Frequency and clinical correlations of allogeneic microchimerism after heart, liver, and lung transplantation

Mixed Donor Chimerism Following Simultaneous Pancreas-Kidney Transplant

OBJECTIVES

Graft-versus-host disease after solid-organ transplant is exceedingly rare. Although the precise pathogenetic mechanisms are unknown, a progressive increase in donor chimerism is a requirement for its development. The incidence of mixed donor chimerism and its timeline after simultaneous pancreas-kidney transplant is unknown.

MATERIALS AND METHODS

After encountering 2 cases of graft-versus-host disease after simultaneous pancreas-kidney transplant at our institution over a period of < 2 years, a collaborative pilot study was conducted by the bone marrow transplant, nephrology, and abdominal transplant surgery teams. We enrolled all consecutive patients undergoing sex-mismatched simultaneous pancreas-kidney transplant over 1 year and longitudinally monitored donor chimerism using fluorescence in situ hybridization for sex chromosomes.

RESULTS

We found no evidence for chimerism in our 7 patients. In a comprehensive literature review, we found a total of 25 previously reported cases of graft-versus-host disease after kidney, pancreas, and simultaneous pancreas-kidney transplants. The median onset of graft-versus-host disease was approximately 5 weeks after transplant, with a median of about 2 weeks of delay between first presentation and diagnosis. Skin, gut, and bone marrow were almost equally affected at initial presentation, and fever of unknown origin occurred in more than half of patients. The median survival measured from the first manifestation of graft-versus-host disease was only 48 days.

CONCLUSIONS

Within the limitations related to small sample size, our results argue against an unusually high risk of graft-versus-host disease after simultaneous pancreas-kidney transplant. Collaboration between solid-organ and stem cell transplant investigators can be fruitful and can improve our understanding of the complications that are shared between the 2 fields.

A mathematical model provides new insights into solid organ transplant-associated acute graft-versus-host disease

Solid organ transplantation-associated acute graft-versus-host disease (SOT-aGvHD) is a rare but highly fatal condition. Our poor understanding of this entity in addition to its rarity has hampered treatment progress and most patients succumb to the disease. A mechanistic mathematical model is developed to replicate and explain the complex pathogenesis of SOT-aGvHD. The model captures a number of important features of SOT-aGvHD including (i) the occurrence of stable and persistent mixed chimerism in some, but not all, cases, (ii) fluctuation in chimerism in some persistently mixed chimeric cases, (iii) rare occurrence of full donor chimerism, and (iv) beneficial effect of escalating immunosuppression in some cases of SOT-aGvHD and detrimental effect in others. In addition, the model predicts the conditions under which escalation or de-escalation of immunosuppression would be the preferred treatment strategy. In an exceedingly rare condition such as SOT-aGvHD, where prospective trials are not feasible, mathematical modeling can provide useful insights into pathogenesis and treatment.

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.

Quantitative real-time ARMS-qPCR for mitochondrial DNA enables accurate detection of microchimerism in renal transplant recipients

The presence of microchimerism in peripheral blood of solid organ transplant recipients has been postulated to be beneficial for allograft acceptance. Kinetics of donor cell trafficking and accumulation in pediatric allograft recipients are largely unknown. In this study, we implemented SNPs of the HVRs I and II of mitochondrial DNA to serve as molecular genetic markers to detect donor-specific cell chimerism after pediatric renal transplantation. Serial dilution of artificial chimeric DNA samples showed a linear correlation coefficient of R > 0.98 and a detection sensitivity of 0.01% with high reproducibility. Longitudinal semiquantitative analysis of donor-specific SNPs was then performed in peripheral blood mononuclear cells samples up to two yr post-transplant. Quantity of donor-specific cell chimerism in peripheral blood was highest in the early post-transplant period reaching values of ~10% after liver-kidney and 2.8% after renal transplantation. From one wk after transplantation, renal transplant patients exhibited an amount of donor-specific mtDNA ranging from 0.01% to 0.1%. We developed a highly accurate, sensitive, and rapid real-time quantitative PCR method using sequence-specific primers and fluorescent hydrolysis probes for the detection of at least 0.01% donor-specific cells in the recipient's peripheral blood after renal 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.

