The present invention concerns antibodies and antigen-binding fragments of antibodies which specifically bind to and neutralize Chikungunya virus (CHIKV) and which are engineered to develop prophylactic and therapeutic solutions for preventing and treating CHIKV disease. The invention also relates to pharmaceutical compositions comprising CHIKV neutralizing antibodies and the use of the antibodies for the prevention and treatment of CHIKV disease.
CHIKV is a reemerging mosquito-borne pathogen. CHIKV is endemic in Africa, India and Southeast Asia but also occurs in unpredictable and large outbreaks with high attack rates beyond these regions, infecting millions of people (Powers AM, Logue CH, 2007, J. Gen. Virol. 88:2363-2377). A mutation in the CHIKV envelope glycoprotein 1 (E1 ) enabled viral transmission through Aedes albopictus mosquitoes, in addition to Aedes aegypti mosquitoes and resulted in 2005 in widespread and severe epidemics in La Reunion, India and Indonesia, with subsequent traveler-initiated outbreaks occurring in Italy, France and China (Tsetsarkin KA et al 2007, PLoS Pathog. 3:e201 ; Schuffenecker I et al 2006, PLoS Med. 3:e263; Wu D, Zhang Y et al 2013, Virol. J. 10:174; Rezza G et al 2007, Lancet 370:1840-1846; Burt FJ 2012, Lancet 379:662-671 ). Due to the extended geographic range of Aedes albopictus mosquitoes, the virus is expected to spread to new areas and Europe and the Americas are now at risk of CHIKV outbreaks.

CHIKV is an enveloped positive strand RNA virus of the alphavirus genus of the Togaviridae family. It is a member of the Semliki Forest virus complex and is closely related to Ross River virus and O'nyong'nyong virus (ONNV); because it is transmitted by arthropods, namely mosquitoes, it can also be referred to as an arbovirus (ARthropod-Borne virus).

CHIKV enters cells via receptor-mediated internalization and a low pH-triggered type II membrane fusion event in early endosomes. CHIKV disease is characterized by acute, post-acute and chronic polyarthritis/polyarthralgia phases, the latter of which is usually symmetric and often incapacitating and can last for months or years. Other symptoms, such as fever, rash, myalgia and/or fatigue are also present during the acute phase. Recent epidemic was also associated with atypical and severe clinical forms of CHIKV disease and some fatalities, which appeared to be restricted to the very young and elderly patients with comorbidities.

There are currently no specific prophylactic or therapeutic treatments for CHIKV disease. CHIKV is treated symptomatically, usually with bed rest, fluids and medicines to relieve symptoms of fever and aching such as simple analgesics and/or non-sterodial anti-inflammatory drugs (NSAID). Although vaccine candidate against CHIKV were first proposed 45 years ago, many vaccine candidates tested to date have ever failed to induce protective antibodies or demonstrated significant safety issues.

There is still a need for treatments showing increased therapeutic efficacies against CHIKV, including the use of specific monoclonal antibodies targeting CHIKV. There is a need in the art for CHIKV neutralizing antibodies suitable for prophylactic and therapeutic uses. In particular, such antibodies need to properly neutralize different strains of the CHIK virus with a high target binding affinity, to exhibit appropriate pharmacokinetic parameters, to display appropriate half-life upon administration, and to allow efficient manufacturing at large scale, while retaining their binding to FcyRllla that is associated with effector functions.

SUMMARY OF THE INVENTION

As disclosed in the present invention, inventors of the present application were able to select and to engineer specific CHIKV neutralizing antibodies improved in their exposure-related pharmacokinetics and maintaining their binding to FcyRllla that is associated with effector functions, making them compatible with a development of therapeutics to prevent and treat CHIKV disease and addressing the need in the art for effective therapies against CHIKV.

