Impact of donor-specific anti-HLA antibodies on graft failure and survival after reduced intensity conditioning-unrelated cord blood transplantation: a Eurocord, Société Francophone d'Histocompatibilité et d'Immunogénétique (SFHI) and Société Française de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC) analysis

Anti-HLA class I donor-specific antibodies are associated with lower overall and event-free survival and late mortality in outpatient haploidentical-related stem cell transplantation from the peripheral blood

BACKGROUND

Donor-specific (DSA) anti-HLA antibodies can adversely influence outcomes of haploidentical hematopoietic stem cell transplantation (haplo-HSCT).

METHODS

Patients who received a haplo-HSCT from a sibling after reduced-intensity conditioning (RIC) and had a virtual cross match against donor's HLA typing performed and a positive single-antigen microsphere-based immunoassay test were studied. DSA were considered positive with a mean fluorescence intensity (MFI) ≥ 1000.

RESULTS

Anti-HLA DSA ≥ 1000, median 2623(range 1000-13,235) MFI were documented in 27/65 (42 %) patients. In 14 (21.5 %) patients, antibodies were anti-HLA class I, in 18 (27.7 %) anti-HLA class II, and in 6 (9.2 %) against both. Overall (OS) and event-free survival (EFS) were lower in patients with anti-HLA Class I DSA (p = 0.026 and p = 0.037, respectively). One-year mortality was higher with anti-HLA DSA of any class (p = 0.009). Nine (64.3 %) of 14 patients with DSA anti-HLA class I died, vs. 11/18 (61 %) with class II DSA (p = 0.238). Anti-HLA DSA were not associated with graft failure (GF) in the cohort. There was no difference in relapse or acute or chronic GVHD in patients with and without DSA.

CONCLUSION

Anti-HLA Class I DSA > 1000 MFI after haplo-HSCT was associated with lower OS and EFS and higher one-year mortality, but no with GF, acute or chronic GVHD, or relapse.

The Combination of Intravenous Immunoglobulin, Dexamethasone, and a High Dose of Mononuclear Cells Transfusion: An Effective Strategy for Decreasing Donor-Specific Antibodies During Haploidentical Hematopoietic Stem Cell Transplantation

Donor-specific antibodies (DSAs) are essential causes of graft rejection in haploidentical hematopoietic stem cell transplantation (haplo-HSCT). DSAs are unavoidable for some patients who have no alternative donor. Effective interventions to reduce DSAs are still needed, and the cost of the current therapies is relatively high. In this study, we retrospectively analyzed the data of 11 DSA-positive patients who received haplo-HSCT at our center and evaluated the therapeutic efficacy of the combination of intravenous immunoglobulin (IVIG), dexamethasone and high dose of transfused mononuclear cells (MNCs) for DSA desensitization. The kinetics of DSAs at different times and the engraftment and transplantation outcomes were also observed. We found that all patients had successful donor-cell engraftment and that no patient developed poor graft function. The median engraftment times of neutrophils and platelets were 14 days (range, 11-24 days) and 13 days (range, 11-123 days), respectively. The DSA levels of all patients became negative or dropped under 2000 within 22 days after HSCT. A total of 36.4% of patients developed grade II-IV acute graft-versus-host disease (aGVHD), and 9.1% of patients died of severe gastrointestinal aGVHD. Of the 7 surviving patients, four were diagnosed with chronic GVHD. After a median follow-up of 28.9 months (2.0-52.1 months), four patients died: of relapse (two), aGVHD (one), and multiple-organ failure (one). The 2-year OS, DFS, and NRM were 63.6%, 45.4%, and 18.2%, respectively. Combination therapy with IVIG, dexamethasone, and a high dose of MNCs transfusion, a simple and efficient procedure, was safe and effective for DSA desensitization and peripheral blood stem cell (PBSC) engraftment.

[Update for cord blood unit selection in hematopoietic stem cell transplantation (workshop SFGM-TC)]

Changing practices and the limited use of cord blood units as a source of cells for allogeneic hematopoietic stem cell transplants (HSC) led us to reconsider the recommendations established in 2011 and 2012, and to propose an update incorporating recent bibliographic data. If HLA compatibility was until now established at low resolution for HLA-A and B loci, and at high resolution for HLA-DRB1, the recent papers are converging towards an increase in the level of resolution, making way for a compatibility now defined in high resolution for all the considered loci, and the inclusion of the HLA-C locus, in order to establish a level of HLA compatibility on 8 alleles (HLA-A, B, C and DRB1). The CD34+ dose is a determining factor in hematopoietic reconstitution but it is not correlated with the total nucleated cells content. This is why we recommend taking these two data into account when choosing a cord blood unit. The recommendations established by our group are presented as a flow chart taking into account the characteristics of the underlying pathology (malignant or non-malignant), the cell dose and the HLA compatibility criteria, as well as criteria linked to the banks in which units are stored.

Outcomes of Hematopoietic Stem Cell Transplantation in Patients With Thalassemia Major: How Do Anti-HLA Antibodies Impact?: The Impact of Anti-HLA Antibodies on Transplantation Outcomes in Thalassemia Major

AIM

To investigate the effects of anti-human Leucocyte Antigen (HLA) antibody positivity on early hematopoietic stem cell transplantation (HSCT) results in patients with thalassemia major (TM).

METHODS

One hundred and twenty-four HLA-matched HSCTs were performed in patients with TM between 2015 and 2022. Ninety-one patients were screened for anti-HLA antibodies by testing panel reactive antigens (PRA). Demographic and transplantation characteristics of patients were recorded. The presence of PRA was tested with the Antibody Testing Assay (Luminex LIFECODES HLA Antibody Identification System).

RESULTS

The number of PRA-positive patients was 54. There was no relationship between acute graft versus host disease (GVHD), chronic GVHD, grade of GVHD, and viral reactivation of the patients. However, platelet engraftment took around 3 days longer in the PRA-positive group (p = 0.05). The median number of erythrocyte transfusions was significantly higher in PRA-positive patients in the post-transplant period (p = 0.003), as was the median number of platelet transfusions (p = 0.003). Treosulfan conditioning increased the stable mixed chimerism (MC) rate by 3.8-fold (p = 0.011). In contrast, reduced rates of MC were found in patients who received matched unrelated donor cells or peripherally derived stem cells (p = 0.011 and p = 0.039, respectively) in the posttransplantation period in TM patients. PRA-positivity did not affect MC (p = 0.478). However, 80% of patients who had primary graft failure (n = 5; p = 0.59) and 75% of patients who died (n = 4) were PRA positive (p = 0.64), but these results were statistically insignificant due to the low number of patients.

CONCLUSION

Anti-HLA antibodies primarily delayed platelet engraftment in TM patients and increased the erythrocyte and thrombocyte transfusion requirements. Although PRA positivity was more common in patients with primary graft failure or who died, there was no statistically significant impact of PRA positivity on chimerism, acute or chronic GVHD, viral activation, or mortality rates.

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.

