Non-human animals carrying a humanized CXCL13 gene

Abstract

Disclosed herein are genetically modified rodents (such as, but not limited to, mice and rats) that contain a humanized Cxcl13 gene. The rodents disclosed herein have been shown to support better engraftment and growth of human cells, such as chronic lymphocytic leukemia cells. Compositions and methods for producing such genetically modified rodents are provided, as well as methods for using such genetically modified rodents to test potential therapeutic agents (e.g., potential anti-cancer agents).

Description

[Background technology]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 013,148, filed April 21, 2020, the entire contents of which are incorporated herein by reference. INCORPORATION BY REFERENCE OF SEQUENCE LISTING

[0002] The Sequence Listing, in the form of a 14 KB ASCII text file entitled 38357WO_10574WO01_SequenceListing, created on April 16, 2021, and submitted to the U.S. Patent and Trademark Office via EFS-Web, is incorporated herein by reference.

[0003] Non-human animals, including rodents, have been used as recipients of human cells, such as human hematopoietic stem cells or patient-derived xenograft tissues or cells. Improved non-human animal systems that support and promote the survival and growth of engrafted human cells are desirable, thereby facilitating a better understanding of the pathogenesis of associated diseases and the development of therapeutics. Summary of the Invention [Means for solving the problem]

[0004] It has been established in accordance with the present disclosure that humanization of the rodent endogenous Cxcl13 gene results in rodents that better support the engraftment and growth of human cells, such as chronic lymphocytic leukemia cells. Thus, disclosed herein are Cxcl13-humanized rodents, compositions and methods for producing such rodents, and methods for using such rodents to test candidate therapeutic agents (e.g., candidate anti-cancer agents).

[0005] In one aspect, disclosed herein is a genetically modified rodent comprising in its genome a humanized Cxcl13 gene comprising a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, wherein the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide.

[0006] In some embodiments, the humanized Cxcl13 polypeptide comprises a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. In some embodiments, the humanized Cxcl13 polypeptide comprises a mature protein sequence that is substantially identical to the mature protein sequence of the human CXCL13 protein. In some embodiments, the human CXCL13 protein comprises the amino acid sequence of SEQ ID NO: 2.

[0007] In some embodiments, the humanized Cxcl13 polypeptide comprises a rodent signal peptide. In some such embodiments, the rodent signal peptide is the signal peptide of an endogenous rodent Cxcl13 protein.

[0008] In some embodiments, the human CXCL13 nucleic acid sequence in the humanized Cxcl13 gene encodes a polypeptide substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3 and 4 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence encodes a polypeptide substantially identical to the mature protein sequence of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3, 4, and the coding portion of exon 5 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3, 4, and 5 of the human CXCL13 gene.

[0009] In some embodiments, the rodent Cxcl13 nucleic acid sequence in the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene. In some embodiments, the rodent Cxcl13 gene is an endogenous Cxcl13 gene.

[0010] In some embodiments, the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene and exons 3-5 of the human CXCL13 gene.

[0011] In some embodiments, the humanized Cxcl13 gene is operably linked to a rodent Cxcl13 promoter. In some embodiments, the rodent Cxcl13 promoter is an endogenous rodent Cxcl13 promoter at the endogenous rodent Cxcl13 locus. In other embodiments, the humanized Cxcl13 gene is operably linked to a human Cxcl13 promoter, optionally at the endogenous rodent Cxcl13 locus.

[0012] In some embodiments, the humanized Cxcl13 gene is located at a locus other than the endogenous rodent Cxcl13 locus. In some embodiments, the humanized Cxcl13 gene is located at the endogenous rodent Cxcl13 locus, and in some such embodiments, the humanized Cxcl13 gene may be formed as a result of substitution of rodent Cxcl13 genomic DNA at the endogenous rodent Cxcl13 locus with a human CXCL13 nucleic acid. In some embodiments, the humanized Cxcl13 gene is formed as a result of substitution of rodent genomic DNA comprising exons 2-3 and the coding portion of exon 4 of the rodent Cxcl13 gene with exons 3-5 of the human CXCL13 gene at the endogenous rodent Cxcl13 locus.

[0013] In some embodiments, the rodents disclosed herein are heterozygous for the humanized Cxcl13 gene. In some embodiments, the rodents disclosed herein are homozygous for the humanized Cxcl13 gene.

[0014] In some embodiments, the genome of a rodent disclosed herein may further comprise a humanized Sirpα gene at the endogenous rodent Sirpα locus, a humanized Baff gene at the endogenous rodent Baff locus, a humanized April gene at the endogenous rodent April locus, a humanized IL-6 gene at the endogenous rodent IL-6 locus, or a combination thereof.

[0015] In some embodiments, the rodents disclosed herein are immunodeficient, such as RAG2 and IL-2RG double knockout rodents.

[0016] In some embodiments, the rodent disclosed herein is selected from a mouse or a rat.

[0017] In another aspect, the present disclosure provides isolated rodent tissues or cells, whose genomes comprise the humanized Cxcl13 gene described herein. In some embodiments, the isolated rodent cells are rodent embryonic stem cells. Also disclosed are rodent embryos comprising rodent embryonic stem cells.

[0018] In a further aspect, the present specification discloses a method for producing a genetically modified rodent, comprising modifying a rodent genome to include a humanized Cxcl13 gene, wherein the humanized Cxcl13 gene comprises a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence and encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein, and producing a rodent comprising the modified rodent genome.

[0019] In some embodiments, the rodent genome is modified by introducing a nucleic acid molecule comprising a human CXCL13 nucleic acid sequence into the genome of a rodent embryonic stem (ES) cell, obtaining rodent ES cells in which the human CXCL13 nucleic acid sequence is integrated into the endogenous rodent Cxcl13 locus to replace the rodent Cxcl13 genomic DNA at the endogenous rodent Cxcl13 locus, thereby forming a humanized Cxcl13 gene, and using the obtained rodent ES cells to generate a rodent.

[0020] In some embodiments, the human CXCL13 nucleic acid sequence introduced into the rodent ES cells encodes a polypeptide substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3-4 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence encodes a polypeptide substantially identical to the mature protein sequence of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3, 4, and the coding portion of exon 5 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence comprises exons 3-5 of the human CXCL13 gene.

[0021] In some embodiments, the humanized Cxcl13 gene formed at the endogenous rodent Cxcl13 locus comprises exon 1 of the endogenous rodent Cxcl13 gene and exons 3 to 5 of the human CXCL13 gene and is operably linked to the endogenous rodent Cxcl13 promoter at the endogenous rodent Cxcl13 locus.

[0022] In another aspect, a targeting nucleic acid construct useful for generating genetically modified animals is disclosed. The targeting construct may include a human CXCL13 nucleic acid sequence to be integrated into a rodent Cxcl13 gene at an endogenous rodent Cxcl13 locus, flanked by 5' and 3' nucleotide sequences homologous to the nucleotide sequences of the endogenous rodent Cxcl13 locus, where integration of the human CXCL13 nucleic acid sequence into the endogenous rodent Cxcl13 gene results in replacement of rodent Cxcl13 genomic DNA with the human CXCL13 nucleic acid sequence, thereby forming a humanized Cxcl13 gene. In some embodiments, the human CXCL13 nucleic acid sequence of the targeting construct includes exons 3 and 4 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence of the targeting construct includes exons 3, 4, and the coding portion of exon 5 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleic acid sequence of the targeting construct comprises exons 3-5 of the human CXCL13 gene.

[0023] In yet another aspect, a method for testing candidate agents for treating a disease is disclosed. The method includes introducing cells from a human subject suffering from the disease into a genetically modified rodent disclosed herein, contacting the rodent with a candidate agent, and analyzing whether the candidate agent is effective in reducing or eliminating the cells. Candidate agents that are effective in reducing or eliminating the cells from the rodent are considered useful for treating the disease.

[0024] In some embodiments, the disease is cancer, e.g., a solid tumor or a blood cancer, hi some embodiments, the disease is leukemia.

[0025] In some embodiments, the candidate agents are anti-cancer compounds, optionally selected from small molecule compounds, nucleic acid molecules (eg, siRNAs), or antibodies. [Brief description of the drawing]

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments and, together with the description, illustrate the compositions and methods of the present disclosure.

[0027] Unless otherwise indicated, the diagram uses open boxes for human exon sequences, closed boxes for mouse exon sequences, single lines for mouse introns, double lines for human introns, and open boxes containing text for selection cassettes (e.g., Loxp). [Brief explanation of the drawings]

[0028] [Figure 1A] Figure 1A shows an exemplary strategy for humanizing the mouse Cxcl13 locus. A continuous mouse Cxcl13 genomic fragment at the endogenous mouse Cxcl13 locus, including mouse exons 2-3 (which encode the mouse Cxcl13 chemokine domain) and the coding portion of mouse exon 4, is replaced with a human CXCL13 genomic fragment including human CXCL13 exons 3-4 (encoding the human CXCL13 chemokine domain) and human CXCL13 exon 5 (including the 3' UTR of human CXCL13 as part of exon 5). The replacement results in a humanized Cxcl13 gene at the endogenous mouse Cxcl13 locus, which contains the mouse native Cxcl13 promoter, operably linked to mouse Cxcl13 exon 1 and human CXCL13 exons 3-5 (including the human CXCL13 3' UTR), followed by the 3' UTR of mouse Cxcl13. The human CXCL13 genomic fragment used for humanization can contain a selection cassette (e.g., a hygromycin resistance gene under the control of the ubiquitin promoter, flanked by LoxP sites) to facilitate screening for correctly targeted clones.

