A Novel B Cell Precursor ALL Cell Line (018Z) with Prominent Neurotropism and Isolated CNS Leukemia in a NOD/SCID/huALL Xenotransplantation Model.

Abstract 1630

Poster Board I-656

Acute lymphoblastic leukemia (ALL) is the most frequent malignant disease in childhood. Despite efforts achieved in treatment resulting in improved long term survival about 20% of the patients encounter relapse of their disease. Involvement of the central nervous system (CNS) is a common feature at diagnosis but also at relapse. About 10% to 20% of relapse patients present with isolated CNS leukemia as first event mainly occurring early within 24 months after diagnosis and associated with a survival of about 50%. However, achievement of effective CNS control is essential for successful treatment. Model systems to study the mechanisms of CNS leukemia but also new treatment strategies are required.

Here we present and characterize a new pediatric B cell precursor (BCP) ALL cell line (018Z) which was established by passage in a NOD/SCID/huALL xenotransplantation model and exhibits a distinct CNS phenotype if re-transplanted onto NOD/SCID mice.

Leukemia cells isolated from a male, adolescent patient at diagnosis were transplanted onto unconditioned NOD/SCID mice by intravenous injection. The patient had no CNS disease at diagnosis, however he died in remission after induction therapy. Upon onset of leukemia in the recipients the animals were killed and the engrafted leukemia cells were isolated and further transplanted onto secondary and tertiary recipients. Cells isolated from subsequent recipients were transferred into cell culture flasks and kept under standard culture conditions in RPMI medium supplemented with 20% fetal calf serum. Autonomous proliferation of the cells was observed for now more than three years.

The cell line remained immunophenotypically stable as regularly assessed by flowcytometry (every 20 passages, from cell line passage 20 up to 160) showing the same BCP-ALL subtype. Infection of the cells with Epstein Barr Virus or Human Herpes Virus 8 was ruled out.

Cytogenetic analysis of the cell line revealed presence of 47, XY, +8, del(9)(p13). The same karyotype was found in two samples isolated from previous xenograft passages (P4 and P6) and in leukemia cells obtained at diagnosis. The same karyotype was also detected if the 018Z cell line cells were re-transplanted and leukemia cells isolated from the recipients. Interestingly, at diagnosis two additional karyotypes were observed but could not be detected in the xenografts or cell line indicating selection and subsequent proliferation of one clone engrafted [47, XY, +8, del(9)(p13)]. Interestingly, chromosome arm 9p abnormalities have been reported to be associated with adverse events in pediatric BCP ALL, including onset of CNS leukemia (Heerema et al., Blood, 1996, 94(5): 1537-44).

The cell line was further characterized and re-transplanted in the NOD/SCIDhuALL model. Unlike leukemia manifestation observed after transplantation of other samples, recipients transplanted with the 018Z cell line presented with a rapid onset of symptoms like seizures and palsies of the limbs pointing to CNS involvement. Infiltration of BCP ALL cells in the CNS of the recipients was detected by immunohistochemistry of the brain and by flowcytometry in cell suspensions prepared from the mice' meninges while only below 5% of human leukemia cells were detected in peripheral blood, spleen or bone marrow.

Taken together, we established a novel BCP ALL cell line showing manifestation of CNS leukemia with rapid onset of about 6 weeks after re-transplantation onto NOD/SCID mice and providing a model system to study CNS disease in ALL.