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.

Significant progress has been made over the past decade in haploidentical transplantation, with the development of novel methods to control intense alloreactive reactions generated in the major HLA-mismatched setting. Application of post-transplantation cyclophosphamide has gained worldwide acceptance as an effective and low-cost way to perform this type of transplantation, with outcomes now similar to those from HLA-matched unrelated donors. These advances have resulted in improved treatment-related mortality, whereas disease relapse has emerged as the most common cause of treatment failure. In addition, improvements in immunologic reconstitution after transplantation are much needed, not only in haploidentical transplantation but in all forms of stem cell transplantation. This symposium has focused on some of the most promising methods to control alloreactivity in this form of transplantation and application of cellular therapy to prevent disease relapse after transplantation, as well as understanding immunologic reconstitution and foreseeable approaches to improve immune recovery after transplantation.

The resurgence of haploidentical stem cell transplantation (HaploSCT) over the last decade is one of the most important advances in the field of hematopoietic stem cell transplantation (HSCT). The modified platforms of T cell depletion either ex vivo (CD34+ cell selection, "megadoses" of purified CD34+ cells, or selective depletion of T cells) or newer platforms of in vivo depletion of T cells, with either post-transplantation high-dose cyclophosphamide or intensified immune suppression, have contributed to better outcomes, with survival similar to that in HLA-matched donor transplantation. Further efforts are underway to control viral reactivation using modified T cells, improve immunologic reconstitution, and decrease the relapse rate post-transplantation using donor-derived cellular therapy products, such as genetically modified donor lymphocytes and natural killer cells. Improvements in treatment-related mortality have allowed the extension of haploidentical donor transplants to patients with hemoglobinopathies, such as thalassemia and sickle cell disease, and the possible development of platforms for immunotherapy in solid tumors. Moreover, combining HSCT from a related donor with solid organ transplantation could allow early tapering of immunosuppression in recipients of solid organ transplants and hopefully prevent organ rejection in this setting. This symposium summarizes some of the most important recent advances in HaploSCT and provides a glimpse in the future of fast growing field.

Significant progress has been made over the past decade in haploidentical transplantation, with the development of novel methods to control intense alloreactive reactions generated in the major HLA-mismatched setting. Application of post-transplantation cyclophosphamide has gained worldwide acceptance as an effective and low-cost way to perform this type of transplantation, with outcomes now similar to those from HLA-matched unrelated donors. These advances have resulted in improved treatment-related mortality, whereas disease relapse has emerged as the most common cause of treatment failure. In addition, improvements in immunologic reconstitution after transplantation are much needed, not only in haploidentical transplantation but in all forms of stem cell transplantation. This symposium has focused on some of the most promising methods to control alloreactivity in this form of transplantation and application of cellular therapy to prevent disease relapse after transplantation, as well as understanding immunologic reconstitution and foreseeable approaches to improve immune recovery after transplantation.

Donor lymphocyte infusion has been used in the management of relapsed hematologic malignancies after allogeneic hematopoietic cell transplantation. It can eradicate minimal residual disease or be used to rescue a hematologic relapse, being able to induce durable remissions in a subset of patients. With the increased use of haploidentical hematopoietic cell transplantation, there is renewed interest in the use of donor lymphocytes to either treat or prevent disease relapse post transplant. Published retrospective and small prospective studies have shown encouraging results with therapeutic donor lymphocyte infusion in different haploidentical transplantation platforms. In this consensus paper, finalized on behalf of the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation, we summarize the available evidence on the use of donor lymphocyte infusion from haploidentical donor, and provide recommendations on its therapeutic, pre-emptive and prophylactic use in clinical practice.