The clinical value of follow-up examinations in childhood T-cell acute lymphoblastic leukemia and T-cell non-Hodgkin's lymphoma

BACKGROUND

The aim of this study was to evaluate the value of follow-up investigations of T-cell acute lymphoblastic leukemia (T-ALL) and T-cell non-Hodgkin's lymphoma (T-NHL), including cerebrospinal fluid (CSF) examination, bone marrow (BM) aspiration, peripheral blood (PB) count, serum lactate dehydrogenase (LDH) and chest X-rays in patients with an initial mediastinal enlargement.

PROCEDURE

We reviewed clinical records of all T-ALL patients from 1987 to 2002 and all T-NHL patients from 1977 to 2002, seen at a single institution.

RESULTS

Of 48 T-ALL patients, 15 suffered from a relapse, 6 (40%) were asymptomatic at the time of relapse. T-ALL (13/30) with mediastinal enlargement at first diagnosis relapsed versus 2/16 of those without mediastinal enlargement. However, at relapse, only one patient had a mediastinal mass, which in addition was symptomatic. Of 39 T-NHL patients, 6 patients relapsed. Forty percent of relapsed T-ALL and 17% of relapsed T-NHL were asymptomatic. The seven asymptomatic relapses were detected by CSF (n = 4), BM (n = 2) or blood count (n = 1) examinations. All T-ALL and T-NHL patients with a mediastinal relapse were symptomatic.

CONCLUSIONS

This study suggests that routine CSF examinations during treatment can detect relapses of T-ALL and T-NHL before onset of symptoms, which might be of clinical value. Relapses are rarely detected by BM or blood examinations and whether this translates in a clinical benefit is unlikely. Routine chest X-rays are not useful.

CD4+CD25+T cells regulate the intensity of hypersensitivity responses to peanut, but are not decisive in the induction of oral sensitization

BACKGROUND

Naturally occurring CD4+CD25+ regulatory T cells (Tregs) play a critical role in the maintenance of self-tolerance and it has been suggested that these Tregs may also be involved in preventing allergic disease.

OBJECTIVE

The precise role of CD4+CD25+ T cells in the regulation of allergic responses to mucosal antigens remains to be elucidated. In the present study, it was investigated whether CD4+CD25+ T cells are involved in the induction of oral tolerance and whether they play a role in controlling hypersensitivity responses to food proteins.

METHODS

CD4+CD25+ T cells were depleted with PC61 mAb before the induction of low dose oral tolerance to peanut extract (PE). In addition, CD4+CD25+ T cell depletion was performed during sensitization or before oral challenge, using a C3H/HeOuJ mouse model of allergic sensitization to peanut.

RESULTS

Oral tolerance to PE could not be induced in CD4+CD25+ T cell-depleted mice. However, CD4+CD25+ T cell depletion during long-term exposure to PE alone did not result in allergic sensitization. In sensitized mice, anti-CD25 treatment during oral exposure resulted in higher levels of PE-specific IgE and increased mast cell degranulation upon an oral challenge. In contrast, anti-CD25 treatment of PE-sensitized mice before oral challenges did not affect the level of mast cell degranulation.

CONCLUSION

These results indicate that CD4+CD25+ Tregs are involved in maintaining tolerance to oral antigens and regulate the intensity of an IgE-mediated food hypersensitivity response, but are not crucial in preventing sensitization. Accordingly, CD4+CD25+ Tregs may represent a potential tool for the treatment of food allergic disorders.

Immunobiological diversity in infant acute lymphoblastic leukemia is related to the occurrence and type of MLL gene rearrangement

The aim of this study was to identify immunobiological subgroups in 133 infant acute lymphoblastic leukemia (ALL) cases as assessed by their immunophenotype, immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangement pattern, and the presence of mixed lineage leukemia (MLL) rearrangements. About 70% of cases showed the pro-B-ALL immunophenotype, whereas the remaining cases were common ALL and pre-B-ALL. MLL translocations were found in 79% of infants, involving MLL-AF4 (41%), MLL-ENL (18%), MLL-AF9 (11%) or another MLL partner gene (10%). Detailed analysis of Ig/TCR rearrangement patterns revealed IGH, IGK and IGL rearrangements in 91, 21 and 13% of infants, respectively. Cross-lineage TCRD, TCRG and TCRB rearrangements were found in 46, 17 and 10% of cases, respectively. As compared to childhood precursor-B-ALL, Ig/TCR rearrangements in infant ALL were less frequent and more oligoclonal. MLL-AF4 and MLL-ENL-positive infants demonstrated immature rearrangements, whereas in MLL-AF9-positive leukemias more mature rearrangements predominated. The immature Ig/TCR pattern in infant ALL correlated with young age at diagnosis, CD10 negativity and predominantly with the presence and the type of MLL translocation. The high frequency of immature and oligoclonal Ig/TCR rearrangements is probably caused by early (prenatal) oncogenic transformation in immature B-lineage progenitor cells with germline Ig/TCR genes combined with a short latency period.

