Adeno-associated virus-mediated gene transfer into human retinal pigment epithelium cells

PURPOSE

Adeno-associated virus (AAV) is emerging as a promising vector for gene therapy

METHOD

To determine the ability of recombinant AAV (rAAV) to express and integrate exogenous DNA into human retinal pigment epithelium (RPE) cells, a rAAV-GFP vector containing the green fluorescent protein (gfp) and neomycin resistance (neo(r)) genes was constructed and used to transduce RPE 407A cell line.

RESULTS

Fluorescent RPE cell clones were obtained and were confirmed to still be expressing GFP after 24 passages (3.5 months).

CONCLUSION

Adeno-associated virus-based vectors are able to efficiently transduce and stably persist in RPE cells.

Ocular gene therapy: the basic science and current state of research

Recent technical advances have led to the demonstration of the molecular basis of many genetic eye diseases. Methods now in use have been able to both suppress and insert genes in vitro and in vivo in ocular cells. The combination of this new knowledge and these techniques offers the potential for a new therapeutic approach to diseases that currently have no treatments. The scientific basis of gene therapy is introduced and then the current state of research is discussed in relation to the eye and ocular tissues.

Retinal GFAP and bFGF expression after multiple argon laser photocoagulation injuries assessed by both immunoreactivity and mRNA levels

The expression of GFAP and bFGF after retinal photocoagulation injury in the rat was assessed by immunocytochemistry and reverse transcriptase PCR. Beta-actin mRNA expression was unaltered after injury and was therefore a good control for the quality of the RNA samples and the PCR reaction. GFAP mRNA increased from undetectable levels in normal retina to relatively high levels at 24 and 48 hr after injury, returning to barely detectable levels at 3 and 7 days. Müller cell GFAP immunoreactivity was elevated by 24 hr, stronger by 48 hr and persisted for 30-45 days. Thus, the expression of GFAP immunoreactivity after photocoagulation was due to new protein synthesis but the mRNA, and therefore the stimulus, was only present for a few days. This indicates that the GFAP protein in Müller cells has a long lifetime similar to that of astrocytes despite different gene control elements. bFGF is a possible stimulus for Müller GFAP expression because Müller cells have bFGF receptors. bFGF mRNA was detectable in normal, 24 and 48 hr retinas but decreased to undetectable levels (even after 35 cycles of PCR) at three days after injury and had only partly recovered by 7 days. Immunocytochemistry demonstrated a rapid change in localization of bFGF at the lesion sites early after lesion. At 2-3 days bFGF in blood vessels was markedly increased while at 7 days there was an increase around the photoreceptors flanking each lesion. These shifts in bFGF localization were too late to be a stimulus for the widespread upregulation of GFAP expression by Müller cells. The reduction in bFGF mRNA at three days was unexpected as studies of brain injury generally show a longer lasting elevation of bFGF expression. Therefore it is likely that bFGF expression is controlled by different mechanisms in the retina compared to the brain. However, a reduction in bFGF synthesis after photocoagulation is consistent with the anti-angiogenic effect of laser photocoagulation in diabetic retinopathy.

Dynamics of gene transfer to retinal pigment epithelium

PURPOSE

To examine the nature and dynamics of gene transfer to human retinal pigment epithelium (RPE) using an adenoviral vector and adjuvants that may enhance the uptake of recombinant adenoviruses.

METHODS

Human RPE cultures (HRPE7) were transfected in vitro with varying concentrations (4, 20, 40, 120, and 200 pfu/microliter) and for varying periods (1, 2, 4, 16, 24, 48, and 72 hours) with a replication-deficient adenovirus (Ad.RSV. beta gal) containing the bacterial beta-galactosidase transgene (beta gal). The expression of beta gal was monitored by counting after X gal staining. The transgene expression profiles were compared to those of human F2000 fibroblasts under the same conditions. The adjuvant effect of sodium hyaluronate (HA) on the expression of beta gal was tested in F2000 and early and late passage human RPE cells for differing concentrations of HA, viral titers, and incubation times. Immunofluorescent cytochemistry was carried on HRPE7 and F2000 cells for the HA receptors, homing receptor CD44 (CD44), intercellular adhesion molecule 1 (ICAM-1), and the receptor for hyaluronan mediated motility (RHAMM).

