fig1 a - 1f are chromatographic analyses of the peptide pools extracted from papain digested hla - dr1 , dr2 , dr3 , dr4 , dr7 , and dr8 , respectively , illustrating the peptide repertoire of each hla - dr as detected by uv absorbance . the uv absorbance for both 210 nm and 277 nm is shown at a full scale absorbance of 500 mau with a retention window between 16 minutes and 90 minutes ( each mark represents 2 minutes ). fig2 is a representative mass spectrometric analysis of the size distribution of isolated hla - dr1 bound peptides . the determined peptide masses in groups of 100 mass units were plotted against the number of isolated peptides identified by mass spectrometry . peptide length was calculated by dividing the experimental mass by an average amino acid mass of 118 daltons . fig3 a is a representation of a minigene of the invention ( seq id no : 147 ), which encodes the indicated amino acid sequence ( seq id no : 275 ), in which the hla - drα chain leader peptide is linked to the amino terminus of a 15 - residue blocking peptide fragment of human invariant chain ii . fig3 b is a representation of a second minigene of the invention ( seq id no : 148 ), which encodes the indicated amino acid sequence ( seq id no : 276 ), in which the hla - drα chain leader peptide is linked to the amino terminus of a 24 - residue blocking peptide fragment : of human invariant chain ii . hla - dr molecules were purified from homozygous , epstein - barr virus - transformed , human b lymphoblastoid lines : dr1 from lg - 2 cells , dr2 from mst cells , dr3 from wt20 cells , dr4 from priess cells , dr7 from mann cells , and dr8 from 23 . 1 cells . all of these cell lines are publicly available . cell growth , harvest conditions and protein purification were as previously described ( gorga , j . et al ., 1991 ). briefly , 200 grams of each cell type was resuspended in 10 mm tris - hcl , 1 mm dithiothreitol ( dtt ), 0 . 1 mm phenylmethylsulfonylflouride ( pmsf ), ph 8 . 0 , and lysed in a thomas homogenizer . the nuclei were removed by centrifugation at 4000 × g for 5 min and the pellets washed and repelleted until the supernatants were clear . all the supernatants were pooled and the membrane fraction harvested by centrifugation at 175 , 000 × g for 40 min . the pellets were then resuspended in 10 mm tris - hcl , 1 mm dtt , 1 mm pmsf , 4 % np - 40 . the unsolubilized membrane material was removed by centrifugation at 175 , 000 × g for 2 hours , and the np - 40 soluble supernatant fraction used in immunoaffinity purification . detergent soluble hla - dr was bound to a lb3 . 1 - protein a , sepharose ™ agarose gel column ( pharmacia ; ( gorga et al ., id ) and eluted with 100 mm glycine , ph 11 . 5 . following elution , the sample was immediately neutralized by the addition of tris - hcl and then dialyzed against 10 mm tris - hcl , 0 . 1 % deoxycholic acid ( doc ). the lb3 . 1 monoclonal antibody recognizes a conformational determinant present on the nonpolymorphic hla - drα chain , and thus recognizes all allotypes of hla - dr . the transmembrane domain of the dr molecules was removed by papain digestion , and the resulting water - soluble molecule further purified by gel filtration chromatography on an s - 200 column equilibrated in 10 mm tris - hcl , ph 8 . 0 . the purified dr samples were concentrated by ultrafiltration , yield determined by bca assay , and analyzed by sds polyacrylamide gel electrophoresis . water - soluble , immunoaffinity - purified class ii molecules were further purified by high - performance size exclusion chromatography ( sec ), in 25 mm n - morpholino ethane sulfonic acid ( mes ) ph 6 . 5 and a flowrate of 1 ml / min ., to remove any residual small molecular weight contaminants . next , centricon ™ ultrafiltration microconcentrators ( molecular weight cutoff 10 , 000 daltons ) ( amicon corp .) were sequentially washed using sec buffer and 10 % acetic acid prior to spin - concentration of the protein sample ( final volume between 100 - 200 μl ). peptide pools were extracted from chosen class ii alleles by the addition of 1 ml of 10 % acetic acid for 15 minutes at 70 ° c . these conditions are sufficient to free bound peptide from class ii molecules , yet mild enough to avoid peptide degradation . the peptide pool was separated from the class ii molecule after centrifugation through the centricon ™ ultrafiltration microconcentrator , with the flow - through containing the previously bound peptides . the collected acid - extracted peptide pool was concentrated in a speed - vac ™ vacuum equipped centrifuge ( savant ) to a volume of 50 μl prior to hplc separation . peptides were separated on a microbore c - 18 reversed - phase chromatography ( rpc ) column ( vydac ) utilizing the following non - linear gradient protocol at a constant flowrate of 0 . 15 ml / min . : 0 - 63 min . 5 %- 33 % buffer b ; 63 - 95 min . 33 %- 60 % buffer b ; 95 - 105 min 60 %- 80 % buffer b , where buffer a was 0 . 06 % trifluoroacetic acid / water and buffer b was 0 . 