Analysis of Pregnancy-Induced Anti-HLA Antibodies Using Luminex Platform

Human leukocyte antigen antibody sensitization, lung transplantation, and health equity

Women with advanced lung disease, particularly Black and Hispanic women, are more likely than other patients to have anti-human leukocyte (HLA) antibodies against potential donors. Sensitized patients, especially those who are highly sensitized, are less likely to be listed for lung transplant or to be considered candidates for mechanical circulatory support. They are also at higher risk for waitlist death. Institutional variability in approach to HLA antibody screening and pre-transplant management creates barriers to transplant that disproportionately impact Black and Hispanic women. At the same time, our understanding of the clinical significance of pre-transplant antibodies lags behind the sophistication of our screening assays. The lack of national data on pre- and post-transplant HLA antibody characteristics hinders research into strategies to mitigate concerns about these antibodies and to improve access to lung transplant among sensitized patients. Ongoing work should be done to identify clinically higher risk antibodies, to develop better strategies for safely crossing antibodies at the time of transplant, and to model changes in lung allocation to give priority to sensitized patients for a HLA antibody-antigen compatible donors. These priorities mandate a commitment to collaborative, multicenter research and to real time translation of results to clinical practice and allocation policy.

Pregnancy-induced humoral sensitization overrides T cell tolerance to fetus-matched allografts in mice

Immunological tolerance to semiallogeneic fetuses is necessary to achieving successful first pregnancy and permitting subsequent pregnancies with the same father. Paradoxically, pregnancy is an important cause of sensitization, resulting in the accelerated rejection of offspring-matched allografts. The underlying basis for divergent outcomes following reencounter of the same alloantigens on transplanted organs versus fetuses in postpartum females is incompletely understood. Using a mouse model that allows concurrent tracking of endogenous fetus-specific T and B cell responses in a single recipient, we show that semiallogeneic pregnancies simultaneously induce fetus-specific T cell tolerance and humoral sensitization. Pregnancy-induced antibodies, but not B cells, impeded transplantation tolerance elicited by costimulation blockade to offspring-matched cardiac grafts. Remarkably, in B cell-deficient mice, allogeneic pregnancy enabled the spontaneous acceptance of fetus-matched allografts. The presence of pregnancy-sensitized B cells that cannot secrete antibodies at the time of heart transplantation was sufficient to precipitate rejection and override pregnancy-established T cell tolerance. Thus, while induction of memory B cells and alloantibodies by pregnancies establishes formidable barriers to transplant success for multigravid women, our observations raise the possibility that humoral desensitization will not only improve transplantation outcomes, but also reveal an unexpected propensity of multiparous recipients to achieve tolerance to offspring-matched allografts.

Placental Immune Tolerance and Organ Transplantation: Underlying Interconnections and Clinical Implications

The immune system recognizes and attacks non-self antigens, making up the cornerstone of immunity activity against infection. However, during organ transplantation, the immune system also attacks transplanted organs and leads to immune rejection and transplantation failure. Interestingly, although the embryo and placenta are semi-allografts, like transplanted organs, they can induce maternal tolerance and be free of a vigorous immune response. Also, embryo or placenta-related antibodies might adversely affect subsequent organ transplantation despite the immune tolerance during pregnancy. Therefore, the balance between the immune tolerance in maternal-fetal interface and normal infection defense provides a possible desensitization and tolerance strategy to improve transplantation outcomes. A few studies on mechanisms and clinical applications have been performed to explore the relationship between maternal-fetal immune tolerance and organ transplantation. However, up to now, the mechanisms underlying maternal-fetal immune tolerance remain vague. In this review, we provide an overview on the current understanding of immune tolerance mechanisms underlying the maternal-fetal interface, summarize the interconnection between immune tolerance and organ transplantation, and describe the adverse effect of pregnancy alloimmunization on organ transplantation.

Memory B Cells in Pregnancy Sensitization

Memory B cells play an important role in immunity to pathogens as these cells are poised to rapidly differentiate into antibody-secreting cells upon antigen re-encounter. Memory B cells also develop over the course of HLA-sensitization during pregnancy and transplantation. In this review, we discuss the potential contribution of memory B cells to pregnancy sensitization as well as the impact of these cells on transplant candidacy and outcomes. We start by summarizing how B cell subsets are altered in pregnancy and discuss what is known about HLA-specific B cell responses given our current understanding of fetal antigen availability in maternal secondary lymphoid tissues. We then review the molecular mechanisms governing the generation and maintenance of memory B cells during infection - including the role of T follicular helper cells - and discuss the experimental evidence for the development of these cells during pregnancy. Finally, we discuss how memory B cells impact access to transplantation and transplant outcomes for a range of transplant recipients.

