Nucleic Acid Testing of Organ Donors: Is the Glass Half Empty or Half Full?

In this issue of the American Journal of Transplantation, Suryaprasad and colleagues present 3 cases of hepatitis C virus (HCV) transmission from seronegative, nucleic acid test (NAT)–negative donors to solid organ transplant recipients. This case series represents one of the greatest contributions to the literature on risk mitigation strategies against donor-derived infections and will most definitely add fuel to the ongoing debate about the benefit of NAT in organ donors. Briefly, all three organ donors had evidence of active nonmedical injection drug use up to the time of the event leading to their demise: Donor 1 was hospitalized due to a heroin overdose; donor 2 with evidence of IV track marks on physical exam; and donor 3 with toxicology results positive for opiates. All of the donors had undetectable NAT at the time of initial evaluation: 2 were tested on the second day of hospitalization and one on the fourth day of hospitalization. Subsequent retrospective testing of stored splenocytes or lymphocytes collected during organ procurement detected HCV RNA. Eight of 12 (66.7%) recipients from these three donors acquired a donor-derived HCV infection with testing of the index recipient at day 9, 32, and 66, respectively. With its findings, the case series greatly informs 3 critical issues that have been the center of an ongoing debate within the transplant community: (1) the limitations of donor NAT, (2) the importance of recipient follow-up testing, and (3) how we define donors at increased risk for disease transmission (read more).

Mutant MHC class II epitopes drive therapeutic immune responses to cancer

Tumour-specific mutations are ideal targets for cancer immunotherapy as they lack expression in healthy tissues and can potentially be recognized as neo-antigens by the mature T-cell repertoire. Their systematic targeting by vaccine approaches, however, has been hampered by the fact that every patient’s tumour possesses a unique set of mutations (‘the mutanome’) that must first be identified. Recently, we proposed a personalized immunotherapy approach to target the full spectrum of a patient’s individual tumour-specific mutations. Here we show in three independent murine tumour models that a considerable fraction of non-synonymous cancer mutations is immunogenic and that, unexpectedly, the majority of the immunogenic mutanome is recognized by CD4+ T cells. Vaccination with such CD4+ immunogenic mutations confers strong antitumour activity. Encouraged by these findings, we established a process by which mutations identified by exome sequencing could be selected as vaccine targets solely through bioinformatic prioritization on the basis of their expression levels and major histocompatibility complex (MHC) class II-binding capacity for rapid production as synthetic poly-neo-epitope messenger RNA vaccines. We show that vaccination with such polytope mRNA vaccines induces potent tumour control and complete rejection of established aggressively growing tumours in mice. Moreover, we demonstrate that CD4+ T cell neo-epitope vaccination reshapes the tumour microenvironment and induces cytotoxic T lymphocyte responses against an independent immunodominant antigen in mice, indicating orchestration of antigen spread. Finally, we demonstrate an abundance of mutations predicted to bind to MHC class II in human cancers as well by employing the same predictive algorithm on corresponding human cancer types. Thus, the tailored immunotherapy approach introduced here may be regarded as a universally applicable blueprint for comprehensive exploitation of the substantial neo-epitope target repertoire of cancers, enabling the effective targeting of every patient’s tumour with vaccines produced ‘just in time’ (read more)

β2-Glycoprotein I/HLA class II complexes are novel autoantigens in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thrombosis and/or pregnancy complications. β2-glycoprotein I (β2GPI) complexed with phospholipid is recognized as a major target for autoantibodies in APS; however, less than half the patients with clinical manifestations of APS possess autoantibodies against the complexes. Therefore, the range of autoantigens involved in APS remains unclear. Recently, we found that human leukocyte antigen (HLA) class II molecules transport misfolded cellular proteins to the cell surface via association with their peptide-binding grooves. Furthermore, immunoglobulin G heavy chain/HLA class II complexes were specific targets for autoantibodies in rheumatoid arthritis. Here, we demonstrate that intact β2GPI, not peptide, forms a complex with HLA class II molecules. Strikingly, 100 (83.3%) of the 120 APS patients analyzed, including those whose antiphospholipid antibody titers were within normal range, possessed autoantibodies that recognize β2GPI/HLA class II complexes in the absence of phospholipids. In situ association between β2GPI and HLA class II was observed in placental tissues of APS patients but not in healthy controls. Furthermore, autoantibodies against β2GPI/HLA class II complexes mediated complement-dependent cytotoxicity against cells expressing the complexes. These data suggest that β2GPI/HLA class II complexes are a target in APS that might be involved in the pathogenesis (read more)