Lymphocyte Crossmatch Testing or Donor HLA-DP and -DQ Allele Typing Effectiveness in Single Cord Blood Transplantation for Patients With Anti-HLA Antibodies Other Than Against HLA-A, -B, -C, and -DRB1

Anti-human leukocyte antigen (HLA) antibodies other than those against HLA-A, -B, -C, and DRB1 are a risk factor for engraftment delay and failure, especially in cord blood transplantation (CBT). The primary objective of this study was to assess the impact of the presence of anti-HLA antibodies on CBT and to evaluate the utility of lymphocyte crossmatch testing or additional HLA-DP and -DQ typing of CB units in improving transplant outcomes. We retrospectively assessed the engraftment rates and transplant outcomes of 772 patients who underwent their first CBT at our hospital between 2012 and 2021. Donors were routinely typed for HLA-A, -B, -C, and-DRB1 alleles, and the anti-HLA antibodies of recipients were screened before donor selection in all cases. Among patients who had antibodies against other than HLA-A, -B, -C, and DRB1 (n = 58), lymphocyte crossmatch testing (n = 32) or additional HLA-DP/-DQ alleles typing of CB (n = 15) was performed to avoid the use of units with corresponding alleles. The median patient age was 57 years (16 to 77). Overall, 75.7% had a high-risk disease status at transplantation, 83.5% received myeloablative conditioning regimens, and >80% were heavily transfused. Two hundred twenty-nine of the 772 recipients (29.6%) were positive for anti-HLA antibodies. There were no statistical differences in the number of infused CD34-positive cells between the anti-HLA antibody-positive and the anti-HLA antibody-negative patients. Of the 229 patients with anti-HLA antibodies, 168 (73.3%) had antibodies against HLA-A, -B, -C, and-DRB1 (Group A), whereas 58 (25.3%) had antibodies against HLA-DP, HLA-DQ, or -DRB3/4/5 with or without antibodies against HLA-A, -B, -C, and -DRB1 (Group B). No patients in both Groups A and B exhibited donor-specific anti-HLA antibodies against HLA-A, -B, -C, and -DRB1. The neutrophil engraftment rate was lower in patients with anti-HLA antibodies than in those without antibodies (89.9% versus 94.1%), whereas nonrelapse mortality (NRM) before engraftment was higher in antibody-positive patients (9.6% versus 4.9%). In patients who received 2 or more HLA allele-mismatched CB in the host-versus-graft (HVG) direction (n = 685), the neutrophil engraftment rate was lower in the anti-HLA antibody-positive recipients than in the antibody-negative recipients with significant differences (88.8% versus 93.8%) (P = .049). Similarly, transplant outcomes were worse in the antibody-positive patients with respect to 2-year overall survival (OS) (43.1% versus 52.3%) and NRM (44.0% versus 30.7%) than in the antibody-negative patients. In contrast, the results of Group B were comparable to those of the antibody-negative patients, while those of Group A were statistically worse than the antibody-negative patients in terms of all engraftment rate (88.6%), OS (34.2%), and NRM (49.0%). The presence of anti-HLA antibodies negatively impacts engraftment, NRM, and OS in CBT. However, HLA-DP/-DQ allele typing of CB units or lymphocyte crossmatch testing could be a useful strategy to overcome poor engraftment rates and transplant outcomes, especially in patients with anti-HLA antibodies against HLA-DP, HLA-DQ, or -DRB3/4/5.

HLA peptide-binding pocket diversity modulates immunological complications after cord blood transplant in acute leukaemia

Pocket motifs and their amino acid positions of HLA molecules are known to govern antigen presentation to effector cells. Our objective was to analyse their influence on the risk of graft-versus-host disease (GVHD) and relapse after umbilical cord blood transplant (UCBT). The transplant characteristics of 849 patients with acute leukaemia were obtained from the Eurocord/EBMT database. Higher acute (a) GVHD was associated with homozygosity of UCB HLA-C amino acid positions 77 and 80 (NN/KK) (p = 0.008). Severe aGVHD was associated with HLA-A pocket B YSAVMENVHY motif (p = 0.002) and NN and RR genotypes of the HLA-C amino acid positions 77 and 156 (p = 0.006 and p = 0.002). Such risk was also increased in case of recipient and UCB mismatches in P4 (p < 0.0001) and P9 (p = 0.003) pockets of HLA-DQB1 alleles. For chronic GVHD, the pocket B YYAVMEISNY motif of the HLA-B*15:01 allele and the absence of mismatch between recipient and UCB in the P6 pocket of HLA-DRB1 were associated with a lower risk (p = 0.0007 and p = 0.0004). In relapse, both UCB pocket B YFAVMENVHY belonging to HLA-A*32:01 and recipient pocket B YDSVGENYQY motif of the HLA-C*07:01 allele were associated with higher risk (p = 0.0026 and p = 0.015). We provide clues on HLA-mediated cellular interactions and their role in the development of GVHD and relapse.

Targeting TFH cells is a novel approach for donor-specific antibody desensitization of allograft candidates: an in vitro and in vivo study

The presence of donor-specific antibodies (DSA) are associated with graft failure either following human leukocyte antigen (HLA)-mismatched allogeneic stem cell transplantation or after organ transplantation. Although targeting B cells and plasma cells have been used for desensitization, there have been reports of failure. T-follicular helper (Tfh) cells assist B cells in differentiating into antibody-secreting plasma cells. We used haploidentical allograft as a platform to investigate the possibility of targeting Tfh cells to desensitize DSA. The quantities of circulating Tfh (cTfh) cell subsets in allograft candidates were abnormal, and these cells, including the cTfh2 and cTfhem cell subsets, were positively related to the production of anti-HLA antibodies. Ex vivo experiments showed that the cTfh cells of anti-HLA antibody-positive allograft candidates could induce B cells to differentiate into DSA-producing plasmablasts. The immune synapse could be involved in the assistance of cTfh cells to B cells in antibody production. In vitro experiments and in vivo clinical pilot studies indicated that targeting cTfh cells with sirolimus can inhibit their auxiliary function in assisting B cells. Ex vivo and in vivo studies demonstrated the effect of sirolimus and rituximab on DSA desensitization compared with either sirolimus or rituximab alone (60%, 43.75%, and 30%, respectively). Our findings provide new insight into the role of Tfh cells in the pathogenesis of DSA production in HLA-mismatched transplant candidates. Our data also indicate that targeting Tfh cells is a novel strategy for DSA desensitization and combination of sirolimus and rituximab might be a potential therapy. The prospective cohort of this study is registered at http://www.chictr.org.cn as #ChiCTR-OPC-15006672.

Scoring system for optimal cord blood unit selection for single cord blood transplantation

BACKGROUND

We conducted a retrospective study to categorize the cord blood unit (CBU)s to identify the optimal units.

METHODS

A total of 8503 adults (female, n = 3592; male, n = 4911) receiving their first single cord blood transplantation (CBT) in 2000-2019 were analyzed. Factors associated with CBUs affecting overall survival (OS) and neutrophil engraftment were selected to create ranked categorization for each outcome, followed by comparison with transplantation using HLA-matched bone marrow (BMT)/peripheral blood stem cell (PBSCT) from unrelated (n = 6052) and related donors (n = 4546).