055 % trifluoroacetic acid / acetonitrile . chromatographic analysis was monitored at multiple uv wavelengths ( 210 , 254 , 277 , and 292 nm ) simultaneously , permitting spectrophotometric evaluation prior to mass and sequence analyses . shown in fig1 are chromatograms for each of the six dr peptide pools analyzed . collected fractions were subsequently analyzed by mass spectrometry and edman sequencing . the spectrophotometric evaluation of the peptides during rpc provides valuable information regarding amino acid composition ( contribution of aromatic amino acids ) and is used as a screening method for subsequent characterization . appropriate fractions collected during the rpc separation were next analyzed using a finnegan - mat lasermat ™ matrix - assisted laser - desorption mass spectrometer ( mald - ms ) to determine the individual mass values for the predominant peptides . between 1 %- 4 % of the collected fraction was mixed with matrix ( 1 μl α - cyano - 4 - hydroxycinnamic acid ) to achieve mass determination of extracted peptides . the result of this analysis for hla - dr1 is shown in fig2 . next , chosen peptide samples were sequenced by automated edman degradation microsequencing using an abi 477a protein sequencer ( applied biosystems ) with carboxy - terminal verification provided by mass spectral analysis using the finnigan - mat tsq 700 triple quadruple mass spectrometer equipped with an electro - spray ion source . this parallel analysis ensures complete identity of peptide composition and sequence . peptide alignment with protein sequences stored in the swiss - prot database was performed using the fasta computer database search program . set forth in tables 1 - 10 are the results of this sequence analysis for each of the dr molecules studied . the hla - dr1 used in this study was papain solubilized to enable the material to be used both for crystallographic and bound peptide analyses . the peptides bound to dr1 were acid extracted and fractionated using rpc ( fig1 ). the absence of any detectable peptidic material following a second extraction / rpc separation verified quantitative peptide extraction . amino acid analysis ( abi 420a / 130a derivatizer / hplc ) of extracted peptide pools demonstrated a 70 - 80 % yield , assuming total occupancy of purified dr1 with a molar equivalent of bound peptides corresponding to the size distribution determined by mass spectrometry ( see fig2 ). the rpc profiles obtained from dr1 extractions of multiple independent preparations were reproducible . furthermore , profiles from either detergent - soluble or papain - solubilized dr1 were equivalent . to confirm that the peptides were in fact identical in detergent - soluble and papain - digested dr1 , mass spectrometry and edman sequencing analyses were performed and revealed identical masses and sequences for analogous fractions from the two preparations . matrix - assisted laser desorption mass spectrometry ( mald - ms ) was used to identify 111 species of unique mass contained within the eluted peptide pool of dr1 with an average size of 18 and a mode of 15 residues ( fig2 ). over 500 additional mass species present within the molecular weight range of 13 - 25 residues were detected ; however , the signal was not sufficient to assign individual masses with confidence . multiple species of varying mass were detected in fractions corresponding to single rpc peaks indicating co - elution of peptides . to characterize these peptides further , samples were analyzed in parallel on a triple quadruple mass spectrometer equipped with an electrospray ion source ( esi - ms ) and by automated edman degradation microsequencing ( lane et al ., j . prot . chem . 10 : 151 - 160 ( 1991 )). combining these two techniques permits crucial verification of both the n - and c - terminal amino acids of peptides contained in single fractions . the sequence and mass data acquired for twenty peptides isolated from dr1 are listed in table 1 . all the identified peptides aligned with complete identity to regions of proteins stored in the swiss - prot database . surprisingly , sixteen of the twenty sequenced dr1 - bound peptides were 100 % identical to regions of the self proteins hla - a2 and class ii - associated invariant chain ( ii ), representing at least 26 % of the total extracted peptide mass . these isolated peptides varied in length and were truncated at both the n - and c - termini , suggesting that : 1 ) antigen processing occurs from both ends after binding to dr1 , or 2 ) class ii molecules bind antigen from a pool of randomly generated peptides . the yields from the peptide microsequencing indicated that hla - a2 ( fig1 ) and ii each represents at least 13 % of the total dr1 - bound peptides . an additional surprising finding concerned a peptide which , although bound to hla - dr and 100 % homologous with hla - a2 peptide , was derived from a cell which does not express hla - a2 protein . evidently this peptide is derived from a protein containing a region homologous with a region of hla - a2 protein . thus , for purposes of this specification , the term “ hla - a2 protein ” is intended to include hla - a2 protein itself , as well as any naturally occurring protein which contains a ten or greater amino acid long region of & gt ; 80 % homology with an hla - dr - binding peptide derived from hla - a2 . an “ hla - a2 peptide ” similarly refers to peptides from any hla - a2 protein , as broadly defined herein . the other four peptides identified in the dr1 studies were derived from two self proteins , transferrin receptor and the na + / k + atpase , and one exogenous protein , bovine serum fetus ( a protein present in the serum used to fortify the medium which bathes the cells ). each of these peptides occupied only 0 . 3 - 0 . 