Abstract:
The invention relates to antibody fragments with simple heavy chain or sdAbs, characterized in that they consist of anti HIV Nef-protein fragments corresponding to all or a portion of the HHV domains of camelids, particularly llamas.

Description:
This application is the U.S. national phase of International Application No. PCT/IB2008/054832, filed 18 Nov. 2008, which designated the U.S. and claims the benefit of FR Application No. 07/08189, filed 22 Nov. 2007, the entire contents of each of which are hereby incorporated by reference. 
     The invention relates to single-domain antibody (sdAb) fragments capable of inhibiting the HIV Nef protein and to the immunological applications thereof, more particularly in immunotherapy for AIDS treatment. 
     BACKGROUND OF THE INVENTION 
     The recognition specificity of antibodies for hitting a given target has been exploited for the diagnosis and therapy of various pathological conditions, and most particularly in the case of acquired immunodeficiency syndrome (AIDS), where the target can be a protein of human immunodeficiency viruses type 1 or 2 (HIV-1 and HIV-2). 
     In the context of the search for candidate antibodies for neutralizing an HIV protein, the inventors have oriented their studies toward particular antibodies, devoid of a light chain, identified in camelids (camel, dromedary, llama) (Hamers-Casterman et al., 1993). 
     Camelid single heavy-chain antibody variable domains (VHH), which specifically recognize one type of antigen, have been selected from an immunized animal and have been produced from plasmid constructs. As shown in the examples, these antibody fragments have been found to be capable of specifically targeting regions of the HIV Nef (negative regulatory factor) protein that are involved in the development of acquired immunodeficiency syndrome (AIDS). 
     The aim of the invention is therefore to provide single heavy-chain antibody fragments (also called sdAbs for single-domain antibodies), having the desired target and epitope recognition properties. 
     The aim of the invention is also to provide a method for producing these antibody fragments. According to yet another aspect, the invention is directed toward the immunotherapeutic applications thereof. 
     SUMMARY OF THE INVENTION 
     The sdAb fragments of the invention are characterized in that they are anti-HIV Nef protein fragments corresponding to all or part of the VHH domains of camelids, in particular llamas. 
     According to an aspect of general interest, these fragments exhibit great stability and can be obtained in large amounts in soluble forms in bacteria, yeasts or any other system of production from prokaryotic or eukaryotic cells. 
     Their high stability enables them to acquire and maintain correct folding and therefore to remain soluble even under conditions which do not allow the formation of disulfide bridges, such as the cytoplasm of bacteria or of eukaryotic cells. 
     The invention is in particular directed toward the anti-Nef antibody fragments having an amino acid sequence as encoded by a nucleotide sequence chosen from the group comprising the sequences SEQ ID Nos. 1 to 6. 
     The invention is thus more especially directed toward the anti-Nef antibody fragments having an amino acid sequence chosen from the group comprising the sequences SEQ ID Nos. 7 to 12. 
     The invention is also directed toward CDRs of these sdAb fragments. 
     The nucleic acids capable of encoding said fragments also come within the field of the invention. The invention is in particular directed toward, as novel products, the nucleic acids corresponding to the sequences SEQ ID Nos. 1 to 6. 
     The invention is also directed toward a method for producing the anti-Nef antibody fragments defined above. 
     This method is characterized in that it comprises:
         immunization of camelids, in particular of llamas, with the Nef protein as immunogen,   purification of the B lymphocytes recovered from the blood,   construction of a VHH library, and   isolation of the sdAb fragments from the library and purification of said fragments.       

     More especially, the Nef protein used for the immunization lacks its first 56 amino acids. 
     The construction of the library advantageously comprises:
         extraction of the total RNA from the B lymphocytes,   reverse transcription of the RNAs so as to obtain the corresponding cDNAs,   PCR amplification of the genes encoding the variable regions of the anti-Nef single heavy-chain antibodies,   ligation of VHH DNA fragments, obtained by enzyme cleavage of the amplified DNAs with a phagemid.       

     Preferably, the sdAbs are isolated from the libraries by means of the phage display technique and are purified. 
     The various sdAbs obtained have been validated in terms of specificity and affinity, as illustrated by the examples. 
     In accordance with the invention, the selected sdAb genes have subsequently been inserted into expression vectors, in particular plasmids, so as to produce various anti-Nef sdAbs capable of binding to Nef in HIV-infected cells. 
     These expression vectors also constitute novel products, and the invention is therefore also directed toward said expression vectors. 
     The invention is more especially directed toward expression vectors, in particular plasmids, containing between two unique restriction enzyme sites, the promoters, the signal sequences and the nucleotide sequences capable of encoding the sdAb fragments defined above, or the CDRs regions of the sdAbs. 
     These vectors, in particular these plasmids, are capable of expressing the fragments of the invention in large amounts, in soluble forms, for example in bacteria. 
     The invention is thus directed towards the plasmids pET14bNef13, pET14bNefW12, pET14bNefW10, pHen6HisGS, pHenPhoA6His, pHen-sdAb Nef1, pHen-sdAb Nef2, pHen-sdAb Nef5, pHen-sdAb Nef12, pHen-sdAb Nef19, pHen-sdAb Nef20, pET-sdAb Nef1, pET-sdAb Nef2, pET-sdAb Nef5, pET-sdAb Nef12, pET-sdAb Nef19, pET-sdAb Nef20, pcDNA-sdAb Nef19 having the sequences SEQ ID Nos. 13 to 30, respectively. 
     The genes encoding the sdAbs are inserted between unique restriction enzyme sites in the various plasmids. 
     The plasmids according to the invention are capable of expressing the sdAbs defined above in large amounts, in soluble forms, for example in bacteria. The regions encoding the sdAbs can be easily transferred into other prokaryotic or alternatively eukaryotic expression systems or else transferred into plasmids intended to be transfected in to eukaryotic cells. 
     The identification, in accordance with the invention, of a new target for intervention, represented by a direct inhibition of the functions of the Nef viral protein during natural infection with HIV, constitutes an original approach for developing antiviral molecules capable of disrupting HIV replication in the target cell, but also of improving the immune response of the infected patients. 
     The invention is therefore directed toward benefiting from the immunological properties of the antibody fragments in immunotherapy. 
     In a first embodiment, the invention is more especially directed toward the antibody fragments defined above, where appropriate, vectorized, for use as medicaments. 
     The pharmaceutical compositions of the invention are then characterized in that they contain an effective amount of at least one sdAb fragment as defined above, in combination with a pharmaceutically acceptable carrier. 
     According to one embodiment of the invention, these compositions can be used as antiviral medicaments. In this application, the sdAb fragments are vectorized in order to cross the cell membrane and to be released within the infected cell. 
     The vector, for example, a peptide sequence, may be conjugated to the sequence of the fragments. 
     As a variant, the vector is combined with the sdAb fragments and corresponds, for example, to lipid compounds. 
     According to another embodiment, the pharmaceutical compositions of the invention are used in immunotherapy in order to inhibit Nef molecules released into the plasma environment. 
     The pharmaceutical compositions above are advantageously in forms suitable for oral or injectable administration. 
     In another embodiment, the invention is directed toward a gene therapy medicament constituted of a transfection vector comprising a nucleic acid as defined above, encoding an sdAb fragment of the invention. 
     Vectors that can be used for gene therapy purposes comprise adenoviruses, adeno-associated viruses (AAVs) and retroviruses. 
     These medicaments are used for intracellular immunization by transfection of infected cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will be given in the examples which follow, in which reference is made to  FIGS. 1 to 10 , which represent, respectively, 
         FIG. 1 , (A) titration curves for the sdAb Nef1-phage, sdAb Nef2-phage, sdAb Nef5-phage and sdAb Nef19-phage on the Nef protein adsorbed in the wells of a microplate and (B) curves of competition for the binding of the sdAb Nef5-phage and sdAb Nef19-phage to the Nef W10 protein adsorbed in the wells of a microplate, by the soluble Nef W10 protein, 
         FIG. 2 , an SDS-PAGE gel showing the fractions of the sdAb Nef19 protein purified on TALON, 
         FIG. 3 , (A) titration curves for sdAb Nef5 and sdAb Nef19 on the Nef W10 protein adsorbed in the wells of a microplate, (B) titration curve for sdAb Nef5 after amplification of the signal, and (C) curve of competition for the binding of sdAb Nef19 to the Nef W10 protein adsorbed in the wells of a microplate, by the soluble Nef W10 protein, 
         FIG. 4 , table of the affinity constants of sdAb Nef19, obtained by Biacore, 
         FIG. 5 , co-localization, analyzed by immuno-fluorescence, of sdAb Nef19 with the Nef protein in HeLa cells, 
         FIG. 6 , (A) flow cytometry analysis of the inhibition, by sdAb Nef19, of the effect of Nef on the level of expression of CD4 at the surface of HPB-ALL T cells and (B) flow cytometry analysis of the inhibition, by sdAb Nef19, of the effect of Nef on the level of expression of CD4 at the surface of HeLa cells, 
         FIG. 7  (A) flow cytometry analysis of the inhibition, by sdAb Nef19, of the ability of Nef to interact with the cellular machinery of the endocytosis pathway when it is expressed in the form of a CD8-Nef fusion in HeLa cells and (B) immunofluorescence analysis of the inhibition, by sdAb Nef19, of the ability of Nef to interact with the cellular machinery of the endocytosis pathway when it is expressed in the form of a CD8-Nef fusion in HeLa cells, 
         FIG. 8 , analysis, by means of coimmuno-precipitation experiments, of the interaction of sdAb Nef19 with the Nef protein in 293T cells, 
         FIG. 9 , analysis of the inhibition, by sdAb Nef19, of the infection capacity of HIV-1 during a single replication cycle measured on (A) HeLa-CD4 cells and (B) HPB-ALL T cells, 
         FIG. 10 , analysis of the incorporation of sdAb Nef19 into viral particles. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Example 1 
     Construction of the various expression vectors for producing recombinant truncated Nef proteins in  E. coli  and for selecting sdAbs from sdAb-phage libraries 
     a—Cloning of Various Versions of The Nef Protein in pET14b for their Production in  E. coli    
     a1—Obtaining of the Nef 13 Clone 
     Oligonucleotides Used: 
                     5′Nef-Nco1-pET       SEQ ID No. 34:       CTTTAAGAAGGAGATATACCATGGGCCAYCAYCAYCAYCAYCAYGGNTCN       GAAGCACAAGAGGAGGAGGAG               3′Nef-Blpl-pET       SEQ ID No. 35:       GGGGTTATGCTAGTTATTGCTCAGCGTTCTTGAAGTACTCCGGATG            
PCR Conditions:
 
