the invention will now be described by way of example only and with reference to the accompanying figures wherein ; fig1 shows a map of hp - 1 / hnrnpa2 locus indicating bamhi , hindiii , esp3i , tth111i and bspei restriction sites defining various 4 , 2 , 1 . 5 and 1 kb cpg island fragments . fig2 shows the nucleotide sequence of hp - 1 / hnrnpa2 locus ( seq id no : 3 ) indicating bamhi , esp3i , bspei and tth111i restriction sites . fig3 shows expression of an egfp reporter gene operably linked to the 4 kb and 1 . 5 kb ( in both orientations ) cpg island fragments . facscan data expressed as median fluorescence over 71 days . fig4 shows expression of an egfp reporter gene operably linked to the 4 kb and 1 . 5 kb ( in both orientations ) cpg island fragments . facscan data expressed as % positive cells over 71 days . fig5 shows expression of an egfp reporter gene operably linked to the 4 kb , 1 . 5 kb and 1 kb cpg island fragments . facscan data expressed as median fluorescence over 68 days fig6 shows expression of an egfp reporter gene operably linked to the 4 kb , 1 . 5 kb and 1 kb cpg island fragments . facscan data expressed as % positive cells over 68 days fig7 shows the structure of the two adenoviral constructs ad . cmv - luc - sv40p ( a ) and ad . 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ), which are based on adenovirus serotype 5 . the luciferase expression cassettes were inserted into the e1 region in a left to right orientation . the e1 and e3 regions are deleted from the viruses . due to deletion of e1 the viruses are replication - defective . cmv ( cytomegalovirus ) is the human cmv enhancer / promoter . sv40p ( a ) is the sv40 virus late polyadenylation signal from pgl3basic ( promega ). fig8 shows that a 1 . 5 kb ucoe boosts gene expression in hela cells when delivered by means of an adenoviral vector . hela cells were infected at an moi of 50 for 2 - 3 hours in 200 μl infection medium ( normal hela medium containing only 1 % fcs ) with the viruses ad . cmv - luc - sv40p ( a ) and ad . 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ). after incubation , 2 ml complete medium was added and cells were seeded into 6 - well plates . luciferase activity was analysed 2 days after infection . results from three independent experiments are shown . experiments were done in triplicates . shown is the mean +/− the standard deviation . fig9 shows that the 1 . 5 kb ucoe effect is independent of the viral preparation . hela cells were infected at an moi of 50 for 2 - 3 hours in 200 μl infection medium ( normal hela medium containing only 1 % fcs ) with the viruses ad . cmv - luc - sv40p ( a ) and ad . 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ) from two independent viral preparations , each . after incubation , 2 ml complete medium was added and cells were seeded into 6 - well plates . luciferase activity was analysed 2 days after infection . results from one representative experiment is shown . experiments were done in triplicates . fig1 shows that the 1 . 5 kb ucoe increases transgene expression level and stability in retrovirally transduced cho - k1 pools . ( a ) mean gfp values over time for facs - sorted cho - k1 pools ( 36 , 000 cells originally facs - sorted ) after retroviral transduction for cmv and 1 . 5ucoe - cmv constructs . day1 refers to the 1 st day of measurement ( 8 days after facs - sorting ). ( b ) histograms of the facs - sorted cho - k1 pools for each time point of measurement . fig1 shows gfp expression of transduced cho - k1 ( pool i ) after low moi infection . ( a ) mean gfp values for gfp positive ( m1 ) cho - k1 populations after retroviral transduction for each time point . the cmv population started with 3 . 19 % gfp - positive cells and the 1 . 5ucoe - cmv population with 4 . 99 % gfp - positive cells . ( b ) histograms for the populations at each time point . fig1 shows gfp expression of transduced cho - k1 ( pool ii ) after intermediate moi infection . ( a ) mean gfp values for gfp positive ( m1 ) cho - k1 populations after retroviral transduction for each time point . the cmv population started with 25 . 