ALBERT

Description: Continuous xenografts from 10 children with acute lymphoblastic leukemia (ALL) were established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Relative to primary engrafted cells, negligible changes in growth rates and immunophenotype were observed at second and third passage. Analysis of clonal antigen receptor gene rearrangements in 2 xenografts from patients at diagnosis showed that the pattern of clonal variation observed following tertiary transplantation in mice exactly reflected that in bone marrow samples at the time of clinical relapse. Patients experienced diverse treatment outcomes, including 5 who died of disease (median, 13 months; range, 11-76 months, from date of diagnosis), and 5 who remain alive (median, 103 months; range, 56-131 months, following diagnosis). When stratified according to patient outcome, the in vivo sensitivity of xenografts to vincristine and dexamethasone, but not methotrexate, differed significantly (P = .028, P = .029, and P = .56, respectively). The in vitro sensitivity of xenografts to dexamethasone, but not vincristine, correlated significantly with in vivo responses and patient outcome. This study shows, for the first time, that the biologic and genetic characteristics, and patterns of chemosensitivity, of childhood ALL xenografts accurately reflect the clinical disease. As such, they provide powerful experimental models to prioritize new therapeutic strategies for future clinical trials.

Description: The acute myelogenous leukemia–1 (AML1)–ETO fusion protein is generated by the t(8;21), which is found in 40% of AMLs of the French-American-British M2 subtype. AML1-ETO interferes with the function of the AML1 (RUNX1, CBFA2) transcription factor in a dominant-negative fashion and represses transcription by binding its consensus DNA–binding site and via protein-protein interactions with other transcription factors. AML1 activity is critical for the development of definitive hematopoiesis, and haploinsufficiency of AML1 has been linked to a propensity to develop AML. Murine experiments suggest that AML1-ETO expression may not be sufficient for leukemogenesis; however, like the BCR-ABL isoforms, the cellular background in which these fusion proteins are expressed may be critical to the phenotype observed. Retroviral gene transfer was used to examine the effect of AML1-ETO on the in vitro behavior of human hematopoietic stem and progenitor cells. Following transduction of CD34+ cells, stem and progenitor cells were quantified in clonogenic assays, cytokine-driven expansion cultures, and long-term stromal cocultures. Expression of AML1-ETO inhibited colony formation by committed progenitors, but enhanced the growth of stem cells (cobblestone area-forming cells), resulting in a profound survival advantage of transduced over nontransduced cells. AML1-ETO–expressing cells retained progenitor activity and continued to express CD34 throughout the 5-week long-term culture. Thus, AML1-ETO enhances the self-renewal of pluripotent stem cells, the physiological target of many acute myeloid leukemias.

Description: Several prognostic scores are used to predict the outcome of patients with follicular lymphoma (FL). Histologic grading is widely used, but poorly reproducible. Scoring systems such as the (FL)IPI consist of surrogate clinical markers that probably reflect underlying biological phenomena. We hypothesized that the proliferation rate of the intra-follicular neoplastic cells in FL may predict clinical outcome. Proliferating cells were identified by using the Mib-1 antibody in pre-treatment lymph node biopsies of 51 patients. In each section 200 cells per follicle were assessed in five follicles. The proliferation ratio (PR) was defined as (no. of Mib-1 positive cells/ total no. of cells) x 100. The PR was assessed only in the follicles, since many proliferating, non-malignant cells are present in the inter-follicular area. The inter-observer variability was assessed by repeating this procedure for 25 cases by a second investigator blinded to the outcome of the first assessment, resulting in a correlation coefficient of 0.81 (p 〈 0.001). All patients participated in a prospective multicenter trial on first-line treatment with the combination of 8 cycles of CVP (cyclophosphamide, vincristine and prednisone) chemotherapy plus interferon-alpha2b, followed by interferon-alpha maintenance in responding patients until relapse or progression. For statistical analysis the Kaplan-Meier product limit method, the log-rank test, the Cox proportional hazard model and the Mann-Whitney-U test were used. The median age of the patients was 53.3 years; 37 patients had stage IV disease; in nine patients a wait and see interval preceded the treatment (median duration 13 months). A low IPI score was present in 27 patients, intermediate in 20 and high in one. (three patients unknown). After central revision of the original diagnosis six patients were classified as grade 3 FL, 45 as grade 1 or 2. The overall median PR was 16.9 (3.1–49.2). In grade 1 and 2 FL the median PR was 16.1, in grade 3 it was 24.2 (p = 0.02). After a median follow-up of 71 months the median progression-free survival (PFS) for all patients was 25 months. The median PFS was not reached in the patients with the PR below the median compared to only 15 months in the patients with the PR above the median (p = 0.00059). In patients with the PR below median, overall survival was not reached compared to only 42 months in patients with a high PR (p = 0.0019). The PR maintained its prognostic impact on PFS and OS when tested as a continuous variable (p = 0.016 and 0.053 resp.). When the six patients with grade 3 FL were excluded from the analysis, the results remained significant. Other parameters that were significantly associated with a worse OS in univariate analysis were male sex, the presence of bulky disease and intermediate or high IPI. In multivariate analysis the association of high PR with a worse OS remained significant. We found that in FL intra-follicular proliferation rate is a strong independent prognostic factor of PFS and OS. Grade 3 FL appeared to have a higher PR than low grade FL, although numbers are small in this study. PR assessment is easy, relatively fast and reproducible. When confirmed in larger series, the intra-follicular PR could be used instead of histologic grading in identifying the aggressive types of follicular lymphoma, requiring other types of treatment.