Lymphodepletion is permissive to the development of spontaneous T-cell responses to the self-antigen PR1 early after allogeneic stem cell transplantation and in patients with acute myeloid leukemia undergoing WT1 peptide vaccination following chemotherapy

Abstract

PR1, an HLA-A*0201 epitope shared by proteinase-3 (PR3) and elastase (ELA2) proteins, is expressed in normal neutrophils and overexpressed in myeloid leukemias. PR1-specific T cells have been linked to graft-versus-leukemia (GVL) effect. We hypothesized that lymphopenia induced by chemo-radiotherapy can enhance weak autoimmune responses to self-antigens such as PR1. We measured PR1-specific responses in 27 patients 30-120 days following allogeneic stem cell transplant (SCT) and correlated these with ELA2 and PR3 expression and minimal residual disease (MRD). Post-SCT 10/13 CML, 6/9 ALL, and 4/5 solid tumor patients had PR1 responses correlating with PR3 and ELA2 expression. At day 180 post-SCT, 8/8 CML patients with PR1 responses were BCR-ABL-negative compared with 2/5 BCR-ABL-positive patients (P = 0.025). In contrast, PR1 responses were detected in 2/4 MRD-negative compared with 4/5 MRD-positive ALL patients (P = 0.76). To assess whether the lymphopenic milieu also exaggerates weak T-cell responses in the autologous setting, we measured spontaneous induction of PR1 responses in 3 AML patients vaccinated with WT1-126 peptide following lymphodepletion. In addition to WT1-specific T cells, we detected PR1-specific T cells in 2 patients during hematopoietic recovery. Our findings suggest that lymphopenia induced by chemo-radiotherapy enhances weak autoimmune responses to self-antigens, which may result in GVL if the leukemia expresses the relevant self-antigen.

Trial registration: ClinicalTrials.gov NCT00433745.

Figures

Fig. 1

CD8+ T-cell responses to PR1 in patients with CML, ALL, and solid tumor after SCT. a Comparison of frequencies of PR1/HLA-A*0201+ CD8+ T cells in patients with CML, ALL, and solid tumor after SCT. The values represent the PR1/ HLA-A*0201+ CD8+ T-cell response for each patient at specific time points after SCT. Bars represent means. b Frequencies of PR1-specific CD8+ T cells by tetramer analysis (black bar) and PR1-specific IFN-γ-producing CD8+ T cells (gray bar)

Fig. 2

PR3 and ELA2 gene expression in the peripheral blood of patients with CML, ALL, and solid tumor after SCT. a Correlation between PR3 and ELA2 expression in PB samples from the patients with CML, ALL, and solid tumor. bELA2 gene expression in peripheral blood samples from the patients with CML, ALL, and solid tumor after SCT. Bars represent medians. Values of genes represent the RQ-PCR expression as a ratio of the gene of interest to the ABL control gene

Fig. 3

PR1-specific CD8+ T-cell responses in peripheral blood in relation to ELA2 gene expression and absolute neutro-phil count (ANC). Results in 6 individual patients are shown. The number of days after transplantation is shown on the x-axis. PR1/HLA-A*0201+ CD8+ T cells are expressed as absolute numbers/mL of peripheral blood (left, y-axis; light blue); the shaded area represents absolute numbers of CMVpp65495/HLA-A*0201+ CD8+ T cells. ELA2 gene expression in peripheral blood is expressed as the ratio of ELA2 to ABL (right, y-axis; dark blue). The ANC × 109/L are represented at each time point (gray line)

Fig. 4

Quality of PR1-specific CD8+ T-cell response and GVL. a Avidity of PR1-specific CD8+ T cells was compared for patients with CML and ALL. Stimulation of PBMC with 0.1 and 10 μM of PR1 determined high- and low-avidity responses. Results show ratios of high- to low-avidity PR1 CD8+ T-cell responses in CML and ALL patients. Ratios were obtained by the following calculation: IFN-γ+ CD8+ T-cell (%) with 0.1 μM peptide/IFN-γ+ CD8+ T-cell (%) with 10 μM peptide. A ratio >1.0 represents predominantly high-avidity responses, whereas a ratio of <1.0 represents predominantly low-avidity responses. b Relationship between IFN-γ+ PR1-specific CD8+ T-cell responses and MRD at day +180 post-SCT, as assessed by BCR-ABL expression in CML and WT1 expression in ALL. Bars represent median values

Fig. 5

PR1-specific CD8+ T-cell responses in patients vaccinated with WT1 peptide only following lymphodepletion. PR1-specific CD8+ T-cell responses (light blue line) are correlated with ELA-2/PR3 expression (dark blue line) and compared with WT1 vaccine-induced CD8+ T cells (red line)