Introduction: We have demonstrated the therapeutic potential of human polyclonal and antigen-specific CAR-modified CD8⁺Tregs cell therapy to prevent allogeneic human skin transplantation rejection and xenogeneic GvHD in humanized NSG mice (Bézie et al., Front Immunol.2017, Blood Adv.2019). However, their potential has never been evaluated in a clinical trial. We are thus preparing the launch of a phase I/IIa human clinical trial using polyclonal CD8⁺Tregs cell therapy in living donors kidney transplant patients.

Method: CD8⁺ cells were isolated from blood of healthy volunteers and patients with kidney failure by Clinimacs System then CD8+CD4-CD45RClow/-CD56^- T cells were sorted by MACSQuant Tyto cell sorter. Cells were stimulated with anti-CD3 and CD28 mAbs every week and cultured in presence of rapamycin, IL-2 and IL-15. Cytotoxicity against allogeneic PBMCs was assessed by Annexin V/DAPI staining and suppression capacity was assessed in vitro on syngeneic CD4⁺T cells proliferation in response to allogeneic APCs and in vivo on 1.5Gy-irradiated NSG mice co-injected with human PBMCs.

Results: We developed a new GMP-compatible cell manufacturing process. First, we determined a new method of isolation of CD8⁺Tregs from peripheral blood using a safe closed system. Next, we identified the optimal clinically compatible culture medium, refined cytokines doses and stimulation methods to preserve a high proliferation rate, phenotypic profile and suppressive function of CD8⁺Tregs. Using this process, we were able to efficiently expand CD8⁺Tregs from peripheral blood of patients with renal failure, with high purity, while preserving their regulatory function. We confirmed the absence of cytotoxicity. In addition, we showed that CD8⁺Tregs were phenotypically and functionally stable for 4h after conditioning, which is important for the logistic delay between cell harvest and patient infusion. Finally, we showed that CD8⁺Tregs persist for more than 90 days in NSG mice without inducing any signs of xenogeneic GVHD, and could withstand combined immunosuppressive drug therapy administered to the patient.

Conclusion: We designed a clinically compatible manufacturing process to isolate and culture CD8⁺Tregs from renal failure patients that preserves their function and patient safety.