Rearrangement of the immunoglobulin heavy chain gene in juvenile chronic myeloid leukaemia

Identification of an immunogenic CD8+ T-cell epitope derived from gamma-globin, a putative tumor-associated antigen for juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a rare clonal myeloproliferative disorder. Although allogeneic stem cell transplantation can induce long-term remissions, relapse rates remain high and innovative approaches are needed. Since donor lymphocyte infusions have clinical activity in JMML, T-cell-mediated immunotherapy could provide a nonredundant treatment approach to compliment current therapies. Gamma-globin, an oncofetal protein overexpressed by clonogenic JMML cells, may serve as a target of an antitumor immune response. We predicted 5 gamma-globin-derived peptides as potential human leukocyte antigen (HLA)-A2 restricted cytotoxic T lymphocyte (CTL) epitopes and showed that 4 (g031, g071, g105, and g106) bind A2 molecules in vitro. Using an artificial antigen-presenting cell (aAPC) that can process both the N- and C-termini of endogenously expressed proteins, we biochemically confirmed that g105 is naturally processed and presented by cell surface A2. Furthermore, g105-specific CD8(+) CTLs generated from A2-positive healthy donors were able to specifically cytolyze gamma-globin(+), but not gamma-globin(-) JMML cells in an A2-restricted manner. These results suggest that this aAPC-based approach enables the biochemical identification of CD8(+) T-cell epitopes that are processed and presented by intact cells, and that CTL immunotherapy of JMML could be directed against the gamma-globin-derived epitope g105.

Engraftment of NOD/SCID/gammacnull mice with multilineage neoplastic cells from patients with juvenile myelomonocytic leukaemia

Several lines of evidence indicate the clonal nature of juvenile myelomonocytic leukaemia (JMML), involving myeloid, erythroid, megakaryocyte and B-lymphoid lineages. However, it is unclear whether the T-lymphocyte lineage is involved. We demonstrated that cells from six patients with JMML repopulated in non-obese diabetic/severe combined immunodeficient/gammac(null) mice and differentiated into granulocytes, monocytes, erythrocytes, B lymphocytes, T lymphocytes and natural killer cells. The percentage of human CD45 antigen-positive cells ranged from 41% to 73% in the murine bone marrow 12 weeks after transplantation. To examine the involvement of lymphocyte subpopulations, we purified human CD3(+), CD19(+) and CD56(+) cells from murine bone marrow cells transplanted from a patient with monosomy 7. Fluorescence in situ hybridization (FISH) showed the clonal marker in 96-100% of purified CD3(+), CD19(+) and CD56(+) subpopulations. These findings support the concept that JMML originates in transplantable multilineage haematopoietic stem cells. This novel murine xenotransplant model should be useful for investigating the nature of stem cells and testing new therapies for patients with JMML.

In vitro culture studies of childhood myelodysplastic syndrome: establishment of the cell line MUTZ-1

Myelodysplastic syndrome (MDS) in childhood is considered to be very rare and detailed pathobiological data are scarce. More biological information regarding MDS in children is clearly needed and in vitro culture studies provide one possibility for gaining further pathophysiological insights into this malignancy. Here, we incubated bone marrow samples from 30 children with MDS in liquid suspension culture in order to grow the transformed cells in vitro. In most cultures, the hematopoietic cells died quickly and only fibroblastic (stromal) background layers proliferated temporarily; several normal Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines (B-LCL) were established. Only in one instance, albeit from the peripheral blood and not from the bone marrow, could we establish a cell line, termed MUTZ-1, from the malignant cells of a 5-year-old girl with MDS (FAB subtype refractory anemia with excess of blasts). The MDS arose from a pre-existing Fanconi anemia and progressed quickly to an acute myeloid leukemia (FAB M2). Despite positivity for EBV, MUTZ-1 is not an EBV + B-LCL and further characterization of MUTZ-1 confirmed the derivation from the transformed clonal cells. Immunophenotyping showed a pre B-cell surface marker profile (CD10+ CD19+ cytoplasmic IgM+); receptor gene rearrangement analyses underlined the clonal B-cell nature of MUTZ-1 cells. MUTZ-1 cells exhibit a highly rearranged, unstable karyotype with a high frequency of spontaneous chromatid breaks and exchanges; del(5q) and additional rearrangements involving chromosome 5 [der(15)t(5;15)] were detected. The present data and results from a few other MDS-derived cell lines suggest that the transforming event in MDS seems to occur in an immature pluripotent progenitor cell. The new MDS-derived continuous cell line MUTZ-1 provides a useful in vitro model system for studies on the pathogenetic events leading to MDS.