Modeling the public health impact of malaria vaccines for developers and policymakers.

BACKGROUND: Efforts to develop malaria vaccines show promise. Mathematical model-based estimates of the potential demand, public health impact, and cost and financing requirements can be used to inform investment and adoption decisions by vaccine developers and policymakers on the use of malaria vaccines as complements to existing interventions. However, the complexity of such models may make their outputs inaccessible to non-modeling specialists. This paper describes a Malaria Vaccine Model (MVM) developed to address the specific needs of developers and policymakers, who need to access sophisticated modeling results and to test various scenarios in a user-friendly interface. The model's functionality is demonstrated through a hypothetical vaccine. METHODS: The MVM has three modules: supply and demand forecast; public health impact; and implementation cost and financing requirements. These modules include pre-entered reference data and also allow for user-defined inputs. The model includes an integrated sensitivity analysis function. Model functionality was demonstrated by estimating the public health impact of a hypothetical pre-erythrocytic malaria vaccine with 85% efficacy against uncomplicated disease and a vaccine efficacy decay rate of four years, based on internationally-established targets. Demand for this hypothetical vaccine was estimated based on historical vaccine implementation rates for routine infant immunization in 40 African countries over a 10-year period. Assumed purchase price was $5 per dose and injection equipment and delivery costs were $0.40 per dose. RESULTS: The model projects the number of doses needed, uncomplicated and severe cases averted, deaths and disability-adjusted life years (DALYs) averted, and cost to avert each. In the demonstration scenario, based on a projected demand of 532 million doses, the MVM estimated that 150 million uncomplicated cases of malaria and 1.1 million deaths would be averted over 10 years. This is equivalent to 943 uncomplicated cases and 7 deaths averted per 1,000 vaccinees. In discounted 2011 US dollars, this represents $11 per uncomplicated case averted and $1,482 per death averted. If vaccine efficacy were reduced to 75%, the estimated uncomplicated cases and deaths averted over 10 years would decrease by 14% and 19%, respectively. CONCLUSIONS: The MVM can provide valuable information to assist decision-making by vaccine developers and policymakers, information which will be refined and strengthened as field studies progress allowing further validation of modeling assumptions.

Can sparsely and heterogeneously expressed proteins be detected using tissue microarrays? A simulation study of the hypoxia marker carbonic anhydrase IX (CA IX) in human soft tissue sarcoma.

Tissue microarrays (TMAs) are often used to evaluate the expression of biological markers across large patient populations. We investigated the number of core biopsies required to accurately classify soft tissue sarcomas with respect to their expression of carbonic anhydrase IX (CA IX), a potential prognostic marker with a sparse and heterogeneous expression pattern. Paraffin-embedded tissue sections from 47 high-grade soft tissue sarcomas had previously been immunostained for CA IX and quantified using image analysis. Sampling of core biopsies was computer simulated by analyzing 2 mm-diameter disc-shaped areas from these images. Core areas were scored as CA IX-positive if the number of CA IX-positive pixels exceeded a threshold value. Overall, 94% of the tumors were correctly classified as CA IX-positive (true-positive rate) if four biopsies at the quadrant centers of each of two sections per tumor were assessed for their CA IX expression with a sensitivity threshold of 0.2%. Similarly, 91% of the tumors were correctly classified as CA IX-positive when only three of the four biopsies per section were assessed. The corresponding false-positive rates were 13% and 11%, respectively. In contrast, sampling of four biopsies at random positions on each section with otherwise similar sampling criteria resulted in only 81% of the tumors being scored as CA IX-positive with a probability >0.80. In conclusion, soft tissue sarcomas can be accurately classified with respect to their expression of CA IX, a protein with sparse and heterogeneous expression, by systematic sampling of at least three 2mm-diameter core biopsy areas from distant locations within a section and from two different areas per tumor. This suggests that TMAs can be used to detect even heterogeneous and sparse markers, but the sampling strategy should be validated for the marker under investigation.

