The Reliability and Validity of Donor Tissue Biopsies in Lung Transplantation

Purpose During lung transplantation, donor biopsies are collected for histologic and biomarker assessments to understand lung injury. Samples are often taken from a single location and it is unknown whether this is truly representative of the injury across the organ. The objective of this study was to investigate the uniformity of cytokine mRNA expression in tissue samples collected from different locations in donor lungs. Methods Eight unused donor lungs were inflated, flash-frozen in liquid nitrogen, and partitioned into 10 to 15 slices from apex to base. Five 1 cm3 biopsies were taken from each lung; three were consistently taken from the third, sixth, and ninth slices, while two were taken from the lingula and a noted potential injury site. Three pieces of each biopsy were used to measure mRNA expression of IL-6, IL-8, IL-10, and IL-1β as markers of lung inflammation by PCR in a total of n=120 samples from the eight lungs. Intra-biopsy and intra-lung variations were analyzed with equal-variance tests, coefficients of variance, one-way ANOVA, and pairwise mean comparisons. Results Across all donors, the intra-biopsy equal-variance F-values ranged from 0.19-0.95 with means of 0.33, 0.57, 0.62, and 0.58 for IL-1β, IL-6, IL-8, and IL-10. The mean biopsy coefficient of variance was 25.9% across all donors. The mean comparisons of biopsies in each donor showed that the three consistent slices were identical in donors rejected for logistics and thrombotic emboli. Both the lingula and focal injury biopsies demonstrated larger differences in cytokine expression from the rest of the donor lung. Conclusion While intra-biopsy variances were present, they were small and consistent across multiple biopsies in donors, indicating the reliability of repeated analysis of banked specimens. Lungs rejected for non-graft related reasons demonstrated more consistent gene expression. The lingula is not a representative site as it often differed from other biopsies in all donors. We conclude that a donor lung biopsy taken from an area other than the lingula reflects the overall condition of the lung, unless there is obvious localized injury (e.g. infection) which has a unique profile. These findings will reassure the scientific community that a biopsy of the donor lung is indeed representative of the whole lung, and will help to guide diagnostic and therapeutic interventions in donor lungs for transplantation.