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Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a Rho-guanosine triphosphate hydrolases involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but, to the best of our knowledge, has never been described to date. We studied 8 male patients, from 7 unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B-lymphoblastoid cell lines from patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. Knock down of DOCK11 recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T-cell (Treg) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found reduced T-cell proliferation and impaired STAT5B phosphorylation upon interleukin-2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and is associated with abnormal actin cytoskeleton remodeling as well as Treg phenotype, culminating in immune dysregulation and severe early-onset autoimmunity., (© 2023 by The American Society of Hematology.)

The development of a second malignancy after the diagnosis of childhood acute lymphoblastic leukemia (ALL) is a rare event. Certain second malignancies have been linked with specific elements of leukemia therapy, yet the etiology of most second neoplasms remains obscure and their optimal management strategies are unclear. This is a first comprehensive report of non-Hodgkin lymphomas (NHLs) following pediatric ALL therapy, excluding stem-cell transplantation. We analyzed data of patients who developed NHL following ALL diagnosis and were enrolled in 12 collaborative pediatric ALL trials between 1980-2018. Eighty-five patients developed NHL, with mature B-cell lymphoproliferations as the dominant subtype (56 of 85 cases). Forty-six of these 56 cases (82%) occurred during or within 6 months of maintenance therapy. The majority exhibited histopathological characteristics associated with immunodeficiency (65%), predominantly evidence of Epstein-Barr virus-driven lymphoproliferation. We investigated 66 cases of post-ALL immunodeficiency-associated lymphoid neoplasms, 52 from our study and 14 additional cases from a literature search. With a median follow-up of 4.9 years, the 5-year overall survival for the 66 patients with immunodeficiency-associated lymphoid neoplasms was 67.4% (95% confidence interval [CI], 56-81). Five-year cumulative risks of lymphoid neoplasm- and leukemia-related mortality were 20% (95% CI, 10.2-30) and 12.4% (95% CI, 2.7-22), respectively. Concurrent hemophagocytic lymphohistiocytosis was associated with increased mortality (hazard ratio, 7.32; 95% CI, 1.62-32.98; P = .01). A large proportion of post-ALL lymphoid neoplasms are associated with an immunodeficient state, likely precipitated by ALL maintenance therapy. Awareness of this underrecognized entity and pertinent diagnostic tests are crucial for early diagnosis and optimal therapy., (© 2023 by The American Society of Hematology.)

Maintenance therapy is the last phase of treatment for acute lymphoblastic leukemia in children and adolescents. Although maintenance therapy is associated with toxicities and specific management issues, it is an essential phase of treatment that reduces the risk of relapse. The objective of this work is to propose a guide for the initiation, administration, and monitoring of maintenance therapy, and for the management of food, schooling, leisure, community life, risk of infection and links with family medicine., (Copyright © 2022 Société Française du Cancer. Published by Elsevier Masson SAS. All rights reserved.)

Aim: To evaluate the prognostic significance of initial central nervous system (CNS) involvement of children with acute lymphoblastic leukemia (ALL) enrolled in the EORTC 58951 trial., Patients and Methods: From 1998 to 2008, 1930 ALL patients were included in the randomized EORTC 58951 trial. Overall treatment intensity was adjusted according to known prognostic factors including the level of minimal residual disease after induction treatment. CNS-directed therapy comprised four to 11 courses of i.v. methotrexate (5g/m 2 ), and 10 to 19 intrathecal chemotherapy injections, depending on risk group and CNS status. Cranial irradiation was omitted for all patients., Results: The overall 8-year event-free survival (EFS) and overall survival (OS) rates were 81.3% and 88.1%, respectively. In the CNS-1, TPL+, CNS-2, and CNS-3 groups, the 8-year EFS rates were 82.1%, 77.1%, 78.3%, and 57.4%, respectively. Multivariable analysis indicated that initial CNS-3 status, but not CNS-2 or TLP+, was an independent adverse predictor of outcome. The 8-year incidence of isolated CNS relapse was 1.7% and of isolated or combined CNS relapse it was 3.7%. NCI high-risk group, male sex, CNS-2 and CNS-3 status were independent predictors for a higher incidence of any CNS relapse., Conclusions: CNS-3 status remains associated with poor prognosis and requires intensification of both systemic and CNS-directed therapy. This trial was registered at https://clinicaltrials.gov/under/NCT00003728., (Copyright © 2021. Published by Elsevier Masson SAS.)

