Human leucocyte antigen‐defined microchimerism early post‐transplant does not predict for stable lung allograft function

Summary Microchimerism is the presence of foreign cells in an individual below 1% of total cells, which can occur in the setting of solid organ transplantation. This study quantitated donor‐derived cellular subsets longitudinally in human leucocyte antigen ( HLA )‐mismatched lung transplant recipients ( LTR ) during the first post‐operative year and evaluated the pattern of peripheral microchimerism with clinical outcomes. Peripheral blood mononuclear cells ( PBMC ) isolated from non‐ HLA ‐ B 44 LTR who received HLA ‐ B 44 allografts were sorted flow cytometrically into three cellular subsets. Real‐time quantitative polymerase chain reaction (q– PCR ) demonstrated that donor‐derived HLA ‐ B 44 microchimerism is a common phenomenon, observed in 61% of patients. The level of donor‐derived cells varied across time and between LTR with frequencies of 38% in the B cells/monocytes subset, 56% in the T / NK cells subset and 11% in the dendritic cells ( DC ) subset. Observations highlighted that microchimerism was not necessarily associated with favourable clinical outcomes in the first year post‐lung transplantation.