[0029] [Figure 1B-C] Figure 1B-1C. Figure 1B shows the nucleic acid construct ("BHR donor") generated and used to modify a mouse Cxcl13 bacterial artificial chromosome (BAC) via bacterial homologous recombination. Figure 1C shows the resulting modified BAC containing the chimeric Cxcl13 gene.

[0030] [Figure 1D-E] Figures 1D-1E show the genome of a mouse heterozygous for the humanized Cxcl13 locus with the selection cassette (1D) and after the cassette has been deleted (1E). The names and locations of the primers and probes used in the modification of allele (MOA) assay (described in Example 1) are also shown.

[0031] [Figure 1F] Figure 1F shows an alignment of mouse Cxcl13 (SEQ ID NO: 4), human CXCL13 (SEQ ID NO: 2), and humanized (hybrid) Cxcl13 (SEQ ID NO: 8) protein sequences. The signal peptide and chemokine IL-8-like domain of the proteins are indicated by boxes. The two N-terminal cysteines within the chemokine IL-8-like domain are indicated by arrows. Triangles indicate where the introns are located (position and size, mouse at the top and human at the bottom) and illustrate that the chemokine IL-8-like domain is encoded by the second and third coding exons (exons 2-3 of mouse Cxcl13 or exons 3-4 of human CXCL13).

[0032] [Figure 2] Figure 2 shows that mice heterozygous for the Cxcl13 humanization described in Example 1 expressed mature human CXCL13 protein in serum (right), along with control mice without Cxcl13 humanization (left). Mice generated from two specifically targeted ES cell clones (clone 1 and clone 2) were examined. Each dot represents one mouse. All mice were from a non-engrafting SIRPα hu / hu RAG2- / - IL2Rγ- / - background.

[0033] [Figure 3]Figure 3 shows the results of comparing Cxcl13-humanized mice with NSG mice as hosts for CLL PDX. Each line represents one engrafted CLL patient sample. An average of 3-4 engrafted mice per CLL sample is shown. SRG-BA6-13 mice (heterozygous for Cxcl13 humanization) exhibited enhanced CLL cell engraftment and proliferation compared to NSG mice, whereas SRG-BA6 mice (without Cxcl13 humanization) did not. DETAILED DESCRIPTION OF THE INVENTION

[0034] Disclosed herein are rodents (such as, but not limited to, mice and rats) that have been genetically modified to contain a humanized Cxcl13 gene. The rodents disclosed herein have been shown to support better engraftment and growth of human cells, such as chronic lymphocytic leukemia cells. Compositions and methods for producing such genetically modified rodents, as well as methods for using such genetically modified rodents to test potential therapeutic agents (e.g., potential anti-cancer agents), are provided and are further described below.

[0035] CXCL13 gene C-X-C motif chemokine ligand 13 (CXCL13), also known as B-lymphocyte chemoattractant (BLC) or B-cell-attracting chemokine 1 (BCA-1), is a protein ligand belonging to the C-X-C chemokine family. The two N-terminal cysteines of C-X-C chemokines are separated by one amino acid and are designated by an "X" in this name.

[0036] CXCL13 is a cytotoxic molecule that stimulates B cells and follicular B helper T cells (or T FH CXCL13 is selectively chemotactic for T cells (T cells) and induces its effects by interacting with the chemokine receptor CXCR5. CXCL13 is highly expressed in the liver, spleen, lymph nodes, and Peyer's patches, and is involved in the transport of B cells and T cells to germinal centers for B cell activation, class switching, and somatic hypermutation. FHIt is thought to be an important chemokine for attracting cells.

[0037] Exemplary sequences, including the nucleic acid and protein sequences of human CXCL13, mouse Cxcl13, and rat Cxcl13, as well as exemplary humanized Cxcl13 nucleic acid and protein sequences, are disclosed in the Sequence Listing and summarized in Table 1. An alignment of the human CXCL13, mouse Cxcl13, and humanized (hybrid) Cxcl13 protein sequences is provided in Figure IF. [Table 1-1] [Table 1-2]

[0038] Cxcl13 humanized rodents The rodents disclosed herein contain a humanized Cxcl13 gene in their germline.

[0039] In some embodiments, the rodent disclosed herein comprises a humanized Cxcl13 gene, the genome of which comprises the nucleotide sequence of the rodent Cxcl13 gene and the nucleotide sequence of the human CXCL13 gene. As used herein, the "nucleotide sequence of a gene" includes the genomic sequence, mRNA sequence, or cDNA sequence of the whole or part of the gene. For example, the nucleotide sequence of the human CXCL13 gene may be the genomic sequence, mRNA sequence, or cDNA sequence of the whole or part of the human CXCL13 gene, and the nucleotide sequence of the rodent Cxcl13 gene may be the genomic sequence, mRNA sequence, or cDNA sequence of the whole or part of the rodent Cxcl13 gene (e.g., endogenous rodent Cxcl13 gene). The nucleotide sequence of the rodent Cxcl13 gene and the nucleotide sequence of the human CXCL13 gene are operably linked to each other, such that the humanized Cxcl13 gene in the rodent genome encodes a humanized Cxcl13 protein that shares a conserved protein structure with human CXCL13 and rodent Cxcl13 proteins, i.e., consists of a signal peptide and a mature protein containing a chemokine IL-8-like domain with an N-terminal C-X-C motif.

[0040] In some embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein.

[0041] In some embodiments, a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein is a polypeptide that is at least 95%, at least 98%, at least 99%, or 100% identical to the chemokine IL-8-like domain of a human CXCL13 protein. In some embodiments, a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein is a polypeptide that differs from the chemokine IL-8-like domain of a human CXCL13 protein by no more than 3, 2, or 1 amino acid. In some embodiments, a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein is a polypeptide that differs from the chemokine IL-8-like domain of a human CXCL13 protein only in the N- or C-terminal portion of the domain, e.g., has amino acid additions, deletions, or substitutions, but differs by no more than 3, 2, or 1 amino acid in the N- or C-terminal portion of the domain. By "N- or C-terminal portion of the domain" is meant within 5 amino acids from the N- or C-terminus of the domain.

[0042] In some embodiments, the chemokine IL-8-like domain of the human CXCL13 protein comprises amino acids 30-91 of SEQ ID NO: 2. Thus, in some embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising a chemokine IL-8-like domain substantially identical to the amino acid sequence set forth in amino acids 30-91 of SEQ ID NO: 2. In certain embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising a chemokine IL-8-like domain whose amino acid sequence is set forth in amino acids 30-91 of SEQ ID NO: 2.

[0043] In some embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising a mature protein sequence that is substantially identical to the mature protein sequence of a human CXCL13 protein.

[0044] In some embodiments, a mature protein sequence that is substantially identical to the mature protein sequence of a human CXCL13 protein is a polypeptide sequence that is at least 95%, at least 98%, at least 99%, or 100% identical to the mature protein sequence of a human CXCL13 protein. In some embodiments, a mature protein sequence that is substantially identical to the mature protein sequence of a human CXCL13 protein is a polypeptide sequence that differs from the mature protein sequence of a human CXCL13 protein by no more than 3, 2, or 1 amino acid. In some embodiments, a mature protein sequence that is substantially identical to the mature protein sequence of a human CXCL13 protein is a polypeptide that differs from the mature protein sequence of a human CXCL13 protein only in the N- or C-terminal portion of a domain, e.g., has amino acid additions, deletions, or substitutions, but differs by no more than 3, 2, or 1 amino acid at the N- or C-terminal portion of the mature protein. "N- or C-terminal portion of the mature protein" means within 5 amino acids from the N- or C-terminus of the mature protein.

[0045] In some embodiments, the mature protein sequence of the human CXCL13 protein comprises amino acids 23-109 of SEQ ID NO: 2. Thus, in some embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising a mature protein sequence substantially identical to the amino acid sequence set forth in amino acids 23-109 of SEQ ID NO: 2. In certain embodiments, the genetically modified rodent comprises a humanized Cxcl13 gene in its genome, which encodes a humanized Cxcl13 protein comprising the mature protein sequence set forth in amino acids 23-109 of SEQ ID NO: 2.

[0046] In some embodiments, the humanized Cxcl13 gene encodes a humanized Cxcl13 protein comprising a signal peptide substantially identical to the signal peptide of the human CXCL13 protein. For example, the humanized Cxcl13 protein may comprise a signal peptide that is at least 95%, at least 98%, at least 99%, or 100% identical in sequence to the signal peptide of the human CXCL13 protein, or that differs from the signal peptide of the human CXCL13 protein by three, two, or one or fewer amino acids. In certain embodiments, the signal peptide of the human CXCL13 protein comprises the amino acid sequence set forth in amino acids 1-22 of SEQ ID NO:2.

