BCR/ABL-specific CD8+ T cells can be detected from CML patients, but are only expanded from healthy donors

Abstract

The BCR/ABL p210 fusion protein has long been considered an ideal target antigen for the development of immunotherapeutic strategies in chronic myeloid leukaemia (CML) due to its central role in malignant transformation and to its unique novel amino acid sequence solely expressed in leukaemia cells. However, the feasibility to expand BCR-ABL-specific T cells remains still controversial. Using BCR/ABL peptide/MHC tetramers, significantly higher frequencies of tetramer positive cells were detected in the peripheral blood of HLA-A*0301 (mean 0.38%) and HLA-B*0801 (mean 0.28%) CML patients than in healthy donors (P = 0.0025 and 0.0026, respectively). However, following stimulation with autologous peptide-pulsed DCs, BCR/ABL-specific T cells were only expanded from some healthy donors, suggesting that CML patients may have a specific immune deficit with respect to the BCR/ABL antigen.

Fig. 1

Frequencies of ex vivo HLA-A*0301 and HLA-B*0801 BCR/ABL-specific T cells. The frequencies of HLA-A*0301/KQSSKALQR (a) and HLA-B*0801/GFKQSSKAL (b) specific CD8⁺ T cells detected in the peripheral blood of CML patients, as well as in healthy individuals and CML patients bearing irrelevant HLA types (non-HLA-A*0301 and/or non-HLA-B*0801) are represented. Tetramer positive cells are expressed as a percentage of CD3⁺CD8⁺ T cells. Bars indicate the mean values for each category. The frequencies of BCR/ABL-specific T cells circulating in the peripheral blood of CML patients are in both the HLA-A*0301 and the HLA-B*0801 group significantly higher than in healthy individuals (P = 0.0025 and 0.0026, respectively, Mann–Whitney U test) or in patients bearing irrelevant HLA types (P < 0.0001, Mann–Whitney U test). N represents the number of samples

Fig. 2

BCR/ABL-specific CD8⁺ T cell responses generated with peptide-pulsed autologous mDCs. The generation of BCR/ABL-specific T cells using monocytes-derived DCs as APCs was assessed from HLA-A*0301 (a) and HLA-B*0801 (b) CML patients (left) and healthy donors (right). In parallel, WT1-specific T cells were primed from HLA-A*0201 CML patients (c). Lymphocytes were stimulated with autologous irradiated DCs pulsed with no peptide (No Peptide) or BCR/ABL-derived 9-mer and 17-mer peptides. Activated T cells were harvested 3 days after the last stimulation (day 21) and stained with the appropriate HLA/CML tetramer. BCR/ABL-specific T cells are expressed as a percentage of CD3⁺CD8⁺ T cells, with the bar mean values shown for each condition. The P values differences between CML patients and healthy individuals were calculated with the Mann–Whitney U test. d Representative tetramer staining dot plots from an HLA-A*0201/HLA-A*0301 healthy donor and CML patient are shown