Effects of donor-specific antibodies on engraftment and long-term survival after allogeneic hematopoietic stem cell transplantation-A systematic review and meta-analysis

Future directions in haploidentical hematopoietic stem cell transplantation

Outcomes of haploidentical hematopoietic stem cell transplantation (haplo-SCT) have improved over time. Graft failure and graft-versus-host disease (GVHD), which were important complications in major human leukocyte antigen (HLA)-disparity stem cell transplantation, have significantly decreased. These improvements have led to an exponential increase in the use of haploidentical donors for transplantation, as well as in the number of publications evaluating haplo-SCT outcomes. Many studies focused on factors important in donor selection, novel conditioning regimens or GVHD prophylaxis, the impact of donor-specific anti-HLA antibodies (DSA), as well as strategies to prevent disease relapse post-transplant. DSA represents an important limitation and multimodality desensitization protocols, including plasma exchange, rituximab, intravenous immunoglobulin and donor buffy coat infusion, can contribute to the successful engraftment in patients with high DSA levels and is currently the standard therapy for highly allosensitized individuals. With regards to donor selection, younger donors are preferred due to lower risk of complications and better transplant outcomes. Moreover, recent studies also showed that younger haploidentical donors may be a better choice than older-matched unrelated donors. Improvement of disease relapse remains a top priority, and several studies have demonstrated that higher natural killer (NK) cell numbers early post-transplant are associated with improved outcomes. Prospective studies have started to assess the role of NK cell administration in decreasing post-transplant relapse. These studies suggest that the incorporation of other cell products post-transplant, including the administration of chimeric antigen receptor T-cells, should be explored in the future.

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.

Pretransplant desensitization of donor-specific anti-HLA antibodies with plasmapheresis and immunoglobulin produces equivalent outcomes to patients with no donor specific antibodies in haploidentical hematopoietic cell transplant

Haploidentical hematopoietic cell transplants (haplo-HCT) with donor-specific anti-HLA antibodies (DSAs) are associated with high rates of primary graft failure and poor overall survival (OS). Limited data exists regarding the effect of desensitization. Our institution began routine desensitization for patients with DSAs in 2014. Adult patients undergoing haplo-HCT at Washington University from 2009-2021 were identified and divided into three cohorts: no DSA, untreated DSA (2009-2014) or treated DSA (2014-2021). Desensitization therapy using plasmapheresis and IVIg was performed. Retrospectively, 304 patients were identified. 14 of 30 patients with DSAs underwent desensitization. By day +2, 57% of patients cleared all DSAs. After multivariable analysis, OS was similar between treated DSA and no DSA (HR: 0.69, p = 0.37). Untreated DSA had significantly lower OS compared to no DSA group (HR 1.80, p = 0.046). Desensitization with a backbone of plasmapheresis and IVIg before haplo-HCT may produce similar outcomes to patients without DSAs.

Updated comparable efficacy of cord blood transplantation for chronic myelomonocytic leukaemia: a nationwide study

Chronic myelomonocytic leukaemia (CMML) is a haematological malignancy with a poor prognosis. Allogeneic haematopoietic stem cell transplantation remains the only curative approach. Without human leucocyte antigen-matched related sibling donors, the optimal alternative donor has yet to be established. Although unrelated bone marrow transplantation (UBMT) has been extensively studied, cord blood transplantation (CBT) for CMML remains largely unexplored. This nationwide retrospective study compared the outcomes of UBMT and single-unit umbilical CBT in patients with CMML. This study included 118 patients who underwent their first allo-HSCT during 2013-2021. Of these, 50 received BMT (UBMT group), while 68 underwent CBT (CBT group). The primary endpoint was the 3-year overall survival (OS). There were comparable 3-year OS rates between the UBMT (51.0%, 95% confidence interval [CI]: 34.1-65.5%) and CBT (46.2%, 95% CI: 33.2-58.1%; P = 0.60) groups. In the inverse probability of treatment weighting analysis, CBT did not show significantly improved outcomes compared with UBMT regarding the 3-year OS rate (hazard ratio 0.97 [95% CI: 0.57-1.66], P = 0.91). Thus, CBT may serve as an alternative to UBMT for patients with CMML. Further research is necessary to optimise transplantation strategies and enhance outcomes in patients with CMML undergoing CBT.

