Fusion Genes in Prostate Cancer: A Comparison in Men of African and European Descent.

Prostate cancer is one of the most prevalent cancers worldwide, particularly affecting men living a western lifestyle and of African descent, suggesting risk factors that are genetic, environmental, and socioeconomic in nature. In the USA, African American (AA) men are disproportionately affected, on average suffering from a higher grade of the disease and at a younger age compared to men of European descent (EA). Fusion genes are chimeric products formed by the merging of two separate genes occurring as a result of chromosomal structural changes, for example, inversion or trans/cis-splicing of neighboring genes. They are known drivers of cancer and have been identified in 20% of cancers. Improvements in genomics technologies such as RNA-sequencing coupled with better algorithms for prediction of fusion genes has added to our knowledge of specific gene fusions in cancers. At present AA are underrepresented in genomic studies of prostate cancer. The primary goal of this study was to examine molecular differences in predicted fusion genes in a cohort of AA and EA men in the context of prostate cancer using computational approaches. RNA was purified from prostate tissue specimens obtained at surgery from subjects enrolled in the study. Fusion gene predictions were performed using four different fusion gene detection programs. This identified novel putative gene fusions unique to AA and suggested that the fusion gene burden was higher in AA compared to EA men.

A Systems Approach to Interrogate Gene Expression Patterns in African American Men Presenting with Clinically Localized Prostate Cancer.

An emerging theory about racial differences in cancer risk and outcomes is that psychological and social stressors influence cellular stress responses; however, limited empirical data are available on racial differences in cellular stress responses among men who are at risk for adverse prostate cancer outcomes. In this study, we undertook a systems approach to examine molecular profiles and cellular stress responses in an important segment of African American (AA) and European American (EA) men: men undergoing prostate biopsy. We assessed the prostate transcriptome with a single biopsy core via high throughput RNA sequencing (RNA-Seq). Transcriptomic analyses uncovered impacted biological pathways including PI3K-Akt signaling pathway, Neuroactive ligand-receptor interaction pathway, and ECM-receptor interaction. Additionally, 187 genes mapping to the Gene Ontology (GO) terms RNA binding, structural constituent of ribosome, SRP-dependent co-translational protein targeting to membrane and the biological pathways, translation, L13a-mediated translational silencing of Ceruloplasmin expression were differentially expressed (DE) between EA and AA. This signature allowed separation of AA and EA patients, and AA patients with the most severe clinical characteristics. AA patients with elevated expression levels of this genomic signature presented with higher Gleason scores, a greater number of positive core biopsies, elevated dehydroepiandrosterone sulfate levels and serum vitamin D deficiency. Protein-protein interaction (PPI) network analysis revealed a high degree of connectivity between these 187 proteins.

Vitamin D binding protein polymorphisms significantly impact vitamin D status in children.

BACKGROUND: Polymorphic alleles of the vitamin D (vitD)-binding protein (VDBP) gene are associated with discriminatory differences in circulating concentrations of 25-hydroxyvitamin D (25-D), the indicator of vitD status (sufficiency defined by the Endocrine Society as ≥75 nmol/L). Within a diverse group of children, we hypothesized that reaching recommended daily allowance (RDA) of vitD intake would have differential impact on vitD status depending on VDBP variability. METHODS: VDBP alleles (Gc1S, Gc1F, Gc2) in 123 children (1-4 annual visits/child; ages 1-8 years) were compared for relationships with serum 25-D concentrations and daily vitD intake. RESULTS: In African-American children, reaching the vitD RDA was associated with significantly higher mean serum 25-D concentrations for the 20% carrying the VDBP 1S allele than for the large majority without this allele (77 vs. 61 nmol/L 25-D; p = 0.038). Children with the Gc1S/1S homozygous genotype (30% Caucasians, 24% Hispanics, 2% African-Americans) who met RDA had 51% (39 nmol/L) greater mean serum 25-D than those below RDA (p < 0.0001). CONCLUSIONS: VDBP genetic variability was a significant factor affecting childhood vitD status when following RDA guidelines. This study may inform public health policy of uniformity in recommended childhood vitD dosage, especially regarding racially/ethnically associated disparities.

Discordance in perceived risk and epidemiological outcomes of prostate cancer among African American men.

