RNA-Based Gene Therapy for HIV with Lentiviral Vector–Modified CD34+ Cells in Patients Undergoing Transplantation for AIDS-Related Lymphoma

Transfected stem cells transplanted into patients with HIV infection resulted in sustained RNA expression of introduced genes in blood cells for up to 2 years. Steps Toward a Stable Source of Therapeutic RNA Gene therapy in humans has not been easy to implement. Genes inserted into complex human cells have triggered serious unintended consequences and have often proven to be short-lived. Yet perseverance may be paying off. DiGiusto et al. report a step toward workable gene therapy in the form of stable expression of a lentiviral vector encoding anti-HIV RNAs in blood stem cells transplanted into AIDS patients. None of these patients is cured, but the vector seems to stably express the potentially therapeutic RNAs. Putting exogenous gene sequences into humans is risky, and review boards are appropriately conservative. But DiGiusto et al. took advantage of a clinical situation to design a trial that minimized extra risk to the subjects. Blood cancer (lymphoma) is common in AIDS patients, and they are often treated by ablation of their diseased bone marrow with chemotherapy followed by a transplant with their own previously saved blood stem cells. Because these patients were being transplanted with their own blood cells anyway, the authors were able to get permission to transfect a few of the blood cells of four patients with a vector carrying anti-HIV entities and reinfuse them along with the normally transplanted cells. The vector made RNAs that could counteract viral replication in several ways: inhibition of viral entry (with a CCR5 ribozyme), inhibition of RNA transport [by a small interfering RNA (siRNA) to tat/rev], and inhibition of viral transcription initiation with a decoy RNA. The good news was that the patients showed no signs of toxicity besides problems usually associated with transplantation and that blood cells from all four patients contained signs of the transplanted genes, with the amounts increasing in two of the patients after 18 months. Although the fraction of cells containing the genes was <0.2%, this was not too different from the fraction of transfected cells that was infused into the patients. The three anti-HIV RNAs could also be detected as long as 1 year after the initial infusion, and examination of T cells, monocytes, and B cells from one patient confirmed the presence of vector in these three cell types. These cells that survived for long periods of time in patients, although too scarce to cure or even improve their HIV infections, nevertheless offer lessons for future applications of gene therapy. We know that this procedure is seemingly safe and that cells given new genetic material via a lentiviral vector outside the patient can survive once reimplanted. Continued perseverance can only bring us closer to realizing the potential of this promising therapy. AIDS patients who develop lymphoma are often treated with transplanted hematopoietic progenitor cells. As a first step in developing a hematopoietic cell–based gene therapy treatment, four patients undergoing treatment with these transplanted cells were also given gene-modified peripheral blood–derived (CD34+) hematopoietic progenitor cells expressing three RNA-based anti-HIV moieties (tat/rev short hairpin RNA, TAR decoy, and CCR5 ribozyme). In vitro analysis of these gene-modified cells showed no differences in their hematopoietic potential compared with nontransduced cells. In vitro estimates of successful expression of the anti-HIV moieties were initially as high as 22% but declined to ~1% over 4 weeks of culture. Ethical study design required that patients be transplanted with both gene-modified and unmanipulated hematopoietic progenitor cells obtained from the patient by apheresis. Transfected cells were successfully engrafted in all four infused patients by day 11, and there were no unexpected infusion-related toxicities. Persistent vector expression in multiple cell lineages was observed at low levels for up to 24 months, as was expression of the introduced small interfering RNA and ribozyme. Therefore, we have demonstrated stable vector expression in human blood cells after transplantation of autologous gene-modified hematopoietic progenitor cells. These results support the development of an RNA-based cell therapy platform for HIV.