Non-donor specific anti-human leukocyte antigen (HLA) antibodies are not associated with poor outcome in hematopoietic stem cell transplant recipients

ASTCT Consensus Recommendations on Testing and Treatment of Patients with Donor-specific Anti-HLA Antibodies

Donor-specific anti-HLA antibodies (DSA) are an important cause of engraftment failure and may negatively impact survival outcomes of patients receiving allogeneic hematopoietic stem cell transplantation (HSCT) using an HLA-mismatched allograft. The incidence of DSA varies across studies, depending on individual factors, detection or identification methods and thresholds considered clinically relevant. Although DSA testing by multiplex bead arrays remains semiquantitative, it has been widely adopted as a standard test in most transplant centers. Additional testing to determine risk of allograft rejection may include assays with HLA antigens in natural conformation, such as flow cytometric crossmatch, and/or antibody binding assays, such as C1q testing. Patients with low level of DSA (<2,000 mean fluorescence intensity; MFI) may not require treatment, while others with very high level of DSA (>20,000 MFI) may be at very high-risk for engraftment failure despite current therapies. By contrast, in patients with moderate or high level of DSA, desensitization therapy can successfully mitigate DSA levels and improve donor cell engraftment rate, with comparable outcomes to patients without DSA. Treatment is largely empirical and multimodal, involving the removal, neutralization, and blocking of antibodies, as well as inhibition of antibody production to prevent activation of the complement cascade. Desensitization protocols are based on accumulated multicenter experience, while prospective multicenter studies remain lacking. Most patients require a full intensity protocol that includes plasma exchange, while protocols relying only on rituximab and intravenous immunoglobulin may be sufficient for patients with lower DSA levels and negative C1q and/or flow cytometric crossmatch. Monitoring DSA levels before and after HSCT could guide preemptive treatment when high levels persist after stem cell infusion. This paper aims to standardize current evidence-based practice and formulate future directions to improve upon current knowledge and advance treatment for this relatively rare, but potentially serious complication in allogeneic HSCT recipients.

Relevance of donor-specific HLA antibodies in hematopoietic cell transplantation

Advances in hematopoietic cell transplantation have expanded the use of alternative donors such as haploidentical family donors or mismatched unrelated donors. However, donor-specific HLA antibodies (DSA) have been recognized as a significant risk factor of primary graft failure after HLA incompatible transplantation. Therefore, screening for HLA antibodies and taking DSA into consideration in the process of donor search play an increasingly important role in donor selection. If an HLA compatible donor is not available, desensitization may enable a successful transplantation. In this review, we describe the currently most widely used methods for HLA antibody detections including their pitfalls. In addition, we summarize the results of the studies on the impact of preformed DSA on transplant outcomes and their treatment options. Many more and larger studies are needed to clarify laboratory issues as well as immunological and clinical aspects in the management of DSA.

Impaired survival of patients with non donor-specific anti-HLA antibodies before HLA-mismatched allogeneic stem cell transplantation

BACKGROUND

While the detrimental role of donor-specific anti-HLA antibodies (DSAs) is well-described in the setting of hematopoietic stem cell transplantation (HSCT), few studies focus on non donor-specific ones and with controversial results.

METHODS

We here report our monocenter experience on 64 adult patients receiving allogeneic HSCT from a HLA-mismatched donor between 2014 and 2022 who were tested for the presence of anti-HLA antibodies before transplant, focusing on fifteen patients with non donor-specific anti-HLA antibodies.

RESULTS

The survival of patients with non donor-specific anti-HLA antibodies was inferior with respect to patients without anti-HLA antibodies and similar to patients with DSAs. Median survival of patients with non donor-specific anti-HLA antibodies was 21 months (95 % CI: 9-42) vs. 61 months (95 % CI: 17-77) among the anti-HLA antibody-negative patients, with a significantly higher mortality incidence rate ratio (3.3 times-fold greater, p = 0.01). No pattern of death causes was found CONCLUSIONS: In this monocenter series of HLA-mismatched HSCTs, impaired survival was observed in adult patients having non donor-specific anti-HLA antibodies before transplant, similar to those with DSAs. Our findings support those antibodies as a negative predictive factor even if they are not directed against the donor, thus warranting further investigation on larger cohorts.

The impact of donor-specific antibodies' presence on the outcome post-allogeneic hematopoietic stem cell transplantation: a survey from a single center

Introduction

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.

Methods

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.

Results

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.

Discussion

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.