P1740KINETICS OF B-CELL SUBSETS RECONSTITUTION FOLLOWING RITUXIMAB TREATMENT IN ABO-INCOMPATIBLE KIDNEY TRANSPLANT RECIPIENTS

Background and Aims With the application of B-cell-depleting agent rituximab, plasmapheresis and powerful immunosuppression, ABO-incompatible kidney transplant recipients (ABOi-KT) have successfully overcome the ABO antibody barrier. As an important immune cell population, B cells are not only involved in antibody-mediated rejection, but also have been reported to have different immunoregulatory effects due to the existence of distinct B cell subsets. Therefore, comprehensively understanding the reconstitution of B-cell subsets in ABOi-KTRs is crucial to know the immune status that may be related to the subsequent complications. Method Fresh whole blood were collected from 22 ABOi-KTRs and 22 ABO-compatible recipients (ABOc-KTRs) at 0, 1week, 2 weeks ,1month, 3months, and 6 months post-transplantation between October 2018 and May 2019. In addition, pre-desensitization samples were also collected from ABOi-KTRs. B cell subsets including total, naïve, memory, plasma, plasma blast and regulatory B cells were determined by flow cytometry. Results The percentages of B cells in ABOi group remained extremely low and significantly lower than ABOc group through the first 6 months after rituximab treatment (Fig. A). Similar trends were observed in total memory and switched memory B cells whose frequencies increased within first 2 weeks, then decreased thereafter. Meanwhile, the significant differences between ABOi and ABOc groups disappeared at 6 months (Fig. B-D). In addition, plasma and plasma blast B cells increased 2 weeks after transplantation and were significantly higher in ABOi group compared to ABOc group (Fig. E, G), while Naïve B cells started to elevate 1 month after transplantation in ABOi-KTRs and significantly higher proportions were found in ABOc group through the entire 6 months (Fig. F). No obvious difference was observed between ABOi and ABOc groups regarding unswitched memory and regulatory B cell percentages (Fig. C, H). Conclusion Our preliminary results indicated that B-cell depletion therapy applied in ABOi-KTRs not only significantly reduced the number of B cells, but also changed the composition of B cell subsets in the remaining B cell population. Whether such alteration would be clinical significance requires further follow-up.