ALBERT

Description: Abstract 3531 Poster Board III-468 The identification of hematopoietic stem cell (HSC)-specific surface markers has been a goal for functional stem cell studies and for clinical applications, including transplantation and gene therapy. In humans, the CD34 cell surface marker is largely used in clinical applications for isolation of hematopoietic stem and progenitor cells, and as a predictor of graft HSC content in hematopoietic stem cell transplant. The combination CD34+CD38- provides further enrichment, but the heterogeneity of this population precludes studies requiring levels of purity achieved in mouse models, such as comparative gene expression profiles or in situ histological analyses. Recently, a simple and broadly applicable method to isolate mouse HSCs has been developed based on expression of cell surface markers members of the Signaling Lymphocyte Activation Molecule (SLAM) family, including CD150, CD48, and CD244 (Kiel MJ et al., Cell 2005; 121:1109-1121). In transplantation assays, 1 in 4.8 CD150+CD48- bone marrow cells provide long-term, multilineage reconstitution in recipient mice. We examined the possibility of using these SLAM markers to facilitate the isolation of highly enriched populations of HSCs in humans and rhesus macaques. We tested the in vivo repopulating and colony forming potential of CD150+CD48- cells (SLAM cells) in comparison with non-SLAM cells which included all viable cells outside the SLAM gate (non-SLAM cells). Human G-CSF mobilized cells were pre-enriched for CD34+ cells to facilitate sorting of the rare population of CD150+CD48- cells. SLAM cells were absent in the CD34- fraction. Using stringent gates defined with isotype controls, we observed that 1.1% of human CD34+ cells were CD150+CD48-. In CFU assays, there was no difference in the frequency of colonies obtained between SLAM, non-SLAM and unfractionated CD34+ cell populations. Sublethally irradiated NOD/SCID/γcnull mice were transplanted by tail-vein injection with 1×103 to 1×104 human SLAM cells, 1×105 to 5×106 human non-SLAM cells, or 1×103 to 1×106 human unfractionated CD34+ cells. Mice transplanted with less than 1×105 cells also received 1×105 CD34- carrier cells. Surprisingly, in contrast to data obtained in murine models, both SLAM and non-SLAM populations had in vivo repopulating potential, and levels of human cell engraftment based on CD45 cell surface expression were similar to those obtained with unfractionated CD34+ cells. Similar results were obtained when human CB cells were used to isolate CD150+ and CD150- populations with no pre-enrichment in CD34+ cells. We next investigated whether SLAM receptors may facilitate the isolation of enriched populations of HSCs in rhesus macaques. In two independent experiments, mobilized peripheral blood CD34+ cells were obtained and further purified into SLAM and non-SLAM populations using human antibody clones cross-reactive with rhesus macaque cells. In each experiment, approximately 0.5% of CD34+ cells were CD150+CD48-. In CFU assays, the number of colonies obtained from each population was similar and comparable to the numbers of CFU derived from unfractionated CD34+ cells. Similar to findings in humans, both SLAM and non-SLAM populations had in vivo repopulating potential and levels of engraftment were similar to those obtained after transplantation of unfractionated CD34+ cells. Therefore, these combinations of antibodies against SLAM markers are not suitable for isolation of HSCs in large mammals. We conclude that human and rhesus macaque repopulating HSCs are not enriched in the CD150+CD48- SLAM population. Disclosures: No relevant conflicts of interest to declare.

Description: High levels of aldehyde dehydrogenase (ALDH) activity have been proposed to be a common feature of stem cells. Adult hematopoietic, neural, and cancer stem cells have all been reported to have high ALDH activity, detected using Aldefluor, a fluorogenic substrate for ALDH. This activity has been attributed to Aldh1a1, an enzyme that is expressed at high levels in stem cells and that has been suggested to regulate stem cell function. Nonetheless, Aldh1a1 function in stem cells has never been tested genetically. We observed that Aldh1a1 was preferentially expressed in mouse hematopoietic stem cells (HSCs) and expression increased with age. Hematopoietic cells from Aldh1a1-deficient mice exhibited increased sensitivity to cyclophosphamide in a non–cell-autonomous manner, consistent with its role in cyclophosphamide metabolism in the liver. However, Aldh1a1 deficiency did not affect hematopoiesis, HSC function, or the capacity to reconstitute irradiated recipients in young or old adult mice. Aldh1a1 deficiency also did not affect Aldefluor staining of hematopoietic cells. Finally, Aldh1a1 deficiency did not affect the function of stem cells from the adult central or peripheral nervous systems. Aldh1a1 is not a critical regulator of adult stem cell function or Aldefluor staining in mice.

