Ets1 Controls the Development of B Cell Autoimmune Responses in a Cell-Intrinsic Manner.

Ets1 is emerging as a key transcription factor that is required to prevent autoimmunity in mice and humans. Ets1 is expressed in both B and T cells, and mice lacking Ets1 are characterized by excess B and T cell activation, leading to enhanced formation of Ab-secreting cells and high titers of autoantibodies. In humans, genome-wide association studies have detected associations of single nucleotide polymorphisms in the human ETS1 gene with autoimmune diseases, including lupus. An increased fraction of CD4+ T cells from Ets1-/- mice have an activated effector-memory phenotype, and there are aberrations in differentiation that contribute to the autoimmune phenotype. In vitro studies of B cells suggest that Ets1 may have B cell-intrinsic effects as well. To confirm B cell-intrinsic roles for Ets1, we crossed CD19-Cre mice to mice with a floxed allele of Ets1. Mice with a B cell-specific deletion of Ets1 show increases in B cell activation, numbers of Ab-secreting cells, and levels of autoantibodies, despite the fact that T cells are normal. However, when compared with conventional Ets1 knockout mice, mice with B cell-specific loss of Ets1 have a significantly milder phenotype. These results demonstrate that Ets1 is required in B cells to prevent autoimmune responses but that loss of Ets1 activity in other cell types is required for maximal autoimmune phenotypes.

Cidofovir Diphosphate Inhibits Adenovirus 5 DNA Polymerase via both Nonobligate Chain Termination and Direct Inhibition, and Polymerase Mutations Confer Cidofovir Resistance on Intact Virus.

Human adenovirus (AdV) can cause fatal disease in immune-suppressed individuals, but treatment options are limited, in part because the antiviral cytidine analog cidofovir (CDV) is nephrotoxic. The investigational agent brincidofovir (BCV) is orally bioavailable, nonnephrotoxic, and generates the same active metabolite, cidofovir diphosphate (CDVpp). However, its mechanism of action against AdV is poorly understood. Therefore, we have examined the effect of CDVpp on DNA synthesis by a purified adenovirus 5 (AdV5) DNA polymerase (Pol). CDVpp was incorporated into nascent DNA strands and promoted a nonobligate form of chain termination (i.e., AdV5 Pol can extend, albeit inefficiently, a DNA chain even after the incorporation of a first CDVpp molecule). Moreover, unlike a conventional mismatched base pair, misincorporated CDVpp was not readily excised by the AdV5 Pol. At elevated concentrations, CDVpp inhibited AdV5 Pol in a manner consistent with both chain termination and direct inhibition of Pol activity. Finally, a recombinant AdV5 was constructed, containing Pol mutations (V303I and T87I) that were selected following an extended passage of wild-type AdV5 in the presence of BCV. This virus had a 2.1-fold elevated 50% effective concentration (EC50) for BCV and a 1.9-fold increased EC50 for CDV; thus, these results confirmed that viral resistance to BCV and CDV can be attributed to mutations in the viral Pol. These findings show that the anti-AdV5 activity of CDV and BCV is mediated through the viral DNA Pol and that their antiviral activity may occur via both (nonobligate) chain termination and (at high concentration) direct inhibition of AdV5 Pol activity.