     One μl (5 ng) of plasmid pNef-GST (gene encoding amino acids 57 to 205 of the Nef protein inserted into the plasmid pGEX-2T (GE Healthcare)), 5 μl of 10× Deep-Vent buffer, 1 μl of 100 mM MgSO 4 , 4 μl of 2.5 mM dNTP mix, 10 μM of each oligonucleotide (5′ Nef-Nco-pET and 3′ Nef-Blp1-pET), 0.5 U of Deep Vent in a final volume of 50 μl (94° C., 3 min; 94° C., 1 min; 55° C., 1 min; 72° C., 1 min, 30 cycles and then 72° C. 10 min). The PCR products are purified using a 2% agarose gel (Qiagen gel extraction kit, final volume 30 μl). 
     Cloning of the PCR Fragment into the Plasmid pET14b: 
     20 μl of the PCR fragment and 5 μl (2.5 μg) of the pET14b vector (Novagen) are cleaved with 10 U of Nco I and Blp I for 16H at 37° C. The enzymes are inactivated for 10 minutes at 65° C. Each DNA is then precipitated and taken up with 20 μl of H 2 O. 
     The ligation is carried out with 5 μl of fragment, 0.5 μl of vector and 3 Weiss units of T4 DNA ligase (Biolabs) in a final volume of 10 μl for 2H at ambient temperature. Competent (CaCl 2  technique) BL21(DE3) bacteria are transformed with 5 μl of the ligation product. The plasmid pET14bNef13, the nucleotide sequence of which is given in the appendix (SEQ ID No. 13), is thus obtained, and makes it possible to produce the Nef13 clone, the amino acid sequence of which is given in the appendix (SEQ ID No. 31). 
     a2—Obtaining of the NefW12 Clone 
     Oligonucleotides Used: 
                     5′Nef.Nco1.W       SEQ ID No. 36:       CTTTAAGAAGGAGATATACCATGGGCCACCACCATCATCATCACGGATCC       GCCTGGCTAGAAGCACAAGAGGAGGAGGAG               3′Nef-Blp1-pET       SEQ ID No. 37:       GGGGTTATGCTAGTTATTGCTCAGCGTTCTTGAAGTACTCCGGATG            
PCR Conditions on pET14bNef13:
 
     One μl (5 ng) of plasmid pET14bNef13, 10 μM of each oligonucleotide (5′ Nef.Nco.W and 3′ Nef-Blp1-pET), 0.5 U of Dynazyme (94° C., 3 min; 94° C., 1 min; 55° C., 1 min; 72° C., 1 min, 30 cycles, then 72° C., 10 min). The PCR products are purified using a 2% agarose gel (Qiagen gel extraction kit, final volume 50 μl). 
     Cloning of the PCR fragment into the plasmid pET14b: 20 μl of PCR fragment and 5 μl (2.5 μg) of the pET14b vector are cleaved with 10 U of NCo I and Blp I for 16H at 37° C. The enzymes are inactivated for 10 minutes at 65° C. Each DNA is then precipitated and the pellet is taken up with 20 μl of H 2 O. 
     The ligation is carried out with 5 μl of fragment, 0.5 μl of vector and 3 Weiss units of T4 DNA ligase (Biolabs) in a final volume of 10 μl for 2H at ambient temperature. Competent (CaCl 2  technique) BL21(DE3) bacteria are transformed with 5 μl of the ligation product. The plasmid pET14bNefW12, the nucleotide sequence of which is given in the appendix (SEQ ID No. 14), is thus obtained and makes it possible to produce the Nef W12 clone, the amino acid sequence of which is given in SEQ ID No. 32. 
     a3—Obtaining of the Nef W10 Clone 
     Oligonucleotides Used: 
                     5′Nef/pET       SEQ ID No. 38:       TTAAGAAGGAGATATACCATGGGCTGGCTNGARGCNCARGARGAGGAGGA       GGTGGGT               3′Nef/pJF-pET       SEQ ID No. 39:       GGGGTTATGCTAGTTAGCTCAGCAAGCTTAGGATCCGTGATGATGATGGT       GGTGTGCGGCCGCGTTCTTGAAGTACTCCGGATG            
PCR Conditions on pET14bNef13:
 
     One μl (5 ng) of plasmid pET14bNef13, 5 μl of 10× Dynazyme buffer, 4 μl of 2.5 mM dNTP mix, 10 μM of each oligonucleotide (5′ Nef.Nco.W and 3′ Nef-Blp1-pET), 0.5 U of Dynazyme, in a final volume of 50 μl (94° C., 3 min; 94° C., 1 min; 55° C., 1 min; 72° C., 1 min, 30 cycles then 72° C., 10 min). The PCR products are purified using a 2% agarose gel (Qiagen gel extraction kit, final volume 50 μl). 
     Cloning of the PCR fragment into the plasmid pET14b: 20 μl of PCR fragment and 5 μl (2.5 μg) of the pET14b vector are cleaved with 10 U of NCo I and Blp I for 16H at 37° C. The enzymes are inactivated for 10 minutes at 65° C. Each DNA is then precipitated and taken up with 20 μl of H 2 O. 
     The ligation is carried out with 5 μl of fragment, 0.5 μl of the vector and 3 Weiss units of T4 DNA ligase (Biolabs) in a final volume of 10 μl for 2H at ambient temperature. Competent (CaCl 2  technique) BL21(DE3) bacteria are transformed with 5 μl of the ligation product. The plasmid pET14bNefW10, the nucleotide sequence of which is given in the appendix (SEQ ID No. 15), is thus obtained and makes it possible to produce the Nef W10 clone, the amino acid sequence of which is given in the annexe (SEQ ID No. 33). 
     All the genes encoding the various versions of Nef inserted into the plasmids of pET14b type were verified by sequencing on an ABI 310 with oligonucleotides internal to Nef: 
                                 5′Int.Nef               SEQ ID No. 40:   CACACAAGGCTACTTCCC                       3′ Int.Nef           SEQ ID No. 41:   CAACTGGTACTAGCTTGTAG            
b—Construction of Phagemids pHen6HisGS and pHen6HisPhoA for Library Construction
 
     b1—Obtaining of the pHen6HisGS Phagemid 
     The 6HisGlySer motif is inserted downstream of the sequence encoding the c-myc tag of the pHen1 phagemid (Hoogenboom et al., 1991) by overlapping PCR. 
     Oligonucleotides Used: 
                     Sup-6HisGS/P3       SEQ ID No. 42:       5′ CATCACCACCATCACCATGGGAGCTAGACTGTTGAAAGTTGTTTAGC       AAAACC               Inf-6HisGS/cmyc       SEQ ID No. 43:       5′ GCTCCCATGGTGATGGTGGTGATGTGCGGCCCCATTCAGATCCTC               Amont[Upstream]-Hind3       SEQ ID No. 44:       5′ AACAGCTATGACCATG               Aval[Downstream]-Bsm1       SEQ ID No. 45:       5′ GCAAGCCCAATAGGAACCC            
PCR1 and PCR2 Conditions:
 