Description: Abstract 536 Long-term outcomes following novel therapies for CLL have rarely been reported. Between 10/90 and 12/94, 509 eligible, untreated patients (pts) with symptomatic CLL were enrolled by 4 cooperative groups onto study C9011; 179 were randomized to F, 193 to C, and 137 to F+C. After slightly more than 5 years median follow up, with the time of last follow-up in June 1999, we reported in 2000 (NEJM 343:1750) that F provided significantly higher response rates and longer remission duration and progression-free survival (PFS) than C (p

Description: We report 2 novel, cryptic chromosomal abnormalities in precursor B-cell acute lymphoblastic leukemia (BCP-ALL): a translocation, either t(X;14)(p22;q32) or t(Y;14)(p11;q32), in 33 patients and an interstitial deletion, either del(X)(p22.33p22.33) or del(Y)(p11.32p11.32), in 64 patients, involving the pseudoautosomal region (PAR1) of the sex chromosomes. The incidence of these abnormalities was 5% in childhood ALL (0.8% with the translocation, 4.2% with the deletion). Patients with the translocation were older (median age, 16 years), whereas the patients with the deletion were younger (median age, 4 years). The 2 abnormalities result in deregulated expression of the cytokine receptor, cytokine receptor-like factor 2, CRLF2 (also known as thymic stromal-derived lymphopoietin receptor, TSLPR). Overexpression of CRLF2 was associated with activation of the JAK-STAT pathway in cell lines and transduced primary B-cell progenitors, sustaining their proliferation and indicating a causal role of CRLF2 overexpression in lymphoid transformation. In Down syndrome (DS) ALL and 2 non-DS BCP-ALL cell lines, CRLF2 deregulation was associated with mutations of the JAK2 pseudokinase domain, suggesting oncogenic cooperation as well as highlighting a link between non-DS ALL and JAK2 mutations.

Description: Abstract 1232 Poster Board I-254 B-Chronic Lymphocytic Leukemia (CLL) shows a strong familial risk and also co-aggregates with other indolent lymphomas. Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic hematologic condition characterized by small B-cell clones, most with a surface phenotype similar to that of chronic lymphocytic leukemia (CLL). These clones are detectable at low absolute lymphocyte cell (ALC) numbers in otherwise healthy individuals using sensitive 6 or 8 color flow cytometry analysis and can be a precursor to CLL. In the general population, MBL increases with age with a prevalence of 5% in individuals over age 65. In contrast, the rate of MBL is 13-18% in first degree relatives of CLL patients in high risk families. In the largest study to date, we report the characteristics of MBL among 430 first-degree relatives of CLL patients (with no associated lymphoproliferative diseases [LPD]) in 132 high risk families. Patients and Methods Individuals studied came from “high risk” families (defined as those with two or more confirmed cases of CLL) that are participating in the Genetic Epidemiology of CLL Consortium. Multi-parameter flow cytometry analysis with a detection sensitivity of 0.02% was performed on either fresh or cryopreserved PBMC and MBL was classified according to previously published criteria (Marti et al, Br. J Haematol 130:325, 2005). Both the ALC and the absolute B cell count (B-ALC) were calculated for each individual. Survival analysis was used to compute the probability of developing MBL with age using the life table method. Results The overall rate of MBL was 17% (73/430) among first–degree relatives but the probability for developing MBL by age 90 was 51%. Males had a slightly higher (but non-significant) risk for MBL than females. MBL patients had significantly higher ALC and B-ALC than did those with normal immunophenotype. The mean ALC was 2.5×109/L among MBL patients, and 20% had an ALC greater than 3 ×109/L. The B-ALC count averaged 0.51 ×109/L. Ninety percent of the MBL cases had a CLL-like phenotype (CD20dim, CD5+, CD23+). Conclusions MBL is found at a very high rate in families selected for having 2 or more patients with CLL suggesting that MBL reflects inherited predisposition to CLL. Although most of the MBL cases in these families had low cell counts and thus have a presumed low likelihood of progressing to CLL or other LPD, a higher proportion of them had lymphocytosis compared to those with normal immunophenotype. We hypothesize that if MBL is an early step in the process of development of CLL, then germ line genes are likely to be acting early in carcinogenesis with more “hits” required before CLL develops. By looking for genes associated with MBL or CLL in families or in the population, we could substantially increase our power to identify germ line genes predisposing to CLL. Disclosures Kay: Biogenc-Idec, Celgene, Genentech, genmab: Membership on an entity's Board of Directors or advisory committees; Genentech, Celgene, Hospira, Polyphenon Pharma, Sanofi-Aventis: Research Funding.