[0047] In some embodiments, the humanized Cxcl13 gene encodes a humanized Cxcl13 protein that includes a signal peptide that is substantially identical to the signal peptide of a rodent Cxcl13 protein, such as an endogenous rodent Cxcl13 protein. For example, the humanized Cxcl13 protein may include a signal peptide that is at least 95%, at least 98%, at least 99%, or 100% identical in sequence to the signal peptide of a rodent Cxcl13 protein, or that differs from the signal peptide of a rodent Cxcl13 protein by no more than three, two, or one amino acid. In certain embodiments, the signal peptide of a mouse Cxcl13 protein includes the amino acid sequence set forth in amino acids 1-21 of SEQ ID NO:4. In other specific embodiments, the signal peptide of a rat Cxcl13 protein includes the amino acid sequence set forth in amino acids 1-21 of SEQ ID NO:6.

[0048] As described above, the humanized Cxcl13 gene in the genome of the genetically modified rodent comprises the nucleotide sequence of the human CXCL13 gene (or "human CXCL13 nucleotide sequence") and the nucleotide sequence of the endogenous rodent Cxcl13 gene (or "endogenous rodent Cxcl13 nucleotide sequence").

[0049] In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein encoded by a human CXCL13 gene (e.g., a polypeptide that is at least 95%, at least 98%, at least 99%, or 100% identical to the chemokine IL-8-like domain of a human CXCL13 protein; a polypeptide that differs from the chemokine IL-8-like domain of a human CXCL13 protein by no more than three, two, or one amino acid; or a polypeptide that differs from the chemokine IL-8-like domain of a human CXCL13 protein only in the N- or C-terminal portion of the domain, e.g., has amino acid additions, deletions, or substitutions, but differs by no more than three, two, or one amino acid in the N- or C-terminal portion of the domain). In some embodiments, the human CXCL13 nucleotide sequence is a cDNA sequence. In some embodiments, the human CXCL13 nucleotide sequence is a genomic fragment of a human CXCL13 gene. In some embodiments, the human CXCL13 nucleotide sequence is a genomic fragment comprising exons 3-4 of the human CXCL13 gene.

[0050] In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide that is substantially identical to the mature protein sequence of a human CXCL13 protein encoded by a human CXCL13 gene (e.g., a polypeptide that is at least 95%, at least 98%, at least 99%, or 100% identical to the mature protein sequence of a human CXCL13 protein; a polypeptide that differs from the mature protein sequence of a human CXCL13 protein by no more than 3, 2, or 1 amino acids; or a polypeptide that differs from the mature protein sequence of a human CXCL13 protein only in the N- or C-terminal portions of a domain, e.g., has amino acid additions, deletions, or substitutions, but differs by no more than 3, 2, or 1 amino acids in the N- or C-terminal portions of the domain). In some embodiments, the human CXCL13 nucleotide sequence is a cDNA sequence. In some embodiments, the human CXCL13 nucleotide sequence is a genomic fragment of a human CXCL13 gene. In some embodiments, the human CXCL13 nucleotide sequence is a genomic fragment that includes exon 3, exon 4, and the coding portion of exon 5 (the last coding exon) of the human CXCL13 gene.

[0051] In some embodiments, the human CXCL13 nucleotide sequence is a genomic fragment comprising exons 3 to 5 of the human CXCL13 gene, including the 3' UTR of exon 5. In some such embodiments, the human CXCL13 nucleotide sequence further comprises a 3' portion of intron 2 of the human CXCL13 gene.

[0052] In some embodiments, the rodent Cxcl13 nucleotide sequence in the humanized Cxcl13 gene encodes a polypeptide that is substantially identical to the signal peptide of a rodent Cxcl13 protein (e.g., a polypeptide that is at least 95%, at least 98%, at least 99%, or 100% identical in sequence to the signal peptide of a rodent Cxcl13 protein, or a polypeptide that differs from the signal peptide of a rodent Cxcl13 protein by no more than 3, 2, or 1 amino acid). In some embodiments, the rodent Cxcl13 nucleotide sequence comprises exon 1 of the rodent Cxcl13 gene. In certain embodiments, the rodent Cxcl13 nucleotide sequence comprises exon 1 of the endogenous rodent Cxcl13 gene, and in some such embodiments, the rodent Cxcl13 nucleotide sequence comprises exon 1 and a 5' portion of intron 1 of the endogenous rodent Cxcl13 gene.

[0053] In some embodiments, the humanized Cxcl13 gene is operably linked to a rodent Cxcl13 regulatory sequence, such as a 5' transcriptional regulatory sequence, such as a promoter and / or enhancer, e.g., an endogenous rodent 5' transcriptional regulatory sequence at the endogenous Cxcl13 locus, such that expression of the humanized Cxcl13 gene is under the control of the rodent Cxcl13 5' regulatory sequence.

[0054] In some embodiments, the humanized Cxcl13 gene is at the endogenous rodent Cxcl13 locus. In some embodiments, the humanized Cxcl13 gene is at a locus other than the endogenous rodent Cxcl13 locus, for example, as a result of random integration. In some embodiments where the humanized Cxcl13 gene is at a locus other than the endogenous rodent Cxcl13 locus, the rodent is unable to express rodent Cxcl13 protein, for example, as a result of inactivation (e.g., deletion in whole or in part) of the endogenous rodent Cxcl13 gene.

[0055] In some embodiments in which the humanized Cxcl13 gene is at the endogenous rodent Cxcl13 locus, the humanized Cxcl13 gene may result from the replacement of the nucleotide sequence of the endogenous rodent Cxcl13 gene with the nucleotide sequence of the human CXCL13 gene at the endogenous rodent Cxcl13 locus.

[0056] In some embodiments, the nucleotide sequence of the endogenous rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus to be replaced is a genomic fragment of the endogenous rodent Cxcl13 gene that substantially encodes the chemokine IL-8-like domain of the rodent Cxcl13 protein. In some embodiments, the replaced rodent genomic fragment comprises exons 2-3 of the endogenous rodent Cxcl13 gene.

[0057] In some embodiments, the nucleotide sequence of the human CXCL13 gene that replaces the genomic fragment of the rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus is a cDNA sequence. In some embodiments, the human CXCL13 nucleotide sequence that replaces the genomic fragment of the rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus is a genomic fragment of the human CXCL13 gene. In some embodiments, the genomic fragment of the human CXCL13 gene that replaces the genomic fragment of the rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus comprises all or a portion of an exon of the human CXCL13 gene, which exon substantially encodes the chemokine IL-8-like domain of the human CXCL13 protein (i.e., encodes a polypeptide that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein). In some embodiments, the genomic fragment of the human CXCL13 gene that replaces the genomic fragment of the rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus comprises all or a portion of the exons of the human CXCL13 gene, which exons substantially encode the mature protein sequence of the human CXCL13 protein (i.e., encode a polypeptide that is substantially identical to the mature protein sequence of the human CXCL13 protein). In some embodiments, the human genomic fragment comprises exons 3-4 of the human CXCL13 gene. In some embodiments, the human genomic fragment comprises exons 3-4 and a coding portion of exon 5 of the human CXCL13 gene. In some embodiments, the human genomic fragment comprises exons 3-5 of the human CXCL13 gene (i.e., including the 3'UTR of exon 5).

[0058] In some embodiments, the genomic sequence of the endogenous rodent Cxcl13 gene that remains at the endogenous rodent Cxcl13 locus after the replacement and is operably linked to the inserted human CXCL13 nucleotide sequence substantially encodes the signal peptide of the endogenous rodent Cxcl13 protein. In some embodiments, the genomic sequence of the endogenous rodent Cxcl13 gene that remains at the endogenous rodent Cxcl13 locus after the replacement comprises exon 1 of the endogenous rodent Cxcl13 gene.

[0059] In some embodiments, a genomic fragment comprising exons 2-3 and the coding portion of exon 4 of the endogenous rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus is replaced with a genomic fragment comprising exons 3-5 of the human CXCL13 gene. As a result, a humanized Cxcl13 gene is formed at the endogenous rodent Cxcl13 locus, comprising exon 1 of the endogenous rodent Cxcl13 gene and exons 3-5 of the human CXCL13 gene (including the 3' UTR of human exon 5), followed by the 3' UTR of the endogenous rodent Cxcl13 gene. Such a humanized Cxcl13 gene encodes a humanized Cxcl13 protein comprising an endogenous rodent signal peptide and a mature human CXCL13 polypeptide.

[0060] In some embodiments, the rodents provided herein are heterozygous for the humanized Cxcl13 gene in their genome. In some embodiments, the rodents provided herein are homozygous for the humanized Cxcl13 gene in their genome.

[0061] In some embodiments, the humanized Cxcl13 gene results in expression of the encoded humanized Cxcl13 protein in the rodent, e.g., in the serum of the rodent. In some embodiments, the humanized Cxcl13 protein is expressed in a pattern similar to or substantially identical to that of the corresponding rodent Cxcl13 protein in a control rodent (e.g., a rodent that does not have a humanized Cxcl13 gene but comprises a complete rodent endogenous Cxcl13 gene), e.g., in the liver, spleen, lymph nodes, and Peyer's patches of the rodent. In some embodiments, the humanized Cxcl13 protein is expressed at levels equivalent to or substantially identical to the corresponding rodent Cxcl13 protein in a control rodent (e.g., a rodent that does not have a humanized Cxcl13 gene but comprises a complete rodent endogenous Cxcl13 gene), e.g., does not differ in its expression by more than 50%, 75%, or 100%.