6 % of the total dr1 population , significantly less than either the hla - a2 or the ii peptides . it is known that class ii molecules en route to the cell surface intersect the pathway of incoming endocytic vesicles . both recycling membrane proteins and endocytosed exogenous protein travel this common pathway . hence , the hla - a2 , transferrin receptor , na + / k + atpase and bovine fetuin derived peptides would all encounter dr1 in a similar manner . ii associates with nascent class ii molecules in the endoplasmic reticulum ( er ) ( jones et al ., mol . immunol . 16 : 51 - 60 ( 1978 )), preventing antigen binding until the class ii / ii complex arrives at an endocytic compartment ( roche and cresswell , nature 345 : 615 - 618 ( 1990 )), where . ii undergoes proteolysis ( thomas et al ., j . immunol . 140 : 2670 - 2675 ( 1988 ); roche and cresswell , proc . natl . acad . sci . usa 88 : 3150 - 3154 ( 1991 )), thus allowing peptide binding to proceed . presumably , the ii peptides bound to dr1 were generated at this step . synthetic peptides corresponding to five of the peptides reported in table 1 were made and their relative binding affinities to dr1 determined . the influenza a hemagglutinin peptide ( ha ) 307 - 319 ( seq id no : 24 ) has been previously described as a high affinity , hla - dr1 restricted peptide ( roche and cresswell , j . immunol . 144 : 1849 - 1856 ( 1990 ); rothbard et al ., cell 52 : 515 - 523 ( 1988 )), and was thus chosen as the control peptide . “ empty ” dr1 purified from insect cells expressing recombinant dr1 cdna was used in the binding experiments because of its higher binding capacity and 10 - fold faster association kinetics than dr1 isolated from human cells ( stern and wiley , cell 68 : 465 - 477 ( 1992 )). all the synthetic peptides were found to compete well ( ki & lt ; 100 nm ) against the ha peptide ( table 2 ). at first approximation , the ii 107 - 120 peptide ( seq id no : 156 ) had the highest affinity of all the competitor peptides measured , equivalent to that determined for the control ha peptide . in addition to the ki determinations , these peptides were found to confer resistance to sds - induced α - β chain dissociation of “ empty ” dr1 when analyzed by sds - page , indicative of stable peptide binding ( sadegh - nasseri and germain , nature 353 : 167 - 170 ( 1991 ); dornmair et al ., cold spring harbor symp . quant . biol . 54 : 409 - 415 ( 1989 ); springer et al ., j . biol . chem . 252 : 6201 - 6207 ( 1977 )). neither of the two control peptides , β 2 m 52 - 64 ( seq id no : 26 ) nor ii 97 - 111 ( seq id no : 25 ), was able to either confer resistance to sds - induced chain dissociation of dr1 or compete with ha 307 - 319 ( seq id no : 24 ) for binding to dr1 ; both of these peptides lack the putative binding motif reported in this study ( see below ). a putative dr1 binding motif based on the sequence alignments of the core epitopes ( the minimum length ) of certain naturally processed peptides is shown in table 3 . the peptides listed in this table include those determined herein for hla - dr1 , as well as a number of peptides identified by others and known to bind dr1 ( reference # 6 in this table being o &# 39 ; sullivan et al ., j . immunol . 145 : 1799 - 1808 , 1990 ; reference # 17 , roche & amp ; cresswell , j . immunol . 144 : 1849 - 1856 , 1990 ; reference # 25 , guttinger et al ., intern . immunol . 3 : 899 - 906 , 1991 ; reference # 27 , guttinger et al . embo j . 7 : 2555 - 2558 , 1988 ; and reference # 28 , harris et al ., j . immunol . 148 : 2169 - 2174 , 1992 ). the key residues proposed in the motif are as follows : a positively charged group is located at the first position , referred to here as the index position for orientation ( i ); a hydrogen bond donor is located at i + 5 ; and a hydrophobic residue is at i + 9 . in addition , a hydrophobic residue is often found at i + 1 and / or i − 1 . every naturally processed peptide sequenced from dr1 conforms to this motif ( with the exception of the hla - a2 peptide 103 - 116 ( seq id no : 3 ) that lacks residue i + 9 ). because the putative motif is not placed in a defined position with respect to the first amino acid and because of the irregular length of bound peptides , it is impossible to deduce a motif from sequencing of peptide pools , as was done for class i molecules ( falk et al ., nature 351 : 290 - 296 ( 1991 )). the ii 97 - 111 peptide ( seq id no : 25 ), a negative control peptide used in binding experiments , has the i and i + 5 motif residues within its sequence , but is missing eight additional amino acids found in ii 106 - 119 ( seq id no : 16 ) ( table 3c ). a sequence comparison of 35 previously described dr1 - binding synthetic peptides ( o &# 39 ; sullivan et al ., j . immunol . 145 : 1799 - 1808 ( 1990 ); guttinger et al ., intern . immunol . 3 : 899 - 906 ( 1991 ); hill et al ., j . immunol . 147 : 189 - 197 ( 1991 ); guttinger et al ., embo j . 7 : 2555 - 2558 ( 1988 ); harris et al ., j . immunol . 