Nonmyeloablative hematopoietic cell transplant for treatment of immune deficiency

Salvage treatment for relapsed/refractory Hodgkin lymphoma: role of allografting, brentuximab vedotin and newer agents

INTRODUCTION

Second-line, salvage chemotherapy followed by high-dose chemotherapy and autologous stem cell transplantation (AUTO-SCT) is the standard of care for patients with relapsed/refractory (R/R) Hodgkin lymphoma (HL). Approximately 50% of patients relapse after AUTO-SCT and their prognosis is generally poor. Brentuximab Vedotin (BV) has demonstrated efficacy in this setting and allogeneic (ALLO)-SCT represents an option with curative potential in this subgroup of patients.

AREAS COVERED

A systematic review has been conducted to explore the actual knowledge on ALLO-SCT, BV and newer agents in R/R HL.

EXPERT OPINION

The introduction of BV in clinical practice has significantly improved the management of post-AUTO-SCT relapses and the drug can induce durable remissions in a subset of R/R HL. Allografting select patients has been used to improve clinical outcomes and recent case series have begun to explore BV as a potential 'bridge' to allo-SCT, even though the optimal timing of ALLO-SCT after BV response remains undetermined. However, reduced tumor burden at the time of ALLO-SCT is a key factor to decrease relapse risk. Based on the unique composition of the tumor, more recently new agents such as PD-1 inhibitors have been developed. The potential role of PD-1 inhibitors with ALLO-SCT remains to be explored.

Reduced-intensity conditioning for allogeneic stem cell transplant in primary immune deficiencies

Conventional myeloablative conditioning regimens prior to hematopoietic cell transplantation (HCT) are associated with significant transplant-related morbidity and mortality in children affected by primary immunodeficiency disorders. Reduced-intensity conditioning regimens have been extensively used without severe acute toxicity in patients with pre-HCT comorbidities, with the additional advantage of reducing or avoiding long-term sequelae such as infertility and growth retardation. Compared with myeloablative HCT, reduced-intensity conditioning regimens are associated with an increased incidence of mixed donor chimerism and graft rejection. While mixed donor engraftment is likely to correct the phenotypic expression of most children with primary immunodeficiency disorders, the use of donor lymphocyte infusion to increase donor chimerism or second HCT procedures may be required in some cases. Here we discuss the most recent data on the use of different reduced-intensity conditioning protocols in children with primary immunodeficiency disorders, highlighting significant clinical lessons and areas that need additional study.

Reduced intensity transplantation for primary immunodeficiency disorders

Studies so far indicate that reduced intensity transplantation (RIT) may have an important role in treating patients with primary immunodeficiency disease (PID). Unlike more standard approaches, such regimens can be used without severe toxicity in patients with severe pulmonary or hepatic disease. RIT also offers the advantage that long-term sequelae such as infertility or growth retardation may be avoided or reduced. RIT appears to be most appropriate for those patients with significant co-morbidities (eg T cell deficiencies) and those undergoing unrelated donor haematopoietic cell transplantation. More studies are required using pharmacokinetic monitoring (eg busulphan, treosulfan and alemtuzumab) and varying stem cell sources to optimise graft vs marrow reactions and minimise graft vs host disease. In certain PID patients RIT will be the "first step" towards establishing donor cell engraftment; second infusions of donor stem cells, donor lymphocyte infusions, or a second myeloablative HCT, which appears to be well tolerated, may be required in some patients with low level donor chimerism or graft rejection.

Reduced intensity transplantation for primary immunodeficiency disorders

Many advances have been made since the first successful hematopoietic cell transplants (HCT) in children with primary immunodeficiency disorders (PID) were reported 40 years ago, and many children with PID can now be cured from their otherwise lethal disorders through well-matched HCT procedures. Preexisting morbidity and infection remain the principal adverse factors for poor outcomes with HCT. To improve current results, earlier diagnosis, well-tolerated pretransplant conditioning regimens, and promotion of immune reconstitution need to be considered. This article addresses modifications in the conditioning regimen that might lead to further improvement in HCT outcomes.

