disclosed are a series of aptamers which bind to murine cd200r1 and stimulate immune inhibitory signalling . these agonistic aptamers ( termed , herein , m49 , m52 , and ccs13 ) exhibit in vitro immunosuppressive properties as measured by suppression of cytotoxic t - lymphocyte ( ctl ) induction in allogenic - mixed lymphocyte cultures ( allo - mlc ). importantly , pegylated conjugates of these aptamers retain bioactivity in - vitro and function as potent immunosuppressants when administered in - vivo . the therapeutic potential of agonistic cd200r1 aptamers is demonstrated — intravenous administration of peg - m49 and peg - m52 prolongs the survival of murine skin allografts to a similar extent as cd200 . fc . ccs13 was also shown to be a cross - species aptamer , having function in both humans and mice . the aptamers showed to suppress ctl induction in 5 day mixed leukocyte culture ( mlc ) and cause rapid phosphorylation of the cd200r1 cytoplasmic tail thereby initiating immune inhibitory signalling . pegylated forms of these aptamers were synthesized and show significant in - vivo immunosuppression . in a murine model of transplantation , intravenous injection of pegylated aptamers enhanced survival of allogeneic skin grafts as effectively as a soluble cd200fc . as dna aptamers exhibit inherent advantages over conventional protein - based therapeutics including low immunogenicity , ease of synthesis , low cost , and long shelf life , the disclosed cd200r1 specific dna aptamers are a useful and safe non - steroidal anti - inflammatory therapeutic agent . cd200r1 aptamers are disclosed at table 1 ( m49 , m52 , ccs8 and ccs13 , having as their nucleotide sequences seq id nos 1 , 2 , 16 and 3 , respectively ); all show high specificity and binding affinity to cd200r1 , and in two cases ( ccs8 and ccs13 ) has been shown capable of cross - species agonistic activity . the cd200r1 - specific regions of these aptamers are shown herein at table 2 , ( tm49 , tm52 , tccs8 and tccs13 ), having as their nucleotide sequences the seq id nos . : 4 , 5 , 15 and 6 , respectively . ssdna aptamers specific towards murine cd200r1 were identified using the pcr - based systematic evolution of ligands by exponential enrichment ( selex ) method -( ellington and szostak , nature , 1990 aug . 30 : 346 ( 6286 ): 818 - 22 ; tuerk and gold , science 1990 aug . 3 249 ( 4968 ): 505 - 10 ; bock et al ; nature 1992 feb . 6 : 355 ( 6360 ): 564 - 6 , all incorporated herein by reference ). a 25 nucleotide long random synthetic oligonucleotide library flanked by 25 - base long 5 ′ and 3 ′ primer regions ( 5 ′- gacgatagcggtgacggcacagacgnnnnnnnnnnnnnnnnnnnnnn nncgtatgccgcttccgtccgtcgctc - 3 ′, seq id no . : 7 ) was synthesized by integrated dna technologies ( idt ) along with the corresponding primer sequences ( forward 5 ′- gacgatagcggtgacggcacagacg - 3 ′ ( seq id no . : 8 ) and reverse 5 ′ gagcgacggacggaagcgg catacg - 3 ′ ( seq id no . : 9 )). a 4 nmol aliquot of the library representing ˜ 2 . 5 × 10 15 sequences was adsorbed onto magnehis ni - particles ( promega ) at 37 c for 1 hr to remove sequences which bound to the solid support . the resulting sub - library was incubated for 1 hr at 37 ° c . with 10 μg of a recombinant his - tagged murine cd200r1 protein immobilized on magnehis ni - particles suspended in 1 ml phosphate buffered saline ( pbs , ph 7 . 4 ). unbound and weakly bound sequences were removed by washing the beads with pbs for 5 minutes and protein - aptamer complexes were eluted with pbs containing 0 . 