Detection of residual acute lymphoblastic leukemia cells in cultures of bone marrow obtained during remission

Kit inhibitor APcK110 induces apoptosis and inhibits proliferation of acute myeloid leukemia cells

Kit is a membrane-bound tyrosine kinase and receptor for stem cell factor (SCF) with a crucial role in hematopoiesis. Mutations of KIT occur in almost half of patients with core-binding factor leukemias, in which they have been associated with worse outcome. Development of new compounds targeting Kit may therefore hold promise for therapy. We investigated the activity and mechanism of action of APcK110, a novel Kit inhibitor, in the mastocytosis cell line HMC1.2 (KITV560G and KITD816V), acute myeloid leukemia (AML) lines OCIM2 and OCI/AML3 (both wild-type), and primary samples from patients with AML. We show that (a) APcK110 inhibits proliferation of the mastocytosis cell line HMC1.2 and the SCF-responsive cell line OCI/AML3 in a dose-dependent manner; (b) APcK110 is a more potent inhibitor of OCI/AML3 proliferation than the clinically used Kit inhibitors imatinib and dasatinib and at least as potent as cytarabine; (c) APcK110 inhibits the phosphorylation of Kit, Stat3, Stat5, and Akt in a dose-dependent fashion, showing activity of APcK110 on Kit and its downstream signaling pathways; (d) APcK110 induces apoptosis by cleavage of caspase-3 and poly(ADP-ribose) polymerase; and (e) APcK110 inhibits proliferation of primary AML blasts in a clonogenic assay but does not affect proliferation of normal colony-forming cells. Although APcK110 activity may partly depend on cytokine responsiveness (e.g., SCF) and not exclusively KIT mutation status, it remains a potent inhibitor of AML and mastocytosis cell lines and primary AML samples. APcK110 and similar compounds should be evaluated in clinical trials of patients with AML.

Tyrenes: synthesis of new antiproliferative compounds with an extended conjugation

A series of substituted styryl-acrylonitriles was designed and synthesized. The new compounds, called tyrenes, were tested for the ability to inhibit acute lymphocytic leukemia (ALL) cancer cell growth, as well as on their toxicity to normal bone marrow (NBM) cells. The results showed that 3,4-dihydroxystyryl-acrylonitriles, in particular CR-4, revealed great potency as antitumor agents, and also exhibited low toxicity to normal cells. The effectiveness of these compounds with extended conjugation may be due to their possible functioning as reactive Michael acceptors.

Adult acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) in adults is a relatively rare neoplasm with a curability rate around 30% at 5 years. This consideration makes it imperative to dissect further the biological mechanisms of disease, in order to selectively implement an hitherto unsatisfactory success rate. The recognition of discrete ALL subtypes (some of which deserve specific therapeutic approaches, like T-lineage ALL (T-ALL) and mature B-lineage ALL (B-ALL)) is possible through an accurate combination of cytomorphology, immunophenotytpe and cytogenetic assays and has been a major result of clinical research studies conducted over the past 20 years. Two-three major prognostic groups are now easily identifiable, with a survival probability ranging from <10 to 20% (Philadelphia-positive ALL) to about 50-60% (low-risk T-ALL and selected patients with B-lineage ALL). These issues are extensively reviewed and form the basis of current knowledge. The second major point relates to the emerging importance of studies that reveal a dysregulated gene activity and its clinical counterpart. It is now clear that prognostication is a complex matter ranging from patient-related issues to cytogenetics to molecular biology, including the evaluation of minimal residual disease (MRD) and possibly gene array tests. On these bases, the role of a correct, highly personalised therapeutic choice will soon become fundamental. Therapeutic progress may be obtainable through a careful integration of chemotherapy, stem cell transplantation, and the new targeted treatments with highly specific metabolic inhibitors and humanised monoclonal antibodies.

Inhibition of acute lymphoblastic and myeloid leukemias by a novel kinase inhibitor

In recent years, synthetic tyrosine kinase inhibitors have made a rapid transition from basic research to therapeutic application. These compounds represent a major clinical advance in the approach to cancer in their relative specificity of action and decreased toxicity. We report here the effects of a novel tyrosine kinase inhibitor CR4 that interferes with growth-promoting pathways to markedly inhibit the growth and survival of both Philadelphia-positive and -negative acute lymphoblastic leukemia (ALL) as well as acute myeloid leukemia (AML). While efficiently ablating leukemic cell growth, normal cell growth and differentiation remain unaffected by CR4. CR4 demonstrates an ability to inhibit the function of multiple growth-critical kinases and yet exhibits a low level of cytotoxicity. These findings suggest that CR4 may prove to be highly effective as a therapeutic agent.

N-(4-Hydroxylphenyl)retinamide (fenretinide, 4-HPR), a retinoid compound with antileukemic and proapoptotic activity in acute lymphoblastic leukemia (ALL)

BACKGROUND

Retinoids have been shown to regulate vital cellular processes including cell proliferation, differentiation and apoptosis. N-(4-Hydroxyphenyl)-all-trans-retinamide (fenretinide, 4-HPR) is a synthetic ATRA derivative with chemopreventive and cytotoxic activity against various cancer cell lines including myeloid leukemia. Although several modes of action have been postulated, its mechanism of action in hematologic malignancies remains unclear. Furthermore, only limited information exists as to its activity in lymphoid malignancies.

