Molecular Evaluation of Biopsy and Autopsy Specimens from Patients Receiving in Vivo Retroviral Gene Therapy

Abstract

We used the polymerase chain reaction (PCR) to assay for the presence of retroviral vector and replication-competent retrovirus (RCR) in autopsy and biopsy specimens from patients who received inoculations of retroviral vector producer cells (VPCs) into brain tumors or apparently normal tissues surrounding resected tumors. The PCR assays were capable of detecting 1 or more proviral copies of vector or RCR in 500,000 cells. Of 113 patients treated in clinical trials between 1994 and 1997, autopsy specimens were available from 32 patients. Brain tumor biopsies were also available from 24 patients. A total of 346 specimens was analyzed. Vector DNA was detected in 55% of tumor samples and 22% of brain samples obtained from resection margins. In contrast, most of the nonbrain tissues were negative for vector DNA; only low levels (<0.03%) of vector sequence were detected in 6 of 240 (2.5%) nonbrain tissues. Vector DNA was not detected in gonadal tissues from 12 men and 10 women. More importantly, RCR was not detected in any of the 134 biopsy and autopsy tissues tested, including all brain tumor, brain, and gonadal specimens. These results comprise the largest data set on molecular analysis of autopsy specimens from patients receiving retroviral gene therapy and indicate that distribution of retroviral vectors following injection of high doses of VPCs is limited to the site of inoculation.

Immune response induced by retrovirus-mediated HSV-tk/GCV pharmacogene therapy in patients with glioblastoma multiforme

“…[31][32][33] with recurrent GBM caused a strong systemic cellular immune response with major intratumoral infiltrates of immunocompetent cells. 18 In tumor specimens taken a week after VPC injection, strong macrophage infiltration and perivascular lymphocytic accumulation were observed.…”

Distribution of retroviral vectors and vector producer cells using two routes of administration in rats

“…8 Vector sequences have also been detected in autopsy specimens from brain tissue, liver, kidney and lung specimens. 9 Importantly, in these studies, vector sequences have not been detected in any gonadal specimens from 22 patients (10 female; 12 male) evaluated to date. While these clinical data are reassuring, the limited sample size does not provide sufficient information for determining the potential risk of vector distribution to unintended tissues and organs.…”

Selective killing of cancer cells based on translational control of a suicide gene

“…Indeed, it has been shown that even when therapeutic vectors are delivered locally to a primary tumor, systemic effects still occur, indicating that the vector has become bloodborne. 32,33 One approach to circumvent this problem is through the use of elements allowing specific transcriptional regulation of the vector, e.g., the use of tissuespecific promoters 3 and inducible promoters. 4 Whereas these approaches are very promising, they require specific knowledge of the cancer cells, and are not applicable to most situations.…”