Specific T-cell immunity against Ki-ras peptides in patients with pancreatic and colorectal cancers

Abstract

Mutations of codon 12 in the Ki-ras gene are frequently found in pancreatic and colorectal cancers. It has been demonstrated that human T-cells have the potential to recognise tumours expressing mutated ras-derived peptides. However, it remains unclear whether T-cells from a given individual can recognise the mutant peptides, which are expressed in that individual's tumour tissues. Mutations of the Ki-ras oncogene were analysed by the mutant-allele-specific amplification (MASA) method in pancreatic and colorectal tumour tissues, and T-cell responses against mutated Ki-ras-derived peptides were measured by [3 H]thymidine incorporation and IFN-g production assays. Specific T-cell responses against Ki-ras-products were found in cancer patients, whereas no immune response was observed in normal individuals (Po0.01). Six of the eight pancreatic cancer patients (75%) and nine of 26 colorectal cancer patients (35%) had T-cell responses to mutated Ki-ras-derived-peptides. T-cell response in a given individual cannot recognise the same mutated ras peptide, which is expressed in that individual's tumour tissues. However, pancreatic and colorectal cancer patients have T-cell immunity against Ki-ras-peptides, and this provides potential target for cancer immunotherapy.

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

“…To detect circulating antigen-specific T cells, we induced IFN-g secretion by 17-mer muRas peptides containing the ras mutation present in the respective primary tumor of the patient. These 17-mer muRas [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] peptides comprised binding motifs for both MHC class I as well as MHC class II molecules (see Table 1) and were chosen based on peptide epitope prediction software SYFPEITHI (31). Following this approach, we found 6 of 19 patients (32%) mounting a specific T-cell response against muRas 5-21 peptides, with muRas-Val12 in four cases and muRas-Asp12 or muRasArg12 in one case, respectively.…”

“…Stimulator cells were incubated for 2 hours at 37jC in serum-free medium (X-VIVO 15, BioWhittaker Europe, Verviers, Belgium) with 10 Ag/mL muRas 5-14 -Val12 or muRas 6-14 -Val12 peptide. After 4 weeks, resulting T-cell cultures were tested for their cytotoxic activity against different targets in varying effector/target ratios (1:5, 1:20, and 1:80): T2 cells (174 Â CEM.T2 hybridoma, HLA-A2 + , TAP1 and TAP2 deficient) not loaded or loaded (10 Ag/mL) with muRas 5-14 -Val12 or muRas 6-14 -Val12 peptide (T2 muRas [5][6][7][8][9][10][11][12][13][14] or T2 muRas [6][7][8][9][10][11][12][13][14] or control peptide (T2 HIV-pol). T2 cells without adding effector cells were used as another negative control.…”

“…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)(2)(3)(4)(5) and healthy donors (6)(7)(8).…”

“…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)(10)(11).…”

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.…”