FR2862313A1 - New nucleic acid construct encoding immunogenic proteins of Leishmania, useful for preparation of vaccines and antibodies, e.g. for diagnosis - Google Patents

Abstract

Nucleic acid construct (A) containing isolated nucleic acids (I) that encode an immunogenic protein (II) of the promastigote or amastigote forms of Leishmania, is new. (I) is any of 5 sequences reproduced (of 2526; 1401; 1684; 1404 and 1501 bp), all from L. amazonensis. Independent claims are also included for: (1) genetically modified strains (B) of Leishmania, as promastigotes or amastigotes, transfected with (A); and (2) transfecting Leishmania with (A). ACTIVITY : Protozoacide. No biological data given. MECHANISM OF ACTION : Vaccine.

Description

New ways to prevent leishmaniasis

  The invention relates to new means for the prevention of leishmaniases in animals and humans.

  In particular, it relates to nucleic acid molecules encoding virulence or pathogenicity factors in Leishmania and their use for producing such factors to develop vaccine compositions against leishmaniases.

  Leishmaniasis is one of the six major parasitic diseases and, as such, is considered a priority by the World Health Organization (WHO). Leishmanias exist in the extracellular promastigote form, inside the digestive tract of the insect vector (the phlebotomine), and in the intracellular amastigote form, in the mammalian host. Several molecules, including lypophosphoglycan (LPG) or a metalloprotease called gp63, seem to play an important role in the parasite's infectivity and pathogenicity. More recently, a family of glycoproteins called promastigote surface antigens, PSA (for "Promastigote Surface Antigens"), has attracted new interest. These PSA are characterized by the presence of leucine-rich repeating units that can intervene in protein / protein interactions and confer a Th1-type cell-mediated protective immunity in mice. In organisms, such as bacteria or plants, it has been found that PSAs are involved in functions such as cell adhesion, pathogen resistance, and signal transduction.

  However, no biological role has been described or suggested in Leishmania.

  This role could be studied by the inventors thanks to the technique that they hold to cultivate promastigotes and amastigotes of Leishmania under asteric and axenic conditions, with a totally defined medium, ie whose constituents are all identified. , and which is the subject of the patent FR 93 05 779 of May 13, 1993 in the name of the IRD (eg ORSTOM). The control of this process allows them to have parasitic forms devoid of contaminants previously provided by the culture media, and antigenic determinants in a highly purified form.

  In said FR patent of the Applicant, the isolation and identification of an excreted / secreted PSA (abbreviated excretion / secretion antigen or AES) of 38 kDa and 45 kDa in the culture supernatant has already been described. of L. amazoniensis. The inventors have now isolated and cloned the cDNA encoding this protein and evaluated its role in parasite biology by developing an additional transgenesis strategy. This work has made it possible to demonstrate the involvement of this PSA as a virulence and / or pathogenicity factor and to develop constructs for overexpressing the Leishmania gene encoding this PSA, which makes it possible to develop for obtaining vaccine compositions against leishmaniasis.

  The object of the invention is therefore to provide nucleic acid sequences capable of encoding PSAs of promastigote forms and amastigote forms of Leishmania, constituting virulence and / or pathogenicity factors.

  It is particularly intended to provide vectors for overexpression of these PSA, as well as genetically modified parasites.

  The invention furthermore relates to the supernatants of the culture media of the PSAs obtained, as well as the isolated, purified PSAs, and the use of their properties to develop vaccine compositions against leishmaniasis.

  The nucleic acid sequences of the invention correspond to isolated nucleic acids capable of encoding a PSA of promastigote forms or amastigote forms of Leishmania, said nucleic acids responding to one of the sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4 and SEQ ID No. 5.

  The nucleic acid sequences of the invention are more especially sequences of cDNA clones belonging to a family corresponding to the characteristics illustrated in FIG. 2 and comprising in particular a SalI restriction site and two HindIII restriction sites, with a stop codon located downstream of the first HindIII site.

  In particular, the invention relates to the cDNA clones of said family having an EcoRV and / or PstI restriction site between the two SalI and HindIII sites, or on either side of the SalI site.

  The invention also relates to isolated immunogenic proteins, characterized in that they have a sequence as encoded by the nucleic acids defined above.