     One μl pHen1 at 50 ng/μl, 10 μl 10× Dynazyme buffer (Biolabs), 2 μl dNTP mix at 100 nM, 2 μl 5′ oligonucleotide at 10 pmol/μl, 2 μl 3′ oligonucleotide at 10 pmol/μl (pairs of primers used: PCR 1: Amont[Upstream]-Hind3 and Inf-6HisGS/cmyc; PCR 2: Sup-6HisGS/P3 and Ava1[Downstream]-Bsm1), 0.7 μl of Dynazyme Taq polymerase (Biolabs), 82 μl H 2 O. 
     PCR program used: 95° C., 3 min; 95° C., 45 s; 50° C., 45 s; 72° C., 45 s; 72° C., 3 min; 30 cycles. The size of the PCR1 and PCR2 fragments is verified on a 1% agarose gel and then the fragments are purified using the “Qiaquick gel extraction” kit (Qiagen). These two fragments are then used for the overlapping PCR3. 
     PCR 3 Conditions: 
     0.75 μl of each product of PCR1 and PCR2, 10 μl 10× Dynazyme buffer (Biolabs), 2 μl dNTP mix at 100 nM, 2 μl oligonucleotide Amont[Upstream]-Hind3 at 10 pmol/μl, 2 μl oligonucleotide Aval[Downstream]-Bsm1 at 10 pmol/μl, 0.7 μl of Dynazyme Taq polymerase (Biolabs), 82 μl H 2 O. 
     PCR program used: 95° C., 3 min; 95° C., 45 s; 50° C., 45 s; 72° C., 45 s; 72° C., 3 min; 30 cycles. The size of the PCR3 fragment is verified on a 1% agarose gel and then the fragments are purified using the “Qiaquick gel extraction” kit (Qiagen). This fragment is then used for cloning. 
     The analysis of the PCR3 product on a 1% agarose gel is in accordance with what is expected (424 bp). This fragment was purified using the “Qiaquick gel extraction” kit (Qiagen) and was then cloned. 
     Cloning: 
     The PCR3 product is purified and cleaved, in a volume of 50 μl, with 20 units of HindIII restriction enzyme in the presence of BSA, at 37° C., for 4 h. Twenty units of the BsmI restriction enzyme are then added, and the sample is incubated at 65° C. for 4 h. The BsmI enzyme is denatured at 80° C. for 20 min. 
     Ten μg of pHen1 are cleaved, in a volume of 50 μl, with 20 units of HindIII restriction enzyme in the presence of BSA, at 37° C., for 4 h. Twenty units of the BsmI restriction enzyme are then added, and the sample is incubated at 65° C. for 4 h. The BsmI enzyme is denatured at 80° C. for 20 min. 
     The cleavage products are analyzed on a 0.7% agarose gel in order to verify the cleavage. 
     The PCR3 product and the pHen1 that have been cleaved with HindIII and BsmI are purified on a 0.7% gel using the “Qiaquick gel extraction” kit (Qiagen). 
     The PCR fragment is then cloned into the pHen1 phagemid between the HindIII and BsmI sites (insert DNA/phagemid molar ratio 1/5; 2000 units of T4 DNA ligase (Biolabs); 2 h at 20° C.). The ligase is denatured at 65° C. for 15 min. 
     Competent TG1 bacteria are transformed with 10 μl of ligation product. A phagemid preparation was then carried out using an isolated column and sequencing was carried out. The expression of the p3 protein of pHen6HisGS was verified by Western blotting using an antibody directed against the p3 protein. The sequence was found to be in accordance with what was expected. The nucleotide sequence of pHen6HisGS is given in the appendix (SEQ ID No. 16). 
     b2—Obtaining of the pHenPhoA6His Phagemid 
     The new pHen6HisGS vector can be directly used for constructing the naive library. It is advantageous to improve it in order to facilitate the evaluation of the cloning efficiency. This is because the isolation of VHH (or sdAb) with good specificity and in large number requires libraries of wide diversity to be obtained. Very good cloning efficiency is therefore necessary during library construction. 
     The phoA gene encoding alkaline phosphatase is inserted into the pHen6HisGS phagemid upstream of the gene encoding the c-myc tag. 
     This gene, inserted in the correct reading frame, allows the synthesis of a “PhoA-cmyc-6HisGs-p3” fusion protein which has the phosphatase activity. A colorimetric selection thus makes it possible to distinguish the vectors closed up on themselves (blue colonies) from the vectors having inserted, in place of the PhoA gene, the genes encoding VHH or sdAb (white colonies). 
     Firstly, the sequencing coding PhoA was amplified, from the plasmid p55PhoA6HisGS/NAB- (Baty et al., CNRS/INSERM patent WO/2006/064136) with specific primers for cloning into the pHen6HisGS phagemid. 
     Oligonucleotides Used: 
                     5′ PhoA/pHen       SEQ ID No. 46:       5′ GGATTGTTATTACTCGCGGCCCAGCCGGCCATGGCAGCCGATCCTCG       AGAGCTCCCG               3′ PhoA/pHen       SEQ ID No. 47:       5′ GAGATGAGTTTTTGTTCTGCGGCCGCTTTCAGCCCCAGAGCGGCTTT       C            
PCR Conditions:
 
     One μl p55PhoA6HisGS/NAB- at 50 ng/μl, 10 μl 10× Dynazyme buffer (Biolabs), 2 μl dNTP mix at 100 nM, 2 μl 5′ PhoA/pHen oligonucleotide at 10 pmol/μl, 2 μl 3′ PhoA/pHen oligonucleotide at 10 pmol/μl, 0.7 μl of Dynazyme Taq polymerase (Biolabs), 82 μl H 2 O. 
     PCR program used: 95° C., 3 min; 95° C., 1 min; 60° C., 1 min; 72° C., 1 min; 72° C., 10 min; 35 cycles. 
     The PCR product is analyzed on a 1% agarose gel. The PCR product purified using the “Qiaquick gel extraction” kit (Qiagen) is cleaved, in a volume of 50 μl, with 20 units of SfiI restriction enzyme in the presence of BSA, at 50° C., 16 h. Twenty units of the NotI restriction enzyme are then added, and the sample is incubated at 37° C. for 4 h. 
     Ten μg of pHen6HisGS are cleaved, in a volume of 50 μl, with 20 units of the SfiI restriction enzyme in the presence of BSA at 50° C. for 4 h. Twenty units of the NotI restriction enzyme are then added, and the sample is incubated at 37° C. for 4 h. 
     The PCR product and the pHen6HisGS that have been cleaved with SfiI and NotI are purified on a 0.7% gel using the “Qiaquick gel extraction” kit (Qiagen). 
     Cloning: 
     The PCR fragment is then cloned into the pHen6HisGS phagemid between the SfiI and NotI sites (insert DNA/phagemid molar ration 1/1; 1000 units of T4 DNA ligase (Biolabs); 2 h at 20° C.). The ligase is denatured at 65° C. for 15 min. 
     Competent TG1 bacteria are transformed with 10 μl of ligation product, and then plated out on LB medium/100 μg/ml ampicillin/30 μg/ml BCIP. 
     A preparation of the phagemid was then prepared using a blue colony. The expression of the PhoA-cmyc-6HisGS-p3 fusion protein was verified, as was the efficiency of the phagemid for infection. The nucleotide sequence of pHenPhoA6His phagemid is given in the appendix (SEQ ID No. 17). 
     c—Immunization of Llamas and Purification of B Lymphocytes 
     A male llama was immunized with region 57 to 205 of the recombinant Nef protein (Nef57-205) of HIV-1. 
     The animal was immunized every month, for three months, with 500 μg of Nef57-205. One hundred ml of blood were taken 15 days after each immunization. For each of the samples taken, the sera and the purified antibodies (IgG1, 2 and 3) were titered in order to detect the presence of antibodies against the Nef57-205 immunogen. The B lymphocytes were then purified on a Ficoll gradient (histopaque-1077, Sigma-Aldrich), and then washed twice with PBS. 
     d—Construction of Phage-sdAb Libraries: Purification of Total RNA, Reverse Transcription, PCR1, PCR2 and Cloning into the pHen6HisGS and pHenPhoA6His Phagemids 
     d1—Purification of Total RNA 
     Total RNA of the B lymphocytes is extracted according to the method using guanidium isothiocyanate (Chomczynski and Sacchi, 1987). After phenol/chloroform extraction in an acidic medium, the total RNA is precipitated with ethanol. The quality of the RNA and the quantification thereof are evaluated on a 1% agarose gel. It is then converted to cDNA by reverse transcription. 
     d2—Reverse Transcription and PCRs 
     Oligonucleotides Used: 
     