RESULTS

Sex-mismatch, CD34+ cell and CFU-GM counts were selected in the OS analysis. Considering the strong interaction between sex mismatch and CD34+ cell counts, we analyzed females and males separately. For females, female CBU with CD34+ cell counts {greater than or equal to} 0.5 × 10e5/kg and CFU-GM counts {greater than or equal to} 15 × 10e3/kg offered the best OS (Group I), followed by other groups with any (Groups II-IV) or all (Group V) of the risk factors. Group I consistently showed favorable OS (Group IV: HR1.22, P = 0.027; Group V: HR1.31, P = 0.047), comparable to those of rBMT/PBSCT (OS: HR1.02, P = 0.654) and uBM/PBSCT in patients with higher rDRI (HR1.07, P = 0.353). Male patients lacked significant factors affecting OS. Categorization for neutrophil engraftment consisting of CD34+ cell and CFU-GM counts, sex-mismatch, presence of donor-specific antibodies, and the number of HLA-mismatches was effective but not predicted OS.

CONCLUSION

Our ranked categorizations sufficiently predicted female OS and engraftment. The best-ranked CBUs offered preferable outcomes comparable to conventional BM/PB donors in female but not in male patients.

Effect of serum panel reactive antibodies on allogeneic hematopoietic stem cell transplantation in pediatric thalassemia patients: A single-center experience

BACKGROUND

The aim of this study was to assess the impact of serum panel reactive antibodies (PRA) on the outcomes of allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric thalassemia patients.

METHODS

A total of 73 pediatric patients with thalassemia were included in this single-center study. Pre-transplant PRA levels were evaluated, and the patients were divided into two groups: PRA-negative (group 1; n = 44) and PRA-positive (group 2; n = 29). Patient characteristics, including age, gender, donor type, stem cell source, and HLA compatibility, were analyzed. Transplant outcomes, including engraftment, transfusion requirements, and transplant-related complications, were compared between the two groups. Further subgroup analysis was performed based on MFI values.

RESULTS

At the time of transplantation, patients in group 1 were younger than those in group 2 (p = .008). The number of fully matched donors within the family (MSD and MFD) was significantly higher in group 1 (p = .049). Additionally, Rh blood group incompatibility was higher in group 2 (p = .03). There was no statistically significant difference in the engraftment days of neutrophils, platelets, and erythrocytes between the two groups. The frequency of poor graft function and graft failure was higher in the group 2, but there was no statistically significant difference. Post-transplant transfusion requirements for platelets and red blood cells were significantly higher in the group 2 (p < .001). Transplant-related complications such as VOD, PRES, and aGvHD were more common in the group 2, but no statistical significance was detected.

CONCLUSIONS

Serum PRA in pediatric thalassemia patients may impact the outcomes of HSCT. PRA-positive patients had higher rates of blood product transfusion requirements. Although poor graft function, graft failure, and post-transplant complications were more common in the group 2, statistical significance was not observed. Identifying patients with high PRA levels can assist in optimizing transplant strategies and post-transplant care, leading to improved outcomes for the patients.

PET assessment of acute gastrointestinal graft versus host disease

Acute gastrointestinal graft versus host disease (GI-GVHD) is a common complication following allogeneic haematopoietic cell transplantation (HCT), and is characterised by severe morbidity, frequent treatment-refractoriness, and high mortality. Early, accurate identification of GI-GVHD could allow for therapeutic interventions to ameliorate its severity, improve response rates and survival; however, standard endoscopic biopsy is inadequately informative in terms of diagnostic sensitivity or outcome prediction. In an era where rapid technological and laboratory advances have dramatically expanded our understanding of GI-GVHD biology and potential therapeutic targets, there is substantial scope for novel investigations that can precisely guide GI-GVHD management. In particular, the combination of tissue-based biomarker assessment (plasma cytokines, faecal microbiome) and molecular imaging by positron emission tomography (PET) offers the potential for non-invasive, real-time in vivo assessment of donor:recipient immune activity within the GI tract for GI-GVHD prediction or diagnosis. In this article, we review the evidence regarding GI-GVHD diagnosis, and examine the potential roles and translational opportunities posed by these novel diagnostic tools, with a focus on the evolving role of PET.

A new beginning: can omidubicel emerge as the next, viable alternative donor source?

Umbilical cord blood (UCB) transplantation (CBT) has been an important alternative donor option for patients lacking matched related donor (MRD) or unrelated donor (URD) grafts. Only 30% of patients with high-risk hematologic malignancies have a human leukocyte antigen (HLA)-identical sibling; subjects without a MRD option are referred for HLA-matched URD selection, or utilize alternative donor sources such as HLA-mismatched URD, UCB, or haploidentical donor grafts. While CBT demonstrates an excellent graft-versus-leukemia (GVL) effect, use of UCB as a graft source is limited due to a lower cell dose that can result in delayed engraftment and an immature immune system with increased infectious risk as a consequence. Together, increased transplant related mortality (TRM) has been associated with UCB allografts. Omidubicel is an ex vivo expanded single cord blood product that has demonstrated rapid engraftment, improved immune reconstitution, and reduced infectious complications in clinical trials. Omidubicel has now been granted U.S. Food & Drug Administration approval to enhance neutrophil recovery and decrease infectious risk. This review will focus on CBT, benefits and barriers to using this alternative donor source, and finally the potential advancements with incorporation of omidubicel in the transplant setting for malignant and non-malignant diseases.

Outcomes of graft failure after umbilical cord blood transplantation in acute leukemia: a study from Eurocord and the Acute Leukemia Working Party of the EBMT

Graft failure has remained a limitation of umbilical cord blood transplantation (CBT). Here, we assessed the outcomes of patients who experienced graft failure after CBT. Inclusion criteria were patients (age ≥ 18 years) experiencing graft failure after unrelated CBT (single or double) between 2005 and 2016, for acute myelogenous leukemia (AML) or acute lymphoblastic leukemia (ALL), no prior allogeneic or autologous transplantation, no other stem cell product. The study included 87 patients. At 1-year, cumulative incidence of relapse and nonrelapse mortality (NRM) was 35% and 37%, respectively. One-year overall survival (OS) and progression-free survival (PFS) was 40% and 29%, respectively. Forty-six patients underwent a salvage second transplantation with 1-year and 2-year OS and PFS from second transplantation 41% and 34% for OS, and 37% and 34% for PFS, respectively. In multivariate analysis, complete remission (CR) at CBT (HR = 0.45, 95% CI 0.25-0.83, P = 0.01) and reduced-intensity conditioning (HR = 0.51, 95% CI 0.29-0.91, P = 0.023) were associated with better OS. In conclusion, in this retrospective study, we observed that approximately one-quarter of patients experiencing graft failure after CBT remained alive without relapse 2 years later.

