Intensive treatment in order to minimize the Ph-positive clone in chronic myelogenic leukemia

Overview of autologous stem cell transplantation

There has been a dramatic increase in the number of autologous peripheral blood stem cell transplants over the last decade. Faster recovery of cell counts, lesser transplant morbidity, shorter hospital stay and reduced cost compared with marrow autografts have been the main advantages of autologous peripheral blood cell over marrow transplants. In this paper we attempt to review the advances in the biology and mobilization of stem cells, and focus on clinical results of autologous peripheral stem cell and marrow transplants for disease specific sites such as breast cancer, myeloma, autoimmune diseases, germ cell tumors, the acute and chronic leukemias, the non-Hodgkin's lymphomas and Hodgkin's disease. We also discuss transplant related complications, gene therapy and the different methods of purging. This review was intended for autologous peripheral stem cell transplants, however, unavoidably, it also discusses autologous marrow transplantation and aspects common to both procedures.

Autologous transplantation for the treatment of chronic myelogenous leukemia

There is evidence that benign, Ph-negative hematopoietic progenitors persist in the marrow and blood of some patients with chronic myelogenous leukemia (CML). A number of pilot studies using purged and unpurged marrow or peripheral blood autografts have demonstrated that autologous transplantation can result in transient cytogenetic responses in CML. Although not curative, this procedure may be associated with longer-than-expected patient survival and represents an alternative treatment for patients ineligible for allogeneic transplantation and not responding to interferon-alpha therapy. Several novel approaches are being developed to improve graft purging and eliminate residual leukemia post-transplantation. Such approaches may allow for long-term restoration of Ph-negative hematopoiesis following the procedure.

Mobilisation and reinfusion of Philadelphia negative peripheral blood mononuclear cells in chronic myeloid leukaemia with hydroxyurea and G-CSF

Unmanipulated autologous transplantation of marrow of peripheral blood stem cells has been performed in small numbers of patients with CML for many years. More recently there has been interest in attempting to 'purge' the autograft of clonal cells as defined by the presence of the Philadelphia chromosome or BCR-ABL rearrangement. One method by which this might be achieved in vivo has been developed in Genoa and involves the administration of high dose chemotherapy and G-CSF followed by peripheral blood stem cell collection. These collections are frequently devoid of Philadelphia positive cells and the hope is that this will enhance the effects of subsequent autograft. We have investigated the use of a less toxic regimen for this procedure using oral hydroxyurea and G-CSF. In this review we describe the background to autografting in CML and the development of strategies to mobilise Philadelphia negative cells into the peripheral blood. We go on to present an update of our data using hydroxyurea and discuss some of the practical and theoretical issues behind the procedure.

Southern technique and cytogenetics are complementary and must be used together in the evaluation of Ph1, M-BCR positive chronic myeloid leukemia (CML) patients treated with alpha interferon (IFN-alpha)

Cytogenetic analysis is the gold standard for the follow-up of CML patients. The sensitivity of cytogenetics is fairly similar to that of Southern detection of M-BCR rearrangement (5%); this last technique has the potential advantage of being independent of cell division and yield of metaphases. IFN alpha treatment can induce lack of growth of hemopoietic precursors and poor yield of metaphases has been observed. For this reason we decided to study the grade of concordance and complementarity between analysis of karyotype and detection of M-BCR rearrangement of Southern blot. We studied 43 Ph1 positive, M-BCR positive pre-BMT CML patients (48 samples) treated with IFN alpha 2a. Karyotype was done on bone marrow cells by direct method, culture, and banding. Southern technique was performed onto DNA from peripheral blood leukocytes treated with BgIII (and Xbal if necessary) and hybridized with the universal probe (Ph1/bcr-3, Transprobe 1) labelled with dCTP32. A highly significant association between both tests was obtained. Of 48 samples analyzed, 34 were evaluable by both methods and 28 gave the same result for both tests. The concordance between the tests was good (kappa index: 0.63). Of total samples 27.1% was not evaluable by cytogenetics; this figure was 31.2% in samples from patients who were previously in complete cytogenetic response. All of the specimens not evaluable by karyotyping were evaluable by Southern. One sample was not analyzable by Southern but it was evaluable by cytogenetic analysis. The information obtained by Southern technique was clinically relevant, and decisions were made according to its results. We conclude that both tests show a significant association and a good concordance, although they are not interchangeable. Cytogenetic and molecular studies are complementary and must be employed together in CML patients treated with alpha-interferon.