METHODS AND RESULTS

To test whether 4-HPR has activity in acute lymphoblastic leukemia (ALL), we first analyzed its antiproliferative effect in five ALL (Z-33, Z-138, Z-119, Z-181, and Jurkat) cell lines. We found that 4-HPR inhibited the proliferation of all cell lines in a dose-dependent manner at concentrations ranging from 1 to 10 microM. We further demonstrated by cell cycle analysis that 5 microM of 4-HPR blocked Z-119 cells in S phase thus preventing their progression through the cycle. Next we tested whether 4-HPR activated the caspase pathway and induced apoptotic cell death. We found that 4-HPR induced apoptosis in Z-119 cells through the activation of caspase-3 and subsequent cleavage of its substrate poly(ADP-ribose) polymerase (PARP). We then asked whether 4-HPR could affect fresh ALL progenitor cells. Therefore, we obtained bone marrow and peripheral blood cells from five patients with newly diagnosed ALL and tested the effect of 4-HPR using the ALL blast colony culture assay. To supplement our results, we also performed the ALL blast assay on one ALL cell line (ALL-1). We found that 4-HPR significantly inhibited ALL colony-forming cell proliferation in a dose-dependent manner.

CONCLUSIONS

Our data show that 4-HPR is a potent inhibitor of ALL cell proliferation and that it induces in vitro apoptotic cell death in ALL blasts. Further studies are warranted to establish the in vivo effect of 4-HPR particularly in patients with ALL.

Autologous stem cell transplantation for acute lymphocytic leukemia in adults

Autologous bone marrow transplantation remains an investigational treatment for adult ALL. Despite many anecdotal studies showing efficacy, the rarity of ALL has prevented the large randomized trials necessary to confirm effectiveness. Candidates for autoBMT include adult patients in first CR with adverse risk factors and all patients who have experienced disease relapse. It remains debatable which preparative regimen is optimal, whether purging is necessary, or if chemotherapy or immunotherapy administered after transplantation can decrease disease relapse. Overall, every effort should be made to enter ALL patients on well-designed randomized multi-institutional trials. These trials should compare autologous transplantation to newer more intensive chemotherapy regimens and should take into account the heterogeneity of ALL. A quality of life analysis should be performed as one high-dose treatment may be less toxic and better tolerated than multiple cycles of consolidation chemotherapy. Strategies aimed at enhancing an autologous graft-versus-leukemia effect after transplantation may enhance long-term survival. Many more studies are needed to further define the optimal role of autoBMT in adult ALL.

Studies of minimal residual disease in acute lymphocytic leukemia

During the past 2 decades, there has been considerable progress made in the treatment of childhood and adult lymphocytic leukemia (ALL). Currently, 70% to 90% of adults achieve a complete remission, and 25% to 50% of these patients may experience prolonged disease-free survival and may be cured of their disease. Unfortunately, most adults with ALL will ultimately experience a recurrence and die of their leukemia. Although most children with ALL may now be cured with current therapeutic regimens, the ability to distinguish good-risk patients from those who are likely to relapse has important clinical implications. Relapse, in most pediatric and adult cases, is thought to result from residual leukemia cells that remain following achievement of "complete" remission but are below the limits of detection using conventional morphologic assessment of the bone marrow. Sensitive techniques are now available to detect subclinical levels of residual leukemia, termed minimal residual disease.

Prevalence and Growth Characteristics of Malignant Stem Cells in B-Lineage Acute Lymphoblastic Leukemia

We used a stroma-supported culture method to study the prevalence and growth characteristics of malignant stem cells in acute lymphoblastic leukemia (ALL). In 51 of 108 B-lineage ALL samples, bone marrow-derived stroma not only inhibited apoptosis of ALL cells but also supported their proliferation in serum-free medium. When single leukemic cells were placed in the stroma-coated wells of microtiter plates, the percentage of wells with leukemic cell growth after 2 to 5 months of culture ranged from 6% to 20% (median, 15%; 5 experiments). The immunophenotypes and genetic features of cells recovered from these cultures were identical to those noted before culture. All cells maintained their stroma dependency and self-renewal capacity. Leukemic clones derived from single cells contained approximately 103 to 106 cells after 1 month of culture; other clones became detectable only after prolonged culture. Cell growth in stroma-coated wells correlated with the number of initially seeded cells (1 or 10; r = .87). However, the observed percentages of positive wells seeded with 10 cells always exceeded values predicted from results with single-cell–initiated cultures (P < .003 by paired t-test), suggesting stimulation of leukemic cell growth by paracrine factors. In conclusion, the proportion of ALL cells with clonogenic potential may be considerably higher than previously thought.

Prevalence and Growth Characteristics of Malignant Stem Cells in B-Lineage Acute Lymphoblastic Leukemia

We used a stroma-supported culture method to study the prevalence and growth characteristics of malignant stem cells in acute lymphoblastic leukemia (ALL). In 51 of 108 B-lineage ALL samples, bone marrow-derived stroma not only inhibited apoptosis of ALL cells but also supported their proliferation in serum-free medium. When single leukemic cells were placed in the stroma-coated wells of microtiter plates, the percentage of wells with leukemic cell growth after 2 to 5 months of culture ranged from 6% to 20% (median, 15%; 5 experiments). The immunophenotypes and genetic features of cells recovered from these cultures were identical to those noted before culture. All cells maintained their stroma dependency and self-renewal capacity. Leukemic clones derived from single cells contained approximately 103 to 106 cells after 1 month of culture; other clones became detectable only after prolonged culture. Cell growth in stroma-coated wells correlated with the number of initially seeded cells (1 or 10; r = .87). However, the observed percentages of positive wells seeded with 10 cells always exceeded values predicted from results with single-cell–initiated cultures (P < .003 by paired t-test), suggesting stimulation of leukemic cell growth by paracrine factors. In conclusion, the proportion of ALL cells with clonogenic potential may be considerably higher than previously thought.

