Neonatal tolerance revisited

HLA Factors versus Non-HLA Factors for Haploidentical Donor Selection

When multiple haploidentical donors are available for transplantation, those of younger generations are generally selected over those of older generations. However, it is unclear who is the optimal donor when selecting candidates from within a generation, such as father versus mother, son versus daughter, or brother versus sister. Although traditionally male donors are favored over female donors, particularly for male recipients, and significant associations of individual HLA mis(matches) on outcomes are being increasingly recognized, the hierarchy of factors for donor selection is indeterminate. To assess whether HLA factors take precedence over non-HLA factors and to isolate the influence of specific characteristics on outcomes, we analyzed 412 patients stratified by donor relationship: child donor (son [n = 202] versus daughter [n = 96]), parent (father [n = 28] versus mother [n = 29]), and sibling (noninherited maternal [NIMA; n = 29] versus paternal [NIPA; n = 28] mismatched). Among siblings, NIMA mismatch was associated with a lower risk of acute graft-versus-host disease (aGVHD); B-leader mismatch was associated with high nonrelapse mortality (NRM), poor progression-free survival, and a trend toward poor overall survival (OS), whereas A-mismatch was associated with lower aGVHD. Among parent donors, the relationship did not impact any outcome; B-leader mismatch was associated with higher NRM and a trend toward poor OS, whereas A-mismatch was associated with lower NRM and improved progression-free survival and OS. Among child donors, no individual HLA mismatch was predictive of any outcome, and daughter donors were not associated with any adverse outcomes in multivariate analyses. Our data suggest that certain HLA factors may be more significant in some cases and should be given priority over simply selecting a donor based on relationship/sex.

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.

Involvement of major histocompatibility complex class I compatibility between dam and calf in the aetiology of bovine retained placenta

The possibility was examined that in cattle compatibility of major histocompatibility complex (MHC) products between dam and calf might negatively influence the placental maturation and expulsion, and therefore increase the risk of retained placenta in healthy, normally calving cattle. Fifteen combinations of a single dam and two offspring were selected; the placenta of the first offspring was normally expelled (control) and the placenta of the second one was retained (case). The MHC class I and class II antigens of the animals were typed by immunoprecipitation and by one-dimensional isoelectric focusing (1D-IEF). Compatibility or incompatibility of class I or class II antigens was established by comparison of the IEF banding patterns of dam and calves. Analysis revealed that MHC class I compatibility between dam and calf increased the risk of retained placenta. In this study, the effect of class II compatibility was not significant, nor was the effect of the interaction of class I and class II. In a subsequent, additional sample the experimental design was extended: induction of tolerance against non-inherited maternal antigens (NIMA) might be implicated in the occurrence of the disorder within the group of class I incompatible cases. In three out of the five class I incompatible retained placenta cases, the banding pattern of the incompatible haplotype of the calf was identical to that of the haplotype of the granddam that was not inherited by the dam (NIMA). Notably, within the nine class I incompatible controls, there were none in which the offspring shared a paternal class I type with the granddam. This might suggest a tolerance-inducing effect of NIMA in cattle in relation to retained placenta.(ABSTRACT TRUNCATED AT 250 WORDS)

Hematopoietic SCT from partially HLA-mismatched (HLA-haploidentical) related donors

Hematopoietic SCT from a partially HLA-mismatched (HLA-haploidentical) first-degree relative offers the benefits of rapid and near universal donor availability but also the risks that result from traversing the HLA barrier; namely, graft failure, severe GVHD and prolonged immunodeficiency. Improvements over the last 10 years in conditioning regimens, graft engineering and pharmacological immunoprophylaxis of GVHD have substantially reduced the morbidity and mortality of HLA-haploidentical SCT. Highly immunosuppressive but nonmyeloablative conditioning extends the availability of HLA-haploidentical SCT to elderly hematologic malignancy patients lacking HLA-matched donors and permits recovery of autologous hematopoiesis in the event of graft failure. Current regimens for HLA-haploidentical SCT are associated with a 2-year non-relapse mortality of 20+/-5%, relapse of 35+/-15% and overall survival of 50+/-20%. Major developmental areas include harnessing natural killer cell alloreactivity to reduce the risk of disease relapse and improving immune reconstitution by delayed infusions of lymphocytes selectively depleted of alloreactive cells. Hematologic malignancy patients who lack suitably matched related or unrelated donors can now be treated with HLA-haploidentical related donor or unrelated umbilical cord blood SCT. Future clinical trials will assess the relative risks and benefits of these two graft sources.

The effect of noninherited maternal antigens in allogeneic transplantation

Confrontation of the unborn child immune system with the noninherited maternal antigens (NIMAs) has a lifelong modulating impact on the immune response of the child against the NIMAs. In this review we summarize the clinical evidence for the existence of the NIMA effect, discuss the possible cellular and molecular basis of the phenomenon, and outline the necessity of further clinical research.

Both self and non-inherited maternal HLA antigens influence the immune response

Recent studies suggest that exposure of the fetus and newborn to non-inherited maternal major histocompatibility complex HLA antigens (NIMA) has a life-long effect on allograft recognition that could influence tolerance of organ grafts. NIMA also appear to influence disease susceptibility. Here, Jon van Rood and Frans Claas discuss evidence that three HLA haplotypes, those inherited from the parents plus NIMA, shape the immune response.

Isoagglutinins following ABO-incompatible bone marrow transplantation

Isoagglutinins were investigated following ABO-incompatible bone marrow transplantation. In major incompatibility anti-A tends to require more time to disappear than anti-B. Correspondingly, A erythrocytes require more time to become demonstrable. There is no such difference in major plus minor incompatibility. In minor incompatibility, isoagglutinins against the recipient blood group may be produced early after bone marrow transplantation, which then give way to a possibly lifelong tolerance for the recipient's old blood group.

The influence of allogeneic cells on the human T and B cell repertoire

Clinical transplantation is often complicated by rejection episodes, in which the immune system of the recipient reacts to the foreign transplantation (HLA) antigens on the graft. This immune response includes humoral and cellular components. In the first, B lymphocytes form antibodies to the HLA alloantigens. In the second, CD8+ T lymphocytes recognize and react to HLA class I antigens, and CD4+ T cells react to HLA class II antigens. The frequency and severity of these rejection episodes can be diminished by immunosuppressive drugs, HLA matching between donor and recipient, and immune modulation by blood transfusion. Effective HLA matching between donor and recipient is not always possible and often not necessary. Insight into the factors that influence the T and B cell repertoire after blood transfusion might lead to new approaches to improve graft survival.