Current aspects of drug therapy in Philadelphia-positive CML: correlation of tumor burden with survival

One therapeutic concept in chronic myeloid leukemia (CML) assumes that a reduction of clonal genetically unstable cells also reduces the rate of secondary genetic changes and thereby postpones blast crisis. According to this concept, the degree of reduction of tumor burden should correlate with a prolongation of survival. The recent literature, in particular on controlled studies of IFN, hydroxyurea or intensive chemotherapy is reviewed and analyzed with regards to this concept. In chronic phase CML, intensity of treatment as determined by the degrees of WBC suppression, and, more recently, of cytogenetic remission, as measures of the reduction of tumor burden appear to correlate directly with survival. The superiority of a therapeutic regimen in chronic phase CML seems to primarily depend on whether its pharmacology permits a sufficiently high dosage to achieve the necessary reduction of tumor burden. The concept underlies present strategies that try to prolong survival in CML by IFN alone or in combination with intensive chemotherapy, by hydroxyurea, alone or in combination with IFN, and by high-dose chemotherapy followed by autografting.

Effects of BCR-ABL antisense oligonucleotides (AS-ODN) on human chronic myeloid leukemic cells: AS-ODN as effective purging agents

We examined phosphorothioate oligodeoxyribonucleotides (ODNs) directed against bcr in exon 3 or exon 2, which are rearranged with exon 2 of abl (B3A2 and B2A2) at t(9;22) of chronic myelogenous leukemia (CML). Since these ODNs are designed to be CML cell specific, we studied their effects on the human CML cell line K562, which is known to have B3A2 rearrangement, and leukemic cells from patients, as well as normal hematopoietic stem cells in vitro. In vitro experiments were performed to determine a potential role of these two ODNs as ex vivo purging agents. Incubation of B3A2 antisense at 40, 80, and 120 micrograms/ml with K562 CML cells for 72 hours at 37 degrees C resulted in 44%, 56%, and 63% reduction of CFU-L as compared to controls. In contrast, B3A2 sense and B2A2 antisense had no significant growth inhibitory effect on K562 cells. Incubation of B3A2 and B2A2 antisense ODNs at concentration of 80 micrograms/ml at 37 degrees C for 36 hours with normal peripheral blood stem/progenitor cells (PBSC) resulted in 124% and 98% CFU-GM formation as compared to untreated controls, respectively. However, incubation of PBSC with B3A2 and B2A2 sense-ODNs resulted in a 22% and 44% reduction in CFU-GM, respectively. In order to determine the ex vivo purging effects of bcr-abl ODNs, the K562 cells were mixed with PBSC from normal donors at a ratio of 1:20 (CML:PBSC). The mixture of cells was then incubated with B3A2 antisense at 80 micrograms/ml for 36 hrs at 37 degrees C. After incubation, no CML cells were detected by fluorescence in situ hybridization (FISH) as compared to untreated controls. These results were confirmed by RT-PCR using bcr-abl primers and mRNA isolated from the mixture of cells. Further, these results support the hypothesis that bcr-abl antisense ODNs are potentially effective agents for ex vivo purging of autologous stem cells before transplantation to eliminate/reduce the burden of leukemic cells. No significant toxicity to normal hematopoietic stem/progenitor cell population by the bcr-abl antisense ODNs was observed. Although unanticipated reductions in normal hematopoietic progenitor cells (CFU-GM) were observed with sense ODNs, no reduction in CFU-GM was observed with unrelated phosphorothioate ODN controls.