Differential dynamics of donor DC and non-DC peripheral blood mononuclear cell microchimerism in lung transplantation

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

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-B44 LTR who received HLA-B44 allografts were sorted flow cytometrically into three cellular subsets. Real-time quantitative polymerase chain reaction (q-PCR) demonstrated that donor-derived HLA-B44 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.

Chimerism of dendritic cell subsets in peripheral blood after lung transplantation

BACKGROUND

Passenger leukocytes of donor origin are transferred to the patient resulting in circulatory microchimerism after lung transplantation (LTx). This chimeric state has been shown to occur in the total leukocyte fraction as well as unseparated peripheral blood mononuclear cells (PBMCs). In this study we determined the microchimerism levels of B cells, monocytes, natural killer (NK) and T cells and dendritic cell (DC) subsets (mDC1, mDC2 and pDC) during the first year after lung transplantation.

METHODS

To identify circulating donor cells, 11 donor-patient combinations were selected, which were mismatched for HLA-B8. Analysis consisted of flow cytometry on a minimum of 1 million PBMCs taken monthly up to 1 year after LTx.

RESULTS

Levels of microchimerism were found to be stable after LTx for all cell types investigated, although for NK+T cells an above-baseline chimerism of donor cells from the donor lung was observed in the first month after transplantation. Circulating PBMCs consisted of, on average, 0.002%, 1.7%, 0.03% and 0.001% of B cells, monocytes, NK+T cells and DCs, respectively, indicating that overall levels of microchimerism differed between the cell types investigated. In 2 patients no B-cell chimerism and in 1 patient no DC chimerism could be detected. Cell types and DC subsets of recipient origin were normally distributed. Conversely, monocytes, B cells and DCs of donor origin were increased and donor NK+T cells were decreased in number, compared with the recipient ratios. Analysis of circulating recipient DCs showed a normal distribution of mDC1s (70%), mDC2s (5%) and pDCs (25%). However, circulating donor DCs consisted of 80%, 20% and <1% of DC subsets mDC1, MDC2 and pDC, indicating that donor plasmacytoid dendritic cells were not detectable in the circulation.

CONCLUSIONS

In the first year after lung transplantation a stable microchimerism was detected for all cell types investigated. However, donor pDCs were consistently absent in all samples investigated, which may be linked with graft rejection often observed after LTx.