Induction of Long-Lasting Regulatory B Lymphocytes by Modified Immune Cells in Kidney Transplant Recipients
Authors: Morath Christian , Schaier Matthias , Ibrahim Eman , Wang Lei , Kleist Christian , Opelz Gerhard , Süsal Caner , Ponath Gerald , Aly Mostafa , Alvarez Cristiam M. , Kälble Florian , Speer Claudius , Benning Louise , Nusshag Christian , Pego da Silva Luiza , Sommerer Claudia , Hückelhoven-Krauss Angela , Czock David , Mehrabi Arianeb , Schwab Constantin , Waldherr Rüdiger , Schnitzler Paul , Merle Uta , Tran Thuong Hien , Scherer Sabine , Böhmig Georg A. , Müller-Tidow Carsten , Reiser Jochen , Zeier Martin , Schmitt Michael , Terness Peter , Schmitt Anita , Daniel Volker 
Published: September 2022

Significance Statement
In previous work, the authors demonstrated that kidney transplant recipients developed donor-specific unresponsiveness when they were given a pretransplant infusion of modified donor-derived PBMCs. In this study, they provide evidence that the immunosuppressive properties of these cells persist and the donor-specific unresponsiveness is long-lasting. In the four patients who received the highest dose of the modified immune cells, administration of these cells was associated with a striking increase in IL-10–producing regulatory B lymphocytes and evidence of the consensus gene expression signature of operational tolerance. In vitro, donor-specific unresponsiveness was abolished after B lymphocyte depletion, suggesting a direct pathophysiologic role for regulatory B lymphocytes. These findings support the notion that modified donor-derived PBMCs may be useful in kidney transplantation, but this approach requires further validation and rigorous controlled randomized studies.

Background
We recently demonstrated that donor-derived modified immune cells (MICs)—PBMCs that acquire immunosuppressive properties after a brief treatment—induced specific immunosuppression against the allogeneic donor when administered before kidney transplantation. We found up to a 68-fold increase in CD19+CD24hiCD38hi transitional B lymphocytes compared with transplanted controls.

Methods
Ten patients from a phase 1 clinical trial who had received MIC infusions before kidney transplantation were followed to post-transplant day 1080.

Results
Patients treated with MICs had a favorable clinical course, showing no donor-specific human leukocyte antigen antibodies or acute rejections. The four patients who had received the highest dose of MICs 7 days before surgery and were on reduced immunosuppressive therapy showed an absence of in vitro lymphocyte reactivity against stimulatory donor blood cells, whereas reactivity against third party cells was preserved. In these patients, numbers of transitional B lymphocytes were 75-fold and seven-fold higher than in 12 long-term survivors on minimal immunosuppression and four operationally tolerant patients, respectively (P<0.001 for both). In addition, we found significantly higher numbers of other regulatory B lymphocyte subsets and a gene expression signature suggestive of operational tolerance in three of four patients. In MIC-treated patients, in vitro lymphocyte reactivity against donor blood cells was restored after B lymphocyte depletion, suggesting a direct pathophysiologic role of regulatory B lymphocytes in donor-specific unresponsiveness.

Conclusions
These results indicate that donor-specific immunosuppression after MIC infusion is long-lasting and associated with a striking increase in regulatory B lymphocytes. Donor-derived MICs appear to be an immunoregulatory cell population that when administered to recipients before transplantation, may exert a beneficial effect on kidney transplants.

Clinical Trial registry name and registration number:
MIC Cell Therapy for Individualized Immunosuppression in Living Donor Kidney Transplant Recipients (TOL-1), NCT02560220