As guidelines for prostate cancer screening have changed from an annual screening recommendation starting at age 50 to discussing the benefits and harms of screening with health care providers, it is necessary to examine other types of factors that are important to prostate cancer screening decisions among African American men. Perceived risk of developing cancer has been shown to predict cancer control behaviors and is lower among African Americans. We characterized perceived risk of developing prostate cancer among African American men from November 2009 to 2011 and evaluated the relationship between prostate cancer risk perceptions and sociodemographic characteristics, health care experiences, and knowledge and exposure to health information about cancer. Chi square tests and logistic regression were employed to determine independent associations. Overall, men did not believe they were at increased risk of developing prostate cancer; they believed their risk was equivalent to or lower than men the same age. Perceived risk of prostate cancer was associated with income (OR = 0.59, 95% CI = 0.26, 1.34, p = 0.03), hypertension (OR = 2.68, 95% CI = 1.17, 6.16, p = 0.02), and beliefs about the association between race and cancer risk (OR = 2.54, 95% CI = 1.24, 5.20, p = 0.01). Clinic and community-based approaches to improve prostate cancer risk comprehension among African American men are needed to reduce the discordance between perceived risk and epidemiological data on prostate cancer risk factors. Risk education interventions that are developed for African American men may need to integrate information about susceptibility for multiple diseases as well as address strategies for risk reduction and prevention, and chronic disease management.

Ever and Annual Use of Prostate Cancer Screening in African American Men.

Since prostate cancer continues to disproportionately affect African American men in terms of incidence, morbidity, and mortality, prostate-specific antigen (PSA) screening plays an important role in early detection, especially when men engage in informed decision making to accept or decline this test. The authors evaluated utilization of PSA testing among African American men based on factors that are important components of making informed decisions. Utilization of PSA testing was evaluated based on whether men had ever had PSA testing and PSA testing during the past year in a community-based sample of African American men ages 50 to 75 ( n = 132). Overall, 64% of men ( n = 85) reported that they had ever had a PSA test; the mean ( SD) age for first use of PSA testing was 47.7 ( SD = 7.4). The likelihood of ever having a PSA test increased significantly with physician communication (odds ratio [OR] = 14.2; 95% confidence interval [CI] = 4.20, 48.10; p = .0001) and with having an annual household income that was greater than $20,000 (OR = 9.80; 95% CI = 3.15, 30.51; p = .0001). The odds of ever having a PSA test were also decreased with each unit increase in future temporal orientation (OR = 0.66; 95% CI = 0.47, 0.93; p = .02). Of the men who had ever had PSA testing, 57% were screened during the past year. Only health insurance status had a significant independent association with having annual PSA testing (OR = 5.10; 95% CI = 1.67, 15.60; p = .004). Different factors were associated significantly with ever having PSA testing and annual testing among African American men. African American men may not be making an informed decision about prostate cancer screening.

Restoration of Immune Responsiveness to Glioma by Vaccination of Mice with Established Brain Gliomas with a Semi-Allogeneic Vaccine.

Prior studies had shown the clinical efficacy of a semi-allogeneic glioma vaccine in mice with lethal GL261 gliomas. This was confirmed in the present study. As subcutaneous vaccination resulted in protection against tumor in the brain, the present study assessed the impact of this vaccination of mice bearing established GL261 brain gliomas on their cytokine production upon in vitro exposure to tumor-derived products. Mice with established GL261 brain gliomas were vaccinated subcutaneously with H-2(b) GL261 glioma cells fused with H-2(d) RAG-neo cells or with a mock vaccine of phosphate-buffered saline. The results of these analyses show that the presence of GL261 tumor-conditioned medium resulted in increased production of Th1, inflammatory and inhibitory cytokines by spleen cells from control mice and from vaccinated glioma-bearing mice. In contrast, spleen cells of tumor-bearing, mock-vaccinated mice produced lower levels of cytokines in the presence of tumor-conditioned media. However, these results also show that there was not a heightened level of cytokine production in the presence of tumor-conditioned medium by spleen cells of vaccinated mice over the production by spleen cells of control mice. Overall, these results show that vaccination slows growth of the GL261 tumors to the point where GL261-vaccinated mice do not show the signs of morbidly or splenic dysfunction exhibited by unvaccinated, late stage glioma-bearing mice.