[0062] In some embodiments, the rodents disclosed herein are unable to express rodent Cxcl13 protein, for example, as a result of inactivation (e.g., deletion in whole or in part) or replacement (in whole or in part) of the endogenous rodent Cxcl13 gene.

[0063] Additional optional genetic characterization in Cxcl13 humanized rodents In some embodiments, the rodent disclosed herein further comprises a humanized Sirpa gene, a humanized Baff gene, a humanized April gene, a humanized IL-6 gene, or a combination thereof in its genome. Humanization of endogenous rodent Sirpa, Baff, April, and IL-6 genes is described in WO2015 / 042557A1 (Regeneron Pharmaceuticals Inc.), WO2015 / 077071A1 (Regeneron Pharmaceuticals Inc.), WO2015 / 077072 (Regeneron Pharmaceuticals Inc.), and WO2013 / 063556A1 (Regeneron Pharmaceuticals Inc.), respectively, all of which are incorporated herein by reference. In some embodiments, the rodent comprises one or more of these additional humanized genes and is homozygous or heterozygous for any of the one or more additional humanized genes. In some embodiments, the rodent comprises all of these additional humanized genes and is homozygous or heterozygous for each of these additional humanized genes. In some embodiments, the rodent is homozygous or heterozygous for the humanized Cxcl13 gene and comprises one or more or all of these additional humanized genes and is homozygous or heterozygous for any of these additional humanized genes. In some embodiments, the rodent is homozygous for the humanized Cxcl13 gene and homozygous for each of these additional humanized genes.

[0064] In some embodiments, the rodent disclosed herein further comprises a humanized Sirpa gene in its genome. In some embodiments, the humanized Sirpa gene encodes a humanized Sirpα protein comprising all or a portion of the extracellular domain of the human SIRPα protein. In some embodiments, the humanized Sirpα gene encodes a humanized Sirpα protein comprising the extracellular portion of the human SIRPα protein involved in ligand binding (i.e., binding to CD47). In some embodiments, the humanized Sirpa gene encodes a humanized Sirpα protein comprising amino acid residues 28-362 of the human SIRPα protein set forth in GenBank accession number NP_001035111.1. In some embodiments, the humanized Sirpα gene comprises exons 2, 3, and 4 of the human SIRPα gene. In some embodiments, the humanized Sirpα gene is located at the endogenous rodent Sirpα locus. In some embodiments, the humanized Sirpα gene is formed as a result of the replacement of exons 2-4 of an endogenous rodent Sirpα gene at the endogenous rodent Sirpα locus with exons 2-4 of the human SIRPα gene. In some embodiments, the humanized Sirpα gene is located at the endogenous rodent Sirpα locus and comprises exon 1 of the endogenous rodent Sirpα gene, exons 2-4 of the human SIRPα gene, and exons 5-8 of the endogenous rodent Sirpα gene, wherein the humanized Sirpα gene is operably linked to a rodent Sirpα promoter at the endogenous rodent Sirpα locus. In some embodiments, the rodent disclosed herein is unable to express endogenous rodent Sirpα protein (e.g., as a result of a disruption or replacement of the endogenous rodent Sirpα gene).

[0065] In some embodiments, the rodent disclosed herein further comprises a humanized Baff gene in its genome. In some embodiments, the humanized Baff gene encodes a humanized Baff protein comprising all or a portion of the extracellular domain of the human BAFF protein. In some embodiments, the humanized Baff gene encodes a humanized Baff protein comprising the extracellular portion of the human BAFF protein involved in receptor binding. In some embodiments, the humanized Baff gene encodes a humanized Baff protein comprising amino acid residues 142-285 of the human BAFF protein, e.g., the human BAFF protein set forth in GenBank accession number NP_006564.1. In some embodiments, the humanized Baff gene comprises exons 3-6 of the human BAFF gene. In some embodiments, the humanized Baff gene is located at the endogenous rodent Baff locus. In some embodiments, the humanized Baff gene is formed as a result of replacement of endogenous rodent Baff genomic DNA, comprising exons 3-6 and the coding portion of exon 7, at the endogenous rodent Baff locus with exons 3-6 of the human BAFF gene. In some embodiments, the humanized Baff gene is located at the endogenous rodent Baff locus and comprises exons 1-2 of the endogenous rodent Baff gene and exons 3-6 of the human BAFF gene, wherein the humanized Baff gene is operably linked to a rodent Baff promoter at the endogenous rodent Baff locus. In some embodiments, the rodent disclosed herein is unable to express endogenous rodent Baff protein (e.g., as a result of a disruption or replacement of the endogenous rodent Baff gene).

[0066] In some embodiments, the rodent disclosed herein further comprises a humanized April gene in its genome. In some embodiments, the humanized April gene encodes a humanized April protein comprising all or part of the extracellular domain of a human April protein. In some embodiments, the humanized April gene encodes a humanized April protein comprising the extracellular portion of a human April protein involved in receptor binding. In some embodiments, the humanized April gene encodes a humanized April protein comprising amino acid residues 87-250 of a human April protein, e.g., the human April protein set forth in GenBank accession number NP_003799.1. In some embodiments, the humanized April gene comprises exons 2-6 of the human April gene. In some embodiments, the humanized April gene is located at the endogenous rodent April locus. In some embodiments, the humanized April gene is formed as a result of replacement of endogenous rodent April genomic DNA comprising the coding portion of exons 2 through 6 with exons 2 through 6 of the human APRIL gene. In some embodiments, the humanized April gene is located at the endogenous rodent April locus and comprises exon 1 of the endogenous rodent April gene and exons 2 through 6 of the human APRIL gene, wherein the humanized April gene is operably linked to a rodent April promoter at the endogenous rodent April locus. In some embodiments, the rodent disclosed herein is unable to express endogenous rodent April protein (e.g., as a result of a disruption or replacement of the endogenous rodent April gene).

[0067] In some embodiments, the rodent disclosed herein further comprises a humanized IL-6 gene in its genome. In some embodiments, the humanized IL-6 gene encodes a human IL-6 protein, e.g., the human IL-6 protein set forth in GenBank Accession No. NP_000591.1. In some embodiments, the humanized IL-6 gene comprises the coding portion of exons 1 through 5 of the human IL-6 gene. In some embodiments, the humanized IL-6 gene is located at the endogenous rodent IL-6 locus. In some embodiments, the humanized IL-6 gene is formed as a result of replacement of endogenous rodent IL-6 genomic DNA comprising the coding portion of exons 1 through 5 with the coding portion of exons 1 through 5 of the human IL-6 gene. In some embodiments, the humanized IL-6 gene is located at the endogenous rodent IL-6 locus and comprises the non-coding portion of exon 1 of the endogenous rodent IL-6 gene and the coding portion of exons 1-5 of the human IL-6 gene, wherein the humanized IL-6 gene is operably linked to a rodent IL-6 promoter at the endogenous rodent IL-6 locus. In some embodiments, the rodent disclosed herein is unable to express endogenous rodent IL-6 protein (e.g., as a result of a disruption or replacement of the endogenous rodent IL-6 gene).

[0068] In some embodiments, the rodents disclosed herein further have disrupted RAG2 and IL-2RG genes, such that they are unable to express endogenous RAG2 or IL-2 receptor gamma chain (also known as "γc") proteins. RAG2 and IL-2RG double knockout (DKO) rodents are known immunodeficient rodents (see, e.g., Traggiai E et al. (2004) Development of a human adaptive immune system in cord blood cell-transplanted mice, Science 304:104-107) and are readily available commercially (e.g., from Taconic Biosciences, Inc., New York).

[0069] In some embodiments, the rodents disclosed herein are homozygous for one or more (e.g., all) of the humanized Sirpα gene, the humanized Baff gene, and the humanized April gene, all at their respective endogenous loci (e.g., as a result of the substitutions described above), and are homozygous null for both the RAG2 gene and the IL-2RG gene.

[0070] In some embodiments, rodents of the present disclosure include, by way of non-limiting example, mice, rats, and hamsters. In some embodiments, rodents are selected from the superfamily Muridea. In some embodiments, rodents of the present disclosure are animals from a family selected from the family Muridae (e.g., mouse-like hamsters), Cricetidae (e.g., hamsters, New World rats and mice, voles), Muridae (pure-breed mice and rats, gerbils, spiny mice, and maned mice), Tetragnathidae (tree mice, rock mice, white-tailed rats, Madagascar rats and mice), Dormiceidae (e.g., spiny dormice), and Mole-rats (e.g., mole rats, bamboo rats, and plateau mole-rats). In some embodiments, rodents of the present disclosure are selected from pure-breed mice or rats (Muridae), gerbils, spiny mice, and maned mice. In some embodiments, mice of the present disclosure are from members of the family Muridae.