Detection of autoimmunity by pharmaceuticals

Despite the important health and economic impact of autoimmunogenicity or allergenicity by pharmaceuticals models to detect such adverse effects are not available yet. The most important reason for this is the related complex interplay of multiple factors, for which reason these adverse effects are also referred to as idiosyncratic in nature. Moreover, clinical effects are quite diverse, and involve both organ-specific and systemic effects, including a diversity of skin diseases. Because of its complexity on the one hand and the fundamental knowledge on certain particular mechanistic effects it may be more relevant to design a rationalistic toolbox of test models from which a predictive strategy can be composed. Since one mechanistic aspect centers around T cell sensitization a straightforward lymph node assay such as the reporter antigen-popliteal lymph node assay (RA-PLNA) would fit in such a toolbox. This RA-PLNA holds a strong promise to distinguish sensitizing and/or neoantigen-forming capacity of low molecular weight pharmaceuticals. In addition, from the pharmacokinetic point of view a rationalistic toolbox should also contain oral exposure models with immunological read out parameters in normal or in genetically predisposed animal strains. This review focuses on these two categories of candidate test methods, PLNA and oral exposure models, and proposes to use these in tandem in order to predict the hazard of induction of allergy or autoimmune phenomena by new pharmaceutical candidates.

In vitro tests to evaluate immunotoxicity: A preliminary study

The implementation of Registration, Evaluation and Authorisation of new and existing Chemicals (REACH) will increase the number of laboratory animals used, if alternative methods will not be available. In the meantime, REACH promotes the use of in vitro tests and, therefore, a set of appropriated alternative testing methods and assessment strategies are needed. The immune system can be a target for many chemicals including environmental contaminants and drugs with potential adverse effects on human health. The aim of this study was to evaluate the predictivity of a set of in vitro assays to detect immunosuppression. The tests have been performed on human, rat and murine cells. Different endpoints have been assessed: cytotoxicity, cytokine release, myelotoxicity and mitogen responsiveness. For each of these endpoints IC50s values have been calculated. Six chemical substances, representative of the full range of in vivo responses and for which good human and/or animal data are available either from databases or literature, have been selected: two chemicals classified as not immunotoxic (Urethane and Furosemide), and four (tributyltin chloride (TBTC), Verapamil, Cyclosporin A, Benzo(a)pyrene) with different effect on immune system. All the tests confirmed the strong immunotoxic effect of TBTC as well as they confirmed the negative controls. For one chemical (Verapamil) the IC50 is similar through the different tests. The IC50s obtained with the other chemicals depend on the endpoints and on the animal species. The clonogenic test (CFU-GM) and the mitogen responsiveness showed similar IC50s between human and rodent cells except for Cyclosporin A and TBTC. All different tests classified the compounds analyzed in the same way.

The MLL recombinome of acute leukemias

Chromosomal rearrangements of the human MLL gene are a hallmark for aggressive (high-risk) pediatric, adult and therapy-associated acute leukemias. These patients need to be identified in order to subject these patients to appropriate therapy regimen. A recently developed long-distance inverse PCR method was applied to genomic DNA isolated from individual acute leukemia patients in order to identify chromosomal rearrangements of the human MLL gene. We present data of the molecular characterization of 414 samples obtained from 272 pediatric and 142 adult leukemia patients. The precise localization of genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) was determined and several new TPGs were identified. The combined data of our study and published data revealed a total of 87 different MLL rearrangements of which 51 TPGs are now characterized at the molecular level. Interestingly, the four most frequently found TPGs (AF4, AF9, ENL and AF10) encode nuclear proteins that are part of a protein network involved in histone H3K79 methylation. Thus, translocations of the MLL gene, by itself coding for a histone H3K4 methyltransferase, are presumably not randomly chosen, rather functionally selected.