Antibodies of the invention have a high binding affinity (within the nanomolar range) toward different CHIKV strains. Hence, they display broad and ultrapotent neutralizing activities against different CHIKV strains. Furthermore, antibodies of the present invention have improved binding to human FcRn receptor while retaining FcyRllla binding making them compatible with an increased half-life while maintaining their binding to FcyRllla that is associated with effector functions.

In a first aspect, the present invention relates to an isolated monoclonal antibody that binds to CHIKV and that comprises three Heavy Chain Complementary Determining Regions (CDRHs) and three Light Chain Complementary Determining Regions (CDRLs), wherein:

i. said CDRHs have amino acid sequences of SEQ ID NO: 5, 6 and 7, and said CDRLs have amino acid sequences of SEQ ID NO: 8, GNT and 10, or

ii. said CDRHs have amino acid sequences of SEQ ID NO: 1 1 , 12 and 13, and said CDRLs have amino acid sequences of SEQ ID NO: 14, GTS and 16, or

iii. said CDRHs and CDRLHs have amino acid sequences differing from the sequences of i. or ii. by one or two amino acid substitutions;

and wherein said antibody further comprises a Fc region comprising at least one residue selected from the group consisting of:

iv. an alanine at position 434, or

v. an alanine at positions 307, 380 and 434, respectively, or vi. a glutamine at position 250 and a leucine at position 428, respectively, or

vii. a leucine at position 428 and a serine at position 434, respectively, or

viii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

In one embodiment, the isolated monoclonal antibody binds to CHIKV and comprises three Heavy Chain Complementary Determining Regions (CDRHs) and three Light Chain Complementary Determining Regions (CDRLs), wherein:

i. said CDRHs have amino acid sequences of SEQ ID NO: 5, 6 and 7, and said CDRLs have amino acid sequences of SEQ ID NO: 8, GNT and 10, or ii. said CDRHs have amino acid sequences of SEQ ID NO: 1 1 , 12 and 13, and said CDRLs have amino acid sequences of SEQ ID NO: 14, GTS and 16, or

iii. said CDRHs and CDRLHs have amino acid sequences differing from the sequences of i. or ii. by one or two amino acid substitutions;

and wherein said antibody further comprises a Fc region comprising at least one residue selected from the group consisting of:

iv. an alanine at position 434, or

v. an alanine at positions 307, 380 and 434, respectively, or vi. a glutamine at position 250 and a leucine at position 428, respectively, or

vii. a leucine at position 428 and a serine at position 434, respectively, or

viii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index;

and wherein the antibody has one or more of the following properties:

ix. binds a CHIKV pE2-E1 target with a binding dissociation equilibrium constant (KD) of less than about 10 nM; x. binds human FcRn with a KD of less than about 200 nM; xi. binds human FcyRIII with a KD of less than about 600 nM.

In another embodiment, the monoclonal antibody comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 5, 6 and 7, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions, and said antibody comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 8, GNT and 10, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions.

In another embodiment, the monoclonal antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 5;

- A CDRH2 consisting of sequence SEQ ID NO: 6;

- A CDRH3 consisting of sequence SEQ ID NO: 7;

- A CDRL1 consisting of sequence SEQ ID NO: 8;

A CDRL2 consisting of sequence GNT;

- A CDRL3 consisting of sequence SEQ ID NO: 10.

In a further embodiment, the monoclonal antibody comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 13, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions, and said antibody comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions.

In another embodiment, the monoclonal antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 13;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

In another embodiment, the monoclonal antibody comprises a Fc region that comprises residues selected from the group consisting of:

i. a leucine at position 428 and a serine at position 434, or

ii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

In a further embodiment, the monoclonal antibody comprises a Fc region wherein said Fc region comprises a leucine at position 428 and a serine at position 434 wherein said amino acid positions are given according to the EU index.

In another embodiment, the monoclonal antibody comprises a kappa light chain or lambda light chain.

In another embodiment, the monoclonal antibody has a Fc region that comprises or consists of a sequence having at least 80% identity with SEQ ID NO: 59, 60, 61 , 62 and 63.