Measurement of residual leukemia during remission in childhood acute lymphoblastic leukemia

BACKGROUND

Complete remission of B-precursor acute lymphoblastic leukemia (ALL) has traditionally been defined as the near absence of lymphoblasts in a light-microscopical examination of stained bone marrow smears, but a patient in remission may still harbor up to 10(10) leukemia cells. We investigated whether there is a relation between the outcome of treatment and submicroscopic evidence of residual disease.

METHODS

We conducted a prospective study of patients during a first clinical remission using a quantitative polymerase-chain-reaction (PCR) assay capable of detecting 1 viable leukemia cell among 200,000 normal marrow mononuclear cells and a clonogenic blast-colony assay. Bone marrow specimens from 24 children were sequentially evaluated during a five-year period, and the results were compared with the clinical outcome.

RESULTS

Seven patients relapsed and 17 remained in remission 2 to 35 months after the completion of treatment. The levels of residual leukemia-cell DNA in the two groups were significantly different (P<0.001; 95 percent confidence interval for the difference in the mean log-transformed ratio of leukemia-cell DNA to normal bone marrow-cell DNA, 0.38 to 1.28). Autoregression analyses identified trends for individual patients that were associated with relapse. Despite continued remission in 17 patients, evidence of residual leukemia was detected by PCR in 15 and by both PCR and blast-colony assays in 7.

CONCLUSIONS

Molecular signs of residual leukemia can persist up to 35 months after the cessation of chemotherapy in children with ALL in remission. This suggests that eradication of all leukemia cells may not be a prerequisite for cure.

Value of colony forming unit-granulocyte macrophage assay in predicting relapse in acute myeloid leukaemia

AIM

To evaluate the validity of the colony forming unit-granulocyte macrophage (CFU-GM) assay for predicting relapse in patients with acute myeloid leukaemia (AML).

METHODS

The study population comprised 32 patients with AML in remission, followed for a median of 18 months. A mean of four studies was carried out per patient. Three patterns of in vitro growth based on the number of CFU-GM in normal bone marrow were defined: 1 = normal (normal number of CFU-GM and a cluster:colony ratio < 2); 2 = hypoplastic (low number of CFU-GM and a cluster:colony ratio < 2); 3 = anomalous (low or normal number of CFU-GM and a cluster:colony ratio > 2).

RESULTS

Eleven patients relapsed, all of whom had previously displayed an abnormal CFU-GM pattern: anomalous in nine and hypoplastic in two. The remaining 25 patients were in complete remission at the time of writing, 16 of whom had a normal growth pattern. The other nine had anomalous (eight patients) or hypoplastic (one patient) growth. The latter may be false positive results. The in vitro growth pattern was not constant during follow up analysis. All 15 patients in whom the growth pattern switched from abnormal to normal remain in complete remission. By contrast, of the five cases in whom the pattern changed from normal to abnormal, three have relapsed and the other two had other indicators of relapse. The growth pattern remained unchanged in the remaining 16 patients.

CONCLUSION

The present data show that the sequential investigation of the CFU-GM growth pattern may be of value in predicting relapse in patients with AML.

Minimal residual disease post-bone marrow transplantation for hemato-oncological diseases

The detection of minimal residual disease (MRD), which is important in cancer treatment, gained special significance in bone marrow transplantation (BMT-) due to the possibility not just to detect but recently also to prevent, treat and reinduce remission in patients that relapsed post-BMT by immunotherapy. The various modern techniques of MRD detection are described including cytogenetics, analysis of restriction fragment length polymorphism, variable number of tandem repeats by Southern Blot or polymerase chain reaction (PCR), microsatellite sequences, PCR amplification products of the Y chromosome or the Amelogenin gene, quantitative PCR and fluorescence in situ hybridization. The role of MRD detection in refinement of indications for BMT, autografting, prediction of relapse, adoptive immunotherapy, mixed chimerism in nonmalignant diseases and in solid organ transplantation is discussed.

Role of granulocyte-macrophage colony-stimulating factor in Philadelphia (Ph1)-positive acute lymphoblastic leukemia: studies on two newly established Ph1-positive acute lymphoblastic leukemia cell lines (Z-119 and Z-181)

