Haematologica 2002; 87:(02)ELT13
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Systemic injection of granulocyte-macrophage colony-stimulating factor increases survival in a murine model of acute leukemia
Rodolphe Vereecque*, Ricardo Gonzalez*, Pierre Fenaux,*° Bruno Quesnel*°
*INSERM U524, IRCL; °Service des Maladies du Sang, CHU, Lille, France

Correspondence: Dr. Bruno Quesnel, Service des maladies du sang, CHU Lille, Rue Polonovski, 59037 Lille France. Phone: (33) 3 20 44 42 84. Fax: (33) 3 20 44 40 94 . Email: bquesnel@nordnet.fr
Recombinant human granulocyte-macrophage colony-stimulating factor (rhuGM-CSF) has been mostly used in hematologic malignancies for its growth factor effect in order to shorten the median duration of leukopenia. However, several reports have shown that rhuGM-CSF could also have a potential anti-tumoral effect.1-3 Systemic injection of rhuGM-CSF with idiotype or rhuGM-CSF-idiotype fusion protein in mice has been reported to generate a strong and long-lasting immunity against lymphoma.4,5 rhuGM-CSF has been reported to activate killer cell activity in patients with acute myeloid leukemia (AML) undergoing autologous bone marrow transplantation and a decrease of risk of relapse was observed when these patients were compared to a historical control group.6 A slight increase of time to progression could be observed in relapsed human AML treated with a combination of intensive chemotherapy and short pulse of GM-CSF.7 This effect could not be correlated to cell cycling induction by GM-CSF in leukemic cells, suggesting that GM-CSF itself might have specific anti-leukemic effects. In order to investigate the potential in vivo anti-leukemic effect of GM-CSF, we repeatedly injected rhuGM-CSF at growing doses in leukemic mice, using the previously described aggressive murine BCR/ABL acute leukemic syngeneic model DA1-3b cells/ C3H/Hej mice.8 The animals were separated into four groups of 10 mice each, receiving 104 DA1-3b cells intraperitoneally followed by 10 subcutaneous injections of rhuGM-CSF per mice or control medium started at day 3 and delivered twice weekly. We observed, in two separate experiments, a significant improvement of survival in leukemic mice receiving 100 ng rhuGM-CSF injections (logrank test, p = 0.0156) (Figure 1). Prolonged survival (one mouse in both groups) was observed in mice receiving 1000 and 5000 ng rhuGM-CSF injections but the difference with control mice was not significant (logrank test, p= 0.082 and p = 0.219, respectively). All the surviving mice were challenged with 104 DA1-3b cells. One of them (from the 100 ng rhuGM-CSF group) was still alive at day 150 and RT-PCR analysis performed on spleen did not show BCR/ABL transcript. Injections of 20 ng rhuGM-CSF had no significant effect on survival (logrank test, p = 0.9). Incubation of DA1-3b cells with rhu-GM-CSF did not modify growth properties or co-stimulatory molecules (CD40, CD54, CD80, CD86, CD154), MHC class I and II, and p210BCR/ABL expression of this cell line. These results suggest that prolonged survival could not be related to direct modification of immunogenicity of DA1-3b cells. rhuGM-CSF's potential adjuvant effect of tumor immunity has not been systematically studied in hematologic malignancies. A few studies in AML and NHL have suggested that the addition of rhuGM-CSF to chemotherapy reduced the relapse rate, as compared to chemotherapy alone, although this was not reproduced in other studies.6,9,10 Our data suggest that favorable results of rhuGM-CSF on leukemic growth could be dose dependent. This antitumor effect is probably moderate and requires randomized large-scale studies for its demonstration. However treatment with rhuGM-CSF at conventional dose (5 to 10 µg/kg/day in humans) induces minor side effects suggesting a favorable therapeutic index and warrants further investigations.

Acknowledgments
Supported by the Ligue Contre le Cancer (Comité du Nord and Comité du Pas de Calais), the Association de Recherche sur le Cancer, the Association Recherche Transfusion, and the Fondation contre la Leucémie.

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