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Human immunodeficiency virus type 1 (HIV-1) evolves in vivo under selective pressure from CD8؉ Tlymphocyte (CTL) responses, which are in turn determined by host and viral genetic factors, such as restricting major histocompatibility complex molecules and the available viral epitope sequences. However, CTL are derived stochastically through the random gene rearrangements to produce T-cell receptors (TCR), and the relative impact of genetic versus stochastic processes on CTL targeting of HIV and immune-driven viral evolution is unclear. Here we evaluate identical twins infected with HIV-1 as neonates from a common blood transfusion, with subsequently similar environmental exposures, thereby allowing controlled comparisons of CTL targeting and viral evolution. Seventeen years after infection, their CTL targeting of HIV-1 was remarkably similar. In contrast, their overall TCR profiles were highly dissimilar, and a dominant epitope was recognized by distinctly different TCR in each twin. Furthermore, their viral epitopes had diverged, and there was ongoing viral phylogenetic divergence between the twins between 12 and 17 years after infection. These results indicate that while CTL targeting is predominately genetically determined, stochastic influences render the interaction of HIV-1 and host immunity, and therefore viral escape and CTL efficacy, unpredictable.

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Vascular calcification impairs vessel compliance and increases the risk of cardiovascular events. We found previously that liver X receptor agonists, which regulate intracellular cholesterol homeostasis, augment PKA agonist-or high phosphateinduced osteogenic differentiation of vascular smooth muscle cells. Because cholesterol is an integral component of the matrix vesicles that nucleate calcium mineral, we examined the role of cellular cholesterol metabolism in vascular cell mineralization. The results showed that vascular smooth muscle cells isolated from LDL receptor null (Ldlr ؊/؊ ) mice, which have impaired cholesterol uptake, had lower levels of intracellular cholesterol and less osteogenic differentiation, as indicated by alkaline phosphatase activity and matrix mineralization, compared with WT cells. PKA activation with forskolin acutely induced genes that promote cholesterol uptake (LDL receptor) and biosynthesis (HMG-CoA reductase). In WT cells, inhibition of cholesterol uptake by lipoprotein-deficient serum attenuated forskolin-induced matrix mineralization, which was partially reversed by the addition of cell-permeable cholesterol. Prolonged activation of both uptake and biosynthesis pathways by cotreatment with a liver X receptor agonist further augmented forskolin-induced matrix mineralization. Inhibition of either cholesterol uptake, using Ldlr ؊/؊ cells, or of cholesterol biosynthesis, using mevastatin-treated WT cells, failed to inhibit matrix mineralization due to up-regulation of the respective compensatory pathway. Inhibition of both pathways simultaneously using mevastatintreated Ldlr ؊/؊ cells did inhibit forskolin-induced matrix mineralization. Altogether, the results suggest that up-regulation of cholesterol metabolism is essential for matrix mineralization by vascular cells.Vascular calcification is frequently found in advanced atherosclerotic lesions and is an independent predictor of cardiovascular morbidity and mortality in patients with chronic kidney disease (1-3). Long considered to be a passive process, there now exists much evidence to suggest that vascular calcification is an active cell-mediated phenomenon that is highly regulated through complex mechanisms under active investigation (4). In vitro and in vivo studies have implicated numerous positive and negative regulatory factors in the pathogenesis of calcification (5-8).A common complication of chronic kidney disease is hyperparathyroidism. Interestingly, parathyroid hormone, an activator of the PKA pathway, has been shown to have a stimulatory role in vascular calcification both in vitro and in vivo. When parathyroid hormone levels are continuously elevated, they induce vascular calcification in rat models, irrespective of renal function (9). Additionally, parathyroid hormone-related protein, also a PKA activator, has been found in calcified atherosclerotic lesions (10). Accordingly, we and others have demonstrated previously that mineralization of vascular smooth muscle cells (VSMCs) 3 is induced by PKA agonists in vitro ...