Discrepant Antibody Testing Results: Which One to Believe?

Crossmatch assays in transplantation: Physical or virtual?: A review

The value of the crossmatch test in assessing pretransplant immunological risk is vital for clinical decisions, ranging from the indication of the transplant to the guidance of induction protocols and treatment with immunosuppressants. The crossmatch tests in transplantation can be physical or virtual, each with its advantages and limitations. Currently, the virtual crossmatch stands out for its sensitivity and specificity compared to the physical tests. Additionally, the virtual crossmatch can be performed in less time, allowing for a reduction in cold ischemia time. It shows a good correlation with the results of physical tests and does not negatively impact graft survival. Proper communication between clinicians and the transplant immunology laboratory will lead to a deeper understanding of each patient's immunological profile, better donor-recipient selection, and improved graft survival.

Humoral response to SARS-CoV-2 mRNA vaccine on in ABO blood type incompatible kidney transplant recipients treated with low-dose rituximab

We aimed to evaluate the humoral response after the second and third doses of SARS-CoV-2 mRNA vaccine in ABO blood type incompatible kidney transplant (KT) recipients treated with rituximab. This retrospective study conducted between June 2021 and June 2022 included 131 KT recipients and 154 nontransplant controls who had received mRNA vaccines. We compared the seropositivity (anti-SARS-CoV-2 spike IgG antibody titer ≥ 0.8 U/mL) after the second and third vaccinations. Furthermore, we evaluated the impact of pretransplant vaccination for seropositivity. Of the 131 KT recipients, 50 had received the third dose of mRNA vaccine. The antibody titer was significantly increased after the third dose of mRNA vaccine. The seropositivity rate after the third dose of mRNA vaccine increased from 36 to 70%. We observed no significant difference in seropositivity after the third dose of mRNA vaccine in ABO incompatibility, rituximab use, mycophenolate mofetil use, and age at KT. Of the nine recipients who had received the second or third dose of the mRNA vaccine prior to the KT, eight of the recipients were seropositive both before and after the KT. Our results suggest that ABO incompatibility or rituximab use was not significantly associated with seropositivity.

HLA Sensitization in the Era of COVID-19: Single-Center Experience

It is well known that several viral infections are capable of triggering the formation of HLA antibodies; however, an association between SARS-CoV-2 and the development of anti-HLA antibodies is not yet confirmed. In this study, we compared the prevalence of HLA antibody before and after COVID-19 infection in a cohort of 3 groups included 58 healthy nonsensitized employees (HNEs), 130 kidney transplant recipients (KTRs), and 62 kidney transplant candidates. There were no significant changes observed in HLA class I antibodies in any of the groups, but evaluation of antibodies to HLA class II revealed a significant change in the KTR group (P = .0184) after acquiring COVID-19 infection and in the HNE group (P = .0043) when compared to the reported prevalence in a similar population. Although we observed the emergence of convalescent de novo donor-specific antibodies in 2 patients, we did not encounter any rejection episodes in the KTR group. Finally, the results of flow cytometry crossmatch in the HNE group were not consistent with the state of antibodies. In conclusion, COVID-19 infection has the potential to produce class II antibodies but with little effect on preexisting sensitization. These antibodies are likely to be transient and not necessarily causing positive crossmatch with the corresponding antigens at the proper mean fluorescent intensity and therefore should not affect access to transplantation. There is a need for further evaluation to ascertain the genuineness of these antibodies and their exact effect on transplant readiness and outcomes.

Seroprevalence of SARS-CoV-2 spike IgG antibodies after the second BNT162b2 mRNA vaccine in Japanese kidney transplant recipients

