A possible role for the production of multiple HLA antibodies in fatal platelet transfusion refractoriness after peripheral blood progenitor cell transplantation from the mother in a patient with relapsed leukemia

Donor-derived anti-HLA antibodies in a haploidentical hematopoietic cell transplant recipient shortly after transplant

A pediatric patient with acute myeloid leukemia was referred to our institution for investigational therapy after disease relapse following a mismatched unrelated donor hematopoietic cell transplant (HCT). Prior to second HCT, the patient's serum was negative for antibodies to class I and class II HLA. Eight days after receiving a maternal donor haploidentical transplant, the patient became platelet refractory and highly sensitized to multiple class I HLA. Serum from the patient's mother was positive for the strongest antibodies present in the patient, suggesting the antibodies were donor-derived. Patient sera showed magnified and expanded sensitization over time in the context of 100% donor chimerism and despite undetectable circulating B cells. Escalating sensitization suggests active transfer of rituximab-resistant antibody-producing passenger lymphocytes from a haploidentical donor to a transplant recipient at the time of progenitor cell infusion. Evaluation of donor sensitization status may be a consideration prior to HLA mismatched HCT.

Detecting the humoral alloimmune response: we need more than serum antibody screening

Whereas many techniques exist to detect HLA antibodies in the sera of immunized individuals, assays to detect and quantify HLA-specific B cells are only just emerging. The need for such assays is becoming clear, as in some patients, HLA-specific memory B cells have been shown to be present in the absence of the accompanying serum HLA antibodies. Because HLA-specific B cells in the peripheral blood of immunized individuals are present at only a very low frequency, assays with high sensitivity are required. In this review, we discuss the currently available methods to detect and/or quantify HLA-specific B cells, as well as their promises and limitations. We also discuss scenarios in which quantification of HLA-specific B cells may be of additional value, besides classical serum HLA antibody detection.

Persistence of recipient human leucocyte antigen (HLA) antibodies and production of donor HLA antibodies following reduced intensity allogeneic haematopoietic stem cell transplantation

The effects of reduced intensity conditioning (RIC) on human leucocyte antigen (HLA)-alloimmunization and platelet transfusion refractoriness (PTR) following allogeneic haematopoietic stem cell transplantation (Allo-HSCT) are unknown. We studied HLA-alloantibodies in a cohort of 16 patients (eight HLA-alloimmunized with pre-transplant histories of PTR and eight non-alloimmunized controls) undergoing Allo-HSCT using fludarabine/cyclophosphamide-based RIC. Pre- and post-transplant serum samples were analysed for HLA-antibodies and compared to myeloid, T-cell and bone marrow plasma cell chimaerism. Among alloimmunized patients, the duration that HLA-antibodies persisted post-transplant correlated strongly with pre-transplant HLA-antibody mean fluorescence intensity (MFI) and PRA levels (Spearman's rank correlation = 0·954 (P = 0·0048) and 0·865 (P = 0·0083) respectively). Pre-transplant MFI >10,000 was associated with post-transplant HLA antibody persistence >100 d (P = 0·029). HLA-antibodies persisted ≥100 d in 3/8 patients despite recipient chimaerism being undetectable in all lympho-haematopoietic lineages including plasma cells. Post-transplant de-novo HLA-antibodies developed in three control patients with two developing PTR; the donors for two of these patients demonstrated pre-existing HLA-antibodies of equivalent specificity to those in the patient, confirming donor origin. These data show HLA-antibodies may persist for prolonged periods following RIC. Further study is needed to determine the incidence of post-transplant PTR as a consequence of donor-derived HLA alloimmunization before recommendations on donor HLA-antibody screening can be made.

The role of HLA antibodies in allogeneic SCT: is the 'type-and-screen' strategy necessary not only for blood type but also for HLA?