RESULTS

The number of HRPE7 and F2000 cells expressing the adenoviral transgene increased consistently with increasing incubation time and viral titer. There was a higher uptake of Ad.RSV. beta gal in HRPE7 cells compared to the F2000 fibroblasts under the same conditions. There was an increase of 28.1% and 41.4% in the number of RPE7 cells expressing adenoviral transgene and 16.2% and 15.8% F2000 fibroblast cells expressing the adenoviral transgene in the presence of 0.001% and 0.005% HA, respectively. Significant adjuvant effects on transgene expression also were shown in HRPE51 cells. It appears that the effects of increasing viral titer, length of incubation, and the presence of HA on transgene expression are at least additive. The appearance of CD44 and ICAM receptors on RPE7 and F2000 cells and RHAMM receptors on F2000 cells was similar. The RHAMM receptors in HRPE7 cells, however, were shown preferentially over the nucleus.

CONCLUSIONS

On the basis of these results, the authors propose that adenovirus transgene expression increases with increasing incubation time and viral titer in cell culture. The rate of increase of expression differs between human RPE cells and the F2000 fibroblast cells, which may offer a targeting opportunity. The authors propose that the use of HA can offer both an adjuvant effect and a targeting advantage in terms of transferring adenoviral transgenes to human RPE in culture.

A preliminary report on a DNA-based screening method for retinitis pigmentosa. A trial on a west Australian population

PURPOSE AND BACKGROUND

Recent reports have linked numerous point mutations in the human genome to retinitis pigmentosa (RP), suggesting that in the near future molecular biology based genetic counselling for patients with RP might become a reality. In this paper we assess the viability of a DNA-based screening method for RP. Specifically, we screened rhodopsin and the beta-subunit of phosphodiesterase (B-PDE) genes for the presence of abnormalities in West Australian RP patients.

METHODS

Blood was collected from 27 patients. Leukocyte DNA was extracted from patients and 50 randomly selected controls. Exons 1-19 and 21 of B-PDE and exons 1, 3 and 5 of rhodopsin were analysed using single-strand conformational polymorphism (SSCP) following DNA amplification. The nature of anomalies detected by SSCP was classified with DNA sequencing.

RESULTS

In RP patient samples, we found anomalous bands in exons 5, 9, 10, 15 and 16 and 17 of B-PDE and in exons 1 and 3 of rhodopsin genes. In B-PDE none of the anomalous bands represented mutations. Some of the anomalous bands in the rhodopsin gene, however, corresponded to silent mutations at nucleotide positions 269 and 3982 in four patients.

CONCLUSIONS

In this study we have demonstrated that SSCP in combination with DNA sequencing is a powerful tool to identify new mutations and to provide information for a 'mutational panel' for future screening.

HLA DQA tissue typing of cadaveric eye bank donor material with polymerase chain reaction

It has been suggested that the provision of HLA matched tissue for corneal transplantation would be beneficial for graft survival especially in high risk patients. In this study we report the application of a polymerase chain reaction (PCR) based tissue typing procedure to type cadaveric donor material. Using beta-globin gene amplification as a test system we found that cornea, corneal rim, conjunctiva, sclera, rectus muscle, optic nerve and neural retina were all suitable for PCR amplification but DNA extracted from pigment epithelial cells and from the iris could not be amplified. HLA DQA typing results of 9 samples identified 5 alleles and 7 genotypes. In two cases the antigens detected by serology reflected the alleles detected by PCR. In a third case in which the class II serological typing was inconclusive we detected two DQA alleles by PCR. These alleles were consistent with those which would be predicted to be present on the basis of known linkage disequilibrium between HLA-Cw, B, DR and DQ. In this study we have shown that PCR based tissue typing is more sensitive and gives more detailed typing results than serology and would be suitable to type cadaveric donor material on a routine basis.