In another embodiment, the monoclonal antibody has a variable region of its heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 1 .

In another embodiment, the monoclonal antibody has a variable region of its light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 2.

In another embodiment, the monoclonal antibody has a heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 31 .

In another embodiment, the monoclonal antibody has a light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 20.

In a second aspect, the isolated monoclonal antibody binds to CHIKV, or an antigen-binding fragment thereof, wherein said antibody or antigen-binding fragment thereof comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 33, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and wherein said antibody or antigen-binding fragment thereof further comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and wherein:

i. the amino acid at position 8 of SEQ ID NO: 33 is not M, and/or

ii. the amino acid at position 12 of SEQ ID NO: 33 is not N; and/or

iii. the amino acid at position 13 of SEQ ID NO: 33 is not G.

In one embodiment, the monoclonal antibody or antigen-binding fragment thereof comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 33;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

A CDRL3 consisting of sequence SEQ ID NO: 16, and wherein:

i. the amino acid at position 8 of SEQ ID NO: 33 is not M, and/or

ii. the amino acid at position 12 of SEQ ID NO: 33 is not N; and/or

iii. the amino acid at position 13 of SEQ ID NO: 33 is not G.

In another embodiment, the monoclonal antibody or antigen-binding fragment thereof comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 33, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and said antibody or antigen-binding fragment thereof further comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and wherein:

i. the amino acid at position 8 of SEQ ID NO: 33 is not M, or

ii. the amino acid at position 12 of SEQ ID NO: 33 is not N; or

iii. the amino acid at position 13 of SEQ ID NO: 33 is not G.

In another embodiment, the isolated monoclonal antibody or antigen-binding fragment thereof comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 33, respectively and said antibody or antigen-binding fragment thereof further comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, and wherein:

i. the amino acid at position 8 of SEQ ID NO: 33 is not M, or

ii. the amino acid at position 12 of SEQ ID NO: 33 is not N; or

iii. the amino acid at position 13 of SEQ ID NO: 33 is not G.

In another embodiment, the monoclonal antibody or antigen-binding fragment thereof comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 33, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and said antibody or antigen-binding fragment thereof further comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, or having amino acid sequences differing from those sequences by one or two amino acid substitutions, and wherein:

i. the amino acid at position 8 of SEQ ID NO: 33 is not M, or

ii. the amino acid at position 12 of SEQ ID NO: 33 is not N; or

iii. the amino acid at position 13 of SEQ ID NO: 33 is not G,

and wherein the antibody has one or more of the following properties:

iv. binds a CHIKV pE2-E1 target with a binding dissociation equilibrium constant (KD) of less than about 10 nM;

v. binds human FcRn with a KD of less than about 200 nM;

vi. binds human FcyRIII with a KD of less than about 600 nM.

In another embodiment, the monoclonal antibody comprises an amino acid at position 8 of SEQ ID NO: 33 selected from the group consisting of I, L, V, Q and N.

In another embodiment, the monoclonal antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 34;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

In another embodiment, the monoclonal antibody comprises an amino acid at position 12 of SEQ ID NO: 33 selected from the group consisting of Q, E, S, T and D.

In a further embodiment, the monoclonal antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 35;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

In another embodiment, the monoclonal antibody comprises an amino acid at position 13 of SEQ ID NO: 33 selected from the group consisting of A, S and T.

In a further embodiment, the monoclonal antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 36;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

In another embodiment, the monoclonal antibody has a variable region of its heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 57.

In another embodiment, the monoclonal antibody has a variable region of its light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 4.

In another embodiment, the monoclonal antibody has its heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 47.

In another embodiment, the monoclonal antibody has a light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 38.

