Helper virus induced T cell lymphoma in nonhuman primates after retroviral mediated gene transfer.

Abstract

Moloney Murine Leukemia Virus (MoMuLV) causes T cell neoplasms in rodents but is not known to be a pathogen in primates. The core protein and enzyme genes of the MoMuLV genome together with an amphotropic envelope gene are utilized to engineer the cell lines that generate retroviral vectors for use in current human gene therapy applications. We developed a producer clone that generates a very high concentration of retroviral vector particles to optimize conditions for gene insertion into pluripotent hematopoietic stem cells. This producer cell line also generates a much lower concentration of replication-competent virus that arose through recombination. Stem cells from rhesus monkeys were purified by immunoselection with an anti-CD34 antibody, incubated in vitro for 80-86 h in the presence of retroviral vector particles with accompanying replication-competent virus and used to reconstitute recipients whose bone marrow had been ablated by total body irradiation. The retroviral vector genome was detected in circulating cells of five of eight transplant recipients of CD34+ cells and in the circulating cells of two recipients of infected, unfractionated bone marrow mononuclear cells. Three recipients of CD34+ cells had a productive infection with replication-competent virus. Six or seven mo after transplantation, each of these animals developed a rapidly progressive T cell neoplasm involving the thymus, lymph nodes, liver, spleen, and bone marrow. Lymphoma cells contained 10-50 copies of the replication-competent virus, but lacked the retroviral vector genome. We conclude that replication-competent viruses arising from producer cells making retroviral vectors can be pathogenic in primates, which underscores the importance of carefully screening retroviral producer clones used in human trials to exclude contamination with replication-competent virus.

Replicating retroviral vectors mediating continuous production and secretion of therapeutic gene products from cancer cells

“…39,40 However, this oncogenic concern is mitigated by a number of considerations when contemplating the application of RCR vectors in anticancer gene therapy. First, MLV-derived RCR vectors possess the unique property of infecting solely mitotically active cells, and hence have natural selectivity for dividing tumorous or neovascular endothelial cells.…”

Retrovirus molecular conjugates: a versatile and efficient gene transfer vector system for primitive human hematopoietic progenitor cells

“…It poses a significant safety risk as it can promote malignant transformation of lymphoid tissues as previously reported in non-human primate trials. 35 Since ecotropic virus cannot infect human cells, occurrence of an event leading to the formation of replication competent ecotropic virus in humans would be theoretically a self-limited problem. Since the conjugation process does not alter the virus genetically, its progeny would remain of ecotropic type.…”

The Flipside of the Power of Engineered T Cells: Observed and Potential Toxicities of Genetically Modified T Cells as Therapy

“…Current retroviral and lentiviral delivery systems are designed to only transduce cells, but early-generation retroviruses were susceptible to helper virus contamination, allowing the production of infectious virions and leading to T cell lymphomas in animal models. 46 In more than 500 patient-years of follow-up, no replication competent retrovirus has been identified. 47 Early replication-competent lentivirus could be generated in vitro by recombination of vector plasmids or in vivo by mobilization of vector DNA in the presence of other infectious lentivirus such as HIV.…”