*Purpose: The kidney allocation system (KAS) was changed in 2015 to increase access to transplants for highly sensitized patients. However, recent data suggests that even in the post-KAS era patents with a cPRA>99% continue to have very limited access to transplant. The peri-operative desensitization protocol previously published by our center for positive flow-cytometric crossmatch (FXM) in deceased donor kidney transplant (DDKT) recipients with plasmapheresis (PLEX) and low-dose IVIg resulted in reasonable long-term outcomes. Here we present our single-center data encompassing a predominantly African-American population from the post-KAS era on peri-operative desensitization with incorporation of a simple point-based algorithm and surveillance biopsies to evaluate for subclinical rejection.

*Methods: We retrospectively looked at outcomes of all patients with a cPRA> 80% who underwent a DDKT and were part of our high risk surveillance biopsy protocol (N=53). Of these, we selected patients for desensitization based on 4 readily available factors including cPRA > 80%, re-transplant status, T and/or B cell FXM match > 100 median channel shifts (MCS) and pre-formed DSA > 4000 MFI. If patients met ≥3 of these criteria they started immediate post-operative desensitization with 6 sessions of PLEX and IVIg (N=19).

*Results: Overall patients were broadly sensitized with a median cPRA of 99%. Of the 53 total patients, 41 were African American (77%). The mean T cell FXM (77±66 MCS vs 15±29; p=<0.0001), B cell FXM (95±44 MCS vs 39±42; p=<0.0001) and cumulative DSA at transplant (6195±5844MFI vs 2745±5527MFI; p=<0.0001) was higher in the desensitized group. There was no difference in GFR at 3 months (62.9±21.5 vs 67.1±23.6 ml/min/1.73m2; p=0.52), 6 months (57.9±25.8 vs 63.5±22.1 ml/min/1.73m2; p=0.41) and 12 months (61.9±24.0 vs 62.1±21.8 ml/min/1.73m2; p=0.98) between the two groups. The desensitization group had a high rate of subclinical ABMR in the first year post transplant (14/19; 74% vs 10/34; 29%; p=0.002) and higher rate of chronic active ABMR (11/19; 58% vs 8/34; 23% p=0.01). All five patients who were re-grafts and had a T cell FXM > 100 developed ABMR. In the entire cohort, a T-Cell FXM>100 was associated with a relative risk of 2.01 (p=0.0072) of subclinical acute ABMR and 2.85 (p=0.0006) of chronic ABMR post-transplant.

*Conclusions: In this report, we find that patients subjected to a post-transplant desensitization protocol had reasonable allograft function in the first year post transplant compared to those who did not undergo desensitization. Based upon a routine surveillance biopsy protocol, we found a very high rate of subclinical ABMR that was seen predominantly in re-transplant patients with a T-cell FXM>100. Pre-operative desensitization using novel strategies currently being investigated may lower the immunologic barriers that these patients face after transplant.

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