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Background: Soluble mesothelin-related peptides (SMRP) have been reported to be potential biomarkers for malignant pleural mesothelioma (MPM). We report analytical and preliminary clinical studies of MESOMARK TM , a quantitative assay for SMRP. Methods: The MESOMARK assay is a 2-step immunoenzymatic assay in an ELISA format with a 6-point calibration curve (0 -32 nmol/L). We assessed analytical imprecision, analyte stability, and analytical interferences. We measured SMRP by this assay in 409 apparently healthy individuals (reference interval study), 177 patients with nonmalignant conditions, and 500 cancer patients, including 88 with MPM. Results: The limit of detection was 0.16 nmol/L. At 2-19 nmol/L, intraassay imprecision (CV) was 1.1%-5.3%, and total imprecision was 4.0%-11.0%. The mean dilution recovery for 5 samples was 109% (range, 99%-113%). No interference was seen from added bilirubin (200 mg/L), hemoglobin (500 mg/L), triglycerides (30 g/L), chemotherapeutic agents, or other tested substances. Recombinant mesothelin was stable in serum upon freeze/thaw at ؊70°C and upon storage for at least 7 days at 2-8°C. The 99 th percentile of the reference group was 1.5 nmol/L [95% confidence interval (CI), 1.2-1.6 nmol/L; n ‫؍‬ 409], and mean SMRP was significantly higher in sera from patients with MPM (7.5 nmol/L; 95% CI, 2.8 -12.1 nmol/L; n ‫؍‬ 88). SMRP was increased in 52% and 5% of MPM patients and asbestosexposed individuals, respectively. Concentrations in other nonmalignant and malignant conditions were similar to those in healthy controls.

The mesothelin family comprises (at least) three variants and includes the precursor for megakaryocyte potentiating factor (MPF). Assaying soluble mesothelin-related protein (SMRP) molecules in serum and other body fluids from patients with certain cancers can provide diagnostically useful information. We have constructed fusion proteins of mesothelin variants 1, 2, and 3, made monoclonal antibodies, and investigated the binding specificity of these and three previously generated monoclonal antibodies to each of the three mesothelin variants. According to flow cytometry, the molecule that is most frequently expressed at the surface of cells from ovarian carcinomas and certain other tumors is mesothelin variant 1. Similarly, SMRP released into ascites from a patient with ovarian carcinoma was shown to have a molecular weight of f40 kDa and, according to sequencing, to be variant 1. A published sandwich ELISA was shown to detect variants 1 and 3 and to be much more sensitive than a newly constructed ELISA, which detects only variant 3, the former being positive in 28 of 41 (68%) sera from patients with ovarian cancer as compared with 6 of 41 sera (15%). A standard curve was constructed to measure SMRP with a limit of detection of 200 pg/mL to facilitate future quantitative studies. (Cancer Epidemiol Biomarkers Prev 2006;15(5):1014 -20)

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Plasmids represent a powerful tool to rapidly introduce genes into bacteria and help them reach high expression levels. In vaccine development, with live vaccine vectors, this allows greater flexibility and the ability to induce larger antigen amounts through multiple gene copies. However, plasmid retention often requires antibiotic resistance markers, the presence of which has been discouraged in clinical applications by the Food and Drug Administration. Therefore, we developed a Listeria monocytogenes-Escherichia coli shuttle plasmid that is retained by complementation of D-alanine racemase-deficient mutant strains both in vitro and in vivo. Our technology potentially allows the production of antibiotic resistance marker-free DNA vaccines as well as bacterial vaccine vectors devoid of engineered antibiotic resistances. As a proof of concept, we applied the D-alanine racemase complementation system to our Listeria cancer vaccine platform. With a transplantable tumor model, we compared the efficacy of the new Listeria vector to that of an established vector containing a conventional plasmid carrying a tumor-specific antigen. Both vaccine vector systems resulted in long-term regression of established tumors, with no significant difference between them. Thus, the Listeria vaccine vector presented here potentially complies with Food and Drug Administration regulations and could be developed further for clinical use.The revolution in genetic engineering over the last two decades has allowed the development of recombinant DNA vaccines and bacterial antigen delivery systems, opening up new horizons in immunization against infectious diseases and even cancer. Recombinant antigens can be presented to the immune system after immunization with DNA directly or with bacterial vectors expressing vaccine antigens. Both approaches have the advantages of potentially low per-dose costs, ease of distribution and storage, and rational vaccine design. However, the required molecular engineering techniques often rely on the use of antibiotic resistance markers for retention of the recombinant gene. For example, the production of plasmid-based DNA vaccines in Escherichia coli usually relies on kanamycin resistance, which ensures plasmid stability during culture in the presence of the antibiotic. Bacterial delivery systems carrying plasmids also contained antibiotic resistance markers for in vitro selection in addition to in vivo retention systems (7,(11)(12)(13)26). Although the use of plasmids could sometimes be circumvented by integrating the recombinant gene into the bacterial genome by homologous recombination, this process is tedious and time-consuming, resulting in reduced vaccine flexibility.A recent accelerated chromosomal integration technology developed for Listeria spp. relied again on the use of antibiotic markers (20). The Food and Drug Administration, however, discouraged the in vivo use of genes transferring antibiotic resistance in several communiqués because of the associated potential risk of environmental spread (9...