Objectives: Allogeneic hematopoietic stem cell transplant provides a curative treatment for a considerable amount of hematologic diseases, and it is widely used today. Successful allogeneic stem cell transplant can be compromised by treatment-related toxicity, graft-versus-host disease, infectious complications, disease relapse, and graft failure. Primary graft failure is an important cause of hematopoietic stem cell transplant failure. Primary graft failure correlates with the level of complement-binding, donor-specific anti-HLA antibodies prior to transplant.
Material and Methods: We evaluated 15 patients who underwent hematopoietic stem cell transplant using peripheral blood stem cells in terms of graft failure and anti-HLA antibody levels before transplant. All were treated between January 2015 and June 2016. Pretreatment serum anti-HLA class I and anti-HLA class II antibody levels were measured in all patients.
Results: Anti-HLA class I antibodies were present in 7 patients (46.6%) and anti-HLA class II antibodies in 8 (53.3%). All three patients who developed primary graft failure were anti-HLA-positive.
Conclusions: Anti-HLA antibodies are a significant cause of graft failure. It is a situation that must be understood with caution. Our results support the considerations that allogeneic hematopoietic stem cell transplant, especially when a fully compatible sibling donor is not present, should include screening of donor-specific antibodies of alternative donors and desensitization therapy for allosensitized patients before transplant.
Key words : Donor screening, Graft-versus-host disease, Hematologic malignancy, Peripheral blood transplant
Allogeneic hematopoietic stem cell transplant (AHSCT) can effectively treat many hematologic diseases. Fewer than 30% of patients requiring AHSCT have fully compatible sibling donors. Thus, noncompatible relatives, nonrelatives, and cord blood are increasingly used as stem cell sources.1,2 However, complications including graft failure (GF), graft-versus-host disease (GVHD), and relapse continue to be serious problems. Primary graft failure (PGF) and secondary GF after AHSCT develop in 5% to 25% of all patients.3,4
Primary graft failure is defined as neutrophil failure and failure to achieve donor-like hematopoiesis within 28 days of stem cell infusion (absolute neutrophil count > 0.5 × 109/L) after complete stem cell transplant.4 Primary graft failure is probably multifactorial in origin; an HLA mismatch between the donor and recipient increases risk of GF. A close relation exists between graft survival after solid-organ transplant and preoperative anti-HLA antibody levels.5 Specifically, before kidney transplant, anti-HLA antibody levels in patient serum is the most important immunologic risk factor.6 It has been suggested that the level of such antibodies is also a major risk factor for PGF after non-HLA-compatible stem cell transplant. With the advent of solid-phase antibody detection methods, the sensitivity of HLA-specific alloantibody detection has improved.7 Indeed, if HSCT using an HLA-incompatible donor is planned, the destructive effects of PGF warrant the need to measure donor-specific antibody levels in all patients.2,8
In this study, we explored the relation between anti-HLA antibody levels and the frequency of GF in patients undergoing AHSCT.
Materials and Methods
From January 2015 to June 2016 at our center (Baskent University Adana Dr. Turgut Noyan Research and Medical Center Hematology Unit), we treated 15 patients with AHSCT using peripheral stem cells. Two patients had chronic myeloid leukemia, 6 had sickle cell anemia, 1 had aplastic anemia, 1 had myelodysplastic syndrome, 4 had acute lymphoblastic leukemia, and 1 had acute myeloid leukemia. We reported GF and donor-specific antibody data in our patients.
Fully HLA-compatible siblings served as donors for 7 patients, a fully compatible relative for 1, unrelated donors for 2, and haplotype-mismatched relatives (haploidentical) for 5 patients. We did not perform T-cell depletion. Both patients and donors were HLA typed for class I (HLA-A, -B, and -C) and class II (HLA-DR and HLA-DQ) antigens using molecular techniques. Pretransplant serum samples from all patients were subjected to HLA/donor-specific antibody determinations (measurement of anti-HLA class I and class II antibody levels using Luminex Lifecodes single-antigen beads; Luminex, Austin, TX, USA). A donor-specific antibody of mean fluorescence intensity ≥ 1,000 was considered positive.8 All immunologic test data predicted the immunologic risk after transplant.
