Patent Abstract:
the invention relates to the regulation of the immune system , and in particular to the finding that the clec9a molecule is a marker for dendritic cells which are capable of cross - presenting extracellular antigens via the mhc class i pathway . this makes them particularly suitable for generation of cytotoxic t lymphocyte responses . materials and methods are provided both for the induction of immune responses against target antigens , and for the inhibition or suppression of undesirable immune responses in which these cells are involved .

Detailed Description:
clec9a is a c - type lectin expressed on dendritic cells . as used in this specification , the term clec9a is intended to embrace the human protein ( nucleic acid and protein sequences as shown in fig1 ), the murine protein ( nucleic acid and protein sequences shown in fig2 ), their homologues ( especially orthologues ) in other species , and variants and derivatives thereof which retain clec9a activity . such variants and derivatives preferably have at least about 30 % sequence identity , more preferably at least about 35 %, 40 %, 45 %, 50 %, 55 %, 60 %, 65 %, 70 %, 75 %, 80 %, 85 %, 90 % or 95 % sequence identity to the human protein sequence shown in fig1 , or at least about 35 % identity , more preferably at least about 40 %, 45 %, 50 %, 55 %, 60 %, 65 %, 70 %, 75 %, 80 %, 85 %, 90 % or 95 % identity to the extracellular domain of the human protein sequence shown in fig1 . in particular , conservative substitutions in the clec9a sequence ( as compared to the reference sequences ) may be particularly well tolerated , without substantial effect on function . a conservative substitution may be defined as a substitution within an amino acid class and / or a substitution that scores positive in the blosum62 matrix . according to one classification , the amino acid classes are acidic , basic , uncharged polar and nonpolar , wherein acidic amino acids are asp and glu ; basic amino acids are arg , lys and his ; uncharged polar amino acids are asn , gln , ser , thr and tyr ; and non - polar amino acids are ala , gly , val , leu , ile , pro , phe , met , trp and cys . according to another classification , the amino acid classes are small hydrophilic , acid / acid amide / hydrophilic , basic , small hydrophobic and aromatic , wherein small hydrophilic amino acids are ser , thr , pro , ala and gly ; acid / acidamide / hydrophilic amino acids are asn , asp , glu and gln ; basic amino acids are his , arg and lys ; small hydrophobic amino acids are met , ile , leu and val ; and aromatic amino acids are phe , tyr and trp substitutions which score positive in the blosum62 matrix are as follows : percent (%) amino acid sequence identity with respect to a reference sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the reference sequence , after aligning the sequences and introducing gaps , if necessary , to achieve the maximum percent sequence identity , and not considering any conservative substitutions as part of the sequence identity . % identity values may be determined by wu - blast - 2 ( altschul et al ., methods in enzymology , 266 : 460 - 480 ( 1996 )). wu - blast - 2 uses several search parameters , most of which are set to the default values . the adjustable parameters are set with the following values : overlap span = 1 , overlap fraction = 0 . 125 , word threshold ( t )= 11 . a % amino acid sequence identity value is determined by the number of matching identical residues as determined by wu - blast - 2 , divided by the total number of residues of the reference sequence ( gaps introduced by wu - blast - 2 into the reference sequence to maximize the alignment score being ignored ), multiplied by 100 . a clec9a agonist is an agent capable of inducing clec9a activity , typically by binding to its extracellular domain ( ecd ) and inducing intracellular signalling via its intracellular domain . signalling may involve one or more of binding of syk to the intracellular domain , phosphorylation ( and hence activation ) of syk , and / or phosphorylation of erk and / or activation of nfat . an illustrative assay is described in the examples , using b3z cells transfected with clec9a and syk . the skilled person will understand that a chimeric protein having the extracellular domain of clec9a and an intracellular domain derived from a different protein may also be used to assay for clec9a agonist activity . the transmembrane domain may be from clec9a , the same protein as the intracellular domain , or from another protein . an example is the cd3ζ - nkrp1 - clec9a illustrated in fig5 and described in more detail in the examples . a clec9a antagonist is an agent capable of inhibiting or blocking clec9a function . for example , it may prevent its normal expression , its ability to bind physiological clec9a ligand , its ability to internalise ( endocytose ) molecules to which it has bound , its ability to signal intracellularly ( see above ), or the ability of its ecd to interact with binding partners ( ligands or receptors ), e . g . on other cells . another possible mechanism of action for an antagonist might be to promote internalisation of clec9a without inducing significant intracellular signalling , and so reduce the pool of clec9a available at the cell surface to interact with natural ligands or other agonists . antagonists include binding agents having affinity for clec9a such as anti - clec9a antibodies which lack significant agonist activity . these may be referred to as “ blocking ” antibodies . monovalent or bivalent antibodies without agonist activity may be particularly suitable as blocking antibodies . other clec9a antagonists include nucleic acid molecules or analogues thereof capable of hybridising with dna or rna encoding clec9a . such agents include ribozymes , rnai , sirna , etc . further clec9a antagonists are competitors for the clec9a ligand , which can block binding sites on the ligand for dendritic cell - associated clec9a and so prevent the ligand from being recognised or bound by the dendritic cell . suitable competitors include soluble molecules comprising the extracellular domain of clec9a or a portion thereof sufficient to bind to the clec9a ligand . thus the molecule may comprise an amino acid sequence having at least 70 % identity , at least 75 % identity , at least 80 % identity , at least 85 % identity , at least 90 % identity , or at least 95 % identity to the extracellular domain ( ctld ) of human clec9a as shown in fig1 , or murine clec9a as shown in fig2 , or a fragment thereof having affinity for the clec9a ligand . the fragment may comprise at least 20 , 30 , 40 , 50 , 60 , 70 , 80 , 90 , 100 , 110 or at least 120 amino acids of the respective extracellular domain sequence or a sequence having the required level of identity therewith . the clec9a extracellular domain ( or portion thereof ) may be associated with a heterologous moiety which may modulate some property of the antagonist , such as its pharmacokinetic properties in vivo . the extracellular domain may be covalently or non - covalently bound to the heterologous moiety , or may be expressed as a fusion protein with the heterologous moiety . for example , the heterologous moiety may be an antibody fc domain , in order to provide increased serum half life and allow efficient clearance of complexes between the antagonist and the clec9a ligand . other possible functions of the heterologous moiety include mediating oligomerisation of the clec9a extracellular domain , and facilitation purification of the antagonist or isolation from a sample . for example , a suitable antagonist may be a soluble molecule comprising or consisting of the clec9a extracellular domain ( or a fragment thereof sufficient to bind clec9a ligand ) associated with an avidin monomer . the avidin monomers will tend to associate into tetramers , providing a complex comprising four clec9a domains and four avidin subunits . this construct can readily be isolated by contact with biotin , which may be provided on a solid support such as a bead . where the binding agent or antagonist is a protein , it may be possible to administer a nucleic acid ( e . g . dna ) encoding the antagonist . typically the nucleic acid will be taken up by cells within the body ( e . g . muscle cells ), expressed , and secreted from those cells . this approach is often referred to as dna vaccination . antibodies are particularly suitable as binding agents and antagonists , and can conveniently be expressed in scfv form . if necessary , an antibody can be encoded as a fusion protein with the antigen , or with an effector moiety as described above . an example of a dna vaccination approach is described in nchinda et al ., j . clin . invest . 