Systems analysis of the prostate transcriptome in African-American men compared with European-American men.

AIM: African-Americans (AA) have increased prostate cancer risk and a greater mortality rate than European-Americans (EA). AA exhibit a high prevalence of vitamin D deficiency. We examined the global prostate transcriptome in AA and EA, and the effect of vitamin D3 supplementation. PATIENTS & METHODS: Twenty-seven male subjects (ten AA and 17 EA), slated to undergo prostatectomy were enrolled in the study. Fourteen subjects received vitamin D3 (4000 IU daily) and 13 subjects received placebo for 2 months prior to surgery. RESULTS: AA show higher expression of genes associated with immune response and inflammation. CONCLUSION: Systems level analyses support the concept that Inflammatory processes may contribute to disease progression in AA. These transcripts can be modulated by a short course of vitamin D3 supplementation.

A therapeutic cancer vaccine against GL261 murine glioma.

BACKGROUND: Glioblastoma (GBM) is the deadliest of brain tumors. Standard treatment for GBM is surgery, followed by combined radiation therapy and chemotherapy. Current therapy prolongs survival but does not offer a cure. We report on a novel immunotherapy against GBM, tested in an animal model of C57BL/6 mice injected intra-cranially with a lethal dose of murine GL261 glioma cells. METHODS: Ten week-old C57BL/6 mice were anesthetized before injection of 2 × 10(4) GL261 cells in the right cerebral hemisphere and after 3 days half of the mice were administered a single subcutaneous (s.c.) injection of irradiated semi-allogeneic vaccine, while mock-vaccinated mice received a s.c. injection of phosphate-buffered saline (PBS). Tumor engraftment was monitored through bioluminescence imaging (BLI). Length of animal survival was measured by Kaplan-Meier graphs and statistics. At time of sacrifice brain tissue was processed for estimation of tumor size and immunohistochemical studies. RESULTS: Overall survival of vaccinated mice was significantly longer compared to mock-vaccinated mice. Five to ten percent of vaccinated mice survived more than 90 days following the engraftment of GL261 cells in the brain and appeared to be free of disease by BLI. Tumor volume in the brain of vaccinated mice was on average five to ten-fold smaller compared to mock-vaccinated mice. In vaccinated mice, conspicuous microglia infiltrates were observed in tumor tissue sections and activated microglia appeared to form a fence along the perimeter of the tumor cells. The results of these animal studies persuaded the Office of Orphan Products Development of the Food and Drug Administration (FDA) to grant Orphan Drug Designation for treatment of GBM with irradiated, semi-allogeneic vaccines. CONCLUSIONS: Our preclinical observations suggest that semi-allogeneic vaccines could be tested clinically on subjects with GBM, as an adjuvant to standard treatment.

Dietary supplementation of GrandFusion(®) mitigates cerebral ischemia-induced neuronal damage and attenuates inflammation.

OBJECTIVES: Dietary supplementation of fruits and vegetables has been the main stay for nutritional benefit and overall well-being. GrandFusion(®) is a nutritional supplement that contains the natural nutrients from whole fruits and vegetables that include complex nutrients and phytonutrients that contain anti-oxidant, anti-inflammatory, and neuroprotective properties. METHODS: In this study, C57BL/6 mice were fed a diet supplemented with GrandFusion(®) for 2 months prior to 1 hour of ischemia induced by occlusion of the middle cerebral artery (MCAo) followed by various times of reperfusion. Mice were subjected to MCAo for 1 hour and then at various times following reperfusion, animals were assessed for behavioral outcomes (open field testing, rotarod, and adhesive test removal), and infarct volumes (cresyl violet and triphenyltetrazolium chloride). In addition, to determine the potential mechanisms associated with treatment, the brain tissue was examined for changes in oxidative stress and inflammatory markers. RESULTS: The GrandFusion(®) diet was able to show a significant protection from infarct damage in the brain and an improvement in neurological outcomes. The diet did not alter heart rate, blood pressure, pO2, pCO2, or pH. In addition, the diet mitigated inflammation by reducing microglial and astrocytic activation following ischemia and reperfusion and limiting oxidative stress. DISCUSSION: The study demonstrates the neuroprotective effect of a diet rich in fruits and vegetables that contain anti-oxidant and anti-inflammatory against the impact of cerebral ischemia and reperfusion injury.

