Carbon Monoxide Administered Only to the Donor Is Sufficient to Prolong Pulmonary Allograft Survival Across a Fully MHC-Mismatched Barrier in CLAWN Miniature Swine

Abstract

Objective: To attempt carbon monoxide (CO) to apply for the clinical setting, we have extensively studied the role of CO using miniature swine as a translational research. We have previously reported that perioperative low-dose CO inhalation decreases IRI using in situ porcine lung IRI model and that perioperative CO inhalation to both donor and recipient prolongs lung graft survival in MHC-inbred CLAWN miniature swine. To understand the mechanisms involved in prevention of graft damage following CO inhalation, we examined whether donor or recipient treatment alone is sufficient to prolong graft survival. Methods: Eighteen CLAWN miniature swine received fully MHC mismatched lungs with 12 days of tacrolimus (days 0-11; 35-45 ng/ml). In the control group (n=6), recipients received FK506 alone. In D+R group (n=5), both donor and recipient additionally inhaled 200-250 ppm CO (180 min for donor; 390 min for recipient until 2-hr reperfusion). In D group (n=4), only donor was treated with CO for 180 min. In R group (n=3), CO was administered only to the recipient for 390 min. The concentration of inhaled CO was adjusted, such that carboxyhemoglobin levels did not exceed 15%. Graft function was monitored by chest radiography and serial open lung biopsy. Immunologic responses were assessed by mixed lymphocyte reaction (MLR), cell-mediated lympholysis (CML) assays and allo-antibody (Ab) development using flow cytometry. Results: All control recipients rejected the grafts by POD63 (47 ± 7 days) with development of cytotoxic antidonor antibodies. Four out of 5 recipients in D+R group accepted the grafts over 63 (82 ± 13) days. Surprisingly, CO therapy only with donor (D group) was effective in prolonging graft survival. Three out of 4 recipients accepted the grafts over 63 (97 ± 26) days with the longest survivor lasting 150 days. In contrast, all three recipients in R group rejected the grafts by POD63 (54 ± 6 days). Development of anti-donor Abs and MLR and CML responses was delayed in D+R and D group. Furthermore, fewer inflammatory cell infiltrates on POD2 biopsies, and decreased serum concentrations of IL-1β and IL-6 were mostly observed in D+R and D group. Conclusions: These data suggest that donor CO alone is sufficient to improve lung graft survival in a clinically relevant large animal model. CO pretreatment might have the effects through some analogue of ischemic preconditioning. Donor cytoprotective preconditioning with CO during organ harvest or preservation could be accomplished in a clinical setting, potentially improving graft survival with little risk of adverse effects on the recipient.