118 ( 4 ), 1427 - 36 , 2008 . the nucleic acid typically comprises a coding region encoding the binding agent or antagonist , optionally in conjunction with any desired fusion partner , in operable linkage with transcriptional and translational regulatory sequences to ensure appropriate expression and secretion of the protein from cells which take up the nucleic acid . such sequences include ( but need not be limited to ) transcriptional initiation sequences ( e . g . promoter and enhancer ), transcriptional termination sequences , appropriate splicing signals , translational initiation and termination sequences , and a signal peptide to enable secretion . thus the invention further provides a nucleic acid ( e . g . a dna ) encoding a clec9a antagonist or binding agent , for use in a method of medical treatment . also provided is a nucleic acid encoding a clec9a antagonist or binding agent for use in a method of and therapeutic uses thereof . the present inventors have found that clec9a recognises a ligand displayed by certain types of dead and dying mammalian cells . in particular , certain types of cell death appear to trigger display of the ligand . this is a surprising finding because many known members of the c - type lectin family ( including dectin - 1 , which is the most closely related protein to clec9a ) are receptors for pathogen - associated molecular patterns , and so recognise structures displayed by pathogens , rather than self molecules . it is well recognised that certain mechanisms of self cell death are capable of triggering an immune response . these may be regarded as immunogenic cell death . it has been proposed that death by apoptosis ( which normally does not result in rupture of the plasma membrane and release of the intracellular contents ) is non - immunogenic , while death by other mechanisms such as necrosis ( which do involve rupture of the plasma membrane and release of the cell contents ) is immunogenic . however , the physiological situation appears to be rather more complex than this . for example , apoptotic cells in vivo are normally absorbed ( phagocytosed ) by neighbouring cells such as macrophages before the process of cell death is complete . however , if the cells are not phagocytosed , so - called secondary necrosis may occur , in which the plasma membrane may be disrupted and cellular contents released . cell death of this nature may be immunogenic , despite being apoptotic at least in part . immunogenic cell death may play a role in the onset , development or persistence of autoimmune disease . this is reviewed , for example , by vioritto et al ( clin immunol 122 ( 2 ), 125 - 134 ( 2007 )), tesniere et al ( curr op immunol 21 , 1 - 8 ( 2008 )) and kim et al ( immunity 27 , 321 - 333 ( 2007 )) dendritic cells may play a role in induction of any immune response caused by immunogenic cell death , by taking up cellular debris from the dead or dying cells ( or even absorbing the entire cell ) and presenting processed fragments to t cells . the present inventors have now found that clec9a is capable of binding to a ligand displayed by dead or dying cells , and that clec9a signalling may be triggered by this interaction . it is also believed that the ligand is not synthesised de novo during the process of cell death . rather , it may be constitutively expressed by some or all mammalian cells but is not accessible for interaction with clec9a while the cell remains healthy . certain types of cell death result in exposure of the ligand and / or release of the ligand from the cell , in a form capable of interacting with clec9a . this may involve disruption of the plasma membrane . experimentally , exposure of the ligand can be caused by treatments such as irradiation ( e . g . with ionising radiation such as uv light ), serum deprivation , at least one freeze / thaw cycle , or by treatment with chemotherapeutic agents such as anthracyclines ( such as doxorubicin and daunorubicin ) and anthracenedione ( such as mitoxantrone ). however death by osmotic shock appears not to expose the ligand . thus , without wishing to be bound by any particular theory , it is believed that clec9a may be involved in generation of the immune response caused by immunogenic cell death . the interaction between clec9a and its ligand can be inhibited by clec9a antagonists . these include binding agents capable of binding to ( the extracellular domain of ) clec9a . other examples include competitors for clec9a binding sites on the ligand , such as soluble agents comprising the extracellular domain of clec9a or a portion thereof ( e . g . at least 20 amino acids , at least 50 amino acids , at least 100 amino acids , at least 150 amino acids , or at least 200 amino acids of the extracellular domain ) which is capable of binding to clec9a ligand . antagonists capable of inhibiting binding between clec9a and its ligand will be capable of inhibiting clec9a signalling when contacted with suitable dead or dying cells ( e . g . uv - irradiated mammalian cells ) or a lysate , extract or fraction thereof capable of inducing clec9a signalling . any suitable test system may be used to assess this capacity . for example , in dendritic cells expressing clec9a , clec9a signalling may be assessed by determining phosphorylation of syk kinase . alternatively an artificial reporter system may be used comprising the clec9a extracellular domain functionally linked to a reporter system such as the cd3zeta chimera described in the examples . any suitable molecule having a sufficiently high affinity and specificity for clec9a may be used as a binding agent . the molecule may be a protein , nucleic acid ( e . g an aptamer ), carbohydrate ( e . g . oligo - or polysaccharide ), small molecule , etc . particularly preferred binding agents are physiological ligands for clec9 , and antibodies against clec9a and functional fragments thereof . the binding agent preferably has a binding affinity ( affinity constant ) for clec9a , particularly for the clec9a ecd , of at least 10 5 m − 1 , at least 10 6 m − 1 , at least 10 7 m − 1 , preferably at least 10 8 m − 1 , more preferably at least 10 9 m − 1 . the binding agent preferably has an affinity at least 2 ×, and preferably at least 5 ×, at least 10 ×, at least 50 × or at least 100 × greater than for any non - clec9a molecule , including other c - type lectins . it is well - known that fragments of a whole antibody can perform the function of binding antigens . examples of functional binding fragments are ( i ) the fab fragment consisting of vl , vh , cl and ch1 domains ; ( ii ) the fd fragment consisting of the vh and ch1 domains ; ( iii ) the fv fragment consisting of the vl and vh domains of a single antibody ; ( iv ) the dab fragment ( ward , e . s . et al ., nature 341 , 544 - 546 ( 1989 )) which consists of a vh domain ; ( v ) isolated cdr regions ; ( vi ) f ( ab ′) 2 fragments , a bivalent fragment comprising two linked fab fragments ( vii ) single chain fv molecules ( scfv ), wherein a vh domain and a vl domain are linked by a peptide linker which allows the two domains to associate to form an antigen binding site ( bird et al , science , 242 , 423 - 426 , 1988 ; huston et al , pnas usa , 85 , 5879 - 5883 , 1988 ); ( viii ) bispecific single chain fv dimers ( pct / us92 / 09965 ) and ( ix ) “ diabodies ”, multivalent or multispecific fragments constructed by gene fusion ( wo94 / 13804 ; p . holliger et al proc . natl . acad . sci . usa 90 6444 - 6448 , 1993 ). as antibodies can be modified in a number of ways , the term “ antibody ” should therefore be construed as covering any specific binding substance having an binding domain with the required specificity . thus , this term covers the antibody fragments described above , as well as derivatives , functional equivalents and homologues of antibodies , including any polypeptide comprising an immunoglobulin binding domain , whether natural or synthetic . chimaeric molecules comprising an immunoglobulin binding domain , or equivalent , fused to another polypeptide are therefore included . cloning and expression of chimaeric antibodies are described in ep - a - 0120694 and ep - a - 0125023 . it will be appreciated that the binding agents used in the methods described herein are generally required to bind the extracellular domain of clec9a in order to exert the required effect . reference to a binding agent capable of binding clec9a should be construed accordingly , unless the context allows otherwise . in certain aspects of the invention , it is desirable to cross - link an antigen ( e . g . a protein or peptide antigen ) to a binding agent as described . the skilled person is well aware of suitable methods and reagents . where the binding agent is a protein , the antigen may be coupled via a sulphydryl group of the binding agent . the sulphydryl group may normally be free , or it may normally be part of a disulphide bond in which case it may be exposed by selective reduction of the binding agent . for example , an antibody can be mildly reduced selectively in the hinge region using the reducing agent mercaptoethanosulfonate . then , the antigen is activated using sulpho - smcc , an hetero - bifunctional cross - linking reagent that reacts with the tertiary amines of the protein , generating groups reactive with free sulphydryls . then , the antibody and the activated antigen are incubated together resulting in the protein being conjugated to the monovalent antibody 18 . alternatively , if a suitably immunogenic peptide sequence from the antigen is known , such a peptide containing a cysteine with a free sulphydryl can be synthesized and coupled to sulpho - smcc activated antibody , which will remain bivalent and with several peptides bound per molecule of antibody . the polypeptides , antibodies , peptides , nucleic acids and cells described herein can be formulated in pharmaceutical compositions . these compositions may comprise , in