Stem cell transplantation in the context of HIV--how can we cure HIV infection?

Modulation of apoptosis and viral latency - an axis to be well understood for successful cure of human immunodeficiency virus

Human immunodeficiency virus (HIV) is the causative agent of the deadly disease AIDS, which is characterized by the progressive decline of CD4(+)T-cells. HIV-1-encoded proteins such as envelope gp120 (glycoprotein gp120), Tat (trans-activator of transcription), Nef (negative regulatory factor), Vpr (viral protein R), Vpu (viral protein unique) and protease are known to be effective in modulating host cell signalling pathways that lead to an alteration in apoptosis of both HIV-infected and uninfected bystander cells. Depending on the stage of the virus life cycle and host cell type, these viral proteins act as mediators of pro- or anti-apoptotic signals. HIV latency in viral reservoirs is a persistent phenomenon that has remained beyond the control of the human immune system. To cure HIV infections completely, it is crucial to reactivate latent HIV from cellular pools and to drive these apoptosis-resistant cells towards death. Several previous studies have reported the role of HIV-encoded proteins in apoptosis modulation, but the molecular basis for apoptosis evasion of some chronically HIV-infected cells and reactivated latently HIV-infected cells still needs to be elucidated. The current review summarizes our present understanding of apoptosis modulation in HIV-infected cells, uninfected bystander cells and latently infected cells, with a focus on highlighting strategies to activate the apoptotic pathway to kill latently infected cells.

Safety and efficacy of a tCD25 preselective combination anti-HIV lentiviral vector in human hematopoietic stem and progenitor cells

The successful suppression of human immunodeficiency virus (HIV) in the "Berlin Patient" has highlighted the ability of HIV-resistant hematopoietic stem cells to offer a potential functional cure for HIV-infected patients. HIV stem cell gene therapy can mimic this result by genetically modifying a patient's own cells with anti-HIV genes. Previous attempts of HIV gene therapy have been hampered by a low percentage of transplanted HIV-resistant cells which has led to minimal clinical efficacy. In our current study, we have evaluated the in vitro and in vivo safety and efficacy of a truncated/mutated form of human CD25 preselective anti-HIV lentiviral vector in human hematopoietic stem cells. This preselective vector allows us to purify vector-transduced cells prior to transplantation so an increased percentage of gene-modified cells can be delivered. Here, we demonstrate the safety of this strategy with successful engraftment and multilineage hematopoiesis of transduced cells in a humanized NOD-RAG1-/-IL-2rγ-/- knockout mouse model. Efficacy was also demonstrated with significant protection from HIV-1 infection including maintenance of human CD4+ cell levels and a decrease in HIV-1 plasma viremia. Collectively, these results establish the utility of this HIV stem cell gene therapy strategy and bring it closer to providing a functional cure for HIV-infected patients.

A roadmap toward clinical translation of genetically-modified stem cells for treatment of HIV

During the past decade, successful gene therapies for immunodeficiencies were finally brought to the clinic. This was accomplished through new gene therapy vectors and improved procedures for genetic modification of autologous hematopoietic stem cells. For HIV, autologous hematopoietic stem cell (HSC) gene therapy with 'anti-HIV genes' promises a functional cure for the disease. However, to develop such a therapy and translate it into a clinical application is rather challenging. The risks and benefits of such a therapy have to be understood, and regulatory hurdles need to be overcome. In this joint paper by academic researchers and regulators, we are, therefore, outlining a high level roadmap for the early stage development of HSC gene therapy as a potential functional cure for HIV.

Optimized lentiviral vectors for HIV gene therapy: multiplexed expression of small RNAs and inclusion of MGMT(P140K) drug resistance gene

Gene therapy with hematopoietic stem and progenitor cells is a promising approach to engineering immunity to human immunodeficiency virus (HIV) that may lead to a functional cure for acquired immunodeficiency syndrome (AIDS). In support of this approach, we created lentiviral vectors with an engineered polycistronic platform derived from the endogenous MCM7 gene to express a diverse set of small antiviral RNAs and a drug resistance MGMT(P140K) marker. Multiple strategies for simultaneous expression of up to five RNA transgenes were tested. The placement and orientation of each transgene and its promoter were important determinants for optimal gene expression. Antiviral RNA expression from the MCM7 platform with a U1 promoter was sufficient to provide protection from R5-tropic HIV in macrophages and resulted in reduced hematopoietic toxicity compared with constructs expressing RNA from independent RNA polymerase III promoters. The addition of an HIV entry inhibitor and nucleolar TAR RNA decoy did not enhance antiviral potency over constructs that targeted only viral RNA transcripts. We also demonstrated selective enrichment of gene-modified cells in vivo using a humanized mouse model. The use of these less toxic, potent anti-HIV vectors expressing a drug selection marker is likely to enhance the in vivo efficacy of our stem cell gene therapy approach in treating HIV/AIDS.