Description: Abstract 539 Introduction: The addition of rituximab to fludarabine-based regimens in CLL has been shown to produce high response rates with extended remissions. The long-term follow-up of these regimens with respect to progression, survival, and development of secondary malignancies has been limited. Patients and Methods: We report the long-term follow up of the chemoimmunotherapy trial CALGB 9712 (Blood 2003;101:6-14). This trial randomized 104 untreated, symptomatic patients to receive either 6 monthly cycles of fludarabine plus rituximab (FR) followed 2 months later by 4 weekly doses of rituximab (concurrent arm) or 6 monthly cycles of single agent fludarabine followed by rituximab consolidation using 4 weekly doses (sequential arm). With a median follow up of 92 months (range: 60-107), we analyzed the updated CALGB database and flow sheets submitted by treating physicians. Results: The overall response rate (ORR) was 84% (95% CI: 77%-91%), with a 90% ORR in the concurrent group (95% CI: 82%-98%) and a 77% ORR in the sequential group (95% CI: 66%-89%). Complete response (CR) was seen in 38% of patients (95% CI: 30%-45%), and partial response (PR) in 46% (95% CI: 38%-54%). The median OS was 85 months (95% CI: 71-95), with 71% of patients alive at 5 years (95% CI: 61%-79%). The median PFS was 37 months (95% CI: 27-45), with 27% progression-free at 5 years (95% CI: 19%-36%). With long-term follow up, the estimated median OS and PFS for the concurrent group were 84 months (95% CI: 57-100) and 32 months (95% CI: 23-55), respectively; the median OS and PFS for the sequential group were 91 months (95% CI: 71-110) and 40 months (95% CI: 23-50), respectively. Patients with del(17p13.1)/del(11q22.3)(18 patients) and unmutated IgVH(43 patients) continue to have an inferior OS (P=0.01 and P=0.04, respectively) and PFS (P=0.03 and P=0.04, respectively) compared to those without these abnormalities. We next assessed the frequency of therapy-related myeloid neoplasms (t-MN) and other cancers occurring after this chemoimmunotherapy regimen. No patient has developed MDS or AML prior to relapse. One patient (1%) developed t-MDS following relapse and receipt of FCR 41 months after completing trial therapy; t-MDS was diagnosed 9 months later. Richter's transformation was noted in three (3%) of the CALGB 9712 patients with large cell (n=2) or Hodgkin lymphoma (n=1). Second malignancies have included localized basal cell or squamous cell skin cancer in 12 (12%) patients whereas 11 (11%) have developed other epithelial malignancies including 4 GI, 3 lung, 3 melanomas, and 1 prostate cancer. Conclusions: Long-term follow up of patients enrolled on CALGB 9712 demonstrates extended OS and PFS with fludarabine plus rituximab, given either concurrently or sequentially, with an estimated 17%(95% CI: 9%-27%) of responders still in remission 8 years later. Looking at other published data, patients treated with FR administered concurrently or sequentially do not appear to have an increased risk of t-MN or second cancers. These long-term data reaffirm that FR is one of several acceptable frontline treatments for symptomatic patients with CLL. Disclosures: Morrison: Genentech: Speakers Bureau.