addition to one of the above substances , a pharmaceutically acceptable excipient , carrier , buffer , stabiliser or other materials well known to those skilled in the art . such materials should be non - toxic and should not interfere with the efficacy of the active ingredient . the precise nature of the carrier or other material may depend on the route of administration , e . g . oral , intravenous , cutaneous or subcutaneous , nasal , intramuscular , intraperitoneal routes . pharmaceutical compositions for oral administration may be in tablet , capsule , powder or liquid form . a tablet may include a solid carrier such as gelatin or an adjuvant . liquid pharmaceutical compositions generally include a liquid carrier such as water , petroleum , animal or vegetable oils , mineral oil or synthetic oil . physiological saline solution , dextrose or other saccharide solution or glycols such as ethylene glycol , propylene glycol or polyethylene glycol may be included . for intravenous , cutaneous or subcutaneous injection , or injection at the site of affliction , the active ingredient will be in the form of a parenterally acceptable aqueous solution which is pyrogen - free and has suitable ph , isotonicity and stability . those of relevant skill in the art are well able to prepare suitable solutions using , for example , isotonic vehicles such as sodium chloride injection , ringer &# 39 ; s injection , lactated ringer &# 39 ; s injection . preservatives , stabilisers , buffers , antioxidants and / or other additives may be included , as required . administration is preferably in a “ prophylactically effective amount ” or a “ therapeutically effective amount ” ( as the case may be , although prophylaxis may be considered therapy ), this being sufficient to show benefit to the individual . the actual amount administered , and rate and time - course of administration , will depend on the nature and severity of what is being treated . prescription of treatment , e . g . decisions on dosage etc , is within the responsibility of general practitioners and other medical doctors , and typically takes account of the disorder to be treated , the condition of the individual patient , the site of delivery , the method of administration and other factors known to practitioners . examples of the techniques and protocols mentioned above can be found in remington &# 39 ; s pharmaceutical sciences , 20th edition , 2000 , pub . lippincott , williams & amp ; wilkins . a composition may be administered alone or in combination with other treatments , either simultaneously or sequentially dependent upon the condition to be treated . a search of the ncbi gene database shows that clec9a sequence has been already identified in mus musculus , pan troglodytes , homo sapiens and macaca mulatta . a blast search using the protein sequence of mouse clec9a , also shows predicted clec9a proteins in rattus norvegicus , canis familiaris and bos laurus . the human cdna sequence and the annotated protein sequence with relevant domains is detailed in fig1 . the mouse cdna sequence which we have cloned from mouse cd8α + dcs and its annotated protein sequence is detailed in fig2 . this sequence differs from the published cdna sequence , which contains an additional g residue causing a frameshift towards the end of the molecule , leading to a longer protein than that shown in fig2 . our sequence appears to be correct , since it matches the published genomic sequence ( nc — 000072 . 4 gi : 94471533 ); as can be seen in this page the position 13480 of the genomic ( a t tt ) matches our cdna sequence . the sequences predict a c - type lectin family protein with a c - type lectin - like domain , ( ctld ), a stalk region , a transmembrane region and a cytoplasmic domain containing one - species - conserved tyrosine highlighted in fig1 and 2 . we have found transcripts for three isoforms of mouse clec9a that we have termed long isoform ( exons 1 - 7 ), short isoform that lacks exon 4 , including a putative cysteine involved in dimerization , and very short isoform , that couples exon 3 to exon 7 , yielding a mrna coding for a transmembrane protein that , if expressed , would share the transmembrane - intracellular domains with clec9a but would have a short and different extracellular domain . we only have evidence of protein expression for the long isoform . the structure of mouse clec9a was analyzed . the core protein has a predicted molecular weight ( mw ) of about 29 . 67 kda however , when expressed in the hek - 293 cell line the mw is about 100 kda in non - reducing conditions , and a mw of about 45 kda in reducing conditions ( fig3 ). these results indicate that the molecule forms dimers through the cysteine in the stalk , like other lectins in the family , and the monomer is strongly glycosylated . clec9a was first detected in our laboratory as a result of a representational difference analysis between samples of mouse spleen cd11c + cd8 + and cd11c + cd8 − cells . the results showed that sequences corresponding to the est clone aw318446 , corresponding to clec9a , were selectively found in the cd11c + cd8 + transcripts . the analysis of the transcripts in sorted subsets of splenic dcs revealed high expression of clec9a in the cd8 + subset , although double negative ( cd4 − cd8 −) and b220 + spleen dc also showed some transcripts for clec9a ( fig4 ). no significant expression was found in gmcsf - derived bmdc ( fig4 ). mouse bone marrow cultured for 10 days in the presence of flt3l ( 50 ng / ml ) generates cd11c + cells that are either cd11b +, functionally corresponding to spleen conventional dc and including a cd8 - like subset 19 , or b220 +, which are functional equivalents of plasmacytoid dc ( pdc ). high expression of clec9a was found in the sorted cd11b + subset , although the pdc subset showed some expression of the molecule ( fig4 ). since the rt - pcr is a sensitive technique that can detect very low level of transcript , it is limited by the quality of purification of the sample . to unequivocally determine the pattern of expression of clec9a , we generated rat monoclonal antibodies ( mab ) against mouse clec9a , using a cd3ζ - nkrp1 - clec9a chimera expressed in b3z cells with a β - gal reporter ( fig5 ) as indicated under methods . we selected three mabs named 1f6 , 397 , and 7h11 . using these mab , we have studied the pattern of expression of the molecule in mouse spleen and bone marrow . clec9a was highly expressed in cd8a + conventional dcs ( mfi ˜ 350 - 400 ) and showed moderate expression ( mfi ˜ 65 - 70 ) in pdcs ( fig6 ). the molecule was not detected in other cell types explored including b cells , t cells , nk cells , nkt cells , monocytes , macrophages and granulocytes . as a model for analysis of clec9a function in vitro , we analyzed expression in mouse gmcsf - and flt3l - derived bmdc . we did not detect expression of the molecule in gmcsf - derived bmdc , whereas clec9a was selectively expressed in the cd11b lo , cd24 hi , b220 - subset of flt3l bmdc , functionally homologous to cd8 + splenic dc 19 , and also in a subset of the cd11b lo b220 +, equivalent to pdc ( data not shown ). sequence analysis reveals tyr7 from mouse that is conserved in all the species with the same structure exxyxxl , which could serve as a putative sh2 binding domain and / or a tyrosine - based sorting signal . this sequence allows / mediates syk binding in mouse dectin - 1 and is termed “ hemitam ” 22 . however , this putative sequence is necessary but not sufficient for predicting syk binding . in consequence , we designed biotinylated peptides with the cytoplasmic tail of mouse clec9a expressing the phosphorylated tyr7 , or with that tyr7 without phosphorylation or even mutated to phe . the tyr7 phosphorylated peptide was able to pull down recombinant syk ( fig7 ) to a similar extent than the cytoplasmic tail from mouse dectin - 1 expressing both tyr phosphorylated as a positive control 23 . to determine if clec9a truly acts as a signalling receptor , we used the rat anti - mouse clec9a mab above described . we generated transfectants expressing clec9a in lk cells , a mouse b cell line negative for clec9a expression but containing endogenous levels of syk 23 . the triggering of clec9a with all three plated anti - clec9a antibodies tested resulted in phosphorylation of syk and erk in lk cells ( fig8 ). to determine whether syk is necessary for clec9a signalling , we used stable transfectants of the reporter t cell line b3z , which does not express syk . the contribution of the tyr7 to clec9a signalling was analyzed using a mutant version of clec9a with the tyr7 mutated to phe ( clec9a y7f ). we transduced b3z cells with clec9a wt or y7f and co - transduced or not with syk kinase . plated anti - clec9a mabs induced nfat activation in b3z - c9 wt - syk through the wt cytoplasmic tail of c9 , but not in the absence of either syk or the y7 ( not shown ). to determine whether signalling through clec9a can contribute to the production of regulatory cytokines or expression of co - stimulatory molecules in the cells where is expressed , we have analyzed lk transfectants with wt clec9 or the y7f mutant . hybridoma cells expressing 397 anti - clec9a and , to a lesser extent , 7h11 triggered specific il - 2 production through the clec9a molecule that was abolished in the y7f