Coexpression of the uracil phosphoribosyltransferase gene with a chimeric human nerve growth factor receptor/cytosine deaminase fusion gene, using a single retroviral vector, augments cytotoxicity of transduced human T cells exposed to 5-fluorocytosine.

Donor T lymphocytes genetically engineered to express a "suicide gene" to facilitate negative selection represent a promising strategy for the management of graft-versus-host disease occurring after allogeneic hematopoietic cell transplantation (HCT). For this purpose, the herpes simplex virus thymidine kinase (HSV-tk) gene, although well studied, has limitations. Cytosine deaminase (CD), an alternative gene for negative selection, converts 5-fluorocytosine (5-FC) to the toxic metabolite 5-fluorouracil (5-FU). Sensitivity of cells to 5-FU can be further increased by expression of uracil phosphoribosyltransferase (UPRT), which catalyzes the conversion of 5-FU to 5-fluorouridine monophosphate. By using a chimeric gene (NG/CD) expressing the truncated human nerve growth factor receptor (NGFR) for positive selection fused to the Saccharomyces cerevisiae CD gene, we investigated strategies to achieve optimal T cell eradication by CD and UPRT expression, utilizing a single retroviral vector. Three vector strategies were compared on the basis of NGFR expression by flow cytometry, western analysis, and enzymatic activity. A construct (NG/CDiU) expressing UPRT and NG/CD, using a bicistronic message, provided the greatest UPRT activity and killing, reducing the lethal dose of 5-FC sufficient to eradicate 90% of cells from 38.7 microg/ml (300 microM) (NG/CD expression alone) to 0.13 microg/ml (1 microM). This approach provides an effective alternative to the HSV-tk system for eradication of donor T lymphocytes after allogeneic HCT.

Purification of Pseudomonas aeruginosa exoenzyme S.

Pseudomonas aeruginosa produces two distinct ADP-ribosyl transferases, exotoxin A and exoenzyme S, which differ in a number of properties including substrate specificity. Exoenzyme S was purified from culture supernatants of P. aeruginosa DG1. The procedure for purification consists of four major steps: ammonium sulfate precipitation, anion-exchange chromatography on DEAE-Sephacel, acetone precipitation in the presence of 1 M NaCl, and G-100 Superfine gel filtration chromatography. Exoenzyme S was monitored during purification by an assay for ADP-ribosyl transferase activity, mouse toxicity, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified material exhibited ADP-ribosyl transferase activity, reacted with monoclonal antibodies to exoenzyme S, and was toxic to mice and a variety of tissue culture cell lines.