In utero exposure to alloantigens primes alloimmunization to platelet transfusion in mice

BACKGROUND

Platelet transfusions remain a mainstay of treatment for many patients with thrombocytopenia, but can lead to alloantibodies to Human Leukocyte Antigens (anti-HLA) resulting in inadequate responses to subsequent platelet transfusions (refractoriness), as well as complicate transplantation. Despite substantial decreases in alloimmunization with the implementation of leukoreduction, a significant percentage of patients still become alloimmunized following platelet transfusions. It remains unclear why some patients make anti-HLA antibodies, but others do not make anti-HLA antibodies even with chronic transfusion. Antecedent pregnancy correlates with risk of alloimmunization due to platelet transfusion in humans - however, isolation of pregnancy as a single variable is not possible in human populations.

STUDY DESIGN AND METHODS

A tractable murine model of pregnancy and transfusion was engineered by breeding C57BL/6 (H-2b ) dames with BALB/c (H-2d ) sires. After pregnancy, female mice were transfused with leukoreduced platelets from F1 (H-2b/d ) donors that expressed the same paternal major histocompatibility complex (MHC) H-2d alloantigens as the sires. Control groups allowed isolation of pregnancy or transfusion alone as independent variables. Alloimmunization was determined by testing serum for antibodies to H-2d MHC alloantigens.

RESULTS

No alloantibodies were detected after pregnancy alone, or in response to transfusion of platelets alone; however, significant levels of alloantibodies were detected when pregnancy was followed by transfusion.

CONCLUSIONS

These findings isolate antecedent pregnancy as a causal contribution to increased frequencies of alloimmunization by subsequent platelet transfusion in mice and provide a platform for ongoing mechanistic investigation.

Immunological Basis for Recurrent Fetal Loss and Pregnancy Complications

Pregnancy stimulates an elaborate assortment of dynamic changes, allowing intimate approximation of genetically discordant maternal and fetal tissues. Although the cellular and molecular details about how this works remain largely undefined, important clues arise from evaluating how a prior pregnancy influences the outcome of a future pregnancy. The risk of complications is consistently increased when complications occurred in a prior pregnancy. Reciprocally, a prior successful pregnancy protects against complications in a future pregnancy. Here, we summarize immunological perturbations associated with fetal loss, with particular focus on how both harmful and protective adaptations may persist in mothers. Immunological aberrancy as a root cause of pregnancy complications is also considered, given their shared overlapping risk factors and the sustained requirement for averting maternal-fetal conflict throughout pregnancy. Understanding pregnancy-induced immunological changes may expose not only new therapeutic strategies for improving pregnancy outcomes but also new facets of how immune tolerance works that may be applicable to other physiological and pathological contexts.

Rethinking the carcinogenesis of breast cancer: The theory of breast cancer as a child deficiency disease or a pseudo semi-allograft

The theory of breast cancer as a child deficiency disease is an inversion of the current paradigm, which considers full-term pregnancies to be a protective factor and uses nulliparous women as the reference group. Instead, the theory of breast cancer as a child deficiency disease says that women with the highest parity (about 20, which is the limit of human fertility) are those with the lowest risk and should be used as the reference group in risk estimations. This theory is explained biologically by converting parity from the simple value of number of children into an understanding of the long-lasting biological and immunological effects of pregnancy. These effects can be reflected, as measured by functional genomics, in gene expression of the immune cells in the blood. Each pregnancy represents a unique fetus or semi-allograft, which provokes the creation and deposit of memory cell clones in the mother. Gene expression levels have been found to change linearly with number of full-term pregnancies in healthy women, but not in breast cancer patients. High hormone levels are necessary for a successful pregnancy, as they modulate the immune response from adaptive to innate in order to protect the fetus (considered as a semi-allograft) from rejection. At the end of the pregnancy, hormone levels drop, and the immune system recognizes the semi-allograft, but not in time for rejection to occur before birth. High hormones levels are also classified as carcinogens illustrating that carcinogenesis in the breast could be viewed as a war or balance between later exposures to hormonal carcinogens and the protection of the immune system. We propose that breast tumors are pseudo semi-allografts made up of transformed breast tissue cells. Assuming that the sensitivity to the exposure to increased levels of endogenous or exogenous hormones in women with breast cancer mimic those that occur in pregnancy, these breast tumor cells are protected against the body's immune reaction, just as the fetus is during pregnancy. However, with more pregnancies, the potential to eradicate the pseudo semi-allograft might increase due to enhanced immune surveillance. The theory of breast cancer as a child deficiency disease proposes that the protective effect of pregnancy on breast cancer incidence via the immune system is independent of other risk factors.

Biologic mechanisms and clinical consequences of pregnancy alloimmunization

Alloimmunization occurs during pregnancy when tissue antigens derived from the fetus and/or placenta prime maternal immune cells to divide and differentiate. For many women, the result of pregnancy alloimmunization is the formation of anti-HLA antibody that can endure for decades and preclude transplantation by limiting donor compatibility. Pregnancy alloimmunization may also generate memory B cells that can rapidly produce anti-HLA antibody after transplantation as well as pathogenic memory T cells, which pose a threat to graft survival. However, emerging data suggest that pregnancy also programs the differentiation of anergic, dysfunctional, and regulatory T cell populations, which may not mediate accelerated graft rejection. Hence, some of the immune mechanisms responsible for maternal immunologic tolerance of the fetus may persist into postpartum life and affect the response to an allograft. This review discusses these emerging data as well as the persistent knowledge gaps that affect women at multiple stages of their transplant care.