148 : 2169 - 2174 ( 1992 ) also supports this motif . of the 35 synthetic peptides , 21 ( 60 %) have the precise motif , nine ( 30 %) contain a single shift at either i or i + 9 , and the remaining five ( 10 %) have a single substitution at i ( table 3b and c ). interestingly , in the latter peptides , a positive charge at i is always replaced by a large hydrophobic residue ( table 8c ); a pocket has been described in class i molecules that can accommodate this precise substitution ( latron et al ., proc . natl . acad . sci . usa 88 : 11325 - 11329 ( 1991 )). contributions by the other eight amino acids within the motif or the length of the peptide have not been fully evaluated and may compensate for shifted / missing residues in those peptides exhibiting binding . evaluation of the remaining 117 non - dr1 binding peptides cited in those studies ( which peptides are not included in table 3 ) indicates that 99 ( 85 %) of these peptides do not contain the dr1 motif proposed herein . of the remaining 18 peptides ( 15 %) that do not bind to dr1 but which do contain the motif , 6 ( 5 %) are known to bind to other dr allotypes ; the remaining 12 peptides may have unfavorable interactions at other positions which interfere with binding . in contrast to the precise n - terminal cleavages observed in the previous study of six peptides bound to the mouse class ii antigen termed i - a b and five bound to mouse i - e b ( rudensky et al ., nature 3563 : 622 - 627 ( 1991 )), the peptides bound to dr1 are heterogeneous at both the n - and c - termini . in contrast to : peptides bound to class i molecules , which are predominantly nonamers ( van bleek and nathenson , nature 348 : 213 - 216 ( 1990 ); rotzschke et al ., nature 348 : 252 - 254 ( 1990 ); jardetzky et al ., nature 353 : 326 - 329 ( 1991 ); hunt et al ., science 255 : 1261 - 1263 ( 1992 )), class ii peptides are larger and display a high degree of heterogeneity both in length and the site of terminal truncation , implying that the mechanisms of processing for class i and class ii peptides are substantially different . furthermore , the present results suggest that class ii processing is a stochastic event and that a dr allotype may bind peptides of different lengths from a complex random mixture . the heterogeneity observed may be solely due to protection of bound peptides from further degradation . thus , class ii molecules would play an active role in antigen processing ( as previously proposed ( donermeyer and allen , j . immunol . 142 : 1063 - 1068 ( 1989 )) by protecting the bound peptides from complete degradation . alternatively , the predominance of 15 mers bound to dr1 ( as detected by both the mald - ms and the yields of sequenced peptides ) could be the result of trimming of bound peptides . in any event , the absence of detectable amounts of peptides shorter than 13 and longer than 25 residues suggests that there are length constraints intrinsic either to the mechanism of peptide binding or to antigen processing . the predominance of peptides bound to dr1 that are derived from endogenously synthesized proteins , and particularly mhc - related proteins , may result from the evolution of a mechanism for presentation of self peptides in connection with the generation of self tolerance . the sequences of naturally processed peptides eluted from each of dr2 , dr3 , dr4 , dr7 and dr8 are shown in tables 4 - 8 , respectively . in addition to those peptides shown in table 4 , it has been found that dr2 binds to long fragments of hla - dr2a β - chain and hla - dr2b β - chain , corresponding to residues 1 - 126 or 127 of each of those proteins . presumably , only a short segment of those long fragments is actually bound within the groove of dr2 , with the remainder of each fragment protruding from one or both ends of the groove . table 9 gives sequences of dr1 from another cell line which does not have wild - type ar , but which has bound a2 - like peptides . table 10 gives sequences of peptides eluted from dr4 and dr11 molecules expressed in cells from a human spleen . these data demonstrate the great prevalence of self peptides bound , compared to exogenous peptides . the data also show that the a2 and ii peptides occur repeatedly . in addition , certain of the tables include peptides that appear to derive from viral proteins , such as epstein - barr virus major capsid protein , which are likely to be present in the cells studied . in order to prepare genetic constructs for in vivo administration of genes encoding immunomodulatory peptides of the invention , the following procedure is carried out . overlapping synthetic oligonucleotides were used to generate the leader peptide / blocking peptide mini - genes illustrated in fig3 by pcr amplification from human hla - drα and invariant chain cdna templates . these mini - genes encode the ii peptide fragments kmrmatpllmqalpm ( or ii 15 ; seq id no : 15 ) and lpkppkpvskmrmatpllmqalpm ( or ii 24 ; seq id no : 7 ). the resulting constructs were cloned into pgem - 2 ( promega corp .) to form the plasmids pgem - 2 - α - ii 15 and pgem - 2 - α - ii 24 , with an upstream t7 promoter for use in the in vitro transcription / translation system described below . for in vivo expression , each mini - gene was subsequently subcloned from the pgem - 2 derivatives into a transfection vector , phβactin - 1 - neo ( gunning et al ., ( 1987 ) proc . natl . acad . sci . u . s . a . 84 : 4831 ), to form the plasmids phβactin - α - ii 15 and phβactin - α - ii 24 . the inserted mini - genes are thus expressed in vivo from the constitutive / strong human β actin promoter . in addition , the mini - genes were subcloned from the pgem - 2 derivatives into the vaccinia virus recombination vector psc11 ( s . chakrabarti et al . ( 1985 ) mol . cell . biol . 