Targeting of heme oxygenase-1 as a novel immune regulator of neuroblastoma.

Heme oxygenase (HO)-1 catalyzes the degradation of cytotoxic heme into biliverdin and blocks antitumor immune responses, thus protecting cancer against host defense. Whether this scenario also applies to neuroblastoma (NB), the most common extracranial solid childhood tumor, is not known. Here, we demonstrate for the first time a prognostic relevance of HO-1 expression in samples from NB patients and show that targeting of HO-1 prevents both cancer resistance against cellular stress and immune escape in the syngeneic NXS2 A/J mouse model of NB. High HO-1 RNA expression in NB tissues emerged as unfavorable prognostic marker, in particular for patients older than 18 months as indicated by univariate as well as multivariate survival probability analyses including disease stage and MYCN status. On the basis of this observation we aimed to target HO-1 by systemic as well as tumor-specific zinc protoporphyrin-mediated HO-1 suppression in a syngeneic immunocompetent NB mouse model. This resulted in 50% reduction of primary tumor growth and a suppression of spontaneous liver metastases. Importantly, HO-1 inhibition abrogated immune cell paralysis affecting CD4 and CD8 T-effector cells. This in turn reverted HO-1-dependent immune escape mechanisms in NB by increasing NB apoptosis and improved DC maturation. In summary, HO-1 emerges as a novel immune regulator in NB and emerges as a promising target for the development of therapeutic approaches.

Neuroblastoma triggers an immunoevasive program involving galectin-1-dependent modulation of T cell and dendritic cell compartments.

The immunosuppressive strategies devised by neuroblastoma (NB), the most common solid extracranial childhood cancer, are poorly understood. Here, we identified an immunoevasive program triggered by NB through secretion of galectin-1 (Gal-1), a multifunctional glycan-binding protein. Human and mouse NB cells express and secrete Gal-1, which negatively regulates T cell and dendritic cell function. When injected subcutaneously in syngeneic A/J mice, knockdown transfectants expressing low amounts of Gal-1 (NXS2/L) showed reduction of primary tumor growth by 83-90% and prevented spontaneous liver metastases in contrast to NXS2 cell variants (NXS2/H, NXS2 wildtype) expressing high amounts of Gal-1. Splenocytes from mice receiving Gal-1 knockdown NXS2/L cells secreted higher amounts of IFN-γ and displayed enhanced cytotoxic T-cell function compared to NXS2/H or NXS2 controls. Immunohistochemical analysis revealed a six- to tenfold increase in the frequency of CD4+ and CD8+ T cells infiltrating tumors from mice receiving knockdown transfectants. This effect was confirmed by in vitro migration assays. Finally, supernatants of NXS2/H or NXS2 cells suppressed dendritic cell (DC) maturation and induce T cell apoptosis, whereas these effects were only marginal on DCs and T cells exposed to supernatants from NXS2/L cells. These results demonstrate a novel immunoinhibitory role of the Gal-1-glycan axis in NB, highlighting an alternative target for novel immunotherapeutic modalities.

Salmonella SL7207 application is the most effective DNA vaccine delivery method for successful tumor eradication in a murine model for neuroblastoma.

Attenuated Salmonella is an approved oral life vaccine that is currently entering pre-clinical cancer vaccination studies as a promising DNA carrier. In a syngeneic mouse model for neuroblastoma, oral gavage of Salmonella typhimurium (SL7207) carrying recent generated survivin DNA vaccines induced a stronger cellular anti-NB immune response than gene gun application or injection of lentivirally transduced bone marrow-derived DCs. The level of Salmonella-associated side effects was not significant as indicated by unaffected survivin-mediated hematopoiesis and wound healing. We believe that our findings provide an important baseline to translate Salmonella-based DNA vaccination into a clinical application for neuroblastoma.