  These proteins belong to the so-called promastigote surface antigen (abbreviated PSA) family and have characteristic regions shown in Figures 3A and 3B. These proteins can be post-translationally modified by N-glycosylations, phosphorylations and the anchoring of a GPI. They have a hydrophobic signal peptide in the carboxy-terminal position.

  By directional cloning of the sequences defined above in an expression vector, the inventors have obtained constructions enabling them to be expressed in the sense position.

  The invention therefore relates to nucleic acid constructs, characterized in that they comprise nucleic acids isolated in the sense position, capable of encoding an immunogenic protein of promastigote forms or of Leishmania amastigote forms corresponding to one of the sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4 and SEQ ID No. 5.

  The invention relates in particular to nucleic acid constructs comprising sequences of cDNA clones belonging to a family corresponding to the characteristics illustrated in FIG. 2 and comprising in particular a SalI restriction site and two HindIII restriction sites, with a codon stop located downstream of the first HindIII site.

  The cDNA clones containing an EcoRV and / or PstI restriction site between the two SalI and HindIII sites, or on either side of the SalI site, are particularly preferred. Particularly advantageous constructs comprise, as nucleic acid sequences, a sequence chosen from SEQ ID No. 1 to SEQ ID No. 5. Preferred constructions comprise said nucleic acid sequences in a fast-multiplication plasmid such as pTex.

  It also relates to Leishmania strains transfected by such constructs, whether they be promastigote forms, or amastigote forms.

  Preferred transfected strains, given the targeted vaccine applications, are L.infantum strains.

  Advantageously, the PSAs are produced in large quantities, constitutively, in the parasites.

  The invention also relates to a method for transfection of a Leishmania parasite, characterized in that a vector as defined above, comprising a marker, is introduced into the Leishmania parasite, the transfected parasites are selected by means of said marker, It is cultured in a totally defined axenic and aseric medium and the culture supernatant is recovered which contains the immunogenic proteins present in concentrations of the order of 10 to 20 times greater than that produced by the Leishmania mother strain.

  The introduction of the vector into the parasite is, for example, carried out by electroporation.

  The insertion of these nucleic acids into the parasites makes it possible to increase the infectivity of these parasites: their capacity to survive in the infected macrophage and to multiply therein is greater than 5 times that of the parasite not transfected by such nucleic acids.

  Said PSA are produced in large quantities in the supernatant of the parasite culture medium. The invention thus also relates to the supernatants of the culture media of said genetically modified parasites, as well as the PSA isolated from these supernatants and purified.

  The invention thus provides means of great interest in responding to the industrial demand for large quantities of virulence / pathogenicity-determining proteins in Leishmania.

  Thanks to their immunogenic capacity, these proteins make it possible to obtain, after immunization of animals according to conventional techniques, polyclonal antibodies and to develop monoclonal antibodies. The immunization of mice thus made it possible to obtain anti-Ig G2A antibodies and that of dogs IgG2 antibodies.

  The invention therefore also aims at such antibodies and makes use of their properties to develop, on an industrially exportable scale, vaccine compositions against leishmanias in humans or animals.

  The diagnostic applications of these antibodies are also part of the invention.

  Other characteristics and advantages of the invention will be given in the examples which follow, in which reference will be made to FIGS. 1 to 6, which represent, respectively: FIG. 1, the 3 'alignment of the nucleotide sequences of clones cDNA according to the invention; FIG. 2, a summary diagram of the nucleotide sequences of the cDNA clones obtained after immunological screening by an anti-AES monoclonal antibody of the expression libraries of the promastigote forms and the amastigote forms of L. amazonensis. Restriction enzyme sites are indicated above each sequence; FIG. 3A, the localization of different protein regions, characterized by their particular amino acid composition, present on the protein sequence deduced from the cDNA of the A3B clone, and FIG. 3B a schematic representation of the protein sequence deduced from the A3B clone cDNA encoding PSA; FIG. 4, analyzes of transcripts by RT-PCR in the promastigote (P) and amastigote (A) forms; FIG. 5, the level of production of the protein by western blotting, using an anti-PSA antibody, and FIG. 6 the effect of the overexpression of a PSA of L. amazonensis on the infectivity of the parasites.