5m imidazole . aptamers were recovered using the qiagen nucleotide removal kit following manufacturer &# 39 ; s recommendations and the ssdna pool was amplified for the next round of selection using asymmetric pcr at a 10 : 1 forward : reverse primer ratio . fifteen rounds of selection were performed with the selection stringency increasing as the concentration of cd200r1 was halved every three rounds while simultaneously increasing the number of wash steps . after the 15 th cycle , selected dna aptamers were cloned into pcr4 - topo vector ( life technologies ) and sequenced . over 20 dna aptamer sequences specifically recognizing a murine cd200r1 recombinant protein were identified after 15 rounds of selex screens . these 75 - base long sequences along with a scrambled control aptamer ( capt ) ( gacgatagcggtgacggcacagacgtcccgcatcctccgccgtgccgacccgta tgccgcttccgtccgtcgctc ( seq id no . : 10 ), containing specific region tcccgcatcctccgccgtgccgacc ( seq id no . : 11 )) were synthesized and systematically screened for cd200r1 agonistic activity by evaluating their capability to suppress the induction of cytotoxic t - lymphocyte ( ctl ) in 5 day allo - mixed lymphocyte cultures . aptamer - induced suppression of ctl induction was monitored using a chromium release assay of labeled p815 mastocytoma serving as target cells for ctl lysis . four aptamers m21 , m48 , m49 , and m52 ( fig1 a ) displayed cd200r1 agonistic properties ( fig1 b ). specifically aptamers m49 and m52 suppressed ctl induction at levels comparable to the soluble cd200fc ligand with less than 5 % ctl specific lysis of p815 cells occurring at aptamer concentrations ≧ 7 . 5 μg / ml . m49 and m52 were chosen for further evaluation . the 75 - base long m49 and m52 aptamer sequences were further truncated based on their predicted secondary structure derived from mfold software ( fig2 a ). m49 retained agonistic activity when truncated to a minimal size of 55 - bases trm49 ( seq id no . : 12 ) while the optimal activity for m52 was retained down to a length of 44 bases trm52 ( seq id no . : 13 ) ( fig2 b ). agonistic cd200r1 aptamers were identified and evaluated for their ability to suppress cytotoxic t - lymphocyte ( ctl ) induction in 5 day allo - mlc . briefly , 2 . 5 × 10 5 c57bl / 6 responder splenocytes were incubated with an equal number of irradiated balb / c stimulator cells in the presence of synthetic aptamers , pegylated aptamers , or cd200fc for 5 days . ctl induction was assayed by monitoring the release of 51 cr from loaded p815 mastocytoma target cells over a 5 hour time period at a 25 : 1 effector - to - target ratio . the 5 ′ termini of aptamer m49 ( seq id no . : 4 ), m52 ( seq id no . : 5 ), and the control aptamer capt ( seq id no . : 10 ) were modified with a 20 kda polyethylene glycol ( peg ) moiety to increase their circulatory half - life , as shown schematically in fig3 a . briefly , a 5 ′ amino group with a hexylamine arm was incorporated into each dna aptamer during synthesis ( idt ). a 100 - molar excess of mpeg - succinimidyl glutarate ester powder ( creative pegworks , winston salem , n . c ., usa ) was added stepwise over a period of 10 hours to 25 μm solutions of the modified aptamers dissolved in 100 mm nahc0 3 / ch 3 cn ( 1 : 1 ph 8 . 5 ). the pegylated aptamers were purified by ultrafiltration using amicon ultra centrifugal filters with a 30 kda mwco ( millipore ) and size exclusion fast protein liquid chromatography ( fplc ) using a superdex 75 10 / 300 column ( ge healthcare ) with 100 mm nh 4 co 3 as eluent . purified pegylated - aptamer conjugates were lyophilized and resuspended in sterile pbs for subsequent experiments . purity of the final pegylated products were confirmed by size exclusion fplc ( fig3 b ) and polyacrylamide gel electrophoresis ( fig3 c ). the pegylated aptamers peg - m49 , peg - m52 , and peg - capt were compared to unconjugated aptamers for their capability to suppress ctl induction in allogeneic - mlc . both peg - m49 and peg - m52 suppressed ctl induction to a greater extent than m49 and m52 ( fig4 a ), confirming that pegylation did not disrupt the structure and function of these aptamers . intracellular phosphorylation of cd200r1 in response to peg - m49 , peg - m52 , and peg - capt was detected using a rabbit polyclonal antibody specific to the phosphorylated cytoplasmic tail of cd200r1 . hek - 293 cells stably expressing cd200r1 were serum starved in optimem media ( life technologies ) for 3 hrs followed by incubation for 30 min with 2 . 