mutant ( fig9 ). dec - 205 control hybridoma did not trigger any response and 1f6 anti - clec9a triggered a reduced response that opens the possibility that these antibodies can behave differentially for cytokine production , which would be very attractive from the prospective of clec9a targeting ( agonist antibody , 397 , versus blocking antibody , 1f6 ). to determine the requirements for clec9a wt tail activation we analyzed stable transfectants of the reporter t cell line b3z , which does not express syk . the contribution of the tyr7 to clec9a signalling was analyzed using a mutant version of clec9a with the tyr7 mutated to phe ( clec9a y7f ). we transduced b3z cells with clec9a wt or y7f and co - transduced or not with syk kinase . plated anti - clec9a mabs induced nfat activation in b3z - c9 wt - syk through the wt cytoplasmic tail of c9 , but not in the absence of either syk or when the y7f mutant was used ( fig1 ). flt3l bmdc respond to plated anti - clec9a mabs by production of il12 - 23 p40 protein ( fig1 ). these results demonstrate that clec9a is a signalling molecule capable of activating dcs . clec9a is an endocytic receptor that selectively targets cd11c + cd8 + dc in vivo the potential of anti - clec9a mab to be internalised by endogenous clec9a expressed in flt3l bmdc was analyzed by facs and revealed that clec9a is an endocytic molecule . confocal analyses showed targeting of the antibody to intracellular compartments ( data not shown ). these results suggest that clec9a is an endocytic receptor that can be targeted by antibodies coupled to antigens ( tumor / viral vaccination ) to specifically deliver the cargo to cell subsets selectively expressing the molecule . to determine whether clec9a mab serve as a targeting tool in vivo , we injected i . v . 7h11 - alexa - 488 or isotype control . after 16 h , we analyzed total splenocytes and the antibody selectively targeted cd8a + dc ( mfi ˜ 350 - 400 ), and , with lower affinity , pdc ( mfi ˜ 65 - 70 ). labelling of splenocytes with anti - rat cy5 suggested that most of the rat anti - mouse clec9a mab was endocytosed , since it did not co - stained with the anti - rat secondary reagent ( not shown ). to explore whether the targeting through clec9a leads to the processing and presentation of antigen by a specific subset in vivo , we coupled a biotinylated derivative of an immunodominant peptide for the ctl response to ova protein ( siinfeklc - biot , named s1 ) to isotype control or anti - clec9a mab as indicated under methods . the biotinylation of the peptide allowed us to determine that there was between 1 - 1 . 2 peptides per antibody in all cases . mice were injected i . v . either with 5 μg of the s1 - coupled anti - clec9a or with the s1 - isotype control . the following day , splenocytes were enriched in cd11c + or cd11c − subsets and tested for their ability to induce ot - i t cell proliferation and cytokine production ( fig1 a and b ). only the anti - clec9a targeted cd11c + cells resulted in proliferation and ifn - γ production by ot - i cells , showing that clec9a targets specifically cd11c + dc resulting in presentation to antigen - specific t cells . to further determine which subset of dendritic cells is targeted by anti - c9 , mice injected with s1 - coupled anti - c9 were sorted in the three major subsets of conventional dcs and tested with ot - i t cells as above . only the cd8 + subset of dcs mediated proliferation and ifn - γ production by t cells , confirming that clec9 targets specifically the cd11c + cd8 + dc resulting in priming of antigen - specific t cells ( fig1 c and d ). targeting in vivo using anti - clec9a mab plus anti - cd40 results in priming of ctls and tumor rejection we explored whether clec9a targeting in vivo could induce specific t cell activation . injection of 2 μg of anti - c9 - s1 , but not the isotype control , results in the induction of specific ctl activity from the endogenous repertoire in vivo when co - administered with anti - cd40 ( fig1 ). this behaviour is similar to that observed with anti - dec205 - s1 , previously described 24 as evidenced by in vivo killing assays ( fig1 a ). mice given s1 coupled to control mab did not eliminate target cells irrespective of anti - cd40 co - administration . in contrast , target cells were completely eliminated from mice given s1 coupled to anti - clec9a together with anti - cd40 . no response was seen when the anti - cd40 mab was omitted . consistent with target cell elimination , significant numbers of tetramer positive ova / h - 2 kb - specific cd8 + t cells were found only in the spleens and blood of mice that had received anti - clec9a - s1 together with anti - cd40 . re - stimulation of the same cells with siinfekl peptide in vitro resulted in secondary expansion , with ifn - γ production and specific killing activity . identical results were obtained using anti - clec9a conjugated to a longer peptide of ova containing the siinfekl epitope (“ s2 ”; siinfekltewtssnvmeerc ; fig1 e ). notably , free s1 peptide was unable to induce in vivo killing responses or elicit a significant number of tetramer positive cells even when given at 100 times excess over the amount present in anti - clec9a - s1 conjugates ( not shown ). we conclude that targeting of exogenous antigen to clec - 9a together with an appropriate adjuvant allows efficient crosspriming of cd8 + t cells . to determine whether clec9a priming of ctl activity can result in tumor therapy , we used the model of b16 melanoma lung metastasis . we inoculated i . v . 2 × 10 5 b16 - ova - gfp melanoma cells and 6 days later different antibodies conjugated to s1 siinfekl derivative ( 10 μg ) together with anti - cd40 ( 25 μg ) were injected s . c . in the paw ( fig1 ). after 18 days following injection of the tumor , the number of lung tumors was analyzed . the results revealed that anti - clec9a plus anti - cd40 is effective for tumor therapy ( p & lt ; 0 . 001 , one way anova ) ( fig1 ). we extended the experiments to determine whether anti - clec9a targeting can also be used to induce immune responses to endogenous melanocyte differentiation proteins that can serve as b16 tumor - associated antigens ( 25 - 27 ). we synthesised biotinylated peptides encompassing h - 2kb and h - 2db - restricted antigenic epitopes from gp100 , trp - 1 and trp - 2 ( 25 - 27 ), coupled these covalently to anti - clec - 9a and immunized mice with the antibody conjugates together with poly i : c and anti - cd40 as adjuvants . as shown in fig1 , a single dose of vaccine given therapeutically three days post transfer of b16 melanoma cells induced nearly complete eradication of lung pseudo - metastases . this was accompanied by the induction of potent ifn - γ responses against the melanoma antigens ( fig1 ). in contrast , the same antigens in untargeted form ( conjugated to a control isotype - matched mab ) failed to induce protection or ifn - γ responses ( fig1 a , b ). similar results were obtained in a prophylactic model in which the vaccine was given prior to b16 challenge ( fig1 c ). we conclude that priming of specific ctl via clec - 9a targeting can be used for prophylactic or therapeutic vaccination against mouse tumors . human clec9a expression is restricted to a small subset of blood dc to extend these findings to humans , we cloned hclec9a and generated mouse mabs against it ( see materials and methods ). one of these mabs was selected to analyze the pattern of clec9a expression among human peripheral blood mononuclear cells . human clec9a expression was absent from lymphocytes , monocytes , nk cells and lineage - negative hladr - cells ( fig1 a ). it was also not detected in monocyte - derived dc generated by culture in gm - csf and il - 4 ( data not shown ). however , clec9a expression was apparent in a discrete subpopulation of blood dc , defined as lineage - negative hla - dr + cells ( fig1 a ). five distinct subsets of blood dc have been reported , including a population of cd123 + pdc and different subsets of putatively myeloid cd123 - dc distinguishable on the basis of expression of cd16 , cd1b / c , bdca - 3 , and cd34 ( 22 ). the clec9a + subpopulation of dc was negative for cd123 , suggesting that human pdc do not express clec9a , unlike pdc in the mouse ( fig1 b ). clec9a + blood dc were also negative for cd34 , cd16 and cd1b / c . however , clec9a + dc were uniformly positive for bdca - 3 ( fig1 b ). human clec9a therefore selectively marks a distinct population of bdca - 3 + dc . finally , we assessed whether human clec - 9a , like its mouse orthologue / can function as an endocytic receptor in dc . bdca - 3 + dc were stained at 4 ° c . with alexa 488 - labelled anti - clec - 9a . after 1 h at 37 ° c . but not at 4 ° c ., fluorescence was found in intracellular compartments ( not shown ). therefore , human clec - 9a mediates endocytosis of bound antibody in bdca3 + dc , thereby suggesting that it could be used for antigen targeting to these cells in humans . bwz cells containing the clec9a - cd3ζ chimera have a short generation time and can easily overgrow , generating a significant proportion of dead cells in the culture . we observed a basal activation in the bwz transfectants expressing clec9a without any further stimulation , correlating with the number of dead cells in the bwz culture ( fig1 a ). to confirm these