The histologic associations and clinical implications of peritubular capillary C4d staining from long-term renal allografts are unknown. We identified 99 renal transplant patients who underwent an allograft biopsy for renal dysfunction at least 10 yr after transplantation, 25 of whom were C4d-positive and 74 of whom were C4d-negative. The average time of the index biopsy from transplantation was 14 yr in both groups. Compared with C4d-negative patients, C4d-positive patients were younger at transplantation (29 Ϯ 13 versus 38 Ϯ 12 yr; P Ͻ 0.05) and were more likely to have received an allograft from a living donor (65 versus 35%; P Ͻ 0.001). C4d-positive patients had more inflammation, were more likely to have transplant glomerulopathy, and had worse graft outcome. The combined presence of C4d positivity, transplant glomerulopathy, and serum creatinine of Ͼ2.3 mg/dl at biopsy were very strong predictors of rapid graft loss. C4d alone did not independently predict graft loss. Retrospective staining of historical samples from C4d-positive patients demonstrated C4d deposition in the majority of cases. In summary, these data show that in long-term renal allografts, peritubular capillary staining for C4d occurs in approximately 25% of biopsies, can persist for many years after transplantation, and strongly predicts graft loss when combined with transplant glomerulopathy.

Invariant or Type 1 NKT cells (iNKT cells) are a unique population of lymphocytes that share characteristics of T cells and natural killer (NK) cells. Various studies have shown that positive costimulatory pathways such as the CD28 and CD40 pathways can influence the expansion and cytokine production by iNKT cells. However, little is understood about the regulation of iNKT cells by negative costimulatory pathways. Here, we show that in vivo activation with α-GalCer results in increased cytokine production and expansion of iNKT cells in the absence of programmed cell death ligand-1 (PD-L1, B7-H1, and CD274). To study whether PD-L1 deficiency on NKT cells would enhance antigen-specific T-cell responses, we utilized CD8+ OT-1 OVA transgenic T cells. α-GalCer enhanced the expansion and cytokine production of OT-1 CD8+ cells after adoptive transfer into wild-type recipients. However, this expansion was significantly enhanced when OT-1 CD8+ T cells were adoptively transferred into PD-L1−/− recipients. To extend these results to a tumor model, we used the B16 melanoma system. PD-L1−/− mice given dendritic cells loaded with antigen and α-GalCer had a significant reduction in tumor growth and this was associated with increased trafficking of antigen-presenting cells and CD8+ T cells to the tumors. These data demonstrate that abrogating PDL1:PD-1 interactions during the activation of iNKT cells amplifies an anti-tumor response when coupled with DC vaccination.

The ability to efficiently and accurately diagnose the cause(s) of platelet (PLT) refractoriness is paramount in providing effective PLT products for transfusion. Recent advances in methods for detecting and identifying alloantibodies against human leukocyte antigens (HLAs) and human PLT antigens, combined with accurate molecular techniques for HLA typing, have provided a framework for the development of clinical algorithms to support such patients. Alloantibodies may be detected and/or identified by several methods, including complement-dependent cytotoxicity, enzyme-linked immunosorbent assays (ELISA), and microbead-based assays using Luminex or flow cytometry. The primary difference in these assays is the sensitivity of detection and the range of antibody specificities that may be reliably identified. Direct PLT cross-matching to identify compatible PLTs can be accomplished by several methods, including solid-phase red cell adherence, modified antigen capture ELISA, and flow cytometry. A survey of blood centers and laboratories providing transfusion support has identified the heterogeneity of testing options available, areas of concern and need for improvement, and common obstacles in providing appropriate and timely support to immune-refractory PLT patients. Depending on the testing methods and the pool of HLA-typed PLT donors available, there are numerous options for developing suitable algorithms to provide effective support to immune-refractory PLT patients.

To increase transplantation access, particularly in living-donor renal transplantation, efforts have been made to overcome the barrier of ABO incompatibility. In adults, the most successful cases have involved renal transplantation. Although the overall goal of reducing antibodies against donor ABO before and after transplantation is a general principle, the protocols used to accomplish this goal vary. More well-designed, controlled clinical trials are needed to establish optimal peritransplantation management protocols. Incompatible liver transplantation still is viewed as a temporary measure until ABO-compatible transplantation can be performed. ABO-incompatible heart and lung transplantation in adults still is not performed intentionally. In children, particularly those with relatively immature immune systems, ABO-incompatible transplantation generally has more success. The immunologic mechanisms leading to successful transplantation are being elucidated. Accommodation is a process whereby the donor organ may participate in its own survival through a series of protective gene responses, possibly in response to low-level incompatible antibody (HLA and ABO). In infants, spontaneous, acquired B-cell tolerance seems to be a primary mechanism. Peritransplantation therapy might be tailored to invoke specific immune graft-sparing mechanisms. The stage is set to eliminate ABO as a barrier to solid-organ transplantation.