We aimed to evaluate the seroprevalence and investigated factors associated with seropositivity after the second SARS-CoV-2 mRNA vaccination in kidney transplant (KT) recipients. This retrospective study conducted between June and November 2021 included 106 KT recipients and 127 healthy controls who received the second dose of the BNT162b2 mRNA vaccine at least 7 days before the measurement of antibody titers. The antibody titer against the receptor-binding domain of SARS-CoV-2 spike (S) protein was determined. We compared seroprevalence rates (immunoglobulin G [IgG] level of ≥ 0.8 or ≥ 15 U/mL) between the healthy controls and KT recipients and identified factors associated with impaired humoral response. The seroprevalence rate of the healthy controls and KT recipients was 98% and 22%, respectively. Univariate logistic regression analysis revealed that age > 53 years, rituximab use, mycophenolate mofetil use, and KT vintage < 7 years were negatively associated with the rate of anti-SARS-CoV-2 S IgG ≥ 15 U/mL in KT recipients. ABO blood type incompatible KT was not significantly associated with seroprevalence. Humoral response after the second BNT162b2 mRNA vaccine was greatly hindered by immunosuppression therapy in KT recipients. Older age, rituximab use, mycophenolate mofetil use, and KT vintage may play key roles in seroconversion.

Frequency, reactivity and evolution of human leukocyte antigen and human platelet antigen antibodies in the setting of hematopoietic cell transplantation

BACKGROUND AND OBJECTIVES

Antibodies (Ab) against HLA and HPA antigens play an important role in HCT. In this prospective study we evaluated prevalence and kinetics of HLA- and HPA-Ab after HCT, including a possible donor-recipient transfer and their clinical relevance in respect to platelet transfusion refractoriness (PTR).

MATERIALS AND METHODS

Patients were consecutively recruited. Ab were determined by microbead assay technique and a mean fluorescence intensity cut-off of 1,000.

RESULTS

At baseline, 21 donors (42 %) and 27 patients (54 %) had HLA-Ab with a mean panel reactivity (cPRA) of 34.9 ± 29.4 % and 46.1 ± 36.5 %, respectively. We observed a significant higher number of HLA-Ab specificities in female donors and patients and a predominance of HLA-class I Ab. At day 0 we detected an increase of HLA-Ab (from 526 to 673) and cPRA (55.2 ± 31.9 %). Thirty-six patients (72 %) developed new HLA-Ab, mainly 3 weeks after HCT. In 7 patients an HLA-Ab with the same specificity as detected in the corresponding donor emerged, suggesting a possible transfer from the donor to the recipient. Overall, MFI showed a high variation. Type and number of transfusions were not associated with number and intensity of HLA-Ab (ρ: -0.05 - 0.02). Number of HLA-Ab, cPRA and intensity were not associated with PTR, which occurred in 9 patients (18 %) and none had bleeding WHO > 2.

CONCLUSIONS

Although a considerable number of patients have and develop HLA-Ab before and early after HCT, we found no association with PTR and bleeding and management should be individualized.

Low incidence of IgA isotype of HLA antibodies in alloantigen exposed individuals

Human leukocyte antigen (HLA) antibodies are induced by pregnancy, transfusion, or transplantation. Serum from transplant recipients is regularly screened for IgG HLA antibodies because of their clinical relevance for transplant outcome. While other isotypes of HLA antibodies, such as IgA may also contribute to the alloimmune response, validated detection assays for IgA HLA antibody detection are lacking. Therefore, we modified the commonly used luminex screening assay for IgG HLA antibody detection (IgG-LMX) into an IgA HLA antibody screening assay (IgA-LMX). Optimization and validation was performed with IgG, IgA1, and IgA2 isotype variants of HLA-specific human recombinant monoclonal antibodies (mAbs). Reactivity patterns of IgA1 and IgA2 isotype HLA-specific mAbs in IgA-LMX were identical to those of the IgG isotype. Cross-reactivity with IgG and IgM antibodies and nonspecific binding to the beads were excluded. Further assay validation showed the absence of IgA HLA antibodies in serum from individuals without alloantigen exposure (n = 18). When the IgA-LMX assay was applied to sera from 289 individuals with known alloantigen exposure through pregnancy (n = 91) or kidney transplantation (n = 198), IgA HLA antibodies were detected in 3.5% of individuals; eight patients on the kidney retransplant waitlist and two women immunized through pregnancy. The majority (90%) of IgA HLA antibodies were directed against HLA class II and were always present in conjunction with IgG HLA antibodies. Results of this study show that this validated IgA-LMX method can serve as a screening assay for IgA HLA antibodies and that the incidence of IgA HLA antibodies in alloantigen exposed individuals is low.