A simplified general method for determination of recombinant retrovirus titers

Systematic comparison of a color reporter gene and drug resistance genes for the determination of retroviral titers

Retroviral vectors usually contain drug resistance genes, which are used to select for infected cells and to determine the viral titers. The viral titer is referred to as colony-forming units (CFUs). Color reporter genes, such as the lacZ gene and the green fluorescent protein gene (gfp), have been widely used as markers in retroviral vectors. In this report, a simple and rapid method for the determination of retroviral titers has been developed. The number of viral particles capable of forming individual green cells per unit volume is defined as marker-forming units (MFUs). The MFUs determined by using gfp as a marker were found to be proportional to the CFUs obtained by using drug selection for five different drug resistance genes. In addition, after adjusting the time factor, the MFUs are higher than CFUs in viruses released from 30 stable helper cell lines. The lower titers determined by CFUs are likely due to the toxicity on transduced cells.

Effects of an internal transcription unit and its orientation on retrovirus titre and expression

Using the retroviral vector pMsp, constructs were produced with different coding sequences under the control of the Herpes simplex virus type 1 (HSV) thymidine kinase (tk) promoter, with the internal coding sequence in the same or reverse orientations with respect to long terminal repeat (LTR)-driven transcription and with or without an internal tk polyadenylation (polyA) signal. Following introduction of these constructs into ecotropic or amphotropic packaging cell lines by transfection or infection, it was found that, most consistently, those constructs in which the internal coding sequence/polyA signal component was inserted in the same orientation as LTR-driven transcription produced lower titres of virus than those in which this component was inserted in the reverse orientation. Also, in a construct containing a coding sequence in the same orientation as LTR-driven transcription, but lacking an internal polyA signal, virus titre was much greater than in the corresponding construct possessing the internal polyA signal. Additionally, although functional assays have previously demonstrated expression of the inserted sequences, transcription from the internal tk promoter was inefficient in all these constructs.

Infectious retrovirus is inactivated by serum but not by cerebrospinal fluid or fluid from tumor bed in patients with malignant glioma

Intravenous gene transfer using recombinant retroviruses tends to suffer from a low infectious viral titer when conducted in vivo. This is, in part, caused by complement-mediated proteolytic inactivation of the retrovirus in human serum. However, if the retroviruses were directly injected into the brain, they might not be inactivated. Supernatant from amphotropic retrovirus-producing cells harboring the BAG vectors was incubated with sera or cerebrospinal fluid (CSF) of patients with gliomas or unrelated disorders. The retroviruses were severely inactivated in sera. However, no such inactivation was noted in CSF or fluid from the tumor bed of glioma patients. These data suggest that gene transfer using recombinant retroviruses could be done into the cavity after removal of the tumor in glioma patients.