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We have used a T-cell receptor transgenic mouse model to study the role of antigen in the changes that occur as T cells age. We find that the characteristic shift in the CD4 population to a predominance of memory phenotype T cells which accompanies aging in non-transgenic mice does not occur, suggesting that this shift is a result of antigenic stimulation. Thus at least one component of aging must be antigen dependent. When responses of naive CD4 T cells from aged and young mice are directly compared in vitro, the former are relatively deficient in their ability to produce IL-2 and IL-3, they express altered levels of P-glycoprotein and they proliferate less well in the absence of exogenous cytokines. When the ability of both naive populations to generate effectors is compared, the number of effectors generated from aged naive cells is much reduced and the effectors generated express lower levels of IL-2R alpha and produce reduced levels of cytokines. Importantly, addition of IL-2 restores proliferation of aged naive T cells, restores efficient effector generation and results in effectors seemingly indistinguishable from those derived from young CD4 cells. Similar phenotypic and functional changes seen with aging are also found in T-cell populations from IL-2 and IL-2R alpha knockout mice. Thus the loss of optimal IL-2 production may participate in the aging process and may represent the main antigen-independent defect in the CD4 T-cell population.

Using transgenic mice that replicate the hepatitis B virus (HBV) genome, we recently demonstrated that class I-restricted, hepatitis B surface antigen-specific cytotoxic T lymphocytes (CTLs) can noncytolytically eliminate HBV pregenomic and envelope RNA transcripts from the hepatocyte. We now demonstrate that the steady-state content of these viral transcripts is profoundly reduced in the nucleus and cytoplasm of CTL-activated hepatocytes, but their transcription rates are only slightly reduced. Additionally, we demonstrate that transcripts covering the HBV X coding region are resistant to downregulation by the CTL. These results imply the existence of CTL-inducible hepatocellular factors that interact with a discrete element(s) between nucleotides 3157 and 1239 within the viral pregenomic and envelope transcripts and mediate their degradation, thus converting the hepatocyte from a passive victim to an active participant in the host response to HBV infection.Hepatitis B virus (HBV) infection causes acute and chronic hepatitis and hepatocellular carcinoma. Clearance of HBV is thought to be mediated by the destruction of infected cells by a major histocompatibility complex class I-restricted cytotoxic T lymphocyte (CTL) response to HBV-encoded antigens (1). Using HBV transgenic mice, we have recently shown that the cytodestructive properties of the CTL response may not be the only mechanism for HBV clearance from the liver. In particular, we have shown that HBV envelope transcripts are specifically degraded in the cytoplasm by a posttranscriptional mechanism when the hepatocytes are activated by the administration or activation of tumor necrosis factor a (TNF-a) (2). We have also shown that injection of hepatitis B surface antigen (HBsAg)-specific CTLs into HBV transgenic mice causes a much more profound reduction in hepatocellular HBV gene expression than TNF-a (3). Furthermore, we have demonstrated that this effect is noncytolytic and that it is mediated by interferon 'y (IFN--y) as well as by TNF-a, both of which are secreted by the CTLs after antigen activation (3).Recently, we have produced transgenic mouse lineages that express high levels of the HBV 3.5-kb pregenomic RNA as well as HBV envelope transcripts. These animals replicate the HBV genome in the liver and secrete HBV virions into the blood (4). Administration of HBsAg-specific CTLs into these mice causes a profound reduction of all of these HBV products in the liver and serum by a process that is inhibitable by the prior administration of antibodies to IFN-,y and TNF-a (L.G.G. and F.V.C., unpublished results). This suggests that the CTLs deliver one or more cytokine-mediated signals to the hepatocyte that induce or activate specific cellular gene products that either inhibit the synthesis, destabilize, or actively degrade these viral gene products, including the viral mRNA, thereby precluding viral replication.We now report that the HBV pregenomic and envelope RNAs are profoundly reduced in the nucleus, as well as the The publication costs of...

Replication-deficient lentiviral vectors (LV) have been shown to enable the stable genetic modification of multiple cell types in vivo. We demonstrate here that vascular and hepatic delivery of a third-generation HIV-derived lentiviral vector encoding human Factor IX (LV-hFIX) produced potentially therapeutic serum levels of hFIX protein with no vector-mediated local or systemic toxicity of adult mice. Portal vein administration produced the highest serum levels of hFIX and demonstrated proportionally higher levels of gene transfer to the liver with up to 4% of hepatocytes expressing hFIX. Vascular delivery of a lentiviral vector encoding GFP resulted in genetic modification of up to 12% of liver cells. Cell proliferation was not required for hepatocyte transduction with either vector. Serum hFIX levels reached 4% of normal levels following vascular LV-mediated hFIX gene transfer and remained stable for months following vector administration.

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