Haematopoietic cytokines in the biology and treatment of acute myeloid leukaemia.

In acute myeloid leukaemia (AML), age has a definite effect on the biology of the disease and also determines the outcome of chemotherapy. AML cells constitutively express mRNA and produce several haematopoietic cytokines. The haematopoietic cytokines: SCF, IL-3, GM-CSF and G-CSF induce leukaemic colonies or activate DNA synthesis in about 80% of AML cases. Both M-CSF and thrombopoietin stimulated AML cell proliferation is seen in vitro in about 50% of cases. Both IL-6 and IL-11 showed little proliferative activity on primary AML cells. The combinations of these cytokines were synergistic in stimulating the proliferation of AML cells. On the other hand, the inhibitory haematopoietic cytokines: TNF-alpha, TGF-beta, IFN-gamma and IL-4 have shown multiple effects on AML blast cell proliferation. In several in vitro systems, haematopoietic cytokines have failed to induce maturation of AML blasts. Only in AML with t(8;21), G-CSF has induced granulocytic maturation of AML blasts in vitro. AML cells with chromosomal abnormalities involving the 21q22 region differentiate in vitro into eosinophils in the presence of IL-5. IL-6 and IFN-alpha have induced megakaryocytic differentiation of blast cells from acute megakaryoblastic leukemia (M7) patients. The haematopoietic cytokines: SCF, IL-3 and GMCSF have protected in vitro AML cells from chemotherapy-induced apoptosis. Many clinical studies have been recently reported evaluating the effect of the haematopoietic cytokines: GM-CSF, G-CSF, IL-3 and PIXY321 as adjuncts to the chemotherapy of AML patients. Most studies have shown these haematopoietic cytokines to be well-tolerated and effective in augmenting neutrophil recovery in elderly AML patients when given after chemotherapy. On the other hand, considerable number of studies using these cytokines before and during chemotherapy to recruit AML cells into cell cycle and thus make them more susceptible to chemotherapy have reaveled no benefit. Several clinical trials have shown promising results after the use of IL-2 either as remission induction therapy in refractory and/or relapsed AML patients or as post-remission consolidative immunotherapy. Haematopoietic cytokines administered after chemotherapy can shorten the duration of neutropenia and hospitalisation without a significant effect on treatment outcome. On the other hand, their use before and during chemotherapy has yielded no benefit, and instead have led to delay of platelet recovery and worse survival rate in some elderly AML patients.