[0071] In some embodiments, the rodent is a mouse, hi some embodiments, the rodent is a C57BL strain mouse selected from C57BL / A, C57BL / An, C57BL / GrFa, C57BL / KaLwN, C57BL / 6, C57BL / 6J, C57BL / 6ByJ, C57BL / 6NJ, C57BL / 10, C57BL / 10ScSn, C57BL / 10Cr, and C57BL / Ola. In some embodiments, the rodent is a 129 strain of mouse selected from the group consisting of strains that are 129P1, 129P2, 129P3, 129X1, 129S1 (e.g., 129S1 / SV, 129S1 / SvIm), 129S2, 129S4, 129S5, 129S9 / SvEvH, 129 / SvJae, 129S6 (129 / SvEvTac), 129S7, 129S8, 129T1, 129T2 (see, e.g., Festing et al., 1999, Mammalian Genome 10:836; Auerbach et al., 2000, Biotechniques 29(5):1024-1028, 1030, 1032). In some embodiments, the rodent is a mouse that is a mix of 129 and C57BL / 6 strains. In some embodiments, the rodent is a mouse that is a mix of the aforementioned 129 strains, or a mix of the aforementioned BL / 6 strains. In some embodiments, the rodent is a BALB strain, e.g., a BALB / c strain mouse. In some embodiments, the rodent is a mouse that is a mix of the BALB strain and another aforementioned strain.

[0072] In some embodiments, the rodent is a rat. In certain embodiments, the rat is selected from Wistar rats, LEA strains, Sprague Dawley strains, Fischer strains, F344, F6, and Dark Agouti. In some embodiments, the rat strains described herein are a mixture of two or more strains selected from the group consisting of Wistar, LEA, Sprague Dawley, Fischer, F344, F6, and Dark Agouti.

[0073] Genetically modified rodent tissues and cells In some embodiments, disclosed herein is an isolated rodent cell or tissue that comprises in its genome a humanized Cxcl13 gene described herein.

[0074] In some embodiments, the tissue is selected from fat, bladder, brain, breast, bone marrow, eye, heart, intestine, kidney, liver, lung, lymph node, muscle, pancreas, plasma, serum, skin, spleen, stomach, thymus, testis, egg, and combinations thereof.

[0075] In some embodiments, the cell is selected from a dendritic cell, a lymphocyte (e.g., a B cell or a T cell), a macrophage, and a monocyte. In some embodiments, the isolated rodent cell is a rodent embryonic stem cell or a rodent egg.

[0076] Compositions and methods for producing humanized rodents Disclosed herein are targeting vectors (or nucleic acid constructs) comprising a human CXCL13 nucleotide sequence that is desired to be integrated into a rodent locus.

[0077] In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide substantially identical to the amino acid sequence set forth in amino acids 30-91 of SEQ ID NO:2. In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide substantially identical to the mature portion of the human CXCL13 protein. In some embodiments, the human CXCL13 nucleotide sequence encodes a polypeptide substantially identical to the amino acid sequence set forth in amino acids 23-109 of SEQ ID NO:2.

[0078] In some embodiments, the human CXCL13 nucleotide sequence comprises exon 3 and exon 4 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleotide sequence comprises exon 3, exon 4, and a coding portion of exon 5 of the human CXCL13 gene. In some embodiments, the human CXCL13 nucleotide sequence comprises exons 3 through 5 of the human CXCL13 gene.

[0079] The targeting vector also contains 5' and 3' rodent sequences, also known as 5' and 3' homology arms, flanking the human nucleotide sequence to be integrated and mediating homologous recombination and integration of the human nucleotide sequence into a target rodent locus (e.g., an endogenous Cxcl13 locus). Typically, the 5' and 3' flanking rodent sequences are nucleotide sequences that flank the corresponding rodent nucleotide sequence to be replaced by the human nucleotide sequence at the target rodent locus. For example, in an embodiment in which a rodent genomic sequence containing rodent Cxcl13 exons 2-4 is replaced with a human genomic sequence containing human CXCL13 exons 3-5, the 5' flanking sequence in the targeting vector may include a 5' portion of intron 1 of the rodent Cxcl13 gene, and the 3' flanking sequence may include a 5' portion of the 3' UTR of exon 4 of the rodent Cxcl13 gene.

[0080] In some embodiments, the targeting vector comprises a selectable marker gene. In some embodiments, the targeting vector comprises one or more site-specific recombination sites. In some embodiments, the targeting vector comprises a selectable marker gene flanked by site-specific recombination sites, such that the selectable marker gene can be deleted as a result of recombination between the sites.

[0081] In an exemplary embodiment, the targeting vector is generated from a bacterial artificial chromosome (BAC) clone carrying rodent Cxcl13 genomic DNA using bacterial homologous recombination and VELOCIGENE® technology (see, e.g., US Pat. No. 6,586,251 and Valenzuela et al. (2003) Nature Biotech. 21(6):652-659). As a result of bacterial homologous recombination, the rodent genomic sequence is deleted from the BAC clone and a human nucleotide sequence is inserted, resulting in a modified BAC clone carrying the human nucleotide sequence flanked by 5' and 3' rodent homologous arms. In some embodiments, the human nucleotide sequence may be a cDNA sequence encoding the mature portion of the human CXCL13 protein, or at least the chemokine IL-8-like domain, or human genomic DNA. Once linearized, the modified BAC clone can be introduced into rodent embryonic stem (ES) cells.

[0082] In some embodiments, the present invention provides methods of using the targeting vectors described herein to generate modified rodent embryonic stem (ES) cells. The targeting vectors can be introduced into rodent ES cells, for example, by electroporation. Both mouse and rat ES cells have been described in the art. See, for example, US 7,576,259, US 7,659,442, US 7,294,754, and US 2008-0078000 A1 (all of which are incorporated by reference in their entirety), which describe mouse ES cells and the VELOCIMOUSE® method of generating genetically modified mice; US 2014 / 0235933 A1 (Regeneron Pharmaceuticals, Inc.), US 2014 / 0310828 A1 (Regeneron Pharmaceuticals, Inc.), which describe rat ES cells and methods of generating genetically modified rats; Tong et al. (2010) Nature 467:211-215; and Tong et al. (2011) Nature. Protoc.6(6):doi:10.1038 / nprot.2011.338 (all of which are incorporated by reference in their entirety), which can be used to generate modified rodent embryos, which can then be used to generate rodent animals.

[0083] In some embodiments, ES cells already containing additional desirable genetic traits (e.g., homozygous for a humanized Sirpa gene, a humanized Baff gene, a humanized April gene, a humanized IL-6 gene, and / or RAG2- / - and IL-2RG- / -) are used as recipient cells in electroporation with a targeting vector containing a human CXCL13 nucleotide sequence. In some embodiments, these additional desirable genetic traits may be subsequently introduced (e.g., by breeding a humanized CXCL13 rodent with a second rodent bearing one or more desirable genetic traits).

[0084] In some embodiments, ES cells having a human CXCL13 nucleotide sequence integrated into their genome can be selected. In some embodiments, ES cells are selected based on a rodent allele loss and / or human allele gain assay. In some embodiments, the selected ES cells are then used as donor ES cells to inject into pre-morula stage embryos (e.g., 8-cell stage embryos) using the VELOCIMOUSE® method (see, e.g., US 7,576,259, US 7,659,442, US 7,294,754, and US 2008-0078000 A1, all of which are incorporated by reference in their entirety), or the methods described in US 2014 / 0235933 A1 and US 2014 / 0310828 A1, both of which are incorporated by reference in their entirety. In some embodiments, embryos containing donor ES cells are incubated and implanted into surrogate mothers to produce F0 rodents. Rodent pups carrying the human nucleotide sequence can be identified by genotyping DNA isolated from tail fragments using assays for loss of rodent alleles and / or gain of human alleles.

[0085] In some embodiments, rodents heterozygous for the humanized gene can be bred to produce homozygous rodents.

[0086] The Cxcl13-humanized rodents described herein can be bred or crossbred with other rodents. Thus, methods of breeding, as well as the progeny resulting from such breeding, are also embodiments of the present disclosure.

[0087] In some embodiments, a method is provided, comprising mating a first rodent described hereinabove, for example, a rodent whose genome comprises a humanized Cxcl13 gene, with a second rodent to generate offspring rodents whose genome comprises a humanized Cxcl13 gene. The offspring may have other desirable phenotypes or genetic modifications inherited from the second rodent used in the mating. In some embodiments, the offspring rodents are heterozygous for the humanized Cxcl13 gene. In some embodiments, the offspring rodents are homozygous for the humanized Cxcl13 gene.

[0088] In some embodiments, offspring rodents are provided whose genomes comprise a humanized Cxcl13 gene, the offspring rodents being generated by a method comprising mating a first rodent whose genome comprises a humanized Cxcl13 gene with a second rodent. In some embodiments, the offspring rodents are heterozygous for the humanized Cxcl13 gene. In some embodiments, the offspring rodents are homozygous for the humanized Cxcl13 gene.

[0089] In some embodiments, the second rodent comprises in its genome a humanized Sirpα gene, a humanized Baff gene, a humanized April gene, a humanized IL-6 gene, or a combination thereof.

[0090] In some embodiments, the second rodent is a RAG2 and IL-2RG double knockout (DKO) rodent (RAG2- / - and IL-2RG- / -).

[0091] In some embodiments, the second rodent comprises in its genome a humanized Sirpα gene, a humanized Baff gene, a humanized April gene, and a humanized IL-6 gene at their respective endogenous loci, and is RAG2− / − and IL-2RG− / −.

