Our group and others have determined that immune effector cells from patients with advanced cancers exhibit reduced activation of IFN signaling pathways. We hypothesized that increases in immune regulatory cells termed myeloid derived suppressor cells (MDSC) could interfere with the host immune response to tumors by inhibiting immune cell responsiveness to interferons. The C26 murine adenocarcinoma model was employed to study immune function in advanced malignancy. C26 bearing mice had significantly elevated levels of GR1+CD11b+ MDSC as compared to control mice, and splenocytes from tumor bearing mice exhibited reduced phosphorylation of STAT1 (P-STAT1) on Tyr 701 in response to IFN alpha or IFN gamma. This inhibition was seen in splenic CD4+ and CD8+ T cells as well as NK cells. In vitro co culture experiments revealed that MDSC inhibited the IFN responsiveness of splenocytes from normal mice. Treatment of C26 bearing mice with gemcitabine or an anti-GR1 antibody led to depletion of MDSC and restored splenocyte IFN responsiveness. Spleens from C26 bearing animals displayed elevated levels of iNOS protein and nitric oxide (NO). In vitro treatment of splenocytes with a nitric oxide donor led to a decreased STAT1 IFN response. The elevation in NO in C26 bearing mice was associated with increased levels of nitration on STAT1. Finally, splenocytes from iNOS knockout mice bearing C26 tumors exhibited a significantly elevated IFN-response as compared to control C26 tumor bearing mice. These data suggest that NO produced by MDSC can lead to reduced interferon responsiveness in immune cells.

Natural killer (NK) cells express an activating receptor for the Fc portion of IgG (FcγRIIIa) that mediates interferon (IFN)–γ production in response to antibody (Ab)–coated targets. We have previously demonstrated that NK cells activated with interleukin-12 (IL-12) in the presence of immobilized IgG secrete 10-fold or more higher levels of IFN-γ as compared with stimulation with either agent alone. We examined the intracellular signaling pathways responsible for this synergistic IFN-γ production. NK cells costimulated via the FcR and the IL-12 receptor (IL-12R) exhibited enhanced levels of activated STAT4 and Syk as compared with NK cells stimulated through either receptor alone. Extracellular signal–regulated kinase (ERK) was also synergistically activated under these conditions. Studies with specific chemical inhibitors revealed that the activation of ERK was dependent on the activation of PI3-K, whose activation was dependent on Syk, and that sequential activation of these molecules was required for NK cell IFN-γ production in response to FcR and IL-12 stimulation. Retroviral transfection of ERK1 into primary human NK cells substantially increased IFN-γ production in response to immobilized IgG and IL-12, while transfection of human NK cells with a dominant-negative ERK1 abrogated IFN-γ production. Confocal microscopy and cellular fractionation experiments revealed that FcγRIIIa and the IL-12R colocalized to areas of lipid raft microdomains in response to costimulation with IgG and IL-12. Chemical disruption of lipid rafts inhibited ERK signaling in response to costimulation and significantly inhibited IFN-γ production. These data suggest that dual recruitment of FcγRIIIa and the IL-12R to lipid raft microdomains allows for enhanced activation of downstream signaling events that lead to IFN-γ production.

This flow cytometry method can be used to monitor STAT1 activation within subsets of immune cells from patients undergoing IFN alpha immunotherapy.

Background The ganglioside GD2 is an attractive target for immunotherapy of neuroectodermal tumors. We tested a unique bispecific antibody anti-CD3 × anti-GD2 (3F8BiAb) for its ability to redirect activated T cells (ATC) to target GD2-positive neuroblastomas. Procedure ATC were generated from normal human peripheral blood mononuclear cells (PBMC) by stimulating the PBMC with OKT3 and expanding the T cells in the presence of interleukin 2 (IL-2) for 14 days. ATC were armed with 3F8BiAb (100 ng/106 cells) or Her2BiAb (50 ng/106 cells) prior to use. 3F8 BiAb were tested for its dual-binding specificity to GD2 expressed on cancer cell lines and CD3 expressed on ATC. 3F8BiAb-armed ATC were further tested ex vivo for their cytotoxicity against GD2 positive tumor targets and its ability to induce cytokine response upon binding to targets. Results GD2 expression in neuroblastoma cells was confirmed by FACS analysis. Specific binding of 3F8BiAb to the tumor targets as well as to ATC was confirmed by FACS analysis. 3F8BiAb-armed ATC exhibited specific killing of GD2 positive neuroblastoma cell lines significantly above unarmed ATC (P < 0.001). GD2BiAb-armed ATC secreted significantly higher levels of Th1 cytokines and chemokines compared to unarmed ATC (P < 0.001). Conclusions These preclinical findings support the potential of a novel immunotherapeutic approach to target T cells to neuroblastoma.