Vitamin D3 supplementation, low-risk prostate cancer, and health disparities.

Vitamin D promotes the differentiation of prostate cancer cells, raising the possibility that vitamin D deficiency over time may contribute to the progression from subclinical prostate cancer to clinical disease. Since low-risk prostate cancers are monitored over time in an effort to determine which progress into clinically important, more aggressive cancers, they provide an excellent model in which to study, over an extended period of time, the effects of enhancing vitamin D status and related changes in tumor progression. This is particularly relevant to African-American men, who exhibit a high prevalence of vitamin D deficiency as well as higher incidence of prostate cancer and higher mortality rates from prostate cancer than Caucasians. Our research team has recently completed an open-label clinical trial aimed at assessing the safety and potential efficacy of vitamin D3 supplementation at 4000 international units (IU) per day for one year in subjects diagnosed with early stage, low-risk prostate cancer. The results of this clinical study suggest that supplementation with vitamin D3 at 4000IU per day may benefit patients with early stage, low-risk prostate cancer on active surveillance, because of the improved outcome (a decreased number of positive cores at repeat biopsy) in more than half of the subjects enrolled in the trial. We also observed that, after one year of supplementation, there was no difference in circulating levels of vitamin D between African-American and Caucasian subjects who completed the study. These clinical results also suggest that robust and sustained vitamin D3 supplementation can reduce prostate cancer-related health disparities in African-American men and that these health disparities are at least in part the result of widespread hypovitaminosis D within the African-American population. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Vitamin D3 supplementation (4000 IU/d for 1 y) eliminates differences in circulating 25-hydroxyvitamin D between African American and white men.

BACKGROUND: African Americans suffer disproportionately from diabetes and cardiovascular disease and are significantly more likely to have suboptimal concentrations of circulating 25-hydroxyvitamin D [25(OH)D]. The results of epidemiologic and observational studies suggest that there is a link between vitamin D deficiency and the risk of cardiometabolic disorders, which underscores the importance of maintaining healthy concentrations of 25(OH)D. OBJECTIVE: The objective was to investigate whether daily supplementation with 4000 IU vitamin D(3) for 1 y would eliminate any disparities in circulating concentrations of 25(OH)D between African American and white men. DESIGN: Serum concentrations of 25(OH)D were measured every 2 mo in 47 subjects who received a daily oral dose of 4000 IU vitamin D(3) for 1 y. RESULTS: More than 90% of African Americans had serum concentrations of 25(OH)D <32 ng/mL, and approximately two-thirds had serum concentrations <20 ng/mL. Furthermore, there were significant disparities in serum concentrations of 25(OH)D between African American and white men. Supplementation with 4000 IU/d for 1 y eliminated any significant differences in circulating concentrations of 25(OH)D between African American and white men. CONCLUSION: The results of this clinical study show the feasibility and efficacy of this approach in the elimination of hypovitaminosis D, which is a widespread health disparity among African Americans. This trial was registered at clinicaltrials.gov as NCT01045109.

Vitamin D3 supplementation at 4000 international units per day for one year results in a decrease of positive cores at repeat biopsy in subjects with low-risk prostate cancer under active surveillance.

CONTEXT: We wanted to investigate vitamin D in low-risk prostate cancer. OBJECTIVES: The objective of the study was to determine whether vitamin D(3) supplementation at 4000 IU/d for 1 yr is safe and would result in a decrease in serum levels of prostate-specific antigen (PSA) or in the rate of progression. DESIGN: In this open-label clinical trial (Investigational New Drug 77,839), subjects were followed up until repeat biopsy. SETTING: All subjects were enrolled through the Medical University of South Carolina and the Ralph H. Johnson Veterans Affairs Medical Center, both in Charleston, SC. PATIENTS AND OTHER PARTICIPANTS: All subjects had a diagnosis of low-risk prostate cancer. Fifty-two subjects were enrolled in the study, 48 completed 1 yr of supplementation, and 44 could be analyzed for both safety and efficacy objectives. INTERVENTION: The intervention included vitamin D(3) soft gels (4000 IU). MAIN OUTCOME MEASURES: Adverse events were monitored throughout the study. PSA serum levels were measured at entry and every 2 months for 1 yr. Biopsy procedures were performed before enrollment (for eligibility) and after 1 yr of supplementation. RESULTS: No adverse events associated with vitamin D(3) supplementation were observed. No significant changes in PSA levels were observed. However, 24 of 44 subjects (55%) showed a decrease in the number of positive cores or decrease in Gleason score; five subjects (11%) showed no change; 15 subjects (34%) showed an increase in the number of positive cores or Gleason score. CONCLUSION: Patients with low-risk prostate cancer under active surveillance may benefit from vitamin D(3) supplementation at 4000 IU/d.

