Use of Alefacept for Preconditioning in Multiply Transfused Pediatric Patients with Nonmalignant Diseases

Abstract

Transfusion-related alloimmunization is a potent barrier to the engraftment of allogeneic hematopoietic stem cells in patients with nonmalignant diseases (NMDs). Memory T cells, which drive alloimmunization, are relatively resistant to commonly used conditioning agents. Alefacept, a recombinant leukocyte function antigen-3/IgG1 fusion protein, targets CD2 and selectively depletes memory versus naive T cells. Three multiply transfused pediatric patients with NMD received a short course of high-dose i.v. alefacept (.25 mg/kg/dose on days -40 and -9 and .5 mg/kg/dose on days -33, -26, -19, and -12) before undergoing unrelated allogeneic transplant in the setting of reduced-intensity pretransplant conditioning and calcineurin inhibitor-based post-transplant graft-versus-host disease (GVHD) prophylaxis. Alefacept infusions were well tolerated in all patients. Peripheral blood flow cytometry was performed at baseline and during and after alefacept treatment. As expected, after the 5 weekly alefacept doses, each patient demonstrated selective loss of CD2(hi)/CCR7(-)/CD45RA(-) effector memory (Tem) and CD2(hi)/CCR7(+)/CD45RA(-) central memory (Tcm) CD4(+) and CD8(+) T cells with relative preservation of the CD2(lo) Tem and Tcm subpopulations. In addition, depletion of CD2(+) natural killer (NK) cells also occurred. Neutrophil recovery was rapid, and all 3 patients had 100% sorted (CD3/CD33) peripheral blood donor chimerism by day +100. Immune reconstitution (by absolute neutrophil, monocyte, and lymphocyte counts) was comparable with a cohort of historical control patients. All 3 patients developed GVHD but are all now off immune suppression and >2 years post-transplant with stable full-donor engraftment. These results suggest that alefacept at higher dosing can deplete both memory T cells and NK cells and that incorporating CD2-targeted depletion into a reduced-intensity transplant regimen is feasible and safe in heavily transfused patients.

Trial registration: ClinicalTrials.gov NCT01319851.

Keywords: Alefacept; Conditioning; Hematopoietic stem cell transplantation; Nonmalignant diseases; Rejection.

Copyright © 2015 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Impact of alefacept preconditioning on post-transplant hematologic reconstitution. Hematologic reconstitution was monitored in all 3 patients receiving alefacept treatment and compared with a cohort of 23 historical control subjects. Black circles indicate patient 1; blue squares, patient 2;red triangles, patient 3; black diamonds (withbroken line), historical control subjects (mean ± SEM). (This figure is available in color online at www.bbmt.org).

Figure 2

Impact of alefacept preconditioning on CD4+ and CD8+ naive and memory T cell subsets and on NK cells. Longitudinal immune monitoring was performed on peripheral blood samples using flow cytometry. Samples were drawn at baseline (day –40, before the first dose of alefacept), during alefacept (day –26, before the third dose of alefacept), after the final dose of alefacept but before the start of conditioning (on day –6 or –10 depending on the conditioning regimen used), and before transplant (day 0). CD20−/CD3+/CD4+/CD8− and CD20−/CD3+/CD4−/CD8+ T cells were divided into naive (CCR7+/CD45RA+), Tcm (CCR7+/CD45RA−), Tem (CCR7−/CD45RA−), and Temra (CCR7−/CD45RA+). T cell subsets were further divided into CD2hi (alefacept target cells) and CD2lo. NK cells were classified as CD3−/CD20−/CD16+/CD56hi/lo.Black circles indicate patient 1; blue squares, patient 2; red triangles, patient 3. Solid lines denote CD2hi cells and dashed lines denote CD2lo cells. *P ≤ .05 comparing baseline with post-alefacept values on combined data. (A) Top panels show comparison of the percent of CD4+ T naive, Tcm, Tem, and Temra that were CD2hi for each patient at baseline and after all alefacept doses were completed. Bottom panels show comparison of absolute numbers (cells/μL) of CD4+ T naive, Tcm, Tem, and Temra that were CD2hi for each patient at baseline and after all alefacept doses were completed. (B) Top panels show comparison of the percent of CD8+ T naive, Tcm, Tem, and Temra that were CD2hi for each patient at baseline and after all alefacept doses were completed. Bottom panels show comparison of absolute numbers (cells/μL) of CD8+ T naive, Tcm, Tem, and Temra that were CD2hi for each patient at baseline and after all alefacept doses were completed. (C) Top panels show comparison of the percentage of total lymphocytes attributed to NK cells or NK cell subpopulations for each patient at baseline and after all alefacept doses were completed. Bottom panels show comparison of the absolute number of NK cells or NK cell subpopulations (cells/μL) for each patient at baseline and after all alefacept doses were completed. (This figure is available in color online at www.bbmt.org).