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The nucleotide excision repair (NER) is one of the major human DNA repair pathways. Defects in one of the proteins that act in this system result in three distinct autosomal recessive syndromes: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). TFIIH is a nine-protein complex essential for NER activity, initiation of RNA polymerase II transcription and with a possible role in cell cycle regulation. XPD is part of the TFIIH complex and has a helicase function, unwinding the DNA in the 5 0 -3 0 direction. Mutations in the XPD gene are found in XP, TTD and XP/CS patients, the latter exhibiting both XP and CS symptoms. Correction of DNA repair defects of these cells by transducing the complementing wild-type gene is one potential strategy for helping these patients. Over the last years, adenovirus vectors have been largely used in gene delivering because of their efficient transduction, high titer, and stability. In this work, we present the construction of a recombinant adenovirus carrying the XPD gene, which is coexpressed with the EGFP reporter gene by an IRES sequence, making it easier to follow cell infection. Infection by this recombinant adenovirus grants full correction of SV40-transformed and primary skin fibroblasts obtained from XP-D, TTD and XP/CS patients.

The introduction of genes through the skin has been an attractive and dynamic field of research in recent years. It gives the first gleam of hope in therapy for the human genetic diseases that mainly affect this tissue, such as patients that suffer from xeroderma pigmentosum, and who experience increased frequency of skin cancer. The first in vitro experiments were successful in correcting the genetic defects of cells from these patients, the ex vivo reconstruction of corrected cells has been achieved, and the skin of model animals has been treated resulting in cancer prevention. Up to now these efforts have been possible, thanks to the high efficiency of viral vectors that provide gene delivery and expression targeted to many of the different skin cells, including those with proliferative and pluripotent features, such as keratinocytes and epidermal cells of hair follicles. Moreover, progress with several other methodologies qualifies them as alternatives to be explored, in some cases in combination with viral vectors, for skin gene therapy in these patients. Exciting and encouraging new approaches promise benefits to xeroderma pigmentosum patients and their families, and open perspectives of new ways for interfering in gene driven metabolism in the skin.

No abstract

Recombinant adenoviral vectors provide efficient means for gene transduction in mammalian cells in vitro and in vivo. We are currently using these vectors to transduce DNA repair genes into repair deficient cells, derived from xeroderma pigmentosum (XP) patients. XP is an autosomal syndrome characterized by a high frequency of skin tumors, especially in areas exposed to sunlight, and, occasionally, developmental and neurological abnormalities. XP cells are deficient in nucleotide excision repair (affecting one of the seven known XP genes, xpa to xpg) or in DNA replication of DNA lesions (affecting DNA polymerase eta, xpv). The adenovirus approach allows the investigation of different consequences of DNA lesions in cell genomes. Adenoviral vectors carrying several xp and photolyases genes have been constructed and successfully tested in cell culture systems and in vivo directly in the skin of knockout model mice. This review summarizes these recent data and proposes the use of recombinant adenoviruses as tools to investigate the mechanisms that provide protection against DNA damage in human cells, as well as to better understand the higher predisposition of XP patients to cancer. Human & Experimental Toxicology (2007) 26, 899—906