2 % gfp - positive cells and the 1 . 5ucoe - cmv population with 14 . 35 % gfp - positive cells . ( b ) histograms of the populations for each time point . fig1 shows that the 1 . 5 kb ucoe increases transgene expression level and stability in retrovirally transduced hela pools . ( a ) mean gfp values over time for facs - sorted hela pools ( 10 , 000 cells originally facs - sorted ) after retroviral transduction for cmv and 1 . 5ucoe - cmv constructs . day1 refers to the 1 st day of measurement ( 5 days after facs - sorting ). ( b ) histograms of the facs - sorted hela pools for each time point of measurement . fig1 shows that the 1 . 5 kb ucoe increases the consistency of gfp expression both with and between retrovirally transduced hela cell clones . facs - sorted hela clones were expanded to 6 - well size and gfp expression was analysed . ( a - c ) histograms for all cmv clones . ( d - e ) histograms for all 1 . 5ucoe - cmv clones . fig1 shows that the 1 . 5 kb ucoe decreases the coefficient of variation ( cv ) of gfp expression in hela cell clones . shown is the average cv value (+/− sd ) of the means for all the retrovirally transduced and facs - sorted hela clones from fig5 . both the cv and its standard deviation ( sd ) of the 1 . 5ucoe - cmv clones are significantly decreased compared to the cmv clones . as discussed in our earlier application wo 00 / 05393 , vector cet20 was generated by cloning an 8 . 3 kb hindiii fragment of the human hp - 1 / hnrnp a2 locus ( which contains the hp1 / rnp promoters and the extended cpg island ) into pbluescript ( stratagene ). a 4186 bp ( referred to as 4 kb ) fragment of the insert was then removed by digestion with bamhi and hindiii . this fragment was end filled using t4 dna polymerase and ligated into pegfpn - 1 ( clontech ) that had been digested with asei and end filled again using t4 dna polymerase . clones were then isolated with the fragment in both orientations . the 1546 bp esp3i ( isoschizomer of bsmbi ) fragment ( referred to as the 1 . 5 kb fragment ) was again isolated from cet20 by digestion with esp3i ( bsmbi ) followed by end filling , this was then ligated into the asei site of pegfpn - 1 as described above and clones identified with the fragment in both orientations ( the ‘ forward ’ orientation being with the rnpa2 promoter oriented in the same 5 ′ to 3 ′ direction as the adjacent downstream operative cmv promoter from which the egfp transgene was transcribed ) cho - k1 cells were transfected and selected in g418 according to standard methods and as described in the co - pending applications incorporated by reference . transfected cells were maintained on g418 selection at 600 μg / ml . cells washed with standard phosphate buffered saline and stripped from the substrate with trypsin / edta according to standard methods . an excess of nutrient mixture f12 ( ham ) medium ( gibco ) was added and the cells transferred to 5 ml round bottom polystyrene tubes for analysis by becton dickinson facscan . gfp fluorescence was detected and compared with the autofluorescence of the parental cell population . expression in the cell population was expressed as both median fluorescence expressed as arbitrary units set relative to the control ( according to standard methods ) on a linear scale in the figures , and in terms of % cells judged as positive expressors . as shown in fig3 , the 1 . 5 kb fragment gave significant enhancement of expression as compared with the control ( approximately 10 - fold over at least 70 days ) in terms of median fluorescence and about 60 % of the enhancement seen with the 4 kb fragment , when inserted in the forward orientation . in the experiment shown in fig5 , expression from the forward 1 . 5 kb fragment is comparable with that obtained with the 4 kb fragment . however , the reverse orientation appears to be rather less effective in terms of median fluorescence , as shown in fig3 . fig4 shows both orientations to be comparable in terms of % positive cells . nevertheless , these data suggest that this fragment may have a degree of directionality and that , for most purposes , the forward orientation is preferable . the 1 kb ucoe containing vector was constructed by digesting the pegfpn - 1 vector with the 1 . 