Background: We have previously shown that cell death is a pathophysiologic consequence of ischemia-reperfusion and that interleukin-10 gene therapy improves the function of transplanted lungs. Interleukin-10 downregulates the inflammatory response and can inhibit apoptosis. The objective was to determine whether donor lung transfection with the interleukin-10 gene ameliorates lung dysfunction by decreasing cell death after transplantation. Methods: Single lung transplants were performed in 3 groups of rats (n = 5 each): AdhIL-10, transtracheal administration of Ad5E1RSVhIL-10 (5 × 109 pfu); EV, empty vector; and VD, vector diluent (3% sucrose). After in vivo transfection, donor lungs were excised, stored at 4°C for 24 hours, and then transplanted. After 2 hours of reperfusion, lungs were flushed with trypan blue and fixed. TUNEL staining was used for the detection of apoptosis. This combined staining technique allows one to determine the mode of cell death by distinguishing apoptotic dead cells from necrotic dead cells. Results: Lung function was superior in the interleukin-10 group (P = .0001) vs the EV and VD group (Pao2: 240 ± 31 mm Hg vs 98 ± 17 mm Hg vs 129 ± 11 mm Hg, respectively). Although the total number of dead cells (as percent of total cells) was similar in all groups (32.7% ± 3.2%, 30.2% ± 2.5%, and 30.3% ± 3.8%), interestingly, apoptosis was highest in interleukin-10 lungs (9.7 ± 1.9 vs 2 ± 1.9 and 1.8 ± 2, P = .0001), and necrosis was lowest in the interleukin-10 group (20.6 ± 5.7 vs 28.3 ± 3.1 and 30.3 ± 4.2, P = .01). Conclusions: AdhIL-10 gene transfection improves function of transplanted lungs. Although the total number of cells dying as a result of the transplant process did not change, the mode of cell death appears to have been modified. It is possible that AdhIL-10, by decreasing proinflammatory cytokine production, ameliorates the overall injury and preserves the ability of damaged cells to undergo a more quiescent and less tissue-damaging mode of cell death-apoptosis, rather than necrosis.