Alterations in DNA repair gene expression under hypoxia: elucidating the mechanisms of hypoxia-induced genetic instability.

Hypoxia is a common feature of solid tumors and is associated with genetic instability and tumor progression. It has been shown previously that alterations in the expression of DNA repair genes in response to hypoxic stress may account for a proportion of such genetic instability. Here, we demonstrate that the expression of RAD51, a critical mediator of homologous recombination (HR), is repressed by hypoxia in numerous cell lines derived from a wide range of tissues. Repression of this gene by hypoxia occurs in a cell cycle- and hypoxia-inducible factor (HIF)-independent manner, and decreased RAD51 expression was observed to persist during the post-hypoxic period. In addition, decreases in Rad51 expression were correlated with functional impairments in HR repair in hypoxic and post-hypoxic cells. Based on these data, we propose a novel mechanism of hypoxia-induced genetic instability via suppression of the HR pathway in cancer cells within the tumor microenvironment.

Down-regulation of Rad51 and decreased homologous recombination in hypoxic cancer cells.

There is an emerging concept that acquired genetic instability in cancer cells can arise from the dysregulation of critical DNA repair pathways due to cell stresses such as inflammation and hypoxia. Here we report that hypoxia specifically down-regulates the expression of RAD51, a key mediator of homologous recombination in mammalian cells. Decreased levels of Rad51 were observed in multiple cancer cell types during hypoxic exposure and were not associated with the cell cycle profile or with expression of hypoxia-inducible factor. Analyses of RAD51 gene promoter activity, as well as mRNA and protein stability, indicate that the hypoxia-mediated regulation of this gene occurs via transcriptional repression. Decreased expression of Rad51 was also observed to persist in posthypoxic cells for as long as 48 h following reoxygenation. Correspondingly, we found reduced levels of homologous recombination in both hypoxic and posthypoxic cells, suggesting that the hypoxia-associated reduction in Rad51 expression has functional consequences for DNA repair. In addition, hypoxia-mediated down-regulation of Rad51 was confirmed in vivo via immunofluorescent image analysis of experimental tumors in mice. Based on these findings, we propose a novel mechanism of genetic instability in the tumor microenvironment mediated by hypoxia-induced suppression of the homologous recombination pathway in cancer cells. The aberrant regulation of Rad51 expression may also create heterogeneity in the DNA damage response among cells within tumors, with implications for the response to cancer therapies.

Carbonic anhydrase IX as a marker for poor prognosis in soft tissue sarcoma.

PURPOSE: Hypoxia is associated with malignant progression and poor outcome in several human tumors, including soft tissue sarcoma. Recent studies have suggested that carbonic anhydrase (CA) IX is an intrinsic marker of hypoxia, and that CA IX correlates with poor prognosis in several types of carcinoma. The aim of this study was to quantify the extent of CA IX expression and to investigate whether CA IX is a marker for poor prognosis in soft tissue sarcoma patients at high risk of developing metastasis. EXPERIMENTAL DESIGN: Archival paraffin-embedded blocks were retrieved from 47 patients with deep, large, high-grade soft tissue sarcoma. Sections from two separate and representative tumor areas were immunostained for CA IX, and the CA IX-positive area fraction was quantified by image analysis, excluding areas of normal stroma and necrosis that were identified from serial H&E-stained sections. Patients were then subject to survival analysis. RESULTS: CA IX-positive area fractions of viable tumor tissue varied significantly between tumors (range, 0-0.23; median, 0.004), with positive membranous CA IX staining in 66% (31 of 47) of the tumors. Patients with CA IX-positive tumors had a significantly lower disease-specific and overall survival than patients with CA IX-negative tumors (P = 0.033 and P = 0.044, respectively). CONCLUSIONS: These data suggest that CA IX, a potential intrinsic marker of hypoxia, predicts for poor prognosis in patients with deep, large, high-grade soft tissue sarcoma. Larger studies are required to determine whether CA IX has independent prognostic value in this group of tumors.