5 kb esp3i fragment in the forward orientation with pcii and bspei to remove the 5 ′ 500 bp , followed by end filling and re - ligation . this generated a vector with the 987 bp bspei - esp3i fragment in one orientation only . the 1 kb ( 987 bp ) fragment in the forward orientation appears comparable with the 1 . 5 kb fragment in the forward orientation in terms both of median fluorescence ( fig5 ) and % positive cells ( fig6 ). a 1 . 5 kb hp - 1 / hnrnp a2 ucoe enhances expression in an adenovirally encoded construct hela were obtained from atcc ( manassas , va .). per . c6 were obtained from crucell , ( leiden , the netherlands ). all purchased cell lines were cultured as recommended by the supplier . 911 cells were kindly provided by prof . l . s . young ( cancer research uk institute for cancer studies , university of birmingham , birmingham , uk ) and were cultured in dmem / 10 % fcs containing antibiotics . pgl3basic was obtained from promega ( madison , wis ., usa ) and contains the luciferase - sv40p ( a ) cassette downstream from the multiple cloning site . the human cmv enhancer / promoter ( 0 . 9 kb ) was cloned into smai digested pgl3basic to generate pgl3 / cmv - luc - sv40p ( a ). to generate pgl3 / 1 . 5 kb ( f ) ucoe - cmv - sv40p ( a ) the 1 . 5 kb ucoe esp3i fragment ( see fig1 and 2 ) was blunted with t4 dna polymerase ( neb , beverly , mass ., usa ) and then ligated into nhei digested and t4 blunted pgl3basic / cmv - luc . to construct pps1128 / cmv - luc - sv40p ( a ) and pps1128 / 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ), the expression cassette were cut out from pgl3 / cmv - luc - sv40p ( a ) by pvui / nhei / bamhi digest and from pgl3 / 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ) by kpni / bamhi digest , both cassettes were then blunted and cloned into spei digested and blunted pps1128 ( djeha et al ., cancer gene therapy 2000 : 721 - 731 ). plasmids were analysed by restriction enzyme digests . the viruses ad . cmv - luc - sv40p ( a ) and ad . 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ) were constructed by homologous recombination in per . c6 using pps1128 / cmv - luc - sv40p ( a ) and pps1128 / 1 . 5 kb ( f ) ucoe - cmv - luc - sv40p ( a ), respectively , and the overlapping adenoviral backbone vector pps1160 ( djeha et al ., cancer gene therapy 2000 : 721 - 731 ), scaled up and cscl - purified and titered as described elsewhere ( lipinski et al ., gene therapy , 8 , 2001 : 274 - 281 ). hela cells ( 5 . 0 × 10 4 per 6 - well ) were infected in suspension with the respective virsues in 200 μl infection medium ( emem / 1 % fcs containing antibiotics ) for 2 - 3 hours . then 1 ml complete medium was added and cells were seeded into 6 - well plates . whole cells extracts were prepared by lysing the cells in 200 μl lysis buffer ( 10 mm sodium phosphate ph 7 . 8 , 8 mm mgcl 2 , 1 mm edta , 1 % triton - x - 100 , 15 % glycerol ) and clearing the lysate by centrifugation ( 1 min 13 , 000 × g , rt ). an aliquot of each supernatant was assayed for luciferase activity in the linear range using a luminometer ( lumat lb 9501 , berthold , wildbad , germany ) at the indicated time points . to analyse whether the ucoe can boost gene expression in an adenoviral vector the 1 . 5 kb ucoe was cloned in a forward orientation upstream ( rnp promoter has the same orientation as the cmv promoter ) of the human cmv enhancer / promoter driving a luciferase reporter gene . fig7 shows schematically the structure of the two viruses that were compared for their luciferase activity . hela cells were infected at an moi of 50 with the respective viruses and luciferase activity was analysed 2 days after infection . fig8 shows clearly that the 1 . 