Peripheral blood progenitor cell transplantation as an alternative to autologous marrow transplantation in the treatment of acute myeloid leukemia

Future perspectives: should Th17 cells be considered as a possible therapeutic target in acute myeloid leukemia patients receiving allogeneic stem cell transplantation?

Th17 cells seem to promote proinflammatory effects, and their development seems to depend on intracellular signaling initiated by IL1β, supported by IL6 and IL23 and mediated by STAT3 and RORC2. Even though primary human AML cells may affect Th17 development through their constitutive cytokine release, the levels of circulating Th17 cells in older patients with untreated AML do not differ from healthy controls and show only minor variations during and following conventional intensive chemotherapy. IL17-A is the signature cytokine of Th17 cells, but in vitro studies have failed to demonstrate a direct antileukemic effect of IL17 on primary human AML cells for most patient samples. However, several observations suggest that Th17 cells mediate antileukemic effects through other mechanisms and are important in allogeneic stem cell transplantation. Firstly, genetic variants in IL23/Th17 pathway have a prognostic impact with regard to both development of GVHD and posttransplant infections. Secondly, circulating IL17-secreting cells are detected during early posttransplant pancytopenia, and their ability to release IL17 is associated with later GVHD. Thirdly, a high number of Th17 cells in allogeneic stem cell grafts are associated with later acute GVHD, levels of circulating Th17 cells are increased at the onset of acute GVHD, and these levels normalize during treatment. In the present article, we review previous studies of Th17 cells in AML and in the development of GVHD, possible therapeutic strategies and available therapeutic tools for targeting of Th17 cells.

Efficacy and safety of imatinib in adult patients with c-kit–positive acute myeloid leukemia

This phase 2 pilot study was conducted to determine the efficacy and safety of imatinib mesylate in patients with c-kit–positive acute myeloid leukemia (AML) refractory to or not eligible for chemotherapy. Twenty-one patients were enrolled and received imatinib 600 mg orally once daily. Five responses were seen primarily in patients, starting with relatively low blast counts in bone marrow (BM) and peripheral blood (PB): 2 patients who were considered refractory on chemotherapy on the basis of persistence of blasts in PB and BM met the criteria for complete hematologic remission, 1 patient had no evidence of leukemia, and 2 patients achieved a minor response. Treatment with imatinib demonstrated a good safety profile and was well tolerated. Western blot analysis and immunohistochemistry demonstrated c-Kit activation in primary AML cells. Further, imatinib treatment of primary AML cells inhibited c-Kit tyrosine-phosphorylation. Genomic DNA-sequencing of c-KIT showed no mutations in exons 2, 8, 10, 11, 12, and 17. Although some of the responses derived from relatively small reductions in leukemic blasts and may be attributable, in part, to prior chemotherapy, these cases suggest that imatinib has interesting clinical activity in a subset of patients with c-kit–positive AML. Further clinical trials are warranted to explore the clinical potential of imatinib in AML and to identify the underlying molecular mechanism.

More efficient mobilisation of peripheral blood stem cells with HiDAC+AMSA+G-CSF than with mini-ICE+G-CSF in patients with AML

We have compared the efficacy of two PBSC mobilisation regimens, mini-ICE+filgrastim (second consolidation) and HiDAC+AMSA+filgrastim (third consolidation), in two consecutive cohorts of patients with AML CR1 receiving treatment according to a joint protocol. Group A: 18 patients, aged 41 (21-65) years, were mobilised with mini-ICE (idarubicin 8 mg/m(2)+cytarabine 800 mg/m(2)+etoposide 150 mg/m(2) days 1-3) followed by filgrastim 300-480 microg once daily s.c. from day 11 after start of chemotherapy. Only four patients reached >5 CD34+ cells/microl blood (B-CD34+) and were able to undergo leukaphereses. Two out of 18 (11%) reached the defined target of >/=2.0 x 10(6) CD34+ cells/kg after 1-3 leukaphereses. Group B: 20 patients, aged 50 (29-67) years, received HiDAC+AMSA (cytarabine 3 g/m(2) b.i.d. days 1, 3, 5+amsacrine 150 mg/m(2) q.d. days 2, 4) followed by filgrastim at a similar dose starting on day 7. A total of 18 patients reached B-CD34+ >5/microl and underwent PBSC harvesting, starting on day 23 (14-29) and yielding 4.0 (0.9-21) x 10(6) CD34+ cells/kg. Of 20 patients, 17 (85%) reached the defined target of >/=2.0 x 10(6) CD34+ cells/kg after 1-3 leukaphereses. We conclude that HiDAC+AMSA+G-CSF - in contrast to mini-ICE+G-CSF - is an efficient regimen for mobilising PBSC in patients with AML CR1.

Comparison of megakaryopoiesis in vitro of paired peripheral blood progenitor cells and bone marrow harvested during remission in patients with acute myeloid leukaemia

We have studied paired peripheral blood progenitor cells (PBPC) and bone marrow (BM) samples from 12 acute myeloid leukaemia (AML) patients following intensive chemotherapy, and assessed direct granulocyte-macrophage colony-forming units (CFU-GM), erythroid burst-forming units (BFU-E), megakaryocyte CFU (CFU-Mk) numbers and the production of CD61+ (platelet glycoprotein IIIa) cells in suspension culture in response to various haemopoietic growth factor combinations. We found that CFU-GM and BFU-E numbers per 105 mononuclear cells were similar in both AML PBPC and BM harvests; CFU-Mk numbers, however, were significantly higher in PBPC than BM. In addition, the higher total white cell count of the PBPC harvests meant that PBPC have much higher numbers of total progenitors per collection. CD61+ cell numbers in suspension cultures of AML PBPC and BM were lower than those of harvested normal marrow. However, response to pegylated recombinant human megakaryocyte growth and development factor (PEGrHuMGDF) both alone and in combination with other growth factors was qualitatively similar to that of normal BM. As with normal BM, response to PEGrHuMGDF alone did not increase further with addition of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), interleukin 6 (IL-6) or erythropoietin (EPO) in the AML PBPC and BM. Further responses over PEGrHuMGDF alone were seen when added with stem cell factor (SCF) or with a combination of SCF + IL-3 + EPO in both AML PBPC and BM cultures; however, the magnitude of the response was greater in the PBPC cultures. Response to PEGrHuMGDF + IL-3 was seen in the PBPC cultures but not in the AML BM. These data suggest that, in AML patients, there are proportionally more megakaryocyte progenitor cells in the mobilized PBPC than in the BM harvests, which would explain the more rapid platelet recovery following PBPC autografts.