The age of the target cell affects B-cell leukaemia malignancy

Abstract

The incidence, malignancy and treatment resistance of many types of human B-cell leukaemias (B-ALL) are directly related to patient age. A major obstacle to elucidate the contribution of age to the development and evolution of leukaemias is the lack of appropriate mouse models where precise control of the timing of oncogene expression is possible. Here we present proof-of-principle experiments showing how a conditional transgenic mouse model of BCR-ABLp190-driven B-ALL offers the opportunity to test the hypothesis that the age of the leukemic cells-of-origin of B-ALL influences B-ALL malignancy. B-ALLs generated from 12- and 20-month-old progenitors gave rise to a more invasive B-ALL than the one developed from 4-month old precursors. This was evidenced by survival analysis revealing the increased malignancy of B-ALLs generated from 20 or 12-month-old transformed progenitors compared with the 4-month equivalents (median survival of 88 days versus 50.5 and 33 days, respectively). Our study shows that the age of target cells at the time of transformation affects B-ALL malignancy.

Figure 1.. Host age does not affect survival outcome

To determine the impact of host age on survival, 1 x 10⁵ cells of a characterized B-ALL cell line Ba/F3-p190 (REF) were IV injected into syngeneic host mice aged 4 months (n = 16) or 20 months (n = 11). Kaplan-Meier survival plot demonstrates no difference in survival (log rank test P = 0.9011).

Figure 2.. Transformed hematopoietic pro-genitor/stem cells express comparable levels of exogenous BCR-ABL

Expression of BCR-ABL was measure by real-time PCR in BM cells of CombitTA-p190 mice at the age of 4 months, 12 months, and 20 months. Doxycycline was given at 4mg/mL for 4 months, 12 months, and 20 months. BCR-ABL expression was measured in CombitTA-p190 mice under doxycycline treatment (+) and mice of the same age once the doxycycline has been removed (−). The mean Ct values of triplicate assays are presented. (BM, bone marrow; wt, wild-type).

Figure 3.. Age-dependent malignancy of transformed hematopoietic progenitor cells in vivo.

(A) Kaplan-Meier survival analysis. Animals where BCR-ABL expression was induced at 4-month of age survived significantly longer than animals where BCR-ABL expression was induced at 12- or 20-month of age (median survival of 88 days versus 50.5 and 33 days, respectively; log rank P < 0.0001 and 0.0001, respectively). (B) CombitTA-p190 mice were evaluated for disease progression by flow citometry. Cells from peripheral blood of CombitTA-p190 and control mice were analyzed by flow cytometry with combination of the specific myeloid (Mac1) and B-cell lymphoid (B220) markers. A representative flow cytometry analysis is shown Characteristic blast cells in BCR-ABL B-cell leukaemia co-expressed B-cell and myeloid markers indicated by the presence of Mac⁺B220⁺ cells. (C) Variability on the percentage of blast cells in the preripheral blood as a function of donor age.