In another aspect of this second aspect, the monoclonal antibody further comprises a Fc region that comprises residues selected from the group consisting of:

i. an alanine at position 434, or

ii. an alanine at positions 307, 380 and 434, respectively, or

iii. a glutamine at position 250 and a leucine at position 428, respectively, or

iv. a leucine at position 428 and a serine at position 434, respectively, or v. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

In another embodiment, the monoclonal antibody has a Fc region that comprises residues selected from the group consisting of:

i. a leucine at position 428 and a serine at position 434or

ii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256,

wherein said amino acid positions are given according to the EU index.

In another embodiment, the monoclonal antibody has a Fc region that comprises a leucine at position 428 and a serine at position 434 wherein said amino acid positions are given according to the EU index.

In another embodiment of this aspect of the invention, the monoclonal antibody comprises a kappa light chain or a lambda light chain.

In another embodiment, the monoclonal antibody has a Fc region comprising or consisting of a sequence having at least 80% identity with SEQ ID NO: 59, 60, 61 , 62 and 63.

In another embodiment, the monoclonal antibody has a variable region of its heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 57.

In another embodiment, the monoclonal antibody has a variable region of its light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 4.

In another embodiment, the monoclonal antibody has a heavy chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 53.

In another embodiment, the monoclonal antibody has a light chain that comprises or consists of a sequence having at least 80% identity with sequence ID NO: 38.

In a fourth aspect, the invention relates to the monoclonal antibody for use as a medicament.

In another embodiment, the monoclonal is for use in the treatment of CHIKV-associated arthralgia.

In another embodiment, the monoclonal antibody is for use in the prevention of CHIKV infection.

In a fifth aspect, the invention relates to a pharmaceutical composition that comprises the monoclonal antibody and at least one excipient.

In a sixth aspect, the invention relates to a cell line producing the monoclonal antibody.

In a seventh aspect, is a method of producing the monoclonal antibody, wherein said method comprises the steps of (i) culturing a cell line according to the sixth aspect; (ii) purifying the produced monoclonal antibody; and optionally (iii) formulating said monoclonal antibody into a pharmaceutical composition.

In an eighth aspect, the invention relates to a polynucleotide comprising a sequence encoding an antibody or an antigen-binding fragment thereof as featured herein. In one embodiment, the polynucleotide encodes a polypeptide having at least 80% identity with one of the sequences SEQ ID NO: 18, 21 , 22, 24, 26, 28, 30, 32, 39, 40, 42, 44, 46, 48, 50, 52 and 54. In one embodiment, the polynucleotide is characterized in that it has a sequence having at least 80% identity with one of the sequences SEQ ID NO: 18, 21 , 22, 24, 26, 28, 30, 32, 39, 40, 42, 44, 46, 48, 50, 52 and 54.

In a ninth aspect, the invention relates to a kit comprising at least one antibody as featured herein. In one embodiment, said kit optionally comprises packaging material.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 : Human lgG1 heavy chain amino acid sequence of CH 1 , hinge, CH2 and CH3 regions; part of the hinge and CH2 and CH3 regions constitute the Fc region. Numbering of the amino acid residues is according to the EU index as set forth in Kabat (Kabat et al., Sequences of Proteins of Immunological Interest, 5th, Ed. Public Health Service, National Institutes of Health, Bethesda, Md. (1991 ). Substituted residues of the Fc region featured in the invention are squared.

Figure 2: lgG1 Fc region sequence alignment: SEQ ID NO: 17; SEQ ID NO: 59; SEQ ID NO: 60; SEQ ID NO: 61 ; SEQ ID NO: 62 and SEQ ID NO: 63.

Figure 3: Effect on E2-E1 target binding of mutations within CDRH3 of mAb2 created to eliminate potential deamination and oxydation motifs. Comparative results are shown in duplicate for each mutants.

Figure 4: Effect on FcRn binding of substitutions in Fc regions of mAbl and mAb2 respectively. Comparative results are shown in duplicate on human FcRn for mAbl (figure 4A) and mAb2 (figure 4C) and on mouse FcRn for mAbl (figure 4B) and mAb2 (figure 4D), at pH 6.0.

