• CD19 is a B-cell surface-specific antigen belonging to the immunoglobulin super family. It is a key component of the B-cell receptor (BCR) signaling complex, regulating B-cell activation, proliferation, and differentiation. CD19 plays an important role in B-cell development and immune responses and is widely expressed on the surface of normal B cells and most B-cell malignant tumor cells. BCMA (B-cell maturation antigen) is a member of the tumor necrosis factor receptor superfamily, primarily expressed on the surface of plasma cells and mature B cells. It is a receptor for two important cytokines, BAFF (B-cell activating factor) and APRIL (a proliferation-inducing ligand), and regulates B-cell survival, proliferation, and antibody production. BCMA is highly expressed in multiple myeloma (MM) and other plasma cell disorders, making it a significant marker for these diseases.
• B-hCD19/hBCMA mice were obtained by crossing B-hCD19 mice (strain 112657) with B-hBCMA mice (strain 110899). In B-hCD19/hBCMA mice, human CD19 and BCMA are expressed, while mouse Cd19 and Bcma are knocked out. Human CD19 protein can be detected on B cells from the spleen and blood of homozygous B-hCD19/hBCMA mice, but not in wild-type mice. Humanization of CD19 and BCMA does not change the overall frequency or distribution of immune cell types in the spleen, blood, and lymph nodes.
• This product is used for the pharmacological and safety evaluation of therapeutic drugs, such as anti-CD19 or anti-BCMA antibodies, bispecific antibodies, CAR-T cell therapies, and other drugs. Disease areas include oncology and autoimmune diseases.

Gene targeting strategy for B-hCD19/hBCMA mice.

• The exon 1 and part of exon 2 which encode the extracellular region of mouse Bcma gene are replaced by human BCMA exon 1 and part of exon 2 in B-hCD19/hBCMA mice. The genomic region of mouse Bcma gene that encodes part of extracellular region, transmembrane domain and cytoplasmic portion is retained. The promoter, 5’UTR and 3’UTR region of the mouse gene are also retained. The chimeric BCMA expression is driven by endogenous mouse Bcma promoter, while mouse Bcma gene transcription and translation will be disrupted.
• A chimeric CDS that encodes human CD19 extracellular domain, mouse CD19 transmembrane and cytoplasmic domain, followed by mouse 3’UTR-STOP is inserted right after mouse Cd19 exon 2. The chimeric CD19 protein expression is be driven by endogenous mouse Cd19 promoter, while mouse Cd19 gene transcription and translation will be disrupted.

Strain specific analysis of CD19 and BCMA mRNA expression in wild-type C57BL/6 mice and homozygous B-hCD19/hBCMA mice by RT-PCR. Spleen RNA were isolated from wild-type C57BL/6 mice (+/+) and homozygous B-hCD19/hBCMA mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse and human primers. Mouse Cd19 and Bcma mRNA were detectable only in wild-type mice. Human CD19 and BCMA mRNA were detectable only in B-hCD19/hBCMA mice but not in wild-type mice.

Strain specific CD19 expression analysis in wild-type C57BL/6 mice and homozygous B-hCD19/hBCMA mice by flow cytometry. Splenocytes were collected from wild-type C57BL/6 mice and homozygous B-hCD19/hBCMA mice (female, 7-week-old). Protein expression was analyzed with anti-mouse CD19 antibody (Biolegend, 115507) and anti-human CD19 antibody (Biolegend, 302234) by flow cytometry. Mouse CD19 was only detectable in wild-type C57BL/6 mice. Human CD19 was exclusively detectable in B cells of homozygous B-hCD19/hBCMA mice, but not in wild-type C57BL/6 mice.

Frequency of leukocyte subpopulations in spleen by flow cytometry. Splenocytes were isolated from wild-type C57BL/6 mice (female, n=3, 7-week-old) and homozygous B-hCD19/hBCMA mice (female, n=3, 7-week-old). A. Flow cytometry analysis of the splenocytes was performed to assess the frequency of leukocyte subpopulations. B. Frequency of T cell subpopulations. Percentages of T cells, B cells, NK cells, dendritic cells (DCs), monocytes, macrophages, CD4+ T cells, CD8+ T cells and Tregs in B-hCD19/hBCMA mice were similar to those in B-hCD19/hBCMA mice. Values are expressed as mean ± SEM.

Frequency of leukocyte subpopulations in blood by flow cytometry. Blood were isolated from wild-type C57BL/6 mice (female, n=3, 7-week-old) and homozygous B-hCD19/hBCMA mice (female, n=3, 7-week-old). A. Flow cytometry analysis of the blood was performed to assess the frequency of leukocyte subpopulations. B. Frequency of T cell subpopulations. Percentages of T cells, B cells, NK cells, dendritic cells (DCs), monocytes, macrophages, CD4+ T cells, CD8+ T cells and Tregs in B-hCD19/hBCMA mice were similar to those in B-hCD19/hBCMA mice. Values are expressed as mean ± SEM.

Frequency of leukocyte subpopulations in lymph nodes by flow cytometry. Lymph nodes cells were isolated from wild-type C57BL/6 mice (female, n=3, 7-week-old) and homozygous B-hCD19/hBCMA mice (female, n=3, 7-week-old). A. Flow cytometry analysis of the Lymph nodes cells was performed to assess the frequency of leukocyte subpopulations. B. Frequency of T cell subpopulations. Percentages of T cells, B cells, NK cells, CD4+ T cells, CD8+ T cells and Tregs in B-hCD19/hBCMA mice were similar to those in B-hCD19/hBCMA mice. Values are expressed as mean ± SEM.