results we used a cell line that does not induce a response when added to the bwz - clec9aζ transfectants . lk cells do not induce a response when exposed to the reporter cells . however , when lk cells were uv - irradiated to induce cell death , they turned into potent inducers of the reporter ( fig1 b ), suggesting that altered cells following uv treatment express ligand / s for clec9a . since bivalent antibodies trigger cross - linking of the molecule expressed in the b3z cell line and reporter activation , blocking antibodies cannot be tested in this system to demonstrate the specificity of the interaction . however , monovalent fab fragments of anti - clec9a antibodies did not trigger the reporter activity and blocked induction by uv - treated cells in a species - specific fashion ( fig1 b ), demonstrating that the antibody acts blocking specifically the clec9a receptor to avoid interaction with the ligand . this result was confirmed in other independent uv - irradiated cell types ( murine 3t3 , lk cells , mefs , el - 4 ), rat rbl cells , and human hek - 293 . when cells are pre - incubated with caffeine ( which prevents uv - induced dna damage and apoptosis ) and then exposed to uv radiation , exposure of the ligand is not induced . we exposed lk cells to different doses of uv and we found that expression of ligand in lk cells correlates with the number of dead lk cells ( fig1 c ), showing that the ligand is selectively expressed in this population . to confirm this in an independent fashion , we generated recombinant soluble extracellular domain ( rsctld ) for mouse clec9a , and mouse dectin - 1 as a control , each coupled to a bira sequence for monobiotinylation . monobiotinylated rsctld was used to generate pe - tetramers . we stained cells treated with uv 24 h earlier and we detected specific binding of clec9a rsctld tetramers to to - pro 3 positive cells ( fig1 d , dot plots ). as a control , dectin - 1 rsctld tetramers did not bind dead cells , yet they bound to their specific ligand zymosan ( fig1 d , histogram ). as uv treatment induces dna damage and a series of related stress markers , we tested whether the induction of ligands was caused by dna damage or mostly by processes involved in cell death . not only dna damage - causing reagents , but also serum deprivation or even freeze - thaw , which has been shown to promote primary necrosis resulting in immunogenic cell death , led to exposure of the ligand ( fig1 e ). however , osmotic shock , which induces instant cell death that has been shown to behave as tolerogenic , did not expose clec9a ligand ( fig1 e and f ). in conclusion , clec9a ligand is exposed in cells following certain types of primary and secondary necrosis . moreover , we have found that fixation ( or fixation and permeabilization ) of the cells instantly promotes changes that make cells permeable to to - pro3 and “ expose ” the ligands for clec9a ( fig2 ) further demonstrating that synthesis of the ligand is not induced as a result of damage response to uv , but is exposed as a result of the process of dying in response to certain stimuli . clec9a mediates an adjuvant signal delivered by dying cells to dendritic cells . uv - dead cells signal through the cytoplasmic domain of clec9a in a syk and y7 - dependent fashion ( fig2 ). this system allowed us to explore whether anti - clec9a antibodies could act as specific blocking reagents for this interaction and we found that both fab and full antibodies in soluble form were powerful blocking reagents ( fig2 ). to test the effects of dying cells in dendritic cells and their effector function in vitro , we designed a cross - presentation assay in which uv - treated bm - 1 cells loaded with ova protein were allowed to interact with flt3l bmdc in the presence or absence of blocking anti - clec9a . bm - 1 cells are from a b6 haplotype but express a mutated h2k b that does not bind the immunodominant class i peptide for ova ( siinfekl ). as a readout for dc capacity for cross - priming , specific ot - i cells were added to the assay . proliferation of ot - i cells , as readout for the amount of antigen that was cross - presented , was not greatly affected ( fig1 a ). however , cytokine production by ot - i cells , which is dependent in the help promoted by dc activated by an adjuvant effect , was severely inhibited when blocking clec9a antibodies were used ( fig1 a and b ). to confirm these results we generated mice deficient in clec9a , expressing egfp under the control of clec9a promoter ( clec9a egfp /− ). we generated flt3l bmdc deficient or not in clec9a and we analyzed whether the uptake of dying cells was affected . fig1 c shows no difference between in the capacity for uptake of dying cells between clec9a + and clec9a − flt3l bmdc . then , we assayed the effect of clec9a deficiency in flt3l bmdc in cross - presentation to ova protein either loaded in uv - treated bm - 1 cells or expressed intracellularly in a non - secreted ova - gfp fusion protein in bm - 1 mefs that were uv treated ( fig1 d ). ot - i proliferation was affected , suggesting a more profound effect in blockade of cross - presentation than the antibody blockade . however , at higher doses of ova , including ova expressed by bm1mefs , proliferation was not affected and ifnγ production was severely inhibited ( fig1 d and e ). these results suggest that there is a blockade in the adjuvant effect associated to dying cells during cross - priming in vitro in the absence of clec9a in dcs . as cd8α + dc expressing clec9a are the main cell type characterized to promote cross - priming to dead cell associated antigen in vivo , we tested the effect of clec9a blockade in this function . mice that received uv - treated bm1 mefs expressing ova showed expanded cd8 + t cells against ova from the endogenous repertoire 6 days later ( fig1 a , left panel ). these cd8 + t cells were able to produce ifn - γ in response to siinfekl , showing that they are effector cells and that dead cells behaved as an immunogenic carrier of antigen associated to adjuvant activity of dead cells ( fig1 a , right panel ). pre - treatment with anti - clec9a blocking antibody , but not with isotype control , blocked both the generation of specific cd8 response and its effector activity ( fig1 a ). to determine the precise role of clec9a in the process of immunogenicity of dead cells related to crosspriming to dead cell - associated antigen , we exploited the assay in clec9a egfp /− mice . the results showed a very significant and partial inhibition of crosspriming to dead cell associated antigen in vivo in the absence of clec9a ( fig1 b , left panel ). as knock - out mice were generated in a mixed c57bl / 6 - 129 background and are being back - crossed with c57bl / 6 ( n3 ), we grouped the 12 female litters whose individuals were pooled in fig1 b , left panel , and we compared the average between clec9a + and clec9a − mice , showing that 12 out of 12 litters showed reduction , with an average 30 . 05 % inhibition ( p & lt ; 0 . 0001 , student &# 39 ; s t test ) ( fig1 b , right panel ). as shown in fig1 b , right panel , differences in background penetrance among different litters could explain significant variability in cross - priming ability among litters and dampen the real difference between clec9a + and clec9a − mice , which is still very significant albeit only partial . moreover , ifn - γ production in response to siinfekl ex vivo was severely affected , showing the deficiency in effector response generated via cross - priming to dead - cell associated antigen in the absence of clec9a ( fig1 c ). in conclusion , clec9a deficiency results in a reduced adjuvancy of the dead - cells with associated antigen that leads to a blockade in specific t cell effector response to dead cell associated antigen . c57bl / 6 mice , ot - i mice on a rag −/− c57bl / 6 background and b6 . sjl background mice ( congenic cd45 . 1 + ) were bred at cancer research uk in specific pathogen - free conditions . k bm − 1 mice were purchased from the jackson laboratory ( bar harbor , me . ; stock number 001060 ), and , together with c57bl / 6 mice , ot - i mice on a rag −/− c57bl / 6 background , myd88 - trif double knock out , clec9a + , and clec9a −/− mice were bred at cancer research uk in specific pathogen - free conditions . bone marrow chimeras were made from syk - deficient fetal liver cells as previously described ( turner et al . nature 378 , 298 ( 1995 )) all animal experiments were performed in accordance with national and institutional guidelines for animal care . culture medium was rpmi 1640 ( invitrogen ) supplemented with glutamine , penicillin , streptomycin , 2 - mercaptoethanol ( all from invitrogen ) and 10 % heat - inactivated foetal calf serum ( bioclear ). antibodies used for flow cytometry analysis experiments were from bd pharmingen and included those specific for cd11c ( clone hl3 , hamster igg1 ), cd24 , cd11b , b220 , ly6c , cd4 ( rm4 - 5 , rat igg2a ), cd8 . antibodies used for elisa were capture ifn - γ ( xmg1 . 2 , rat igg1 ) detection / il12 - 23 p40 . purified 2 . 4g2 ( anti - fcgriii / ii , rat igg2b , used to block unspecific ab binding ) was from cancer research uk antibody production service . for flow cytometry , cell suspensions were stained in ice - cold pbs supplemented with 2 mm edta , 1 % fcs and 0 . 