Acute promyelocytic leukemia (AML-M3)--Part 2: Molecular defect, DNA diagnosis, and proposed models of leukemogenesis and differentiation therapy.

OBJECTIVES: To identify the chromosomal translocation common in M3 and discuss its diagnostic use to: Compare acute leukemia with chronic leukemia and other forms of cancer. Describe the molecular defect including the fusion gene and fusion protein produced from the translocation. Discuss the proposed mechanism of leukemogenesis in M3. Discuss the proposed mechanism of differentiation induction stimulated by ATRA therapy. Present the future direction of this and other forms of therapy. DATA SOURCES: Current literature. DATA SYNTHESIS: Acute promyelocytic leukemia (AML-M3) is a form of acute leukemia that presents with a less dramatic leukocytosis, anemia, and thrombocytopenia than other acute leukemias. However, AML-M3 has a lower first remission rate and a higher morbidity and mortality rate than most of the other acute leukemias when treated with conventional chemotherapy. AML-M3 frequently stimulates a serious concomitant coagulation disorder, disseminated intravascular coagulation, which is a major contributor to the high mortality rate. This and other devastating sequela of M3 have prompted clinicians and investigators to develop methods of improving diagnosis and therapy. In 1977 the method of diagnosis confirmation was improved by the identification of a consistent chromosomal translocation involving the long arms of chromosomes 15 and 17. Identification of the specific molecular lesion that produced the t(15;17) translocation occurred in 1990 and was shown to involve the retinoic acid receptor alpha gene (RAR alpha). Because the RAR alpha gene is mutated in all AML-M3 patients studied so far and because it is often the only mutation identified, several proposed mechanisms of leukemogenesis have evolved. From these discoveries a novel approach to cancer treatment focusing on differentiation therapy instead of traditional chemotherapy emerged. All-trans retinoic acid (ATRA) has been shown to stimulate differentiation of promyelocytes from the malignant clone and has become an important element in the treatment of patients with AML-M3. CONCLUSION: Since the discovery of the t(15;17) translocation, the identification of the fusion gene containing the retinoic acid receptor alpha, and the success of ATRA as a form of differentiation therapy, the diagnosis and treatment of AML-M3 has dramatically improved. In addition, AML-M3 has become a model system used to study the mechanisms that produce uncontrolled growth and lack of differentiation in leukemic cells (leukemogenesis) and the mechanisms of therapeutic reversal of this block in differentiation (differentiation therapy).

Acute promyelocytic leukemia (AML-M3)--Part 1: Pathophysiology, clinical diagnosis, and differentiation therapy.

OBJECTIVES: The objectives of this review paper are to: Compare acute leukemia with chronic leukemia and other forms of cancer. Review the pathophysiology and discuss the clinical and diagnostic features of M3. Describe the variant of M3 (M3m or M3v). Compare conventional chemotherapy with all-trans retinoic acid differentiation therapy (ATRA) in the treatment of M3. Discuss the future direction of differentiation therapy. DATA SOURCES: Current literature. DATA SYNTHESIS: Until the late 1970s, the methods of diagnosis and treatment of AML-M3 were similar to the other forms of acute myelocytic leukemia. One notable difference between M3 and other acute myelocytic leukemias involved the common occurrence of life-threatening consumptive coagulopathies in M3 patients that dramatically affected patient outcomes. In 1977 the method of diagnosis confirmation was altered by the identification of a consistent chromosomal translocation involving the long arms of chromosomes 15 and 17. Reports in the 1970s and 1980s indicated that certain types of active metabolites of vitamin A, collectively termed retinoids, could induce differentiation in a variety of cancer derived cell lines, in vitro. It was shown in the early 1980s that 13-cis-retinoic acid (13cRA) could stimulate differentiation in bone marrow cells collected from patients with various acute leukemias, including M3. The first clinical trial of a retinoid, given as a remission induction therapeutic regimen, involved all-trans retinoic acid (ATRA) administered to M3 patients in 1988. Since then, ATRA therapy has been shown to reduce tumor burden by stimulating differentiation of the leukemic cells, induce long-term clinical remission when administered in conjunction with chemotherapy, and lower the incidence of consumptive coagulopathies in patients with AML-M3. CONCLUSION: The diagnosis and treatment of AML-M3 has improved dramatically in the past decade, which has greatly enhanced the prognosis of patients with this disease. First remission rates have increased to greater than 85% world wide, the incidence of disseminated intravascular coagulation (DIC) has declined dramatically, and 60% to 70% of patients with AML-M3 have achieved long term survival and are potentially cured.

The mast cell-committed progenitor. I. Description of a cell capable of IL-3-independent proliferation and differentiation without contact with fibroblasts.

We have identified a late, committed stage in the differentiation of the mast cell progenitor just before granulation. Mast cell committed progenitors (MCCP) are nongranulated cells with a density of 1.060 to 1.070 g/ml which can be harvested from the mesenteric lymph node of mice infected with Nippostrongylus brasiliensis. Mast cell-committed progenitors are able to proliferate and differentiate in the absence of IL-3 or IL-4 when cultured on a monolayer of embryonic skin or 3T3 fibroblasts and can form colonies in methylcellulose supplemented with fibroblast conditioned medium. Fibroblast conditioned medium appears to contain a soluble MCCP proliferation factor that maintains biologic activity when heated to 56 degrees C for 45 min but is destroyed by incubation with either trypsin or chymotrypsin. It can be selectively precipitated with 60 to 70% saturated ammonium sulfate. The factor is not absorbed by immobilized antibodies to nerve growth factor. The MCCP proliferation activity of the factor could not be mimicked by IL-1, IL-2, IL-4, granulocyte-macrophage-CSF, granulocyte-CSF, macrophage-CSF, IFN-alpha/beta, IFN-gamma, nerve growth factor, epidermal growth factor, serum fibronectin, heparin, or a number of glycosaminoglycans. At high salt concentrations, the factor passes through a 50-kDa membrane and can be concentrated above a 5-kDa membrane. MCCP acquire a connective tissue phenotype when cultured on a fibroblast monolayer and a mucosal phenotype when cloned in the presence of conditioned medium from PWM-stimulated spleen cells. When cultured in the absence of IL-3 on a monolayer of embryonic skin or 3T3 fibroblasts, mast cell-committed progenitors produce mast cells which stain with berberine sulfate suggesting a connective tissue phenotype; however, the mast cells that develop when mast cell-committed progenitors are cultured in the presence of IL-3 or conditioned media from PWM-stimulated spleen cells do not stain with berberine sulfate. MCCP intercalate into monolayers of embryonic skin or 3T3 fibroblasts, but T cells are not able to associate with the monolayer and can be completely washed away. Attempts to enrich mast cell-committed progenitors by intercalation and elution from embryonic skin monolayers proved unsuccessful, but some enrichment of mast cell-committed progenitors could be achieved by discontinuous Percoll gradients. Thus, we have identified a way to obtain late-stage, mast cell-committed progenitors in an environment that is virtually uncontaminated with other hematopoietic progenitors.