Philadelphia chromosome (Ph1)-positive acute lymphoblastic leukemia (ALL) is a malignant disorder characterized by a poor prognosis. In recent years hematopoietic growth factors have been used to recruit myeloid leukemia blasts into the proliferative phase of the cell cycle and as supportive agents, both with cytotoxic regimens and in the setting of bone marrow transplantation. This approach prompted us to investigate whether myeloid growth factors have a role in Ph1 positive ALL. To do this, we utilized two newly established Ph1-positive cell lines, Z-119 and Z-181. Both lines have L2 morphology, ultrastructural characteristics of lymphoblasts and typical B-lineage surface markers identical to those observed in the two Ph1-positive ALL patients from whom they were derived. In addition, a single rearranged immunoglobulin heavy-chain gene (JH) band was found in both cell lines by Southern blot analysis, confirming B-cell clonality. Cytogenetic analysis of the two lines revealed t(9;22). Polymerase chain reaction (PCR) amplified cDNA from both Z-119 and Z-181 cells revealed an e1--a2 BCR-ABL junction, and p190BCR-ABL protein was detected in them by the immune complex kinase assay. Both cell lines produce interleukin (IL)-1 beta, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage CSF (GM-CSF), but neither IL-1 beta, G-CSF, their corresponding antibodies and inhibitory molecules, nor GM-CSF, affected the cell lines' growth. However, GM-CSF neutralizing antibodies inhibited Z-181 but not Z-119 colony formation in a dose-dependent fashion by up to 77% and addition of GM-SCF reversed this inhibitory effect. Receptor studies with radiolabeled GM-CSF demonstrated specific binding to Z-181 but not to Z-119 cells, and Scatchard analysis revealed that Z-181 cells express high-affinity GM-CSF receptors. Furthermore, PCR analysis showed that Z-181 but not Z-119 bears the transcript for the GM-CSF receptor. Finally, studies using PH1-positive ALL patients' marrow cells revealed similar data. In 3 of 8 samples we detected significant concentrations of GM-CSF (7.5-13 pg/2 x 10(7) cells) and in 2 of 3 cases GM-CSF significantly stimulated Ph1-positive ALL colony proliferation. These data suggest that Ph1-positive ALL cells may produce GM-CSF, express GM-CSF receptors and thus show a proliferative response to this cytokine.

Acute lymphoblastic leukemia. A comprehensive review with emphasis on biology and therapy

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. It is now curable in 60-70% of children. Most of the current understanding of the biology and treatment of ALL originates from studies of children. In adults, although much progress has been achieved, ALL is curable in only 20-35% of patients.

METHODS

A review of the biology and treatment of ALL from the English literature was performed.

RESULTS

Immunophenotypic and cytogenetic analyses of ALL have contributed to a more rational classification of ALL. These analyses have identified subgroups with poor prognosis or with different therapeutic requirements. Overall, 60-70% of adults with ALL have poor prognostic features, including older age, a high leukocyte count, non-T-cell immunophenotype, Ph-positive genotype, and longer time to achieve a complete remission. These patients have a cure rate of 20-25%, whereas those without these risk factors, have a 60-70% probability of survival. The use of more intensive induction regimens with growth factor support may improve survival rates. Also, intensive consolidation-intensification may improve survival rates. Most patients benefit from maintenance therapy, but the dose schedule must be optimized. Central nervous system (CNS) prophylaxis is beneficial, particularly for patients with a high risk for CNS relapse and when introduced early during induction of remission. Patients with high risk characteristics may benefit from allogeneic bone marrow transplantation (BMT) during first remission, and all other patients may benefit from it during first or subsequent relapse. Autologous BMT may be a valuable option for poor compliant patients.

CONCLUSIONS

Although the prognosis of patients with ALL has improved markedly during the past decades, newer strategies, including more dose-intensive therapy, the search for new drugs, and more target-specific therapy, are needed to improve the current cure rates.

Culture methods for the detection of minimal tumor contamination of hematopoietic harvests: a review

The evaluation of minimal residual disease in patients and hematopoietic cell grafts is of considerable importance for staging disease, determining the response to treatment, and monitoring the efficiency of ex vivo purging or positive selection procedures. The most widely used techniques are immunocytochemical staining and the polymerase chain reaction; however, these assays do not measure the viability or clonogenic capacity of the detected cells. For this purpose, a culture technique must be used. This paper reviews the status, advantages, and limitations of this approach and the detection of tumor cells in bone marrow and peripheral blood.

Elevated plasma thrombopoietic activity in patients with metastatic cancer-related thrombocytosis

BACKGROUND AND PURPOSE

High platelet counts are occasionally seen in patients suffering from progressive malignant disorders. While granulocyte colony-stimulating factor (G-CSF) has been implicated in paraneoplastic leukemoid reactions, the stimulus for thrombocytosis is unknown. Our purpose in this study was to determine if plasma from cancer patients with thrombocytosis contains a factor or factors with thrombopoietic activity.

METHODS

We tested the effects of plasma obtained from 5 individuals with advanced tumors and high platelet counts and from 4 patients with advanced cancer and normal platelet counts on megakaryocytic differentiation of two megakaryoblastic cell lines (Dami and HEL). Differentiation was evaluated by assessing the expression of the platelet-specific cell-surface antigens CD41 (HUPL-mI) and glycoprotein IIb-IIIa using an immunocytochemical staining score. In addition, plasma samples from 7 of the 9 patients and from 5 additional cancer patients with thrombocytosis were assayed for the levels of interleukin (IL)-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, and IL-1 beta protein using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Expression of platelet-specific cell-surface antigen was increased in HEL cells after exposure to plasma from all 5 of the cancer patients with thrombocytosis, and in Dami cells after exposure to plasma from 4 of the 5. Similar, but less significant, results were found when these cells were incubated with control combinations of recombinant GM-CSF plus IL-6 or of IL-3 plus IL-6. Platelet-specific cell-surface-antigen expression was not increased in HEL or Dami cells after exposure to the plasma from the 4 cancer patients with normal platelet counts or to normal control plasma. ELISA revealed elevated levels of IL-6 in the plasma from 4 patients with thrombocytosis (38, 40, 63, and 99 pg/mL). In addition, GM-CSF concentration was high in 3 of these 4 patients (33, 47, and 127 pg/mL), and the G-CSF level was elevated in 1 (543 pg/mL). IL-1 beta and IL-3 levels were undetectable.

