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Despite advances in our understanding of the molecular basis for particular subtypes of acute myeloid leukemia (AML), effective therapy remains a challenge for many individuals suffering from this disease. A significant proportion of both pediatric and adult AML patients cannot be cured and since the upper limits of chemotherapy intensification have been reached, there is an urgent need for novel therapeutic approaches. The transcription factor c-MYB has been shown to play a central role in the development and progression of AML driven by several different oncogenes, including mixed lineage leukemia (MLL)-fusion genes. Here, we have used a c-MYB gene expression signature from MLL-rearranged AML to probe the Connectivity Map database and identified mebendazole as a c-MYB targeting drug. Mebendazole induces c-MYB degradation via the proteasome by interfering with the heat shock protein 70 (HSP70) chaperone system. Transient exposure to mebendazole is sufficient to inhibit colony formation by AML cells, but not normal cord blood-derived cells. Furthermore, mebendazole is effective at impairing AML progression in vivo in mouse xenotransplantation experiments. In the context of widespread human use of mebendazole, our data indicate that mebendazole-induced c-MYB degradation represents a safe and novel therapeutic approach for AML.

Trials with second generation CD19 chimeric antigen receptors (CAR) T-cells report unprecedented responses but are associated with risk of cytokine release syndrome (CRS). Instead, we studied the use of donor Epstein–Barr virus-specific T-cells (EBV CTL) transduced with a first generation CD19CAR, relying on the endogenous T-cell receptor for proliferation. We conducted a multi-center phase I/II study of donor CD19CAR transduced EBV CTL in pediatric acute lymphoblastic leukaemia (ALL). Patients were eligible pre-emptively if they developed molecular relapse (>5 × 10−4) post first stem cell transplant (SCT), or prophylactically post second SCT. An initial cohort showed poor expansion/persistence. We therefore investigated EBV-directed vaccination to enhance expansion/persistence. Eleven patients were treated. No CRS, neurotoxicity or graft versus host disease (GVHD) was observed. At 1 month, 5 patients were in CR (4 continuing, 1 de novo), 1 PR, 3 had stable disease and 3 no response. At a median follow-up of 12 months, 10 of 11 have relapsed, 2 are alive with disease and 1 alive in CR 3 years. Although CD19CAR CTL expansion was poor, persistence was enhanced by vaccination. Median persistence was 0 (range: 0–28) days without vaccination compared to 56 (range: 0–221) days with vaccination (P=0.06). This study demonstrates the feasibility of multi-center studies of CAR T cell therapy and the potential for enhancing persistence with vaccination.

The strongest predictor of relapse in B-cell acute lymphoblastic leukemia (B-ALL) is the level of persistence of tumor cells after initial therapy. The high mutation rate of the B-cell receptor (BCR) locus allows high-resolution tracking of the architecture, evolution and clonal dynamics of B-ALL. Using longitudinal BCR repertoire sequencing, we find that the BCR undergoes an unexpectedly high level of clonal diversification in B-ALL cells through both somatic hypermutation and secondary rearrangements, which can be used for tracking the subclonal composition of the disease and detect minimal residual disease with unprecedented sensitivity. We go on to investigate clonal dynamics of B-ALL using BCR phylogenetic analyses of paired diagnosis-relapse samples and find that large numbers of small leukemic subclones present at diagnosis re-emerge at relapse alongside a dominant clone. Our findings suggest that in all informative relapsed patients, the survival of large numbers of clonogenic cells beyond initial chemotherapy is a surrogate for inherent partial chemoresistance or inadequate therapy, providing an increased opportunity for subsequent emergence of fully resistant clones. These results frame early cytoreduction as an important determinant of long-term outcome.