"Incidence and significance of donor-specific antibodies in haploidentical stem cell transplantation"

PGF is a devastating complication after allogeneic transplant. We retrospectively analyzed our haploidentical transplant registry to report the incidence and impact of DSA and anti-HLA on engraftment. 107 patients were identified. Median recipient-age of 22, median donor-age of 31. Sixty-two patients had AML (58%), 29 had ALL (27%), 16 (15%) had other malignancies. Sixty-one recipients (57%) had positive anti-HLA, 56 of them had the DSA results available, of these 17 patients had DSAs (15% of the total number of patients, or 28% of patients who have anti-HLA antibodies). The median cumulative MFI was 2062. Sixty-three percent of the DSA were against class-II HLA antigens. The OS, CIR, aGvHD, and cGvHD did not differ between patients with and without anti-HLA antibodies, nor between patients with and without DSA. The gender of the recipient and donor, as well as the gender mismatch between recipient and donor, were statistically associated with the incidence of anti-HLA antibodies. Three patients only developed GF (2.8%), one was primary (0.9%) and the other two secondary GF (1.9%). None of the GF cases was in patients with anti-HLA antibodies or DSA. The presence of anti-HLA or DSAs did not affect the outcomes including the incidence of PGF.

Adverse effect of donor-specific anti-human leukocyte antigen (HLA) antibodies directed at HLA-DP/-DQ on engraftment in cord blood transplantation

BACKGROUND AIMS

While donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) in the recipient before transplantation are associated with graft failure in cord-blood transplantation (CBT), effects of DSAs other than against HLA-A, -B or -DRB1 on transplantation outcomes remained poorly understood.

METHODS

We retrospectively analyzed 567 single-unit CBT recipients to evaluate impact of DSAs against HLA-DP and -DQ on CBT outcomes.

RESULTS

Among 143 recipients (25.2%) who had anti-HLA antibodies, nine harbored DSAs against HLA-DP or -DQ. DSAs against HLA-DP or -DQ were associated with a significantly lower neutrophil engraftment rate (55.6% versus 91.8%, P = 0.032) and with a marginally lower platelet engraftment rate (46.7% versus 75.3%, P = 0.128) at day 100 after transplantation, compared with patients without anti-HLA antibodies. Time to neutrophil and platelet engraftment in patients with DSAs for HLA-DP or -DQ was significantly longer than that in patients without anti-HLA antibodies (median, 25 versus 21 days, P = 0.002 in neutrophil; median 61 versus 46 days, P = 0.014 in platelet). Cumulative incidence of bacterial infection at day 100 was significantly greater (88.9% versus 57.1%, P = 0.024), and re-transplant-free survival was marginally lower (55.6% versus 76.8%, P = 0.132) in patients with DSAs against HLA-DP or -DQ, compared with those without anti-HLA antibodies. These findings suggest that DSAs against HLA-DP or -DQ lead to unfavorable engraftment, which may increase risk of bacterial infection, and reduce survival soon after CBT.

CONCLUSIONS

Our results suggest the importance of evaluating DSAs against HLA-DP and -DQ in recipients before selecting CB units.

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

The presence of donor-specific antibodies (DSAs) have been reported to be associated with an increased risk of primary graft failure following allogeneic hematopoietic stem cell transplantation (allo-HSCT), but its effects on the time to engraftment and long-term outcomes remain unclear. We performed a systematic review and meta-analysis of studies investigating the impact of DSAs on engraftment and long-term survival of patients undergoing allo-HSCT. We systematically searched PubMed, Embase, the Cochrane Library, and CBM. Data were analyzed using RevMan5.4. Pooled hazard ratio (HR), standard mean difference (SMD) or odds ratio (OR) and corresponding 95% confidence interval (CI) are calculated for time-to-event data, continuous data, discontinuous data respectively. 17 eligible studies were included, involving 2169 patients main receiving haploidentical SCT (haplo-SCT) or umbilical cord blood transplantation (UCBT). Meta-analysis showed that DSAs-positive patients are associated with significantly higher risk of GF(OR = 12.87, 95%CI, 6.45-25.70; P < 0.00001; OR = 4.76, 95%CI, 2.88-7.87), poorer neutrophil engraftment (HR = 2.20, 95%CI, 1.02-4.73; P = 0.04; HR = 1.83, 95%CI, 1.46-2.30; P < 0.00001), worse OS (HR = 3.19, 95%CI, 1.85-5.50; P < 0.0001; HR = 1.68, 95%CI, 1.04-2.71; P = 0.03), and inferior PFS (HR = 4.25, 95%CI, 1.59-11.40; P = 0.004; HR = 4.83, 95%CI, 1.65-14.12; P = 0.004) in haplo-SCT and UCBT, respectively.

Prevalence and risk factors of antibodies to HLA according to different cut-off values of mean fluorescence intensity in haploidentical allograft candidates: A prospective study of 3805 subjects

The importance of anti-HLA antibodies in transplantation settings, such as HLA-mismatched or haploidentical hematopoietic stem cell transplantation and platelet refractoriness, is widely recognized. In previous reports, it was mentioned that several cut-off values of donor-specific anti-HLA antibodies mean fluorescence intensity (MFI) were related to graft rejection in the environment of HLA mismatched stem cell transplantation and the aim of this study was to investigate the prevalence and risk factors of anti-HLA antibodies according to those cut-off values of MFI. A total of 3805 patients with hematologic disease were prospectively enrolled and analyzed. When using MFI of anti-HLA antibodies ≥500, ≥1000, ≥1500, ≥2000, ≥5000, and ≥ 10,000 as cut-off values for positivity, the prevalence of class I or II anti-HLA antibodies ranged from 4.6% to 20.2% in all cases. When the MFI cut-off value was ≥500 for positivity, multivariate analysis indicated that platelet transfusion, underlying disease, and pregnancy were the most important risk factors for the presence of anti-HLA antibodies for the total patients. Subgroup analysis according to age, gender, and underlying disease showed that pregnancy was the most important risk factor for the presence of anti-HLA antibodies. For all patients (n = 3805), when anti-HLA antibody positivity was defined according to different MFI cut-off values, including ≥1000, ≥1500, ≥2000, ≥5000, and ≥ 10,000, an association of platelet transfusion and pregnancy with anti-HLA antibodies was also demonstrated. Our results suggest that pregnancy and platelet transfusion are the main risk factors for the prevalence of anti-HLA antibodies in haploid allograft candidates, providing evidence for guiding the evaluation of anti-HLA antibodies and helping donor selection for HLA-mismatched transplant candidates.

Recent Advancements in Poor Graft Function Following Hematopoietic Stem Cell Transplantation

Poor graft function (PGF) is a life-threatening complication that occurs after transplantation and has a poor prognosis. With the rapid development of haploidentical hematopoietic stem cell transplantation, the pathogenesis of PGF has become an important issue. Studies of the pathogenesis of PGF have resulted in some success in CD34⁺-selected stem cell boosting. Mesenchymal stem cells, N-acetyl-l-cysteine, and eltrombopag have also been investigated as therapeutic strategies for PGF. However, predicting and preventing PGF remains challenging. Here, we propose that the seed, soil, and insect theories of aplastic anemia also apply to PGF; CD34⁺ cells are compared to seeds; the bone marrow microenvironment to soil; and virus infection, iron overload, and donor-specific anti-human leukocyte antigen antibodies to insects. From this perspective, we summarize the available information on the common risk factors of PGF, focusing on its potential mechanism. In addition, the safety and efficacy of new strategies for treating PGF are discussed to provide a foundation for preventing and treating this complex clinical problem.