The reporter antigen popliteal lymph node assay

Many chemicals, including drugs and environmental pollutants, may have the intrinsic capacity to stimulate or dysregulate immune responses. These responses may create considerable problems for exposed subjects in terms of development of autoimmunity or hypersensitivity reactions. The popliteal lymph node assay (PLNA) provides a suitable tool to assess the immunostimulating potential of chemicals and might be a potential candidate as a screening tool in immunotoxicological hazard identification. The use of so-called reporter antigens (RA) in this assay additionally enables differentiation between immunosensitizing (sensitizers), immunostimulating (irritants), and innocent chemicals. In the RA-PLNA, the compound of interest is injected into the hind footpad together with a nonsensitizing dose of the RA. After 6 to 8 days, RA-specific responses are monitored in the draining PLN by measuring RA-specific antibody formation, cytokine secretion, and shifts in immune cell numbers. Hence, this simple and straightforward assay provides immunologically relevant information about the immunomodulating properties of a chemical.

Differential expression of p73 isoforms in relation to drug resistance in childhood T-lineage acute lymphoblastic leukaemia

The T-lineage phenotype of childhood acute lymphoblastic leukaemia (ALL) is associated with an increased relapse-risk and in vitro resistance to drugs as compared to a precursor B phenotype. Antiapoptotic isoforms of p73 that lack part of the transactivation (TA) domain (DeltaTA-p73, i.e. p73Deltaex2, p73Deltaex3, p73Deltaex2/3 and DeltaN-p73) may cause resistance to anticancer agents through inhibition of p53 and/or proapoptotic p73 family members (TA-p73). We demonstrate in our study that the expression of total p73 mRNA was higher in childhood T-ALL compared to controls (P=0.004). In T-ALL, the relative contribution of antiapoptotic DeltaTA-p73 (88%) was larger than of proapoptotic TA-p73 (12%). Leukaemic cells of T-ALL patients expressing higher levels of antiapoptotic p73 were more resistant to the DNA-damaging drug daunorubicin compared to cells of patients with low or negative expression or these isoforms (P(trend)=0.045). Interestingly, p73Deltaex2 was the most abundantly expressed antiapoptotic isoform in daunorubicin-resistant patient cells (44% of total p73). No association was found between high expression of proapoptotic TA-p73 or antiapoptotic DeltaTA-p73 and relapse-risk. Our results suggest that childhood T-ALL is associated with a high expression of DeltaTA-p73. These isoforms may play a role in cellular resistance to DNA-damaging drugs in children at initial diagnosis of T-ALL.

A new recurrent 9q34 duplication in pediatric T-cell acute lymphoblastic leukemia

Over the last decade, genetic characterization of T-cell acute lymphoblastic leukemia (T-ALL) has led to the identification of a variety of chromosomal abnormalities. In this study, we used array-comparative genome hybridization (array-CGH) and identified a novel recurrent 9q34 amplification in 33% (12/36) of pediatric T-ALL samples, which is therefore one of the most frequent cytogenetic abnormalities observed in T-ALL thus far. The exact size of the amplified region differed among patients, but the critical region encloses approximately 4 Mb and includes NOTCH1. The 9q34 amplification may lead to elevated expression of various genes, and MRLP41, SSNA1 and PHPT1 were found significantly expressed at higher levels. Fluorescence in situ hybridization (FISH) analysis revealed that this 9q34 amplification was in fact a 9q34 duplication on one chromosome and could be identified in 17-39 percent of leukemic cells at diagnosis. Although this leukemic subclone did not predict for poor outcome, leukemic cells carrying this duplication were still present at relapse, indicating that these cells survived chemotherapeutic treatment. Episomal NUP214-ABL1 amplification and activating mutations in NOTCH1, two other recently identified 9q34 abnormalities in T-ALL, were also detected in our patient cohort. We showed that both of these genetic abnormalities occur independently from this newly identified 9q34 duplication.