Protective effects of incensole acetate on cerebral ischemic injury.

The resin of Boswellia species is a major anti-inflammatory agent that has been used for centuries to treat various conditions including injuries and inflammatory conditions. Incensole acetate (IA), a major constituent of this resin, has been shown to inhibit NF-κB activation and concomitant inflammation, as well as the neurological deficit following head trauma. Here, we show that IA protects against ischemic neuronal damage and reperfusion injury in mice, attenuating the inflammatory nature of ischemic damage. IA given post-ischemia, reduced infarct volumes and improved neurological activities in the mouse model of ischemic injury in a dose dependent fashion. The protection from damage was accompanied by inhibition of TNF-α, IL-1ß and TGF-ß expression, as well as NF-κB activation following injury. In addition, IA is shown to have a therapeutic window of treatment up to 6h after ischemic injury. Finally, the protective effects of IA were partially mediated by TRPV3 channels as determined by the TRPV3 deficient mice and channel blocker studies. This study suggests that the anti-inflammatory and neuroprotective activities of IA may serve as a novel therapeutic treatment for ischemic and reperfusion injury, and as a tool in the ongoing research of mechanisms for neurological damage.

Vitamin D3-enriched diet correlates with a decrease of amyloid plaques in the brain of AßPP transgenic mice.

In addition to its function in calcium and bone metabolism, vitamin D is neuroprotective and important for mitigating inflammation. Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the central nervous system, characterized by neuronal loss in many areas of the brain, and the formation of senile (neuritic) plaques, which increase in number and size over time. The goal of this project was to investigate whether vitamin D3 supplementation would affect amyloid plaque formation in amyloid-ß protein precursor (AßPP) transgenic mice that spontaneously develop amyloid plaques within 3-4 months of birth. AßPP mice were fed control, vitamin D3-deficient or vitamin D3-enriched diets for five months, starting immediately after weaning. At the end of the study, the animals were subjected to behavioral studies, sacrificed, and examined for bone changes and brain amyloid load, amyloid-ß (Aß) peptide levels, inflammatory changes, and nerve growth factor (NGF) content. The results obtained indicate that a vitamin D3-enriched diet correlates with a decrease in the number of amyloid plaques, a decrease in Aß peptides, a decrease in inflammation, and an increase in NGF in the brains of AßPP mice. These observations suggest that a vitamin D3-enriched diet may benefit AD patients.

Transcranial laser therapy attenuates amyloid-ß peptide neuropathology in amyloid-ß protein precursor transgenic mice.

Transcranial laser therapy (TLT) was tested for efficacy in a mouse model of Alzheimer's disease (AD) using a near-infrared energy laser system. TLT is thought to stimulate ATP production, increase mitochondrial activity, and help maintain neuronal function. Studies were performed to determine the effect of TLT in an amyloid-ß protein precursor (AßPP) transgenic mouse model. TLT was administered 3 times/week at various doses, starting at 3 months of age, and was compared to a control group (no laser treatment). Treatment was continued for a total of six months. Animals were examined for amyloid load, inflammatory markers, brain amyloid-ß (Aß) levels, plasma Aß levels, cerebrospinal fluid Aß levels, soluble AßPP (sAßPP) levels, and behavioral changes. The numbers of Aß plaques were significantly reduced in the brain with administration of TLT in a dose-dependent fashion. Administration of TLT was associated with a dose-dependent reduction in amyloid load. All TLT doses mitigated the behavioral effects seen with advanced amyloid deposition and reduce the expression of inflammatory markers in the AßPP transgenic mice. All TLT doses produced an increase in sAßPPα and a decrease in CTFß levels consistent with inhibition of the ß-secretase activity. In addition, TLT showed an increase in ATP levels, mitochondrial function, and c-fos suggesting an overall improvement in neurological function. These studies suggest that TLT is a potential candidate for treatment of AD.