Umbilical Cord Blood Transplantation after Graft Failure from a Previous Hematopoietic Stem Cell Transplantation

Graft failure (GF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (HCT). In the absence of autologous recovery, a second HCT is necessary to attempt to prevent death due to prolonged pancytopenia. Previous studies describing outcomes of second HCT performed after GF with different types of donor sources report widely ranging overall survival (OS) and transplantation-related mortality (TRM); however, studies including a large number of patients undergoing a second HCT with umbilical cord blood (UCB) as the graft source are scarce. This study examined UCB transplantation (UCBT) performed after GF following a previous HCT. This retrospective registry-based study used data extracted from Eurocord and the European Society for Blood and Marrow Transplantation (EBMT) databases to evaluate outcomes of 247 UCBTs performed in EBMT transplant centers after GF following a previous HCT. Data were analyzed separately for patients with malignant diseases (n = 141) and those with nonmalignant diseases (n = 106). The most frequent HCT that resulted in GF was also UCBT (65.0% for patients with malignant diseases and 68.9% for those with nonmalignant diseases), and most GFs occurred within 100 days after transplantation (92.3% and 85.9%, respectively). The median follow-up was 47 months for surviving patients with malignant diseases and 38 months for those with nonmalignant diseases. We observed a similar cumulative incidence of neutrophil engraftment of 59.1% (95% confidence interval [CI], 51.4% to 67.9%) and 60.4% (95% CI, 51.7%-70.6%), respectively, at a median time of 23 days and 24 days, respectively. The 3-year OS was 28.9% (95% CI, 21.8% to 37.3%) in the malignant disease group and 49.1% (95% CI, 39.5%-58.8%) in the nonmalignant disease group. In patients with malignancies, TRM was 39.9% (95% CI, 32.5% to 49.1%) at 100 days and 57.5% (95% CI, 49.4%-66.8%) at 3 years. In multivariate analyses, none of the characteristics studied was statistically significantly associated with engraftment or OS. Although survival is not optimal in patients requiring a second HCT, UCBT remains a valid life-saving option for patients with GF.

Treatment of allosensitized patients receiving allogeneic transplantation

Treatment with PE, rituximab, IVIg, and donor buffy coat is effective in promoting engraftment in patients with DSA <20 000 MFI.

Patients with persistent positive C1q at transplant have a higher risk of engraftment failure and poor survival.

Donor-specific anti-HLA antibodies (DSAs) are a major cause of engraftment failure in patients receiving haploidentical stem cell transplantation (HaploSCT). Effective treatments are needed for these patients, who often have no other donor options and/or are in need to proceed urgently to transplantation. We studied a multimodality treatment with alternate-day plasma exchange (PE), rituximab, intravenous γ globulin (IVIg) and an irradiated donor buffy coat for patients with DSAs at 2 institutions. Thirty-seven patients with a median age of 51 years were treated with this desensitization protocol. Treatment outcomes were compared with a control group of HaploSCT patients without DSAs (n = 345). The majority of patients in the DSA group were female (83.8% vs 37.1% in controls, P < .001) and received stem cells from a child as the donor (67.6% vs 44.1%, P = .002). Mean DSA level before and after desensitization was 10 198 and 5937 mean fluorescence intensity (MFI), respectively, with mean differences of 4030 MFI. Fourteen of 30 tested patients (46.7%) had C1q positivity, while 8 of 29 tested patients (27.6%) remained positive after desensitization. In multivariable analysis, patients with initial DSA > 20 000 MFI and persistent positive C1q after desensitization had a significantly lower engraftment rate, which resulted in significantly higher non-relapse mortality and worse overall survival (OS) than controls, whereas graft outcome and survival of patients with initial DSA < 20 000 MFI and those with negative C1q after treatment were comparable with controls. In conclusion, treatment with PE, rituximab, IVIg, and donor buffy coat is effective in promoting engraftment in patients with DSAs ≤20 000 MFI.

Donor-Specific Antibodies and Primary Graft Failure in Allogeneic Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

With the increasing number of non-matched donor hematopoietic stem cell transplantations (HSCTs) has come increasing evidence regarding factors affecting graft outcomes. One factor affecting graft outcomes currently being evaluated is anti-HLA donor-specific antibodies (DSAs). In this, we analyzed the clinical relevance of anti-HLA DSAs in patients who have undergone HSCT at a population level by conducting a systematic review of existing literature. A comprehensive search was conducted through PubMed, Embase, the Cochrane library, and Web of Science from inception to January 1, 2021. A meta-analysis was performed of the association between anti-HLA DSAs and primary graft failure (PGF) with further subgroup analyses. The search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 920 eligible citations were identified, out of which 15 studies were included in the final meta-analyses after application of rigorous selection criteria and independent review. A total of 2436 patients were included in these 15 studies. Patients with anti-HLA DSAs prior to undergoing HSCT had a 7.47-fold increased risk of PGF failure compared with patients without anti-HLA DSAs (odds ratio, 7.47; 95% confidence interval, 4.54 to 12.28, P < .001; I²= 28.91%, P = .1315). In subgroup and meta-regression analyses, area, Newcastle Ottawa Scale score, mean fluorescence intensity cutoff, primary disease, HSCT type, graft source, and pretransplantation desensitization did not affect the impact of anti-HLA DSAs on PGF. There also was no significant difference in impact between HLA class I and II on PGF. We conclude that the prior presence of anti-HLA DSAs has a negative impact on graft outcomes in recipients of haploidentical and umbilical cord blood HSCT.

Successful Salvage Therapy by Second Haploidentical Allogeneic Hematopoietic Stem Cell Transplantation in a Severe Aplastic Anemia Patient Presenting Donor-Specific Anti-HLA Antibodies After Graft Failure From Matched Sibling Donor HSCT: A Case Report and Review

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is potentially curative for severe aplastic anemia (SAA). Graft failure (GF) remains a life-threatening complication after HSCT. Preexisting anti-HLA antibodies, especially HLA-specific antibodies (DSA), have been demonstrated as a risk of GF.

CASE PRESENTATION

This report describes a woman with acquired SAA who presented with anti-HLA antibodies and GF. After the treatment of anti-HLA antibodies, engraftment was achieved through a second alternative donor HSCT. This work complied with the Declaration of Helsinki and the Declaration of Istanbul.

CONCLUSIONS

Based on our experience in treating this case, we hold that the presence of preoperative anti-HLA antibodies could discount the efficacy of HSCT and anti-HLA antibody screening should be performed before HSCT. Additionally, a second HSCT is feasible to prolong survival.