Bone marrow transplantation for primary immunodeficiency diseases

Advances in immunology have led to a breathtaking expansion of recognized primary immunodeficiency diseases (PID) with over 120 disease-related genes identified. In North America alone more than 1000 children have received allogeneic blood or marrow transplant over the past 30 years, with the majority surviving long term. This review presents results and highlights challenges and notable advances, including novel less toxic conditioning regimens, to transplant the more common and severe forms of PID. HLA-matched sibling donors remain the ideal option, however, advances in living donor unrelated HSCT and banked umbilical cord blood grafts provide hope for all children with severe PID.

Allogeneic hematopoietic cell transplantation: from experimental biology to clinical care

PURPOSE

For more than half a century, researchers have explored myeloablative, high-dose chemo/radiotherapy followed by allogeneic hematopoietic stem cell transplantation (HCT) for therapy of malignant and nonmalignant hematological diseases. Continuous advances in the field have changed this approach from one that was initially thought to be fraught by insurmountable complications to one that is now considered standard therapy for many diseases.

METHODS

In order to extend allogeneic HCT to include elderly patients, who represent the main population affected by hematological malignancies, and to those who are medically unfit to undergo conventional HCT, novel non-myeloablative approaches have been developed. These approaches rely on graft-vs-tumor effects for tumor eradication rather than high-dose chemoradiotherapy, and, accordingly, have lower toxicities than conventional regimens.

RESULTS

Results with non-myeloablative regimens have been gratifying, and this may change the future of allogeneic HCT. Advances could not have been possible without basic research and studies in pre-clinical animal models.

CONCLUSION

Further work is focused on improving graft-vs-tumor effects while achieving better control of graft-vs-host disease.

Clinical developments in reduced intensity haematopoietic stem cell transplantation

Reduced intensity conditioning regimens prior to allogeneic haematopoietic stem cell transplantation (HSCT) were first described in the 1970s, and have developed rapidly over the past few years to become an important consideration as immunological therapy for patients with haematological and selected solid organ malignancies. This is especially the case for patients considered ineligible for conventional allogeneic HSCT due to age or medical contraindications. With the development of minimally toxic conditioning regimens, additional potential applications include the provision of normal haematopoietic repopulating cells to patients who have an inherited gene defect such as an haemoglobinopathy or an inborn error of metabolism. Intensive investigation in stem cell research promises to provide dramatic new insights into human biology, paving the way for new therapeutic approaches to malignant and inherited disorders.

New approaches to hematopoietic cell transplantation for hematological diseases in children

Hematopoietic cell transplantation (HCT) has been used for more 30 years for the treatment of selected malignant and nonmalignant diseases. Traditionally, HCT for hematological disorders has relied on myeloablative conditioning before HLA-identical sibling bone marrow transplantation to correct the underlying hematological defect. Most children with hematological diseases who are referred to HCT have features that portend significant morbidity and early mortality. Among SAA patients who have HLA-identical sibling donors, younger patients with profound pancytopenia might be considered early for HCT. For others who lack sibling donors, patients who receive HCT from alternate sources have generally failed one or more courses of intensive immunosuppressive therapy and remain transfusion-dependent, some with hemosiderosis, red cell alloimmunization, and platelet transfusion refractoriness [44,46,48]. Currently, HCT for SCD is generally restricted to those who have experienced a significant sickle-related complication such as stroke, recurrent acute chest syndrome, or recurrent painful episodes [7,13]. In contrast, most reserve HCT in thalassemia for younger, Lucarelli class I, good-risk patients who have HLA-identical sibling donors, and veer away from older, high-risk thalassemics for whom transplantation is a riskier clinical intervention. For groups such as young adults with thalassemia major, HCT might become more widely applicable if its toxicity was reduced. Several approaches undergoing development include reduced-intensity conditioning and attempts to prevent GVHD. New methods to reduce the intensity and toxicity of conditioning as well as to use highly purified stem cells with the reduction in graft versus host disease may allow for the use of matched unrelated donors or haploidentical donors. This would serve to provide potentially more children who could benefit from stem cell transplantation with donors. These advances will hopefully lead to benefits for the majority of children who lack HLA-identical donors.