Anti-TIM-4 mediates long-term engraftment of islet allografts by promoting IL-10 expression by TIM-1+ Bregs and inhibiting IFNγ expression by proinflammatory “Be1” B cells (IRC3P.464)

Abstract We previously defined TIM-1 as an inclusive marker for IL-10+ regulatory B cells (Bregs). Moreover, α-TIM-1 mAb prolongs islet allograft survival (GS) through induction of TIM-1+ Bregs. We recently noted that TIM-4, a TIM-1 ligand, identifies B cells enriched for IFNγ (Be1). We therefore hypothesized that TIM-4 blockade should also prolong GS and that this may involve B cells. In fact, α-TIM-4 (RMT4-53) treatment resulted in long-term GS in BALB/c recipients of B6 islets (MST >100d). Moreover, α-TIM-4 increases Th2 cytokines (IL-4, IL-10) and Foxp3+Tregs, while reducing both Th1 cytokines (IFNγ) and CD4 proliferation. However, these α-TIM-4-mediated changes and long-term GS were B cell dependent, and did not occur in either B cell deficient (JHD) or depleted (α-CD20) recipients. To address whether α-TIM-4 directly targets (TIM-4+) Be1 cells, we showed that adoptive transfer of WT, but not TIM-4-/- B cells, into μMT recipients, reconstitutes long-term GS mediated by α-TIM-4. We also found that α-TIM-4 inhibits IFNγ expression by TIM-4+ B cells by 40%. Bregs were also required for α-TIM-4 induced transplant tolerance. Transfer of B cells from TIM-1Δmucin (mucin domain deletion) mice, which exhibit a defect in Bregs, is unable to prolong GS in B deficient mice. In wt mice, α-TIM-4 increases TIM-1+ IL-10+ Bregs by ~100%. Taken together, our data reveal that targeting TIM-4 enhances IL-10 expressing Bregs and also reduces inflammatory Be1 B cells to promote allograft tolerance.