Adenovirus type 2 polypeptide synthesis in arginine-deprived cells

Production and formulation of adenovirus vectors

Adenovirus vectors have attracted considerable interest over the past decade, with ongoing clinical development programs for applications ranging from replacement therapy for protein deficiencies to cancer therapeutics to prophylactic vaccines. Consequently, considerable product, process, analytical, and formulation development has been undertaken to support these programs. For example, "gutless" vectors have been developed in order to improve gene transfer capacity and durability of expression; new cell lines have been developed to minimize recombination events; production conditions have been optimized to improve volumetric productivities; analytical techniques and scaleable purification processes have advanced towards the goal of purified adenovirus becoming a "well-characterized biological"; and liquid formulations have been developed which maintain virus infectivity at 2-8 degrees C for over 18 months. These and other advances in the production of adenovirus vectors are discussed in detail in this review. In addition, the needs for the next decade are highlighted.

Inhibition of lytic infection of pseudorabies virus by arginine depletion

Pseudorabies virus (PRV) is a member of Alphahepesviruses; it is an enveloped virus with a double-stranded DNA genome. Polyamines (such as spermine and spermidine) are ubiquitous in animal cells and participate in cellular proliferation and differentiation. Previous results of our laboratory showed that the PRV can accomplish lytic infection either in the presence of exogenous spermine (or spermidine) or depletion of cellular polyamines. The amino acid arginine is a precursor of polyamine biosynthesis. In this work, we investigated the role of arginine in PRV infection. It was found that the plaque formation of PRV was inhibited by arginase (enzyme catalyzing the conversion of arginine into ornithine and urea) treatment whereas this inhibition can be reversed by exogenous arginine, suggesting that arginine is essential for PRV proliferation. Western blotting was conducted to study the effect of arginine depletion on the levels of structural proteins of PRV in virus-infected cells. Four PRV structural proteins (gB, gE, UL47, and UL48) were chosen for examination, and results revealed that the levels of viral proteins were obviously reduced in long time arginase treatment. However, the overall protein synthesis machinery was apparently not influenced by arginase treatment either in mock or PRV-infected cells. Analyzing with native gel, we found that arginase treatment affected the mobility of PRV structural proteins, suggesting the conformational change of viral proteins by arginine depletion. Heat shock proteins, acting as molecular chaperons, participate in protein folding and translocation. Our results demonstrated that long time arginase treatment could reduce the expression of cellular heat shock proteins 70 (hsc70 and hsp70), and transcriptional suppression of heat shock protein 70 gene promoter was one of the mechanisms involved in this reduced expression.

Production of adenovirus vector for gene therapy

The field of gene therapy is rapidly expanding with a major focus on the treatment of cancer. Replication-defective adenoviruses are vectors of choice for delivering corrective genes into human cells. Major efforts are directed to design new generations of adenoviral vectors that feature reduced immunogenicity and improved targeting ability. However, the production of adenoviral vectors for gene therapy applications faces a number of challenges that limit the availability of high quality material at the early stages of research and development in the gene therapy field. Moreover, very few papers have been published on the subject and information on large-scale production methods are only available through specialized conference proceedings. This review outlines the problems associated with mass production of adenovirus vectors and describes research efforts by a number of groups who have contributed to optimize production methods. Better understanding of the adenovirus infection and replication kinetics as well as better understanding of complementing cell line physiology and metabolism greatly contributed to improving vector titers and volumetric productivity at higher cell densities. Also, the critical aspect of viral vector quantitation is discussed.

Interferon-gamma-induced assembly block in the replication cycle of adenovirus 2: augmentation by tumour necrosis factor-alpha

Replication of adenovirus 2 (Ad-2) is inhibited in A 549 cells pretreated with interferon-gamma (IFN-gamma). The antiviral effect is synergistically enhanced by the simultaneous presence of tumor necrosis factor-alpha (TNF-alpha) before infection. Under conditions of strong inhibition of virus progeny formation, viral DNA synthesis and [35S]methionine incorporation into most late viral proteins are only marginally impaired. Pulse chase experiments indicate a partial inhibition of processing of viral proteins. Viral proteins are not degraded and capsomeres accumulate in the inhibitor-treated cells. Capsid formation, on the other hand, is strongly inhibited in the cytokine-treated cells. The inhibition of Ad-2 replication in A 549 cells by IFN-gamma and TNF-alpha is caused, therefore, by a block in the maturation of Ad-2.

Restricted replication of adenovirus type 2 in mouse Balb/3T3 cells

The nature of the infection of mouse B3T3 cells by adenovirus type 2 (Ad2) has been studied in vitro. Following infection with an adsorbed MOI of 225, more than 90 percent of the cells synthesized both early and late virus-specific antigens. In contrast, the yield of progeny virus varied from only 2 X 10(4) to 2 X 10(6) FFU/2 X 10(5) cells. The range in yields was related, in part, to the number of cell generations from the time of the initial subcloning, the yield increasing with passage level. Infectious center analysis suggested that fewer than 0.5 percent of infected cells synthesized progeny virus. Analysis of DNA synthesis in infected multiplying B3T3 cells demonstrated that cellular DNA synthesis began to be shut off at 12 hours p.i., a time when viral DNA synthesis was beginning. The maximum rate of viral DNA synthesis was approximately 12 percent of that in infected human cells. In contrast to infected multiplying cells, infection of quiescent B3T3 cell cultures resulted in the induction of cellular, along with viral, DNA synthesis. Analysis of late gene expression detected synthesis of most viral polypeptides, but revealed greater than 90 percent reductions in the rate of synthesis of polypeptides II, III, IV, and IX, as compared with infected human cells.