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Université René Descartes - Paris V, CNRS URA 1461, Hôpital Necker, Paris, France
Key Words. CFU-C • IL-3 • GM-CSF • Histamine
Correspondence:
Dr. Elke Schneider, CNRS URA 1461, Hôpital Necker, 161 rue de Sèvres, 75743 Paris Cedex 15, France.
| Abstract |
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| Introduction |
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The hamster mAb 145-2C11 [5], directed against the CD3
portion of the murine T cell receptor for antigen (TCR) complex shares similar features. It induces a monocyte-dependent T cell activation, resulting in a massive release of both T cell- and monocyte-derived cytokines into the circulation [6-8], as well as a long-term immunosuppression in vivo [9]. Among the cytokines generated in response to 145-2C11 mAb, one can distinguish between those mainly involved in the immune response, like tumor necrosis factor-
, interferon-
, interleukin 4 (IL-4) and IL-2, and those with potential effects on hematopoiesis, namely IL-3, GM-CSF and IL-6. So far, most of the studies addressing the mechanisms of anti-CD3-induced tumor rejection and short-term morbidity have focused on the first category of cytokines [10, 11]. The purpose of the present study was to examine hematopoietic modifications resulting from anti-CD3-induced release of growth factors. To this end, we injected the antibody at a dose which induces a potent T cell activation without significant T cell depletion from the spleen [10], as well as a substantial release of GM-CSF and IL-3 into the circulation. We then compared the hematopoietic changes observed to those promoted by the injection of the recombinant forms of IL-3 and GM-CSF.
| Materials and Methods |
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Cytokines and Antibodies
Recombinant murine (rm) IL-3 (specific activity: 1-2 x 107 U/mg, as assessed on the NFS-60 cell line) and rmGM-CSF (1-2 x 107 U/mg, as assessed on the DA-3 cell line) were purchased from R & D (Oxon, Great Britain).
The hamster 145 2C11 mAb (IgG), specific for the murine CD3
chain, as well as its F(ab')2 fragments, prepared by pepsin digestion, were kindly provided by Dr. L. Chatenoud. Hamster IgG from Jackson ImmunoResearch Laboratories (West Grove, PA) were used as specificity control. Polyclonal sheep antisera against IL-3 [12] and GM-CSF [13] were kindly provided by Dr. H. Ziltener.
Injection Schedule
Mice received a single i.v. injection of 10 µg of anti-CD3 mAb, 10 µg of control hamster IgG or 50 µg of the anti-CD3 F(ab')2 fragment diluted in 100 µl saline. rmIL-3 and rmGM-CSF were administered i.v. twice on a single day, at a dose of 1 µg of each factor diluted in 100 µl saline.
WBC Count
Mice were anesthetized with ether, and orbital plexus blood was obtained using micropipettes. WBCs were counted in hemocytometers (Unopette, Becton Dickinson; Rutherford, NJ) and differential counts were performed on blood films stained with May-Grünwald-Giemsa. No mouse was examined more than once to avoid misleading cell counts from previously damaged vessels.
Cell Preparations
Bone marrow cells were removed from femurs and tibias by flushing with Hanks' balanced salt solution (HBSS; GIBCO; Grand Island, NY). Spleen cells were homogenized in HBSS by gently teasing with forceps. The cells were centrifuged, resuspended in minimal essential medium (MEM) supplemented with 10% horse serum at a concentration of 107 cells/ml. These cell suspensions, prepared at different times after treatment, were used for progenitor cell assays and cytocentrifuge preparations examined after May-Grünwald-Giemsa staining.
Spleen and bone marrow cell suspensions were also distributed into 96-well microtiter plates (200 µl/well) at a concentration of 107 and 2.5 x 106 cells per ml respectively. They were incubated for 48 h in MEM supplemented with 10% horse serum with or without 1 ng/ml of rmIL-3. Cell-free supernatants were then prepared and stored at -20°C until histamine and cytokine assay.
Histamine and Cytokine Assays
Histamine was measured by an automated continuous flow fluorometric technique previously described [14], whose lower limit of sensitivity is about 0.5 ng/ml. The specificity of this assay has been verified by a radioimmunoassay (Immunotech; Marseilles, France).