Pretransplant Desensitization of Donor-Specific Anti-HLA Antibodies with Plasmapheresis and Immunoglobulin Produces Equivalent Outcomes to Patients with No Donor Specific Antibodies in Haploidentical Hematopoietic Cell Transplant

In patients requiring haploidentical hematopoietic cell transplant (haplo-HCT), the presence of donor specific anti-HLA antibodies (DSAs) is associated with high rates of primary graft failure and poor overall survival (OS). There is limited data regarding the effect of desensitization. Adult patients undergoing haplo-HCT at Washington University School of Medicine from 2009-2021 were identified. Patients were divided into three cohorts: no DSA, untreated DSA or treated DSA. DSA testing was performed. Desensitization therapy using plasmapheresis and IVIg (immunoglobulin) was performed. We retrospectively identified 304 patients for study inclusion. 14 of 30 patients with DSAs underwent desensitization. By day +2, 57% of patients cleared all DSAs. OS was expectedly worse in patients with untreated DSAs. There were similar results between treated DSA and patients without DSA (OS median: control: 352 days vs. treated: 1331 days vs. untreated: 137 days, p = 0.02). RFS was also significantly different between the groups however with similar RFS in treated DSA and control groups (RFS median: control: 248 vs. treated: 322 v. untreated: 119, p = 0.03). Desensitization before haplo-HCT produces similar outcomes to patients without DSAs. While the optimal desensitization protocol has not been established, all patients received a backbone of plasmapheresis and immunoglobulin.

Double filtration plasmapheresis combined with rituximab for donor-specific antibody desensitization in haploidentical haematopoietic stem cell transplantation

Donor-specific anti-HLA antibodies (DSA) are a major cause of engraftment failure in patients receiving haploidentical haematopoietic stem cell transplantation (Haplo-HSCT). Double filtration plasmapheresis (DFPP) avoids the unnecessary loss of plasma proteins and increases the efficiency of purification. To investigate the effectiveness of the desensitization protocol including DFPP and rituximab, we conducted a nested case-control study. Thirty-three patients who had positive DSA were desensitized by the protocol and 99 patients with negative DSA were randomly matched as control. The median DSA mean fluorescence intensity values before and after DFPP treatment were 7505.88 ± 4424.38 versus 2013.29 ± 4067.22 (p < 0.001). All patients in DSA group achieved haematopoietic reconstitution and the median neutrophils and platelets engraftment times were 13 (10-21) and 13 (10-29) days respectively. Although the cumulative incidence of II-IV aGVHD (41.4% vs. 28.1%) and 3-year moderate to severe cGVHD (16.8% vs. 7.2%) were higher in DSA cohort than in the control, no statistical significance was observed. The 3-year non-relapse mortality and the overall survival were 6.39% and 72.0%, respectively, in the DSA cohort, which were comparable to the negative control. In conclusion, DFPP and rituximab could be effectively used for desensitization and overcome the negative effects of DSA in Haplo-HSCT.

Case report: Curing a rare, unstable hemoglobin variant Hb Bristol-Alesha using haploidentical hematopoietic stem cell transplantation

Unstable hemoglobinopathies are a rare, heterogeneous group of diseases that disrupt the stability of hemoglobin (Hb), leading to chronic hemolysis and anemia. Patients with severe phenotypes often require regular blood transfusions and iron chelation therapy. Although rare, studies have reported that hematopoietic stem cell transplantation (HSCT) seems to be an available curative approach in transfusion-dependent patients with unstable hemoglobinopathies. Here, we describe successful haploidentical HSCT for the treatment of an unstable Hb variant, Hb Bristol-Alesha, in a 6-year-old boy with severe anemia since early childhood. Two years after transplantation, he had a nearly normal hemoglobin level without evidence of hemolysis. DNA analysis showed complete chimerism of the donor cell origin, confirming full engraftment with normal erythropoiesis.