Cellular Therapy with Donor Mesenchymal Stem Cells Combined with Co-Stimulation Blockade Prolongs Solid Organ Allograft Survival.

Abstract

<h3>Introduction</h3> Co-stimulation blockade (CoB) has emerged as a promising immunosuppression strategy and potential alternative to calcineurin inhibitors in solid organ transplantation. Despite recent advancements, CoB based regimens are hampered by increased rates of acute cellular rejection. Bone marrow derived mesenchymal stem cells (BM-MSCs) offer a clinically relevant cellular therapy to suppress T cell alloreactivity and prolong allograft survival. <h3>Objectives</h3> Here we studied the effects of combined donor BM-MSCs and CoB on allograft survival in both murine and non-human primate (NHP) models of transplantation. <h3>Methods</h3> BM-MSCs were cultured and serially passaged in an alpha Minimum Essential Medium based media and subsequently characterized by flow cytometry. A mouse model of MHC mismatched skin transplantation (Balb/C C57BL/6) was used to assess the effect of donor splenocytes vs. BM-MSCs on allograft survival. Next, we investigated whether donor BM-MSCs could prolong renal allograft survival in a fully MHC mismatched NHP model. Mixed lymphocyte reactions (MLRs) were also performed to assess the impact of NHP BM-MSCs on T cell responses <i>in vitro</i>. <h3>Results</h3> Balb/C BM-MSCs administered intravenously on days 1,3, and 5 post-transplant (10⁵ cells per infusion) significantly prolonged skin graft survival compared to identical administration of Balb/C splenocytes in the setting of CoB treatment (CTLA-4Ig + anti-CD154) (MST 40 days vs. 21 days, p = 0.04*). In NHP, BM-MSCs were characterized by expression of CD3-/CD11b-/CD16-/CD20-/CD34-/HLA-DR-/CD44+/CD73+/CD90+/CD105+. Repeated infusions of donor BM-MSCs (2 × 10⁶ cells/kg per infusion) combined with CoB (anti-CD28 + anti-CD154) (n=4) prolonged renal allograft survival compared to CoB alone (n = 3) (MST 228.5 days vs. 41 days, p = 0.09). <i>In vitro</i>, NHP BM-MSCs suppressed allo-stimulated T cell proliferation and cytokine effector function in a contact independent fashion. <h3>Conclusion</h3> Donor BM-MSCs prolong allograft survival in both murine and NHP models of transplantation when combined with CoB treatment. These data suggest BM-MSCs are a promising cellular therapy to suppress co-stimulation resistant T cell alloreactivity and prevent cellular rejection in clinical solid organ transplantation.