(116) - Cardiac Allograft Tolerance Induction via Anti-LFA-1 Monotherapy Is Dependent on an Indirect CD8 T-Cell

Abstract

Requirements for tolerance induction appear to be agent specific. Having previously demonstrated that NK and NKT cells are not required, in this study, we sought to investigate some further requirements for tolerance induction to cardiac allografts utilizing anti-LFA-1 mAb monotherapy. BALB/c or C3H hearts were transplanted into B6, B6rag-/- or beta2M mice and were untreated or treated with anti-LFA-1 or control rat IgG or anti-CD8 (at time of transplant or at POD 28) or anti-CD40L or adoptively transferred with tolerized or naive splenocytes. Dominant tolerance (BALB/c-B6rag-/- + tolerant and naïve splenocytes) and linked suppression (BALB/c/C3H F1-B6rag-/- + tolerant splenocytes) experiments were also performed. To investigate a possible role for the direct pathway of antigen presentation, beta2M hearts (MHC class I deficient) were transplanted into BALB/c mice +/- anti-LFA-1 mAb. Untreated or IgG treated B6 mice rejected their BALB/c grafts acutely while anti-LFA-1 treated B6 recipients did not (96.6 ± 16.5 days). Recipients with graft survival >100 days demonstrated transferable donor specific tolerance with BALB/c hearts exposed to tolerized splenocytes surviving >100 days in B6rag-/- recipients, whereas C3H hearts rejected acutely. Transferred naive cells also caused acute rejection. Unlike other tolerizing therapies no dominant tolerance or linked suppression was observed with both groups rejecting their grafts. Of major importance removal of host (indirect pathway) MHC class I, but not donor (direct pathway) MHC class I, prevented tolerance induction. Surprisingly when CD8 T cells were depleted at the time of transplant, grafts were acutely rejected, but when depleted 4 weeks post-transplant, grafts survived indefinitely demonstrating that CD8 T cells contribute to tolerance induction but not the maintenance of tolerance. Additionally, when recipients treated with anti-CD40L alone were compared with those treated with anti-CD40L + anti-CD8 mAb there was no difference between the groups indicating the requirement for CD8 T cells is therapy specific. anti-LFA-1 mAb monotherapy produces potent tolerance-induction in fully vascularized cardiac allografts. Host MHC class I expression is necessary, and more importantly, CD8 T cells are critical for the induction of, but not the maintenance of that tolerance.