       
         
               
             
           
               
                 3′CH2FORTA4 
               
               
                 SEQ ID No. 48: 
               
               
                 CGCCATCAAGGTACCAGTTGA 
               
               
                   
               
               
                 3′CH2-2 
               
               
                 SEQ ID No. 49: 
               
               
                 GGTACGTGCTGTTGAACTGTTCC 
               
               
                   
               
               
                 3′RC-IgG2 
               
               
                 SEQ ID No. 50: 
               
               
                 GGAGCTGGGGTCTTCGCTGTGGTGCG 
               
               
                   
               
               
                 3′RC-IgG3 
               
               
                 SEQ ID No. 51: 
               
               
                 TGGTTGTGGTTTTGGTGTCTTGGGTT 
               
               
                   
               
               
                 5′VH1-Sfi 
               
               
                 SEQ ID No. 52: 
               
               
                 CATGCCATGACTCGCGGCCCAGCCGGCCATGGCCCAGGTGCAGCTGGTGC 
               
               
                 AGTCTGG 
               
               
                   
               
               
                 5′VH2-Sfi 
               
               
                 SEQ ID No. 53: 
               
               
                 CATGCCATGACTCGCGGCCCAGCCGGCCATGGCCCAGGTCACCTTGAAGG 
               
               
                 AGTCTGG 
               
               
                   
               
               
                 5′VH3-Sfi 
               
               
                 SEQ ID No. 54: 
               
               
                 CATGCCATGACTCGCGGCCCAGCCGGCCATGGCCGAGGTGCAGCTGGTGG 
               
               
                 AGTCTGG 
               
               
                   
               
               
                 5′VH4-Sfi 
               
               
                 SEQ ID No. 55: 
               
               
                 CATGCCATGACTCGCGGCCCAGCCGGCCATGGCCCAGGTGCAGCTGCAGG 
               
               
                 AGTCGGG 
               
               
                   
               
               
                 3′VHH-Not 
               
               
                 SEQ ID No. 56: 
               
               
                 CACGATTCTGCGGCCGCTGAGGAGAC(AG)GTGACCTGGGTCC 
               
             
          
         
       
     
     Five μg of total RNA are hybridized with 1 pmol of 3′ CH2FORTA4 (Arbabi Ghahroudi et al., 1997) or CH2-2 oligonucleotide specific for the CH2 domain of llama single heavy-chain IgGs, and reverse-transcribed with 150 U of superscript II (BRL) for 30 min at 50° C. The oligonucleotides specific for the hinge regions of IgG2 and 3, 3′ RC-IgG2 and 3′ RC-IgG3, can also be used. The single-stranded cDNAs are purified on beads (BioMagR Carboxyl Terminator, Polyscience Inc) and eluted with 17 μl of 10 mM Tris-acetate, pH 7.8. 
     d3—PCR1, PCR2 
     PCR1 Conditions: 
     Four μl of cDNA are amplified by PCR with 0.5 U of Dynazyme Extend DNA polymerase (Finnzymes), 10 pmol of the same 3′ CH2FORTA4 or CH2-2 primer and 10 pmol of the four 5′ VH1-4 Sfi primers specific for the VH domain of human IgGs, in a volume of 50 μl (94° C., 3 min; 94° C., 1 min; 60° C., 1 min; 72° C., 1 min; 37 cycles, then 72° C., 10 min). 
     Three DNA fragments are amplified: a fragment of approximately 900 bp encoding the VH-CH1-CH2 domains of IgG1; and 2 fragments of approximately 600 bp encoding the VHH-CH2 domains of IgG2 and 3. 
     PCR2 Conditions: 
     The 600 bp fragments are purified on a 1% agarose gel (“Qiaquick gel extraction” kit, Qiagen) and then amplified by PCR with 1 U of Deep Vent (Biolabs) and 10 pmol of the four 5′ VH1-4 Sfi primers specific for the VH domain of human IgG and 10 pmol of the 3′ VHH-NotI primer (94° C., 3 min; 94° C., 45 sec; 65° C., 45 sec; 72° C., 45 sec; 15 cycles, then 94° C., 45 sec; 60° C., 45 sec; 72° C., 45 sec; 15 further cycles, then 72° C., 10 min). 
     The fragments of approximately 400 bp encoding the VHHs are purified on a 1% agarose gel (“Qiaquick gel extraction” kit, Qiagen), combined and precipitated with ethanol. They are then cleaved with the NcoI and NotI, or BglI and NotI, restriction enzymes (Biolabs) so as to be cloned into the pHen16hisPhoA phagemid at the NcoI and NotI or SfiI and NotI sites. 
     d4—Cloning into the Phagemids 
     Preparation of the pHen6HisGS Phagemid (or pHen6HisPhoA phagemid for the “naive” library): 
     Twenty μg of pHen6HisGS phagemid are cleaved, in a volume of 300 μl, with 50 U of SfiI in the presence of BSA, at 50° C. for 16 h; or with 50 U of NcoI in the presence of BSA, at 37° C. for 16 h. The linearized phagemid is purified on a 0.7% agarose gel (“Qiaquick gel extraction” kit, Qiagen). The DNA eluted is then cleaved with 50 U of NotI at 37° C. in a volume of 200 μl for 16 h. The enzyme is destroyed by heat for 15 minutes at 65° C. and the DNA is extracted with phenol/chloroform and precipitated with ethanol. The cleaved pHen6HisGS is checked on a 0.7% agarose gel, quantified and adjusted to 200 ng/μl. 
     Preparation of the DNA Fragments Encoding the sdAbs: 
     Five μg of VHH fragments are cleaved, in a volume of 300 μl, with 50 U of BglI and NotI in the presence of BSA, at 37° C. for 16 h; or with 50 U of NcoI and NotI in the presence of BSA, at 37° C. for 16 h. The enzymes are denatured at 65° C. for 15 min; the DNAs are then extracted with phenol/chloroform and precipitated with ethanol in the presence of 10 μg of glycogen (Roche). The VHH fragments cleaved with NcoI and NotI are purified on a 1% agarose gel, and then checked on a 2% agarose gel, quantified and adjusted to 100 ng/μl. 
     Ligation: 
     One hundred and fifty ng of pHen6HisGS cleaved with SfiI and NotI are ligated with 60 ng of VHH fragment cleaved with BglI and NotI, in a volume of 20 μl, with 2000 U of T4 DNA ligase (Biolabs) at 16° C. for 17 h. 
     The ligase is inactivated at 65° C. for 15 min, and the ligation product is cleaved with 20 U of XhoI (Biolabs) so as to eliminate the unligated residual vector, at 37° C. for 4 h. Six ligations are thus performed. The ligation products are then combined in two tubes and extracted with phenol/chloroform, precipitated in the presence of 10 μg of glycogen and taken up in 2×18 μl of ultrapure H 2 O. Two μl are used by electroporation. The colonies from various electroporations are combined. The male llama sdAb-phage library represents 4.1×10 4  clones. 
     e—Construction of the “Naive” sdAB-Phage Library Using Nonimmunized Llamas 
     The library was constructed exactly as described for the immune library, with the following modifications:
         the phagemid used is pHenPhoA6His,   the blood (approximately 2400 ml) was taken from about sixty nonimmunized llamas originating from 4 different farms.       