Lack of expression of the chondroitin sulphate proteoglycan neuron-glial antigen 2 on candidate stem cell populations in paediatric acute myeloid leukaemia/abn(11q23) and acute lymphoblastic leukaemia/t(4;11)

It has increasingly been acknowledged that only a few leukaemic cells possess the capability to renew themselves and that only these self-renewing leukaemic stem cells are able to initiate relapses. Therefore, these leukaemic stem cells should be the target cells for therapy and for minimal residual disease (MRD) detection. Because of its presence on blasts of 11q23-rearranged high-risk leukaemic patients, neuron-glial antigen 2 (NG2) is thought to be a valuable marker for detecting leukaemic stem cells. Six acute myeloid leukaemia (AML)/abn(11q23) and three acute lymphoblastic leukaemia (ALL)/t(4;11) samples were analysed by four-colour flow cytometry for NG2 expression on primitive cell populations. Candidate leukaemic cell populations were defined by the antigen profiles CD34+CD38- in AML and CD34+CD19-CD117+ in ALL. Surprisingly, in all patients these candidate stem cell populations were shown to lack expression of NG2. Instead, a correlation between the expression of the myeloid differentiation marker CD33 and increasing levels of NG2 on maturing cells could be demonstrated. Similarly, in ALL patients CD34+CD19+ cells showed a higher expression of NG2 mRNA compared with CD34+CD19-. Thus, NG2 appears to be upregulated with differentiation and not to be expressed on primitive disease-maintaining cells. This hampers the clinical use of NG2 as a therapeutic target and as a sensitive marker for MRD detection.

Incidence of additional genetic changes in the TEL and AML1 genes in DCOG and COALL-treated t(12;21)-positive pediatric ALL, and their relation with drug sensitivity and clinical outcome

Clinical heterogeneity within t(12;21) or TEL/AML1-positive ALL (25% of childhood common/preB ALL) indicates that additional genetic changes might contribute to outcome. We studied the relation between additional genetic changes in TEL(ETV6) and AML1(RUNX1) (FISH), drug sensitivity (MTT assay) and clinical outcome in 143 DCOG and COALL-treated t(12;21)-positive ALL patients. Additional genetic changes in TEL and AML1 were present in 83% of the patients, and consisted of (partial) deletion of the second TEL gene (70%), an extra AML1 gene (23%) or an extra der(21)t(12;21) (10%). More than one additional change was observed in 20%. Disease-free survival (pDFS) of DCOG patients without additional genetic changes (4 years pDFS +/- s.e. 53 +/- 17%) and of those with an extra der(21)t(12;21) (60 +/- 22%) is poorer than that of compared to patients with other additional genetic changes in TEL or AML1 (79 +/- 6%; P-trend = 0.02). This was mainly due to the occurrence of early relapses within 2.5 years after the first diagnosis. Similar observations were found in the COALL cohort, albeit not significant owing to limited follow-up. Multivariate analysis including age, WBC and genetic abnormalities in TEL and/or AML1 showed that especially, in vitro resistance to prednisolone (hazard ratio 5.78, 95% CI 1.45-23.0; P=0.01) is an independent prognostic factor in DCOG- and COALL-treated t(12;21)-positive ALL.

Silencing of the tumor suppressor gene FHIT is highly characteristic for MLL gene rearranged infant acute lymphoblastic leukemia

MLL rearranged acute lymphoblastic leukemia (MLL) is an aggressive type of acute lymphoblastic leukemia (ALL), diagnosed predominantly in infants (<1 years of age). Since current chemotherapy fails in >50% of patients with MLL, new therapeutic strategies are desperately needed. For this, understanding the biological features characterizing MLL is necessary. Analysis of gene expression profiles revealed that the expression of the tumor suppressor gene FHIT is reduced in children with MLL rearranged ALL as compared to ALL patients carrying germ line MLL. This finding was confirmed by quantitative real-time PCR. In 100% of the infant MLL cases tested, methylation of the FHIT 5'CpG region was observed, resulting in strongly reduced mRNA and protein expression. In contrast, FHIT methylation in infant and non-infant ALL patients carrying germ line MLL was found in only approximately 60% (P< or =0.004). FHIT expression was restored upon exposing leukemic cells to the demethylating agent decitabine, which induced apoptosis. Likewise and more specifically, leukemic cell death was induced by transfecting MLL rearranged leukemic cells with expression vectors encoding wild-type FHIT, confirming tumor suppressor activity of this gene. These observations imply that suppression of FHIT may be required for the development of MLL, and provide new insights into leukemogenesis and therapeutic possibilities for MLL.