Figure 5: Effect on E2-E1 target binding of mutations in Fc regions of mAbl and mAb2 respectively. Results are shown in duplicate for E1 -E2 antigen derived from strains LR2006 (figure 5A) and SL15649 (figure 5B), respectively.

Figure 6: Effect on FcyRNIa binding of substitutions in Fc regions of mAbl and mAb2 respectively. Binding results are shown in duplicate on human FcyRNIa high affinity receptor (FcyRlllaV158) for mAbl (figure 6A) and for mAb2 (figure 6B) as well as on human FcyRNIa low affinity receptor (FcyRlllaF158), respectively (figure 6C for mAbl and figure 6D for mAb2).

Figure 7: Neutralization activity of mAbl and mAb7 using Standard Plaque Reduction Assay. MAbl and mAb7 inhibit Chikungunya viruses from all three genotypes i.e. Asian (figure 7A), East-Central and South African (ESCA) (figure 7B) and West African (figure 7C) with ultrapotent activity.

Figure 8: Mab prophylaxis studies in mice. Effect of mAbl and mAb7 given at 25C^g/mouse at 2, 7 or 14 days prior to CHIKV infection on the virus titer at 3 days post-inoculation in the right hind leg of DBA/1 J mice. Viral titer is plotted as 50% cell culture infectious dose (CCID50) per gram of tissue.

Figure 9: Mab post-exposure therapy in mice. Virus titer in the Right Hind Leg at 5 days post-inoculation (dpi) after single intra-peritoneal administration of fixed 25C^g dose of mAbs 2, 7, 1 1 and 14 at 3 dpi (figure 9A). Dose range effect on virus titer in the Right Hind Leg at 5 dpi of mAb7 and mAb14 after single administration of various doses (from 10 to 250μg / mouse) at 3 dpi (figure 9B). Viral titer is plotted as 50% cell culture infectious dose (CCID50) per gram of tissue. Upper dashed line is the average limit of detection for tissue homogenates.

Figure 10: Mab Pharmacokinetics in Non-Human Primate. Comparison of pharmacokinetics for mAbl and mAb7 administered by intravenous (IV) bolus, 2.5 mg/kg into male Cynomolgus Monkey (Macaca Fascicularis).

DETAILED DESCRIPTION OF THE INVENTION

Definitions

An "antibody" may be a natural or conventional antibody in which two heavy chains are linked to each other by disulfide bonds and each heavy chain is linked to a light chain by a disulfide bond. In mammals, antibodies are classified into five main classes or isotypes, IgA, IgD, IgE, IgG and IgM. They are classed according to the heavy chain they contain, alpha, delta, epsilon, gamma or mu, respectively. These differ in the sequence and number of constant domains, hinge structure and the valency of the antibody. There are two types of light chain, lambda (I) and kappa (k) with kappa light chains being the more common of the two. Although these are relatively dissimilar in protein sequence they share a similar structure and function.

The five main heavy chain classes (or isotypes) determine the functional activity of an antibody molecule: IgM, IgD, IgG, IgA and IgE. Each chain contains distinct sequence domains. IgG is the most abundant antibody in normal human serum, accounting for 70-85% of the total immunoglobulin pool. It is monomeric with a molecular weight of approximately 150kDa, is the major antibody of the secondary immune response and has the longest half-life of the five immunoglobulin classes. IgG consists of four human subclasses (lgG1 , lgG2, lgG3 and lgG4) each containing a different heavy chain. They are highly homologous and differ mainly in the hinge region and the extent to which they activate the host immune system. lgG1 and lgG4

contain two inter-chain disulphide bonds in the hinge region, lgG2 has 4 and lgG3 has 1 1 .