02 % sodium azide . data were acquired on a facscalibur ( bd biosciences ) and analyzed using flowjo software ( treestar , san carlos , calif .). mouse bone marrow - derived dcs ( bmdcs ) were generated using gm - csf and purified from bulk cultures by magnetic selection with anti - cd1c microbeads ( gm - csf bmdcs ). alternatively , bmdcs were generated by culturing bone marrow cells in the presence of 100 ng / ml of flt3l ( r & amp ; d ) for 10 days , by which time all living cells were positive for cd11c ( flt3l bmdcs ). spleen cells were prepared by liberase / dnase digestion and enriched for dc by positive selection with anti - cd11c microbeads . ot - i t cells ( from lymph nodes and spleen ) were purified by negative selection using a cocktail of biotinylated antibodies ( anti - cd11c , cd11b , b220 , fcγr , gr - 1 , and cd4 ) followed by streptavidin microbeads . human peripheral blood mononuclear cells ( pbmcs ) were prepared from single donor leukocyte buffy coats ( national blood transfusion service ) by sedimentation over ficoll - hypaque ( ge - healthcare ). total rna was extracted using trizol ( invitrogen ) from subsets of splenic dc enriched in cd11c with anti - cd11c microbeads ( miltenyi ) and sorted for cd4 and cd8 expression in a facsaria sort ( bd ). in addition , rna was extracted from sorted subsets of gmcsf and flt3l in vitro derived bmdc . rna was prepared by dnase digestion ( dna - free , ambion ) and reverse transcribed using superscript ii reverse transcriptase ( gibco ), 1 μm dntps and 10 μm random hexanucleotides ( gibco ). cdna was amplified using 35 pcr - cycles , consisting of 30 s 94 ° c ., 30 s 55 ° c ., 1 m 72 ° c . sequences of primers were : mclec9a fw 5 ′ agactgcttcaccactccaa ; mclec9a rv : 5 ′ cttggcacaatggacaaggt ; b - actin fw : 5 ′ gtttgagaccttcaacacccc , b - actin rv : 5 ′ gtggccatctcctgctcgaagtc ; hclec9a fw : 5 ′ cccaagtctcatttggagga ; hclec9a - 1 rv : 5 ′ aaatctggacggtgtggaag . wistar rats were immunized with rbl - 2h3 cells transfected with clec9a fused to an ha epitope and fusion of splenocytes from hyper - immunized rats with the rat myeloma cell line y3 was performed following standard procedures . for the detection of positives , we used the b3z cell line 25 expressing a chimera with the extracellular domain of clec9a , the transmembrane region from nkrp1b and the intracellular tail of cd3ζ and followed by an ires - gfp , a strategy that has been described 21 . the cdna sequence of the fusion chimera for mclec9a is shown in fig3 . the b3z cell line contains a reporter for nfat coupled to β - gal activity and any engagement of the chimerical molecule results in the activation of nfat and the reporter , that can be then revealed following standard assays for b - gal activity . the screening for antibodies was by functional activation of the b3z expressing the chimera compared with the parental cell line . those antibodies that were selected as positives were confirmed by facs analysis in the parental cell line ( egfp −) compared to the clec9a chimera expressing cells ( egfp +). this method allowed the selection of three mabs named 1f6 , 397 , and 7h11 as shown in fig4 . mab were then conjugated to biotin or to alexa488 for staining ( invitrogen ), or used for conjugation with s1 peptide . balb / c mice were immunized 3 - 4 times with rbl - 2h3 cells expressing human clec9a fused to an ha epitope . fusion of splenocytes with the mouse myeloma line sp2 / 0 was carried out using standard procedures . for hybridoma screening , we used the b3z cell line , which expresses a β - gal reporter for nfat ( 23 ). this cell line was transduced with a retrovirus encoding a chimera of the extracellular domain of human clec9a fused to the transmembrane region from nkrp1b and the intracellular tail of cd3 followed by an ires sequence and the gfp gene ( 24 ). hybridoma supernatants were screened for the ability to bind to the clec9a chimera , resulting in the activation of the nfat reporter and induction of β - gal activity ( 24 ). supernatants that tested positive in this assay were further screened by flow cytometry using a mixture of b3z cells expressing the chimera clec9a ( gfp +) and parental b3z cells ( gfp −). this method allowed the selection of one mouse mab specific for hclec9a ( 8f9 ( igg2a )). flow cytometry fluorochrome - or biotin - labeled antibodies specific for mouse cd11c , cd24 , cd11b , b220 , ly6c , cd4 and cd8α were from bd pharmingen . purified 2 . 4g2 ( anti - fcγriii / ii ) was from cancer research uk antibody production service . mouse cell suspensions were incubated with 10 μg / ml of 2 . 4g2 mab to block fcγ receptors and were then stained in icecold pbs supplemented with 2 mm edta , 1 % fcs and 0 . 02 % sodium azide . for endocytosis studies , fcγr - blocked cells were labeled with 5 μg / ml of biotinylated anti - clec9a mab for 30 min at 4 ° c . cells were then washed twice and incubated for different times at 4 ° c . or 37 ° c . before transferring to ice and adding streptavidin pe . for in vivo labeling studies , alexa - 488 conjugated anti - clec9a or isotype - matched control mabs were injected i . v . at the indicated dose and tissues were prepared and analyzed after 16 h . antibodies specific for human cd3 , cd14 , cd19 , cd56 , hla - dr , cd34 , cd123 and cd16 were purchased from bd , and cd1b / c , and bdca - 3 were from abcam ( cambridge , uk ). human mononuclear cells were blocked with 100 μg / ml human igg ( sigma - aldrich ) and stained as above . data were acquired on a facscalibur ( bd biosciences ) and analyzed using flowjo software ( treestar , san carlos , calif .). gm - csf bm - dc were generated as described 26 and dc were purified from bulk cultures with anti - cd11c microbeads before use ( miltenyi biotec ). bm - dc purity was checked by facs and was routinely & gt ; 98 % ( data not shown ). flt3l bmdc were generated from bone marrow cultured in the presence of 75 ng / ml or 50 ng / ml of flt3l ( r & amp ; d ) for 10 days . for cytokine production and surface marker expression analyses , 5 - 10 × 10 4 flt3l bm - dc per well were cultured for 18 - 24 hours in 200 ml culture medium containing flt3l in 96 - well flat - bottomed plates previously coated with isotype control or anti - clec9a mab . cytokine levels in the supernatants were measured by sandwich elisa using capture anti - il - 12 p40 - p70 ( c15 . 6 ) and detection biotin anti - il12p40 - p70 ( c17 . 8 ), both from bd . for endocytosis in flt3l bmdc , fcγr were blocked with 10 μg / ml of 2 . 4g2 mab and cells were then cultured with 5 μg / ml of biotinylated mab for 30 min at 4 ° c . or 37 ° c ., washed and allowed for 1 . 5 h or 0 . 5 h at the assay temperature before washing and adding simultaneously the secondary reagent ( streptavidin pe ) at 4 ° c . for confocal analysis , alexa 488 conjugated mab were added to fcγr - blocked flt3l - bmdc at 5 mg / ml for 30 min at 4 ° c . or 37 ° c . and then washed and allowed for a further 1 . 5 h at the assay temperature before allowing to adhere to poly - l - lysine - coated coverslips and fixation in 2 % pfa for 20 min rt . samples were mounted in slides with fluoromount ( southern biotech , birmingham , ala .). a confocal series of differential interference contrast and fluorescence images was obtained simultaneously with a laser scanning confocal microscope ( axioplan 2 , zeiss , germany ) with a 63 °— plan - apochromat na 1 . 4 oil objective . image analysis was performed with lsm 510 software ( zeiss , germany ). for peptide pull - downs , biotin - conjugated peptides were dissolved in 40 % dmso before dilution in lysis buffer . recombinant human syk ( upstate ) diluted in lysis buffer was incubated with the indicated biotinylated peptides corresponding to the clec9a and dectin - 1 intracellular tail ( cancer researchuk peptide synthesis laboratory ) and streptavidin - sepharose ( sigma biosciences ab , uppsala , sweden ). after affinity purification , sepharose beads were washed once in lysis buffer and boiled in sds gel - loading buffer containing 10 % β - mercaptoethanol . proteins were separated by sodium - dodecyl - sulfate - polyacrylamide gel electrophoresis ( sds - page ), transferred onto immobilon pvdf membranes ( millipore corporation , bedford , mass . ), and probed with rabbit anti - syk ( a combination of 2131 serum raised against a synthetic peptide corresponding to amino acids 318 - 330 of murine syk 2 ° and anti - syk from cell signaling technology , inc ., catalog number 2712 , raised against a synthetic peptide corresponding to the c terminus of human syk ) followed by chemiluminescent detection . in the lk cell activation assay , lk cells were plated in 6 - well plates coated with anti - c9 or isotype control for the indicated times . cell extracts were prepared in lysis buffer ( 50 mm hepes [ ph 7 . 4 ], 150 mm sodium chloride , 100 mm sodium fluoride , 10 mm tetrasodium pyrophosphate , 1 mm sodium orthovanadate [ ph 10 . 0 ], 1 mm edta [ ph 8 . 0 ], 1 . 