Abstract

Graft-verus-leukemia (GVL) effect in hematopoietic stem cell transplantation (HSCT) is usually complicated by the alloreactivity of donor T cells which leads to acute graft-versus-host (GVH) disease. GVL and GVH reactions are proved to be mediated by different T cell clones. The objective of this study was to identify and characterize T cells clones with specific antileukemia activity without mediating GVHD. We have performed primary mixed leukocyte reaction (MLR) using patient non-leukemic irradiated peripherial blood mononuclear cells (PBMC) as stimulators and donor PBMC as responders. To prepare GVL specific T cells, activated alloreactive T cells were first selectively depleted with an anti-CD25 immunotoxin (

Michalek, et al.
PNAS
2003
,
100
:
1180
–4
). Allodepleted T cells were then stimulated in secondary MLR using irradiated leukemia cells from the same patient. Activated leukemia-reactive cells were purified by immunomagnetic selection or by FACS based on INF-γ or CD25 expression, respectively. Clonotypic assay was used for identification of individual leukemia-specific T cell clones (
Michalek, et al.
Lancet
2003
,
361
:
1183
–5
;
Michalek, et al.
J Immunol
2007
,
178
:
6789
– 5
). This highly sensitive assay is based on detailed analysis of T cell receptor β VDJ unique sequence (TCRB-VDJ). mRNA was extracted from sortred activated cells and cDNA synthetized by anchored reverse transcription. Target TCRB-VDJ gene sequence was amplified by anchor PCR and used to transform bacteria. Bacterial colonies were picked for plasmid isolation and subsequent direct automated sequencing of the TCRBVDJ sequences. We assume that the frequency of particular TCRB-VDJ sequences among bacterial clones after transformation are proportional to the frequency of those sequences in the original population of T cells activated by GVH or GVL reaction. We investigated the presence of individual antileukemic T cell clones in patients with acute myeloid leukemia (AML) and chronic lymphatic leukemia (CLL), and defined them by the TCRB-VDJ unique sequence. The sequences that occured in more than 10% bacterial colonies are likely to represent the most immunodominant clones. Populations of antileukemic T cell clones were oligoclonal, i.e. we observed limited number of individual immunodominat clones which plays important role in GVL reaction. In first CLL patient who had undergone HSCT, six antileukemic T cell clones were identified, four of them are considered to be immunodominant. In second CLL patient after HSCT, only one highly immunodominat autileukemic T cell clone was observed. This specific clone was further monitored by quantitative real-time PCR in patients peripherial blood.

Disclosures: No relevant conflicts of interest to declare.

Supported by the Ministry of Education of the Czech Republic, NPVII-2B06058.

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