The light chain includes two domains or regions, a variable domain (VL) and a constant domain (CL). The heavy chain includes four domains, a variable domain (VH) and three constant domains (CH 1 , CH2 and CH3, collectively referred to as CH). The variable regions of both light (VL) and heavy (VH) chains determine binding recognition and specificity to the antigen. The constant region domains of the light (CL) and heavy (CH) chains confer important biological properties such as antibody chain association, secretion, trans-placental mobility, complement binding, and binding to Fc receptors (FcR). The Fv fragment is the N-terminal part of the Fab fragment of an immunoglobulin and consists of the variable portions of one light chain and one heavy chain. The specificity of the antibody resides in the structural complementarity between the antibody combining site and the antigenic determinant. Antibody combining sites are made up of residues that are primarily from the hypervariable or complementarity determining regions (CDRs). Occasionally, residues from nonhypervariable or framework regions (FR) influence the overall domain structure and hence the combining site. "Complementarity Determining Regions or CDRs" refer to amino acid sequences which together define the binding affinity and specificity of the natural Fv region of a native immunoglobulin binding site. The light and heavy chains of an immunoglobulin each have three CDRs, designated CDR1 -L, CDR2-L, CDR3-L (for Light Chain Complementary Determining Regions) or CDRL1 , CDRL2, CDRL3 and CDR1 -H, CDR2-H, CDR3-H (for Heavy Chain Complementary Determining Regions) or CDRH1 , CDRH2, CDRH3, respectively. A conventional antibody antigen-binding site, therefore, includes six CDRs, comprising the CDR set from each of a heavy and a light chain V region.

"Framework Regions" (FRs) refer to amino acid sequences interposed between CDRs, i.e. to those portions of immunoglobulin light and heavy chain variable regions that are relatively conserved among different immunoglobulins in a single species. The light and heavy chains of an immunoglobulin each have four FRs, designated FR1 -L, FR2-L, FR3-L, FR4-L, and FR1 -H, FR2-H, FR3-H, FR4-H, respectively.

As used herein, a "human framework region" is a framework region that is substantially identical (about 85%, or more, in particular 90%, 95%, 97%, 99% or 100%) to the framework region of a naturally occurring human antibody.

In one embodiment, CDR/FR definition in an immunoglobulin light or heavy chain is to be determined based on IMGT definition (Lefranc, M.P. et al., 2003, Dev

Comp Immunol. 27(1 ): 55-77; www.imgt.org). CDR sequences featured in the invention are given according to IMGT's nomenclature.

As used herein, the term "antibody" refers to conventional or full-length antibodies (i.e. antibodies comprising two heavy chains and two light chains), to single domain antibodies, and to fragments of conventional and of single domain antibodies. As used herein, the term "antibody" includes but is not limited to chimeric antibodies, humanized antibodies, human antibodies, and multispecific antibodies (such as e.g. bispecific and trispecific antibodies). The term "antibody" refers both to an antibody comprising the signal peptide (or pro-peptide, if any), and to the mature form obtained upon secretion and proteolytic processing of the chain(s).

As used herein, antibody or immunoglobulin also includes "single domain antibodies" which have been more recently described and which are antibodies whose complementary determining regions are part of a single domain polypeptide. Examples of single domain antibodies include heavy chain antibodies, antibodies naturally devoid of light chains, single domain antibodies derived from conventional four-chain antibodies, engineered single domain antibodies. Single domain antibodies may be derived from any species including, but not limited to mouse, human, camel, llama, goat, rabbit and bovine. Single domain antibodies may be naturally occurring single domain antibodies known as heavy chain antibody devoid of light chains. In particular, Camelidae species, for example camel, dromedary, llama, alpaca and guanaco, produce heavy chain antibodies naturally devoid of light chain. Camelid heavy chain antibodies also lack the CH1 domain.