The impact of methylmercury on 1,25-dihydroxyvitamin D3-induced transcriptomic responses in dolphin skin cells.

The Atlantic bottlenose dolphin has been the focus of much attention owing to the considerable impact of environmental stress on its health and the associated implications for human health. Here, we used skin cells from the dolphin to investigate the protective role of the vitamin D pathway against environmental stressors. We previously reported that dolphin skin cells respond to 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive metabolite of vitamin D3, by upregulation of the vitamin D receptor (VDR) and expression of several genes. Methylmercury is a highly bioaccumulative environmental stressor of relevance to the dolphin. We currently report that in dolphin cells sublethal concentrations of methylmercury compromise the ability of 1,25D3 to upregulate VDR, to transactivate a vitamin D-sensitive promoter, and to express specific target genes. These results help elucidate the effects of vitamin D and methylmercury on innate immunity in dolphin skin and potentially in human skin as well, considering similarities in the vitamin D pathway between the two species.

The vitamin D3 transcriptomic response in skin cells derived from the Atlantic bottlenose dolphin.

The Atlantic bottlenose dolphin has attracted attention due to the evident impact that environmental stressors have taken on its health. In order to better understand the mechanisms linking environmental health with dolphin health, we have established cell cultures from dolphin skin as in vitro tools for molecular evaluations. The vitamin D3 pathway is one mechanism of interest because of its well established chemopreventative and immunomodulatory properties in terrestrial mammals. On the other hand, little is known of the physiological role of this molecule in aquatic animals. 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive and hormonal form of vitamin D3, exerts its biological function by binding to the vitamin D receptor (VDR), a ligand-activated regulator of gene transcription. Therefore, we investigated the transcriptomic changes induced by 1,25D3 administration in dolphin skin cells. Identification of specific genes activated by 1,25D3 has provided clues to the physiological function of the vitamin D3 pathway in the dolphin. We found that exposure of the cells to 1,25D3 upregulated transactivation of a vitamin D-sensitive promoter. cDNA microarray analysis, using a novel dolphin array, identified specific gene targets within this pathway, and real-time PCR (qPCR) confirmed the enhanced expression of select genes of interest. These transcriptional changes correlated with an increase in VDR levels. This is the first report of the presence and activation of the vitamin D3 pathway in a marine mammal, and our experimental results demonstrate a number of similarities to terrestrial animals. Conservation of this pathway in the Atlantic bottlenose dolphin is consistent with the importance of nonclassic functions of vitamin D3, such as its role in innate immunity, similar to what has been demonstrated in other mammals.

Semi-allogeneic vaccines and tumor-induced immune tolerance.

Experimental results from studies with inbred mice and their syngeneic tumors indicated that the inoculation of semi-allogeneic cell hybrids (derived from the fusion between syngeneic tumor cells and an allogeneic cell line) protects the animal host from a subsequent lethal challenge with unmodified syngeneic tumor cells. Semi-allogeneic somatic cell hybrids were generated by the fusion of EL-4 T lymphoma cells (H-2b) and BALB/c-derived renal adenocarcinoma RAG cells (H-2d). Cell hybrids were injected intra-peritoneally (i.p.) in C57BL/6 mice (H-2b) before challenging the mice with a tumorigenic dose of EL-4 cells. Semi-allogeneic tumor cell hybrids could not form a tumor in the animal host because they expressed allogeneic determinants (H-2d) and were rejected as a transplant. However, they conferred protection against a tumorigenic challenge of EL-4 cells compared to control mice that were mock-vaccinated with i.p.-injected phosphate-buffered saline (PBS) and in which EL-4 lymphomas grew rapidly to a large size in the peritoneal cavity. Screening of spleen-derived RNA by means of focused microarray technology showed up-regulation of genes involved in the Th-1-type immune response and in the activation of dendritic antigen-presenting cells (APC). The results of our studies confirm the role of APC in mediating the immune protection induced by semi-allogeneic vaccines by activating a Th-1 response; these studies also reveal that semi-allogeneic vaccines are able to interfere with or even block the tumor-mediated induction of immune tolerance, a key mechanism underlying the suppression of anti-tumor immunity in the immune competent host.