5 μm peg - m49 , peg - m52 , peg - capt , or a cd200 positive cell lysate ( positive control ) in optimem . cells were washed in pbs , lysed in ripa buffer with protease inhibitor , and cd200r1 immunoprecipitated using an anti - cd200r1 ( clone 2a10 ) monoclonal antibody ( overnight 4 c ) and protein g agarose beads ( pierce ). the phosphorylated form of cd200r1 was detected by western blot using the rabbit polyclonal antibody ( 1 : 1000 dilution ) and anti - rabbit hrp ( 1 : 15 , 000 dilution ). the immediate signalling event following cd200 : cd200r1 ligation is the phosphorylation of the tyrosine residue in the npxy motif on the c - terminal cytoplasmic tail of cd200r1 . the phosphorylated npxy motif interacts with adaptor proteins thereby transducing immune inhibitory signalling 5 - 8 . to confirm that the suppression of ctl induction observed in our allo - mlc assays was indeed a consequence of aptamer - induced cd200r1 signalling , we verified whether peg - m49 and peg - m52 could induce the phosphorylation of this motif . hek - 293 cells were stably transfected to express murine cd200r1 ( fig4 b ) and treated with aptamers peg - m49 and peg - m52 . the phosphorylation of cd200r1 was detected using a phosphospecific antibody . both peg - m49 and peg - m52 induced the rapid phosphorylation of the c - terminal tail of cd200r1 ( fig4 c ). there was no detectable signal from medium alone or peg - capt ( fig7 ) confirming that the identified aptamers signal through cd200r1 in a similar manner to cd200 . to stimulate an immune response c57bl / 6 mice received balb / c skin allografts ( day 0 ) followed by five tail vein injections of 15 μg peg - m49 , peg - m52 , peg - capt , or cd200fc dissolved in 0 . 3 ml pbs , ph 7 . 4 every 72 hours over 12 days in combination with low dose ( 0 . 5 mg / kg ) rapamycin administered intraperitoneally every 48 hours ( shown schematically in fig5 a ). on day 14 , mice were sacrificed and splenocytes used as responder cells in 5 day ex - vivo allo - mlc with or without further aptamer addition in vitro . ctl induction was significantly suppressed by treating animals with peg - m49 , peg - m52 , or cd200fc alone but not with peg - capt ( p & lt ; 0 . 01 ) ( fig5 b , grey bars ). exposure of circulating lymphocytes to peg - m49 and peg - m52 both in - vivo and after their recovery ( in - vitro ) did not significantly improve the suppression of ctl induction as compared to in - vivo alone ( fig5 b ). this finding suggests that the administration of pegylated cd200r1 agonistic aptamers is sufficient to down regulate immune responses in - vivo and that such aptamers may serve as anti - inflammatory agents for diseases in which cd200 : cd200r1 signalling is implicated . peg - m49 and peg - m52 were evaluated for their capability to prolong survival of allogeneic murine skin grafts . c57bl / 6 mice ( n = 6 ) received balb / c skin allografts ( day 0 ) prior to receiving 6 tail vein injections of 15 μg peg - m49 , peg - m52 , peg - capt or cd200fc in 72 hr intervals over 15 days in combination with low dose ( 0 . 5 mg / kg ) rapamycin administered intraperitoneally every 48 hrs . graft survival was monitored daily by a blinded investigator . rapamycin at this dosage has been shown to have no effect no graft survival when administered alone . treatment with peg - m49 and peg - m52 significantly extended allograft survival as compared to pbs or peg - capt groups ( fig6 b ) ( p & lt ; 0 . 