Potential Novel Biomarkers in Chronic Graft-Versus-Host Disease

Prognostic, diagnostic or predictive biomarkers are urgently needed for assessment of chronic graft-versus-host disease (cGvHD), a major risk for patients undergoing allogeneic hematopoietic stem cell transplantation. The main goal of this review generated within the COST Action EUROGRAFT "Integrated European Network on Chronic Graft Versus Host Disease" was to identify potential novel biomarkers for cGvHD besides the widely accepted molecular and cellular biomarkers. Thus, the focus was on cellular biomarkers, alloantibodies, glycomics, endothelial derived particles, extracellular vesicles, microbiome, epigenetic and neurologic changes in cGvHD patients. Both host-reactive antibodies in general, and particularly alloantibodies have been associated with cGvHD and require further consideration. Glycans attached to IgG modulate its activity and represent a promising predictive and/or stratification biomarker for cGVHD. Furthermore, epigenetic changes such as microRNAs and DNA methylation represent potential biomarkers for monitoring cGvHD patients and novel targets for developing new treatment approaches. Finally, the microbiome likely affects the pathophysiology of cGvHD; bacterial strains as well as microbial metabolites could display potential biomarkers for dysbiosis and risk for the development of cGvHD. In summary, although there are no validated biomarkers currently available for clinical use to better inform on the diagnosis, prognosis or prediction of outcome for cGvHD, many novel sources of potential markers have shown promise and warrant further investigation using well characterized, multi-center patient cohorts.

Second haploidentical stem cell transplantation for primary graft failure

We report the outcome of 19 patients who experienced primary graft failure (PrGF) after a haploidentical (HAPLO), unmanipulated bone marrow transplant. The median age of patients was 52 years; the conditioning regimen of the first HAPLO transplant was either full dose total body irradiation (TBI) or fludarabine, busulfan, and thiotepa (TBF); PTCY was given to all patients together with cyclosporine and mycophenolate. All 19 patients with PrGF received a second HAPLO graft, at a median interval of 42 days (34-82) after HSCT, using the Baltimore protocol and G-CSF mobilized PB from the same (n = 13) or another HAPLO family donor (n = 6). GvHD prophylaxis was again PTCY-based; 14/19 patients had trilineage recovery (74%) and 1-year survival was 66%. Engraftment at second HAPLO was seen in 7/8 patient with, and in 5/7 patients without donor-specific antibodies (DSA). In a multivariate logistic regression analysis on the original group of 503 patients, there was a trend for a reduced dose of busulfan, to increase the risk of PrGF (p = 0.1). In conclusion, patients with PrGF following a HAPLO transplant, can be rescued with a second early HAPLO transplant, using the same or a different donor.

The impact of pre-existing HLA and red blood cell antibodies on transfusion support and engraftment in sickle cell disease after nonmyeloablative hematopoietic stem cell transplantation from HLA-matched sibling donors: A prospective, single-center, observational study

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is curative for patients with sickle cell disease (SCD). Prior to HSCT, patients with SCD commonly receive RBC transfusions with some becoming RBC or HLA alloimmunized. This alloimmunization may impact post-HSCT transfusion requirements and donor engraftment.

METHODS

The study population included patients with SCD transplanted on a single-center nonmyeloablative, HLA-matched sibling HSCT trial at the National Heart, Lung, and Blood Institute (NHLBI) who had a pre-HSCT sample available for HLA class I antibody testing. We evaluated transfusion requirements and engraftment outcomes comparing patients with and without pre-existing HLA and RBC antibodies.

FINDINGS

Of 36 patients studied, 10 (28%) had HLA class I antibodies and 11 (31%) had a history of RBC alloantibodies. Up to day +45 post-HSCT, patients with HLA antibodies received more platelet transfusions (median 2.5 vs 1, p = 0.042) and those with RBC alloantibodies received more RBC units (median 7 vs 4, p = 0.0059) compared to respective non-alloimmunized patients. HLA alloimmunization was not associated with neutrophil engraftment, donor chimerism, or graft rejection. However, RBC alloimmunization correlated with a decreased donor T cell chimerism at 1 year (median 24% vs 55%, p = 0.035).

INTERPRETATION

Pre-existing HLA and RBC alloantibodies are clinically significant for patients undergoing HLA-matched nonmyeloablative HSCT. Testing for both HLA and RBC antibodies is important to help estimate transfusion needs peri‑HSCT. The association of lower donor T cell chimerism and pre-existing RBC alloantibodies needs further investigation.

FUNDING

NIH Clinical Center and NHLBI Intramural Research Program (Z99 CL999999, HL006007-11) and the Thrasher Research Fund.

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

Testing for anti-human leukocyte antigen (HLA) antibodies has now become standard practice in allogeneic hematopoietic stem cell transplantation (HSCT), and anti-HLA antibodies (both donor specific and non-donor specific) are being identified and have many potential consequences. Most studies suggest that donor-specific HLA antibodies lead to adverse outcomes, though little is reported on non-donor specific anti-HLA antibodies. We present the results of a retrospective cohort analysis of 157 patients who received HSCT at the University of Rochester over a period of four years. We identified 45 patients (28.7%) who had detectable anti-HLA antibodies, while only one patient (0.6%) had donor-specific anti-HLA antibodies. Patients with prior pregnancies and multiple transfusions were at increased risk to develop antibodies. In our cohort, the presence of non-donor specific anti-HLA antibodies did not significantly impact overall survival, progression free survival, graft failure, or transplant-related mortality.

Rituximab for desensitization during HLA-mismatched stem cell transplantation in patients with a positive donor-specific anti-HLA antibody

To define the efficacy of a single dose of 375 mg/m² rituximab for DSA-positive patients with 2000 ≤ MFI < 10,000, we enrolled a prospective clinical cohort including patients with positive DSA treated with rituximab (n = 55, cohort A), a matched-pair cohort including cases with negative DSA (n = 110, cohort B) and a historical cohort including subjects with 2000 ≤ MFI < 10,000 without receiving any treatment for DSA (n = 22, cohort C). The incidences of primary poor graft function (PGF) in cohort A and cohort B were 5% and 1% (P = 0.076), respectively, both of which were lower than that in cohort C (27%, P < 0.001, for all). Rituximab was associated with a reduced incidence of primary PGF (HR 0.200, P = 0.023). The 3-year nonrelapse mortality of patients in cohort A and cohort B were 23% and 24%, respectively, both of which were lower than that in the cohort C (37%), although no statistical significance was observed. These results led to a low 3-year overall survival in patients in the cohort C (58%) compared with those in the cohort A (71%) and the cohort B (73%). We suggest that a single dose of rituximab could be effectively used to prevent the onset of primary PGF. The prospective cohort of this study is registered at http://www.chictr.org.cn/ChiCTR-OPC-15006672.