CONCLUSIONS

Our data suggest that the thrombocytosis observed in individuals with advanced malignant disease is mediated by a humoral mechanism. Levels of IL-6, GM-CSF, and G-CSF are elevated in some of these patients, but the plasma concentrations are generally lower than those required for in vitro induction of megakaryocytic differentiation. Plasma from patients with paraneoplastic thrombocytosis may therefore contain thrombopoietins that have not yet been identified, and which might have clinical usefulness.

Long-term disease-free survival after autologous bone marrow transplantation in a primary plasma cell leukaemia: detection of minimal residual disease in the transplant marrow by third-complementarity-determining region-specific probes

Primary plasma cell leukaemia (PPCL) is a rare form of plasma cell neoplasm. Treatments of PPCL have been most disappointing. A patient with PPCL received high-dose melphalan plus total body irradiation and autologous bone marrow transplantation (ABMT). By using third-complementarity-determining region (CDRIII)-specific probes, minimal residual disease (MRD) was detected in remission marrow, collected 1 month before ABMT. MRD was no longer detected by CDRIII-specific probes 6, 19 and 26 months after transplantation. The patient remained in complete remission up to 59 months after ABMT.

Elimination of B-lineage leukemia and lymphoma cells from bone marrow grafts using anti-B4-blocked-ricin immunotoxin

Bone marrow is the primary site of disease in patients with acute lymphoblastic leukemia (ALL) and is frequently involved in patients with non-Hodgkin's lymphoma (NHL). At the time of autologous bone marrow transplantation, marrow grafts from patients with leukemia and lymphoma are often still contaminated by malignant cells, even when such patients achieve complete clinical remission. In this study, we evaluated the potential of anti-B4-blocked-ricin (anti-B4-bR) immunotoxin to eliminate residual ALL and NHL cells from bone marrow. Anti-B4-bR binds to the CD19 antigen, which is B-lineage specific, and, at concentrations of 5 x 10(-9) M or greater, could eliminate more than 3 logs of CD19+ Nalm-6 or Namalwa cells in a 20-fold excess of normal irradiated bone marrow after only 5 hr of incubation. This activity was abrogated by the addition of anti-B4 but not by the presence of galactose, which is the natural ligand for native ricin. Also, when used at these high concentrations, anti-B4-bR showed little nonspecific toxicity against normal hematopoietic progenitors. In conclusion, a single short exposure to anti-B4-bR is capable of inducing high levels of depletion of CD19+ leukemia and lymphoma cells without significant nonspecific toxicity against normal marrow progenitors. Therefore, anti-B4-bR offers an interesting approach to the elimination of B-lineage malignant cells prior to autologous bone marrow transplantation.

Techniques for detection of minimal residual disease

Analysis of leukemia-specific and leukemia-associated markers following standard or high-dose treatments is crucial in order to evaluate the efficacy of therapeutic strategies. During the last decade, several techniques have been proposed and used for detecting minimal residual disease (MRD). Each approach is characterized by advantages and limitations, mainly related to its sensitivity and specificity. The general limitations of such tests originates from the size of the sample which can be analysed and the heterogeneous distribution of leukemia after treatment. Clinically useful methods for detecting residual leukemia require not only sensitivity but also speed and reproducibility. The rate of false negative tests is low with polymerase chain reaction as well as flow cytometric analysis. Usually, patients without persistent cells carrying leukemia-associated markers have a lower risk of relapse. However, the detection of a persistent marker at one time point in complete remission cannot be considered a reliable indicator of MRD, whereas increase of positive signals or reappearance of leukemic markers usually precedes relapse. It is likely that one single approach will not allow the monitoring of the majority of patients and that a combination of techniques will be needed. Definitive results will be obtained only through prospective studies in patients receiving standardised therapy. Studies in which therapeutic strategies are designed according to the results provided by techniques for detecting MRD will be necessary to assess the relevance of their contribution to the treatment of leukemia.

Granulocyte-colony stimulating factor, granulocyte-macrophage colony stimulating factor, PIXY-321, stem cell factor, interleukin-3, and interleukin-7: receptor binding and effects on clonogenic proliferation in acute lymphoblastic leukemia

Cytokines are frequently used after chemotherapy of leukemias and solid tumors to augment recovery of normal hematopoiesis. While the regulation of normal and leukemic myelopoiesis is well investigated, little is known about effects of cytokines on growth and differentiation of lymphoblastic leukemia. In this study, we investigated the expression of receptors for G-CSF, GM-CSF, SCF, IL-3, and IL-7 on acute lymphoblastic leukemia (ALL) blasts and the effects of these growth factors (GF) on ALL blast colony formation. The binding of fluorescence-tagged cytokines to receptors on ALL blasts was studied by flow-cytometry in 27 cases of ALL (24 precursor B-ALL, 3 T-ALL). Receptor-binding for myeloid-associated GF was observed in the majority of precursor B-ALL (G-CSF = 100%, GM-CSF = 65%, IL-3 = 83%, SCF = 74%), but not in T-ALL. Binding of labelled IL-7 was detected in both precursor B- (92%) and T-ALL (100%). The presence of receptors for SCF in ALL was confirmed by polymerase chain reaction for c-kit mRNA in 19/21 cases tested. Expression of receptors for G-CSF, GM-CSF, IL-3, and SCF was not associated with expression of myeloid antigens, or with specific cytogenetic abnormalities. The effects of these GF on clonogenic cells were tested in the ALL blast colony assay and varied between samples, but all cytokines were able to increase clonogenic growth. The GM-CSF/IL-3 fusion molecule PIXY-321 was most effective in promoting colony growth. In some cases inhibition of colony formation was found. We conclude that ALL blast cells have receptors not only for IL-7, but also for G-CSF, GM-CSF, SCF, and IL-3. ALL precursors can respond to these GF with changes in their clonogenic growth indicating the presence of functional receptors. Results may have implications for therapeutic approaches combining cytokines and chemotherapy.

