Eva Kabrna

Recombinant human megakaryocyte growth and development factor increases levels of circulating haemopoietic progenitor cells post chemotherapy in patients with acute myeloid leukaemia

By participating in a randomized safety and efficacy study of pegylated‐recombinant human megakaryocyte growth and development factor (PEG‐rHuMGDF) post induction and consolidation chemotherapy for de novo acute myeloid leukaemia, serial determinations of circulating haemopoietic progenitor cells were performed during 18 chemotherapy courses in eight patients (three receiving placebo; one, 2.5; and four, 5.0 μg/kg/d MGDF, respectively). Whereas failure to achieve complete remission (CR) was generally associated with poor progenitor cell increments following chemotherapy, substantial progenitor cell mobilization consistently occurred during haemopoietic recovery in patients entering, or in CR, with significantly higher peak values in patients receiving 5 μg/kg/d of MGDF as compared to controls. The median increases of progenitor cell numbers by chemotherapy alone and chemotherapy plus 5.0 μg/kg/d MGDF over that in normal individuals with steady‐state haemopoiesis were 10‐ and 45‐fold for CFU‐GM, 3‐ and 17‐fold for BFU‐E, and 2‐ and 18‐fold for CFU‐mix. CFU‐Mk levels were not increased above normal by chemotherapy alone but were 15‐fold enhanced by chemotherapy plus MGDF. Recruitment of CD34+ cells post chemotherapy was also potentiated by MGDF. Our results suggest MGDF as a potent agent to augment progenitor cell mobilization after successful induction or consolidation chemotherapy in patients with AML.

Cytogenetic risk groups in acute myeloblastic leukaemia differ greatly in their semi-solid colony growth

We have analysed the results of semi‐solid bone marrow cultures in 296 patients with de novo acute myeloblastic leukaemia (AML) and correlated them with the leukaemic karyotype. A favourable prognostic karyotype was found in 52 patients (group A, 18·3%), an intermediate karyotype in 163 patients (group B, 57·4%), and unfavourable cytogenetics were observed in 69 patients (group C, 24·3%). Median colony growth according to the three risk groups was 2 (range 0–344) in group A, 14·5 (range 0–5000) in group B and 50·0 (0–3000) in group C (A vs. B, P < 0·001; A vs. C, P < 0·001; B vs. C, P < 0·01). Among the patients treated with chemotherapy (n = 257), median colony growth was 10 (range 0–5000) in those who achieved complete remission (CR) compared with 56·5 (range 0–1000) in patients without remission (NR) (P = 0·002). The median colony growth of all patients [13/105 bone marrow mononuclear cells (BMMCs); range 0–5000] significantly discriminated between patients regarding survival (OS 11 vs. 7 months, P = 0·044). However, multiple Cox regression analysis revealed cytogenetic risk groups as the most important predictor for achieving CR, disease‐free and overall survival, with colony growth adding no additional prognostic information. In 64 patients, colony growth was also investigated without the addition of exogenous cytokines. Interestingly, none of the patients with a favourable karyotype exhibited autonomous growth, whereas 50% with an intermediate and 73% of patients with an unfavourable karyotype displayed either partial or full autonomous growth in vitro (P = 0·0004). Our data suggest that the growth potential of the leukaemic clone seems to be critically influenced by the molecular changes emerging from chromosomal abnormalities.

Decrease of circulating hematopoietic progenitor cells During interleukin-2 treatment is associated with an increase of vascular cell adhesion molecule-1, a critical molecule for progenitor cell adhesion.

Administration of interleukin-2 (IL-2) to cancer patients has been shown to transiently decrease the number of circulating hematopoietic progenitor cells, but the mechanism of this phenomenon is unknown. Recently, the interaction of vascular adhesion molecule-I (VCAM-I) with leukocyte very late antigen-4 (VLA-4) has been demonstrated to play a crucial role in the adhesion of progenitor cells to bone marrow stromal elements. Cytokine induced upregulation of VCAM-1 leads to increased binding of progenitor cells to stromal cells in vitro and inhibition of this interaction by monoclonal antibodies is associated with marked progenitor cell mobilisation in vivo. In the present study we serially determined peripheral blood progenitor cell numbers during IL-2 treatment (10 courses) in 6 cancer patients and determined in parallel levels of soluble VCAM-1 as a surrogate marker for the in vivo activation of this molecule. Our data indicate that continuous intravenous administration of IL-2 for 5 days leads to a marked decrease of circulating progenitor cells associated with a substantial increase of circulating VCAM-1. Circulating myeloid progenitor cells (CFU-GM) dropped from a mean value of 167 ± 187/ml pre IL-2 to 16 ± 15/ml on day 3 (p < 0.01). Similarily, mean erythroid progenitors (BFU-E) decreased from 282 ± 204/ml before IL-2 administration to 86 ± 61/ml on day 3 (p < 0.005). In contrast, soluble VCAM-1 rose from a mean value of 1814 ± 451 ng/ml before to 4607 ± 736 ng/ml at the end of IL-2 therapy (p < 0.0001). Sera from IL-2 treated patients did not inhibit hematopoietic colony formation from normal bone marrow. These results suggest redistribution and increased adhesion of progenitor cells to stromal and/or endothelial elements during IL-2 via the VCAM-I/VLA-4 interaction as a possible mechanism for the decrease of circulating progenitor cells during IL-2 therapy.

Failure of Identical Twin Bone Marrow to Restore Haemopoiesis in 2 Patients with Severe Aplastic Anemia (SAA) without Immunosuppressive (IS) Conditioning

The role of mononuclear cells (MNC) in the regulation of aplastic haemopoiesis is poorly understood.Evidence for an important role of T-lymphocytes in SAA is strengthened by a frequent clinical response after treatment with Anti-T-cellglobulin. The occurrence of SAA in patients who are fortunate enough to have an identical twin bone marrow donor can provide insight into “immune”-mediated aplasia,as half of these patients ultimately require pretreatment with Cyclophosphamide to obtain haemopoietic recovery.We had the rare opportunity to study mononuclear leucocytes and bone marrow cells from 2 patients with SAA who ultimately required Cyclophosphamide to recover following twin bone marrow grafting.In coculture studies performed with donor cells, major or minor histocompatibility differences as a cause of colony growth alteration could be excluded (1).