Donor carbon monoxide treatment alone prolongs pulmonary allograft survival and suppresses brain death-induced graft inflammation in CLAWN miniature swine

Background: We have previously reported that perioperative carbon monoxide (CO) inhalation in both donors and recipients prolongs lung graft survival in MHC-inbred CLAWN miniature swine. To better understand the mechanism and establish a more clinically applicable strategy, we investigated whether CO treatment of the donor or recipient alone could prolong graft survival and whether CO inhalation in brain-dead donors could improve graft function and survival.
Methods: In Study 1, seven CLAWN miniature swine received fully MHC-mismatched lung allografts under 12 days of continuous tacrolimus treatment (days 0–11; 35–45 ng/mL). In Group D (n=4), only the donor received CO, whereas in Group R (n=3), only the recipient received CO. The results were compared with those of previously published groups in which both the donor and recipient received CO (Group D+R, n=6) or neither received CO (control, n=5). In Study 2, lungs were transplanted from non-brain-dead donors (n=6), untreated brain-dead donors (BD group, n=3), or brain-dead donors treated with CO for 3 h before procurement (BD+CO group, n=4). Brain death was induced by subdural balloon inflation and maintained for 6 h before transplantation. In all CO-treated groups, inhaled CO was administered at approximately 250 ppm and adjusted to maintain the blood carboxyhemoglobin levels below 15%.
Results: All recipients in the control group rejected their grafts by POD63 (47 ± 7 days). In contrast, four of five recipients in Group D+R maintained graft survival beyond POD63 (82 ± 13 days). Donor-only CO treatment was comparably effective, with three of four recipients in Group D surviving beyond POD63 (97 ± 26 days), including one recipient who survived　150 days. In contrast, all recipients in Group R rejected their grafts by POD63 (54 ± 6 days post-transplantation).

Donor CO treatment delayed the development of anti-donor antibodies, reduced inflammatory cell infiltration in POD2 graft biopsies, lowered serum IL-1β and IL-6 concentrations, and markedly suppressed the upregulation of pro-inflammatory cytokines. In the brain-death model, brain death markedly shortened pulmonary allograft survival to 26 ± 5 days in untreated BD donors. CO treatment of BD donors significantly prolonged allograft survival to 82 ± 13 days.

Importantly, brain death induced upregulation of inflammatory cytokines within the donor graft before transplantation, and this response was markedly reduced by CO inhalation. These findings indicate that donor CO treatment attenuated early inflammatory injury that developed in the graft during the brain-death period before transplantation.
Conclusions: Donor CO therapy alone is sufficient to prolong pulmonary allograft survival across a fully MHC-mismatched barrier in miniature swine. Its protective effect appears to be mediated by the suppression of early graft inflammation, including the inhibition of brain death-induced inflammatory cytokine upregulation within the donor lung before transplantation, as well as delayed humoral sensitization. Therefore, donor-targeted CO therapy may represent a clinically relevant graft-protective strategy for lung transplantation.