title: Development of human B cells and antibodies following human hematopoietic stem cell transplantation to Rag2(-/-)γc(-/-) mice.
abstract: Humanized mice represent a valuable model system to study the development and functionality of the human immune system. In the RAG-hu mouse model highly immunodeficient Rag2(-/-)γc(-/-) mice are transplanted with human CD34(+) hematopoietic stem cells, resulting in human hematopoiesis and a predominant production of B and T lymphocytes. Human adaptive immune responses have been detected towards a variety of antigens in humanized mice but both cellular and humoral immune responses tend to be weak and sporadically detected. The underlying mechanisms for inconsistent responses are poorly understood. Here, we analyzed the kinetics of human B cell development and antibody production in RAG-hu mice to better understand the lack of effective antibody responses. We found that T cell levels in blood did not significantly change from 8 to 28 weeks post-engraftment, while B cells reached a peak at 14 weeks. Concentrations of 3 antibody classes (IgM, IgG, IgA) were found to be at levels about 0.1% or less of normal human levels, but human antibodies were still detected up to 32 weeks after engraftment. Human IgM was detected in 92.5% of animals while IgG and IgA were detected in about half of animals. We performed flow cytometric analysis of human B cells in bone marrow, spleen, and blood to examine the presence of precursor B cells, immature B cells, naïve B cells, and plasma B cells. We detected high levels of surface IgM(+) B cells (immature and naïve B cells) and low levels of plasma B cells in these organs, suggesting that B cells do not mature properly in this model. Low levels of human T cells in the spleen were observed, and we suggest that the lack of T cell help may explain poor B cell development and antibody responses. We conclude that human B cells that develop in humanized mice do not receive the signals necessary to undergo class-switching or to secrete antibody effectively, and we discuss strategies to potentially overcome these barriers.
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Anne
authors.initials: A
authors.lastname: Tanner
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Hallam
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Stanton J
authors.initials: SJ
authors.lastname: Nielsen
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA.
authors.forename: German I
authors.initials: GI
authors.lastname: Cuadra
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA. Electronic address: brad.berges@gmail.com.
authors.forename: Bradford K
authors.initials: BK
authors.lastname: Berges
mesh_terms: D000818:Animals; D000917:Antibody Formation; D001402:B-Lymphocytes / Q000502:physiology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D002678:Chimera; D004268:DNA-Binding Proteins / Q000235:genetics; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D017578:Immunoglobulin Class Switching; D007075:Immunoglobulin M / Q000097:blood; D007142:Immunoglobulin gamma-Chains / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D010950:Plasma Cells / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D007075:Immunoglobulin M; D007142:Immunoglobulin gamma-Chains; C499308:Rag2 protein, mouse
keywords: Adaptive immunity; B cells; Human antibodies; Human immunity; Humanized mice; RAG-hu mice