     The “naive” sdAb-phage library represents 3 107 clones. 
     f—Selection of sdAbs from the Libraries Using the Phage-Display Technique 
     The various sdAbs were isolated using the phage-display technique (Smith, 1985; Hoogenboom et al., 1991) irrespective of the library used. 
     f1—Production of the Phage Library: 
     Ten μl of the library stock (TG1 cells transformed with the phagemids) are inoculated into 50 ml of 2TY containing 100 μg/ml of ampicillin and 2% glucose, and incubated at 37° C. until an OD600 equal to 0.5 is obtained. Five ml of the culture are then infected with 5 ml of M13KO7 at 10 13  pfu/ml and incubated for 30 min at 37° C. with no agitation. After centrifugation, the phage pellet is taken up in 25 ml of 2TY containing 100 μg/ml of ampicillin and 25 μg/ml kanamycin. The culture is incubated for 16 h at 30° C. with agitation. The phages are then precipitated with 1/5 vol of 2.5M NaCl/20% PEG 6000 and concentrated 25-fold in PBS. 
     f2—sdAb Selection: 
     Two hundred μl of streptavidin-coated beads (Dynabeads M-280, Dynal) are equilibrated with 1 ml of 2% milk/PBS for 45 min at ambient temperature with agitation on a wheel. 10 12  phages from the production previously described are also equilibrated with 2% milk/PBS in a final volume of 500 μl for 60 min at ambient temperature with agitation on a wheel. 
     The beads are compacted with a magnet, suspended in 250 μl of 2% milk/PBS and incubated with 200 μl of biotinylated antigen for 30 min at ambient temperature on a wheel. 150, 75 and 25 nM, final concentration, of biotinylated antigen are used in the 1st, 2nd and 3rd round, respectively. 
     500 μl of phages are added to the 450 μl of beads/antigen-biotin for 3 h at ambient temperature with agitation on a wheel. The beads/antigen-biotin/phage mixture is washed 5 times with 800 μl of 4% milk/PBS, and then transferred into a new Eppendorf tube. Five other washes are carried out with 800 μl of PBS/0.1% Tween, and the mixture is then transferred into a new Eppendorf tube. Finally, 5 washes are carried out with 800 μl of PBS. 
     The antibody phages bound to the beads/antigen-biotin are suspended in 200 μl of PBS and incubated for 30 min at 37° C., with no agitation, with 1 ml of TG1 made competent for binding of the phages to the pili (competent cells: starting from an overnight culture of TG1 in 2YT, a 1/100 dilution is made and 50 ml of 2YT are inoculated at 37° C. with agitation until an OD600 close to 0.5 is obtained). At each selection, the phages are counted and amplified for a further round of selection. 
     f3—Counting the Selections: 
     Dilutions of the TG1 cells transfected with the phages (see above) of 10 −2  to 10 −5  are made with 2YT. One, 10 and 100 μl of each dilution are plated out onto Petri dishes (2YT/100 μg/ml ampicillin/2% glucose). The dishes are incubated for 16 h at 30° C. 
     f4—Plating Out the Selection for Isolation of Colonies: 
     The 5 ml of transfected TG1 are centrifuged for 10 min at 3000 g in order to concentrate the cells, and the pellet is taken up with 1 ml of 2YT. Two hundred and fifty μl are plated out per Petri dish (12 cm×12 cm)(2TY/100 μg/ml ampicillin/2% glucose) and incubated for 16 h at 30° C. 
     f5—Selection Results Assessment 
     f6—“Immune” Library 
     Two sdAbs specific for the Nef protein were isolated by this method: sdAb Nef19 (SEQ ID Nos. 1 and 7) and sdAb Nef20 (SEQ ID Nos. 2 and 8). 
     f7—“Naive” Library 
     Four sdAbs specific for the Nef protein were isolated by this method: sdAb Nef1 (SEQ ID Nos. 3 and 9), sdAb Nef2 (SEQ ID Nos. 4 and 10), sdAb Nef5 (SEQ ID Nos. 5 and 11) and sdAb Nef12 (SEQ ID Nos. 6 and 12). 
     The sequences were aligned according to the IMGT international nomenclature (The international ImmunoGeneTics information system)(Lefranc, 2003). 
     g—Production of sdAb-Phages and Counting 
     g1—Unitary sdAb-Phage Production: 
     Twenty ml of 2TY (100 μg/ml ampicillin; 2% glucose) are inoculated with one isolated colony of TG1 containing the phagemid corresponding to the sdAb-phage selected. The culture is incubated at 37° C. with agitation until an OD600 nm close to 0.5 is obtained. Five ml of this culture are infected with 5 to 10 μl of M13KO7 helper phage (10 13  pfu/ml) and incubated for 30 min at 37° C. in a water bath (with no agitation). The culture is centrifuged for 10 min at 3000 g and the supernatant is removed. The pellet is taken up with 25 ml of 2TY (100 μg/ml ampicillin; 25 μg/ml kanamycin). The culture is incubated at 30° C. for 16 h with agitation, and then the vessel is placed in ice for 10 min. The culture is then centrifuged for 20 min at 3000 g, 4° C. The supernatant is removed and precipitated by adding 1/5 volume of 2.5M NaCl/20% PEG 6000 for 1 h in ice. The solution is centrifuged for 20 min at 3000 g, 4° C. The pellet is taken up with 1 ml of PBS and transferred into a siliconized Eppendorf tube. A rapid precipitation is carried out by adding 200 μl of NaCl/PEG, followed by centrifuging at 13 000 rpm. The pellet is taken up with 1 ml of PBS and centrifuged for 1 min at 13 000 rpm. The supernatant is filtered through 0.45 μm and transferred into a siliconized Eppendorf tube and then stored at 4° C. 
     g2—Counting of the sdAb-Page Solution: 
     TG1 cells are cultured in 2YT at 37° C. Successive dilutions (10-fold) of sdAb-phage are made in siliconized Eppendorf tubes containing 500 μl of 2YT. When the TG1 cells are at an OD600 nm of 0.5, 500 μl of TG1 are added, and then the cells are left for 30 min at 37° C. without agitation. One hundred μl of each tube are plated out on 2YT (100 μg/ml ampicillin; 2% glucose) Petri dishes. The dishes are incubated for 16 h at 30° C. or 37° C. The colonies are counted in order to determine the number of sdAb-phages in the starting solution. This solution will be used to characterize the sdAb-phages by ELISA. 
     h—Characterization of Anti-Nef sdAb-Phages by ELISA 
     h1—sdAb-Phage ELISA: 
     Five μg/ml of biotinylated antigen (Nef W10) are bound to a streptavidin plate (BioBind Assembly Streptavidin Coated, ThermoLabsystems) presaturated with 2% milk/PBS. Various sdAb-phage dilutions are brought into contact with the antigen. The antigen/antibody binding is detected by means of an ELISA composed of a monoclonal antibody directed against the P8 protein of the phage (HRP/anti-M13 monoclonal conjugate, Pharmacia). Addition of the substrate, 10 mg ABTS (diammonium salt of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), to 20 ml of revealing buffer (18 ml PBS, 1 ml of 1M citric acid, 1 ml of 1M sodium citrate, 10 ml of 30% H 2 O 2 ) makes it possible to read the reaction at 405 nm (Tecan). 
       FIG. 1A  shows the results obtained with the sdAb Nef1-phage, sdAb Nef2-phage and sdAb Nef5-phage obtained with the “naive” library and the sdAb Nef19-phage obtained from the “immune” library. In all the titration curves, a decrease in the measurement of the interaction between the sdAb-phages and the biotinylated Nef W10 protein, bound in streptavidin-coated wells of a microplate, is observed when the amount of sdAb-phage decreases. In order to demonstrate that this interaction is specific, competition ELISAs were carried out. For this, a constant amount of sdAb-phage (approximately 10 10  phage particles) was preincubated with various amounts of nonbiotinylated Nef W10 protein for 16 h at 4° C. The ELISAs are then carried out as described previously.  FIG. 1B  shows that the binding of the sdAb Nef5-phage and the sdAb Nef19-phage to the biotinylated Nef W10 decreases when the nonbiotinylated Nef W10 protein is increased in the assay. This decrease proves the specificity of the interaction between the sdAb-phages and the Nef W10 protein. Equivalent results are obtained with the other sdAb-phages selected. 
