Activating mutation of D835 within the activation loop of FLT3 in human hematologic malignancies.

Mutations of receptor tyrosine kinases are implicated in the constitutive activation and development of human malignancy. An internal tandem duplication (ITD) of the juxtamembrane (JM) domain-coding sequence of the FLT3 gene (FLT3/ITD) is found in 20% of patients with acute myeloid leukemia (AML) and is strongly associated with leukocytosis and a poor prognosis. On the other hand, mutations of the c-KIT gene, which have been found in mast cell leukemia and AML, are clustered in 2 distinct regions, the JM domain and D816 within the activation loop. This study was designed to analyze the mutation of D835 of FLT3, which corresponds to D816 of c-KIT, in a large series of human hematologic malignancies. Several kinds of missense mutations were found in 30 of the 429 (7.0%) AML cases, 1 of the 29 (3.4%) myelodysplastic syndrome (MDS) cases, and 1 of the 36 (2.8%) acute lymphocytic leukemia patients. The D835Y mutation was most frequently found (22 of the 32 D835 mutations), followed by the D835V (5), and D835H (1), D835E (1), and D835N (1) mutations. Of note is that D835 mutations occurred independently of FLT3/ITD. An analysis in the 201 patients newly diagnosed with AML (excluding M3) revealed that, in contrast to the FLT3/ITD mutation (n = 46), D835 mutations (n = 8) were not significantly related to the leukocytosis, but tended to worsen disease-free survival. All D835-mutant FLT3 were constitutively tyrosine-phosphorylated and transformed 32D cells, suggesting these mutations were constitutively active. These results demonstrate that the FLT3 gene is the target most frequently mutated to become constitutively active in AML.

[Extramedullary relapse in the external auditory canal in a patient with acute promyelocytic leukemia treated with all-trans retinoic acid and autologous peripheral blood stem cell transplantation].

A 41-year-old man was given a diagnosis with of acute promyelocytic leukemia (APL) in August 1994. A chromosome analysis showed 46, XY, t(15; 17) and 47, XY, idem, +8 at that time. Because initial induction chemotherapy (BHAC-DMP) has not been successful, the patient was given 45 mg/m2 of all-trans retinoic acid (ATRA) and achieved complete remission (CR) after 26 days on this regimen. Following intensified chemotherapy, he received an autologous peripheral blood stem cell transplant (PBSCT) with high-dose busulfan and cyclophosphamide in April 1995. Competitive RT-PCR for PML-RAR alpha mRNA did not find any of APL cells in the collected stem-cell fraction. Although the patient remained in CR without therapy, a myeloblastoma was found in his left external auditory canal in August 1996. Recurrence in bone marrow, moreover, was discovered the following month. A chromosome analysis of bone marrow cells showed 47, XY, t(15; 17), +8 at this time. Thus, the extramedullary relapse developed after autologous PBSCT. This case provides information linking ATRA to the development of extramedullary relapse in patients with APL.

Effect of granulocyte colony-stimulating factor on hematopoietic recovery after peripheral blood progenitor cell transplantation.

To examine the effect of granulocyte colony-stimulating factor (G-CSF) on hematopoietic recovery after high-dose chemotherapy and peripheral blood progenitor cell transplantation (PBPCT), 20 patients with hematologic malignancies were divided into two groups. One group was given G-CSF at a daily dose of 50 micrograms/m2 subcutaneously, the other received no G-CSF. Neutrophil recovery was accelerated in the G-CSF treated patients and exceeded 0.5 x 10(9)/l at a median of 10 days post-PBPCT compared with 14 days in the control group (p < 0.01). This reduction led to a decrease in antibiotic use and a trend toward fewer febrile days in the G-CSF treated group.

Autoimmune thrombocytopenia following peripheral blood stem cell autografting.