The aim of our study was to analyze the factors contributing to heterogeneity of prognosis in patients with hyperdiploidy>50 chromosomes (HD>50), a group of B-cell precursor acute lymphoblastic leukemia with favorable outcome. The 541 HD>50 patients registered prospectively in the 58951 European Organisation for Research and Treatment of Cancer (EORTC) Children's Leukemia Group (CLG) trial, identified by karyotype (446 patients) and by DNA index (DI) (490 patients), had a 6-year event-free survival (EFS) of 89.0% (standard error [SE] = 1.5%) and a 6-year overall survival (OS) of 95.9% (SE = 0.9%). The strongest prognostic factor was the modal number of chromosomes (MNC): the 6-year EFS of 51-53, 54-57, and 58-66 MNC groups were 80%, 89%, and 99%, respectively (P < .0001). Ploidy assessed by DI was also a favorable factor: the higher the DI, the better the outcome. The 6-year EFS of the 3 subgroups of DI < 1.16/≥1.16-<1.24/≥1.24 were 83%, 90%, and 95%, respectively (P = .009). All usual combinations of trisomies (chromosomes 4, 10, 17, 18) were significant favorable factors but had lower EFS when MNC was lower than 58. In multivariate analysis, MNC remained the strongest factor. Consequently, the best indicator for excellent outcome was ploidy assessed by karyotype because patients with 58-66 chromosomes stood every chance of being cured (OS of 100% at 6-year follow-up) with less-intensive therapy. This trial was registered at www.clinicaltrials.gov as #NCT00003728. Registered: http://www.eortc.org/, http://clinicaltrials.gov/show/NCT00003728.

Unlabelled: Congenital neutropenia is a group of genetic disorders that involve chronic neutropenia and susceptibility to infections. These neutropenias may be isolated or associated with immunologic defects or extra-hematopoietic manifestations. Complications may occur as infectious diseases, but also less frequently as myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Recently, the transcription factor GATA2 has been identified as a new predisposing gene for familial AML/MDS. In the present study, we describe the initial identification by exome sequencing of a GATA2 R396Q mutation in a family with a history of chronic mild neutropenia evolving to AML and/or MDS. The subsequent analysis of the French Severe Chronic Neutropenia Registry allowed the identification of 6 additional pedigrees and 10 patients with 6 different and not previously reportedGATA2 mutations (R204X, E224X, R330X, A372T, M388V, and a complete deletion of the GATA2 locus). The frequent evolution to MDS and AML in these patients reveals the importance of screening GATA2 in chronic neutropenia associated with monocytopenia because of the frequent hematopoietic transformation, variable clinical expression at onset, and the need for aggressive therapy in patients with poor clinical outcome., Key Points: Mutations of key transcription factor in myeloid malignancies.

A primary HCMV infection or virus reactivation may cause severe disease in hosts with a deficient immune system. The virus can disturb both innate and adaptive immunity by targeting dendritic cell (DC) functions. Monocytes, the precursors of DCs in vivo (MoDCs), are the primary targets of HCMV; they can also harbor latent virus. The DCs generated from infected monocytes (CMV-MoDCs) have an altered phenotype and functional defects. We have shown that CMV-MoDCs do not secrete IL-12 in response to lipopolysaccharide stimulation, cannot ingest dead cells, induce T(H)1 differentiation, or the proliferation of naive allogeneic CD4(+) T cells. We found that the GM-CSF signaling in an entire population of CMV-MoDCs was impaired, although only half of the cells were productively infected, and that IL-6 secretion and suppressors of cytokine signaling 3 induction contributed to this bystander effect. We also showed that MoDCs derived ex vivo from monocytes of viremic patients had the same altered phenotype as CMV-MoDCs, including decreased STAT5 phosphorylation, indicating defective GM-CSF signaling. We have thus described a new mechanism of HCMV-induced immunosupression, indicated how infection may disturb both GM-CSF-dependent physiologic processes and proposed GM-CSF-based therapeutic approaches.

