UNASSIGNED: Donor-specific antibodies (DSAs) correspond to anti-HLA antibodies of the recipient that are specifically directed to a mismatched antigen of the donor. In the setting of solid organ transplantation DSAs are associated with rejection. Their role is still debated in allogeneic cell transplantation. International guidelines recommend testing patients for DSA before transplant, and if possible, choosing a donor with negative screening.
UNASSIGNED: We collected clinical data of 236 recipients of alloSCT, performed at our institution from March 2019 to October 2023, to evaluate their impact on engraftment. Serum from all patients was tested for DSA.
UNASSIGNED: 186 patients (79%) achieved sustained myeloid engraftment within day 30 post alloSCT. Thirty-two out 236 (13%) patients engrafted after day 30 post alloSCT. The median times to neutrophil engraftment and platelet engraftment were respectively 21 days (range 11-121 days) and 19 days (range 10-203 days). Fourteen out 236 patients (6%) experienced PrGF. .Twenty-nine patients (12 %) were DSA-positive. Among 29 patients with DSA positivity, 17 had a haploidentical donor and 12 had a UD donor. DSA positivity directly correlates respectively with neutrophil and platelets engraftment failure at 30 days after alloSCT (p=0.01 and p= 0.0004). Univariate Cox analysis showed that factors, including DSAs positivity, disease type, disease status, donor type, conditioning regimen, patient\'s age, and CD34+ were correlated with neutrophil and platelet engraftment failure at 30 days after alloSCT. Younger patients with DSA negativity, with acute leukemia, in complete response at the time of transplant, who received a higher dose of CD34+ cells from a sibling donor after a myeloablative conditioning regimen, have a reduced risk of neutrophil and platelet engraftment failure at day +30 post alloSCT.Multivariate analysis confirmed the impact of the presence of DSA only for platelet engraftment, confirming the role of type and status disease, donor type, recipient age, and CD34+ cells infused on engraftment. DSA presence has no impact on TRM, DFS, and OS.
UNASSIGNED: PrGF has a multifactorial pathogenesis, where DSA is not the only player, but its impact could vary depending on the transplant platform. Thus patient screening may be helpful to choose the best donor and transplant strategy.

BACKGROUND: Donor human leukocyte antigen (HLA)-specific antibodies (DSA) and non-HLA antibodies can cause allograft injury, possibly leading to chronic lung allograft dysfunction (CLAD) after lung transplantation. It remains unclear whether these antibodies are produced locally in the graft or derived solely from circulation. We hypothesized that DSA and non-HLA antibodies are produced in CLAD lungs.
METHODS: Lung tissue was prospectively collected from 15 CLAD patients undergoing retransplantation or autopsy. 0.3 g of fresh lung tissue was cultured for 4 days without or with lipopolysaccharide or CD40L: lung culture supernatant (LCS) was sampled. Protein eluate was obtained from 0.3 g of frozen lung tissue. The mean fluorescence intensity (MFI) of DSA and non-HLA antibodies was measured by Luminex and antigen microarray, respectively.
RESULTS: LCS from all 4 patients who had serum DSA at lung isolation were positive for DSA, with higher levels measured after CD40L stimulation (CD40L+LCS). Of these, only 2 had detectable DSA in lung eluate. MFI of non-HLA antibodies from CD40L+LCS correlated with those from lung eluate but not with those from sera. Flow cytometry showed higher frequencies of activated lung B cells in patients whose CD40L+LCS was positive for DSA (n = 4) or high non-HLA antibodies (n = 6) compared to those with low local antibodies (n = 5). Immunofluorescence staining showed CLAD lung lymphoid aggregates with local antibodies contained larger numbers of IgG+ plasma cells and greater IL-21 expression.
CONCLUSIONS: We show that DSA and non-HLA antibodies can be produced within activated B cell-rich lung allografts.

Antibody-mediated rejection (ABMR) is a significant obstacle to achieving optimal long-term outcomes after solid organ transplantation. The presence of donor-specific antibodies (DSA), particularly against HLA, increases the risk of allograft rejection and subsequent graft loss. No effective treatment of ABMR currently exists, warranting novel approaches to target the HLA-specific humoral alloimmune response. Cellular therapies may hold promise to this end. According to publicly available sources as of now, three independent laboratories have genetically engineered a chimeric HLA-antibody receptor (CHAR) and transduced it into human T cells, based on the demonstrated efficacy of chimeric antigen receptor T cell therapies in malignancies. These CHAR-T cells are designed to exclusively eliminate B cells that produce donor-specific HLA antibodies, which form the cornerstone of ABMR. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA-specific B cells, sparing B cells with other specificities. Thus, CHAR technology may be used as a selective desensitization protocol and to treat antibody-mediated rejection after solid organ transplantation.