A 22-year-old woman diagnosed as AML (M3) received myeloablative chemotherapy followed by autologous peripheral stem cell transplantation (PBSCT). Rapid hematopoietic reconstitution occurred. By day 10, the neutrophil count was > 0.5 x 10(9)/l and the platelet count > 50 x 10(9)/l. The platelet count was 145 x 10(9)/l on day 20. Purpura developed on the anterior chest and legs on day 50, at which time the platelet count fell to 17 x 10(9)/l. The BM was hypocellular with an increase in megakaryocytes. Platelet-associated IgG (PAIgG) was 88.1 ng/10(7) platelets (normal range 9-25 ng/10(7)); a diagnosis of idiopathic thrombocytopenic purpura (ITP) was made. Prednisolone administration led to an increase in the platelet count and a decrease in PAIgG. Analysis of lymphocyte subsets revealed an increased number of CD3+ gamma/delta T cells. It is postulated that the thrombocytopenia in this case was due to an autoimmune mechanism such as ITP.

Collection of peripheral blood stem cells mobilized by high-dose Ara-C plus VP-16 or aclarubicin followed by recombinant human granulocyte-colony stimulating factor.

We developed an effective method for harvesting large numbers of peripheral blood stem cells (PBSC) for use in autotransplantation. Twenty patients with hematological malignancies were treated with high doses of Ara-C (12 g/m2) and VP-16/aclarubicin followed by administration of rhG-CSF (50 micrograms/m2). The optimal time for starting PBSC collection was determined by monitoring the CD34-positive stem cells in blood using immunomagnetic beads. PBSC were collected with a CS-3000 blood cell separator. A total blood volume between 7000 and 9000 ml was processed in each apheresis. Under these conditions, a total of 64 apheresis procedures was performed in the 20 patients. The mean numbers of mononuclear cells and of CFU-GM harvested per apheresis were 4.1 x 10(8)/kg and 110 x 10(4)/kg, respectively. A number of CFU-GM sufficient for engraftment (> 30 x 10(4)/kg) could be harvested by a single apheresis in 15 of the 20 patients. So far, 11 patients have been transplanted with PBSC and obtained rapid hematopoietic recovery. The median time to recover neutrophils more than 0.5 x 10(9)/l was 10 days, and that for platelets 50 x 10(9)/l was 11 days. This method for harvesting large numbers of PBSC allows safer autotransplantation in patients with chemoradiosensitive tumors, and is applicable to older patients.

Photoradiation methods for purging autologous bone marrow grafts.

The potential of various photoradiation therapy for the in vitro purging of residual tumor cells from autologous bone marrow (BM) transplants is discussed in this paper. The results with fluorescent dyes, Dihematoporphyrin Ether (DHE) and Merocyanine-540 (MC-540) are detailed. Following photoradiation of cells with white light, both DHE and MC-540 showed high cytocidal activity towards lymphoid and myeloid neoplastic cells, but had significantly less effect on normal granulocyte-macrophage (CFU-GM), erythroid (BFU-E) and mixed colony-forming (CFU-GEMM) progenitor cells. Acute promyelocytic leukemia (HL-60), non-B, non-T, cALLa positive acute lymphoblastic leukemia (Reh), and diffuse histiocytic B-cell lymphoma (SK-DHL-2) cell lines were exposed to different drug concentrations in combination with white light at a constant illumination rate of 50,000 lux. With DHE doses varying from 2.0 to 2.5 ug/ml and MC-540 concentrations of 15 to 20 ug/ml, clonogenic tumor cells could be reduced by more than 4 logs, when treated alone or in mixtures with normal irradiated human marrow cells. However, preferential cytotoxicity towards neoplastic cells was highly dependent on the mode of light activation. MC-540 had no substantial effect on malignant lymphoid (SK-DHL-2) and myeloid (HL-60) cells, and on normal marrow myeloid (CFU-GM) precursors, when the drug incubation was performed in the dark and followed by light exposure of washed cells. Equal doses of MC-540 (15-20 ug/ml) could preferentially eliminate tumor cells under conditions of simultaneous light and drug treatment (30 minutes at 37 degrees C). Using DHE (2.5 ug/ml), 29.3%, 46.8%, and 27.5% of normal marrow CFU-GM, BFU-E, and CFU-GEMM, respectively, were spared, following sequential drug and light exposure of cells, while simultaneous treatment reduced both normal (CFU-GM) and neoplastic cells below the limits of detection. The data from various centers is briefly discussed with special emphasis on clinical trials. Our results provide a useful model for leukemia and lymphoma cells and suggest that these phototherapy experiments can be implemented into clinical trials.