Persistence of dormant leukemic progenitors during interferon-induced remission in chronic myelogenous leukemia. Analysis by polymerase chain reaction of individual colonies

Interferon-alpha induces durable cytogenetic remissions in about one-quarter of newly diagnosed patients with chronic myelogenous leukemia (CML). Even so, after short-term follow-up, previous studies have shown that residual leukemic cells can be detected by the polymerase chain reaction (PCR) in all of these individuals. The objectives of our study were therefore to obtain long-term follow-up data on residual disease in a cohort of complete responders and to determine if leukemic cells with clonogenic potential are present in patients despite the absence of relapse. We performed (a) serial analysis of blood and/or bone marrow for a reverse transcriptase PCR amplified BCR-ABL transcript at times well beyond the point that cytogenetic remission was first attained and (b) reverse transcriptase PCR of individually plucked myeloid and erythroid colonies for the presence of the same transcript. Seven CML patients who had previously attained complete cytogenetic remission while on interferon-alpha were investigated. Six of the seven patients were in complete cytogenetic remission at the time of analysis, whereas one patient had early evidence of cytogenetic relapse. With ongoing therapy, five patients with the longest follow-up eventually achieved PCR negativity at time periods of 27, 32, 36, 49, and 67 mo after a complete cytogenetic remission was first noted. Even so, residual disease was detected in progenitor cells derived from two patients, each of whom had been in continuous cytogenetic remission for approximately 2.5 and 3.5 yr, respectively. Progenitors expressing BCR-ABL transcripts were also detected in the patient with early cytogenetic relapse. These observations demonstrate that residual disease resides in colony-forming cells that should have the potential to repopulate the bone marrow. However, the presence of a minority of Ph-positive CML progenitor cells for a very long period of time is still compatible with durable remission, confirming that a situation of tumor dormancy may be induced in CML by interferon therapy.

Genetic changes: relevance for diagnosis and detection of minimal residual disease in acute lymphoblastic leukaemia

Cure can now be achieved in a proportion of patients with ALL. However, relapse and eventual treatment failure occur in many cases receiving identical treatment, presumably as a result of failure to eradicate MRD. While for many years marrow morphology has been the standard by which leukaemic remission has been assessed, more sensitive techniques have been developed for detection of MRD including immunophenotypic analysis, and as discussed in this chapter, methods which detect leukemia-associated clonal genetic changes at the karyotypic and genomic levels. Table 10 lists the applicability and sensitivity of various markers used in MRD analysis in ALL. It is apparent that of the karyotypic and molecular approaches described, only PCR-based strategies for detection of either leukaemia-specific translocations or clonal Ag receptor rearrangements are reliably applicable to a high proportion of both B- and T-ALL at sufficiently high sensitivity. Initial clinical studies of patients undergoing therapy for ALL using a variety of PCR-based methods suggest that in some cases a persistent or increasing level of residual disease may be predictive for clinical relapse, although a number of technical factors and the phenomena of oligo-clonality and clonal evolution may limit the usefulness of this analysis in a few instances. From current available data it appears that in order to define the potential predictive value of PCR detection of MRD a large number of patients will need to be prospectively assessed over several years at multiple time points during and after therapy, preferably using more than one semi-quantitative PCR approach. In addition to reliable prediction of clinical relapse allowing appropriate individual treatment modification, progress in the molecular detection of MRD in ALL is also likely to be of benefit in the assessment of the efficacy of autograft purging and the evaluation of new therapeutic strategies such as the use of biological response modifiers to eliminate a low tumour burden.

Pretransplantation burden of leukemic progenitor cells as a predictor of relapse after bone marrow transplantation for acute lymphoblastic leukemia

BACKGROUND

We developed a test to discern small numbers of residual leukemic progenitor cells in the bone marrow of patients with acute lymphoblastic leukemia (ALL) in remission. Preliminary studies revealed that before undergoing bone marrow transplantation such patients differed in their burden of leukemic progenitor cells. These observations suggested that the burden of these cells might influence the risk of relapse after transplantation.

METHODS

The number of residual leukemic progenitor cells before bone marrow transplantation was determined for 83 patients with high-risk ALL. We combined multiparameter flow cytometry and cell sorting with assays for leukemic progenitor cells in a quantitative method for the detection of minimal residual disease.