     i—Production and Purification of sdAbs from the pHen6HisGS or pHen6HisPhoA Phagemids 
     i1—sdAb Production: 
     An isolated colony is inoculated into 3 ml of 2YT/100 μg/ml ampicillin/2% glucose and incubated at 37° C. with agitation. Fifty ml of 2YT/100 μg/ml ampicillin/2% glucose are then inoculated with a dilution of the previous culture and incubated for 16 h at 30° C. with agitation. Four hundred ml of 2YT/100 μg/ml ampicillin are inoculated with the equivalent of 0.1 OD600 nm units, and incubated at 30° C. with agitation, until an OD600 nm of 0.5 to 0.7 is obtained. The culture is then induced with IPTG (isopropyl-β-D-thiogalactopyranoside; 0.1 mM of final concentration) and cultured at 30° C. for 16 h. 
     i2—Extraction of the Soluble Fraction of the Periplasm: 
     The cultures from which the sdAbs are produced are centrifuged at 4200 g, 4° C., for 40 min. The pellet is taken up in 4 ml of ice-cold TES (0.2M Tris-HCl, ph 8.0; 0.5 mM EDTA; 0.5M sucrose). 160 μl of lysozyme (10 mg/ml in TES, freshly prepared) are then added, followed by 24 ml of cold TES diluted to 1/2 in H 2 O. The mixture is incubated for 30 min in ice. 150 μl of DNAse (10 mg/ml) and a final concentration of 5 mM of MgCl 2  are then added for 30 min at ambient temperature. After centrifugation at 4200 g, 4° C., for 40 min, the supernatant (corresponding to the periplasmic fraction) is recovered. The solution is dialyzed for 16 h against the equilibrating buffer (50 mM sodium acetate, 0.1M NaCl, pH 7.0). 
     i3—sdAb Purification: 
     The column (BD TALON™ Metal affinity, BD Biosciences Clontech) is equilibrated with the equilibrating buffer (50 mM sodium acetate, 0.1M NaCl, pH 7.0). The periplasmic fraction is loaded onto the column. After the column has been washed with 5 volumes of equilibrating buffer, the sdAb is eluted by means of a pH or imidazole gradient (gradient between the equilibrating buffer, pH 7.0, and the 50 mM sodium acetate solution, pH 5.0, or the imidazole solution from 0 to 200 mM). Each fraction is checked on an SDS/PAGE gel (15% acrylamide) after staining with coomassie blue. The fractions of interest are combined and dialyzed against PBS. The sdAb is concentrated on a membrane (Amicon Ultra 5000MWCO, Millipore) and assayed by the Lowry colorimetric method using the Biorad Protein Assay kit. 
       FIG. 2  shows a purification profile (C: load; NR: fraction not retained on the column; L: loading buffer wash). sdAb Nef19 is eluted (fractions 9 to 56) with a pH gradient of 7 to 5. 
     i4—Characterization of the Anti-Nef sdAbs by ELISA 
     Five μg/ml of biotinylated antigen (Nef W10) are bound to a streptavidin plate (BioBind Assembly Streptavidin Coated, ThermoLabsystems) presaturated with 2% milk/PBS. Each sdAb (range of 0.001 μg/ml to 1 μg/ml) is bound to the antigen adsorbed in the microwells. The binding is revealed with a monoclonal antibody, 9E10, directed against the c-myc tag (Santa Cruz Biotechnology, Inc), diluted to 1/1000, and a peroxidase-coupled goat polyclonal antibody directed against mouse IgG, diluted to 1/5000 (ref 55556, ICN), in the presence of ABTS (diammonium salt of 2,2′-azinobis(3-ethylbenzthiazoline sulfonate)(Roche). 
       FIG. 3A  gives the results obtained with sdAb Nef5 and sdAb Nef19. In all the titration curves, a decrease in the measurement of the interaction between the sdAbs and the biotinylated Nef W10 protein; bound in streptavidin-coated wells of a microplate, is observed when the amount of sdAb decreases. Since sdAb Nef5 has a lower affinity than sdAb Nef19, an amplification of the signal ( FIG. 3B ) was obtained by preincubating sdAb Nef5 with the mAb 9E10 for 1 h at 25° C. before depositing in the wells of the microplate. As a control, the mAb 9E10 was used in the absence of sdAb. 
     As for the sdAb-phages, competition ELISAs were carried out. For this, a constant amount of sdAb (5 μg/ml) was preincubated with various amounts of nonbiotinylated Nef W10 protein for 16 h at 4° C. The ELISAs are then carried out as described previously.  FIG. 3C  shows that the binding of sdAb Nef19 to the biotinylated Nef W10 decreases when the amount of nonbiotinylated Nef W10 protein in the assay is increased. This decrease proves the specificity of the interaction of sdAb Nef19 for the Nef W10 protein. Equivalent results are obtained with the other sdAbs. 
     j—Cloning of sdAb Nef19 into the Plasmid pET14bNefW10 
     10 μl of the pET14bNefW10 vector and 5 μl of the pHen-sdAb Nef19 vector are cleaved with 10 U of NcoI and NotI for 16 h at 37° C. The fragments are purified on 1% agarose (Qiagen gel extraction kit, final volume 50 μl for the pET14bNefW10 vector and 20 μl for the fragment corresponding to the sequence of sdAb Nef19). 
     The ligation is carried out with 10 μl of fragment and 1 μl of vector in a final volume of 15 μl in the presence of 3 Weiss units of T4 DNA ligase (Biolabs) for 2 h at ambient temperature. 
     Competent (CaCl 2  technique) BL21(DE3) bacteria are transformed with 7.5 μl of the ligation product. The plasmid pET-sdAb Nef19 (SEQ ID No. 28), the sequence of which is indicated in the appendix, is obtained. 
     h—Affinity Constants of The Anti-Nef Antibody Using Biacore 
     BIACORE uses the principle of surface plasmon resonance (SPR) to follow, in real time, the interactions between molecules without labeling said molecules. One of the interaction partners is covalently immobilized on a biosensor, while the other is injected in a continuous stream. The principle of detection by SPR makes it possible to follow the changes in mass at the surface of the biosensor, due to the formation and then the dissociation of molecular complexes. The response, quantified in resonance units (RU), is a direct indication of the degree of binding of the analyte by the measurement of the variation in refractive index. The recording of the signal (a sensorgram) is processed mathematically so as to obtain the association rate constant ka and the dissociation rate constant kd and the equilibrium association constant KA (KA=ka/kd) and the equilibrium dissociation constant KD (KD=kd/ka). 
     The interactions between Nef W10 and sdAb Nef19 produced either from the periplasm (sdAb Nef19P) or from the cytoplasm (sdAb Nef19C) of bacteria were studied on a BIACORE 3000 equipped with a CM5 biosensor on which 1089 RU of Nef W10 were covalently immobilized according to the standard amine-coupling procedure proposed by BIACORE (activation with NHS/EDC). sdAb Nef19P or sdAb Nef19C (in buffer: 10 mM HEPES; 150 mM NaCl; 3 mM EDTA; 0.005% surfactant P20) is then injected. In parallel, the injections are carried out on a control channel which has undergone the same chemical coupling, but without injection of protein. The affinity constants for sdAb Nef19P and sdAb Nef19C, of SEQ ID Nos. 1 and 7, are indicated in  FIG. 4  (it should be noted that sdAb Nef19P and sdAb Nef19C have the same amino acid sequences). 
     k—Construction of The Plasmid Allowing Intracellular Expression of the sdAB Nef19 in Eukaryotic Cells and Study of the Cellular Distribution of sdAb Nef19 
     k1—Obtaining of the Plasmid pcDNA-sdAb Nef19 
     Oligonucleotides Used: 
     
