Humoral autoimmunity after solid organ transplantation: Germinal ideas may not be natural

New insights in immunomodulation for intestinal transplantation

Tolerance is the Holy Grail of solid organ transplantation (SOT) and remains its primary challenge since its inception. In this topic, the seminal contributions of Thomas Starzl at Pittsburgh University outlined foundational principles of graft acceptance and tolerance, with chimerism emerging as a pivotal factor. Immunologically, intestinal transplantation (ITx) poses a unique hurdle due to the inherent characteristics and functions of the small bowel, resulting in increased immunogenicity. This necessitates heavy immunosuppression (IS) while IS drugs side effects cause significant morbidity. In addition, current IS therapies fall short of inducing clinical tolerance and their discontinuation has been proven unattainable in most cases. This underscores the unfulfilled need for immunological modulation to safely reduce IS-related burdens. To address this challenge, the Leuven Immunomodulatory Protocol (LIP), introduced in 2000, incorporates various pro-tolerogenic interventions in both the donor to the recipient, with the aim of facilitating graft acceptance and improving outcome. This review seeks to provide an overview of the current understanding of tolerance in ITx and outline recent advances in this domain.

Bioequivalence evaluation and blood concentration estimation of generic and branded tacrolimus in healthy subjects under fasting: A randomized, four-periods, two-sequences, complete repeated, crossover study

OBJECTIVE

The demand for generic tacrolimus is enormous. Our randomized trial was an open-label single-dose testing with four-periods and two-sequences; we aimed to evaluate the bioequivalence between a generic and branded tacrolimus by establishing their area under concentration-time curve (AUC) predictive equations. For better comparison, each tacrolimus served either as test vs. reference in sequence 1 or vice versa as reference vs. test in sequence 2.

METHODS

Forty healthy subjects were randomized into two groups, namely a sequence 1 group (N = 20 in test-reference-test-reference) or sequence 2 (N = 20, reference-test-reference-test) received a test tacrolimus (Ruibeirong®; Chengdu Shengdi Medicine Co., Ltd.) and a reference tacrolimus (Astagraf XL®, Astellas Ireland Co., Ltd.) under the fasting condition with a wash-out period of ≥14 days between every two phases. Blood samples were collected sequentially until 120 h after oral administration of tacrolimus.

RESULTS

A 95% upper confidence bound was -0.05% for the peak concentration (Cmax), -0.02% for the AUC from 0 to the last time point (AUC0-t), and - 0.02% for the AUC from 0 to infinity (AUC0-∞). The geometric least square means ratio (test/reference) with 90% of confidence interval (CI)) was 96.10% (90.58%-101.95%) for Cmax, 93.80% (88.52%-99.39%) for AUC0-t, and 94.34% (89.20%-99.77%) for AUC0-∞. Meanwhile, the ratio of within-subject standard deviation of test/reference (σWT/WR) with 90% CI was 0.66 (0.50-0.86) for Cmax, 0.73 (0.55-0.96) for AUC0-t, and 0.75 (0.57-0.98) for AUC0-∞. These results fulfilled the bioequivalence criteria by the Food and Drug Administration. Both products showed acceptable safety. Moreover, the AUC predictive equations (by linear regression plus limited sampling strategy) with 2-5 sampling time point showed the high performance (all R > 0.970, predictive error (PE) >0.5%, absolute PE <5.1%, which were interchangeable between test and reference products.

CONCLUSION

Generic tacrolimus (Ruibeirong®) is bioequivalent to branded tacrolimus (Astagraf XL®) with tolerable safety, which AUC predictive equations work well and are interchangeable between the two products.

Destructive inflammatory reaction after an autologous retinal pigment epithelium and choroid transplantation: no detection of an auto-immune response

Purpose

Five patients who underwent uncomplicated retinal pigment epithelium (RPE)-choroid transplantation for neovascular age-related macular degeneration developed a destructive inflammatory reaction causing subretinal fluid accumulation and extensive RPE atrophy in the graft. We hypothesized that this inflammation could be caused by an auto-immune response against the graft, resulting in circulating auto-antibodies. The aim of our study was to examine a potential autoimmune origin, which would allow a more targeted therapy approach.

Methods

Five above-mentioned patients and four control groups of five patients each were included: 1) after uncomplicated RPE-choroid transplantation, 2) after full macular translocation, 3) treated with anti-vascular endothelial growth factor, and 4) healthy controls. Histopathology of rejected graft tissue was performed using standard procedures. Presence of RPE-choroid autoantibodies in serum was examined by indirect immunofluorescence and Western blot, and human leukocyte antigen (HLA) typing was performed.

Results

Histopathological examination of an explanted graft showed infiltration of T-lymphocytes and macrophages in the choroid and RPE, and an increased number of B-cell lymphocytes were found in the choroid. Indirect immunofluorescence showed weak RPE-choroid autoantibody immunoreactivity in three patients of different groups. Western blot did not show specific RPE-choroid autoantibody immunoreactivity and no difference of HLA genotypes between the groups was found.