RESULTS

The count of leukemic progenitor cells in bone marrow specimens from patients in remission varied markedly between patients, ranging from 0 to 12,546 cells per million mononuclear cells, or from 0 to 1.255 percent (median, 51 leukemic progenitor cells per million mononuclear cells, or 0.005 percent). Patients whose count of leukemic progenitor cells exceeded the median value had a higher likelihood of relapse than did patients with values below the median (relapse rate at one year, 100 percent vs. 41 percent; P < 0.001). There was a statistically significant inverse relation between the leukemic progenitor-cell content of bone marrow before transplantation and the duration of remission after transplantation (P < 0.001). The estimated risk of relapse for patients with > or = 51 leukemic progenitor cells per million mononuclear cells was more than 3.5 times the risk for patients with lower counts, after adjustment for the effects of other covariates (P = 0.005).

CONCLUSIONS

The count of residual leukemic progenitor cells is a powerful predictor of relapse after autologous bone marrow transplantation, particularly among male patients. Its measurement may be useful for analyzing and improving the treatment of patients with high-risk ALL in remission.

Detection of minimal residual disease in Philadelphia chromosome positive acute lymphoblastic leukemia: rationale for bone marrow transplantation from the polymerase chain reaction point of view

Bone marrow transplantation (BMT) is performed as curative therapy for acute lymphoblastic leukemia (ALL). In most patients, BMT is performed at the time of remission which implies that the number of leukemic cells is less than 5% of all hematopoietic cells, namely, 0 to 10(10) leukemia cells in the body. Thus, some patients may well undergo BMT despite the fact that no leukemic cells are left in the body. In this respect, more accurate diagnosis of complete remission status would be to the patients' benefit. To detect minimal residual disease (MRD) not found by light-microscopy, further strategies are required after achieving hematological remission. Cytogenetic methods, Southern blot analysis and conventional immunological techniques can all provide accurate diagnosis, however, the sensitivity of these techniques for the detection of MRD is just as low as that of the light microscopy. Recently, polymerase chain reaction (PCR) has become available for the detection of low levels of chimeric bcr-abl transcripts in Philadelphia chromosome positive (Ph1) ALL patients. With this assay, investigators have reported MRD in patients after chemotherapy or BMT. Most patients who achieve hematological remission after conventional chemotherapy still have bcr-abl transcript detectable by PCR, confirming the general concept that this particular leukemia needs BMT in order to cure the disease. Some patients who had MRD prior to BMT continued disease free survival > 1 year after BMT with a negative PCR result and in these patients, MRD seems to have been eradicated by the BMT procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Immature and differentiated neoplastic populations in acute lymphoid leukemia of childhood: biological and clinical implications

Despite significant improvement in the therapy for acute lymphoid leukemia (ALL) of childhood, approximately 30% of patients relapse. Unfortunately, since no successful treatment for recurrent disease has been developed, the majority of these patients die. Recently, we presented evidence consistent with the presence of a limited program of differentiation in B-precursor ALL that is reminiscent of normal B-cell development. We found that ALL cell populations consist of both a subpopulation of progenitors with the immunophenotype of normal B-cell precursors that has self-renewal capability and a second subpopulation with a more mature early B-cell immunophenotype that is without self-renewal capability but can proliferate to a limited extent. In our recent studies we were able to grow the progenitor cells in the ALL blast colony assay and establish their leukemic origin using the polymerase chain reaction. Our results suggest that these progenitors are the cells that sustain the disease. We hypothesize that these cells may remain quiescent, for a time, and either eventually die or regain proliferative capability and cause relapse. Further studies aimed both at detecting residual ALL and determining changes in their biology may provide an understanding of the mechanisms of relapse in this disease.

Lymphoblast colony-culture assay in acute lymphoblastic leukemia: a quantitative approach

Lymphoblast colony-culture of adult acute lymphoblastic leukemia (ALL) was studied to explore its clinical implication. Among 13 marrow cultures from ALL patients with full-blown disease, 11 developed leukemic colonies. A type of colony, very similar to a lymphoblastic colony and possibly T-cell in origin, could be found in four cultures of the six control marrows. To minimize the difficulty in differentiating a leukemic blast colony and a normal lymphocyte colony, based solely on morphology, a quantitative approach was used. Since both the mean of blast colony count and the mean of blast percentage of leukemic marrow were significantly higher than those of the control group, mean value plus two standard deviations of the control group were defined arbitrarily as upper normal limits. The defined normal range was then used to examine the relationship between results of the cultures and clinical outcome for the ALL patients. Early relapse or incomplete remission following chemotherapy could be predicted in four patients by these quantitative colony-culture assays 0.5-2 months before full-blown disease. The low colony count and low blast percentage in the colony-culture assay of the fifth patient is compatible with the clinical observation of continuous remission. One culture, growing clusters only, had an increased blast percentage; this correlated well with cytogenetic relapse two months later. In summary, the quantitative colony-culture assay could detect morphologically unidentifiable leukemic cells in ALL patients with early relapse or incomplete remission. This quantitative colony-culture system, though not ultrasensitive in the detection of minimal residual leukemic cells, was of potential value as a prognostic assay.