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

Donor cell microchimerism induces tolerance in animal models and may increase graft survival in man. Since dendritic cells (DC) are critical for induction of both tolerance and alloreactivity we developed a method to quantitate microchimerism in donor DC and non-DC in peripheral blood mononuclear cells (PBMC) after lung transplantation. Longitudinal analysis of donor cell microchimerism in eleven sex mismatched lung transplant recipients (LTR) up to 12 months post-transplant used Y chromosome based real-time PCR on sorted cells. Total DC or a proportion of DC subsets in PBMC did not change but there were heterogeneous and dynamic changes in microchimerism in DC and non-DC. Analysis of changes in DC using a mixed model analysis showed significantly less reduction in DC compared to non-DC over time (0.49, p=0.001). Preferential DC persistence compared to non-DC may indicate tolerance induction but future studies are required to determine if DC microchimerism after transplantation affects clinical outcomes.

Review of vascularized bone marrow transplantation: Current status and future clinical applications

In this review, we examine the applicability of the vascularized bone marrow transplant (VBMT) as an alternative to conventional bone marrow transplantation (BMT). As a new surgical approach, the VBMT is unique by transplantation of the stromal environment that eliminates the need for an engraftment period, provides critical signaling and modulatory functions, and may potentiate tolerance induction. Thus far, VBMT studies have demonstrated an absence of graft-versus-host disease (GVHD) and robust engraftment into nonmanipulated as well as irradiated recipients with evidence of immunological tolerance. Further investigation is needed to determine the applicability of VBMT as an alternative to BMT.

Microchimerism in bone marrow–derived CD34+ cells of patients after liver transplantation

Lymphoid and dendritic cells of donor origin can be detected in the recipient several years after a solid organ transplantation. This phenomenon is termed microchimerism and could play a role in the induction of tolerance. The fate of other hematopoietic cells transferred by liver transplantation, in particular of stem and progenitor cells, is unknown. For this reason, we studied peripheral blood and bone marrow samples of 12 patients who had received a liver transplant from an HLA-DR mismatched donor. Eight patients were long-term survivors between 2.8 and 10.1 years after allografting. CD34+ cells from bone marrow were highly enriched with the use of a 2-step method, and a nested polymerase chain reaction was applied to detect donor cells on the basis of allelic differences of the HLA-DRB1 gene. Rigorous controls with DRB1 specificities equal to the donor and host were included. In 5 of 8 long-term liver recipients, donor-specific CD34+ cells could be detected in bone marrow. Microchimerism in the CD34+ cell fraction did not correlate to the chimeric status in peripheral blood. In conclusion, our results demonstrate a frequent microchimerism among bone marrow–derived CD34+ cells after liver transplantation. The functional role of this phenomenon still needs to be defined.

Microchimerism in bone marrow–derived CD34+ cells of patients after liver transplantation

Lymphoid and dendritic cells of donor origin can be detected in the recipient several years after a solid organ transplantation. This phenomenon is termed microchimerism and could play a role in the induction of tolerance. The fate of other hematopoietic cells transferred by liver transplantation, in particular of stem and progenitor cells, is unknown. For this reason, we studied peripheral blood and bone marrow samples of 12 patients who had received a liver transplant from an HLA-DR mismatched donor. Eight patients were long-term survivors between 2.8 and 10.1 years after allografting. CD34+ cells from bone marrow were highly enriched with the use of a 2-step method, and a nested polymerase chain reaction was applied to detect donor cells on the basis of allelic differences of the HLA-DRB1 gene. Rigorous controls with DRB1 specificities equal to the donor and host were included. In 5 of 8 long-term liver recipients, donor-specific CD34+ cells could be detected in bone marrow. Microchimerism in the CD34+ cell fraction did not correlate to the chimeric status in peripheral blood. In conclusion, our results demonstrate a frequent microchimerism among bone marrow–derived CD34+ cells after liver transplantation. The functional role of this phenomenon still needs to be defined.