       
         
               
               
             
           
               
                   
                 SEQ ID No. 57: 
               
               
                   
                 ANefEcoK5p 
               
               
                   
                 5′GAATTCCACCATGGCCGAGGTGCAGCTGGTG3′ 
               
               
                   
                   
               
               
                   
                 SEQ ID No. 58: 
               
               
                   
                 ANefXho3p 
               
               
                   
                 5′CTCGAGCTAGCTCCCATGGTGATGGTG 
               
             
          
         
       
     
     The sequence encoding sdAb Nef19, truncated by removal of its signal peptide but tagged at its C-terminal end with the c-myc and 6His epitopes, was amplified by PCR from the pHEN-sdAb Nef19 vector using the 2 nucleotide primers ANefEcoK5p and ANefXho3p. 
     PCR Conditions: 
     One μl of pHen-sdAb Nef19 at 50 ng/μl, 10 μl of 10× Dynazyme buffer (Biolabs), 2 μl of dNTP mix at 100 nM, 2 μl of 5′ oligonucleotide at 10 pmol/μl, 2 μl of 3′ oligonucleotide at 10 pmol/μl (pairs of primers used: ANefEcoK5p and ANefXho3p), 0.7 μl of Dynazyme Taq polymerase (Biolabs), 82 μl of H 2 O. 
     PCR program used: 95° C., 3 min; 95° C., 45 s; 50° C., 45 s; 72° C., 45 s; 72° C., 3 min; 30 cycles. The size of the PCR fragment is verified on a 1% agarose gel, and the fragments are then purified using the “Qiaquick gel extraction” kit (Qiagen). 
     Cloning: 
     Twenty μl of the purified PCR product are cleaved, in a volume of 100 μl, with 10 U of EcRI restriction enzyme and 10 U of XhoI restriction enzyme in the presence of BSA, at 37° C., for 12 h. The enzymes are then denatured at 65° C. for 20 min. 
     The pcDNA3.1+ vector (Invitrogen) was used for the expression of sdAb Nef19 in mammalian cells. 2.5 μg of pcDNA3.1+ are cleaved, in a volume of 100 μl, with 10 units of EcoRI restriction enzyme and 10 units of XhoI restriction enzyme in the presence of BSA, at 37° C., for 12 h. The enzymes are then denatured at 65° C. for 20 min. 
     The digestion products are analyzed on a 0.7% agarose gel in order to verify the digestion. 
     The PCR product and the pHen-sdAb Nef19 that have been cleaved with EcoRI and HindIII are purified on a 0.7% gel using the “Qiaquick gel extraction” kit (Qiagen). 
     The ligation is carried out with 5 μl of PCR fragment, 0.5 μl of the vector and 3 Weiss units of T4 DNA ligase (Biolabs) in a final volume of 10 μl, for 2 h at ambient temperature. 
     Competent TG1 bacteria are transformed with 10 μl of ligation product. A preparation of the plasmid was then carried out using an isolated colony and sequencing was carried out. The resulting plasmid, called pcDNA-sdAb Nef19, allows the production of sdAb Nef19 in eukaryotic cells transfected with this plasmid. The sequence of pcDNA-sdAb Nef19 is given in the appendix (SEQ ID No. 30).
         k2—Colocalization of sdAb Nef19 with the Nef Protein at the Level of Cytoplasmic Membrane Structures       