We evaluated 15 patients who underwent AHSCT. Graft-versus-host disease was detected in 4 patients and PGF in 3 patients. Anti-HLA class I antibodies were detected in 7 patients (46.6%) and anti-HLA class II antibodies in 8 patients (53.3%). In terms of donor source, the anti-HLA status was positive in 2 of 5 patients who underwent haploidentical transplant (40%) and in 5 of 10 patients who received transplants from fully compatible donors. Eight patients were male and seven were female. Five female and 3 male patients were anti-HLA antibody positive. Of the 3 patients who developed PGF, both the donors and the recipients were males. In the 3 patients with PGF, anti-HLA antibodies were detected as positive. In the 4 patients who developed GVHD, only 1 was anti-HLA antibody positive. Two of the 3 patients who developed PGF died of infection (Table 1).
Hematopoietic stem cell transplant cures many hematologic diseases. Allogeneic hematopoietic stem cell transplant may be valuable for patients with no HLA-compatible siblings or who have siblings who do not wish to donate. Alternative donors can include HLA-compatible nonrelative donors and HLA noncompatible family members (haploidentical donors).9,10 Cord blood can also be used. Despite the important advances made in recent years, GVHD and PGF remain major problems after AHSCT.
As mentioned, PGF is defined as neutrophil engraftment insufficiency over 3 sequential days (using absolute neutrophil count) 28 days after stem cell infusion and failure to achieve donor hematopoiesis. Measurements of GF after AHSCT include an inability to attain 2 or 3 measures of adequate blood cell count (absolute neutrophil count ≤ 0.5 × 109/L), platelet count ≤ 20 × 109/L, and hemoglobin level of ≤ 80 g/L. Various studies have reported PGF rates of 2% to 15% in patients undergoing HLA-compatible sibling donor transplant, nonrelative donor transplant, and umbilical cord blood transplant.3,4,11
Primary graft failure is a multifactorial condition; the risks for PGF after stem cell transplant include lower CD34-positive stem cell numbers infused during transplant, HLA differences between the donor and the recipient, the preparation regimen used, chemotherapy-naive status, and patient age < 30 years.12 In this study, we evaluated the existence of anti-HLA antibodies, GVHD development, and PGF status in 15 patients who received AHSCT from different donor sources but without T-cell depletion. Our study included analyses of anti-HLA antibodies before transplant on all 15 prospective patients.
A retrospective study conducted by the Center for International Blood and Marrow Transplant Research found that, in those undergoing bone marrow graft transplant procedures, low cell levels (total nucleated cells ≤ 2.4 × 108/kg) increased the PGF risk by 40%. In addition, in those receiving peripheral blood transplants, a CD34-positive cell dose < 2 × 106/kg had no effect on PGF, and no GF threshold was apparent. It has been suggested that CD34 cell dose is an important predictor of secondary GF.13,14 In our study, the lowest total nucleated cell dose infused was 4.3 × 108/kg, and the lowest CD34 dose was 5.29 × 106/kg, which were apparently adequate. Data for our study patients are shown in Table 2.
The use of cord blood in patients with nonmalignant disease and in those who have received reduced-intensity conditioning regimens is associated with low engraftment ratios.13,15 Primary graft failure can result in death caused by infections, with complications of elongated pancytopenia expected in the absence of a second transplant. All 3 patients who developed PGF were females, with 1 of these patients (who died) receiving only 1 haploidentical transplant. The second patient (who also died) received a second haploidentical transplant but had high levels of anti-HLA antibodies before the second transplant procedure. The third patient received more CD34-positive cells from the same sibling and underwent a nonmyeloablative regimen of allogeneic stem cell transplant. The transplant procedure was ultimately successful for this patient.