Assessing Antibody Strength: Comparison of MFI, C1q, and Titer Information

The presence of donor-specific HLA antibodies before or after transplantation may have different implications based on the antibody strength. Yet, current approaches do not provide information regarding the true antibody strength as defined by antigen–antibody dissociation rate. To assess currently available methods, we compared between neat mean fluorescence intensity (MFI) values, C1q MFI values, ethylenediaminetetraacetic acid (EDTA)-treated samples, as well as titration studies and peak MFI values of over 7000 Luminex-based single-antigen HLA antibody data points. Our results indicate that neat MFI values do not always accurately depict antibody strength. We further showed that EDTA treatment (6%) does not always remove all inhibitory factors compared with C1q or titration studies. In this study of patients presenting with multiple antibody specificities, a prozone effect was observed in 71% of the cohort (usually not affecting all antibody specificities within a single serum sample, though). Similar to titration studies, the C1q assay was able to address the issue of potential inhibition; however, its limitation is its low sensitivity and inability to detect the presence of weak antibodies. Titration studies are the only method among the approaches used in this study to provide information suggesting antigen–antibody dissociation rates and are, therefore, likely to provide better indication of true antibody strength (read more)

Transfer of HLA-Specific Allosensitization From a Highly Sensitized Deceased Organ Donor to the Recipients of Each Kidney

We report for the first time the adoptive transfer of donor HLA-specific allosensitization in two recipients following kidney transplantation from a highly sensitized donor. Kidneys from a donation after circulatory death donor were transplanted into two nontransfused, HLA-specific antibody negative males receiving their first transplant. Antibody screening 7 days after transplant showed high level de novo IgG HLA class I- and class II-specific antibodies in both recipients, with largely overlapping antibody profiles but no antibodies to donor HLA. The unusually rapid appearance of de novo alloantibodies in immunosuppressed nonsensitized recipients and absence of donor HLA-specific antibody prompted testing of stored donor serum that revealed high antibody levels with specificities very similar to those seen in both recipients, but in addition the presence of strong antibodies to each recipient HLA. Alloantibody levels gradually declined but were still detectable at 3 months. These findings suggest that alloreactive passenger B cells/plasma cells within the kidneys of highly sensitized donors may give rise to rapid development of posttransplant de novo HLA-specific alloantibodies. While the clinical significance of this phenomenon is uncertain it provides one explanation for the appearance of de novo HLA-specific antibodies directed against third party but not donor HLA (read more)

Maintaining immunosuppressive treatment after early allograft nephrectomy does not reduce the risk of anti-HLA allo-sensitization

Early loss of a kidney allograft within the first days or weeks after transplantation occurs in 3–5% of kidney-transplant patients (1) (2). It is mainly caused by artery and/or vein allograft thrombosis (2), and requires a rapid allograft nephrectomy. We have previously shown that, even after a short transplant period, donor-specific antibodies (DSAs) and non-DSA anti-HLA antibodies develop in up to 50% of patients who stop immunosuppressive treatments immediately after an early allograft nephrectomy (3). Mechanisms leading to sensitization are incompletely explained, but could involve the persistence of the donor's antigens after allograft removal, particularly in the vascular patches (read more)

The old transplant recipient that becomes a liver donor

The success of transplantation has made it inevitable that there will be more transplant recipients that become potential cadaveric donors. The re-use of allografts and utilization of other organs from former transplant recipients will add to the limited donor pool. In addition, many transplant recipients will want the opportunity to donate in return. The following is a short report on two liver donors who were former transplant recipients (read more)