Bone marrow purging for autologous bone marrow transplantation

High dose therapy with the resulting myeloablation rescued by infusion of autologous bone marrow (ABMT) has become a major treatment option for an increasing number of patients with hematologic and solid tumors. ABMT has several potential advantages over allogeneic transplantation. However, the major obstacle to the use of ABMT is that the infusion of occult tumor cells harbored within the harvested marrow would result in more rapid relapse of disease. To minimize the effects of the infusion of significant numbers of malignant cells, marrow for ABMT is obtained when the patient is either in complete remission or when there is no histologic evidence of bone marrow infiltration of disease. There is increasing evidence that minimal numbers of malignant cells can be detected within the remission marrow of these patients, particularly when assessed by sensitive clonogenic assays or polymerase chain reaction amplification. A variety of methods, pharmacologic and immunologic have been developed to "purge" malignant cells from the marrow. The aim of purging is to eliminate any contaminating malignant cells and leave intact the hematopoietic stem cells that are necessary for engraftment. Although the rationale for removing any contaminating cells from the autologous marrow appears compelling, the issue of purging remains highly controversial. Intense argument persists as to whether attempts to remove residual tumor cells from the harvested bone marrow have contributed to improving disease-free survival in these patients. To date there have been no clinical trials testing the efficacy of purging by comparison of infusion of purged versus unpurged autologous bone marrow. This is due primarily to the large number of patients that would be required for such studies.

The detection of minimal residual disease in acute lymphoblastic leukaemia

The detection of minimal residual disease in acute lymphoblastic leukaemia (ALL) can be achieved by assessing leukaemia-specific features at a cellular, chromosomal or molecular level. The application of the polymerase chain reaction to the amplification of leukaemia-specific chromosomal translocations and clone-specific immunoglobulin and T-cell receptor gene rearrangements allows assessment of the majority of cases of ALL. The sensitivity of detection of this technique is around one leukaemia cell in 10(5) normal marrow cells. A comparative review of the advantages and pitfalls of the different methods of detecting minimal disease is presented. The clinical relevance of such detection is discussed, with early results suggesting that this may have predictive value for future disease relapse.

Collection of blood mononuclear cells by leukapheresis for transplantation in a Yucatan miniature swine model

A large animal model is needed to evaluate new apheresis technologies. These technologies include novel methods of harvesting the blood mononuclear cell population which contains the hematopoietic stem cells needed to restore hematopoiesis in recipients of hematopoietically lethal therapy and the use of cytokines to provide a safe and predictable method of manipulating these circulating hematopoietic stem cells. We describe the methods used to collect mononuclear cells by leukapheresis from Yucatan miniature swine. These animals are of sufficient size to tolerate the procedures and have many physiologic and hematologic similarities to man. They are of good temperament and are easily trained. Long-term venous access was obtained using single lumen silicone rubber catheters placed in the inferior vena cava. The animals were apheresed while fully awake using a Haemonetics Model V50 machine and a modified lymphocyte collection protocol. The procedure was highly efficient for the collection of mononuclear cells and a 10 pass procedure yielded a product which contained 19.7 x 10(9) mononuclear cells, 10.7 x 10(9) granulocytes, and 17 ml of erythrocytes in a volume of approximately 100 ml. This product can be cryopreserved and used for subsequent transplantation. The content of four apheresis procedures provides hematopoietic reconstitution of lethally irradiated swine on a time scale equivalent to transplantation of optimal numbers of bone marrow cells.

Use of the Polymerase Chain Reaction for the Detection of Tumor Cell Involvement of Bone Marrow and Peripheral Blood: Implications for Purging

Bone marrow purging is being performed increasingly in an effort to deplete residual tumor cells from the graft prior to reinfusion. Several studies have suggested that the removal of tumor cells is an important clinical goal. In this review the utility of the polymerase chain reaction (PCR) for the detection of small numbers of tumor cells in bone marrow and peripheral blood is discussed. Using sensitive assays such as PCR, it is expected that the efficacy of bone marrow purging strategies will be improved and this will hopefully result in decreased relapse rates following autologous bone marrow transplantation.

Transplantation of normal and leukemic human bone marrow into immune-deficient mice: development of animal models for human hematopoiesis

The successful engraftment of human hematopoietic cells into immune-deficient mice offers a novel approach to characterize the developmental program of human hematopoiesis. While it is not yet possible to achieve high-level engraftment of all human lineages, several methods have been developed to successfully engraft human lymphoid cells and reconstitute partial immune function. In addition to mature cell types, there is evidence that progenitors and perhaps stem cells can engraft the murine bone marrow. Recent work suggests that provision of exogenous human cytokines significantly increases the level of human cell engraftment and stimulates the development of multiple lineages. Progress has also been made to establish animal models of human hematopoietic diseases such as leukemia, autoimmunity, and infectious diseases.

Bone marrow processing for transplantation

As indications for BMT increase, so do variations in bone marrow processing and manipulation techniques. Many centers have their own unique methods of mononuclear cell purification, concentration and storage. This is particularly evident in the processing of bone marrow for autologous BMT to allow dose intensification as salvage therapy for malignant disease. Unique procedures have been developed to maximize yields, concentrate mononuclear cells necessary for engraftment, and reduce the likelihood of GVH disease. Graft rejection and disease relapse still remain a problem in some of these "manipulated" marrows. Newer procedures may allow titration of the optimum numbers of immune reconstituting cells; however, at this time, these techniques are not precise and the balance between preventing GVH disease at the expense of graft failure or relapse may still jeopardize disease-free survival. Innovative purging techniques that include pharmacologic and immunologic methods, continue to evolve, necessitating standards for bone marrow processing that are flexible yet practical. Quality control and viability assays are essential to verify the biologic proliferative potential of progenitor cells capable of marrow reconstitution. Although no standards are yet established, all centers should have criteria to monitor the quality of the processed marrow. Blood banks and transfusion services are well versed in regulations governing processing, labeling, storage, and quality control of blood components. Bone marrow is the ultimate blood component, and it stands to reason that methods outlined in this article be integrated into transfusion medicine.