The human equilibrative nucleoside transporter 1 mediates in vitro cytarabine sensitivity in childhood acute myeloid leukaemia

Cytarabine (ara-C) is the most effective agent for the treatment of acute myeloid leukaemia (AML). Aberrant expression of enzymes involved in the transport/metabolism of ara-C could explain drug resistance. We determined mRNA expression of these factors using quantitative-real-time-PCR in leukemic blasts from children diagnosed with de novo AML. Expression of the inactivating enzyme pyrimidine nucleotidase-I (PN-I) was 1.8-fold lower in FAB-M5 as compared to FAB-M1/2 (P=0.007). In vitro sensitivity to deoxynucleoside analogues was determined using the MTT-assay. Human equilibrative nucleoside transporter-1 (hENT1) mRNA expression and ara-C sensitivity were significantly correlated (r_p=−0.46; P=0.001), with three-fold lower hENT1 mRNA levels in resistant patients (P=0.003). hENT1 mRNA expression also seemed to correlate inversely with the LC₅₀ values of cladribine (r_p=−0.30; P=0.04), decitabine (r_p=−0.29; P=0.04) and gemcitabine (r_p=−0.33; P=0.02). Deoxycytidine kinase (dCK) and cytidine deaminase (CDA) mRNA expression seemed to correlate with in vitro sensitivity to gemcitabine (r_p=−0.31; P=0.03) and decitabine (r_p=0.33; P=0.03), respectively. The dCK/PN-I ratio correlated inversely with LC₅₀ values for gemcitabine (r_p=−0.45, P=0.001) and the dCK/CDA ratio seemed to correlate with LC₅₀ values for decitabine (r_p=−0.29; 0.04). In conclusion, decreased expression of hENT1, which transports ara-C across the cell membrane, appears to be a major factor in ara-C resistance in childhood AML.

Multidrug resistance proteins and folate supplementation: therapeutic implications for antifolates and other classes of drugs in cancer treatment

Over the past decades, numerous reports have covered the crucial role of multidrug resistance (MDR) transporters in the efficacy of various chemotherapeutic drugs. Specific cell membrane-associated transporters mediate drug resistance by effluxing a wide spectrum of toxic agents. Although several excellent reviews have addressed general aspects of drug resistance, this current review aims to highlight implications for the efficacy of folate-based and other types of chemotherapeutic drugs. Folates are vitamins that are daily required for many biosynthetic processes. Folate supplementation in our diet may convey protective effects against several diseases, including cancers, but folate supplementation also makes up an essential part of several current cancer chemotherapeutic regimens. Traditionally, the folate leucovorin, for instance, is used to reduce antifolate toxicity in leukemia or to enhance the effect of the fluoropyrimidine 5-fluorouracil in some solid tumors. More recently, it has also been noted that folic acid has the ability to increase antitumor activity of several structurally unrelated regimens, such as alimta/pemetrexed and cisplatin. Moreover, studies from our laboratory demonstrated that folates could modulate the expression and activity of at least two members of the MDR transporters: MRP1/ABCC1, and the breast cancer resistance protein BCRP/ABCG2. Thus, folate supplementation may have differential effects on chemotherapy: (1) reduction of toxicity, (2) increase of antitumor activity, and (3) induction of MRP1 and BCRP associated cellular drug resistance. In this review the role of MDR proteins is discussed in further detail for each of these three items from the perspective to optimally exploit folate supplementation for enhanced chemotherapeutic efficacy of both antifolate-based chemotherapy and other classes of chemotherapeutic drugs.

Relation between genetic variants of the ataxia telangiectasia-mutated (ATM) gene, drug resistance, clinical outcome and predisposition to childhood T-lineage acute lymphoblastic leukaemia

The T-lineage phenotype in children with acute lymphoblastic leukaemia (ALL) is associated with in vitro drug resistance and a higher relapse-risk compared to a precursor B phenotype. Our study was aimed to investigate whether mutations in the ATM gene occur in childhood T-lineage acute lymphoblastic leukaemia (T-ALL) that are linked to drug resistance and clinical outcome. In all, 20 different single nucleotide substitutions were found in 16 exons of ATM in 62/103 (60%) T-ALL children and 51/99 (52%, P = 0.21) controls. Besides the well-known polymorphism D1853N, five other alterations (S707P, F858L, P1054R, L1472W, Y1475C) in the coding part of ATM were found. These five coding alterations seem to occur more frequently in T-ALL (13%) than controls (5%, P = 0.06), but did not associate with altered expression levels of ATM or in vitro resistance to daunorubicin. However, T-ALL patients carrying these five coding alterations presented with a higher white blood cell count at diagnosis (P = 0.05) and show an increased relapse-risk (5-year probability of disease-free survival (pDFS) = 48%) compared to patients with other alterations or wild-type ATM (5-year pDFS = 76%, P = 0.05). The association between five coding ATM alterations in T-ALL, their germline presence, white blood cell count and unfavourable outcome may point to a role for ATM in the development of T-ALL in these children.