     The intracellular distribution of sdAb Nef19 was analyzed by indirect immunofluorescence on HeLa cells transiently expressing the Nef-GFP fusion protein or the GFP control protein, the expression vectors of which have been previously described (Burtey et al., 2007). The cells (4×10 5 ) were transfected by the lipofection technique with Lipofectamine 2000 (Invitrogen) according to the procedure recommended by the manufacturer. 
     24 h after transfection, the cells were fixed for 20 min at 4° C. with a solution of PBS/4% paraformaldehyde (PFA), and then permeabilized with a solution of PBS/0.1% Triton X100 for 10 min. The sdAb was then detected using an antibody (Ab) directed against the c-myc epitope (9E10, Roche) in PBS/0.1% BSA, and then an anti-mouse IgG second Ab coupled to Alexa594 (Jackson Laboratories). The localization of the sdAb was compared with that of Nef-GFP by fluorescence microscopy using a Leica DMB microscope, and the images were edited using the Adobe Photoshop software. 
     The results are illustrated in  FIG. 5 . While the sdAb is distributed diffusely between the cytoplasm and the nucleus (part A, central panel) in the cells expressing the GFP control protein (left panel), it becomes redistributed towards cytoplasmic membrane structures located in the perinuclear region where it colocalizes perfectly with the Nef-GFP protein (part B). 
     l—Study of the Effect of sdAb Nef19 on the Functional Properties of Nef 
     l1—Inhibition of the Effect of Nef on the Level of CD4 Expression at the Cell Surface 
     In order to explore the potential effects of sdAb Nef19 on the functional properties of Nef, its ability to modulate the expression of the CD4 receptor at the surface of CD4+ T lymphocytes was firstly analyzed in cells expressing the sdAb. Human T lymphoid cells of the HPB-ALL line (10 7 ), constitutively expressing the CD4 receptor, were cotransfected by electroporation (Burtey et al., 2007) with 10, 20 or 30 μg of the vector for expression of sdAb Nef19 (pcDNA-sdAb Nef19) and 5 μg of the vector for expression of the Nef-GFP fusion or of the GFP control protein. 24 h after transfection, the level of CD4 expression at the cell surface was analyzed on the cells expressing Nef-GFP or GFP by flow cytometry using a Cytomics FC500 instrument after labeling for 1 h at 4° C. with an anti-CD4 Ab directly coupled to phycoerythrin-CY5 (RPA-4, Beckton-Dickinson), and then fixing of the cells with a 3.7% formaldehyde solution. 
     The results are illustrated in  FIG. 6A . While a representative experiment is shown on the top panel, the bottom panel corresponds to the average of the results obtained from 3 independent experiments. In the absence of sdAb Nef19, Nef leads to a decrease of approximately 70% in the level of CD4 expression at the cell surface. The expression of increasing amounts of sdAb results in a dose-dependent reversion of this effect (black bars), since the level of CD4 present at the surface of the cells expressing Nef and transfected with 30 μg of the vector for expression of sdAb Nef19 is virtually comparable to that measured in the absence of Nef. The expression of the sdAb does not induce a nonspecific effect, since said expression, even at the highest dose, does not modify the level of CD4 present at the surface of the cells expressing the GFP control protein (white bars). 
     This inhibitory effect of sdAb Nef19 is also observed on nonlymphoid cells stably expressing the CD4 receptor. HeLa cells stably expressing CD4 (HeLa-CD4) were cotransfected as previously using the lipofection technique, with 1, 2 or 3 μg of the vector for expression of sdAb Nef19 and 1 μg of the vector expression of Nef-GFP or of the GFP control (Coleman et al., 2006). The level of CD4 surface expression was analyzed as previously by flow cytometry on the cells expressing Nef-GFP or GFP. 
     The results corresponding to the averages of 3 independent experiments are reported on  FIG. 6B . They show that sdAb Nef19 is capable of inhibiting to a large extent the effect of the Nef-GFP fusion on the level of CD4 surface expression (black bars). 
     l2—Study of the Inhibition by sdAb Nef19 of the Ability of Nef to Interact Directly with the Cellular Machinery of the Endocytosis Pathway 
     The use, by several teams, of a CD8-Nef fusion protein in which the extracellular and membrane regions of CD8 are fused to the N-terminal end of Nef (CD8-Nef) has made it possible to show that the sequence of Nef contains determinants which allow it to interact directly with the machinery for vesicular transport of proteins in the endocytosis pathway. The CD8-Nef membrane chimera has, like the myristoylated native Nef protein, the property of modulating in trans the surface expression of the CD4 receptor, but also of modulating in cis its own level of expression at the cell surface, thus reflecting its ability to connect directly to the cellular machinery of the endocytosis pathway. 
     The inhibitory effect of sdAb Nef19 on the level of surface expression of the CD8-Nef chimera was therefore explored, by flow cytometry and by immunofluorescence, on HeLa cells. 
     For the cytometry analysis, the cells are cotransfected by lipofection with 1, 2 or 3 μg of the vector for expression of sdAb Nef19, 0.7 μg of the vector for expression of CD8-Nef or of the CD8-Stop control corresponding to the CD8 receptor devoid of cytoplasmic domain, and 0.3 μg of the vector for expression of GFP. 
     24 h after transfection, the cells are fixed for 20 min with a solution of PBS-4% PFA, and the level of expression of the CD8-Nef chimera at the surface of the cells expressing GFP was evaluated using an anti-CD8 Ab (SK1, Becton-Dickinson) coupled to phycoerythrin-Cy5. 
     For the immunofluorescence analysis, the cells were transfected with 1 μg of the vector for expression of CD8-Nef or CD8-Stop and 1 μg of the vector for expression of the sdAb. 24 h after transfection, the cells are fixed for 20 min with a solution of PBS-4% PFA and permeabilized with a solution of PBS-0.1% Triton X100. The sdAb was detected as previously (see  FIG. 5 ), whereas the CD8-Nef fusion is detected with an anti-CD8 Ab coupled to FITC (SFCI, Coulter). 
     The results of these experiments are illustrated in  FIG. 7 . Part A corresponds to the results of the analysis by cytometry; the top panel represents a representative experiment while the bottom panel corresponds to the averages of 3 independent experiments. In the absence of sdAb Nef19, the level of expression of the CD8-Nef chimera is approximately five times lower than that of the control CD8-Stop protein (white bars). The expression of increasing amounts of the sdAb results in a gradual accumulation of the CD8-Nef protein at the cell surface (black bars). The expression of the sdAb has no effect on the level of expression of the CD8-Stop control (white bars). 
     The data from the immunofluorescence experiments reported on the top panels of  FIG. 7B  confirm these results, since a clear increase in labeling of the CD8-Nef protein at the plasma membrane is observed in the cells coexpressing sdAb Nef19 (indicated by arrows), whereas this labeling is almost exclusively concentrated in a perinuclear membrane compartment in the absence of the sdAb (cell indicated by an arrow head). As in  FIG. 5 , sdAb Nef19 is distributed diffusely between the cytoplasm and the nucleus in the control cells expressing the CD8-Stop protein (bottom panels), whereas it relocalizes to the intracellular membrane structures and at the plasma membrane that are also labeled with the anti-CD8 Ab in the cells expressing the CD8-Nef fusion (top panels). 
     The results of  FIG. 7  confirm the recognition of Nef by sdAb Nef19 in the cell context; they also confirm the inhibitory effects of the sdAb on the interactions of Nef with the cellular machinery of the endocytosis pathway. 
     l3—Interaction of sdAb Nef19 with the Nef Protein in the Cell Context 
     The direct recognition of Nef by sdAb Nef19 was explored at the cell level by means of coimmuno-precipitation experiments. 293T cells (3×10 6 ) were cotransfected, by means of the calcium phosphate precipitation technique, with 5 μg of the vector for expression of the sdAb in combination with 5 μg of a vector for expression of the CD8-wild-type Nef fusion (CD8-Nef WT), or point mutants (CD8-NefLL164-165AA and CD8-NefE62-65A) or deletion mutants of Nef (CD8-Nef 1-61 and CD8-Nef 58-189). These constructs have been previously described (Janvier et al., 2003a,b; Madrid et al., 2005). The same type of experiment was also carried out on cells coexpressing the sdAb and the CD8 protein devoid of cytoplasmic domain (CD8-Stop) used as a control. 24 h after transfection, the cells were lyzed in a buffer containing 100 mM of (NH 4 ) 2 SO 4 , 20 mM of Tris (pH 7.5), 10% of glycerol, 1% of IGEPAL and a cocktail of protease inhibitors (Roche). The cell lyzate (600 μg of total proteins) was incubated for 1 h at 4° C. with 3 μg of the anti-CD8 Ab (32M4, Santa Cruz) and 30 μl of beads coated with protein A-sepharose. The immunoprecipitates were then analyzed by immunoblotting using an anti-CD8 Ab (H160, Santa Cruz) and an anti-c-myc Ab (9E10). 
     The results are illustrated in  FIG. 8 . As expected (left-hand panels), the band corresponding to sdAb Nef19 is specifically detected in the material immunoprecipitated from the cells expressing the CD8-Nef fusion protein, whereas it is not detected in the material immunoprecipitated from the cells expressing the control CD8-Stop protein. The analysis of the material immunoprecipitated from the cells expressing the mutated fusion proteins indicates that the sdAb is still capable of associating with the point mutants CD8-NefLL164-165AA and CD8-NefE62-65A, whereas the deletion mutants, CD8-Nef 1-61 and CD8-Nef 58-189, are not recognized by the sdAb. Since the immunogen used to generate sdAb Nef19 corresponded to a recombinant protein lacking the first 57 amino acids, the results of  FIG. 8  suggest that the zone recognized by the sdAb is located at the C-terminal end of Nef, on a region between residues 190 and 206 of the protein. 
     l4—Inhibition, by sdAb Nef19, of the Positive Effects of Nef on the Infectious Capacity of HIV 
     The inhibitory activity of sdAb Nef19 on the contribution of Nef to the infectious properties of the viral particles was analyzed in an experimental system for evaluating the infectious capacity of HIV-1 during a single replication cycle (Madrid et al., 2005). Recombinant viral particles carrying the GFP reporter gene were produced by cotransfection of 293T cells as previously described (Basmaciogullari et al., 2006) with 8 μg of the vector for expression of the proteins derived from the gag and pol genes of HIV-1 (NL43 isolate) (Owens et al., 2003), 8 μg of the vector for expression of the GFP transgene, 2 μg of the vector for expression of the envelope of HIV-1 (89.6 isolate) or of VSV (VSV-G), 1 μg of the vector for expression of the Nef protein tagged at its C-terminal end with the HA epitope (Dorfman et al., 2002), and 8 μg of the vector for expression of the sdAb. The viral particles pseudotyped with the HIV-1 envelope or the VSV envelope were recovered in the culture supernatant 48 h after transfection and stored at −80° C. The virus stocks were titered by measuring reverse transcriptase (RT) activity, and then used to infect HeLa-CD4 cells or T cells of the HPB-ALL line. 3×10 4  HeLa-CD4 cells were infected in 24-well plates with 500 it of a dilution of 5×10 5  and 5×10 4  arbitrary units of RT/ml, of the virus stocks pseudotyped, respectively, with the HIV-1 or VSV envelope. In the case of the HPB-ALL line, 10 5  cells were infected with 1 ml of a dilution to 17×10 4  and 17×10 3  arbitrary units of RT/ml, of the virus stocks pseudotyped, respectively, with the HIV-1 or VSV envelope. 60 h after infection, the cells were recovered and fixed in a solution of PBS-3.7% formaldehyde, and then the percentage of cells infected, and therefore expressing GFP, is evaluated by flow cytometry. 
     The results corresponding to the averages of 3 independent experiments are reported in  FIG. 9 . The top panel (A) corresponds to the infectious capacity of the viral particles, measured on HeLa-CD4 cells, and the bottom panel (B) corresponds to the infectious capacity measured on HPB-ALL T cells. The results are reported as a function of the infectious capacity of the viral particles pseudotyped with the HIV-1 envelope (blue bars) or the VSV envelope (maroon bars) and produced in the absence of Nef. As expected, Nef expression in the producer cells results in a clear increase in the infectious capacity of the viral particles expressing the HIV-1 envelope (14 times and 3 times, respectively, in the HeLa-CD4 and HPB-ALL cells), whereas the viruses expressing the VSV envelope are not influenced by the expression of Nef. The expression of sdAb Nef19 causes a significant and specific inhibition, of the order of 75%, of the effect of Nef on the infectious capacity of the viral particles, independently of the cell type used. Conversely, the expression of the sdAb does not influence the infectious capacity of the viral particles expressing the VSV G protein, whether the particles are produced in the absence or in the presence of Nef. 
     l5—Incorporation of sdAb Nef19 into the Viral Particles 
     Since several studies had shown that the Nef protein of HIV-1 was incorporated into the viral particles budding at the surface of the infected cells, the influence of the expression of sdAb Nef19 in the producer cells, on the incorporation of Nef into the viral particles, was therefore explored. The viral particles were produced as previously (see  FIG. 9 ) in 293T cells cotransfected with 1 or 4 μg of the vector for expression of sdAb Nef19. The culture supernatants were subjected to ultracentrifugation at 27 000 rpm for 1 h 30 at 4° C. on a PBS/sucrose cushion. The viral particles thus purified were then taken up in Laemli buffer and analyzed by immunoblotting using anti-HA (3F10, Roche), anti-c-myc (9E10, Roche) and anti-p24 (obtained from the “NIH AIDS Research and Reference Reagent Program”) antibodies; the lysates of the producer cells were also analyzed by immunoblotting. 
     The results are illustrated in  FIG. 10A . The left-hand panels correspond to the analysis of the cell lysates, whereas the right-hand panels correspond to the analysis of the purified viruses. In the absence of sdAb Nef19, the Nef-HA protein is correctly incorporated into the viral particles, as indicated by the detection of the 2 bands revealed with the anti-HA Ab (top panel), corresponding to the whole protein of 27 kDa and to the cleavage product of approximately 25 kDa (Chen et al., 1998; Welker et al., 1998). The incorporation of Nef does not appear to be disrupted by the expression of the sdAb, but the latter is also incorporated only when the viral particles have been produced from cells expressing Nef. These results show that the sdAb is specifically recruited into the infectious viral particles, probably by direct interaction with the Nef protein established in the producer cell. This recruitment of the sdAb could be responsible for its inhibitory effect on the infectious capacities of the viral particles produced. 
     In order to confirm that the incorporation of sdAb Nef19 into the viral particles is indeed the result of association with the Nef protein in the producer cells, the ability of the sdAb to interact with the Nef-HA protein was explored as previously by coimmunoprecipitation from 293T cells cotransfected with the vectors for, respectively, the expression of the sdAb and of Nef-HA. 600 μg of proteins derived from the soluble fraction of the cell lysates were incubated for 1 h at 4° C. with 3 μg of the anti-HA Ab (3F10) and 30 μl of beads coated with protein A-sepharose. The immunoprecipitated material was then analyzed by immunoblotting using an Ab specifically directed against the Nef protein (Ab a56 obtained from the “NIH AIDS Research and Reference Reagent Program”) and the anti-c-myc Ab (9E10). 
     As shown by the results reported in part B of  FIG. 10 , the sdAb is detected only in the immunoprecipitate of the cells expressing Nef-HA, but is not detected in the material precipitated from the cells transfected with the Nef-Stop control vector (left-hand panels) enabling the expression of a polypeptide corresponding to the first 46 residues of the Nef protein, even though the sdAb is clearly expressed in these cells (right-hand panels). 
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