[0092] Methods using humanized rodents The rodents disclosed herein provide a useful in vivo system and source of biomaterials for identifying and testing compounds for the potential treatment of human disease.

[0093] In some embodiments, the rodents disclosed herein are used to develop drugs that target human CXCL13 and / or modulate CXCL13-CXCR5 interaction.In some embodiments, the rodents disclosed herein are used to screen and develop candidate drugs (e.g., antibodies) that specifically bind to human CXCL13.In some embodiments, the rodents disclosed herein are used to determine the binding profile of drugs (e.g., anti-human CXCL13 antibodies).

[0094] In some embodiments, rodents disclosed herein are used to measure the effects of blocking or modulating human CXCL13 activity. In some embodiments, rodents disclosed herein are exposed to candidate agents that bind to and inhibit human CXCL13 and analyzed for their effects on human CXCL13-dependent processes. For example, a CXCL13-humanized rodent disclosed herein can be exposed to candidate agents that bind to and inhibit human CXCL13 and analyzed for their effects on germinal center development, B cell development, and serum human immunoglobulin levels after engraftment of human hematopoietic CD34+ cells. The rodent is preferably an immunodeficient animal, for example, a rodent with a Rag2- / - IL-2RG- / - genotype, more preferably a Rag2- / - IL-2RG- / - Sirpa hu / hu Baff hu / hu April hu / hu IL-6 hu / hu Have a genotype.

[0095] In some embodiments, the rodents disclosed herein provide an improved in vivo system for the maintenance of patient-derived xenograft tissues or cells. In some embodiments, the patient-derived xenograft cells are cancer cells. In some embodiments, the cancer cells are cells of a solid tumor. In some embodiments, the cancer cells are cancerous blood cells, e.g., blood cells of a patient with leukemia, myeloma, Hodgkin's lymphoma, or non-Hodgkin's lymphoma. In some embodiments, the patient-derived xenograft cells are chronic lymphocytic leukemia (CCL) cells.

[0096] The rodents disclosed herein can be used to evaluate the efficacy of therapeutic drugs targeting human cancer cells. In various embodiments, the rodents disclosed herein are engrafted with human cancer cells (e.g., CCL cells), and drug candidates targeting such human cancer cells are administered to the rodents. The therapeutic efficacy of the drug is then determined by monitoring human cells in the rodent after drug administration, e.g., by assessing whether the growth or metastasis of human cancer cells in the rodent is inhibited as a result of drug administration. Drugs that can be tested in non-human animals include both small molecule compounds, i.e., compounds with a molecular weight of less than 1500 kD, 1200 kD, 1000 kD, or 800 daltons, and large molecule compounds (such as proteins, e.g., antibodies, or antigen-binding fragments of antibodies), which have their intended therapeutic effect in treating human diseases and conditions by targeting (e.g., binding to and / or acting on) human cells.

[0097] The present specification is further illustrated by the following examples, which should not be construed as limiting. All cited references (including literature references, issued patents, and published patent applications cited throughout this application) are expressly incorporated herein by reference in their entirety. [Example]

[0098] The following examples are put forth so as to provide a complete disclosure and description to those of ordinary skill in the art as to how the compounds, compositions, articles, devices, and / or methods claimed herein are made and evaluated, and are intended to be merely illustrative and not limiting of the present disclosure.

[0099] Example 1 Generation of humanized CXCL13 mice The mouse Cxcl13 locus was humanized using VELOCIGENE® technology (see, e.g., U.S. Patent No. 6,586,251 and Valenzuela et al. (2003) High-throughput engineering of the mouse genome couple with high-resolution expression analysis. Nat. Biotech. 21(6):652-659, both incorporated herein by reference). The resulting humanized Cxcl13 locus contains the endogenous mouse Cxcl13 promoter, operably linked to mouse Cxcl13 exon 1, human CXCL13 exons 3 and 4 (encoding the human CXCL13 chemokine domain), and human CXCL13 exon 5 (containing the human 3'UTR), followed by the endogenous mouse Cxcl13 3'UTR. See Figure 1A.

[0100] To humanize the mouse Cxcl13 locus, an initial plasmid was generated to carry nucleic acid encoding the human CXCL13 chemokine domain flanked by mouse Cxcl13 sequences. More specifically, this initial plasmid contained, from 5' to 3', (i) an XhoI site, (ii) 249 bp of mouse Cxcl13 sequence (the 5' portion of mouse intron 1) ("Up-Box"), (iii) human CXCL13 nucleic acid sequence, including the 3' portion of intron 2 (150 bp), exon 3 (133 bp), intron 3 (2778 bp, including AgeI and SalI sites), exon 4 (81 bp), intron 4 (293 bp), and exon 5 (847 bp, including the 3' UTR), (iv) the 5' portion of the 3' UTR of mouse Cxcl13 (140 bp, "Down-Box"), and (v) an XhoI site. The plasmid also contained a selection cassette containing a hygromycin resistance gene operably linked to a ubiquitin promoter flanked by LoxP sites. This BHR donor plasmid ("BHR" for bacterial homologous recombination) was then digested with XhoI to release a fragment (referred to herein as "BHR donor") containing the human CXCL13 nucleic acid sequence and selection cassette, flanked by mouse CXCL13 sequences (Up-Box and Down-Box). See Figure 1B.

[0101] The BHR donor was then used to modify the mouse Cxcl13 bacterial artificial chromosome (BAC) clone RP23-162n18 (Thermo-Fisher / Invitrogen). Via bacterial homologous recombination, a contiguous nucleic acid fragment of the mouse Cxcl13 BAC, including mouse exons 2–3 (encoding the mouse Cxcl13 chemokine domain) and the coding portion of mouse exon 4, was replaced with the human CXCL13 nucleic acid sequence from the BHR donor, resulting in a modified BAC carrying a chimeric humanized Cxcl13 nucleic acid containing mouse Cxcl13 exon 1 and human CXCL13 exons 3–5 (with a hygromycin cassette inserted between human exons 3 and 4), followed by the 3' UTR of mouse Cxcl13. See Figure 1B–1C.

[0102] The modified BAC was then used as a targeting vector to electroporate mouse embryonic stem (ES) cells containing the hSIRP-alpha (or human SIRPa), RAG2- / -, and IL2Rg- / - modifications. Successful integration was confirmed by modification of allele (MOA) assays, as described, for example, in Valenzuela et al., supra. The primers and probes used in the MOA assays to detect the presence of the human CXCL13 sequence and confirm the loss and / or retention of the mouse Cxcl13 sequence are listed in Table 2, and their locations are shown in Figure 1D. After selecting properly targeted ES cell clones, the hygromycin selection cassette was excised using Cre recombinase. The humanized Cxcl13 locus after deletion of the cassette is shown in Figure 1E. The coding sequence and encoded amino acid sequence of the resulting humanized Cxcl13 gene are set forth in SEQ ID NO:7 and SEQ ID NO:8, respectively. An alignment of human CXCL13 (SEQ ID NO: 2), mouse Cxcl13 (SEQ ID NO: 4), and humanized Cxcl13 (SEQ ID NO: 8) protein sequences is provided in Figure 1F. [Table 2-1] [Table 2-2]

[0103] Specifically targeted ES cells were used as donor ES cells and microinjected into pre-morula (8-cell) stage mouse embryos using the VELOCIMOUSE® method (see, e.g., US 7,576,259, US 7,659,442, US 7,294,754, and US 2008-0078000A1, all of which are incorporated herein by reference). Mouse embryos containing donor ES cells were incubated in vitro and then implanted into surrogate mothers to generate F0 mice entirely derived from donor ES cells. Mice carrying the humanized Cxcl13 gene were identified by genotyping using the MOA assay described above. Mice heterozygous for the humanized Cxcl13 gene were bred to homozygosity.

[0104] To determine whether mice homozygous for CXCL13 humanization expressed the humanized protein, humanized or control mice (mice expressing mouse CXCL13 protein) were tested, all on a non-engrafting hSIRP-alpha Rag2- / - IL-2RG- / - background. Mice derived from two different clones of humanized CXCL13 ES cells (designated clone 1 and clone 2) were tested. Mice were euthanized, and blood was collected via cardiac puncture. Serum was prepared, and human CXCL13 levels in serum were assessed using the Human CXCL13 Quantikine ELISA (R&D systems; catalog number DCX130) according to the manufacturer's instructions.

[0105] Mice heterozygous for the Cxcl13 humanization described above were found to express mature human CXCL13 in serum (Fig. 2).

[0106] Example 2. Humanized Cxcl13 mice exhibited enhanced human chronic lymphocytic leukemia cell engraftment. material and method Mice - NSG mice were purchased from Jackson Labs. hu / hu Rag2 - / - IL2Rg - / - and mice containing humanized BAFF, APRIL, IL-6 (SRG-BA6), and SIRPα hu / hu Rag2 - / - IL2Rg - / -Mice containing humanized BAFF, APRIL, IL-6, and CXCL13 (SRG-BA6-13) were generated at Regeneron using a combination of sequential targeting and breeding of embryonic stem cells. The humanization of the mouse Sirpα, Baff, APRIL, and IL-6 genes in these mice is described in WO2015 / 042557A1 (Regeneron Pharmaceuticals Inc.), WO2015 / 077071A1 (Regeneron Pharmaceuticals Inc.), WO2015 / 077072 (Regeneron Pharmaceuticals Inc.), and WO2013 / 063556A1 (Regeneron Pharmaceuticals Inc.), respectively (all of which are incorporated herein by reference). Mice were between 6 and 16 weeks old and sublethally irradiated (2 Gy) when xenotransplantation was performed.

