (12). However, this method is not always applicable to cancer patients because of the requirement of large numbers of PBMC to generate DC.…”