X-linked lymphoproliferative syndromes (XLP) are primary immunodeficiencies characterized by a particular vulnerability toward Epstein-Barr virus infection, frequently resulting in hemophagocytic lymphohistiocytosis (HLH). XLP type 1 (XLP-1) is caused by mutations in the gene SH2D1A (also named SAP), whereas mutations in the gene XIAP underlie XLP type 2 (XLP-2). Here, a comparison of the clinical phenotypes associated with XLP-1 and XLP-2 was performed in cohorts of 33 and 30 patients, respectively. HLH (XLP-1, 55%; XLP-2, 76%) and hypogammaglobulinemia (XLP-1, 67%; XLP-2, 33%) occurred in both groups. Epstein-Barr virus infection in XLP-1 and XLP-2 was the common trigger of HLH (XLP-1, 92%; XLP-2, 83%). Survival rates and mean ages at the first HLH episode did not differ for both groups, but HLH was more severe with lethal outcome in XLP-1 (XLP-1, 61%; XLP-2, 23%). Although only XLP-1 patients developed lymphomas (30%), XLP-2 patients (17%) had chronic hemorrhagic colitis as documented by histopathology. Recurrent splenomegaly often associated with cytopenia and fever was preferentially observed in XLP-2 (XLP-1, 7%; XLP-2, 87%) and probably represents minimal forms of HLH as documented by histopathology. This first phenotypic comparison of XLP subtypes should help to improve the diagnosis and the care of patients with XLP conditions.

Duodenal obstruction by Superior Mesenteric Artery (SMA) is a misdiagnosed vomiting syndrome in children. Several factors are involved, including rapid weight loss, rapid statural growth without weight augmentation. Diagnosis is suspected when an improvement is achieved by ventral decubitus and it is confirmed by plain films of the abdomen, GI study with barium and echography, measuring the aortomesenteric angle (inferior to 25-30 degrees ). Patients must at first be treated conservatively. Surgery is indicated for occlusive episodes with unsuccessful conservative therapy. The authors report 3 cases with different clinical presentation. However, all the patients presented important weight loss and vomiting.

Iron accumulation in the liver in hereditary hemochromatosis (HH) has been shown to be highly variable. Some studies point to the importance of major histocompatibility complex (MHC) class I (MHC-I) and CD8(+) cells as modifiers of iron overload. In this report, using mice knockout for H2K(b-/-) and H2D(b-/-) genes, it is demonstrated that lack of classical MHC-I molecules results in a spontaneous increase of nonheme iron content in the liver (mainly located in the hepatocytes) when compared to wild-type mice. In CD8(-/-) and Rag2(-/-) mice, no spontaneous hepatic iron accumulation was observed. These results demonstrate for the first time that classical MHC-I molecules could be involved in the regulation of iron metabolism and contribute to the established genotype/phenotype discrepancies seen in HH.

Background: Human cytomegalovirus (HCMV) infection and reactivation following allogeneic bone marrow transplantation is a major source of complications in grafted patients including pneumonitis, graft rejection and even death. Adoptive immunotherapy consisting in transfer of CD4(+) and CD8(+) T cells directed against HCMV has proved its worth. Nevertheless, established procedures have to be improved in terms of safety and waiting period required to obtain specific T cells., Methods: As an alternative to infectious virus used in current strategies, we purified a recombinant protein IE1-pp65 resulting from the fusion of the regulatory IE1 and matrix pp65 proteins, both known as the major targets of the overall anti-HCMV T cell response. Based on our previous data demonstrating its use for in vitro stimulation and expansion of anti-HCMV CD4(+) and CD8(+) T cells (Vaz-Santiago et al, 2001, J.Virol, 75:7840-47) from peripheral blood mononuclear cells (PBMC) of seropositive donors, we planned to improve its in vitro immunogenicity through association with a nanoparticulate carrier, SMBV., Results: We demonstrated that using of SMBV/IE1-pp65 formulation allowed to potentiate in vitro activation of T cells and to expand more CD8(+) T cells than with soluble IE1-pp65, following stimulation of PBMC., Discussion: These data suggest the use of SMBV/IE1-pp65 formulation as a potential source of antigen for efficient T cells expansion in the development of safe anti-HCMV immunotherapy.