Changes in retinal pigment epithelial cell autofluorescence and protein expression associated with phagocytosis of rod outer segments in vitro

The accumulation of autofluorescent lipofuscin was quantified in cultured human retinal pigment epithelial (RPE) cells phagocytosing bovine rod outer segments (BROS) and the expression of proteins in these cells was investigated. Results showed a steady increase in autofluorescence of RPE cells over a 4-week period as measured by fluorophotometric flow cytometry. A significantly greater increase in autofluorescence was found in the cultured RPE cells from a 7-year-old donor compared with those from a 47-year-old donor. Within both groups the BROS-challenged cells had significantly higher fluorescence readings than the control cells which were not challenged. Autoradiography of 35S-labelled proteins separated by polyacrylamide gel electrophoresis (PAGE) revealed a small distinct band at 102 kDa in BROS-challenged RPE cells of both bovine and human origin that did not appear in control or microsphere-phagocytosing RPE cells. The intensity of the signal was unrelated to the duration of the challenge period.

Time trends in the prevalence of human papillomavirus infections in archival Papanicolaou smears: analysis by cytology, DNA hybridization, and polymerase chain reaction

A retrospective study was undertaken to determine the prevalence of human papillomavirus (HPV) infections in routine Papanicolaou (Pap) smears collected by general practitioners from Western Australian women in each of the years 1972, 1982, and 1987. HPV infection was detected by cytology, dot-blot hybridization, or polymerase chain reaction (PCR). It was found that the prevalence of HPV infection remained unchanged over the 15 year study period, was independent of age, and was associated with normal cytology at a rate far greater than previously recognized. Indeed, the prevalence of cervical intraepithelial neoplasia (CIN) lesions, as detected by cytology, was 3.0% in 1972 and 3.8% in 1982 and 1987. The prevalence of HPV infection, detected as koilocytosis or parakeratosis, was 6.5%, 6.8%, and 5.3% in smears collected in 1972, 1982, and 1987, respectively, from 1,800 women. In 237 cytologically normal smears reprocessed for HPV-DNA studies, the prevalence of HPV 16 was determined to be 15.6%, 11.2%, and 17.8% in 1972, 1982, and 1987, respectively, as determined by dot-blot hybridization. However, the PCR detected HPV 16 in an additional 55.5%, 62.9%, and 57.0% of cytologically normal and dot-blot negative smears. The prevalence of HPV 16 infection in cytologically normal smears was estimated to be 71.0%, 74.1%, and 74.8% in 1972, 1982, and 1987, respectively, by combining the HPV 16 dot-blot and PCR-positive results. The high prevalence of HPV 16 in cytologically normal Pap smears suggests that infection with HPV 16, as detected by PCR amplification, does not place women in a high-risk category for cervical cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of human papillomavirus in reprocessed routine Papanicolaou smears by DNA hybridization

DNA dot blot hybridization was used for the detection of human papillomavirus (HPV) types 6, 11, 16, and 18 in reprocessed routinely collected Papanicolaou smears. DNA was extracted from the smears with alkaline lysis and applied onto a nitrocellulose filter. The specificity and sensitivity of the dot blot hybridization on reprocessed Papanicolaou smears were confirmed by Southern blot analysis of selected samples, using CaSki, SiHa cell lines as positive controls and HF 32 as negative controls. From 42 normal smears and 44 abnormal smears with koilocytosis present, 9 (21%) and 43 (98%), respectively, were positive for HPV 6/11/16 or 18. These results show that reprocessed Papanicolaou smears in combination with DNA hybridization have potential application in retrospective studies on the prevalence and distribution of HPV infection.

