*Purpose: The UNOS KAS system incorporates A2 to B deceased donor kidney transplants (DDKTx) to improve access and reduce disparities in wait times for B recipients. Previous studies of A2 to B DDKTx have shown equivalent outcomes to ABO compatible DDKTx with recipient pre-transplant anti-A IgG titers <1:8. The significance of pre-transplant IgM titers is unclear although previous data by our group and others suggest recipients with elevated pre-transplant IgM titers (>1:8) are at increased risk for allograft rejection and graft loss and may benefit from additional immunosuppression. In addition, there are no data on post-transplant anti-A titers and correlation with outcomes. We report a study of anti-A titers and outcomes post A2 to B DDKTx since introduction of KAS.

*Methods: We retrospectively reviewed all A2 to B DDKTx performed at our center since January 2014 (n=32) to evaluate the relationship of pre- and post-transplant anti-A1 titers with rejection- and adverse event-free survival (rejection/graft failure/death). Eligibility included anti-A IgG titers <1:8 and anti-A IgG/M titers < 1:128. Recipients with IgG/M titers >1:8 (n=20) received PLEX/IVIG/rituxan at the time of transplant. Post-transplant titers were prospectively measured at discharge, 2 weeks, 4 weeks, and 3 months. Statistical methods included comparisons of means and survival analyses.

*Results: 24 (75%) of recipients were African American. Post-transplant IgG titers ranged from 1 to 2048 and IgG/M from 1 to 2048. Paired tests showed both IgG and IgG/M were significantly increased (p≤0.032) at 4 weeks compared to pre-transplant. Six rejection episodes occurred. There was no relationship between pre-transplant IgG or IgG/M titers and rejection- or adverse event-free survival (all p≥0.373). Similarly, there was no relationship between change in IgG or IgG/M pre- to 4 weeks post-transplant and rejection- or adverse event-free survival (all p≥0.362). PLEX/IVIG/rituxan was not associated with rejection- or adverse event-free survival (p≥0.318).

*Conclusions: Our 3-year experience shows that anti-A titers increased significantly post-transplant but does not affect outcomes. Recipients with high pre-tx IgG/M (>1:8 but <1:128) treated with PLEX/IVIG/rituxan had comparable outcomes to low IgG/M (<1:8) recipients. Whether this additional immunosuppression in this high titer group is warranted requires further study.

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