Impact of in Vivo Lymphodepletion on Outcome in Children with Nonmalignant Disorders Receiving Peripheral Blood Stem Cell Transplantation

Allogeneic Hematopoietic cell Transplantation Using Alemtuzumab in Asian Patients with Inborn Errors of Immunity

Alemtuzumab is used with reduced-toxicity conditioning (RTC) in allogeneic hematopoietic cell transplantation (HCT), demonstrating efficacy and feasibility for patients with inborn errors of immunity (IEI) in Western countries; however, the clinical experience in Asian patients with IEI is limited. We retrospectively analyzed patients with IEI who underwent the first allogeneic HCT with alemtuzumab combined with RTC regimens in Japan. A total of 19 patients were included and followed up for a median of 18 months. The donors were haploidentical parents (n = 10), matched siblings (n = 2), and unrelated bone marrow donors (n = 7). Most patients received RTC regimens containing fludarabine and busulfan and were treated with 0.8 mg/kg alemtuzumab with intermediate timing. Eighteen patients survived and achieved stable engraftment, and no grade 3-4 acute graft-versus-host disease was observed. Viral infections were observed in 11 patients (58%) and 6 of them presented symptomatic. The median CD4+ T cell count was low at 6 months (241/µL) but improved at 1 year (577/µL) after HCT. Whole blood cells continued to exhibit > 80% donor type in most cases; however, 3/10 patients exhibited poor donor chimerism only among T cells and also showed undetectable levels of T-cell receptor recombination excision circles (TRECs) at 1 year post-HCT. This study demonstrated the efficacy and safety of alemtuzumab; however, patients frequently developed viral infections and slow reconstitution or low donor chimerism in T cells, emphasizing the importance of monitoring viral status and T-cell-specific chimerism. (238 < 250 words).

Alemtuzumab, Dual Graft-versus-Host Disease Prophylaxis, and Lower CD3+ T Cell Doses Equalize Rates of Acute and Chronic Graft-versus-Host Disease in Pediatric Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation with Matched Unrelated Donor Peripheral Blood Stem Cells or Bone Marrow Grafts

Data comparing hematopoietic stem cell transplantation (HSCT) using bone marrow (BM) or peripheral blood stem cell (PBSC) grafts in children after alemtuzumab-based conditioning are lacking. We investigated whether in vivo T cell depletion using alemtuzumab could reduce the risk of severe acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD) after HSCT with matched unrelated donor (MUD) BM or PBSCs. This retrospective multicenter study included 397 children (BM group, n = 202; PBSC group, n = 195) who underwent first MUD HSCT at 9 pediatric centers in the United Kingdom between 2015 and 2019. The median age at transplantation was 7.0 years (range, .1 to 19.3 years), and the median duration of follow-up was 3.1 years (range, .3 to 7.5 years). The 3-year overall survival was 81% for the entire cohort (BM group, 80%; PBSC group, 81%). The incidence of grade II-IV aGVHD was significantly higher in the PBSC group (31%) compared to the BM group (31% versus 19%; P = .003), with no difference in the incidence of grade III-IV aGVHD (BM, 7%; PBSC, 12%; P = .17). CD3+ T cell dose >5 × 108/kg and the use of PBSCs were independent predictors of grade II-IV aGVHD. When considering CD3+ T cell dose and GVHD prophylaxis, PBSC transplantation with a calcineurin inhibitor (CNI) and mycophenolate mofetil (MMF) and a CD3+ T cell dose ≤5 × 108/kg had a comparable grade II-IV aGVHD to BM transplantation plus a CNI (20% versus 18%; P = .52). PBSC transplantation was associated with a lower incidence of cGVHD compared to BM transplantation (6% versus 11%; P = .03). Within the limits of this study, we identified a potential strategy to reduce the risk of severe GVHD in pediatric PBSC recipients that includes a combination of in vivo T cell depletion using alemtuzumab and dual GVHD prophylaxis (with a CNI and MMF) and limiting the CD3+ T cell dose to ≤5 × 108/kg.

The role of graft T-cell size in patients receiving alemtuzumab serotherapy for non-malignant disorders: results of an institutional protocol

Although graft T cells assist in engraftment, mediate antiviral immune-reconstitution, and cause graft-versus-host disease, graft size is not determined by T-cell content of the graft. The conventional method of graft size determination based on CD34+ cells with alemtuzumab serotherapy is associated with delayed immune reconstitution, contributing to an increased risk of viral infections and graft failure. Alemtuzumab, a long half-life anti-CD52 monoclonal antibody is a robust T-cell depleting serotherapy, and relatively spares memory-effector T cells compared to naïve T cells. We therefore hypothesized that graft size based on T-cell content in patients receiving peripheral blood stem cell graft with alemtuzumab serotherapy would facilitate immune-reconstitution without increasing the risk of graft-versus-host disease. We retrospectively analysed twenty-six consecutive patients with non-malignant disorders grafted using alemtuzumab serotherapy and capping of graft T cells to a maximum of 600 million/kg. The graft T-cell capping protocol resulted in early immune-reconstitution without increasing the risk of severe graft-versus-host disease. Graft T-cell content correlated with CD4+ T-cell reconstitution and acute graft-versus-host disease. The course of CMV viraemia was predictable without recurrence and associated with early T-cell recovery. No patient developed chronic graft-versus-host disease. Overall survival at one year was 100% and disease-free survival was 96% at a median of 899 days (range: 243-1562). Graft size determined by peripheral blood stem cell graft T-cell content in patients receiving alemtuzumab serotherapy for non-malignant disorders is safe and leads to early T-cell immune-reconstitution with excellent survival outcomes.

T-lymphocyte depleted transplants for inborn errors of immunity

INTRODUCTION

Hematopoietic stem cell transplantation is a curative treatment for many inborn errors of immunity (IEI). Incremental improvements and advances in care have led to high rates of >85% survival and cure in many of these diseases. Improvements in HLA-classification and matching have led to increased survival using HLA-matched donors, but survival using T-lymphocyte-depleted mismatched grafts remained significantly worse until fairly recently. Advances in T-lymphocyte depletion methods and graft engineering, although not specific to IEI, have been widely adopted and instrumental in changing the landscape of donor selection, such that a donor should now be possible for every patient.

AREAS COVERED

A literature review focusing on T-lymphocyte depletion methodologies and treatment results was performed. The importance of early T-lymphocyte immunoreconstitution to protect against viral infection is reviewed. Two main platforms now dominate the field - immune-magnetic selection of specific cell types and post-transplant chemotherapeutic targeting of rapidly proliferating allo-reactive T-lymphocytes - the emerging literature on these reports, focusing on IEI, is explored, as well as the impact of serotherapy on early immunoreconstitution.

EXPERT OPINION

Pharmacokinetic monitoring of serotherapy agents, and use of co-stimulatory molecule blockade are likely to become more widespread. Post-transplant cyclophosphamide or TCR depletion strategies are likely to become the dominant methods of transplantation for nonmalignant diseases.