Functional leukemia-associated antigen-specific memory CD8+ T cells exist in healthy individuals and in patients with chronic myelogenous leukemia before and after stem cell transplantation

Antigens implicated in the graft-versus-leukemia (GVL) effect in chronic myeloid leukemia (CML) include WT1, PR1, and BCR-ABL. To detect very low frequencies of these antigen-specific CD8(+) T cells, we used quantitative polymerase chain reaction (qPCR) to measure interferon-gamma (IFN-gamma) mRNA production by peptide-pulsed CD8(+) T cells from HLA-A*0201(+) healthy volunteers and from patients with CML before and after allogeneic stem cell transplantation (SCT). Parallel assays using cytomegalovirus (CMV) pp65 tetramers demonstrated the IFN-gamma copy number to be linearly related to the frequency of tetramer-binding T cells, sensitive to frequencies of 1 responding CD8(+) T cell/ 100 000 CD8(+) T cells. Responses to WT1 and PR1 but not BCR-ABL were detected in 10 of 18 healthy donors. Responses to WT1, PR1, or BCR-ABL were observed in 9 of 14 patients with CML before SCT and 5 of 6 after SCT, often to multiple epitopes. Responses were higher in patients with CML compared with healthy donors and highest after SCT. These antigen-specific CD8(+) T cells comprised central memory (CD45RO(+)CD27(+)CD57(-)) and effector memory (CD45RO(-)CD27(-)CD57(+)) T cells. In conclusion, leukemia-reactive CD8(+) T cells derive from memory T cells and occur at low frequencies in healthy individuals and at higher frequencies in patients with CML. The increased response in patients after SCT suggests a quantitative explanation for the greater effect of allogeneic SCT. (Blood. 2003; 102:2892-2900) (C) 2003 by The American Society of Hematology.