*Purpose: We previously reported that B cells in recipients made tolerant to fully mismatched heart allografts by anti-CD154+donor spleen cells (CoB) become dysfunctional in their ability to enter into a germinal center (GC) response and fail to develop into antibody-secreting cells (ASC). In addition, they acquire the ability to suppress naïve B cells in a donor-specific manner, by preventing their differentiation into GC B cells and ASCs. In contrast to naïve B cells, memory B cells differentiate directly into ASCs upon alloantigen reencounter, without entering into a GC reaction. In this study, we tested whether tolerant B cells could inhibit recall responses by donor-specific memory B cells.

*Methods: On post-operative day 30, tolerant B cells were enriched from B/6 recipients of B/c hearts treated with CoB, while memory B cells were from congenic B/6 mice sensitized with B/c skin grafts. Enriched tolerant and memory B cells, either alone or at a 1:1 ratio, were adoptively transferred to a secondary host (MD4 mice) and challenged with B/c-donor spleen cells (DSC). Donor-specific IgG was quantified by flow cytometry using B/c T cells as targets.

*Results: In this adoptive transfer model + B/c DSC sensitization, memory B cells produced ~5-fold more donor-specific IgG compared to naïve B cells, while tolerant B cells failed to produce DSA. When memory and tolerant B cells were co-transferred at a 1:1 ratio, tolerant B cells retained their dysfunction and did not produce DSA, even in the presence of memory B cells. Remarkably, DSA production from memory B cells was suppressed by tolerant B cells.

*Conclusions: Transplantation tolerance induced by CoB induces a cell-intrinsic dysfunction state that prevents B cell differentiation into ASCs, and these tolerant B cells not only inhibit naïve B cell differentiation into GC B cells but also the differentiation of memory donor-specific B cells directly into ASCs. Currently, we are conducting transcriptional analyses to test whether suppression is mediated by the induction of regulatory T cells or direct B:B cell interaction.

« Back to 2022 American Transplant Congress