For patients younger than 30 years, there is an associated increased risk of GF, emphasizing that the younger immune system is more resistant to conditioning regimens than hematopoiesis. In patients with progressive disease and in recipients who perform poorly, the tendency toward GF is probably a microenvironmental issue. The incidence of PGF is markedly lower in patients who receive peripheral blood than in those who receive bone marrow grafts. Moreover, ABO incompatibility, male recipient-female donor status, ex vivo T-cell depletion,16 and splenomegaly are also associated with an increased risk of GF. A total body irradiation-cyclophosphamide regimen, posttransplant tacrolimus-based immunosuppression, and a granulocyte colony-stimulating factor prescription reduce the risk of PGF.13,14,17 Donor-recipient HLA incompatibility is the prime cause of GF. The GF risk increases as the mismatch HLA allele count increases and when anti-HLA antibodies are evident in patient serum.18 Nondonor-specific anti-HLA antibody levels do not correlate with PGF. Specifically, a high mean fluorescence intensity value (> 5,000) and the presence of complement-binding donor-specific antibodies are associated with a high-level risk of PGF. Complement-binding donor-specific antibody levels must be reduced before transplant.19,20
When GF is detected after mismatched transplant, donor antibodies are also usually evident. After fully compatible sibling or unrelated transplant procedures, the levels of antibodies against HLA-DP antigens are generally considered important. Fully compatible siblings (30%) and compatible unrelated donors (> 80%) exhibit HLA-DPB1 incompatibilities. Ciurea and associates reported a 20% prevalence of anti-HLA antibodies in matched unrelated donor transplant recipients and an anti-HLA-DPB1 antibody ratio of 3.4%. The presence of anti-HLA-DPB1 donor-specific antibodies was associated with GF incidence after matched unrelated donor HSCT.21,22
Yamamoto and associates showed the negative effects of HLA antibodies against HLA-C, -DQ, -DP, and -DRB3/B4/B5 rather than donor nonspecific HLA-A, -B, or -DRB1 antibodies in their retrospective study of cord blood transplant. They suggested the possible existence of donor specific antibodies (DSA) against these antigens, which are not screened routinely with cord blood transplant.12 Repeat blood infusions, pregnancy, and prior transplants may trigger the emergence of anti-HLA antibodies, with greater prevalence of this condition in female patients suggesting a pregnancy number disparity.23 One study found no difference in the anti-HLA antibody levels between male patients and female patients who had never been pregnant.22 Anti-HLA antibodies detected in the posttransplant era may reflect recipient memory responses; it may be possible that donor (memory) antibodies develop after blood transfusion or these may be de novo antibodies.24 The prevalence of anti-HLA class I or class II antibodies before AHSCT was 37% in one study11 and 20.2% in another study.25 Eight of our 15 patients (53.3%) were anti-HLA-positive.
In HSCT, the effects of GF are destructive, resulting in death in many patients. Because of the increasing use of mismatched donors as a graft source, we need to take alloimmunization into consideration from the point of PGF and GVHD. In our study, although few patients were evaluated, we observed the importance of the existence of anti-HLA antibodies and the justification of donor-specific antibody screening. It is seen as needed for a successful transplant, along with desensitization treatments pretransplant on allosensitized patients and detection of the specific antibodies in the recipient before donor selection.
Volume : 15
Issue : 1
Pages : 219 - 223
DOI : 10.6002/ect.mesot2016.P99
From the 1Department of Immunology, Baskent University, Ankara, Turkey; and the 2Department of Hematology and the 3Immunology Tissue Typing Laboratory, Baskent University, Adana, Turkey
Acknowledgements: The authors declare that they have no sources of funding for this study, and they have no conflicts of interest to declare.
Corresponding author: Bilkay Basturk, Baskent University, Faculty of Medicine, Department of Immunology, Adana Dr Turgut Noyan Research and Medical Center, Transplantation and Tissue Typing Laboratory, Adana, Turkey
Phone: +90 322 3272727 ext. 2500
Table 1. Panel Reactive Antibody Positivity in Hematopoietic Stem Cell Transplant Patients
Table 2. Parameters in Hematopoietic Stem Cell Transplant Patients