PTEN gene inactivation by mutation or deletion is common in pediatric T-cell acute lymphoblastic leukemia (T-ALL), but the impact on outcome is unclear, particularly in patients with NOTCH1/FBXW7 mutations. We screened samples from 145 patients treated on the MRC UKALL2003 trial for PTEN mutations using heteroduplex analysis and gene deletions using single nucleotide polymorphism arrays, and related genotype to response to therapy and long-term outcome. PTEN loss-of-function mutations/gene deletions were detected in 22% (PTENABN). Quantification of mutant level indicated that 67% of mutated cases harbored more than one mutant, with up to four mutants detected, consistent with the presence of multiple leukemic sub-clones. Overall, 41% of PTENABNcases were considered to have biallelic abnormalities (mutation and/or deletion) with complete loss of PTEN in a proportion of cells. In addition, 9% of cases had N- or K-RAS mutations. Neither PTEN nor RAS genotype significantly impacted on response to therapy or long-term outcome, irrespective of mutant level, and there was no evidence that they changed the highly favorable outcome of patients with double NOTCH1/FBXW7 mutations. These results indicate that, for pediatric patients treated according to current protocols, routine screening for PTEN or RAS abnormalities at diagnosis is not warranted to further refine risk stratification.

Allogeneic sibling bone marrow transplantation (BMT) is the recommended treatment for relapsed childhood acute lymphoblastic leukaemia (ALL), but appropriate donors are only available in 30% of cases. Unfortunately, BMT from unrelated donors (UD) has been associated with high rates of severe graft‐versus‐host disease (GvHD) and transplant‐related mortality (TRM). In an attempt to improve outcome in UD‐BMT we have assessed the impact of T‐cell depletion using CAMPATH‐1 (anti‐CD52) monoclonal antibodies in 50 consecutively referred patients with relapsed ALL in second remission. All were previously treated according to MRC protocols UKALL X and XI, and then given chemotherapy on MRC R1 from relapse until UD‐BMT. 19 patients had relapsed on and 31 off therapy. Patients and donors were fully matched at HLA‐A, ‐B, ‐DR and ‐DQ loci in 29 cases and mismatched in 21 (four mismatched for more than one antigen). Pre‐transplant conditioning comprised CAMPATH‐1G, cyclophosphamide and total body irradiation. Bone marrow was T‐cell depleted in vitrousing CAMPATH‐1 antibodies. Additional GvHD prophylaxis consisted of cyclosporin A (42 cases), cyclosporin plus methotrexate (four) or none (four). 47 patients engrafted. The incidence of acute GvHD was very low: two patients with grade II disease in the matched group, four with grade II–IV in the mismatched group. Only four patients have chronic GvHD. The actuarial event‐free survival (EFS) at 2 years is 53%, with no significant difference between the matched and mismatched group. Further leukaemic relapse was the most important cause of failure. These results are similar to the most favourable published reports for HLA‐matched sibling BMT in relapsed ALL.

Hematopoietic chimerism was analyzed in serial bone marrow samples taken from 28 children following T-cell depleted unrelated donor bone marrow transplants (UD BMT) for acute lymphoblastic leukemia (ALL). Chimeric status was determined by polymerase chain reaction (PCR) of simple tandem repeat (STR) sequences (maximal sensitivity, 0.1%). At least two serial samples were examined in 23 patients. Of these, two had evidence of complete donor engraftment at all times and eight showed stable low level mixed chimerism (MC) (<1% recipient hematopoiesis). All 10 of these patients remain in remission with a minimum follow-up of 24 months. By contrast, 13 patients demonstrated a progressive return of recipient hematopoiesis. Five of these relapsed (4 to 9 months post BMT), one died of cytomegalovirus pneumonitis and seven remain in remission with a minimum follow-up of 24 months. Five children were excluded from serial analysis as two serial samples were not collected before either relapse (3) or graft rejection (2). We conclude that as with sibling transplants, ex vivo T depleted UD BMT in children with ALL is associated with a high incidence of MC. Stable donor engraftment and low level MC always correlated with continued remission. However, detection of a progressive return of recipient cells did not universally correlate with relapse, but highlighted those patients at greatest risk. Serial chimerism analysis by PCR of STRs provides a rapid and simple screening technique for the detection of relapse and the identification of patients with progressive MC who might benefit from detailed molecular analysis for minimal residual disease following matched volunteer UD BMT for childhood ALL.