Prevalence and risk factors of having antibodies to class I and II human leukocyte antigens in older haploidentical allograft candidates

The effect of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) has been recognized as a factor in graft failure (GF) in patients who underwent umbilical cord blood transplantation (UBT), matched unrelated donor transplantation (MUDT), or haploidentical stem cell transplantation (haplo-SCT). Presently, we know little about the prevalence of and risk factors for having anti-HLA antibodies among older transplant candidates. Therefore, we analyzed 273 older patients with hematologic disease who were waiting for haplo-SCT. Among all patients, 73 (26.7%) patients had a positive panel-reactive antibody (PRA) result for class I, 38 (13.9%) for class II, and 32 (11.7%) for both. Multivariate analysis showed that females were at a higher risk for having a PRA result for class II (P = 0.001) and for having antibodies against HLA-C and HLA-DQ. Prior pregnancy was a risk factor for having a PRA result for class I (P < 0.001) and for having antibodies against HLA-A, HLA-B and HLA-DQ. Platelet transfusions were risk factors for the following: having a positive PRA result for class I (P = 0.014) and class II (P < 0.001); having antibodies against HLA-A, HLA-B, HLA-C, HLA-DP, HLA-DQ, and HLA-DR; and having higher mean fluorescence intensity (MFI) of PRA for class I (P = 0.042). In addition, previous total transfusions were at high risk for having higher numbers of antibodies to specific HLA loci (P = 0.005), and disease course (7.5 months or more) (P = 0.020) were related to higher MFI of PRAs for class I. Our findings indicated that female sex, prior pregnancy, platelet transfusions and disease courses are independent risk factors for older patients with hematologic disease for having anti-HLA antibodies, which could guide anti-HLA antibody monitoring and be helpful for donor selection.

Optimizing cord blood selection

Nowadays a donor can be found for virtually all patients in need of an allogeneic stem cell transplantation, and the decision whether to use a matched or mismatched unrelated donor, an unrelated donor for umbilical cord blood transplantation (UCBT), or a haploidentical donor depends not only on the availability of the donor but also on patient-, disease-, and center-related factors. This paper summarizes the recent criteria in the selection of cord blood unit, including the cell dose requirement and the HLA typing for the optimal donor choice. The main strategies to optimize the results of UCBT, the conditioning regimens, and the use of antithymocyte globulin and the other platforms of graft-versus-host disease prophylaxis are discussed. The paper describes the results of UCBT in children and adults with malignant and nonmalignant diseases and the comparative analysis with other donor type and stem cell sources. Emerging strategies, focusing on the different platforms of ex vivo expansion and the new applications using cord blood stem cell, are also examined.

Impact of pretransplant donor-specific anti-HLA antibodies on cord blood transplantation on behalf of the Transplant Complications Working Group of Japan Society for Hematopoietic Cell Transplantation

Graft failure (GF) remains a major complication of cord blood transplantation (CBT). Although the presence of pretransplant, donor-specific anti-HLA antibodies (DSA) was reported to be associated with an increased risk of GF after CBT, data are still limited. Thus, we conducted a retrospective analysis of recipients of single-unit CBT with pretransplant anti-HLA antibodies using the database of Japan Society for Hematopoietic Cell Transplantation (JSHCT). Data for recipients of single-unit CBT with pretransplant anti-HLA antibodies from 2010 to 2014 were obtained. In total, 343 patients who received CBT and who had detailed information about anti-HLA antibodies were included. The median age was 51 years (range, 0-71). Regarding DSA, 25 patients had a mean fluorescence intensity (MFI) ≥ 1000 (DSA-positive group) and 318 patients had a MFI <1000 (DSA-negative group). The cumulative incidence of neutrophil engraftment at 60 days after CBT was 75.7% (95% CI, 70.6-80.1) in the DSA-negative group and 56.0% (95% CI, 34.1-73.1) in the DSA-positive group (P = 0.03). In conclusion, pretransplant DSA with a MFI ≥ 1000 was associated with an increased risk of GF in single-unit CBT.

Dissecting Allo-Sensitization After Local Administration of Human Allogeneic Adipose Mesenchymal Stem Cells in Perianal Fistulas of Crohn's Disease Patients

Adipose mesenchymal stem cells (ASC) are considered minimally immunogenic. This is due to the low expression of human leukocyte antigens I (HLA-I), lack of HLA-II expression and low expression of co-stimulatory molecules such as CD40 and CD80. The low rate of observed immunological rejection as well as the immunomodulatory qualities, position ASC as a promising cell-based therapy for the treatment of a variety of inflammatory indications. Yet, few studies have addressed relevant aspects of immunogenicity such as ASC donor-to-patient HLA histocompatibility or assessment of immune response triggered by ASC administration, particularly in the cases of presensitization. The present study aims to assess allo-immune responses in a cohort of Crohn's disease patients administered with allogeneic ASC (darvadstrocel formerly Cx601) for the treatment of complex perianal fistulas. We identified donor-specific antibodies (DSA) generation in a proportion of patients and observed that patients showing preexisting immunity were prone to generating DSA after allogeneic therapy. Noteworthy, naïve patients generating DSA at week 12 (W12) showed a significant reduction in DSA titer at week 52 (W52), whereas DSA titer was reduced in pre-sensitized patients only with no specificities against the donor administered. Remarkably, we did not observe any correlation of DSA generation with ASC therapeutic efficacy. In vitro complement-dependent cytotoxicity (CDC) studies have revealed limited cytotoxic levels based upon HLA-I expression and binding capacity even in pro-inflammatory conditions. We sought to identify CDC coping mechanisms contributing to the limited cytotoxic killing observed in ASC in vitro. We found that ASC express membrane-bound complement regulatory proteins (mCRPs) CD55, CD46, and CD59 at basal levels, with CD46 more actively expressed in pro-inflammatory conditions. We demonstrated that CD46 is a main driver of CDC signaling; its depletion significantly enhances sensitivity of ASC to CDC. In summary, despite relatively high clearance, DSA generation may represent a major challenge for allogeneic cell therapy management. Sensitization may be a significant concern when evaluating re-treatment or multi-donor trials. It is still unknown whether DSA generation could potentially be the consequence of donor-to-patient interaction and, therefore, subsequently link to efficacy or biological activity. Lastly, we propose that CDC modulators such as CD46 could be used to ultimately link CDC specificity with allogeneic cell therapy efficacy.

Hematopoietic stem cell transplantation with unrelated cord blood or haploidentical donor grafts in adult patients with secondary acute myeloid leukemia, a comparative study from Eurocord and the ALWP EBMT

Survival of patients with secondary acute myeloid leukemia (sAML) is poor. Cord blood transplantation (UCBT) and non-T-cell-depleted stem cell transplantation from haploidentical donors (HAPLO) are both strategies that have shown encouraging results in patients who do not have an human leukocyte antigen (HLA)-matched sibling or unrelated donor. We retrospectively analyzed outcomes of 409 adults with sAML receiving either UCBT (n = 163) or HAPLO (n = 246) in EBMT centers. Myelodysplastic syndrome (MDS) or myeloproliferative disorder (MPD) was the antecedent diagnosis in 79% of UCBT and 85% of HAPLO recipients. In multivariate analysis, UCBT was associated with higher risk of grade II-IV acute GVHD (HR 1.9, p = 0.009) and lower GHVD-free-relapse-free-survival (GRFS) (HR 1.57, p = 0.007) compared to HAPLO. Chronic-GVHD, RI, NRM, LFS, and OS were not statistically different between the two. Early disease stage at transplant was independently associated with lower RI and NRM and higher OS and LFS. These results indicate that HAPLO is associated with better GRFS and lower aGvHD compared to UCBT in patients with sAML and that UCBT can be a valid alternative for sAML patients who lack a matched sibling, a proper haploidentical or an unrelated donor.