WE CLAIMS

An isolated monoclonal antibody that binds to CHIKV and that comprises three Heavy Chain Complementary Determining Regions (CDRHs) and three Light Chain Complementary Determining Regions (CDRLs), wherein:

i. said CDRHs have amino acid sequences of SEQ ID NO: 5, 6 and 7, and said CDRLs have amino acid sequences of SEQ ID NO: 8, GNT and 10, or ii. said CDRHs have amino acid sequences of SEQ ID NO: 1 1 , 12 and 13, and said CDRLs have amino acid sequences of SEQ ID NO: 14, GTS and 16, or

iii. said CDRHs and CDRLHs have amino acid sequences differing from the sequences of i. or ii. by one or two amino acid substitutions;

and wherein said antibody further comprises a Fc region comprising at least one residue selected from the group consisting of:

iv. an alanine at position 434, or

v. an alanine at positions 307, 380 and 434, respectively, or vi. a glutamine at position 250 and a leucine at position 428, respectively, or

vii. a leucine at position 428 and a serine at position 434, respectively, or

viii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

The isolated monoclonal antibody according to claim 1 wherein said antibody has one or more of the following properties:

i. binds a CHIKV pE2-E1 target with a binding dissociation equilibrium constant (KD) of less than about 10 nM;

ii. binds human FcRn with a KD of less than about 200 nM;

iii. binds human FcyRIII with a KD of less than about 600 nM.

The monoclonal antibody according to claim 1 or claim 2 wherein said antibody comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 5, 6 and 7, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions, and wherein said antibody comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 8, GNT and 10, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions.

4. The monoclonal antibody according to claim 1 or claim 2 wherein said antibody comprises three Heavy Chain Complementary Determining Regions (CDRHs) having amino acid sequences of SEQ ID NO: 1 1 , 12 and 13, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions, and said antibody comprises three Light Chain Complementary Determining Regions (CDRLs) having amino acid sequences of SEQ ID NO: 14, GTS and 16, respectively, or amino acid sequences differing from those sequences by one or two amino acid substitutions.

5. The monoclonal antibody according to any one of claims 1 to 3, wherein said antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 5;

- A CDRH2 consisting of sequence SEQ ID NO: 6;

- A CDRH3 consisting of sequence SEQ ID NO: 7;

- A CDRL1 consisting of sequence SEQ ID NO: 8;

A CDRL2 consisting of sequence GNT;

- A CDRL3 consisting of sequence SEQ ID NO: 10.

6. The monoclonal antibody according to any one of claims 1 , 2 and 4, wherein said antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 13;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

7. The monoclonal antibody according to any one of claims 1 to 6, wherein said Fc region comprises residues selected from the group consisting of:

i. a leucine at position 428 and a serine at position 434, or

ii. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

8. The monoclonal antibody according to any one of claims 1 to 7, wherein said Fc region comprises a leucine at position 428 and a serine at position 434 wherein said amino acid positions are given according to the EU index.

9. The monoclonal antibody according to any one of claims 1 to 6, wherein said Fc region comprises or consists of a sequence having at least 80% identity with SEQ ID NO: 59, 60, 61 , 62 and 63.

10. The monoclonal antibody according to any one of claims 1 to 3, 5, 7 to 9, wherein the variable region of its heavy chain comprises or consists of a sequence having at least 80% identity with sequence ID NO: 1.

1 1 . The monoclonal antibody according to any one of claims 1 to 3, 5, 7 to 10, wherein the variable region of its light chain comprises or consists of a sequence having at least 80% identity with sequence ID NO: 2.

12. The monoclonal antibody according to any one of claims 1 to 3, 5, 7 to 1 1 , wherein its heavy chain comprises or consists of a sequence having at least 80% identity with sequence ID NO: 31 .

13. The monoclonal antibody according to any one of claims 1 to 3, 5, 7 to 12, wherein its light chain comprises or consists of a sequence having at least 80% identity with sequence ID NO: 20.

14. An isolated monoclonal antibody that binds to CHIKV and that comprises or consists of an heavy chain of SEQ ID NO: 31 and a light chain of SEQ ID NO: 20.