Description: Abstract 581 Patients with iAMP21 (intrachromosomal amplification of chromosome 21) represent a distinct cytogenetic subgroup of childhood B cell precursor ALL (BCP-ALL; incidence ∼2%) with a poor prognosis on standard therapy (29% EFS at 5 years). From cytogenetic studies the amplification of chromosome 21 appears to be the primary genetic change, however, whether this or associated abnormalities provide the initiating event of leukaemogenesis remains to be elucidated. Currently fluorescence in situ hybridisation (FISH) with probes directed to the RUNX1 gene provides the only reliable detection method. Knowledge of the underlying genetic mechanism will lead to improved diagnosis and determine those patients at high risk of relapse who require more intensive therapy. Our previous study using genomic arrays (1Mb aCGH, n=10; NimbleGen chromosome 21 custom oligonucleotide array, n=5) identified a common region of amplification (CRA) on 21q of 6.6 Mb and a common region of deletion (CRD) of 3.3 Mb within the telomeric region in 100% and 70% of patients, respectively. However, expression profiling (Affymetrix U133A, n=8) indicated that no important genes within the CRA or CRD were differentially expressed. We now have clinical, cytogenetic and FISH data on 94 iAMP21 patients (44 F, 50 M; median age 9.5y, range 2-30); the largest iAMP21 cohort investigated to date. Higher resolution analysis of 17/94 diagnostic samples by aCGH (Agilent 185K platform) have refined these regions to 5.1 Mb and 2.5 Mb in 100% and 88% of patients, respectively. Recent genome mapping has highlighted the presence of the microRNA miR-802 within the CRA and shown this region overlaps with the Down Syndrome Critical Region at 21q22.3 encompassing the genes DSCR1, DSCR3 and DYRK1. Detailed analysis of chromosome 21 identified recurrent breakpoints centromeric of the CRD within three genes: PDE9A (n=2), COL6A2 (n=2) and DSCAM (n=2). The role of these genes in the initiation of the chromosomal instability associated with iAMP21 is currently under investigation. Global analysis of the iAMP21 genome identified an average of 13 copy number alterations (CNA) per case with recurrent deletions of the leukaemia associated genes PAX5 (n=2), IKZF1 (n=4) and CDKN2A (n=4). To determine the incidences of PAX5, IKZF1 and CDKN2A deletions among the cohort of 94 iAMP21 patients, FISH using probes targeting these genes was carried out on availabel samples. IKZF1 (exons 3-6) was deleted at the highest incidence of 21% (13/62), while CDKN2A and PAX5 were deleted at a lower incidence of 17% (12/71) and 8% (4/48), respectively. The high incidence of IKZF1 deletions found in this patient group correlates with their association with high risk ALL. We have recently reported a deletion within the PAR1 region of the sex chromosomes, centromeric of the CRLF2 gene involving CSF2RA and IL3RA, which leads to deregulated expression of CRLF2. This deletion occurred at an incidence of 23% (17/73), as determined by FISH. Among pairs of matched diagnostic and relapse samples; one had this deletion at both diagnosis and relapse while the second had a deletion in the diagnostic sample only. Gain of an additional × chromosome was identified in 28% (18/65). Of note is that the 3 aberrations: abnormalities of chromosome 21, gain of the × chromosome and high incidence of deletions centromeric of CRLF2 in this patient group mirror the findings in Down Syndrome (DS) ALL, although we have not identified any mutations of the JAK2 kinase domain among this cohort of iAMP21 patients to date. This genome-wide study provides further support for the proposal that amplification of genes within the CRA on chromosome 21 is the primary event driving leukaemogenesis in iAMP21 patients. It has also highlighted that the 3 abnormalities in common with DS ALL and/or deletions of IKZF1, which all occur at a high incidence, contribute towards the progression of this high risk subtype of childhood BCP-ALL. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 1733 Poster Board I-759 Introduction Outcomes for relapsed pediatric acute lymphoblastic leukemia (ALL) are poor overall but depend on the timing of relapse, with lower survival rates for patients that relapse early (defined as 〈 36 months from diagnosis). Previously we sought to discover underlying biological pathways that mediate relapse by analyzing gene expression profiles in a large cohort of diagnosis/relapse paired bone marrow samples on the Affymetrix U133A arrays (Bhojwani et al, ASH 2008). We determined that early relapse was characterized by over-expression of cell cycle genes reflective of a proliferative state but late relapse was characterized by genes involved in nucleotide biosynthesis including targets of anti-folate agents. Given the potential therapeutic implications of these results we sought to validate these findings in an independent set of samples. Patients and Methods Validation of the first 60 pairs was performed using 26 additional pairs analyzed on Affymetrix U133Plus2 arrays. This validation set consisted of 17 early and 9 late diagnosis/relapse pairs. All patients had B precursor ALL and were at first relapse. Probesets differentially expressed between early and late relapse were identified in a supervised pair-wise analysis using an FDR cutoff of

