Background
Reconstructive transplantation is a clinical reality. Graft sustenance requires life-long immunosuppression with coincident adverse effects. Therapies incorporating adipose tissue- and bone marrow-derived mesenchymal stem cells (AD-MSC/BM-MSCs) have shown promising effects in experimental autoimmune diseases, solid organ transplantation and vascularized composite allotransplantation (VCA). Clinical translation of these therapies must consider collateral effects of depletional conditioning protocols. For the first time, we compare AD-MSCs versus BM-MSCs in VCA.
Methods
Lewis (LEW) rats received full-mismatched Brown-Norway (BN) limbs (Day 0). AD-MSCs/BM-MSCs (CD29+CD73+ CD90+CD45-) were tested for suppressive function in mixed lymphocyte reaction assays. Donor (BN) lymphocyte stimulators and recipient (LEW) responders were used, along with peripheral blood mononuclear cells. First, AD-MSC/BM-MSCs were compared for immunomodulatory efficacy in-vivo using different dosages (1x10^6 or 5x10^6). Different timing and frequency of AD-MSC administration was then tested (single/repetitive, early/delayed). Animals were conditioned with anti-lymphocyte-serum (Days −4 and +1) followed by tacrolimus (21 days). Microchimerism and regulatory T-cell (Treg) function were investigated.
Results
AD-MSCs were superior to BM-MSCs in dose-dependent immunosuppressive function in-vitro (P< 0.001). In-vivo, all animals revealed transient peripheral chimerism (4 weeks), associated with Treg induction (AD-MSC vs. control, P < 0.01). Notably >50% of AD-MSC/BM-MSC-treated animals showed long-term acceptance of allotransplants (>120 d). This correlated with microchimerism in marrow, spleen and lymphnodes. In the second in-vivo experiment, single-early (Day 1) and repetitive AD-MSC injection (Days 4, 8, 15) resulted in 50% long-term graft acceptance. Single treatment on Day 4 resulted in rejection comparable to controls (<50 d). Repetitive administration showed most pronounced peripheral microchimerism (4 weeks; P < 0.01) and induced Tregs (P < 0.01).
Conclusion
Immunomodulatory effects of AD-MSCs/BM-MSCs could potentially reduce intensity, frequency and duration of immunosuppressive drug-regimens in VCA. Given their superior immunomodulatory efficacy, higher cell and pro-neuroregenerative benefits, AD-MSCs are a promising cell ripe for translation in clinical VCA.
Funding
Funded by Department of Defense Grant W81XWH-11–2–0215. JP, JS and RS were recipients of Swiss National Science Foundation funding.