Adverse Outcomes of Tacrolimus Withdrawal in Immune-Quiescent Kidney Transplant Recipients

Abstract

Concerns about adverse effects of calcineurin inhibitors (CNIs) have prompted development of protocols that minimize their use. Whereas previous CNI withdrawal trials in heterogeneous cohorts showed unacceptable rates of acute rejection (AR), we hypothesized that we could identify individuals capable of tolerating CNI withdrawal by targeting immunologically quiescent kidney transplant recipients. The Clinical Trials in Organ Transplantation-09 Trial was a randomized, prospective study of nonsensitized primary recipients of living donor kidney transplants. Subjects received rabbit antithymocyte globulin, tacrolimus, mycophenolate mofetil, and prednisone. Six months post-transplantation, subjects without de novo donor-specific antibodies (DSAs), AR, or inflammation at protocol biopsy were randomized to wean off or remain on tacrolimus. The intended primary end point was the change in interstitial fibrosis/tubular atrophy score between implantation and 24-month protocol biopsies. Serially collected urine CXCL9 ELISA results were correlated with outcomes. The study was terminated prematurely because of unacceptable rates of AR (4 of 14) and/or de novo DSAs (5 of 14) in the tacrolimus withdrawal arm. Positive urinary CXCL9 predated clinical detection of AR by a median of 15 days. Analyses showed that >16 HLA-DQ epitope mismatches and pretransplant, peripheral blood, donor-reactive IFN-γ ELISPOT assay results correlated with development of DSAs and/or AR on tacrolimus withdrawal. Although data indicate that urinary CXCL9 monitoring, epitope mismatches, and ELISPOT assays are potentially informative, complete CNI withdrawal must be strongly discouraged in kidney transplant recipients who are receiving standard-of-care immunosuppression, including those who are deemed to be immunologically quiescent on the basis of current clinical and laboratory criteria.

Keywords: immunosuppression; rejection; renal transplantation.

Figure 1.

Tacrolimus withdrawal resulted in adverse outcomes in a highly-selected, low-risk study population. Consort diagram depicting the outcomes of the 52 enrolled subjects, 47 of whom underwent transplantation. Twenty-one of 47 transplanted patients met the criteria for randomization. Outcomes of the 14 randomized to Tacrolimus withdrawal arm and 7 randomized to the control arm are delineated at the bottom of the diagram. ACR: acute cellular rejection, DSA: donor specific antibody. DR and DQ refer to the HLA locus to which the DSA was reactive.

Figure 2.

ACR and/or de novo DSA developed at the time of, or rapidly after, stopping Tacrolimus. Clinical outcomes of the 21 randomized subjects. Each line represents a timeline for each of 7 control subjects and 14 subjects with TAC withdrawal (separated by a bold line). Time of initiating TAC withdrawal (black x), completion of TAC withdrawal (green x), time of clinically evident, biopsy–proven cellular rejection (red arrowhead), and time of detection of de novo DSA (blue arrowhead) are shown. One of seven control subjects (below the dotted line) was retrospectively noted to have a DSA before randomization that was not detected on the 6-month prerandomization sample but was detected on day 315 postrandomization. This subject was not considered to have developed a de novo DSA during the randomization period.

Figure 3.

Tacrolimus withdrawal did not have an impact on kidney allograft function. Kidney function in the randomized cohort: (upper panel) 24-month eGFR and (lower panel) change in eGFR between 6 and 24 months are depicted for each randomized subject stratified by control versus TAC withdrawal groups. There were no significant differences in either eGFR or change in eGFR between those who failed TAC withdrawal (developed rejection and/or de novo DSA and required reinstitution of full-dose TAC; black circles) and those who remained off TAC for >18 months (green circles) or between those who failed TAC withdrawal and controls. P value is NS between groups for both analyses. M, month.

Figure 4.

Urinary CXCL9 values were elevated prior to the clinical detection of ACR in study subjects undergoing Tacrolimus withdrawal. Individual timelines for six subjects in the TAC withdrawal arm with positive urinary CXCL9 test results that illustrate associations with biopsy-proven ACRs. The two subjects who had positive urine CXCL9 results but did not experience ACR (the first two subjects) were diagnosed with BK polyoma or systemic viral infections, no biopsies were performed, and serum creatinine remained unchanged. All urine tests in seven subjects in the control arm were negative for CXCL9.

Figure 5.

Epitope mismatches and pretransplant ELISPOT results correlate with de novo DSA and AR. (A) Epitope mismatches at HLA-DQ loci. The bars depict the total numbers of randomized subjects with (left bar) >16 epitope mismatches and (right bar) ≤16 mismatches at HLA-DQ loci. The shaded portions of each bar (and accompanying percentages) depict those subjects in each group who developed a de novo post-transplant DSA. Mismatches at HLA-DR loci were not informative (not shown). (B) Results of pretransplant antidonor IFN-γ ELISPOT assays available in 15 of 21 randomized subjects. The bars depict the total numbers of randomized subjects with (left bar) positive pretransplant ELISPOT results (>25 per 300,000 peripheral blood mononuclear cells) and (right bar) negative pretransplant ELISPOT results. The shaded portions of each bar (and accompanying percentages) depict those subjects in each group who developed an episode of AR and/or a de novo DSA in the post-transplant period.