A number of receptors and signaling pathways can influence the ability of dendritic cells (DC) to promote CD4+ Th type 1 (Th1) responses. In contrast, the regulatory pathways and signaling events that govern the ability of DC to instruct Th2 cell differentiation remain poorly defined. In this report, we demonstrate that NF-κB1 expression within DC is required to promote optimal Th2 responses following exposure to Schistosoma mansoni eggs, a potent and natural Th2-inducing stimulus. Although injection of S. mansoni eggs induced production of IL-4, IL-5, and IL-13 in the draining lymph node of wild-type (WT) mice, NF-κB1−/− hosts failed to express Th2 cytokines and developed a polarized Ag-specific IFN-γ response. In an in vivo adoptive transfer model in which NF-κB-sufficient OVA-specific DO11.10 TCR transgenic T cells were injected into OVA-immunized WT or NF-κB1−/− hosts, NF-κB1−/− APCs efficiently promoted CD4+ T cell proliferation and IFN-γ responses, but failed to promote Ag-specific IL-4 production. Further, bone marrow-derived DC from NF-κB1−/− mice failed to promote OVA-specific Th2 cell differentiation in in vitro coculture studies. Last, S. mansoni egg Ag-pulsed NF-κB1−/− DC failed to prime for Th2 cytokine responses following injection into syngeneic WT hosts. Impaired Th2 priming by NF-κB1−/− DC was accompanied by a reduction in MAPK phosphorylation in Ag-pulsed DC. Taken together, these studies identify a novel requirement for DC-intrinsic expression of NF-κB1 in regulating the MAPK pathway and governing the competence of DC to instruct Th2 cell differentiation.

8547 Background: Immunotherapy has demonstrated notable effects in metastatic melanoma (MM) with durable responses achieved by high-dose IL-2 and IFNα2b, leading to approval of these therapies for treatment of melanoma. However, complete responses occur in only a minority of patients. KW2871 is a chimeric monoclonal antibody (mAb) targeting the GD3 ganglioside with demonstrated antitumor activity and enhancement of antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). IFNα2b has potent immunoregulatory, anti-proliferative, differentiation-inducing, pro-apoptotic, and anti-angiogenic properties against a variety of malignancies including melanoma. Combining high dose IFNα2b (HDI) + KW2871 was hypothesized to have synergistic anti-tumor activity due to (1) the ability of HDI to enhance KW2871 induced ADCC in vitro (Liu, Cancer Immun 2002); (2) improved mAb targeting due to increased GD3 expression and induced inflammatory cytokines (TNF-α, IL-4 and IFN-γ) (Hoon, Cancer Res, 1991); (3) increased tumor-infiltrating immune cells (Kirkwood, Cancer 2002; Moschos, J Clin Oncol 2006). Methods: This is an open label, dose-escalation, phase II study of KW2871 plus HDI in patients with measurable MM. Primary objectives are progression-free survival (PFS) and safety. Secondary objectives include assessment for tumor response by RECIST, ADCC, CDC, pharmacokinetics, human antichimeric antibodies (HACA), tumor-infiltrating immune cells, biomarkers and OS. Patients with measurable disease by RECIST, stable brain metastases, and performance status ECOG 0 or 1 are eligible. Patients with severe comorbidities or autoimmune disease or prior exposure to anti-GD3 antibodies are excluded. Sequential enrollment to cohorts of KW2871 at 5, 10 , 20 mg/m2 IV every 2 week in combination with HDI 20 MU/m2 IV once daily x 5 Days for 4 weeks, then 10 MU/m2 SC three times weekly until disease progression. Results: To date, Cohort 1 (5 mg/m2 KW2871) and Cohort 2 (10 mg/m2 KW2871) have been completed safely. Cohort 3 (20 mg/m2 KW2871) has enrolled of 18 of 27 planned patients. Conclusions: Will be presented at study completion.

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