[0107] Patient material—Mononuclear cells from fresh peripheral blood of patients with chronic lymphocytic leukemia (CLL) were isolated by gradient centrifugation and then used directly or cryopreserved. Cells were labeled with TraceVilot or CFSC (Invitrogen) according to the manufacturer's protocol and injected intravenously into mice. 5 × 10 7 ~1×10 8 The cells were injected into each mouse.

[0108] Flow cytometry—Mice were bled retroorbitally 2 weeks after xenotransplantation. Red blood cells were lysed. Mononuclear cells were suspended in PBS with 2% fetal bovine serum, stained with the antibodies listed below, mixed with CountBright absolute cell counting beads (Invitrogen), and subjected to flow cytometry. The following monoclonal antibodies (mAbs) from Biolegend or eBioscience were used: anti-mCD45 (30F11), anti-Ter119, anti-hCD45 (HI30), anti-hCD3 (UCHT1), anti-hCD19 (HIB19), and anti-hCD5 (L17F12). Antibodies were directly coupled to APC, APCCy7, Alexa Fluor 700, BV-605, or BV-711. Data were acquired on a BD Fortessa X20 instrument and analyzed using the FlowJo program.

[0109] Gating strategy—Singlet live cells were gated on the hCD45+mCD45- population. CLL cells were further gated as hCD19+hCD5+hCD3-. Proliferating CLL cells were further gated as either TraceViolet-low or CFSE-low.

[0110] result The engraftment of 12 CLL patient samples was compared between NSG and SRG-BA6 mice or between NSG and SRG-BA6-13 mice. Two to three mice from each strain were xenotransplanted with the same patient sample. Two weeks after xenotransplantation, blood samples were collected from the mice to assess CLL engraftment. No clear differences in CLL cell frequency (hCD19+hCD5+hCD3-) or their proliferation status (TraceViolet-low or CFSE-low) were observed between the NSG and SRG-BA6 strains. In contrast, proliferation (four out of five patient samples) and CLL cell number (three out of three patient samples) were significantly increased in SRG-BA6-13 mice compared with NSG mice (Figure 3). The results indicate that humanization of the endogenous Cxcl13 gene enhanced the engraftment of CLL patient samples in immunodeficient mice. The present invention provides, for example, the following items. (Item 1) A genetically modified rodent animal having in its genome a humanized Cxcl13 gene comprising a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, wherein the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. (Item 2) 2. The genetically modified rodent of item 1, wherein the humanized Cxcl13 polypeptide comprises a mature protein sequence that is substantially identical to the mature protein sequence of the human CXCL13 protein. (Item 3) 3. The genetically modified rodent of item 1 or 2, wherein the human CXCL13 protein comprises the amino acid sequence of SEQ ID NO: 2. (Item 4) A genetically modified rodent according to any one of items 1 to 3, wherein the humanized Cxcl13 protein comprises a rodent signal peptide. (Item 5) 5. The genetically modified rodent of item 4, wherein the rodent signal peptide is the signal peptide of an endogenous rodent Cxcl13 protein. (Item 6) 2. The genetically modified rodent according to item 1, wherein the human CXCL13 nucleic acid sequence comprises exons 3 to 4 of the human CXCL13 gene. (Item 7) 2. The genetically modified rodent of item 1, wherein the human CXCL13 nucleic acid sequence comprises exon 3, exon 4, and the coding portion of exon 5 of the human CXCL13 gene. (Item 8) 8. The genetically modified rodent according to any one of items 1 to 7, wherein the human CXCL13 nucleic acid sequence comprises exon 3, exon 4, and exon 5 of the human CXCL13 gene. (Item 9) 9. A genetically modified rodent according to any one of items 1 to 8, wherein the rodent Cxcl13 nucleic acid sequence comprises exon 1 of the rodent Cxcl13 gene. (Item 10) 10. The genetically modified rodent of item 9, wherein the rodent Cxcl13 gene is an endogenous Cxcl13 gene. (Item 11) 2. A genetically modified rodent according to item 1, wherein the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene and exons 3 to 5 of the human CXCL13 gene. (Item 12) 12. A genetically modified rodent animal according to any one of items 1 to 11, wherein the humanized Cxcl13 gene is operably linked to a rodent Cxcl13 promoter. (Item 13) 13. A genetically modified rodent animal as described in item 12, wherein the rodent Cxcl13 promoter is an endogenous rodent Cxcl13 promoter of an endogenous rodent Cxcl13 locus. (Item 14) 13. A genetically modified rodent according to any one of items 1 to 12, wherein the humanized Cxcl13 gene is located at the endogenous rodent Cxcl13 locus. (Item 15) 15. A genetically modified rodent animal as described in item 14, wherein the humanized Cxcl13 gene is formed as a result of replacement of rodent Cxcl13 genomic DNA with the human CXCL13 nucleic acid at the endogenous rodent Cxcl13 locus. (Item 16) 15. The genetically modified rodent of item 14, wherein the humanized Cxcl13 gene is formed as a result of the replacement of rodent genomic DNA containing exons 2-3 and the coding portion of exon 4 of the rodent Cxcl13 gene with exons 3-5 of the human CXCL13 gene at the endogenous rodent Cxcl13 locus. (Item 17) 17. The genetically modified rodent of any one of items 1 to 16, wherein the rodent is homozygous for the humanized Cxcl13 gene. (Item 18) 18. The genetically modified rodent according to any one of items 1 to 17, further comprising in its genome a humanized Sirpα gene at the endogenous rodent Sirpα locus, a humanized Baff gene at the endogenous rodent Baff locus, a humanized April gene at the endogenous rodent April locus, a humanized IL-6 gene at the endogenous rodent IL-6 locus, or a combination thereof. (Item 19) 19. The genetically modified rodent according to any one of items 1 to 18, wherein the RAG2 gene and the IL-2RG gene are disrupted. (Item 20) 20. The genetically modified rodent according to any one of items 1 to 19, wherein the rodent is a mouse or a rat. (Item 21) An isolated rodent tissue or cell, the genome of which comprises a humanized Cxcl13 gene comprising a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, and the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. (Item 22) 22. The isolated rodent tissue or cell of item 21, wherein the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene and exons 3 to 5 of the human CXCL13 gene. (Item 23) 23. The isolated rodent tissue or cell of item 21 or 22, wherein the rodent cell is a rodent embryonic stem cell. (Item 24) 24. The isolated rodent tissue or cell of any one of items 21 to 23, wherein the rodent is a mouse or a rat. (Item 25) A rodent embryo comprising the rodent embryonic stem cell of item 23. (Item 26) 1. A method for producing a genetically modified rodent, comprising: modifying the rodent genome to include a humanized Cxcl13 gene, wherein the humanized Cxcl13 gene comprises a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence and encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein; and generating a rodent comprising said modified rodent genome. (Item 27) The modification is introducing a nucleic acid molecule comprising the human CXCL13 nucleic acid sequence into the genome of a rodent embryonic stem (ES) cell; Obtaining rodent ES cells in which the human CXCL13 nucleic acid sequence has been integrated into the endogenous Cxcl13 locus to replace rodent Cxcl13 genomic DNA, thereby forming the humanized Cxcl13 gene; and generating a rodent from the obtained rodent ES cells. (Item 28) 28. The method according to item 26 or 27, wherein the human CXCL13 nucleic acid sequence comprises exons 3 to 4 of the human CXCL13 gene. (Item 29) 28. The method of claim 26 or 27, wherein the human CXCL13 nucleic acid sequence encodes a polypeptide that is substantially identical to the mature protein sequence of the human CXCL13 protein. (Item 30) 30. The method of item 29, wherein the human CXCL13 nucleic acid sequence comprises exon 3, exon 4, and the coding portion of exon 5 of the human CXCL13 gene. (Item 31) 30. The method of item 29, wherein the human CXCL13 nucleic acid sequence comprises exons 3 to 5 of the human CXCL13 gene. (Item 32) 28. The method of claim 27, wherein the humanized Cxcl13 gene comprises exon 1 of the endogenous rodent Cxcl13 gene and exons 3 to 5 of the human CXCL13 gene and is operably linked to the endogenous rodent Cxcl13 promoter at the endogenous rodent Cxcl13 locus. (Item 33) 33. The method of any one of items 26 to 32, wherein the rodent is a mouse or a rat. (Item 34) A targeting nucleic acid construct comprising: a human CXCL13 nucleic acid to be integrated into a rodent Cxcl13 gene at the endogenous rodent Cxcl13 locus, flanked by 5' and 3' nucleotide sequences that are homologous to nucleotide sequences at the rodent Cxcl13 locus; integration of the human CXCL13 nucleic acid sequence into the rodent Cxcl13 gene results in replacement of rodent Cxcl13 genomic DNA with the human CXCL13 nucleic acid sequence, thereby forming a humanized Cxcl13 gene; A targeted nucleic acid construct, wherein the human CXCL13 nucleic acid sequence encodes a polypeptide that is substantially identical to the chemokine IL-8-like domain of the human CXCL13 protein. (Item 35) 35. The targeting nucleic acid construct of item 34, wherein the human CXCL13 nucleic acid sequence comprises exons 3 to 5 of the human CXCL13 gene. (Item 36) 36. The targeting nucleic acid of item 34 or 35, wherein the rodent is a mouse or a rat. (Item 37) 1. A method of testing a candidate agent for treating a disease, comprising: Introducing cells derived from a human subject suffering from the disease into the genetically modified rodent animal according to any one of items 1 to 20; contacting the rodent with a candidate agent; and analyzing whether the candidate agent is effective in reducing or eliminating said cells. (Item 38) 38. The method of claim 37, wherein the disease is cancer. (Item 39) 39. The method of claim 38, wherein the disease is leukemia. (Item 40) 40. The method of claim 38 or 39, wherein the candidate agent is an anti-cancer compound, optionally selected from a small molecule compound, a nucleic acid molecule, or an antibody. (Item 41) A rodent genome comprising a humanized Cxcl13 gene, wherein the humanized Cxcl13 gene comprises a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, and wherein the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is substantially identical to the chemokine IL-8-like domain of a human CXCL13 protein.