5 , 3403 - 3409 ) to form the plasmids psc11 - α - ii 15 and psc11 - α - ii 24 . following recombination into the viral genome the inserted mini - genes are expressed from the strong vaccinia p 7 . 5 promoter . short amino acid sequences can act as signals to target proteins to specific intracellular compartments . for example , hydrophobic signal peptides are found at the amino terminus of proteins destined for the er , while the sequence kferq ( seq id no : 153 ) ( and other closely related sequences ) is known to target intracellular polypeptides to lysosomes , while other sequences target polypeptides to endosomes . in addition , the peptide sequence kdel ( seq id no : 152 ) has been shown to act as a retention signal for the er . each of these signal peptides , or a combination thereof , can be used to traffic the immunomodulating peptides of the invention as desired . for example , a construct encoding a given immunomodulating peptide linked to an er - targeting signal peptide would direct the peptide to the er , where it would bind to the class ii molecule as it is assembled , preventing the binding of intact ii which is essential for trafficking . alternatively , a construct can be made in which an er retention signal on the peptide would help prevent the class ii molecule from ever leaving the er . if instead a peptide of the invention is targeted to the endosomic compartment , this would ensure that large quantities of the peptide are present when invariant chain is replaced by processed peptides , thereby increasing the likelihood that the peptide incorporated into the class ii complex is the high - affinity peptides of the invention rather than naturally - occurring , potentially immunogenic peptides . the likelihood of peptides of the invention being available incorporation into class ii can be increased by linking the peptides to an intact ii polypeptide sequence . since ii is known to traffic class ii molecules to the endosomes , the hybrid ii would carry one or more copies of the peptide of the invention along with the class ii molecule ; once in the endosome , the hybrid ii would be degraded by normal endosomal processes to yield both multiple copies of the peptide of the invention or molecules similar to it , and an open class ii binding cleft . dnas encoding immunomodulatory peptides containing targeting signals will be generated by pcr or other standard genetic engineering or synthetic techniques , and the ability of these peptides to associate with dr molecules will be analyzed in vitro and in vivo , as described below . it is proposed that the invariant chain prevents class ii molecules from binding peptides in the er and may contribute to heterodimer formation . any mechanism that prevents this association would increase the effectiveness of class ii blockade . therefore , a peptide corresponding to the site on ii which binds to the class ii heterodimer , or corresponding to the site on either the α or β subunit of the heterodimer which binds to ii , could be used to prevent this association and thereby disrupt mhc class ii function . cell free extracts are used routinely for expressing eukaryotic proteins ( krieg , p . & amp ; melton , d . ( 1984 ) nucl . acids res . 12 , 7057 ; pelham , h . and jackson , r . ( 1976 ) eur . j . biochem . 67 , 247 ). specific mrnas are transcribed from dna vectors containing viral rna polymerase promoters ( melton , d . et al . ( 1984 ) nucl . acids res . 12 , 7035 ), and added to micrococcal nuclease - treated cell extracts . the addition of 35 s methionine and amino acids initiates translation of the exogenous mrna , resulting in labeled protein . proteins may be subsequently analyzed by sds - page and detected by autoradiography . processing events such as signal peptide cleavage and core glycosylation are initiated by the addition of microsomal vesicles during translation ( walter , p . and blobel , g . ( 1983 ), meth . enzymol ., 96 , 50 ), and these events are monitored by the altered mobility of the proteins in sds - page gels . the ability of peptides containing a signal peptide sequence to be accurately processed and to compete with invariant chain for class ii binding in the er are assayed in the in vitro system described above . specifically , dr1 α - and β - chain and invariant chain peptide constructs described above are transcribed into mrnas , which will be translated in the presence of mammalian microsomal membranes . association of the dr heterodimer with ii is determined by immunoprecipitation with antisera to dr and ii . addition of mrna encoding the peptide of the invention to the translation reaction should result in a decreased level of coimmunoprecipitated ii , and the concomitant appearance of coimmunoprecipitated peptide , as determined by sds - page on tris - tricine gels . these experiments will provide a rapid assay system for determining the potential usefulness of a given blocking peptide as a competitor for ii chain binding in the er . those peptides of the invention which prove to be capable of competing successfully with ii in this cell - free assay can then be tested in intact cells , as described below . human ebv - transformed b cell lines lg - 2 and hom - 2 ( homozygous for hla - dr1 ) and the mouse b cell hybridoma lk35 . 2 are transfected with either 50 μg of linearized phβactin - α - ii 15 or phβactin - α - ii 24 or ( as a control ) phβactin - 1 - neo by electroporation ( 150 mv , 960 μf , 0 . 