Comparison of the Luminex xTAG Respiratory Viral Panel Fast v2 Assay With Anyplex II RV16 Detection Kit and AdvanSure RV Real-Time RT-PCR Assay for the Detection of Respiratory Viruses

Background

The accurate and rapid identification of the causative viruses is important for the timely diagnosis and management of respiratory infections. Multiplex molecular diagnostic techniques have been widely adopted to detect respiratory viruses. We compared the results of a newly upgraded, multiplex, molecular bead-based respiratory viral panel (RVP) assay with the results of Anyplex II RV16 detection kit and AdvanSure RV real-time RT-PCR assay.

Methods

We tested 254 respiratory specimens and cultured viral strains using the Luminex xTAG RVP Fast v2 assay (Luminex Molecular Diagnostics, Canada) and Anyplex II RV16 detection kit and compared the results. Specimens showing discordant results between the two assays were tested with a AdvanSure RV real-time RT-PCR assay.

Results

Of the 254 respiratory specimens, there was total agreement in the results between the xTAG RVP Fast v2 assay and the other real-time PCR assay in 94.1–100% of the specimens. The agreement levels were relatively low (94.1–97.6%) for specimens of adenovirus, coronavirus NL63, and parainfluenza type 3. In comparison to the other assay, the xTAG RVP Fast v2 assay detected a higher number of parainfluenza type 3 (4 cases) and metapneumovirus (9 cases).

Conclusions

The xTAG RVP Fast v2 assay showed comparable capabilities compared with the other assays; it will be useful for identifying respiratory viral infections in patients with respiratory symptoms. Clinicians should be aware of the characteristics of the assays they use, since different assays show different detectability for each virus.

Platelet component transfusion and alloimmunization: Where do we stand?

Platelet transfusion in patients, particularly in onco-haematology, is frequent and can become chronic in some cases. Post-transfusion alloimmunization is often seen, in practice. The risk of this is significantly improved in multitransfused patients. Several classes of antigens binding on platelets (HLA and HPA) are involved and also red blood cell antigens (residual red blood cells in platelet concentrates). Platelet alloimmunization causes a poor transfusion response, refractoriness and, more rarely, post-transfusion purpura. In an alloimmunized recipient, the efficiency of platelet transfusion is based on the selection of compatible products. Significant technical progress means that several methods are currently available to ensure a good post-transfusion platelet count and a satisfactory clinical outcome for the patient.

Complement-dependent cytotoxicity and Luminex technology for human leucocyte antigen antibody detection in kidney transplant candidates exposed to different sensitizing events

Background

The aim of this study was to determine the frequency of exposure to different sensitizing events (SEs) and to assess their effects on human leucocyte antigen (HLA) alloimmunization in transplant candidates using two different HLA antibody screening techniques: complement-dependent cytotoxicity (CDC) and Luminex.

Methods

This retrospective study included HLA antibody screening results for 163 patients on the kidney transplant waiting list (WL) tested from March 2012 until the end of December 2015 at the Tissue Typing Laboratory, Rijeka, Croatia. All sera samples were tested using the CDC and Luminex techniques in parallel.

Results

Two-thirds of the patients [114 (70%)] on the WL were exposed to transfusions, pregnancies and/or kidney transplant. The pre-transplant sera of 104 (63.80%) patients were negative for antibodies. In the sera of 23 (14.11%) patients, HLA antibodies were detected by CDC and Luminex and in the sera of 36 (22.09%) patients by Luminex only.

Conclusion

In patients on kidney WL, previous organ transplantation represents the strongest immunogenic stimulus, followed by blood transfusions (the most frequent SE) and pregnancies. Although Luminex is more sensitive than CDC in HLA antibody detection, the decision on unacceptable HLA antigens in WL patients has to be based on the results of both assays and the patient's immunization history.

Immunological implications of pregnancy-induced microchimerism

Immunological identity is traditionally defined by genetically encoded antigens, with equal maternal and paternal contributions as a result of Mendelian inheritance. However, vertically transferred maternal cells also persist in individuals at very low levels throughout postnatal development. Reciprocally, mothers are seeded during pregnancy with genetically foreign fetal cells that persist long after parturition. Recent findings suggest that these microchimeric cells expressing non-inherited, familially relevant antigenic traits are not accidental 'souvenirs' of pregnancy, but are purposefully retained within mothers and their offspring to promote genetic fitness by improving the outcome of future pregnancies. In this Review, we discuss the immunological implications, benefits and potential consequences of individuals being constitutively chimeric with a biologically active 'microchiome' of genetically foreign cells.