This randomized clinical trial tested the use of an immunotherapy regimen administered after autologous stem-cell transplantation, in order to enhance antibody-dependent cell-mediated cytotoxicity to GD2-positive tumor cells. The results indicate that the inclusion of the immunotherapy resulted in significantly superior event-free and overall survival. The rate of event-free survival during this study was superior in the immunotherapy group as compared with the standardtherapy group (66% vs. 46% at 2 years). The rate of overall survival was also superior with immunotherapy (85% at 2 years). At the time of this report, the data for overall survival had not yet met the stringent statistical criteria for early stopping that the data for event-free survival did, and the results are extremely unlikely to differ from those showing a benefit in event-free survival, though this is admittedly not out of the realm of statistical possibility. Even so, the 2-year estimate of event-free survival of 66% indicates that a substantial proportion of the 113 patients in the immunotherapy group had events (1 died from an interleukin-2 overdose, and 32 had a relapse, 18 of whom died after the relapse). Regarding the patients who were still alive after relapse, previous studies indicate that children with recurrent or progressive disease are rarely cured.22
Not surprisingly, immunotherapy was more effective in patients with minimal, rather than substantial, residual disease: the outcome was superior among patients who had been randomly assigned to a treatment group than among those nonrandomly assigned to receive immunotherapy for residual disease. Thus, despite the significant improvement in the rates of event-free survival and overall survival with this immunotherapy regimen, there is need for further improvement in treatment.
Though the use of the ch14.18 monoclonal antibody in combination with cytokines is associated with important toxic effects, these effects differ in scope, type, and duration from the myelosuppressive, renal, and gastrointestinal toxic effects of chemotherapy regimens used during the induction and consolidation phases of treatment.10,11
The toxic effects seen with the immunotherapy regimen used in our study were expected and were primarily attributable to antibody binding to GD2 expressed on normal nerve cells,23,24
to cytokine-mediated capillary leak,25
or to hypersensitivity reactions associated with the ch14.18 antibody or cytokines. These toxic effects may also reflect the proposed mechanism of action of this combination: effector functions induced by the monoclonal antibody, including complement activation, and distinct pathways of antibody-dependent cell-mediated cytotoxicity mediated by natural killer cells,16
The immunotherapy regimen tested in this study was based on several considerations and preclinical data. Antibody-dependent cell-mediated cytotoxicity is often depressed in patients with cancer,29
and antibody-dependent cell-mediated cytotoxicity modulated by various effector cells can be augmented by independent cytokines, namely GM-CSF and interleukin-2. These cytokines increase the number of granulocytes or macrophages and natural killer cells, respectively, and enhance their ch14.18-directed antibody-dependent cell-mediated cytotoxicity.13
The feasibility of combining anti-GD2 monoclonal antibodies with cytokines was shown in a Pediatric Oncology Group phase 2 trial of ch14.18 and GM-CSF12
and a Children’s Cancer Group phase 1 study of 14.G2a and interleukin-2.30
Another consideration was that greater clinical effects would be seen if immunotherapy was given in patients with minimal residual disease.31
This hypothesis is consistent with the relatively small number of complete or partial responses to anti-GD2 monoclonal antibodies (administered with or without cytokines) in children who have a relapse of neuroblastoma and adults who have melanoma with bulky disease.10–12,14
In patients with newly diagnosed high-risk neuroblastoma, we chose to achieve minimal residual disease through the use of conventional induction therapy and intensive consolidation therapy with autologous stem-cell transplantation. Providing anti-GD2 antibody with cytokines after autologous stem-cell transplantation may also promote immune-cell activation and elimination of immunosuppression, a concept being tested in separate ongoing studies of cell-mediated cancer immunotherapy.32
Our two small, sequential pilot phase 1 studies of ch14.18 in combination with GM-CSF or with GM-CSF and interleukin-217,18
showed the feasibility of giving ch14.18 with these cytokines during the early post-transplantation period. The second of these studies showed a 3-year estimate of overall survival of 78%, reflecting a benefit in a comparison with historical controls,17
a benefit now confirmed in the current randomized trial.
In a separate, nonrandomized study, Simon and colleagues performed a retrospective analysis involving 334 children with high-risk neuroblastoma.33
All the children had completed initial induction therapy (with or without autologous stem-cell transplantation), and 166 received ch14.18 at doses similar to the dose used in the current study. In contrast to our results, there was no significant improvement in the rate of event-free survival or overall survival among children receiving ch14.18 as compared with those not receiving the antibody, although an updated analysis with a median follow-up period of 10.3 years (range, 2.3 to 17.7) indicated that ch14.18 may prevent late relapse.34
Although our study differs from the study by Simon and colleagues with respect to the dosing schedule (six cycles of immunotherapy, with cycles every other month, vs. five cycles, with cycles every month) and the timing of the start immunotherapy (within 100 days after autologous stem-cell transplantation vs. a range of 39.5 to 343 days [median, 65.5 days]), the primary difference may be that our study included treatment with GM-CSF and interleukin-2 to activate antibody-dependent cell-mediated cytotoxicity and treatment with isotretinoin. The difference in outcome between the study by Simon and coworkers and our study therefore suggests, though does not prove, that the addition of GM-CSF and interleukin-2 augments the antibody-dependent cell-mediated cytotoxicity in vivo conferred by the ch14.18 monoclonal antibody and improves survival. Although we cannot entirely rule out the possibility that the observed therapeutic benefit was due to the cytokines alone, clinical studies showing the efficacy of interleukin-2 or GM-CSF monotherapy in patients with neuroblastoma are lacking.
Other tumor-reactive monoclonal antibodies being used or tested as cancer treatment can induce antibody-dependent cell-mediated cytotoxicity; these include rituximab, trastuzumab, and cetuximab.35–37
To date, published clinical trials of regimens in which interleukin-2 or GM-CSF was added to these other monoclonal antibodies have not shown any benefit over treatment with the monoclonal antibody alone.38,39
However, these published studies have focused on treatment for refractory or relapsed disease. The results from our study suggest that the efficacy of ch14.18 used in combination with GM-CSF and interleukin-2 may be detected more readily when tested as adjuvant therapy or in patients with minimal residual disease. Our findings also suggest that protocol designs similar to that used in the COG study may be appropriate for testing of other monoclonal antibodies that mediate antibody-dependent cell-mediated cytotoxicity.
In summary, the addition of ch14.18, GM-CSF, and interleukin-2 to isotretinoin therapy was associated with improved event-free and overall survival among children with high-risk neuroblastoma who had a response to initial chemotherapy and received immunotherapy within 100 days after autologous stem-cell transplantation. Our data suggest that more routine use of this immunotherapy regimen for such patients may be beneficial. Future avenues of investigation include developing more effective and less toxic ways to stimulate ch14.18-mediated antibody-dependent cell-mediated cytotoxicity and identifying more efficacious GD2-targeted monoclonal antibodies40
or genetically modified constructs targeting GD2.