2 cm cuvette gap ). following electroporation , the cells are cultured in g418 - free medium until total recovery ( approximately 4 days ). each population is then placed under g418 selection until neomycin - expressing resistant populations of transfectants are obtained ( approximately 1 - 2 months ). the resistant populations are subcloned by limiting dilution and the clonality of stable transfectants determined by pcr amplification of blocking peptide mrna expression . stable transfectants of lg - 2 and hom - 2 carrying blocking peptide mini - genes or negative control vectors are grown in large - scale culture conditions until 20 grams of pelleted cell mass is obtained . the hla - dr expressed by each transfectant is purified , and the bound peptide repertoire ( both from within the cell and from the cell surface ) analyzed as described above . successful demonstration of a reduction in the total bound peptide diversity will be conclusive evidence of intracellular delivery of immuno - modulatory peptides . a second cell - based assay utilizes stable transfectants of lk35 . 2 cells carrying blocking peptide mini - genes or negative control vectors ; these cells are used as apcs in t cell proliferation assays . each transfectant is cultured for 24 hours in the presence of different dilutions of hen egg lysozyme ( hel ) and hel - specific t cell hybridomas . the relative activation of the t cells present in each assay ( as measured by lymphokine production ) is determined using the publicly available lymphokine dependent cell line ctll2 in a 3 h - thymidine incorporation assay ( vignali et al . ( 1992 ) j . e . m . 175 : 925 - 932 ). successful demonstration of a reduction in the ability of blocking peptide expressing transfectants to present hel to specific t cell hybridomas will be conclusive evidence of intracellular delivery of immuno - modulatory peptides . cells of the human tk − cell line 143 ( atcc ) are infected with vaccinia virus ( strain wr , tk + ) ( atcc ), and two hours postinfection , psc11 - α - ii 15 or psc11 - α - ii 24 or psc11 is introduced into the infected cells by calcium phosphate precipitation . tk − recombinants are selected for with bromodeoxyuridine at 25 μg / ml . recombinant plaques are screened by pcr for the presence of mini - gene dna . recombinant virus is cloned by three rounds of limiting dilution to generate pure clonal viral stocks . in experiments analogous to the transfection experiments described above , recombinant vaccinia viruses encoding mini - genes or vector alone will be used to infect large - scale cultures of the human ebv transformed b cell lines lg - 2 and hom - 2 . following infection , the hla - dr is purified and the bound peptide repertoire analyzed as described above . a reduction of the complexity of the bound peptide population and a significant increase in the relative amount of ii peptides bound are conclusive evidence that vaccinia can deliver blocking peptides to human apcs . the same recombinant vaccinia viruses encoding mini - genes or vector will be used to infect mice experiencing experimentally - induced autoimmunity . a number of such models are known and are referred in kronenberg , cell 65 : 537 - 542 ( 1991 ). liposomes have been successfully used as drug carriers and more recently in safe and potent adjuvant strategies for malaria vaccination in humans ( fries et al . ( 1992 ), proc . natl . acad . sci . usa 89 : 358 ). encapsulated liposomes have been shown to incorporate soluble proteins and deliver these antigens to cells for both in vitro and in vivo cd8 + mediated ctl response ( reddy et al ., j . immunol . 148 : 1585 - 1589 , 1992 ; and collins et al ., j . immunol . 148 : 3336 - 3341 , 1992 ). thus , liposomes may be used as a vehicle for delivering synthetic peptides into apcs . harding et al . ( cell ( 1991 ) 64 , 393 - 401 ) have demonstrated that the targeting of liposome - delivered antigen to either of two intracellular class ii - loading compartments , early endosomes and / or lysosomes , can be accomplished by varying the membrane composition of the liposome : acid - sensitive liposomes were found to target their contents to early endosomes , while acid - resistant liposomes were found to deliver their contents to lysosomes . thus , the peptides of the invention will be incorporated into acid - sensitive liposomes where delivery to endosomes is desired , and into acid - resistant liposomes for delivery to lysosomes . liposomes are prepared by standard detergent dialysis or dehydration - rehydration methods . for acid - sensitive liposomes , dioleoylphosphatidylethanolamine ( dope ) and palmitoylhomocystein ( phc ) are utilized , while dioleoylphospatidylcholine ( dopc ) and dioleoylphosphatidylserine ( dops ) are used for the preparation of acid - resistant liposomes . 10 − 5 mol of total lipid ( dopc / dops or dope / phc at 4 : 1 mol ratios ) are dried , hydrated in 0 . 2 ml of hepes buffered saline ( hbs ) ( 150 mm nacl , 1 mm egta , 10 mm hepes ph 7 . 4 ) and sonicated . the lipid suspensions are solubilized by the addition of 0 . 1 ml of 1 m octylglucoside in hbs . the peptides to be entrapped are added to 0 . 2 ml of 0 . 