In situ Vaccine Plus Checkpoint Blockade Induces Memory Humoral Response.

In a syngeneic murine melanoma (MEL) model, we recently reported an in situ vaccination response to combined radiation (RT) and intra-tumoral (IT) injection of anti-GD2 hu14. 18-IL2 immunocytokine (IC). This combined treatment resulted in 71% complete and durable regression of 5-week tumors, a tumor-specific memory T cell response, and augmented response to systemic anti-CTLA-4 antibody checkpoint blockade. While the ability of radiation to diversify anti-tumor T cell response has been reported, we hypothesize that mice rendered disease-free (DF) by a RT-based ISV might also exhibit a heightened B cell response. C57BL/6 mice were engrafted with 2 × 106 GD2+ B78 MEL and treated at a target tumor size of ~200 mm3 with 12 Gy RT, IT-IC on day (D)6-D10, and anti-CTLA-4 on D3, 6, and 9. Serum was collected via facial vein before tumor injection, before treatment, during treatment, after becoming DF, and following rejection of subcutaneous 2 × 106 B78 MEL re-challenge on D90. Flow cytometry demonstrated the presence of tumor-specific IgG in sera from mice rendered DF and rejecting re-challenge with B78 MEL at D90 after starting treatment. Consistent with an adaptive endogenous anti-tumor humoral memory response, these anti-tumor antibodies bound to B78 cells and parental B16 cells (GD2-), but not to the unrelated syngeneic Panc02 or Panc02 GD2+ cell lines. We evaluated the kinetics of this response and observed that tumor-specific IgG was consistently detected by D22 after initiation of treatment, corresponding to a time of rapid tumor regression. The amount of tumor-specific antibody binding to tumor cells (as measured by flow MFI) did not correlate with host animal prognosis. Incubation of B16 MEL cells in DF serum, vs. naïve serum, prior to IV injection, did not delay engraftment of B16 metastases and showed similar overall survival rates. B cell depletion using anti-CD20 or anti-CD19 and anti-B220 did not impact the efficacy of ISV treatment. Thus, treatment with RT + IC + anti-CTLA-4 results in adaptive anti-tumor humoral memory response. This endogenous tumor-specific antibody response does not appear to have therapeutic efficacy but may serve as a biomarker for an anti-tumor T cell response.

Antitumor Activity and Tolerability of hu14.18-IL2 with GMCSF and Isotretinoin in Recurrent or Refractory Neuroblastoma: A Children's Oncology Group Phase II Study.

PURPOSE: Combining anti-GD2 (disialoganglioside) mAb with GM-CSF, IL2, and isotretinoin is now FDA-approved for high-risk neuroblastoma minimal residual disease (MRD) therapy. The humanized anti-GD2 antibody conjugated to IL2 (hu14.18-IL2) has clinical activity in neuroblastoma and is more effective in neuroblastoma-bearing mice than antibody and cytokine given separately. We therefore evaluated the safety, tolerability, and antitumor activity of hu14.18-IL2 given with GM-CSF and isotretinoin in a schedule similar to standard MRD therapy. PATIENTS AND METHODS: Hu14.18-IL2 was given at the recommended phase II dose of 12 mg/m2/day on days 4-6 of a 28-day cycle with GM-CSF (250 mg/m2/dose, days 1-2 and 8-14) and isotretinoin (160 mg/m2/day, days 11-25). Tolerability was determined on the basis of the number of unacceptable toxicities observed. Response was evaluated separately for patients with disease measurable by standard radiologic criteria (stratum 1), and for patients with disease evaluable only by I123-metaiodobenzylguanidine (I123-MIBG) scan and/or bone marrow histology (stratum 2). RESULTS: Fifty-two patients with recurrent or refractory neuroblastoma were enrolled; 51 were evaluable for toxicity and 45 were evaluable for response. Four patients had unacceptable toxicities, well below the protocol-defined rule for tolerability. Other grade 3 and 4 nonhematologic toxicities were expected and reversible. No responses were seen in stratum 1 (n = 14). In stratum 2 (n = 31), 5 objective responses were confirmed by central review (3 complete, 2 partial). CONCLUSIONS: Hu14.18-IL2 given in combination with GM-CSF and isotretinoin is safe and tolerable. Patients with MIBG and/or bone marrow-only disease had a 16.1% response rate, confirming activity of the combination.

Soluble interleukin-2 receptor α activation in a Children's Oncology Group randomized trial of interleukin-2 therapy for pediatric acute myeloid leukemia.

PURPOSE: To assess associations of soluble IL-2 receptor alpha (sIL-2rα) concentration with outcomes in pediatric acute myeloid leukemia (AML) in a phase 3 trial of IL-2 therapy. PROCEDURES: We randomized 289 children with AML in first remission after intensive chemotherapy to receive IL-2 infused on days 0-3 and 8-17 (IL-2 group) or no further therapy (AML control group). We measured sequential serum sIL-2rα concentrations in both groups before, during and after therapy in both groups and in reference controls without AML. RESULTS: Before treatment, mean sIL-2rα concentrations were similar in the IL-2 group and AML controls, but significantly higher than in reference controls. Both AML groups experienced reduction in sIL-2rα concentration after chemotherapy. Thereafter in the IL-2 group, mean sIL-2rα concentration increased from 2,669 pg/ml before IL-2 to 15,534 pg/ml on day 4 (P < 0.001) and 10,585 pg/ml on day 18 (P < 0.001). In the control group sIL-2rα concentration did not change after 28 days of follow-up. Five-year disease-free survival (DFS) was 51% in the IL-2 group and 58% in the controls (P = 0.489) and overall survival was 70% and 73%, respectively (P = 0.727). CONCLUSION: SIL-2rα concentration was elevated in AML at diagnosis and tended to normalize after chemotherapy. IL-2 infusion significantly increased sIL-2rα concentration, but did not improve DFS or survival in pediatric AML. Furthermore, sIL-2rα concentration was not predictive of outcome before, during or after treatment for AML.