Recombinant interleukin 2 and anti-Tac influence the growth of enriched multipotent hemopoietic progenitors: proposed hypotheses for different responses in early and late progenitors

Possible role of granulocyte colony-stimulating factor in increased serum soluble interleukin-2 receptor-alpha levels after allogeneic bone marrow transplantation

Serum soluble interleukin-2 receptor - alpha (sIL-2R) levels markedly increased at the engraftment period in patients who underwent allogeneic bone marrow transplantation (BMT). Since serum G-CSF levels increased during G-CSF administration and decreased after the cessation, increased sIL-2R levels appeared to be induced by G-CSF administration. There was no increase in sIL-2R levels in a patient given macrophage colony-stimulating factor (M-CSF). The sIL-2R levels at the engraftment period and the onset of acute graft-versus-host disease (GVHD) were higher in patients who developed acute GVHD during G-CSF administration than in those who developed acute GVHD after G-CSF cessation. This finding suggests that G-CSF administration may possibly augment acute GVHD. However, it appears to be unlikely, because in the entire population, 18 of 35 patients had acute GVHD while only 6 of 17 patients had acute GVHD during G-CSF administration. Further analysis is still needed in order to draw definite conclusions. Preconditioning regimens did not appear to affect the sIL-2R levels, when the variable frequencies of methotrexate (MTX) administration were compared.

Abnormal Myelocytic Cell Development in Interleukin-2 (IL-2)–Deficient Mice: Evidence for the Involvement of IL-2 in Myelopoiesis

Mice lacking interleukin-2 (IL-2) developed a severe hematopoietic disorder characterized by the abnormal development of myeloid cells and neutropenia. Analysis of the bone marrow of IL-2–deficient (IL-2−/−) mice showed that the number of mature polymorphonuclear cells was decreased by 65% to 75%, and granulocyte/macrophage precursor cells were reduced by 50%. Bone marrow cells from IL-2−/− mice were unable to sustain myelopoiesis in lethally irradiated mice and in long-term bone marrow cultures (LTBMC). The addition of exogenous IL-2 to LTBMC of IL-2−/− cells partially restored hematopoietic progenitor activity. In the bone marrow of wild-type mice, immature (Mac-1lo) myeloid cells, including myeloblasts and promyelocytes, constitutively expressed the β-chain of the IL-2R, and the number of Mac-1loIL-2Rβ+ cells was increased by twofold to threefold in IL-2−/− mice. During culture in the presence of IL-2 and the absence of stromal cells, Mac-1loIL-2Rβ+ immature myeloid cells proliferated and gave rise to mature granulocytes and macrophages. Collectively, these observations indicate that defective myelopoiesis in IL-2−/− mice is at least in part a consequence of their direct dependency on IL-2, and by regulating the growth of immature myeloid cells, IL-2 plays an important role in the homeostatic regulation of myelocytic cell generation.

Clinical relevance of serum soluble interleukin-2 receptor levels in acute and chronic graft-versus-host disease

Soluble interleukin-2 receptor (sIL-2R) levels were analyzed in the sera from 27 patients who underwent allogeneic bone marrow transplantation (BMT) in order to to examine whether there was any correlation between sIL-2R levels and graft-versus-host disease (GVHD). The sIL-2R levels markedly increased at the engraftment period, mainly due to cytokine administration shortly after BMT. Although the sIL-2R levels increased at the onset of acute GVHD, the subsequent development of GVHD could not be predicted by the sIL-2R levels documented before acute GVHD. As acute GVHD improved, the sIL-2R levels decreased, thus showing that the sIL-2R levels correlated with the disease status. In patients without acute GVHD, the sIL-2R levels gradually decreased with time and returned to the pretransplant levels after about 12 weeks post BMT. The sIL-2R levels were higher in unrelated allogeneic BMT patients with acute GVHD when compared with related allogeneic BMT patients. There was a significant increase in the sIL-2R levels at the engraftment period and at the onset of acute GVHD. At the onset of chronic GVHD, the sIL-2R levels once again increased and then decreased as chronic GVHD improved. Prolonged increase in sIL-2R levels was followed by subsequent development of chronic GVHD. Patients with a poor prognosis had higher sIL-2R levels than those with a good prognosis. Therefore, it seems that sIL-2R is a useful marker for monitoring the disease status of acute and chronic GVHD.