  1 - Molecular characterization of the major immunogens of the AES of the promastigote and amastigote forms of L. amazonensis. This characterization was performed by screening cDNA expression libraries of promastigote forms and amastigote forms of L. amazonensis using a monoclonal antibody directed against the major immunogen of AES.

  Characteristics of the cDNA libraries: Two expression libraries of cDNA, respectively promastigote forms, and amastigote forms of L. amazonensis were produced. The characteristics of these libraries are presented in Table I. The exponential phase and stationary parasites were mixed in order to have access to the different transcripts that can be expressed during the various stages of their in vitro culture. 5 × 10 4 phages per library were then immunologically screened with monoclonal antibody F5 diluted 1: 500. Obtaining this antibody is the subject of the example in the FR patent mentioned above.

Table I

  Lma cDNA library Promastigotes Amastigotes J4 + J7 harvests J4 + J7 7.8.109 7.8.109 Titration after packaging 350 000 500 000 Title after amplification 8.32.107 ph / ul 2.16.108 ph / ul J4 + J7 = parasites harvested at 4th day, exponential phase, and the 7th day, stationary phase of their growth.

  - Isolation and sequencing of the clones recognized by the monoclonal antibody F5 13 clones of the promastigote library and 11 clones proved to be positive from the amastigote library were found to be positive. All these clones were isolated by secondary and tertiary screening.

  Plasmid DNA from all isolated clones was analyzed after various enzymatic digests and cDNAs with larger inserts by EcoRI / XhoI digestion were retained to remove 5 'truncated cDNAs.

  As shown in Table II, the clones 1A1, 1B1, 2B3, 2C1, 2D1 and 2E1 of the promastigote cDNA library and the A3B, V4A, V5, W2 and W3 clones of the amastigote library display the bigger size.

  The analysis of these clones, by determining the presence or absence of two restriction enzyme sites (HindIII and SalI) previously selected, showed that they had a strong homology of their nucleotide sequence.

  By double HindIII / SalI digestion, three different classes of clones were detected with a HindIII / SalI fragment of less than 400 bp in size (clone 2G1), 500 bp (type 2C1 clones and A3B) or 600 bp (type 1A1 or W2 clones). Thus five types of clones, chosen according to the particular characteristics of their DNA (the size of the insert and the location of certain restriction enzyme sites) are shown in bold in Table II.

Table II

  CDNA library of Lma promastigotes Clones 1A1 1B1 1C1 1D5 1F1 2A2 2B3 2C1 2D1 2E1 2F1 2G1 B3 cDNA A Size of 2.5 2.5 2-2.2 0.5 2 2 (>) 2.5 2, 4 2,4 2,4 2 1,7-2 1,7 inserts EcoRI / XhoI (kb) restriction map Sali OOONNNOOOONON HindIII 1.1 1.1 1.1 / 1.1 1.1 1.1 1, 1 1.1 1.1 1.1 1.1 1.1 HindIII / Saline 600 600 500 NNN 600 500 500 500 N <400 N (bp) Expression of recombinant protein e (kDa) 45/40 / / / / 42 , 5 / / 39? 18 Lma amastigote cDNA Clones A3B V1B V2D V3A V4A V5 W1A W1C W2 W3 W5 cDNA Inserts size 2862313 8 EcoRI / XhoI 2.3 2-2.2 2.2? 2,3 2,3 2 2 2,3 2,2 1,7 (kb) Restriction map Sall OOONOONNOON HindIII 1,1 1,1 1,1 1,1 1,1 1,1 1,1 1,1 1,1 1.1 1.1 1.1 HindIII / SalI 505 500 500 N 500 500 NN 600 500 <N (pb) Expression of recombinant protein (kDa) 42.5 / 36.5 / 36.5 43 / / 45 / / 0 = yes, for present site; N = no, for absent site; / = realized; ? = result not obtained.

  Table II also gives the results relating to the ability of clones to express a recombinant protein. IPTG has been used as an induction agent. The samples were analyzed by SDS-PAGE and immunoblot in the presence of the anti-AES antibody of the promastigote forms and / or amastigote forms, previously absorbed in the presence of E. coli lysate. Equivalent results are obtained. For the clones of interest, the expression of different recombinant proteins ranging from 42.5 kDa of apparent molecular weight (clone 2C1) to 43 kDa (A3B clone) or 45 kDa (1A1 and W2) is noted.