6 mm peptide in 20 % hbs . the mixture is then frozen , lyophilized overnight , and rehydrated . these liposomes will be treated with chymotrypsin to digest any surface - bound peptide . liposome delivery to ebv - transformed cell lines ( as described above ) will be accomplished by 12 - 16 hour incubation at 37 ° c . hla - dr will be purified from the liposome treated cells and bound peptide analyzed as above . alternatively , the liposomes are formulated with the dna mini - gene constructs of the invention , and used to deliver the constructs into apcs either in vitro or in vivo . human immunization will be carried out under the protocol approved by both the johns hopkins university joint committee for clinical investigation and the human subject research review board of the office of the surgeon general of the u . s . army ( fries et al . ( 1992 ), proc . natl . acad . sci . u . s . a . 89 : 358 - 362 ), using dosages described therein , or other dosages described in the literature for liposome - based delivery of therapeutic agents . iscoms are negatively charged cage - like structures of 30 - 40nm in size formed spontaneously on mixing cholesterol and quil a ( saponin ). protective immunity has been generated in a variety of experimental models of infection , including toxoplasmosis and epstein - barr virus - induced tumors , using iscoms as the delivery vehicle for antigens ( mowat and donachie ) immunology today 12 : 383 - 385 , 1991 . doses of antigen as low as 1 μg encapsulated in iscoms have been found to produce class i mediated ctl responses , where either purified intact hiv - 1 - iiib gp 160 envelope glycoprotein or influenza hemagglutinin is the antigen ( takahashi et al ., nature 344 : 873 - 875 , 1990 ). peptides are delivered into tissue culture cells using iscoms in a manner and dosage similar to that described above for liposomes ; the class ii peptide binding of delivered peptides are then determined by extraction and characterization as described above . iscom - delivered peptides of the invention which are effectively utilized by cultured cells are then tested in animals or humans . in addition to delivery of the therapeutic synthetic peptides , iscoms could be constituted to deliver the mini - gene constructs to apcs , and thus serve as an alternative to the above - outlined vaccinia strategy . in addition to using the above - described intracellular delivery systems to deliver nonimmunogenic self peptides with the specific aim of down - modulating the immune system ( thus alleviating autoimmune conditions ), the delivery systems of the invention may alternatively be used as a novel means of vaccination , in order to stimulate a portion of the immune system of an animal . in the latter context , the delivery system is employed to deliver , into appropriate cells , dna constructs which express immunogenic , pathogen - derived peptides intended to stimulate an immune response against a specific pathogen . because the antigenic peptide is produced inside the target cell itself , the vaccine method of the invention ensures that there is no circulating free antigen available to stimulate antibody formation and thereby induce potentially deleterious or inappropriate immunological reactions . the immune response stimulated by vaccines of the invention is , because the vaccines are targeted solely to apc &# 39 ; s , limited to the t cell mediated response , in contrast to standard vaccine protocols which result in a more generalized immune response . although some of the peptide - presenting apc &# 39 ; s will initially be lysed by host t cells , such lysis will be limited because , inter alia , the virus - based vaccine is non - replicative , i . e ., each carrier virus can infect only one cell . the model antigen that will be used to perfect and test the system of the invention is hen egg lysozyme ( hel ). it is arguably the most well characterized protein for antigen presentation studies , to which there are numerous monoclonal antibodies and class i - and class ii - restricted mouse t cell clones and hybridomas . the primary epitopes that will be studied are the peptide hel 34 - 45 , as both monoclonal antibodies and cd4 + t cell hybridomas are available , and peptide hel 46 - 61 , as both class i and class ii - restricted t cell clones and hybridomas have been raised and are publicly available . these two sequences are thus proven immunogenic epitopes . initially , four constructs encoding different polypeptides are analyzed : ( a ) whole , secreted hel , ( b ) hel 34 - 45 , ( c ) hel 46 - 61 , and ( d ) hel 34 - 61 . the last three include a signal sequence known to be cleaved in these cells , e . g ., ia k ( mprsralilgvlalttmlslcgg ; seq id no : 274 , which would result in targeting to the er . all constructs are then subcloned into phβapr - 1 neo . the methodology for making these constructs is similar to that outlined above . the constructs are introduced into appropriate apcs , e . g ., lk35 . 2 cells , by means of a conventional eukaryotic transfection or one of the delivery vehicles discussed above ( e . g ., vaccinia , liposomes , or iscoms ). lk35 . 