Detection of human papillomavirus type 16 DNA in cervical swabs and formalin-fixed, paraffin-embedded squamous cell carcinomas of non-genital tissues using a synthetic oligodeoxynucleotide probe

The potential of using a chemically synthesized oligodeoxynucleotide as a diagnostic probe to detect human papillomavirus type 16 (HPV-16) in genital infections was evaluated by comparing it with a cloned full-length HPV-16 probe in dot-blot DNA hybridizations. An oligonucleotide sequence, 20 bases in length from the E6 region of HPV-16 (E6 oligo) and different from the DNA sequences of HPV types 6, 11 and 18 by at least 2 base pairs, was chosen for chemical synthesis. The oligoprobe, which was 5'-end labelled with [32P]dATP, was found to be specific, but approximately ten times less sensitive than the full-length radiolabelled probe of HPV-16, in dot-blot hybridizations with the DNA of HPV-6, -11, -16 and -18, HPV positive and negative cell-lines. From 36 cervical or vulval scrapes two samples were found positive with both cloned HPV-16 and oligoprobe hybridization. Of 21 samples of formalin-fixed, paraffin-embedded squamous cell carcinomas originating from anus, oesophagus, penis, colon, breast and skin only 4 anal squamous cell carcinomas were positives when hybridized with cloned HPV-16 DNA or with the oligoprobe. This study confirms that HPV-16, which is frequently associated with squamous cell carcinoma of the cervix is also strongly associated with squamous cell carcinoma of the anus.

Human papillomavirus coinfections of the vulva and uterine cervix

DNA filter in situ hybridisation (FISH) was used to determine the presence of human papillomavirus (HPV) genotypes 6/11, 16/18, and 31/33 in cell scrapes of the cervix and vulva of 128 women who had precancerous lesions and/or HPV infection of the cervix diagnosed by cytology, colposcopy, and histology. HPV-DNA was found in 87 (68%) vulval and 95 (74%) cervical cell scrapes, and in both the vulval and cervical scrapes of 73 (57%) women, but not in either the vulva or the cervix of 19 women (15%). Of the HPV-DNA-positive smears, the prevalence of the HPV types was 61% HPV 16/18, 14% HPV 6/11, 3% HPV 31/33, and 22% HPV 6/11 and 16/18. By contrast, HPV-DNA was not detected in the cervical smears of a control group of 35 women who were assessed to be free of cervical abnormalities by colposcopy and cytology. The epithelial response of the vulva and the cervix to application of 5% acetic acid was assessed by colposcopy and the results correlated with the presence of HPV genotypes. A possible or definite disorder of the cervix and vulva was detected by colposcopy in 95 (74%) and 96 (75%) of the 128 cases, respectively. The colposcopic assessment of the vulva was inconclusive in ten cases (8%), and only eight women (6%) were found to be free of both a vulval and cervical disorder. This study shows subclinical papillomavirus infections of the vulva frequently coexist with HPV infections and precancerous lesions of the cervix.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of human papillomavirus DNA in cell scrapes and formalin-fixed, paraffin-embedded tissue of the uterine cervix by filter in situ hybridisation

Filter in situ hybridisation (FISH) was used to detect the presence of DNA of human papillomavirus (HPV) types 6/11 or 16/18 in cell scrapes (CYTOFISH) and formalin-fixed, paraffin-embedded biopsies (HISTOFISH) taken from the uterine cervices of 19 women. Paraffin tissue sections collected for HISTOFISH were either digested with pepsin or lysed with alkali/Triton X-100. The digest or lysate of the tissue sections and cell scrapes were applied to nylon or nitrocellulose membranes for nucleic acid hybridisation using 32P-labeled HPV-DNA probes. CYTOFISH and HISTOFISH were compared directly by taking samples for each method from the cervices of the same women. Of 19 women examined by colposcopy, cytology, and histology, eight were assessed as normal and 11 had evidence of a cervical disorder and/or the presence of HPV infection. Whereas no HPV-DNA was detected in the normal cases, the presence of HPV-DNAs was detected by both CYTOFISH and HISTOFISH in 11 cases with histological evidence of HPV infection and/or dysplasia. In these HPV positive cases, eight contained HPV 16/18, two HPV 6/11, and one a mixed infection of HPV 6/11/16/18. The high correlation between the results of CYTOFISH and HISTOFISH shows that formalin-fixed, paraffin-embedded cervical biopsies are suitable specimens for the detection and typing of HPV-DNA by FISH. Both CYTOFISH and HISTOFISH should facilitate studies on the prevalence and distribution of HPVs and their association with neoplasia.