  Sequence results are reported on the "Sequence Listing" document: - of the following three types of clones of the promastigote library: the type 1A1 clone, which expresses a protein of greater molecular weight. Type 1B1 and 2B3 clones are of the same type as this clone; clone 2C1 (SEQ ID No. 2), which expresses a recombinant protein of lower molecular weight than clone 1A1; clone 2G1, which has the particularity of having a small HindIII / SalI fragment; the following two clones of the amastigote library: the A3B type clones, which express a recombinant protein of approximately 43 kDa and have a HindIII / SalI fragment of 500 bp, the clone V5 appearing to be identical. Clones V2D and V4A are considered truncated clones of the same type; . clone W2, which expresses a recombinant protein of 45 kDa and which has a HindIII / SalI fragment of 600 bp.

  Study of the five cDNA sequences The alignment of the five cDNA sequences obtained is shown in FIG. 1 where the differences between these clones are solely due to the presence of a 5 'truncated sequence and / or the insertion of sequences of about 72 nucleotides on the 5 'side. The clones thus have (clones 2C1 and A3B) or three (clones 1A1 and W2) insertions. Apart from these insertion zones, the clones have homologies of the order of 99% and can be considered as belonging to a cDNA family. Only the A3B clone has the initiation ATG codon, the other clones being truncated at 5 '. However, the A3B cDNA does not have the 39 nt sequence coding for the "splice leader" found in 5 'on all Leishmania mRNAs.

  The cDNAs of the A3B and 2C1 clones have almost complete homology and are therefore considered to be identical, the clone 2C1 cDNA corresponding to a 5 'truncated portion of the A3B clone cDNA.

  The A3B clone, representative of this family, has been sequenced in both directions.

  The restriction enzyme sites for each of these clones have been reported in Figure 2.

  The sequences SEQ ID Nos. 1 to 5 correspond respectively to those of the cDNAs of A3B, 2C1, 1A1, 2G1 and W2.

  Analysis of the Different Derived Protein Sequences The translation of the various cDNA sequences into protein sequences was carried out by choosing the reading frame corresponding to that suggested by the position of the initiation codon on the plasmid pB-SK, the transcription is under the control of the lacZ gene promoter subjected to induction by IPTG.

  The A3B protein has the regions shown in Figures 3A and 3B. In NH 2 -terminal, there is identified a hydrophobic, cleavable peptide which is described in the literature as a signal peptide of the secretion pathway. We then meet the repeat domain rich in leucine, the number of 6 repeats for the A3B clone. At a dozen amino acids at the end of this domain is a region rich in proline, threonine and serine, hereinafter referred to as poly P / T / S region. This region is followed by a region rich in cysteines, which may be involved in disulfide bridges. Finally, the protein sequence ends with a hydrophobic signal peptide.

  The cDNAs of the A3B and 2C1 clones have almost complete homology and are therefore considered to be identical, the clone 2C1 cDNA corresponding to a 5 'truncated portion of the A3B clone cDNA.

  Clone A3B, representative of this family, was sequenced in both directions.

  The restriction enzyme sites for each of these nucleotide Nt clones have been reported in Figure 2; ATG = initiation codon; TAG = stop codon.

  Analysis on the PROSITE database shows that the A3B protein has a localized N-glycosylation site at the end of each leucine-rich repeat domain, and 12 potential phosphorylation sites.

  Analysis of the location of this protein on the PSORT server predicts a cytoplasmic location at 92%, indicating that the protein is soluble. This protein is presumably anchored to the surface by a Glycosyl Phosphatidyl Inositol or GPI. The hydrophobic signal peptide can therefore be cleaved and allow GPI to be anchored at the level of asparagine (D).

  The theoretical molecular weight of the A3B clone protein differs by about 2.9 kDa from that of the 1A1 and W2 proteins, consistent with the 2.5 kDa difference observed between the corresponding recombinant proteins. This difference is due to the presence of a variable number of leucine or LRR-rich repeats, each of which also has a particular amino acid composition.