15. An isolated monoclonal antibody that binds to CHIKV and that comprises three Heavy Chain Complementary Determining Regions (CDRHs) and three Light Chain Complementary Determining Regions (CDRLs), wherein:

i. said CDRHs have amino acid sequences of SEQ ID NO: 1 1 , 12 and 33, and said CDRLs have amino acid sequences of SEQ ID NO: 14, GTS and 16, or

ii. said CDRHs and CDRLHs have amino acid sequences differing from the sequences of i. by one or two amino acid substitutions;

and wherein :

iii. the amino acid at position 8 of SEQ ID NO: 33 is not M, and/or iv. the amino acid at position 12 of SEQ ID NO: 33 is not N; and/or v. the amino acid at position 13 of SEQ ID NO: 33 is not G.

16. The monoclonal antibody according to claim 15, wherein said antibody has one or more of the following properties:

i. binds a CHIKV pE2-E1 target with a binding dissociation equilibrium constant (KD) of less than about 10 nM;

ii. binds human FcRn with a KD of less than about 200 nM;

iii. binds human FcyRIII with a KD of less than about 600 nM.

17. The monoclonal antibody according to claim 15 or claim 16, wherein said antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 34;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

18. The monoclonal antibody according to any one of claims 15 to 17, wherein said antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 35;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

19. The monoclonal antibody according to any one of claims 15 to 18, wherein said antibody comprises:

- A CDRH1 consisting of sequence SEQ ID NO: 1 1 ;

- A CDRH2 consisting of sequence SEQ ID NO: 12;

- A CDRH3 consisting of sequence SEQ ID NO: 36;

- A CDRL1 consisting of sequence SEQ ID NO: 14;

- A CDRL2 consisting of GTS;

- A CDRL3 consisting of sequence SEQ ID NO: 16.

20. The monoclonal antibody according to any one of claims 15 to 19, wherein said antibody further comprises a Fc region that comprises residues selected from the group consisting of:

i. an alanine at position 434, or

ii. an alanine at positions 307, 380 and 434, respectively, or iii. a glutamine at position 250 and a leucine at position 428, respectively, or

iv. a leucine at position 428 and a serine at position 434, respectively, or v. a tyrosine at position 252, a threonine at position 254 and a glutamic acid at position 256, respectively,

wherein said amino acid positions are given according to the EU index.

21 . The monoclonal antibody according to claim 20, wherein said antibody has a Fc region that comprises a leucine at position 428 and a serine at position 434 wherein said amino acid positions are given according to the EU index.

22. The monoclonal antibody according to any one of claims 15 to 21 , wherein said antibody has a Fc region comprising or consisting of a sequence having at least 80% identity with SEQ ID NO: 59, 60, 61 , 62 and 63.

23. The monoclonal antibody according to anyone of claims 1 to 22, for use as a medicament.

24. The monoclonal antibody according to claim 23, for use in the treatment of CHIKV- associated arthralgia.

25. The monoclonal antibody according to claim 23, for use in the prevention of CHIKV infection.

26. A pharmaceutical composition comprising the monoclonal antibody according to any one of claims 1 to 22 and at least one excipient.

27. A cell line producing the monoclonal antibody according to any one of claims 1 to 22.

28. A method of producing the monoclonal antibody according to any one of claims 1 to 22, wherein said method comprises the steps of:

culturing a cell line producing said monoclonal antibody;

purifying the produced monoclonal antibody; and optionally iii. formulating said monoclonal antibody into a pharmaceutical composition.

29. A polynucleotide comprising a sequence encoding the monoclonal antibody according to any one of claims 1 to 22.

30. The polynucleotide of claim 29 encoding a polypeptide having at least 80% identity with one of the sequences SEQ ID NO: 18, 21 , 22, 24, 26, 28, 30, 32, 39, 40, 42, 44, 46, 48, 50, 52 and 54.

31 . A kit comprising one antibody according to any one of claims 1 to 22 and optionally packaging material.