Childhood acute lymphocytic leukaemia (ALL) is highly responsive to chemotherapy and ∼70% of children are cured. However, children with persistent minimal residual disease are high risk for relapse post-transplantation and may require more effective treatment strategies. Adoptive immunotherapy, using anti-leukaemic cytotoxic T-lymphocytes, may improve survival in these patients. Dendritic cells (DC) are professional antigen presenting cells which play an essential role in induction of immune responses. In this investigation, we have attempted to generate DC from ALL samples at presentation and from samples taken prior to bone marrow transplantation (BMT). Mononuclear BM cells from 5 newly diagnosed ALL patients and 22 patients in clinical remission were enriched for CD34+cells by immunomagnetic selection. CD34+cells were expanded in serum free medium (SFM) supplemented with Flt3 ligand, G-CSF, GM-CSF, IL-3, IL-6, and SCF for 7 days. Subsequently, cells were cultured for 14 days in SFM supplemented with Flt3 Ligand, GM-CSF and TGFβ. In presentation cases, IL-1β and IL-7 were also added to promote growth of lymphoid DC. Cells were then analysed by flow cytometry for expression of DC-associated antigens. There was a 3 log increase in the proportion of ALL blast cells which expressed the DC-associated antigens CD1A/CD83 following the culture period. These CD1A+/CD83+cells also expressed CD80, CD86 and HLA-DR. The majority of these cells (65-88%) retained their expression of CD34, CD10 and CD19 suggesting that the DC were of lymphoid origin. A 2-3 log increase in the proportion of cells expressing CD1A/CD83 was obtained using the 22 pre-BMT samples; these cells also co-expressed CD80, CD86. To date, significant antigen specific proliferation of CD8+T cells has been induced with HLA-A2 pulsed DC. This was verified using tetrameric complexes of HLA class I/antigenic peptide. These findings suggest that functional DC can be generated from cells of ALL patients at presentation and in remission. It may be possible to utilise these ex vivo generated DC for immunotherapeutic strategies in ALL.

We studied the influence of patient, leukaemia and treatment characteristics on the kinetics of Minimal Residual Disease (MRD) clearance in children with lymphoblastic leukaemia treated using an intensive risk stratified approach. UK MRC protocol ALL97 (1997–1999), and its amended version ALL 97/99 (1999–2002), compared the efficacy and toxicity of dexamethasone (DEX) with prednisolone (PRED), and 6-thioguanine (TG) with 6-Mercaptopurine (MP) in a randomised fashion. The trial produced a 5 year event-free survival (EFS) of 80%, with better systemic and Central Nervous System outcomes in DEX compared with PRED recipients but no difference between TG and MP recipients. Several changes to the risk stratification and treatment regimens during the period of the trial provided an opportunity to determine their impact on MRD clearance. We compared this with clearance in those treated on the successor trial ALL 2003 (more intensive induction containing DEX and Pegylated Asparaginase). The variables investigated for their potential influence on MRD status at the end of induction (EOI) were: NCI Risk; Asparaginase intensity (Erwinia Asparaginase [ERW] in ALL 97 and early part of ALL97/99 vs native or Pegylated E. Coli Asparaginase [E. Coli] in later part of ALL 97/99 and ALL2003); DEX vs PRED; and marrow response at day 8/15 of induction (Slow Early Response [SER] >25% blasts vs Rapid Early Response [RER] ⩽ 25% blasts). MRD was assessed using either a semi-quantitative sequence-specific PCR (ALL97) or Real-Time Quantitative PCR (ALL99 and ALL 2003) of antigen receptor gene re-arrangements at EOI. MRD status was defined as NEG if no MRD was detected by two markers sensitive to 10−4; POS if > 10−4, and Positive Outside Quantitative Range (POQR) if positive < 10−4. Results were available from retrospective testing in 66 ALL97 and 76 ALL97/99 patients, and 204 ALL2003 patients monitored prospectively. There was no significant difference in the proportions of patients MRD NEG, POS or POQR in steroid or NCI sub-groups. Significantly more ERW Asparaginase recipients were MRD POS compared with E.Coli (p< 0.0005). Although SER was predictive of slow MRD clearance, 80/235 (34%) RERs were MRD POS and 9/27(33%) SERs were MRD NEG. Relapse risk at 4 years is 8% in NEG v 28% in POS group in ALL97, 0% in NEG/POQR, versus 15% in POS group in ALL97/99 (p=.001) 2 of the ALL2003 patients have relapsed; one was POS and the other POQR. In the context of intensive risk stratified treatment of childhood ALL, type of Asparaginase influenced rapidity of MRD clearance, whilst NCI risk and type of steroid had no significant influence. Patients with detectable MRD < 10−4 at EOI have the same low risk of relapse as those who have undetectable MRD.

