Therefore, the mode of tumor suppressive function of maspin and its molecular interactions may depend on its subcellular localization. maturation, activation and antibody-dependent cytotoxicity, and decreased peritumoral lymphangiogenesis. These results reveal a novel biological function of maspin in directing host immunity towards tumor elimination that helps explain the significant reduction of xenograft tumor incidencein vivoand the clinical correlation of maspin with better prognosis of several types of cancer. Taken together, our data raised the possibility for novel 4-HQN maspin-based cancer immunotherapies. Keywords:prostate tumor xenograft, tumorigenicity, flow cytometry, CD11b+Ly6Ghighneutrophils, neutrophil maturation and chemotaxis, B-cell antibody response,51Cr-release assay, antibody-dependent cellular cytotoxicity, lymphangiogenesis, intratumoral fibrosis, angiogenesis, leukocyte-filled lytic and necrotic centers == INTRODUCTION == Maspin, an epithelial-specific member of the serine protease inhibitor (serpin) superfamily, was first discovered in 1994 as a tumor suppressor in breast cancer [1]. Since then, a large number of clinical studies have shown that maspin down-regulation correlates primarily with cancer progression at the step of tumor invasion [2-5], and maspin expression correlates with better prognosis and better overall patient survival [2,6-8]. Consistent with clinical data, functional studies revealed tumor suppressive functions of maspin in a range of biological processes in tumor cells, including cell differentiation, apoptosis, and angiogenesis [9-14]. We recently showed that maspin expression in prostate carcinoma cells was sufficient to drive prostate tumor cells through a spectrum of temporally and spatially polarized cellular processes of re-differentiation [12]. Genes commonly regulated by maspin were a subset of histone deacetylase 1 (HDAC1) target genes that were closely associated with epithelial differentiation and transforming growth factor- (TGF-) signaling. In the same study, we demonstrated that maspin functions as a master regulator of the transcription program inducing specific and significant changes in protein expression 4-HQN patterns involved in apoptosis [12,13]. Moreover, we have previously shown that maspin can specifically sensitize tumor cells to drug induced apoptosisin vitro[15]. Maspin has been shown to reduce tumor-derived vascular endothelial growth factor (VEGF) expression and angiogenesis [11,16]. Maspin displays unique biochemical and biophysical properties that deviate significantly from classical inhibitory serpins. It only inhibits serine protease-like targets and is further regulated by its subcellular compartmentalization [10,14,17-20]. Although maspin does not have any specific subcellular localization sequence motif, it has been found to be nuclear, cytosolic, cell membrane-associated and secreted protein [20]. Therefore, the mode of tumor suppressive function of maspin and its molecular interactions may depend on its subcellular localization. For example, we demonstrated clinical andin vitroevidence that nuclear maspin acts an endogenous inhibitor of HDAC1 [17], one of the most promising therapeutic targets for cancer [21]. We and others have shown that nuclear maspin, in particular, predicts better overall patient survival [7,18,22-27], perhaps because of its interaction and inhibition of HDAC1. Earlier, we also showed that cell surface associated maspin inhibits the cell surface-associated zymogen form of urokinase type plasminogen (pro-uPA), contributing to the inhibition of cell detachment, cell motility, extracellular matrix remodeling and tumor invasion [10,14]. Independently, the inverse correlation between maspin and uPA has been demonstrated as a significant feature in prostate cancer metastasis [28]. These findings collectively demonstrate that maspin is a multi-faceted suppressor of epithelial tumorigenesis and stromal responses. However, the role 4-HQN of maspin in host anti-tumor immune responses has not been elucidated. Here, we utilized the athymic nude mouse model capable of supporting the growth and progression of xenogeneic human prostate cancer cells to investigate the role of maspin in host anti-tumor immunity. This mouse model retains innate and humoral immunity and is suitable for testing the immunotherapeutic responses against human cancer cells [29]. We provide the first evidence that maspin expression in the prostate cancer xenograft elicits neutrophil- and B cells-dependent host immunity to promote tumor elimination. These findings are likely to open a new avenue for the development of novel maspin-based cancer immunotherapies. == RESULTS == == Maspin expression results in reduced tumor incidence and proliferation == To directly investigate the effect of maspin manifestation in tumor cells on tumor growth and connection with the sponsor environmentin vivo, we inoculated athymic nude mice subcutaneously (s.c.) with either DU145 cells stably transfected with human being maspin (M7) or those transfected with an empty vector (Neo). The animals bearing M7 or Neo tumors experienced related body Bmp8b weights (Numbers1). The tumor incidence in mice inoculated with M7 cells was 74% (46/62), whereas 100% of mice inoculated with Neo cells developed tumors (50/50).While the total volume of M7 tumors was larger than that of Neo tumors (p< 0.01) (Number1A), M7 tumors were found to contain a large volume of semi-solid fluid (Number1B). Consistently, M7.