Human cytomegalovirus (CMV) infection of bone marrow transplant recipients can cause pancytopenia, as well as life-threatening interstitial pneumonia. CMV replicates actively in bone marrow stromal cells, whereas it remains latent in hematopoietic progenitors. Our aim was to study the influence of CMV infection on adherence of CD34(+) cells to the myofibroblastic component of human bone marrow and examine transmission of virus from myofibroblasts to CD34(+) cells. We show that smooth actin, but not fibronectin, organization is markedly modified by CMV infection of bone marrow stromal myofibroblasts. Nonetheless, CMV infection led to increased adherence of the CD34(+) progenitor cell line, KG1a, relative to adherence to uninfected myofibroblasts from the same donors. Adherence of CD34(+) cells to infected bone marrow myofibroblasts resulted in transfer of virions and viral proteins through close cell-to-cell contacts. This phenomenon may play a role in the pathophysiology of CMV bone marrow infection and in eventual virus dissemination.

Background: Patient-controlled analgesia (PCA) has been shown to be superior to a continuous morphine infusion for the treatment of ongoing pain in children over five years of age. Nevertheless, prescription parameters such as the bolus dosage and the possible association of a continuous background infusion have not yet been standardized., Patients and Methods: Thirty-three children, aged four to 17, hospitalized in a pediatric hematology ward, benefited from PCA with a standardized prescription: a bolus dosage of at least 25 mg/kg, without a background infusion. Morphine consumption, side effects and efficacy on pain relief were followed., Results: Median of mean morphine consumption was 0.32 mg.kg-1.d-1. Median of maximal consumption was 0.58 mg.kg-1.d-1. Mean duration was nine days. No important side effects were noted, except in two patients. They presented prolonged constipation and a poor quality of nocturnal sleep, but they also had a major depressive syndrome persisting after resolution of pain. Efficacy was comparable to a continuous intravenous infusion, and nocturnal sleep was of good quality for 31 children., Conclusion: This standardized technique of PCA can be used extensively in children over five years of age. It can be used as a reference for further studies.

Although hereditary spherocytosis (HS) is a common disorder of the red cell membrane, its clinical and biologic expression at birth and in early infancy has received little attention. In order to obtain insights into the natural history of HS during infancy, we studied 46 neonates, 39 from families in which 1 of the parents had previously been given a diagnosis of HS and 7 presenting with nonimmune hemolytic anemia and no family history of HS. Of these 46 neonates, 23 were subsequently confirmed to have HS and 23 were found to be healthy. The hematologic and biologic analyses carried out in this cohort of 46 newborns enabled us to develop guidelines for early diagnosis of HS. A careful clinical follow-up of 34 HS patients during the first year of life allowed us to define several important clinical features of HS during this period. Hemoglobin values are usually normal at birth but decrease sharply during the subsequent 20 days, which leads, in many cases, to a transient and severe anemia. The anemia is severe enough to warrant blood transfusions in a large number of infants with HS (26 of 34 in our series). The aggravation of anemia appears to be related to the inability of these infants to mount an appropriate erythropoietic response to anemia and to the development of splenic filtering function. These findings indicate that careful monitoring of infants with HS during the first 6 months of life is important for appropriate clinical management. (Blood. 2000;95:393-397)