Simultaneous liver and kidney (SLK) transplantation is considered the best treatment modality among selected patients with both chronic kidney disease (CKD) and end-stage liver disease (ESLD). Since the first SLK transplant in 1983, the number of SLK transplants has increased worldwide, and particularly in the United States since the implementation of the MELD system in 2002. SLK transplants are considered a relatively low immunological risk procedure evidenced by multiple studies displaying the immunomodulatory properties of the liver on the immune system of SLK recipients. SLK recipients demonstrate lower rates of both cellular and antibody-mediated rejection on the kidney allograft when compared to kidney transplant-alone recipients. Therefore, SLK transplants in the setting of preformed donor-specific HLA antibodies (DSA) are a common practice, at many centers. Acceptance and transplantation of SLKs are based solely on ABO compatibility without much consideration of crossmatch results or DSA levels. However, some studies suggest an increased risk for rejection for SLK recipients transplanted across high levels of pre-formed HLA DSA. Despite this, there is no consensus regarding acceptable levels of pre-formed DSA, the role of pre-transplant desensitization, splenectomy, or immunosuppressive management in this unique population. Also, the impact of post-transplant DSA monitoring on long-term outcomes is not well-studied in SLK recipients. In this article, we review recent and relevant past articles in this field with a focus on the immunological risk factors among SLK recipients, and strategies to mitigate the negative outcomes among them.

The formation of antibodies against donor human leukocyte antigens poses a challenging problem both for donor selection as well as postoperative graft function in lung transplantation. These donor-specific antibodies limit the pool of potential donor organs and are associated with episodes of antibody-mediated rejection, chronic lung allograft dysfunction, and increased mortality. Optimal management strategies for clearance of DSAs are poorly defined and vary greatly by institution; most of the data supporting any particular strategy is limited to small-scale retrospective cohort studies. A typical approach to antibody depletion may involve the use of high-dose steroids, plasma exchange, intravenous immunoglobulin, and possibly other immunomodulators or small-molecule therapies. This review seeks to define the current understanding of the significance of DSAs in lung transplantation and outline the literature supporting strategies for their management.

UNASSIGNED: De novo donor-specific antibody (dnDSA) is a strong biomarker associated with the development of antibody-mediated rejection (AMR) and graft loss after kidney transplantation. This procedure is expensive; however, systematic annual screening was recommended by some national organ transplant agencies or societies even though its clinical utility was not clearly established.
UNASSIGNED: To address this question, we retrospectively assessed the incidence of dnDSA according to the test justification (clinically indicated or systematic) in a cohort of low-immunological risk patients, defined by being nonhuman leukocyte antigen (non-HLA)-sensitized and having no previous kidney transplants.
UNASSIGNED: A total of 1072 patients, for whom 4611 anti-HLA tests were performed, were included in the study. During the follow-up period of 8 (interquartile range, IQR: 5-11) years, 77 recipients developed dnDSA (prevalence of 7.2%). Thirty-five of these dnDSAs (45.5%) were detected during the first year posttransplantation. In 95% of patients with dnDSA, an immunizing event was identified in their medical records. dnDSA was detected in 46 of 4267 systematic screening tests (1.08%) performed. Active and chronic AMR were frequently observed in biopsies performed after systematic DSA testing (17.9% and 15.4%, respectively).
UNASSIGNED: Our results suggest that the detection by systematic screening of dnDSA in low-immunological risk kidney transplant patients without sensitizing events is a rare event, especially after 1 year. Moreover, in real life, systematic annual screening for dnDSA, seems having a limited impact to detect AMR at an earlier stage compared to patients in whom dnDSA was detected after a clinically indicated test.

Donor exchange programs were designed to allocate organs for highly sensitized (HS) patients. The allocation algorithm differs slightly among countries and includes different strategies to improve access to transplants in HS patients. However, many HS patients with a calculated panel reactive of antibodies (cPRA) of 100 % remain on the waiting list for a long time. Some allocation algorithms assume immunological risk, including Imlifidase treatment, to increase the chance of transplantation in very HS patients. Here, we describe our unicenter experience of low-risk delisting strategy in 15 HS patients included in the Spanish donor exchange program without donor offers. After delisting, 7 out of 15 HS patients reduced the cPRA below 99.95 % and impacted the reduction of time on the waiting list (p = 0.01), where 5 out of 7 achieved transplantation. Within those HS that remained above 99.95 %, 1 out of 8 was transplanted. All the HS were transplanted with delisted DSA, and only one with DSA level rebounded early after transplantation. All HS transplanted after delisting maintain graft function. The transplant immunology laboratories are challenged to search intermediate risk assessment methods for delisting high HS patients.