5 kb ucoe fragment can dramatically increase the level of reporter gene expression in hela cells . to exclude a specific effect associated with the viral preparations we prepared new preparations of both viruses and repeated the experiments . fig9 shows that the ucoe effect was not dependent on the viral preparation and was fully reproducible with the new , independent preparations . a 1 . 5 kb hp - 1 / hnrnp a2 ucoe enhances expression in a retrovirally encoded construct hela , cho - k1 and 293 were obtained from atcc ( manassas , va .). hela and 293 were both cultured in dmem , 10 % fcs adding 1 % neaa and containing antibiotics . cho - k1 were cultured in nutrient mix f12 ( ham ) medium containing 10 % fcs and antibiotics . the plasmids pvpack - gp and pvpack - vsv - g were obtained from stratagene ( lajolla , calif ., usa ) and express retroviral gag - pol and envelope vsv - g proteins , respectively . the retroviral vector pqcxix was obtained from bd bioscience and it contains the human cmv promoter for transgene expression ( palo alto , calif ., usa ). the plasmid phrgfp - 1 was obtained from stratagene and was used as source for a modified gfp cdna . to clone pqcxix - cmv - hrgfp the hrgfp cdna was cut out from phr - gfp - 1 by bamhi / ecorv digest and cloned into bamhi / ecorv digested pqcxix . to generate pqcxix - 1 . 5ucoe - cmv - hrgfp , the 1 . 5 kb ucoe fragment ( esp3i / bsmbi fragment ) was cloned as a blunted fragment into xbai digested and blunted pqcxix - cmv - hrgfp . all viruses were pseudotyped with the amphotropic vsv - g ( vesicular stomatitis virus glycoprotein ) envelope enabling highly effective and broad host range transduction . the retroviral vector used ( pqcxix ) generates self - inactivating viruses due to a deletion in the u3 region of the 3 ′ ltr which is copied to the 5 ′ ltr after reverse transcription and therefore inhibits any further transcription from the 5 ′ ltr . 4 . 5 × 10 6 293 cells ( next day cells should be 80 - 90 % confluent ) were seeded in collagenase type i coated 8 . 4 cm diameter ( 55 . 6 cm 2 ) dishes the day before transient transfection . the next day 114 μl lipofectamine 2000 ( invitrogen , groenningen , the netherlands ) was mixed with 286 μl optimem ( invitrogen ) and incubated for 5 min at room temperature ( rt ). in parallel , 1 . 5 μg of each plasmid pvpack - gp , pvpack - vsv - g and retroviral vector was mixed with optimem to give a final volume of 400 μl . the dna mix was added to the lipofectamine 2000 solution and incubated for 20 - 30 min at rt . during this incubation the 293 cells were washed once with pbs and 6 ml optimem / 10 % fcs was added to the cells . finally the dna / lipofectamine mix was added dropwise to the cells and the cells were incubated in a 5 % co2 incubator at 37 ° c . for 5 hours . the medium was then replaced by 8 ml fresh 293 culture medium and the cells were incubated for a further 24 - 36 hours . finally , supernatant containing the viral particles was harvested from the cells , centrifugated for 5 min at 1000 rpm to pellet cells and cell debris , and the supernatant was filter sterilized using millex - hv pvdf low protein binding 0 . 45 μm filters ( millipore , molsheim , france ). the supernatant was aliquoted , snap frozen with liquid nitrogen and stored at − 80 ° c . target cells ( hela , cho - k1 ) were seeded at 1 × 10 5 cells / well in 6 - well plates the day before infection . for viral transduction , different amounts of virus containing supernatant were added in the presence of 8 . 0 μg / ml polybrene ( sigma , st . louis , mo ., usa ). cells were incubated with the virus for 24 hours and the medium was then replaced by fresh medium . gene expression can be observed from two days post transduction . to prevent multiple copy per cell effects , for all analyses target cells were infected with a virus amount that resulted in much less than 100 % transduction efficiency ( normally giving 1 - 20 % gfp - positive cells ). within this range of transduction efficiency , the volume of supernatant used for infection correlates linearly with the number of positive cells whereas the mean expression