Optimizing the effectiveness of hematopoietic growth factors

Comparison of cytokines in children with recurrent solid tumors treated with intensive chemotherapy

PURPOSE

To compare the relative hematopoietic protective effects of recombinant human interleukin-1alpha (rhuIL-1alpha), recombinant human granulocyte macrophage colony-stimulating factor (rhuGM-CSF), and PIXY321, a genetically engineered fusion protein combining interleukin-3 and rhuGM-CSF, in children with refractory solid tumors after treatment with ifosfamide, carboplatin, and etoposide (ICE).

PATIENTS AND METHODS

A total of 53 children who had not responded to at least one earlier chemotherapy regimen were enrolled on consecutive trials of ICE chemotherapy alone (n = 14) or with rhuGM-CSF (n = 8), rhuIL-1alpha (n = 10), or PIXY321 (n = 21). The relative hematopoietic effects of these three cytokines were compared retrospectively to each other and to values for patients who received ICE alone. Because one cannot assume that hematopoietic toxicity and response to a given cytokine are independent of the course of chemotherapy, the analysis was restricted to the first treatment course.

RESULTS

In this retrospective comparison, 1000 microg/m2/day of rhuGM-CSF reduced the median duration of grade 4 neutropenia (<500/microL) from a median of 17 days (range 3 to 34) in children who received ICE alone to 9 days (range 5 to 11, p = 0.003); it appeared to have a beneficial effect on severe thrombocytopenia (<20,000/microL), reducing the median duration from 4.5 days with ICE alone to 3 days (p = 0.08) and the number of platelet transfusions from a median of 5.75 transfusions (range 0 to 13) to 0 in these two cohorts. No significant improvement in these measures was seen with rhuIL-1alpha or PIXY321.

CONCLUSIONS

This analysis suggests that 1000 microg/m2/day of rhuGM-CSF has clinically significant effects on platelet recovery and more effectively ameliorates thrombocytopenia and neutropenia than either rhuIL-1alpha or PIXY321 in the context of ICE chemotherapy. Further dose-intensification will require a combination of cytokines; the optimal dose and combination of these agents awaits further study.

Host immunologic augmentation for the control of infection

The emergence of resistance to pharmacologic antimicrobial agents and the desire to increase chemotherapy dose-intensity have necessitated the search for alternative means to control infectious disease. Enhancement of host immunity against infection has been permitted through the use of hematopoietic growth factors, which can shorten the duration of neutropenia and reduce the risk for bacterial and fungal infections. Hematopoietic growth factor-mobilized hematopoietic stem cells have also proven to be highly efficacious in permitting high-dose chemotherapy. Interferons, immunoregulatory cytokines, immune globulins, and immune lymphocytes also hold promise to enhance host immunity and reduce susceptibility for serious infectious morbidity.

Cytokine measurements and interpretation of cytokine assays in human disease

Cytokines are powerful mediator and communication molecules capable of regulating a wide spectrum of biologic functions, including immune responses. Although the role of cytokines in the pathogenesis of human disease is not yet understood, assays for cytokines have become a common feature in research and clinical laboratories. However, numerous pitfalls accompany measurements of cytokine levels in body fluids and of cytokine synthesis or gene expression in tissue. Interpretation of results obtained in cytokine assays, especially those performed with pathologic specimens, is fraught with difficulties. While cytokine assays are clearly of value in monitoring patients treated with recombinant cytokines or receiving anticytokine therapy, the clinical significance of cytokine assays is not yet fully established. In this review, some of the complexities associated with cytokine monitoring are discussed. The crucial importance of understanding cytokine biology for meaningful assay interpretation is emphasized.