The role of HLA antibodies in SCT has drawn increasing attention because of the significantly increased number of patients who receive HLA-mismatched SCT, including cord blood transplantation, haploidentical SCT and unrelated SCT. Technical advancements in the methods of HLA Ab testing have realized rapid, accurate and objective identification, as well as quantification of specific HLA antibodies. Recent clinical studies have suggested that the presence of donor-specific HLA antibodies (DSA) in patients is associated with graft failure in HLA-mismatched SCT when the above-listed stem cell sources are used and results in different impacts. Of note, most of the 'HLA-matched' unrelated SCT actually involve HLA mismatches in HLA-DP and the presence of antibodies against this locus has been reported to be associated with graft failure. Thus, HLA Ab should be examined as a work-up for all patients who undergo SCT from 'alternative donors.' The simplest route for preventing HLA Ab-mediated graft failure in Ab-positive patients is to avoid donors who possess the target Ag of HLA antibodies. If SCT from such donors must be performed, treatment for DSA before SCT may improve the chances of successful donor engraftment.

Platelet transfusion refractoriness attributable to HLA antibodies produced by donor-derived cells after allogeneic bone marrow transplantation from one HLA-antigen-mismatched mother

PTR is a serious problem in patients being treated for hematologic disorders. Two patients with acute leukemia developed PTR after allogeneic BMT from one HLA-antigen-mismatched mother attributable to HLA antibodies, which could not be detected in their serum before BMT. HLA antibodies, whose specificity resembled that of each patient, were detected in each donor's serum. Each donor had probably been immunized during pregnancy by their partner's HLA antigens expressed by the fetus, consequently, transplanted donor-derived cells provoked HLA antibodies in each recipient early after BMT, and those HLA antibodies induced PTR. If the mothers are selected as donors for their children, they should be tested for the presence of HLA antibodies.

Low toxicity of a conditioning with 8-Gy total body irradiation, fludarabine and cyclophosphamide as preparative regimen for allogeneic hematopoietic stem cell transplantation in pediatric hematological malignancies

We here report the efficacy and toxicity of a conditioning regimen with fractionated 8-Gy TBI, fludarabine, and cyclophosphamide in allogeneic HSCT for pediatric hematological malignancies. Among 22 children who received related or unrelated HSCT, nine were transplanted with refractory disease and/or from HLA two or more loci-mismatched family donors. None of the patients developed graft failure. The Seattle grading system revealed that 18 patients had no RRT, and the remaining patients had grade I gastrointestinal toxicity alone. The estimated overall survival and leukemia-free survival at two yr were 57.1% and 48.0%, respectively, in 10 patients with acute lymphoblastic leukemia; 91.7% and 71.3%, respectively, in 12 patients with myeloid leukemia. The incidence of TRM was 4.8% at two yr. The rates of RRT above grade II and TRM in an 8-Gy TBI-containing regimen were significantly lower than the data of historical control patients who underwent 12-Gy TBI and cyclophosphamide with or without etoposide. The intermediate-dose TBI-based conditioning regimen may confer successful engraftment combined with minimized RRT, although its efficacy should be further evaluated.

Existence of an immunoglobulin G component of naturally occurring HLA class I antibodies that are not directed against self-antigens in human serum

We compared the frequency of immunoglobulin G (IgG) type of human leukocyte antigen (HLA) class I antibodies between patients with systemic lupus erythematosus (SLE) and healthy controls using a highly sensitive FlowPRA method. Sixteen of 130 normal healthy males and 2 of 10 normal females without a history of pregnancy (none had ever been transfused) possessed HLA class I antibodies. In SLE, male, but not female patients, showed a significant increase in the frequency of the antibodies compared with the corresponding controls. The antibodies did not appear to be involved in the development of SLE because of no substantial relationship to the incidence of cytopenia or SLE disease activity index score. Each individual had 1-31 types of HLA class I antibodies. Interestingly, HLA class I antibodies did not correspond to the individual's own HLA antigens. Eight of 32 types of HLA class I antigens detected were rare in the Japanese population. These results suggest that an IgG component of naturally occurring HLA class I antibodies exists in human serum and that these antibodies are not antibodies against self-antigens.