Background: Despite high-dose therapy and ASCT some patients with aggressive HD fail to achieve long-term survival., Patients and Methods: Forty-three patients with induction failure (n = 19) or very unfavorable (UF) relapse (n = 24) from HD were included in a multicentric study of tandem ASCT. They planned to receive two course of IVA75 with GCSF and blood stem cell collection. ASCT1 was conditioned with CBV + mitoxantrone (30 mg/m2) and ASCT2 (cytarabine 6 g/m2 melphalan 140 mg/m2 and total body irradiation at 12 Gy or busulfan 16 (n = 4) than 12 mg/kg). After salvage therapy, response > 50% was observed in 63% of the patients (six patients were included for refractory relapse). Four patients had no ASCT for disease progression; seven patients had only ASCT1 (disease progression, n = 3) and thirty-two patients (74%) received the two ASCT., Results: Hematologic recovery was normal after ASCT1 but delayed platelet recovery was observed after ASCT2 with busulfan in the conditioning regimen. Two VOD with one fatal occurred with busulfan at 16 mg/kg and one hemorrhagic cystic, no further grade 4 toxicity was observed with the reduced doses of busulfan (12 mg/kg). After ASCT2, 83% of these UF patients were in remission and 20% relapsed within the first year. On an intent-to-treat analysis, 22 of 43 patients are in continuous CR (including 8 patients with induction failure). For the whole population (n = 43) and for patients receiving the two ASCT (n = 32), the two-year survival from the date of progression were respectively at 65% and at 74%., Conclusion: Double ASCT is feasible in very UF relapse from HD and may lead to some prolonged remission.

Unlabelled: Alloimmune neonatal neutropenia is a rare event. Usually asymptomatic, it may however in some cases result in a severe sepsis. Treatment with recombinant granulocyte colony-stimulating factor (G-CSF) has been recently proposed., Case Report: We report two new cases in infected newborns of a successful treatment of alloimmune neonatal neutropenia with G-CSF, resulting in complete neutrophil recovery in less than 72 hours. Moreover, the treatment was well tolerated., Conclusion: The analysis of these two cases and of those previously reported indicates that G-CSF represents the first-choice treatment in this affection when infectious signs are present in the neonate.

Although blood transfusion (BT) therapy remains a key component of the weaponry used to treat acute and chronic sickle cell disease complications, its indications and modalities are currently the focus of a critical reappraisal prompted by the introduction of hydroxyurea, recent improvements in allogeneic bone marrow transplantation, and increasing attention to safety concerns. Expected benefits of each BT should be carefully weighed against the risks of infections, immunologic complications, and iron overload. Simple or exchange BT can be used. In emergency situations, the only effective means of improving tissue oxygenation and limiting blood vessel occlusion is dilution or removal of HbS by simple or exchange BT, respectively; simple BT is indicated in severe anemia or acute hypovolemia and exchange BT in acute vasoocclusive crisis or acute infection. In nonemergency situations, long-term exchange BT programs geared to maintain the HbS level around 30% are used to stabilize existing lesions and to prevent recurrences; they have been proved effective in preventing recurrent stroke in patients who are not candidates for allogeneic bone marrow transplantation. Situations in which BT therapy is widely used despite controversy regarding its value and modalities include the prevention of complications of pregnancy, the prevention of perioperative complications, and the prevention of recurrences of severe vaso occlusive crisis in patients eligible for hydroxyurea therapy. Advances have been made in the minimization of BT-related complications (alloimmunization, viral infections, iron overload) through critical appraisal of the need for each BT, careful selection of the most appropriate blood product, and a change in BT technique resulting in a reduction in the number of blood donors.

Bone marrow (BM) trephine biopsies from 15 pediatric patients with acute lymphoid (ALL) or myeloid (AML) leukemia were engrafted subcutaneously into severe combined immunodeficiency (SCID) mice conditioned by 200 cGy total-body irradiation. Implants were harvested 5 to 19 weeks later for histologic, cytologic, and/or flow cytometric analysis of the residing marrow. Eighteen of 19 grafts contained viable human leukemic cells to various extents as assessed by one or more of these methods. Thirteen of 14 implants analyzed by flow cytometry included high numbers of tumor cells, accounting for 85% to 100% of the total nucleated cells in seven of them. Histologically, engrafted marrow samples exhibited areas of blastic infiltration, and tumor-specific gene rearrangements were retrieved in long-term engrafted biopsies. Importantly, engrafted mice remained perfectly healthy even 5 months posttransplantation, and no human tumor cell dissemination was detected in the hematolymphoid and nonhematopoietic tissues at the time of autopsy. These results demonstrate that human malignant hematopoiesis can be sustained long-term in its original, intact marrow stromal environment transplanted in appropriately conditioned immunodeficient mice.

