Antibody-secreting plasma cells with unique CD5+IgG+CD21lo phenotype developed in humanized NOG mice

Abstract

The developmental process of human antibody (Ab)-secreting B cells in humanized mice is not fully defined. To examine the characteristics of class-switched and Absecreting B cells in humanized mice, we analyzed NOD/Shi-scid, common γc-null mice reconstituted with cord blood-derived hematopoietic stem cells (CB-NOG). Most of the CD138-positive plasmablasts (PBs)/plasma cells (PCs) in the NOG spleen maintained CD5 expression. Moreover, IgG-bearing B cells, including PBs and memory cells, predominantly had a CD21-CD24hiCD5+ phenotype. We examined the expression of CD21, CD24 and CD5 on B cells developed in CB-NOG mice. We observed three types of B cells (CD24high CD21-; T1, CD24low/CD21-; T2, CD24-CD21 + ; T3) within CB-NOG CD5+ cells, which are similar to transitional B cells. However, the surface marker expression was different from normal transitional B cells. First, CD21 expression was significantly lower than in human peripheral blood and CB-derived mature B cells. Second, the expression of CD5 increased according to the developmental stage. The splenocytes were sorted according to the transitional subsets and examined for IL-10 expression. The CD21-CD24hiCD5+ fraction had the highest IL-10 expression among the CD5 + cells, suggesting the involvement of regulatory B cells. The same fractions were cultured in the presence of CpG and IgM. These stimulated B cells secreted a low level of IgM and IgG Abs to CpG and IgM stimulation in vitro and maintained a CD5+CD21low phenotype. These results demonstrate that IgG-bearing B cells with a CD21-CD24hiCD5+ irregular phenotype are developed in humanized NOG mice and have become the source of antibodies in CB-NOG mice. (250 words).

Humanized Mice as an Effective Evaluation System for Peptide Vaccines and Immune Checkpoint Inhibitors

“…We reconstructed human immunity in NOG mice transplanted with HSC and immunized with CH401MAP, a specific HER2 peptide antigen for patients with breast cancer, and keyhole limpet hemocyanin (KLH), or toxic shock syndrome toxin-1 (TSST-1), with Freund's complete adjuvant and measured the specific antibody titer by ELISA. As a result, although antigen-specific IgM and nonspecific IgG were detected in the sera, antigen-specific IgG was not detected in mice (Table 1) [114][115][116]. These mice did not develop a germinal center, which has a structure composed of T, B, and follicular DCs and plays a crucial role in highly specific crass-switched IgG antibody production.…”