5 mm magnesium chloride , 10 % glycerol , 1 % triton x - 100 , 1 mm pmsf , and “ complete ” protease inhibitor cocktail tablets [ roche ]); insoluble material was discarded and a fixed amount of lysate was run by sds - page as described above . for wb rabbit anti - syk as above and anti - p - syk , anti - erk , anti - p - erk were from cell signaling . b3z cells containing a reporter plasmid for nfat coupled to lacz activity have been previously described 25 . clec9a wt or a mutant version y7f ( stratagene ) were transduced in wt or syk - transduced b3z cells . cells were plated in 96 well plates coated with isotype control or anti - clec9a mab and after overnight culture , were washed in pbs and lysed in cprg - containing buffer as described 21 . four hours later a595 was measured , using od 655 as a reference . for detection of clec9a ligands , bwz cell line was transduced with a retrovirus encoding a chimera of the extracellular domain of mouse or human clec9a fused to the transmembrane region from nkrp1b and the intracellular tail of cd3 followed by an ires sequence and the gfp gene ( 24 ). ligand binding to the clec9a chimera would result in the activation of the nfat reporter and induction of β - gal activity . to assay basal activation of bwz cells expressing mouse and human clec9a - cd3 chimeric receptors , 4 , 2 , 1 , or 0 . 5 × 10 5 cells / ml were cultured in 3 ml in a 6 well plate and allowed to ( over ) grow for two days . frequency of dead cells was determined using to - pro3 dye ( invitrogen ) and live cells were plated in fresh medium at 2 × 10 5 / well in 96 - well flat bottom plates . after overnight culture , lacz activity was measured as above . to determine exposure of ligand in different cell types , lk ( b cell line ), sv - 40 immortalized mouse embryonic fibroblasts ( mefs ) derived from bm - 1 mice { ref } using standard protocols , rbl rat leukemia , 3t3 fibroblasts , and hek - 293 human embryonic kidney cells were uv irradiated ( 240 mj / cm 2 ) and left 24 h to induce cell death before adding to 2 × 10 5 bwz transfectants in a 96 - well flat bottom plate at a 1 : 1 ratio in the presence or absence of control fab or anti - mouse clec9a ( 1f6 ) and anti - human clec9a ( 8f9 ) fab ( sancho et al , j clin invest . 2008 ; 118 ( 6 ): 2098 - 110 ). after overnight culture , lacz activity was measured as above . in some assays , bwz cells transfected with clec9a wt were used to determine if the ligand signals through the cytoplasmic tail and evaluate full antibodies as blocking reagents comparable to the fab . uv dose response was performed irradiating lk cells with the following doses of uv ( mj / cm 2 ): 0 , 0 . 5 , 1 . 5 , 5 , 15 , 50 , 240 . frequency of dead cells was determined 24 h later using to - pro3 dye and cells were plated 1 : 1 with bwz transfectants ( 2 × 10 5 cells / well ) in fresh medium . after overnight culture , lacz activity was measured as above . different treatments for lk cells and bm - 1 immortalized mefs were evaluated in exposure of the ligand . cells were cultured for 24 h with mitoxantrone ( 1 μm ) or in the absence of serum ( serum deprivation ). osmotic shock was performed as previously described ( liu et al . 2002 . j . exp . med . 196 : 1091 - 1097 ). three cycles of freeze - thaw were performed in the pellet of cells , freezing in liquid n 2 and thawing at 37 ° c . after these treatments , frequency of dead cells was determined using to - pro3 dye and cells were stained for rsctld as indicated below . cells were plated 1 : 1 with bwz transfectants ( 2 × 10 5 cells / well ) in fresh medium . after overnight culture , lacz activity was measured as above . to conjugate the immunodominant ova peptide siinfekl to the bivalent antibody , a derivative of the siinfekl peptide , named s1 , containing an added cysteine ( c ) to generate a free sulfhydril group and biotin to track the labelling was synthesized and purified by high - performance liquid chromatography at cancer research uk . the mab were treated with sulfo - smcc 30 min at rt , generating sulfo - reactive groups in the tertiary amines , followed by purification of the activated antibody in a molecular size exclusion chromatography column ( pierce ). then , the s1 peptide was freshly prepared and allowed to react in equimolecular amounts with the activated antibody 1 h at 37 ° c ., and purified in a chromatography column . the extent of biotinylation of the mab allowed us to quantify in 1 - 1 . 2 peptides coupled per mab molecule in all antibody conjugates generated , using the fluoreporter kit ( invitrogen ) and following manufacturer &# 39 ; s instructions . coupling of s2 peptide and melanocyte differentiation antigen peptides to mab s2 peptide ( siinfekltewtssnvmeerc - biotin ) was synthesized and purified by hplc at cancer research uk . mabs in pbs were treated with sulfo - smcc for 30 min at room temperature to generate sulfo - reactive groups in tertiary amines . the activated antibody was purified by molecular size exclusion chromatography ( pierce ), s2 peptide was added ( 2 : 1 molar ratio ) and the reaction was allowed to proceed for 1 h at 37 ° c . conjugates were purified using an immunobind sepharose column . the extent of biotinylation of the mab was assessed using the fluoreporter kit ( invitrogen ) as per manufacturer &# 39 ; s instructions . the same strategy was used to synthesize peptides from the melanocyte differentiation antigens , gp100 ( egsrnqdwl and kvprnqdwl ; h - 2db - restricted ( 25 )), trp - 1 ( twhryhll and tayryhll ; h - 2kb - restricted ( 26 )) and trp - 2 ( svydffvwl ; h - 2kb - restricted ( 27 )), each modified by addition of cysteine - eahx - biotin at the c - terminus . anti - clec9a , isotype control , or anti - dec - 205 were coupled to alexa488 ( invitrogen ) or to s1 peptide . for the experiment of targeting using alexa488 abs , mab - alexa488 were injected i . v . ( 20 μg ) and splenocytes were extracted and analyzed after 16 h . in the experiment of targeting of antigen to specific subsets in vivo , s1 - abs were injected i . v . ( 5 μg ) and splenocytes were extracted and purified in the cd11c positive and negative fraction with anti - cd11c microbeads ( miltenyi biotec ). ot - i cells were obtained from lymph nodes and splenocytes of ot - i rag −/− mice and purified by negative selection using a cocktail of biotinylated antibodies ( anti - cd11c , cd11b , b220 , fcgr , gr - 1 , and cd4 ) followed by streptavidin microbeads ( miltenyi biotec ). different amounts of in vivo targeted dc , as indicated in the figure legend , were cultured with 10 5 ot - i cells labelled with 2 μm cfse ( invitrogen ) in u - bottomed plates . three days later , proliferation was determined by cfse dilution in cells positive for vβ5 . 1 and cd8 and negative for to - pro 3 . cells were acquired with true count beads ( . . . ) to quantify the absolute number of cells . ifn - γ in the supernatants was determined by sandwich elisa . in the experiment of targeting in vivo to evaluate specific ctl response , mab - s1 were injected s . c . in the hind paws ( 2 μg ) together or not with 25 μg of anti - cd40 ( 3 / 23 , bd pharmingen ) and five days later in vivo killing assays were performed as described 27 . briefly , target splenocytes from b6 . sjl background ( congenic cd45 . 1 + ) were loaded with 20 nm , 200 nm or no siinfekl peptide and respectively labelled with 0 . 03 μm , 0 . 3 μm or 3 μm of cfse for 20 min at 37 ° c . labelled splenocytes ( 10 7 ) were i . v . injected . the following day splenocytes were extracted and the cd45 . 1 positive population was analyzed for cfse . in addition , 5 × 10 5 splenocytes were cultured in the presence or absence of 1 μm siinfekl for 24 h and supernatants were quantified for ifnγ by elisa . blood and spleen cells were also labeled with siinfekl - h2kb tetramer ( beckman coulter ), anti - cd8 and anti - thy 1 . 2 and analyzed for the % tetramer + cells among the cd8 + t cell population . b16 melanoma cells were transduced with ova - gfp fusion protein and sorted for gfp expression . tumor cells ( 2 × 10 5 ) were injected i . v . in the tail of congenic b6 mice and 6 days later the therapeutic treatment consisting of ab - s1 + anti - cd40 was injected s . c . in the paw . at day 18 post - tumor injection , lung tumors were counted . tumor therapy experiments were done in an analogous fashion except that mice received b16 - ova 3 days prior to antibody treatment . tumor therapy and prophylaxis experiments were also carried out with non - transduced parental b16 cells . these were given i . v . ( 5 × 105 / mouse ) either 3 days before ( therapy ) or 1 day after ( prophylaxis ) immunization with anti - clec - 9a or control antibody covalently coupled to a mixture of 5 peptides derived from gp100 , trp - 1 and trp - 2 ( 1 μg / paw ) together with anti - cd40 ( 12 . 