Sera from anti-CD3-injected and control mice were tested for their proliferative effect on the FDCP-2 cell line which in our hands responds exclusively to IL-3. The GM-CSF assay was performed on the FDCP-1 cell line that also responds to IL-3 [15]. For this reason, all samples were tested in the presence of a 1/40 dilution of polyclonal sheep antiserum against IL-3 resulting in 90% inhibition of the proliferation induced by 1 ng of rmIL-3 per ml. Cell proliferation was evaluated after a 48-h incubation by the colorimetric MTT assay. The cytokines were quantified in relation to rmIL-3 and rmGM-CSF at optimal concentrations (1 ng/ml and 5 ng/ml, respectively), 1 unit/ml being defined as the concentration that leads to half-maximal cell proliferation in the assay. The specificity of the IL-3 and GM-CSF assays was assessed in the presence of the neutralizing anti-IL-3 and anti-GM-CSF antisera.
Colony Forming Assays
Nonerythroid colony forming units-culture (CFU-C) were quantified in semisolid culture medium (
-modification of Dulbecco's MEM) containing 0.8% methylcellulose (Fluka; Buchs, Switzerland), 10% fetal calf serum (FCS) and 1 ng/ml of rmIL-3. Cells were plated in a final volume of 1 ml at concentrations ranging from 5-50 x 104 cells per culture dish (Falcon 1008). Colonies were scored on day 7. To evaluate BFU-E, and CFU-Mix frequencies, cultures were performed in the same medium, supplemented with 20% FCS, 1% deionized bovine serum albumin, 1 ng/ml of rmIL-3, 2 U/ml of human erythropoietin, 200 ng/ml of rm stem cell factor and 1,000 U/ml of rmIL-6. Colonies were scored on days 7-10 for BFU-E and CFU-Mix.
The statistical significance of all data was established by Student's t-test.
| Results |
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-fluoromethylhistidine, a specific inhibitor of histamine synthesis, thus excluding degranulation. It is also noteworthy that spleen cells from anti-CD3-injected mice displayed a transient incapacity to produce histamine in response to IL-3 the day following the injection.
In the same experimental conditions, we detected only minor alterations in the bone marrow. Progenitor frequencies, as well as the capacity to respond to IL-3 in terms of histamine synthesis increase, remained the same after anti-CD-3 injection as in untreated mice (data not shown). Cytological analysis (Table 2
) revealed a slight rise in the frequency of immature myeloid cells on day 1 post-injection and a more marked diminution of lymphocyte counts on day 4. The granulocyte compartment was also slightly increased at this time point, while other subsets were not modified by the treatment with anti-CD3.
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Hematopoietic Changes Induced by i.v. Injection of IL-3 and GM-CSF
To evaluate the part of anti-CD3-induced IL-3 and GM-CSF in the hematopoietic changes observed, we tried to block the activity of these cytokines by injecting their corresponding antisera prior to anti-CD3 treatment. The antibodies used in this study were only effective at high concentrations in vitro (1 mg/ml). They did not neutralize IL-3 and GM-CSF in vivo. For this reason, we injected IL-3 and GM-CSF and compared the hematopoietic changes induced to those resulting from anti-CD3 mAb treatment. On account of the transient growth factor release promoted by the mAb, we limited the treatment to two injections performed on a single day at an interval of 6 h.
We observed a number of qualitative and quantitative differences between the effect of anti-CD3 and that of the two hematopoietic growth factors. In contrast with anti-CD3 mAb, IL-3 and GM-CSF did not modify spleen cell populations on the first day after injection (see uninjected controls in Table 1
). On day 4, we observed a significant increase in the proportion of immature myeloid cells and nucleated RBCs, with a preferential expansion of the former population (Table 3
). Unlike anti-CD3 mAb, IL-3 and GM-CSF did not increase the number of spleen cells. Growth factor injection did, however, augment the incidence of nonerythroid clonogenic progenitors on day 4, though to a lesser extent than anti-CD3 (Table 4
). As shown in the same table, these cells also displayed an enhanced response to IL-3, in terms of histamine synthesis. Injection of IL-3 and GM-CSF had no consistent effect on the number and distribution of bone marrow cells, except for a small increase in myeloid precursors on day 4 (data not shown). The proportion of clonogenic progenitors in this organ also remained unchanged.