We studied the influence of patient, leukaemia and treatment characteristics on the kinetics of Minimal Residual Disease (MRD) clearance in children with lymphoblastic leukaemia treated using an intensive risk stratified approach. UK MRC protocol ALL97 (1997–1999), and its amended version ALL 97/99 (1999–2002), compared the efficacy and toxicity of dexamethasone (DEX) with prednisolone (PRED), and 6-thioguanine (TG) with 6-Mercaptopurine (MP) in a randomised fashion. The trial produced a 5 year event-free survival (EFS) of 80%, with better systemic and Central Nervous System outcomes in DEX compared with PRED recipients but no difference between TG and MP recipients. Several changes to the risk stratification and treatment regimens during the period of the trial provided an opportunity to determine their impact on MRD clearance. We compared this with clearance in those treated on the successor trial ALL 2003 (more intensive induction containing DEX and Pegylated Asparaginase). The variables investigated for their potential influence on MRD status at the end of induction (EOI) were: NCI Risk; Asparaginase intensity (Erwinia Asparaginase [ERW] in ALL 97 and early part of ALL97/99 vs native or Pegylated E. Coli Asparaginase [E. Coli] in later part of ALL 97/99 and ALL2003); DEX vs PRED; and marrow response at day 8/15 of induction (Slow Early Response [SER] >25% blasts vs Rapid Early Response [RER] ⩽ 25% blasts). MRD was assessed using either a semi-quantitative sequence-specific PCR (ALL97) or Real-Time Quantitative PCR (ALL99 and ALL 2003) of antigen receptor gene re-arrangements at EOI. MRD status was defined as NEG if no MRD was detected by two markers sensitive to 10−4; POS if > 10−4, and Positive Outside Quantitative Range (POQR) if positive < 10−4. Results were available from retrospective testing in 66 ALL97 and 76 ALL97/99 patients, and 204 ALL2003 patients monitored prospectively. There was no significant difference in the proportions of patients MRD NEG, POS or POQR in steroid or NCI sub-groups. Significantly more ERW Asparaginase recipients were MRD POS compared with E.Coli (p< 0.0005). Although SER was predictive of slow MRD clearance, 80/235 (34%) RERs were MRD POS and 9/27(33%) SERs were MRD NEG. Relapse risk at 4 years is 8% in NEG v 28% in POS group in ALL97, 0% in NEG/POQR, versus 15% in POS group in ALL97/99 (p=.001) 2 of the ALL2003 patients have relapsed; one was POS and the other POQR. In the context of intensive risk stratified treatment of childhood ALL, type of Asparaginase influenced rapidity of MRD clearance, whilst NCI risk and type of steroid had no significant influence. Patients with detectable MRD < 10−4at EOI have the same low risk of relapse as those who have undetectable MRD.