05 , mantel - cox test ). interestingly , at the time of last injection ( day 15 ) only 16 % of mice receiving peg - m49 or peg - m52 had rejected the allografts . after this time point , differences between cd200fc and pegylated aptamers may be linked to differing pharmacokinetic profiles as the circulatory half - life of pegylated aptamers and therefore their bioavailability may differ from the protein cd200fc . the existing enriched libraries from selex to human and mouse cd200r1 were deep sequenced using iontorrent and compared to each other to identify overlapping sequences . these sequences were synthesized and screened for cd200r1 agonistic activity ( suppression of ctl in allo - mlc ) with cells of both human and mouse origin . the identified agonists termed ccs13 and ccs8 ( seq id nos . : 3 and 16 , respectively , see table 1 , above ) were pegylated and activity verified by human and mouse allo - mlc . to evaluate in - vivo immunosuppression c57bl / 6 mice received balb / c allografts ( day 0 ) and were treated with 15 ug pegylated aptamers or cd200 . fc in combination ( 72 hrs , i . v ) with low dose rapamycin ( 0 . 5 mg / kg , 36 hrs , i . p .). immune responses were monitored at day 15 by ex - vivo allo - mlc . lastly therapeutic potential was evaluated by monitoring the capability of peg - ccs13 and peg - ccs8 to prolong survival of the c57bl / 6 allografts using the same treatment regimen described above to a total of 15 days . graft survival was monitored by a blinded investigator . aptamers ccs13 and ccs8 induced potent suppression of ctl induction (& lt ; 50 % specific lysis ) in both human ( fig8 b ) and mouse allo - mlc ( fig8 c ). ccs13 and ccs8 were pegylated and found to retain activity in 5 - day in both human and mouse allo - mlc ( fig9 ). in - vivo administration of peg - ccs8 and peg - ccs13 significantly suppressed immune activity as measured by ex - vivo allo - mlc . ( fig1 ). finally , peg - ccs8 and peg - ccs13 were found to significantly prolong allograft survival ( fig1 ). thus the aptamers ccs8 and ccs13 potently induced immunosuppression in both human and mouse allo - mlc . furthermore pegylated ccs13 and ccs8 retained this ability and functioned in - vivo to suppress immune response and prolong allograft survival . intracellular phosphorylation of cd200r1 in response to m49 , as well as full length and truncated versions of ccs13 was detected using a rabbit polyclonal antibody specific to the phosphorylated cytoplasmic tail of cd200r1 50 . hek - 293 cells stably expressing murine cd200r1 were serum - starved in optimem ( life technologies , burlington , canada ) medium for 3 hrs and subsequently incubated for 30 min in optimem medium containing either m49 ( 1 . 5 μm ), negative control aptamer capt ( 3 μm ), cd200fc ( 3 . 5 μm ), or full length ( fl ) or truncated ( t1 , t2 ) versions of ccs13 ( 3 μm ). cells were washed with pbs and lysed in ripa buffer ( 150 mm nacl , 1 . 0 % igepal , 0 . 5 % sodium deoxycholate , 0 . 1 % sds , and 50 mm tris , ph 8 . 0 ) containing 50 mm naf , 1 mm na3vo4 , and protease inhibitors . phosphorylated and unphosphorylated forms of cd200r1 were recovered by immunoprecipitation using an anti - cd200r1 ( clone 2a10 ) monoclonal antibody ( overnight 4 ° c .) and protein g agarose beads ( pierce ). the phosphorylated form of cd200r1 was detected by western blot using the rabbit polyclonal antibody ( 1 : 1000 dilution ) and anti - rabbit hrp ( 1 : 15 , 000 dilution ) ( fig1 ). full - length ccs13 but not its truncated versions were capable of inducing phosphorylation of the cd200r1 .
disclosed are short dna aptamers that selectively recognize cd200r1 , a protein expressed on the surface of myeloid and lymphoid cells that delivers immune inhibitory signals to modulate inflammation when engaged with its ligand , cd200 . also disclosed is the use of said aptamers as therapeutic agents , for the purpose of decreasing inflammatory response ; treatment of spinal cord injury ; treatment of an immune related disease such as arthritis , allergy , infection ; as a course of treatment during or after transplantation ; or for treatment of an autoimmune disorders such as systemic lupus erythematosus , parkinson &# 39 ; s disease , or multiple sclerosis .