Glioblastoma multiforme (GBM), the most common primary malignant brain tumors, resist conventional therapies, including surgery, radiation, and chemotherapy. As such, new strategies are being explored that include immune and gene therapies. The use of conventional replication-defective retroviral vectors in glioblastoma patients resulted in therapeutically inadequate levels of transduction. Replication-competent retroviral (RCR) vectors for gene transfer would be more efficient, since each successfully transduced tumor cell would itself become a virus producer cell (VPC) that would sustain further transduction events after initial administration. We previously demonstrated that intratumoral injection of RCR vector preparations achieved efficient tumor-restricted suicide gene transfer in glioma models. Prodrug administration significantly prolonged survival without causing systemic side effects. We improved the efficiency of this approach by engineering alloreactive cytotoxic T lymphocytes (alloCTL) to become RCR VPCs. We propose that alloCTL/VPC will act as motile cellular delivery platforms that will not only penetrate the tumor mass, but facilitate multifocal spread of the replicating vectors to infiltrating glioma cells. AlloCTL are activated against tumor host human leukocyte antigens, which are absent in normal CNS tissue but highly expressed by gliomas. They traffic through tumors and serve also as effector cells. The clinical feasibility of intratumoral alloCTL as an adoptive immunotherapy approach has been confirmed in a Phase I study. RCR vectors expressing GFP and pseudotyped with amphotropic MLV or Gibbon ape leukemia virus (GALV) envelope proteins were tested for their ability to transduce primary human alloCTL. Their conversion into VPCs was tested under various conditions, including viral precipitation with chondroitin sulfate, on fibronectin-coated plates, spinoculation, and coculture with VPCs. Precipitated virus supernatant transduced <20% of the alloCTL. However, alloCTL cocultured with human glioma cells producing RCR vectors resulted in simultaneous cellular activation and efficient viral transduction of >90% of the alloCTL in a dose-dependent manner. When the transduced alloCTL were placed into a culture with glioma cells to which the alloCTL were sensitized, or another glioma expressing 2 HLA antigens in common with the relevant target cells, highly efficient secondary horizontal transduction of the RCR vector from the alloCTL to the glioma cells was observed in a dose- and time-dependent manner. The results demonstrate that human alloCTL can be successfully converted into RCR VPCs, thus indicating the feasibility of combining adoptive immunotherapy with gene therapy.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]