  The apparent and theoretical molecular weights of the four types of PSA of the invention are summarized in the following Table III. Table III Type of PSA PM of the theoretical PM protein (non-PM without truncated recombinant peptide) signal (3.2 kDa) 4 LRR (2G1) / 33.5 kDa 30.3 kDa 6 LRR (A3B) 42.5 kDa 38 , 5 kDa 35.3 kDa 7 LRR (1A1 and W2) 45 kDa 41.4 kDa 38.2 kDa 2 - Obtaining genetically modified parasites: Directional cloning of the LaPSA 38s gene in the pTex expression vector allowed obtain a construct capable of expressing the PSA gene in the sense position.

  The plasmid pTex-LaPSA 38s sense orientation and the empty pTex vector were then electroporated into the wild strain Leishmania infantum Mon 1 Clone 1, and then the parasites were selected by genetycin.

  The study was carried out on wild-type L. infantum parasites (Sau), those transfected with empty pTex (pTex) and those transfected with pTex containing the nucleotide sequence of interest (Sens).

  Molecular characterization: Southern blot analysis of total DNA shows that the sense construct is stable and amplified in the transformed strain. The results are illustrated in Figure 4 which gives transcripts analyzes by RT-PCR in both forms, promastigotes (P) and amastigotes (A). Figure 5 shows the level of production of the protein by western-blotting, using an anti-PSA antibody (Figure 5A: constitutive proteins, Figure 5B: excreted / secreted proteins) Phenotypic characterization of mutants: The comparison of Growth kinetics between Ldi WT, Ldi pTex and Ldi Sens 25 show that overexpression of LaPSA 38s does not interfere with the growth of parasite 2862313. Only a longer lag phase is observed for the transformed strains compared to the wild-type strain.

  The sensitivity to lysis by the human complement has also been studied. Recently, it has been shown that L. amazoniensis PSA has the property of inhibiting the complement action in vitro. Promasigotes "sense" are more sensitive to complement. The excess of PSA on the surface of the parasites can thus lead to a cleavage as well as a greater formation of complexes generating an increased lysis.

  Study of infectivity of parasites.

  To study the effect of overexpression of LaPSA 38s on the infectivity of parasites, the first approach was to put promastigotes of transformed strains into contact with dog macrophages, which is the natural home reservoir of visceral leishmaniasis.

  FIGS. 6A and 6B give the results obtained, respectively, 2 h after contact with the promastigotes and 48 h after contact with the amastigotes in these figures, the parasite index corresponds to the% of macrophages infected with the strain S x the number of parasites by macrophage /% of macrophages infected with the control strain (pTex) x the number of parasites per macrophage.

  Promastigotes overexpressing LaPSA 38s, have a double infectivity of canine macrophages. In addition, after phagocytosis, the amastigotes expressing the transgene have a capacity to survive and multiply in the parasitophorous vacuole significantly higher (2.5 to 5 times) than that of the control transfected with the empty vector.

2862313 13

Claims (7)

  1. Nucleic acid constructs, characterized in that they comprise nucleic acids isolated in the sense position, capable of encoding an immunogenic protein of promastigote forms or of Leishmania amastigote forms, said nucleic acids responding to one of the sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4 and SEQ ID No. 5.   2. Constructs according to claim 1, characterized in that the nucleic acid sequences are sequences of cDNA clones comprising in particular a SalI restriction site and two HindIII restriction sites, with a stop codon located downstream of the first one. Hindlll site.   3. Constructs according to claim 2, characterized in that said nucleic acid sequences comprise an EcoRV and / or PstI restriction site between the two SalI and HindIII sites, or on either side of the SalI site.   4. Constructs according to any one of claims 1 to 3, characterized in that said nucleic acid sequences are cloned in the sense position in a plasmid, such as pTex.   5. Leishmania strains genetically modified, characterized in that they correspond to amastigote forms or promastigotes of Leishmania transfected with a construct according to any one of claims 1 to 4.   6. Strains according to claim 5, characterized in that they are strains of L.infantum.   7. A method of transfection of a Leishmania parasite, characterized in that a construct according to any one of claims 1 to 4, comprising a marker, is introduced into the Leishmania parasite, the parasites transfected with the said marker are selected, they are cultured in a totally defined axenic and aseric medium and the culture supernatant is recovered which contains the immunogenic proteins present in concentrations of the order of 10 to 20 times greater than that produced by the mother strain of Leishmania .