Macrophages are involved in hexachlorobenzene-induced adverse immune effects

Hexachlorobenzene (HCB) is a persistent environmental pollutant that causes adverse immune effects in man and rat. The Brown Norway (BN) rat is very susceptible to HCB-induced immunopathology and oral exposure causes inflammatory skin and lung lesions, splenomegaly, lymph node (LN) enlargement, and increased serum levels of IgE and anti-ssDNA IgM. T cells play an important role but do not account for all adverse effects induced by HCB. Macrophages are probably also important and the relationship between macrophages and T cells was further investigated. To eliminate macrophages clodronate-liposomes were used. Furthermore, a kinetic study was performed to obtain insight in the early phase of the HCB-induced immune response. Also, experiments were performed to detect specific memory T cells. Therefore, an adoptive transfer study was performed. Our results indicate that macrophages are indeed involved in HCB-induced skin lesions, lung eosinophilia, and elevation of IgM against ssDNA. Kinetics showed that both skin and lung lesions appeared early after exposure. Moreover, immune effects could not be adaptively transferred. Thus, both macrophages and T cells are involved in HCB-induced immune effects but HCB exposure does not lead to specific T cell sensitization. Presumably, HCB exposure induces macrophage activation, thereby generating adjuvant signals that polyclonally stimulate T cells. Together, these events may lead to the observed immunopathology in BN rats.

Differential Requirement for CD28/CTLA-4-CD80/CD86 Interactions in Drug-Induced Type 1 and Type 2 Immune Responses to Trinitrophenyl-Ovalbumin

The use of mAbs to abrogate costimulatory interactions has attracted much attention with regard to prevention and modulation of adverse (auto)immune-like reactions. However, the role of costimulatory molecules and possible therapeutic use of Ab-treatment in drug-induced immunostimulation is poorly elucidated. In the present studies, we show that CD28/CTLA-4-CD80/CD86 costimulatory interactions differently regulate drug-induced type 1 and type 2 responses to an identical bystander Ag, TNP-OVA, in BALB/c mice using the reporter Ag popliteal lymph node assay. The antirheumatic drug D-Penicillamine, which may induce lupus-like side-effects, stimulated type 2 responses against TNP-OVA, characterized by the production of IL-4 and TNP-specific IgG1 and IgE. These responses were abrogated in CD80/CD86-deficient mice and in wild-type mice that were treated with anti-CD80 and anti-CD86, or CTLA-4-Ig. Anti-CTLA-4 intensively enhanced the D-Penicillamine-induced effects. In contrast, the type 1 response (IFN-gamma, TNF-alpha, IgG2a) to TNP-OVA induced by the diabetogen streptozotocin still developed in the absence of CD80/CD86 costimulatory signaling. In addition, it was demonstrated that coadministration of anti-CD80 and anti-CD86 mAbs slightly enhanced streptozotocin-induced type 1 responses, whereas the CTLA-4-Ig fusion protein completely abrogated this response. In conclusion, different drugs may stimulate distinct types of immune responses against an identical bystander Ag, which are completely dependent on (type 2) or independent of (type 1) the CD28/CTLA-4-CD80/CD86 pathway. Importantly, the effects of treatment with anti-CD80/CD86 mAbs and CTLA-4-Ig may be considerably different in responses induced by distinct drugs.

The seventh international childhood acute lymphoblastic leukemia workshop report: Palermo, Italy, January 29--30, 2005

Between 1995 and 2004, six International Childhood Acute Lymphoblastic Leukemia (ALL) Workshop have been held, and the completion of several collaborative projects has established the clinical relevance and treatment options for several specific genetic subtypes of ALL. This meeting report summarizes the data presented in the seventh meeting and the discussion.