Humoral immunity emerges as a risk factor for graft failure after visceral transplantation (VTx) and development of donor-specific anti-HLA antibodies (DSAs) has been linked with poor outcomes. In most cases, a simultaneous liver transplant can be safely performed in sensitized patients with DSA and appears protective against lymphocytotoxic antibodies. We investigated the incidence of acute (AR) and chronic rejection (CR) in 32 VTx without any B cell-depleting pre-treatment (6 isolated intestinal transplants (IT) and 26 liver-containing, multivisceral transplants (MVT) and assessed the presence of donor-specific antibodies (DSA) pre- and post-transplantation. Twenty-one patients (65 %) developed AR, 15 (57 %) of the MVT and 6 (100 %) of the IT (p = 0.05). CR occurred in 4 IT (60 %, p < 0.001). At one month, de novo DSA were present in 71 % of VTx (66 % MVT vs 100 % IT, p = 0.09). At the last available follow-up, 69 % of the MVT and 50 % of the IT patients were DSA-free. De novo DSA seemed more persistent (7/19, 37 %) than pre-Tx DSA (1/6, 17 %; p = n.s.), de novo DSA were more frequently specific for HLA class II than class I, 16/19 (84 %) vs. 7/19 (37 %; p = 0.003), and HLA-DQ was their most frequent target HLA. DQ mismatches appeared to be a risk factor for developing de novo DSA. In conclusion, liver-containing visceral allografts have superior short- and long-term outcomes compared with liver-free allografts. De novo DSA develop early and frequently after VTx performed without B cell-depleting induction therapy, but the exact role of DSA in the pathogenesis of rejection remains unclear.

Two semi-quantitative, Luminex-based, single-antigen bead (SAB) assays are available to detect anti-HLA antibodies and evaluate their reactivity with complement binding. Sera from 97 patients with positive panel reactive antibody tests (>5%) were analyzed with two SAB tests, Immucor (IC) and One-Lambda (OL), for anti-HLA antibody detection and the evaluation of their complement-binding capacity. IC detected 1608/8148 (mean fluorescent intensity (MFI) 4195 (1995-11,272)) and 1136/7275 (MFI 6706 (2647-13,184)) positive anti-HLA class I and II specificities, respectively. Accordingly, OL detected 1942/8148 (MFI 6185 (2855-12,099)) and 1247/7275 (MFI 9498 (3630-17,702)) positive anti-HLA class I and II specificities, respectively. For the IC assay, 428/1608 (MFI 13,900 (9540-17,999)) and 409/1136 (MFI 11,832 (7128-16,531)) positive class I and II specificities bound C3d, respectively. Similarly, OL detected 485/1942 (MFI 15,452 (9369-23,095)) and 298/1247 (MFI18,852 (14,415-24,707)) C1q-binding class I and II specificities. OL was more sensitive in detecting class I and II anti-HLA antibodies than IC was, although there was no significant difference in the number of class II specificities per case. MFI was higher for complement vs. non-complement-binding anti-HLA antibodies in both assays. Both methods were equal in detecting complement-binding anti-HLA class I antibodies, whereas the C3d assay was more sensitive in detecting complement-binding anti-HLA class II antibodies.

Given the risk of rejection, the presence of preformed donor specific antibodies (DSA) contraindicates transplantation in most allocation systems. However, HLA-Cw and -DP DSA escape this censorship. We performed a multicentric observational study, in which the objective was to determinate risk factors of acute antibody-mediated rejection (aABMR) in recipients transplanted with preformed isolated Cw- or DP-DSA. Between 2010 and 2019, 183 patients were transplanted with a preformed isolated Cw- or DP-DSA (92 Cw-DSA; 91 DP-DSA). At 2 years, the incidence of aABMR was 12% in the Cw-DSA group, versus 28% in the DP-DSA group. Using multivariable Cox regression model, the presence of a preformed DP-DSA was associated with an increased risk of aABMR (HR = 2.32 [1.21-4.45 (p = 0.001)]) compared with Cw-DSA. We also observed a significant association between the DSA\'s MFI on the day of transplant and the risk of aABMR (HR = 1.09 [1.08-1.18], p = 0.032), whatever the DSA was. Interaction term analysis found an increased risk of aABMR in the DP-DSA group compared with Cw-DSA, but only for MFI below 3,000. These results may plead for taking these antibodies into account in the allocation algorithms, in the same way as other DSA.