Kinetics of neutrophil engraftment in allogeneic stem cell transplantation

Primary graft failure is a lethal complication that occurs after allogeneic stem cell transplantation (allo-SCT) and requires retransplantation. We retrospectively assessed 1,355 patients who underwent allo-SCT at our institute. Following allo-SCT, the cumulative incidence of subsequent neutrophil engraftment was calculated each day after day 5 among patients with white blood cell (WBC) count<100 cells/μL on the respective day. The number of patients with WBC count<100 cells/μL at days 14, 21, and 28 were 372, 55, and 21, respectively. In patients with WBC count<100 cells/μL on day 14, the cumulative incidence of engraftment was lower in recipients of peripheral blood stem cells (PBSCs) and cord blood (CB) compared with recipients of bone marrow (BM) (BM vs. PBSCs vs. CB, 93% vs. 79% vs. 77%, P<0.01). In patients with WBC count<100 cells/μL after day 14, the cumulative incidence of engraftment in recipients of PBSCs became progressively lower (25% at day 21 and 0% at day 28). In patients with WBC count<100 cells/μL on day 28, the cumulative incidence of engraftment was 100% in patients with donor chimerism≥95%, while it was only 13% in those with chimerism<95% (P<0.01). These data provide important information that could be useful in deciding the appropriate time for performing tests in patients with donor chimerism and in those that require retransplantation.

The European Society for Blood and Marrow Transplantation (EBMT) consensus recommendations for donor selection in haploidentical hematopoietic cell transplantation

The number of HLA-haploidentical hematopoietic cell transplants continues to increase worldwide due to recent improvements in outcomes, allowing more patients with hematological malignancies and non-malignant disorders to benefit from this procedure and have a chance to cure their disease. Despite these encouraging results, questions remain as multiple donors are usually available for transplantation, and choosing the best HLA-haploidentical donor for transplantation remains a challenge. Several approaches to haploidentical transplantation have been developed over time and, based on the graft received, can be grouped as follows: T-cell depleted haploidentical transplants, either complete or partial, or with T-cell replete grafts, performed with post-transplant cyclophosphamide-based graft-versus-host disease (GVHD) prophylaxis, or G-CSF-primed bone marrow graft and enhanced GVHD prophylaxis. Carefully selecting the donor can help optimize transplant outcomes for recipients of haploidentical donor transplants. Variables usually considered in the donor selection include presence of donor-specific antibodies in the recipient, donor age, donor/recipient gender and ABO combinations, and immunogenic variables, such as natural killer cell alloreactivity or KIR haplotype. Here we provide a comprehensive review of available evidence for selecting haploidentical donors for transplantation, and summarize the recommendations from the European Society for Blood and Marrow Transplantation (EBMT) on donor selection for different transplant platforms.

Who is the best donor for haploidentical stem cell transplantation?

Recent advances in haploidentical stem cell transplantation have enabled the use of human leukocyte antigen-half matched related donors for allogeneic stem cell transplantation and helped overcome one of the most important limitation in transplantation, which is donor availability, especially for the non-Caucasian population and mixed race individuals, extending allogeneic stem cell transplant for almost all patients in need. As many multiple potential related donors may now be available, it is increasingly clear that not all of these donors can provide equivalent transplant outcomes. Here we review the current available evidence of donor characteristics known to be associated with transplant outcomes for different types of haploidentical transplants using unmanipulated grafts (with post-transplant cyclophosphamide-based graft-vs-host prophylaxis and G-CSF and anti-thymocyte globulin approach) as well as modified grafts (with either selective or complete T-cell depletion). While various platforms use haploidentical donors, graft manipulation and approach to prevent graft-vs-host post-transplant may impact on donor selection and transplant outcomes.

Better outcomes of modified myeloablative conditioning without antithymocyte globulin versus myeloablative conditioning in cord blood transplantation for hematological malignancies: A retrospective (development) and a prospective (validation) study

Cord blood transplantation (CBT) is an effective option for treating hematological malignancies, but graft failure (GF) remains the primary cause of therapy failure. Thus, based on myeloablative conditioning (MAC) of busulfan with cyclophosphamide (Bu/Cy) or total body irradiation with Cy (TBI/Cy), fludarabine (Flu) was added to Bu/Cy and cytarabine (CA) to TBI/Cy for a modified myeloablative conditioning (MMAC). To compare the prognosis of MMAC with MAC, we conducted a retrospective study including 58 patients who underwent CBT with MAC or MMAC from 2000 to 2011. Neutrophil and platelet engraftment rate, overall survival (OS) and disease free survival (DFS) were significantly higher in the MMAC group (adjusted hazard ratio [HR], 2.58, 2.43, 0.36 and 0.37; p < 0.01, p = 0.01, p = 0.02 and p = 0.02, separately). Nonrelapse mortality (NRM) was comparable (p = 0.183). To validate the outcomes noted in the MMAC group, we conducted a prospective single‐arm clinical trial including 188 patients who underwent CBT with MMAC from 2011 to 2015. Engraftment rate, survival and NRM of the MMAC group in the prospective trail (MMAC‐P) were similar to the MMAC group in the retrospective study (MMAC‐R). This study is the first to demonstrate the superiority of MMAC to MAC in CBT for hematological malignancies.

What's new?

Cord blood transplants can help patients with blood cancer, but too often, the transplant fails due to immune rejection or other problems. Typically, patients receive myeloablative conditioning (MAC) prior to CBT, but more intense regimen might improve transplant success. Here, the authors compared the success of modified myeloablative conditioning (MMAC) with conventional MAC by looking at 58 patients over an 11‐year period. They then followed up with a four‐year prospective study, including 188 patients who received cord blood transplant with MMAC. The modified conditioning regimen boosted graft success and improved survival of patients with hematological cancers.

The European Society for Blood and Marrow Transplantation (EBMT) Consensus Guidelines for the Detection and Treatment of Donor-specific Anti-HLA Antibodies (DSA) in Haploidentical Hematopoietic Cell Transplantation

Haploidentical donors are now increasingly considered for transplantation in the absence of HLA-matched donors or when an urgent transplant is needed. Donor-specific anti-HLA antibodies (DSA) have been recently recognized as an important barrier against successful engraftment of donor cells, which can affect transplant survival. DSA appear more prevalent in this type of transplant due to higher likelihood of alloimmunization of multiparous females against offspring's HLA antigens, and the degree of mismatch. Here we summarize the evidence for the role of DSA in the development of primary graft failure in haploidentical transplantation and provide consensus recommendations from the European Society for Blood and Marrow Transplant Group on testing, monitoring, and treatment of patients with DSA receiving haploidentical hematopoietic progenitor cell transplantation.