5 μg / paw ) and poly 1 : 0 ( 5 μg / paw ). tumor burden was assessed by counting lung foci . when these were too numerous to count (& gt ; 250 per mouse ), they are shown as 250 . ctl responses were monitored as described above . mice were generated using red / et recombineering ( gene bridges , heidelberg , germany ) to capture directly the region of the gene to modify from the bac clone rp - 23 248 - k14 ( c57bl / 6 bac clone from invitrogen ). a conventional gene - targeting replacement vector : pfloxri + tk , which uses the strategy of both positive ( neomycin resistance gene ) and negative ( herpes simplex virus thymidine kinase gene ) selection for the isolation of homologous recombinant es cells clones was amplified by pcr using the primers indicated with 20 nucleotides pairing with the vector and 70 nucleotides pairing with regions of clec9a to capture . the primers used were fw 3arm 24330 pflox 5 ′ ataatatcat atttctataa tatcattgta atgacaaaac cactgaacta gtgcctgtaa aggcaggagg ggtaccgagc tcgaattcta ccg 3 ′; rv pflox 5arm 5 ′ tgctatatta cagattttca agtggggtag cctggagtaa caagatggca gggcataatc actagtgcgg ccgccaccgc ggtggagctc cagcttt 3 ′. once the region to modify was included in the amp - resistant vector , a cassette including farnesylated egfp , and the pgk - gb2 promoter followed by kan / neo allowed to repeat the recombineering homologous recombination step with selection for kan . the primers used for amplification of the egfp - f kan - neo resistant cassette were : rv neokan 3arm 5 ′ tgcttttgta cttacacttg atgcccaaga aaatggacgt tgctaacaag cccatacaga ccacacctcg agataacttc gtataatgta t3 ′ and fw 5arm egfp - f 5 ′ tttgtgccag gctcctatgt agactgcttc accactccaa gcgccttcag catgcatgtc gacatggtga gcaagggcga ggag 3 ′. the targeting vector was prepared to express egfp - f with a strong polya immediately downstream the first two amino acids from clec9a and disrupted exons 1 and 2 , terminating transcription with the strong polya the targeting vector was linearized prior to transfection using not i . transfection of s6b6 hybrid 129s6 / c57bl / 6 f1 derived embryonic stem ( es ) cells was achieved by electroporation and recombinant clones were isolated after culture in g418 and gancyclovir . es cells surviving selection were screened by pcr using two independent primer pairs with one of the primers external to the short arm . the primer pairs used were : scr fw1 5 ′ gatctgtgtg ttggtttttg tgtgc 3 ′; scr rv1 , 5 ′ tagcatggca cttctccatt acctt 3 ′ amplicon fw1rv1 : 2138 bp . scr fw2 , 5 ′ gcgaattcgg taccaataaa agagc 3 ′; scr rv2 , 5 ′ cagaagcttc ctggttttgg ttttt 3 ′ amplicon fw2rv2 : 2352 . correctly targeted , karyotypically euploid es clones were micro - injected into 3 . 5 day post coitum c57bl / 6 blastocysts and resulting offspring with coat - color chimerism were bred with c57bl / 6 females to identify germ - line transmission . germ - line transmitting chimeras were subsequently bred with c57bl / 6 females to secure the gene - targeted allele in the pure c57bl / 6 background . heterozygous animals were interbred to generate homozygous deficient animal and matched littermate controls . the expression of nk1 . 1 c57bl / 6 gene , ligated to clec9a , in the knock out mice shows that the homologous recombination of the targeted c57bl / 6 bac clone was integrated in the c57bl / 6 copy of the f1 in s6b6 es cells . clec9a −/− mice used in this work were on a mixed 129 / sv × c57bl / 6 genetic background in the third generation of backcrossing to c57bl / 6 . the ctlds for mouse clec9a and dectin - 1 were independently cloned in frame in the p3 × flag - cmv - 9 expression vector from sigma with an added bira monobiotinilation sequence . primers used for ctld amplification were mclec9a fw 5 ′ ggatcc mclec9a rv 5 ′ ggatcc cho cells were transfected and selected with g418 ( 1 mg / ml ). stable transfectants were cloned twice by limiting dilution , selecting clones secreting rsctld from dectin - 1 or clec9a to the supernatant , detected by a sandwich elisa using as capture anti - flag m2 ( sigma ) and for detection biotin - 2a11 anti - dectin - 1 or biotin - 1f6 anti - clec9a . concentrated supernatants from cho clones were generated in celline bioreactors ( integra biosciences , chur , switzerland ) and were purified using anti - flag m2 agarose ( sigma ). monobiotinylation was then performed using standard procedures { ref } and tetramers were generated using pe - streptavidin ( sigma ). pe - tetramers of rsctld were then used for staining of dead cells or zymosan for 30 min at 4 ° c . in normal facs buffer . samples were counter - stained with to - pro3 and acquired by flow cytometry . in the cross - presentation assay in vitro we co - cultured three cell types : dead cells loaded with ova or expressing ova , flt3l bmdc from different origins in the presence or absence of antibodies blocking clec9a and the readout , ot - i ova - specific transgenic t cells . we tested flt3l bmdc from clec9a −/− or clec9a + littermates . in addition , flt3l bmdc from c57bl / 6 were cultured in the absence or presence of control fab , or anti - clec9a ( 1f6 ) fab ( 10 μg / ml ), as well as with full antibodies against clec9a or isotype control ( 20 μg / ml ). where indicated , cd8α - like flt3l bmdc with cd11b lo and cd24 hi , as described ( 19 ), were sorted . as a source of dead cells associated to ova antigen for cross - presentation , we used bm - 1 splenocytes , a c57bl / 6 congenic mouse that express a mutation in the h2k b molecule that prevents the binding of siinfekl , the immunodominant class i ova peptide for h2k b . in that way , cells loaded with ova will not be able to present directly the ova peptide and should be processed and cross - presented to generate a response . to load the ova by adsorption , we incubated the indicated doses of soluble ova ( calbiochem ) with low levels of endotoxin with bm - 1 splenocytes in pbs for 20 min before washing five times in pbs . alternatively , we generated bm - 1 mouse embryonic fibroblasts ( mefs ) and we immortalized them with sv - 40 t large antigen . then , we transduced then with a truncated non - secreted ova - gfp fusion protein and sorted for homogeneous expression of ova - gfp . both , ova - loaded splenocytes and ova - expressing mefs were then uv - irradiated ( 240 mj / cm 2 ) and cultured overnight in complete medium . the following day , splenocytes were co - cultured 5 : 1 ratio to flt3l bmdc ( 10 5 cells / well , 96 u - bottom ) and ova - mefs were cultured with flt3l bmdc in a 1 : 1 ratio . ot - i cells negatively selected ( purity & gt ; 800 ) using macs beads ( miltenyi ) and labelled with cfse ( 2 μm ) were added to the assay ( 10 5 cells / well ). three days later supernatants were harvested to detect il - 2 and ifn - γ by sandwich elisa and cells were stimulated with pma ( 10 ng / ml ) and ionomycin ( 500 ng / ml ) for 4 h , adding brefeldin a ( 10 μg / ml , sigma ) during the last 3 h of culture . cells were then stained for vβ5 , cd8 and ifn - γ by intracellular staining and acquired by flow cytometry to determine absolute counts , loading samples with a fixed number of calibration beads ( bd ) and ifn - γ production by intracellular staining . wt or clec9a −/− cd8α - like flt3l bmdc were incubated for 2 h with different ratios of splenocytes that were treated 24 h before with uvc ( 240 mj / cm 2 ) and labelled with pkh26 ( sigma ). as flt3l bmdc were labelled for cd24 , double positive for pkh26 and cd24 could be due to binding ( 4 ° c .) or binding + uptake ( 37 ° c .) of dying cells and the frequencies were quantified by flow cytometry for each type of dc . ova - expressing immortalized bm - 1 mefs generated as indicated above were uvc - treated ( 240 mj / cm 2 ) and cultured overnight before being injected i . v . ( 0 . 75 × 10 6 cells / mouse ). mice ( c57bl / 6 ) were pre - treated with an i . p . injection of pbs or 400 μg isotype control ( afro - mac 49 , rat igg1 ) or 1f6 anti - clec9a 30 min before the i . v . injection . alternatively , clec9a −/− or littermates clec9a + were used . six days later , induction of cd8 + t cell effector response arising from the endogenous repertoire was tracked by the number of h2k b - ova peptide tetramer positive cells and ifnγ production in response to siinfekl ex vivo in the cd8 subset . in fig1 c and 19 d in which data were pooled from several litters in independent experiments , we performed a normalization of the data before pooling . each litter ( females ) was considered an independent experiment and raw data in each litter were normalized to the mean of clec9a + mice in that litter and multiplied by the arithmetic mean obtained for the total population of clec9a + mice in all the litters in independent experiments . for the analysis of fold change in litters , arithmetic mean for clec9a + mice or clec9a −/− mice was calculated in each litter . all 12 litters out of 12 analyzed showed fold reduction in the arithmetic mean of % tetramer positive cells in cd8 t cell subset of clec9a −/− mice compared to clec9a + . statistical analysis was performed with a two - tailed student &# 39 ; s t test for differences among groups or u mann - whitney when normality of data could not be inferred . p & lt ; 0 . 05 was considered statistically significant . quantitative data are expressed as means ± sem unless otherwise stated . while the invention has been described in conjunction with the exemplary embodiments described above , many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure . accordingly , the exemplary embodiments of the invention set forth are considered to be illustrative and not limiting . various changes to the described embodiments may be made without departing from the spirit and scope of the invention . all documents cited herein are expressly incorporated by reference . 1 . reis e sousa , c . activation of dendritic cells : translating innate into adaptive immunity . curr opin immunol 16 , 21 - 5 ( 2004 ). 2 . engering , a . et al . the dendritic cell - specific adhesion receptor dc - sign internalizes antigen for presentation to t cells . j immunol 168 , 2118 - 26 ( 2002 ). 3 . sallusto , f ., cella , m ., danieli , c . & amp ; 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