Interleukin 2 interacts with myeloid growth factors in serum-free long-term bone marrow culture

IL2 infusion may benefit patients with haematological malignancies by lowering the disease burden. However, conflicting data have been reported on IL2 effects on myelopoiesis, in vitro as well as in vivo. In the present study we investigated the ability of IL2 to act on committed and primitive bone marrow progenitor cells in defined serum-free (SF) culture conditions which avoid many technical biases such as interference by exogenous stimulating or inhibiting factors. Low doses of IL2 (0.1-1000 U/ml) were studied without or in combination with recombinant IL3, GM-CSF and erythropoietin, in SF long-term marrow culture (LTMC). We report data in favour of an inhibitory activity of IL2 limited to committed progenitors and excluding more primitive haemopoietic stem cells, as shown by an alteration of CFU-GM proliferation during the first 5 weeks of LTMC, decreasing with time, unaffected BFU-E and increased nucleated cell production. Beyond week 5, no difference was observed between IL2 supplemented cultures and the SF control cultures. In parallel, IL2 induced the adherence of fibroblastic cells and their progeny. In addition to the inhibitory effect, IL2 appeared to limit the stimulating effect on granulopoiesis and erythropoiesis of myeloid growth factors (GF) such as combination of IL3, GM-CSF and EPO. Indeed, in SF-LTMC conditions, IL2 inhibitory effect is effective on CFU-GM production throughout the 7 weeks of LTMC and on BFU-E during the first 2 weeks only. These data confirm the interaction of IL2 with other GFs in the complex interplay of the cytokine network.

Granulocyte-colony-stimulating factor induces increased serum levels of soluble interleukin 2 receptors preceding engraftment in autologous bone marrow transplantation

The serum levels of soluble interleukin 2 receptors (sIL-2R) were determined in 19 patients who received high-dose chemotherapy and an autologous or syngeneic bone marrow transplant (BMT) for treatment of Hodgkin's disease (n = 18) or non-Hodgkin's lymphoma (n = 1). Twelve patients received granulocyte colony-stimulating factor (G-CSF) from day 0 or day +1 after autologous BMT until the white blood cell count had been stable for 9 d above 1 x 10(9)/l, the remaining seven patients did not receive growth factors. In all G-CSF-treated patients the sIL-2R levels increased steadily in the early post-transplant course, even in the absence of infection. This increase was statistically significant 2-4 d prior to the appearance of leucocytes in the peripheral blood (median 340 pM versus median 256 pM immediately after BMT, P < 0.025) and peaked with the appearance of first peripheral blood leucocytes (median 536 pM, P < 0.001). Cessation of G-CSF administration resulted in a decline of sIL-2R levels. In contrast, five of seven patients without G-CSF treatment did not exhibit an sIL-2R increase before or at the time of engraftment. Infection was associated with a rise of sIL-2R levels. A correlation between sIL-2R levels and total leucocyte count, lymphocyte count, or CD25+ lymphocyte count was not evident. These data suggest that after autologous BMT G-CSF induces increased sIL-2R levels, which occur independent of lymphocyte activation. This may be compatible with involvement of immature bone marrow cells in G-CSF-induced sIL-2R release.

IL-2 abolishes fibroblast proliferation in long-term bone marrow culture by inhibition of an accessory cell

Addition of interleukin-2 (IL-2 (greater than 250 U/ml) during the first 3 d of long-term bone marrow culture (LTBMC) permanently abolished the fibroblast component of the stromal layer, even when IL-2 was removed after the 3 d culture period. When IL-2 was added at more than 72 h after initiation of culture, no effect was observed. Stromal growth in IL-2-treated culture was restored by addition of irradiated bone marrow, indicating that the IL-2 inhibited an accessory cell rather than the fibroblast directly. Accessory cells were shown to be necessary for fibroblast proliferation at low cell densities and were also inhibited by IL-2. The accessory cell effect could not be replaced by LTBMC supernatants or extracellular matrix. It is suggested that these observations are relevant to the suppression of haemopoiesis observed in patients receiving IL-2.

Acute myeloid leukaemia relapsing following interleukin-2 treatment expresses the alpha chain of the interleukin-2 receptor