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| Discussion |
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Anti-CD3 mAb injection results in rapid and pronounced hematopoietic modifications in peripheral blood and spleen, while the bone marrow remains relatively unchanged. The dose of anti-CD3 used throughout this study has been previously shown to promote a potent T cell activation but no significant T cell depletion from the spleen [10, 17]. Yet, even in these conditions, we observed a striking fall of blood lymphocyte levels within 24 h after injection. The disappearance of these cells might be explained either by destruction or sequestration following TCR coating [9].
The day after anti-CD3 injection, the percentages of CD4+ and CD8+ subsets in the spleen vary little from those found in control mice. Among the early changes promoted by anti-CD3 injection, a significant increase in neutrophil levels both in peripheral blood and in the spleen occurs on day 1. This phenomenon, like the decrease of circulating lymphocytes, was not mimicked by IL-3 and GM-CSF injection.
Since in vivo treatment of mice with antisera against IL-3 and GM-CSF did not neutralize the corresponding activities in the circulation of anti-CD3-injected mice, we injected the recombinant growth factors to evaluate to what extent they were implicated in the hematopoietic changes observed. The proportion of immature myeloid cells and nucleated RBCs is substantially increased by either treatment, though growth factors expand preferentially myeloid rather than erythroid cells, conversely to anti-CD3. Clonogenic progenitor frequencies are also augmented in both situations. Yet, anti-CD3 is much more effective in this respect since it increases the incidence of CFU-C around 10-fold and nearly doubles the number of spleen cells. At the doses injected, IL-3 and GM-CSF do not change the total number of spleen cells, and clonogenic progenitor frequencies are not increased more than two to three times. The expansion of the immature spleen compartment is accompanied by enhanced responsiveness to IL-3 in terms of histamine synthesis, though this effect is less marked in response to the growth factor combination. This is in accordance with previous results, associating this biological activity with relatively undifferentiated myeloid cells [18].
It is also noteworthy that neither anti-CD3 nor growth factor injection consistently modifies bone marrow cell populations, as previously reported for in vivo experiments with IL-3 [19, 20]. The diminution of lymphocytes in the bone marrow of mice having received anti-CD3 four days before does not occur after injection of IL-3 and GM-CSF, and also has not been documented by other in vivo studies on these factors [20, 21].
One of the characteristic features of IL-3 is its capacity to trigger bone marrow CFU-spleen (CFU-S) into the cell cycle [22, 23]. The higher percentage of dividing stem cells is associated in vivo with elevated numbers of circulating CFU-S [24] and increased frequencies of these early progenitors in spleen and liver. These cells probably achieve their full maturation in extramedullary sites. They may therefore account for the increase of CFU-C, BFU-E, CFU-Mix and morphologically recognizable precursor cells occurring four days after injection of anti-CD3 in the spleen, rather than locally differentiated stem cells.
Even though injection of IL-3 and GM-CSF reproduces most of the hematopoietic changes induced by anti-CD3, the latter is probably directly responsible for the rapid loss of lymphocytes from peripheral blood. The early increase in granulocyte levels in these compartments is also not promoted by growth factor injection, but may be due to other mediators generated in response to anti-CD3. This notion is also consistent with the less striking hematopoietic modifications seen in response to IL-3 and GM-CSF, suggesting that other cytokines released in response to anti-CD3 [7] might amplify the effect of the growth factors.
Given the variety of clinical settings in which anti-CD3 mAb could be of potential use, the striking hematopoietic modifications induced by this treatment deserve consideration. Our observations could be of particular interest in the context of allogeneic bone marrow transplantation, where a beneficial effect of endogenous colony-stimulating factors on engraftment has been documented [25]. In this situation, the protection against allograft rejection by colony-stimulating factors might be a consequence of their capacity to accelerate hematopoietic recovery [26].
| Acknowledgments |
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| References |
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This article has been cited by other articles:
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J. P. Monteiro, A. Benjamin, E. S. Costa, M. A. Barcinski, and A. Bonomo Normal hematopoiesis is maintained by activated bone marrow CD4+ T cells Blood, February 15, 2005; 105(4): 1484 - 1491. [Abstract] [Full Text] [PDF] |
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