Anti-gene padlocks eliminate Escherichia coli based on their genotype

Successful gene therapy requires targeting the vast majority of cancer cells

Suicide gene therapy using gene-directed enzyme prodrug therapy (GDEPT) is based on delivering a gene-encoded enzyme to cells that converts a nontoxic prodrug into its toxic metabolite. The bystander effect is thought to compensate for inefficiencies in delivery and expression because the produced toxic metabolite can spread to adjacent non-expressing cells.

The purpose of this study was to assess the significance of bystander effect in GDEPT over the long term in vivo.

We performed experiments using mixtures of yeast cytosine deaminase (yCD) expressing and empty vector (EV) containing cells. First, the bystander effect was assessed in various ratios of colon cancer cell lines RKO with yCD/EV in 2D and 3D culture. Next, tumors raised from RKO with yCD/EV in mice were treated with the prodrug 5-fluorocytosine (5-FC) for 42 days to assess bystander effect in vivo. Cell types constituting relapsed tumors were determined by 5-FC treatment and PCR.

We were able to demonstrate bystander effect in both 2D and 3D. In mice, tumors initially regressed, but they all eventually recurred including those produced from 80% yCD expressing cells. Cells explanted from the recurrent tumors demonstrated that suicide gene expressing cells had been selected against during in vivo treatment with 5-FC.

We conclude that gene therapy of malignant tumors in patients using the yCD/5-FC system will require targeting well over 80% of the malignant cells, and therefore will likely require improved bystander effect or repeated treatment.

Analysis of genes, transcripts, and proteins via DNA ligation

Analytical reactions in which short DNA strands are used in combination with DNA ligases have proven useful for measuring, decoding, and locating most classes of macromolecules. Given the need to accumulate large amounts of precise molecular information from biological systems in research and in diagnostics, ligation reactions will continue to offer valuable strategies for advanced analytical reactions. Here, we provide a basis for further development of methods by reviewing the history of analytical ligation reactions, discussing the properties of ligation reactions that render them suitable for engineering novel assays, describing a wide range of successful ligase-based assays, and briefly considering future directions.

Cellular reservoirs of HIV-1 and their role in viral persistence

A major obstacle in human immunodeficiency virus type 1 (HIV-1) eradication is the ability of the virus to remain latent in a subpopulation of the cells it infects. Latently infected cells can escape the viral immune response and persist for long periods of time, despite the presence of successful highly active antiretroviral therapy (HAART). Given the appropriate stimulus, latently infected cells can reactivate and start producing infectious virions. The susceptibility of these cell populations to HIV-1, their life span, their proliferative capacity, and their ability to periodically produce infectious virus subsequent to alterations in cellular physiology and/or immunologic controls are critical issues which determine the contribution of these cells to viral persistence. Memory CD4+ T cells due to the long life span, which may be several years, and their ability to reactivate upon encounter with their cognate antigen or other stimulation, are considered a critical reservoir for maintenance of latent HIV-1 proviral DNA. Cells of the monocyte-macrophage lineage, which originate in the bone marrow (BM), are of particular importance in HIV-1 persistence due to their ability to cross the blood-brain barrier (BBB) and spread HIV-1 infection in the immunoprivileged central nervous system (CNS). Hematopoietic progenitor cells (HPCs) are also a potential HIV-1 reservoir, as several studies have shown that CD34+ HPCs carrying proviral DNA can be found in vivo in a subpopulation of HIV-1-infected patients. The ability of HPCs to proliferate and potentially generate clonal populations of infected cells of the monocyte-macrophage lineage may be crucial in HIV-1 dissemination. The contribution of these and other cell populations in HIV-1 persistence, as well as the possible strategies to eliminate latently infected cells are critically examined in this review.