Abstract:

Memory T-cells have been identified as a significant factor in the resistance to tolerance induction by agents targeting T-cell co-stimulation. The impact of memory B cells and preformed antibody in tolerance induction has yet to be fully elucidated. We developed a heart transplant model that specifically generates allospecific memory B-cells and not memory T cells. 3.83 BCR (BALB/c) knock-in mice harboring 3.83 B-cells with dual-specificity for H-2Kk and H-2Kb were used as recipients of C3H hearts. To test whether memory 3.83 B-cells could prevent tolerance induction, C3H-primed-3.83 recipients (60 days post-heart transplant) received a 2 nd heart and anti-CD154 (MR1). Second C57BL/6 (B6) hearts were acutely rejected (MST=12d). To confirm the importance of memory B cells in facilitating anti-CD154-resistant rejection, we transferred memory B-cells from C3H-presensitized 3.83 mice into na?ve BALB/c (B/c) treated with anti-CD154 and rejection occurred in only half of recipients. Surprisingly, transfer of low doses of serum from C3H-presensitized 3-83 recipients could not overcome anti-CD154 therapy; however, transfer of low dose serum alloantibodies (alloAbs) with memory 3-83 B cells elicited rejection in 100% of B/c recipients treated with anti-CD154. To investigate the ability of alloantibodies to prevent tolerance induction, independently of memory B cells, a single dose of alloAbs was injected into B6 recipients of B/c skin grafts post-transplantation. Long-term acceptance was induced with anti-CD154 plus donor specific transfusion (DST). The impact of alloAbs was investigated using anti-Kd (HB159; mouse IgG2a) mAbs, administered at the time of transplantation. Anti-Kd mAbs prevented anti-CD154-mediated graft acceptance in a T cell dependent manner (MST=12d). We hypothesize that alloAbs can facilitate cellular rejection by enhancing T cell activation. We used CFSE-labeled T cells from three different TCR-Tg mice to measure T cell responses in B6 recipients of OVA-B/c skin ? anti-CD154/DST ? anti-Kd mAbs to assess the ability of alloAbs to facilitate the activation of alloreactive T cells via the indirect pathway. Anti-Kd mAbs enhanced proliferation of all three TCR-Tg T cells in anti-CD154/DST-treated recipients compared to anti-CD154/DST alone-treated recipients. In conclusion, memory B cells and alloAbs prevent transplantation tolerance by facilitating the activation of alloreactive T cells in a CD154-independent manner.