Conclusions

Although local mononuclear inflammatory cell infiltration and a high number of B-lymphocytes were observed in an explanted graft, we did not detect serological evidence of an autoimmune origin of the postoperative inflammation using direct immunofluorescence and Western Blot. Alternatively, the graft failure may have been caused by local innate inflammation, triggered by breakdown of tolerance. Based on our current findings of this small study group, we have no rationale to pursue therapies targeted towards autoreactive graft failure. More research is needed to confirm our findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12348-022-00305-2.

Allorecognition and the spectrum of kidney transplant rejection

Detection of mismatched human leukocyte antigens by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection or antibody-mediated rejection. This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several observations have recently emerged that question this dichotomization between T-cell mediated rejection and antibody-mediated rejection, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-human leukocyte antigen antibodies, the immunogenicity of donor-recipient non-human leukocyte antigen mismatches, and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies, and better outcome after kidney transplantation.

Selenium Deficiency Due to Diet, Pregnancy, Severe Illness, or COVID-19-A Preventable Trigger for Autoimmune Disease

The trace element selenium (Se) is an essential part of the human diet; moreover, increased health risks have been observed with Se deficiency. A sufficiently high Se status is a prerequisite for adequate immune response, and preventable endemic diseases are known from areas with Se deficiency. Biomarkers of Se status decline strongly in pregnancy, severe illness, or COVID-19, reaching critically low concentrations. Notably, these conditions are associated with an increased risk for autoimmune disease (AID). Positive effects on the immune system are observed with Se supplementation in pregnancy, autoimmune thyroid disease, and recovery from severe illness. However, some studies reported null results; the database is small, and randomized trials are sparse. The current need for research on the link between AID and Se deficiency is particularly obvious for rheumatoid arthritis and type 1 diabetes mellitus. Despite these gaps in knowledge, it seems timely to realize that severe Se deficiency may trigger AID in susceptible subjects. Improved dietary choices or supplemental Se are efficient ways to avoid severe Se deficiency, thereby decreasing AID risk and improving disease course. A personalized approach is needed in clinics and during therapy, while population-wide measures should be considered for areas with habitual low Se intake. Finland has been adding Se to its food chain for more than 35 years-a wise and commendable decision, according to today's knowledge. It is unfortunate that the health risks of Se deficiency are often neglected, while possible side effects of Se supplementation are exaggerated, leading to disregard for this safe and promising preventive and adjuvant treatment options. This is especially true in the follow-up situations of pregnancy, severe illness, or COVID-19, where massive Se deficiencies have developed and are associated with AID risk, long-lasting health impairments, and slow recovery.

A Comprehensive Overview of the Clinical Relevance and Treatment Options for Antibody-mediated Rejection Associated With Non-HLA Antibodies

Although solid organ transplant results have improved significantly in recent decades, a pivotal cause of impaired long-term outcome is the development of antibody-mediated rejection (AMR), a condition characterized by the presence of donor-specific antibodies to HLA or non-HLA antigens. Highly HLA-sensitized recipients are treated with desensitization protocols to rescue the transplantation. These and other therapies are also applied for the treatment of AMR. Therapeutic protocols include removal of antibodies, depletion of plasma and B cells, inhibition of the complement cascade, and suppression of the T-cell-dependent antibody response. As mounting evidence illustrates the importance of non-HLA antibodies in transplant outcome, there is a need to evaluate the efficacy of treatment protocols on non-HLA antibody levels and graft function. Many reviews have been recently published that provide an overview of the literature describing the association of non-HLA antibodies with rejection in transplantation, whereas an overview of the treatment options for non-HLA AMR is still lacking. In this review, we will therefore provide such an overview. Most reports showed positive effects of non-HLA antibody clearance on graft function. However, monitoring non-HLA antibody levels after treatment along with standardization of therapies is needed to optimally treat solid organ transplant recipients.

Immunogenic properties of immunoglobulin superfamily members within complex biological networks

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Antibody-based therapies induce CDR-specific T and B cell responses.

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Idiotype-anti-idiotype network alters immune system memory compartment.

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Antigenized antibodies are efficient vaccine immunogen.

Antibodies, T cell receptors and major histocompatibility complex molecules are members of the immunoglobulin superfamily and have pivotal roles in the immune system. The fine interrelation between them regulates several immune functions. Here, we describe lesser-known functions ascribed to these molecules in generating and maintaining immune response. Particularly, we outline the contribution of antibody- and T cell receptor-derived complementarity-determining region neoantigens, antigenized antibodies, as well as major histocompatibility complex class I molecules-derived epitopes to the induction of protective/therapeutic immune responses against pathogens and cancer. We discuss findings of our own and other studies describing protective mechanisms, based on immunogenic properties of immunoglobulin superfamily members, and evaluate the perspectives of application of this class of immunogens in molecular vaccines design.