Introduction: Rodent studies have demonstrated the utility of regulatory T cell (Treg) infusion for the promotion of tolerance to organ allografts. Here, we evaluated the therapeutic potential of ex vivo-expanded autologous polyclonal Treg in rhesus monkeys with life-supporting kidney allografts.
Methods: One week before transplantation (Tx), CD4⁺CD25⁺Treg were isolated from peripheral blood (using MACS), followed by polyclonal expansion using artificial APCs (L-cells) and IL-2. Recipients and donors were MHC-mismatched. Immunosuppression in the form of co-stimulation blockade (CTLA4Ig; 20mg/kg, with tapering until d180) and tacrolimus (trough levels 10-15ng/ml, with tapering until d60) was given to recipients without (n=3) or with (n=4) Treg infusion. Purity and phenotype of the expanded Treg were validated by flow cytometry. Treg infusions (total: 8 per graft recipient) were administered on d6 & d10 (10x10⁶/kg per infusion), d13 & d16 (30x10⁶/kg), and d20, d23, 27 & d30 (50x10⁶/kg). Graft survival was determined by serum creatinine level, weight loss and urinary protein/creatinine ratio.
Results: With no Treg infusion, graft survival times were 15, 35, and 40 days (median 35 days), compared to 38, 58, 86, and 234 days (median 72 days) with Treg infusion (p<0.05). In peripheral blood, no significant differences in memory CD4⁺ and CD8⁺T cell subsets were observed between recipients with or without Treg infusion. However, the percentages of CD4⁺CD28^-CD95⁺ T cells in peripheral blood were significantly lower in recipients with Treg infusion (p<0.05). In both groups, no increase in donor-specific allo-antibodies was observed. With or without Treg infusion, the incidences of CD4⁺CD25^hiFoxp3^hi Treg in peripheral blood were markedly reduced after Tx. On the day of Tx (d0), the incidences of CD4⁺CD25^hiFoxp3^hi Treg in mesenteric lymph nodes (LN) were similar in both groups. However, on d35, mesenteric LN from Treg-infused monkeys exhibited significantly higher percentages of CD4⁺CD25^hiFoxp3^hi Treg than monkeys without Treg infusion (p<0.05).
Conclusions: Multiple infusions of ex vivo-expanded polyclonal autologous Treg are safe and delay kidney allograft rejection in non-lymphodepleted monkeys treated with CTLA4Ig and tacrolimus. Furthermore, Treg were enriched in secondary lymphoid organs of recipients given Treg infusions.