Immunotherapy with recombinant human Interleukin-2 (rhIL-2) was given to nine patients in first complete remission from acute myeloid leukaemia (AML). Five patients relapsed. The median time to relapse after commencing rhIL-2 was 26 weeks (range 2-44). Four patients were studied at relapse. The morphological and cytochemical features at relapse and presentation were similar. Cytogenetic analysis at relapse in patients 1 and 3 showed a normal karyotype. At relapse, patient 4 had the abnormality 46,XY, t(2;3). Patient 2 had the chromosomal abnormality t(8;21) at presentation and relapse. Patients 3 and 4 with M5 AML relapsed rapidly at 2 and 9 weeks after starting rhIL-2 treatment. Relapse leukaemia cells had features normally associated with lymphoid development. Patient 3 was TdT positive, with rearranged immunoglobulin genes, and a proportion of cells expressing the CD7 antigen; patient 4 also expressed the CD7 antigen. Relapse leukaemic cells from three of four patients expressed the alpha chain of the IL-2 receptor as assessed by flow cytometry. After overnight incubation and removal of T-lymphocytes the proportion of cells from these patients expressing the alpha chain increased from 15% to 61% (P less than 0.01). Using tritiated thymidine uptake to assess cell proliferation, two of three patients who expressed the IL-2 receptor alpha chain proliferated in response to 1000 u/ml of rhIL-2 in vitro, with a stimulation index greater than 1.95 (P less than 0.05). Following rhIL-2 immunotherapy for AML, relapse cells may express an inducible form of the alpha chain of the IL-2 receptor, which can mediate a proliferative response. It is possible that rhIL-2 when administered to AML patients in remission, may induce relapse. This may be a particular risk in patients with the M5 subtype.

Interleukin-2 treatment-associated eosinophilia is mediated by interleukin-5 production

During a trial using recombinant human interleukin-2 (rhIL-2) immunotherapy for acute myeloblastic leukaemia (AML) in remission, eosinophilia was observed in all patients. We used in-vitro clonogenic assays to investigate the mechanism of the eosinophilia in five patients. The mean eosinophil count increased from 0.05 x 10(9)/l before rhIL-2 to 0.98 x 10(9)/l within 48 h of stopping the infusion, and an exponential correlation between the pretreatment lymphocyte CD4:CD8 ratio and the maximum eosinophil count was observed. RhIL-2 did not stimulate eosinophil colony formation by normal bone marrow. However, serum collected from patients during rhIL-2 infusion was a potent stimulator of eosinophil colony forming units (CFU-Eo), but had no significant stimulatory effect on granulocyte-macrophage colony forming units (CFU-GM). The CFU-Eo stimulation by pre-treatment serum was 2.8-fold higher than control serum. Serum collected during treatment stimulated CFU-Eo 12 times more than control serum (P less than 0.05). By pre-incubating patient serum, collected during rhIL-2 treatment, with monoclonal antibodies to murine IL-5, or human granulocyte-macrophage colony stimulating factor (GM-CSF), a reduction of 80% and 38% respectively in eosinophil and GM colony production was found. The CFU-Eo stimulating effect of patient serum was in the range of the CFU-Eo stimulating effect of normal serum, after the addition of 5 u/ml of recombinant murine IL-5. The results suggest that eosinophilia was caused by IL-5 and GM-CSF production by rhIL-2 stimulated CD4 positive lymphocytes. The location on chromosomes 5 of the genes for IL-5, GM-CSF and IL-3 may be associated with regulation of expression, by a common mechanism, of all the factors known to be involved in eosinophil production. This mechanism may be activated by IL-2 stimulation. The separate location on chromosome 17 of the G-CSF gene may explain the ability of IL-2 to produce a distinct stimulus to eosinophil but not neutrophil production.

IL-2 and myelopoiesis: IL-2 induces blast cell proliferation in some cases of acute myeloid leukaemia

Interleukin-2 (IL-2) stimulated H-thymidine incorporation in the blasts of six of 21 cases of acute myeloid leukaemia (AML). An IL-2 induced increase in cell numbers was directly demonstrated in the two patients studied in this way, and T-cell contamination was rigorously excluded. The IL-2-induced proliferation was usually less marked than that caused by granulocyte-macrophage colony stimulating factor (GM-CSF), and IL-2 moderately enhanced GM-CSF-induced stimulation in five of the six patients; in the sixth, IL-2 and GM-CSF were strongly synergistic. IL-2-induced proliferation was observed only in AML with a monocytic component (M4/M5), but not all M4/M5 leukaemias responded to IL-2. There was no correlation between expression of the light-chain of the IL-2 receptor and IL-2-induced stimulation. It is suggested that IL-2 is involved at a restricted stage of early myelopoiesis, perhaps when cells are becoming committed to the monocytic lineage; and that IL-2 is a growth factor for early myeloid cells in a proportion of cases of AML.

Stem cells: a tree model

A tree model is presented in order to illustrate the hypotheses that earlier stem cells will respond differently than later progenitors to the same stimuli. Experimental data and decision analysis tools are shown to demonstrate the concept.