level shows a much lower increase . for facs analysis target cells were washed with pbs , trypsinized and resuspended in complete medium and hrgfp ( green fluorescent protein ) expression was analysed with a becton dickinson facscan ( bd , franklin lakes , n . j ., usa ) using constant instrument settings for each study . data were analysed with cellquest software for apple mcintosh . to sort gfp expressing hela and cho - k1 cells , cells were prepared as for facs analysis and then sorted with a bd bioscience facs - sorter ( kindly provided by the institute for cancer studies , university of birmingham , uk ). sorted single clones and pools were then expanded and gfp expression was followed up over time . in a first study cho - k1 cells were transduced with cellular supernatants containing the retroviruses cmv - hrgfp ( cmv ) and 1 . 5ucoe - cmv - hrgfp ( 1 . 5ucoe - cmv ). cho - k1 cells were transduced as described in material and methods and three days after infection gfp - positive cells were facs - sorted as a population pool ( 36 , 000 cells for each viral constructs ) and then expanded . gfp expression and histogram pattern were followed over time and are illustrated in fig1 a and b , respectively . on day 17 of analysis the mean value for the 1 . 5ucoe - cmv pool is 2 . 6 - fold higher than the mean from the cmv pool . additionally , as the histograms show in fig1 b , the 1 . 5ucoe - cmv pool gives a tighter peak of gfp expression than the cmv pool . the average cv value ( coefficient of variation ; this is a marker for the homogeneity of gfp expression ) for the gfp - positive cells in marker 1 is 146 . 0 for the cmv pool and 83 . 0 for 1 . 5ucoe - cmv pool . comparable to this study cho - k1 were transduced and the population was followed up over time without facs - sorting . the moi was chosen to give relatively low percentage of positive cells to exclude multiple copy per cell effects . as shown in fig1 a ( pool i with about 5 % gfp - positive cells ), the mean of the positive cells for the 1 . 5ucoe - cmv population at the last time point of measurement is 2 . 8 - fold higher than the mean of the cmv population . for pool ii ( about 15 - 25 % gfp - positive cells ; fig1 a ), the mean for the 1 . 5ucoe - cmv population at the latest time point of measurement is 2 . 3 - fold higher than the mean for the cmv population . comparable to the facs - sorted population , the 1 . 5ucoe - cmv populations give a clearly tighter peak of expression compared to the cmv populations at all time points analysed ( fig1 b and fig1 b ). as for cho - k1 , pools of 10 , 000 hela cells stably transduced with the retroviral constructs were facs - sorted . in fig1 a the mean gfp value is shown including the mean value at the day of facs - sorting ( day — 5 ). at the last time of measuring the mean of the 1 . 5ucoe - cmv pool is 1 . 6 - fold higher than the mean of the cmv pool . as illustrated by the histograms in fig1 b , many of the cmv cells loose their high gfp expression level over time ; in contrast most of the 1 . 5ucoe - cmv cells retain their high gfp expression . hela single cell clones were also facs - selected and expanded into 6 - well plates . the cmv clones tend to give slightly higher peak expression than the 1 . 5ucoe - cmv clones , however , consistency of expression level , both within a clone and between clones , is significantly increased by the presence of the ucoe as indicated by the histograms for the all the analysed clones ( fig1 a - e ). fig1 shows the average coefficient of gfp expression variation ( cv ) and its standard variation ( sd ). the cv +/− sd value for the cmv clones is 135 . 0 +/− 165 . 3 and for the 1 . 5ucoe - cmv clones 49 . 4 +/− 10 . 9 .
the invention relates to improved genetic elements providing high levels of expression of operably - linked genes in a variety of tissues . in particular , fragments of unmethylated , cpg islands of less than 2 kb are shown to provide enhanced transgene expression and have advantages in terms of vector construction and cloning capacity .