2 cells , which possess the mouse mhc class ii restriction molecules ia k and ie k , transfected with each of the constructs are tested for their ability to stimulate the appropriate class i and class ii - restricted t cell hybridomas and clones using standard techniques . whether class i stimulation is observed will depend on whether peptide trimming can occur in the er , in order to produce an 8 - 10 - mer suitable for binding to class i molecules . if these constructs are ineffective for class i stimulation , they can be modified in order to produce a more effective peptide for class i binding . if these constructs prove to be less effective for class ii - restricted responses , they can be tagged with endosomal and / or lysosomal targeting sequences as discussed in section v . the effectiveness of targeting signals used to direct immunogenic peptides to particular intracellular organelles would be monitored using electron microscopic analysis of immunogold stained sections of the various transfectants . rabbit anti - peptide antisera would be produced and affinity purified for this application . in addition , monoclonal antibody hf10 , which recognizes hel 34 - 45 , will be used . once a construct is defined that can be effectively presented by transfectants in vitro , its effectiveness in vivo will be determined . this can be tested by injection of the transfectants i . p . and / or s . c . into c3h / balb / c f1 mice , or by injection of the construct incorporated into an appropriate delivery vehicle ( e . g ., liposome , iscoms , retrovirus , vaccinia ). optimal protocols and doses for such immunizing injections can be determined by one of ordinary skill in the art , given the disclosures provided herein . efficiency of immunization can be tested by standard methods such as ( a ) proliferation of class ii - restricted t cells in response to hel pulsed apcs , ( b ) ctl response to 51 cr - labeled targets , and ( c ) serum antibody titre as determined by elisa . once the details of the vaccine delivery system of the invention are optimized , constructs encoding peptides with useful immunizing potential can be incorporated into the system . such peptides can be identified by standard means now used to identify immunogenic epitopes on pathogen - derived proteins . for example , candidate peptides for immunization may be determined from antibody and t cell analysis of animals infected with a particular pathogen . in order to obtain a protective and effective anamnestic response , the peptides used for vaccination should ideally be those which are presented with the highest frequency and efficiency upon infection . this could best be determined by using the procedures outlined in the experimental section above to extract and characterize the peptides bound by mhc class ii molecules from infected cells . given allelic restriction of immunogenic peptides ( in contrast to the observed degenerate binding of self peptides of invention ), a mini - gene encoding several immunogenic peptides will probably be required to provide a vaccine useful for the entire population . vaccine administration and dosage are as currently employed to smallpox vaccination . a the first six entries correspond to peptides found associated with hla - dr1 and the sequences are shown in table 1 . two control peptides were also tested : β 2 m 52 - 64 , sdlsfskdwsfyl ( seq id no : 26 ), is from human β 2 - microglobulin and ii 97 - 111 , lpkppkpvskmrmat ( seq id no : 25 ) is a truncated version of the longest invariant chain derived peptide isolated from hla - dr1 . peptides were synthesized using solid - phase fmoc chemistry , deprotected and cleaved using # standard methods , then purified by rpc . purified peptides were analyzed by mass spectrometry and concentrations were determined by quantitative ninhydrin analysis . b inhibition constants ( ki ) were measured as the concentration of test peptide which inhibited 50 % of the 125 i - labeled ha 307 - 319 binding to “ empty ” hla - dr1 produced in sf9 insect cells ( 20 ). ha 307 - 319 was labeled using na 125 i and chloramine - t and isolated by gel filtration . specific activity , determined by bca assay ( pierce ) and gamma counting , was 26 , 000 cpm / pmol . 10 nm labeled peptide and 10 nm purified hla - dr1 were mixed with 10 different concentrations # ( 10 nm to 10 μm ) of synthetic cold competitor peptide in phosphate - buffered saline , ph 7 . 2 , containing 1 mm edta , 1 mm pmsf , 0 . 1 mm iodoacetamide , and 3 mm nan 3 , and incubated at 37 ° c . for 85 hours . free and bound peptide were separated by native gel electrophoresis ( 33 ) and bound radioactivity was quantitated using a fujix imaging plate analyzer ( bas 2000 ) after four hour exposures on the phospho - imaging plates . percent inhibition was calculated as the ratio of # background - corrected radioactivity in the sample to background - corrected radioactivity in a parallel sample containing no competitor peptide . under these conditions , ki measurements & lt ; 10 nm could not be accurately determined . c the ability of the synthetic peptides to confer resistance to sds - induced chain dissociation of hla - dr1 produced in insect cells was determined as described ( 20 ). briefly , 20 μm hla - dr1 was incubated with five - fold excess of synthetic peptide at 37 ° c . for 85 hours , in phosphate - buffered saline ( ph 7 . 2 ) with the protease inhibitor mixture described above . after incubation , the samples were analyzed by sds - page with and without boiling prior to loading . peptides which # prevented sds - induced chain dissociation are indicated positive (+) and those that did not negative (−).
a purified preparation of a peptide consisting essentially of an amino acid sequence identical to that of a segment of a naturally - occurring human protein , said segment being of 10 to 30 residues in length , inclusive , wherein said peptide binds to a human major histocompatibility complex class ii allotype .