Description: Abstract 2389 Poster Board II-366 Children with Down syndrome (DS) have a 10 to 20-fold increased risk of developing acute lymphoblastic leukemia (ALL), and they have experienced poorer outcomes on recent major protocols worldwide. The cytogenetic abnormalities which are generally common in childhood ALL and contribute to risk-based treatment assignment are markedly less frequent in children with DS-ALL. Recently, activating mutations in Janus kinase 2 (JAK2) have been identified in approximately 20% of DS-ALL, and interstitial deletions involving cytokine receptor-like factor 2 (CRLF2) in approximately 50% of DS-ALL. Global gene expression profiling may provide insights into the biologic consequences of these molecular lesions. We performed microarray analysis of RNA from diagnostic bone marrow samples in 23 DS-ALL and 26 non-DS ALL cases using the Affymetrix Human Genome U133 Plus 2.0 array. CRLF2 expression was high in 10 of the 23 DS-ALL cases, 3 of which also bore JAK2 mutations, and in a single non-DS ALL case. Unsupervised hierarchical clustering analysis demonstrated clustering of non-DS ALL cases belonging to known cytogenetic subgroups such as E2A-PBX1, MLL rearrangement, and high hyperdiploidy. In contrast, neither DS-ALL cases overall nor the JAK2-mutated or high CRLF2 expressing cases formed a cohesive cluster. Supervised analysis identified 43 genes that were differentially expressed between CRLF2 high versus low cases with a false discovery rate

Description: IMiDs immunomodulatory drugs, including lenalidomide and pomalidomide represent a novel class of small molecule anticancer and anti-inflammatory drugs with broad biologic activities. However, the molecular mechanism through which these drugs exert their effects is largely undefined. Using pomalidomide and primary human monocytes, we report that pomalidomide rapidly and selectively activated RhoA and Rac1, but not Cdc42 or Ras, in the absence of any costimulation. Consistent with the activation of Rho GTPases, we found that pomalidomide enhanced F-actin formation, stabilized microtubules, and increased cell migration, all of which were blocked by selective inhibitors of ROCK1 and Rac1. Further, we showed that in Swiss 3T3 cells, pomalidomide only activated RhoA, not Rac1 or Cdc42, and potently induced stress fiber formation. The pomalidomide effect on actin cytoskeleton was blocked by the ROCK1 inhibitor, but not Rac1 inhibitor. Finally, we demonstrated that pomalidomide was able to regulate the activity of Rho GTPases and the formation of F-actin in primary human T cells as it did in monocytes and showed that the activation of RhoA was essential for pomalidomide-induced interleukin-2 expression in T cells. These novel activities provide what we believe a critical mechanism by which IMiDs drugs function as therapeutic immunomodulatory agents.