Kidney‐Induced Cardiac Allograft Tolerance in Miniature Swine is Dependent on MHC‐Matching of Donor Cardiac and Renal Parenchyma

Kidney allografts possess the ability to enable a short course of immunosuppression to induce tolerance of themselves and of cardiac allografts across a full‐MHC barrier in miniature swine. However, the renal element(s) responsible for kidney‐induced cardiac allograft tolerance (KICAT) are unknown. Here we investigated whether MHC disparities between parenchyma versus hematopoietic‐derived “passenger” cells of the heart and kidney allografts affected KICAT. Heart and kidney allografts were co‐transplanted into MHC‐mismatched recipients treated with high‐dose tacrolimus for 12 days. Group 1 animals (n = 3) received kidney and heart allografts fully MHC‐mismatched to each other and to the recipient. Group 2 animals (n = 3) received kidney and heart allografts MHC‐matched to each other but MHC‐mismatched to the recipient. Group 3 animals (n = 3) received chimeric kidney allografts whose parenchyma was MHC‐mismatched to the donor heart. Group 4 animals (n = 3) received chimeric kidney allografts whose passenger leukocytes were MHC‐mismatched to the donor heart. Five of six heart allografts in Groups 1 and 3 rejected <40 days. In contrast, heart allografts in Groups 2 and 4 survived >150 days without rejection (p < 0.05). These data demonstrate that KICAT requires MHC‐matching between kidney allograft parenchyma and heart allografts, suggesting that cells intrinsic to the kidney enable cardiac allograft tolerance.     

Vascular Management During Live Donor Nephrectomy: An Online Survey Among Transplant Surgeons

In 2006, a survey from the American Society of Transplant Surgeons disclosed significant and sometimes fatal hemorrhagic events in live donor nephrectomies (LDN) related to failure of clips, leading to the contraindication of the Weck® Hem‐o‐lok® clip for control of the renal artery during LDN. A survey regarding vascular control techniques, their perceived safety ratings and their failures was sent to 645 European Society for Organ Transplantation members who profiled their profession as “surgeon” and selected “kidney” as organ type. Two hundred forty‐three (41%) members responded, of whom 171 (63.3%) independently perform LDN. Their responses were analyzed. For arterial and venous vascular control, the GIA? and TA?stapler are used most frequently, and were rated the safest. Of the 121 reported hemorrhagic events, slippage and dislodgement of clips occurred at least 58 times, while stapler malfunction occurred at least 40 times. One donor death from hemorrhage related to clip dysfunction was reported. Hemorrhagic complications of LDN with fatal and non‐fatal outcomes still occur. Strikingly, many surgeons do not use the vascular closing technique that they consider most safe. Failure of non‐transfixion techniques is associated with greater risks for the donor. Control of major vessels in LDN must employ transfixion techniques for optimal donor safety.

     

Immunophenotypic Profile and Increased Risk of Hospital Admission for Infection in Infants Born to Female Kidney Transplant Recipients

Children born to female kidney recipients are exposed to immunosuppressive drugs during gestation. Little is known about their immune system at birth or in the long term. Twenty‐eight children born to female kidney recipients and 40 full‐term children born to healthy mothers were evaluated. T, B, NK, NKT, γδT cells were assessed by flow cytometry and functional evaluation of T and dendritic cells after in vitro activation was performed at birth and at 8 months of age. At birth, infants born to female kidney recipients showed lower numbers of CD4+ T, NKT and intense reduction of B cells (median cells/mm³, transplant: 153.7 X control: 512.4; p < 0.001). There was also a reduced percentage of activated CD8+ T and of CD4+ regulatory T cells. Activated memory and exhausted memory B cells showed higher percentages among children exposed to immunosuppressors when compared to control group. At 8 months, most immune alterations were no longer observed, but four children still had low numbers of some lymphocyte subsets at this age. Children born to female kidney recipients had 4.351 (95% CI: 1.026–15.225; p = 0.046) higher risk of hospital admission in the first months of life—some, with severe clinical manifestations—than those born to healthy women.     

siRNA Mediated Knockdown of Tissue Factor Expression in Pigs for Xenotransplantation

Acute vascular rejection (AVR), in particular microvascular thrombosis, is an important barrier to successful pig‐to‐primate xenotransplantation. Here, we report the generation of pigs with decreased tissue factor (TF) levels induced by small interfering (si)RNA‐mediated gene silencing. Porcine fibroblasts were transfected with TF‐targeting small hairpin (sh)RNA and used for somatic cell nuclear transfer. Offspring were analyzed for siRNA, TF mRNA and TF protein level. Functionality of TF downregulation was investigated by a whole blood clotting test and a flow chamber assay. TF siRNA was expressed in all twelve liveborn piglets. TF mRNA expression was reduced by 94.1 ± 4.7% in TF knockdown (TFkd) fibroblasts compared to wild‐type (WT). TF protein expression in PAEC stimulated with 50 ng/mL TNF‐α was significantly lower in TFkd pigs (mean fluorescence intensity TFkd: 7136 ± 136 vs. WT: 13 038 ± 1672). TF downregulation significantly increased clotting time (TFkd: 73.3 ± 8.8 min, WT: 45.8 ± 7.7 min, p < 0.0001) and significantly decreased thrombus formation compared to WT (mean thrombus coverage per viewing field in %; WT: 23.5 ± 13.0, TFkd: 2.6 ± 3.7, p < 0.0001). Our data show that a functional knockdown of TF is compatible with normal development and survival of pigs. TF knockdown could be a valuable component in the generation of multi‐transgenic pigs for xenotransplantation.     

Early Changes in Liver Distribution Following Implementation of Share 35

In June 2013, a change to the liver waitlist priority algorithm was implemented. Under Share 35, regional candidates with MELD ≥ 35 receive higher priority than local candidates with MELD < 35. We compared liver distribution and mortality in the first 12 months of Share 35 to an equivalent time period before. Under Share 35, new listings with MELD ≥ 35 increased slightly from 752 (9.2% of listings) to 820 (9.7%, p = 0.3), but the proportion of deceased‐donor liver transplants (DDLTs) allocated to recipients with MELD ≥ 35 increased from 23.1% to 30.1% (p < 0.001). The proportion of regional shares increased from 18.9% to 30.4% (p < 0.001). Sharing of exports was less clustered among a handful of centers (Gini coefficient decreased from 0.49 to 0.34), but there was no evidence of change in CIT (p = 0.8). Total adult DDLT volume increased from 4133 to 4369, and adjusted odds of discard decreased by 14% (p = 0.03). Waitlist mortality decreased by 30% among patients with baseline MELD > 30 (SHR = 0.70, p < 0.001) with no change for patients with lower baseline MELD (p = 0.9). Posttransplant length‐of‐stay (p = 0.2) and posttransplant mortality (p = 0.9) remained unchanged. In the first 12 months, Share 35 was associated with more transplants, fewer discards, and lower waitlist mortality, but not at the expense of CIT or early posttransplant outcomes.