A research group led by Visiting Associate Professor Yoshie Kametani from the School of Medicine at Tokai University announced that they have developed a next-generation "humanized immune mouse model" that reproduces individual human immune responses. The researchers developed mice that continuously produce IL-4 (interleukin-4) in their bodies. The mice successfully maintained human B cells for extended periods and succeeded in producing highly functional human IgG antibodies on their surface. The group also confirmed that structures resembling human lymphoid tissue were formed in the mouse body (spleen). The model is expected to be used for evaluating antibody drug candidates and cancer vaccines. The results were published in Frontiers in Immunology on November 26.
B. Specificity of the antibodies were evaluated. Antibodies that selectively reacted with the immunizing antigens were obtained in the immunized mice.
Provided by Tokai University
As treatments utilizing human immune responses, such as immune checkpoint inhibitors and cancer vaccines, become more widespread, there is a growing need for preclinical models that can more accurately reproduce individual human antibody responses during the pre-treatment stage.
Meanwhile, conventional immunodeficient mice had short survival periods for human B cells, making it difficult to evaluate the induction of antibody-specific IgG production.
Human B cells are lymphocytes that recognize pathogens and protect the body by producing antibodies, and they exist at levels of approximately 5 to 10 percent in the blood. Specific IgG is a type of immunoglobulin produced in response to specific antigens, and is classified into five types (IgM, IgD, IgG, IgA, and IgE). It is primarily IgG that is used to eliminate pathogenic bacteria and for immunotherapy in clinical settings, making it the most useful.
In this study, the research group transplanted human peripheral blood mononuclear cells (PBMCs) into transgenic NOG mice that systemically express human IL-4 and examined the reconstitution of individual human immune systems. IL-4 is produced by activated T cells, mast cells, and macrophages, plays a role in information transmission, and regulates antibody production.
Until now, it has been known that humanized mice transplanted with PBMCs using immune cells from peripheral blood developed GVHD and died because only human T cells rapidly activated and proliferated in the mouse body.
In contrast, the humanized mice developed in this study enabled the survival and proliferation of human B cells through limited plasma IL-4 concentrations ranging from 100 pg/ml to 1000 pg/ml, significantly delayed GVHD, and promoted class switching to IgG. Immunoglobulins are initially produced as IgM, but upon stimulation, they undergo class switching that converts the constant region to IgG or IgA without changing the variable region.
The researchers also confirmed high engraftment rates of B cells at four weeks post-transplantation. It was found that following transplantation, B cell clones producing IgG increased and that the subclass composition of IgG followed a similar course to that of humans over time from immediately after transplantation.
Numerous amino acid substitutions were observed in the variable regions of the IgG clones produced, and it was confirmed that somatic hypermutation (SHM), which is important for antigen recognition, had occurred.
Multiple human IgG clones that react to HER2 (human epidermal growth factor receptor 2)-derived peptides (CH401MAP and BAL6MAP) were obtained from individuals immunized with these peptides.
Furthermore, the group confirmed that human B cell hybridomas for mass-producing monoclonal antibodies could be generated.
They also observed the formation of tertiary lymphoid structure (TLS)-like structures composed of human B cells and T cells in the spleen. TLS is thought to function as a command center for immunity on a local level. Although the structure of this TLS was not complete, it was considered to have the potential to support immune responses and limited immune maturation.
By using the developed mice, it is possible to evaluate what types of antibodies the B cells of donors such as patients can produce.
Going forward, the researchers will proceed with elucidating environmental factors that enable long-term survival of human B cells and will also work on developing methods for more efficiently producing hybridomas that generate highly specific human antibodies.
Kametani commented: "Although NOG-hIL-4-Tg was not our initial focus among humanized mice, we accumulated research on it as a mouse capable of reconstituting individual acquired immune systems and were finally able to publish a convincing paper. Going forward, we plan to proceed with improvements to further enhance antibody production capacity."
Journal Information
Publication: Frontiers in Immunology
Title: Human interleukin-4-dependent facilitation of human IgG production in PBL-NOG-hIL-4-Tg mice
DOI: 10.3389/fimmu.2025.1670682
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.