Donor brain death inhibits tolerance induction in miniature swine recipients of fully MHC-disparate pulmonary allografts

Abstract

We have previously shown that a short course of high-dose tacrolimus induces long-term tolerance to fully mismatched lung allografts procured from healthy MHC-inbred miniature swine. Here, we investigate whether donor brain death affects tolerance induction. Four recipient swine were transplanted with fully mismatched lung grafts from donors that were rendered brain dead and mechanically ventilated for 4 h before procurement (Group 1). These recipients were compared to two control groups (Group 2: 4 h of donor ventilation without brain death [n = 5]; and Group 3: no donor brain death with <1 h of ventilation [n = 6]). All recipients were treated with a 12-day course of tacrolimus. In contrast to both groups of control animals, the swine transplanted with lung allografts from brain dead donors all rejected their grafts by postoperative day 45 and showed persistent responsiveness to donor antigen by MLR. Several additional swine underwent brain death induction and/or mechanical ventilation alone to determine the effects of these procedures on the expression of proinflammatory molecules. Significant increases in serum concentrations of IL-1, TNF-α and IL-10 were seen after brain death. Upregulation of IL-1 and IL-6 gene expression was also observed.

Figure 1. Allograft survival

Allografts from brain dead donors (Group 1, n = 4) demonstrate accelerated rejection as compared to historical controls (Group 3; n = 6; p 0.001) and when compared to donor animals that were subjected to mechanical ventilation only (n = 5; p = 0.004).

Figure 2. Graft histology

(A) Animal #17447 (recipient of lung from a brain dead donor [Group 1]) demonstrates severe acute cellular rejection (ISHLT A4) 45 days after transplantation. The lung was not viable and the animal was sacrificed. (B) Animal #17556 (recipient of lung from an animal subjected to 4 h of mechanical ventilation (Group 2) demonstrates no evidence of rejection (ISHLT A0) at the time of sacrifice (POD 516).

Figure 3. Mixed lymphocyte responses

(A) The MLR responses (mean±SD) of each of the recipients of the brain dead lungs (Group 1) at the time of sacrifice is shown (n = 4). As expected, these animals show strong responses to both donor and third-party stimulators. (B) In contrast, MLRs performed at a similar time point in the historical tolerant controls (Group 3) show donor-specific hyporesponsiveness (n = 6).

Figure 4. Serum cytokines

Significant increases in serum concentrations of (A) IL-1, (B) TNF-α and (C) IL-10 after the induction of brain death are shown (171 ± 17.9 pg/mL vs. 297 ± 79.2 pg/mL [p = 0.046]; 63.5 ± 24.6 pg/mL vs. 105 ± 24.0 pg/mL [p ± 0.050]; 5.25 ± 1.71 pg/mL vs. 38.0 ± 17.4 pg/mL [p = 0.031]; respectively; n = 4 in all cases).