Claims

1. 1. A genetically modified rodent comprising in its genome a humanized Cxcl13 gene comprising a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is at least 95% identical to amino acids 30-91 of SEQ ID NO:2; the humanized Cxcl13 gene is located at the endogenous rodent Cxcl13 locus; A genetically modified rodent, wherein the rodent is a mouse or a rat.

2. A) the humanized Cxcl13 polypeptide comprises a mature protein sequence that is at least 95% identical to amino acids 23 to 109 of SEQ ID NO:2; B) the human CXCL13 protein comprises the amino acid sequence of SEQ ID NO: 2; C) the humanized Cxcl13 protein comprises a rodent signal peptide, optionally the rodent signal peptide is the signal peptide of an endogenous rodent Cxcl13 protein; D) the humanized Cxcl13 polypeptide comprises a mature protein sequence that is at least 95% identical to amino acids 23-109 of SEQ ID NO:2, and the humanized Cxcl13 protein comprises a rodent signal peptide, optionally the rodent signal peptide is the signal peptide of the endogenous rodent Cxcl13 protein; or E) the human CXCL13 protein comprises the amino acid sequence of SEQ ID NO:2, and the humanized Cxcl13 protein comprises a rodent signal peptide, optionally the rodent signal peptide is the signal peptide of the endogenous rodent Cxcl13 protein; The genetically modified rodent of claim 1.

3. A) the human CXCL13 nucleic acid sequence comprises exons 3 to 4 of the human CXCL13 gene; B) the human CXCL13 nucleic acid sequence comprises the coding portion of exon 3, exon 4, and exon 5 of the human CXCL13 gene; or C) the human CXCL13 nucleic acid sequence comprises exon 3, exon 4, and exon 5 of the human CXCL13 gene; The genetically modified rodent of claim 1.

4. 4. The genetically modified rodent of claim 1, wherein the rodent Cxcl13 nucleic acid sequence comprises exon 1 of the rodent Cxcl13 gene, and optionally the rodent Cxcl13 gene is an endogenous Cxcl13 gene.

5. 2. The genetically modified rodent of claim 1, wherein the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene and exons 3-5 of the human CXCL13 gene.

6. 6. The genetically modified rodent of any one of claims 1 to 5, wherein the humanized Cxcl13 gene is operably linked to a rodent Cxcl13 promoter, and optionally the rodent Cxcl13 promoter is an endogenous rodent Cxcl13 promoter of an endogenous rodent Cxcl13 locus.

7. 2. The genetically modified rodent of claim 1, wherein the humanized Cxcl13 gene is formed as a result of replacement of rodent Cxcl13 genomic DNA with the human CXCL13 nucleic acid at the endogenous rodent Cxcl13 locus, and optionally, the humanized Cxcl13 gene is formed as a result of replacement of rodent genomic DNA comprising exons 2-3 and a coding portion of exon 4 of the rodent Cxcl13 gene with exons 3-5 of the human CXCL13 gene at the endogenous rodent Cxcl13 locus.

8. A genetically modified rodent according to any one of claims 1 to 7, wherein the rodent is homozygous for the humanized Cxcl13 gene.

9. A) the genome further comprises a humanized Sirpα gene at the endogenous rodent Sirpα locus, a humanized Baff gene at the endogenous rodent Baff locus, a humanized April gene at the endogenous rodent April locus, a humanized IL-6 gene at the endogenous rodent IL-6 locus, or a combination thereof; and / or B) The RAG2 gene and the IL-2RG gene are disrupted; A genetically modified rodent according to any one of claims 1 to 8.

10. An isolated rodent tissue or cell comprising a humanized Cxcl13 gene, the genome of which comprises a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is at least 95% identical to amino acids 30-91 of SEQ ID NO:2; the humanized Cxcl13 gene is located at the endogenous rodent Cxcl13 locus; The isolated rodent tissue or cell, wherein the rodent is a mouse or a rat.

11. The isolated rodent tissue or cell of claim 10, wherein the humanized Cxcl13 gene comprises exon 1 of the rodent Cxcl13 gene and exons 3-5 of the human CXCL13 gene.

12. 12. The isolated rodent cell of claim 10 or 11, wherein the rodent cell is a rodent embryonic stem cell.

13. A rodent embryo comprising the rodent embryonic stem cell of claim 12.

14. 1. A method for producing a genetically modified rodent, comprising: Modifying a rodent genome to include a humanized Cxcl13 gene, the humanized Cxcl13 gene comprises a rodent Cxcl13 nucleic acid sequence and a human CXCL13 nucleic acid sequence, and the humanized Cxcl13 gene encodes a humanized Cxcl13 polypeptide comprising a chemokine IL-8-like domain that is at least 95% identical to amino acids 30-91 of SEQ ID NO:2; To modify, Including, the humanized Cxcl13 gene is introduced into the endogenous rodent Cxcl13 locus; The method, wherein the rodent is a mouse or a rat.

15. The modification is introducing a nucleic acid molecule comprising the human CXCL13 nucleic acid sequence into the genome of a rodent embryonic stem (ES) cell; Obtaining a rodent ES cell in which the human CXCL13 nucleic acid sequence has been integrated into the endogenous Cxcl13 locus to replace rodent Cxcl13 genomic DNA, thereby forming the humanized Cxcl13 gene; and generating a rodent from the obtained rodent ES cells.

16. The method of claim 14 or 15, wherein the human CXCL13 nucleic acid sequence encodes a polypeptide that is at least 95% identical to amino acids 23 to 109 of SEQ ID NO:

2.

17. The method of claim 14 or 15, wherein the human CXCL13 nucleic acid sequence comprises (i) exons 3 to 4 of the human CXCL13 gene, (ii) the coding portions of exons 3, 4, and 5 of the human CXCL13 gene, or (iii) exons 3 to 5 of the human CXCL13 gene.

18. 16. The method of claim 14 or 15, wherein the humanized Cxcl13 gene comprises exon 1 of the endogenous rodent Cxcl13 gene and exons 3 to 5 of the human CXCL13 gene and is operably linked to the endogenous rodent Cxcl13 promoter at the endogenous rodent Cxcl13 locus.

19. A targeting nucleic acid construct comprising: (i) a human CXCL13 nucleic acid sequence encoding a polypeptide comprising a chemokine IL-8-like domain that is at least 95% identical to amino acids 30-91 of SEQ ID NO:2; (ii) a 5' rodent nucleotide sequence that is homologous to a nucleotide sequence adjacent to a rodent nucleotide sequence at the endogenous rodent Cxcl13 locus, the 5' rodent nucleotide sequence being 5' to the human CXCL13 nucleic acid sequence; and (iii) a 3′ rodent nucleotide sequence that is homologous to a nucleotide sequence adjacent to the rodent nucleotide sequence at the endogenous rodent Cxcl13 locus, wherein the 5′ rodent nucleotide sequence is 3′ to the human CXCL13 nucleic acid sequence. wherein the targeting nucleic acid construct is for replacing the rodent nucleotide sequence at the endogenous rodent Cxcl13 locus with the human CXCL13 nucleic acid sequence, and the rodent is a mouse or a rat.

20. 20. The targeting nucleic acid construct of claim 19, wherein the human CXCL13 nucleic acid sequence comprises exons 3 to 5 of the human CXCL13 gene.

21. 1. A method of testing a candidate agent for treating a disease, comprising: A) introducing cells derived from a human subject suffering from said disease into a genetically modified rodent animal according to any one of claims 1 to 6; B) contacting the rodent with a candidate agent; C) analyzing to determine whether the candidate agent is effective in reducing or eliminating said cells.

22. 22. The method of claim 21, wherein the disease is cancer, optionally wherein the disease is leukemia.

23. 23. The method of claim 22, wherein the candidate agent is an anti-cancer compound, optionally selected from a small molecule compound, a nucleic acid molecule, or an antibody.

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