Unlabelled: Autoimmune neutropenia (AIN) is a frequent cause of chronic neutropenia especially in youngest children. Its diagnosis is established by immunological proof of the autoimmune mechanism. The aim of this study is to better describe this autoimmune process and to show the contribution of bone marrow smears to this diagnosis., Patients and Methods: Ten children, six girls and four boys, were examined between 1990 and 1995. Eight of them had typical AIN, confirmed by the presence of antibodies against neutrophils. Two other patients were included on the basis of bone marrow pictures. Five non-neutropenic children with normal bone marrow smears were chosen as controls. Bone marrow analysis was always performed by the same cytologist according to a reproducible technique., Results: Six out of ten patients had important features of elective phagocytosis of neutrophils by marrow macrophages (unlike controls) without signs of dysgranulopoiesis or hemophagocytosis. Antibodies against neutrophils were detected in six patients with phagocytosis and in four patients without these cytological features. In two other children presenting the same bone marrow picture and clinical profile, an autoimmune process was probable, even in the absence of antibodies against neutrophils. Some patients had several infections and were given immunoglobulins and/or granulocyte colony-stimulating factor (G-CSF) therapy. The efficacy of Immunoglobulin was not constant, whereas G-CSF was effective at low doses and shortened the duration of infections., Conclusion: Prolonged neutropenia in childhood must lead to look for phagocytosis by marrow macrophages in bone marrow smears, as a possible sign of autoimmunity. Growth factors may temporarily be used associated with antibiotics therapy in severe and prolonged infections.

Chediak-Higashi syndrome is a rare condition characterized by susceptibility to bacterial infections, defective natural killer activity, and episodes of macrophage activation known as accelerated phases. Chemotherapy can induce transient remission of the accelerated phase, but relapses become less and less sensitive to treatment and ultimately lead to death. Allogenic bone marrow transplantation (BMT) has been proposed as a curative treatment for Chediak-Higashi syndrome. We report the outcome of BMT in 10 such children. Seven received marrow from an HLA-identical related donor and three from an HLA-nonidentical related donor. Three patients died, two from a new accelerated phase after rejection of transplanted bone marrow and one from cytomegalovirus (CMV) pneumonia. Six of seven recipients of HLA-identical marrow and one of three recipients of HLA-nonidentical marrow are alive and well without treatment 1.5 to 13 years after transplantation (median, 6.5 years). No manifestations of accelerated phases have occurred in these seven patients, and significant natural killer activity is detectable. Interestingly, BMT prevented recurrence of accelerated phases in patients with limited numbers of donor-type leukocytes after transplantation. Ocular and cutaneous albinism were not corrected after transplantation. None of the patients developed serious toxic reactions to the BMT conditioning regimen or have long-term sequelae. These results show that HLA-identical BMT is an acceptable curative treatment for Chediak-Higashi syndrome, whereas HLA-nonidentical BMT remains an experimental approach.

We have developed a strategy based on polymerase chain reaction (PCR) for detecting all possible gamma T-cell receptor (gamma TCR) rearrangements and the most common delta TCR rearrangements found in B-lineage and T-acute lymphoblastic leukemia (T-ALL). The segments amplified from blasts are then directly sequenced to derive clonospecific probes. From a series of 45 patients aged 1 to 15 years (42 B-lineage ALL, 3 T-ALL), 35 (83%) could be followed for minimal residual disease with at least one clonospecific probe. Detection of clonal markers using clonospecific probes routinely allowed the detection of 1 to 10 blasts out of 10(5) cells as determined by serial dilutions of the initial samples. Residual disease was quantitated by a competitive PCR assay based on the coamplification of an internal standard. Twenty children were prospectively followed for periods varying from 7 to 30 months. In most children, a progressive decrease of the tumor load was observed, and blasts became undetectable within 6 months after the initiation of treatment. A slower kinetics of decrease in tumor cells was found in three children. These three patients relapsed with blasts that continued to display the initial clonospecific markers. Three other children had a central nervous system relapse despite the absence of detectable medullary residual disease. The use of both delta and gamma TCR genes as clonal markers, as well as simplification in the methods to detect and quantify residual blasts reported here, will allow the study of the large number of patients required to determine the role of the detection of minimal residual disease by PCR in the follow-up of childhood ALL.