Haploidentical CD45RA-Negative Donor Lymphocyte Infusions Are Feasible, Safe and Associated with Clinical Benefit

Abstract

<h3>Introduction</h3> Donor T-cell reconstitution following hematopoietic cell transplantation (HCT) is critical for infection and leukemic control. Donor lymphocyte infusions (DLI) provide additional donor T cells, but may cause graft-versus-host-disease (GVHD) from alloreactive T-cells. As GVHD risk increases with increasing HLA-mismatch, conventional haploidentical DLI doses are often limited to 1 × 10⁵ T cells/kg. Since the majority of alloreactive T cells reside in the naïve (CD45RA-positive) subset, CD45RA-depleted DLI may provide a diverse lymphocyte repertoire to aid in infection and leukemic disease control, with decreased GVHD risk. Herein, we report on feasibility, safety, and early efficacy of escalating doses of haploidentical memory DLI. <h3>Methods</h3> Donors underwent leukapheresis without mobilization; 2 total blood volumes were collected. Depletion of CD45RA-positive cells was performed using the CliniMACS device (Miltenyi Biotec). DLI dosing typically started at 1 × 10⁵ T cells/kg, with dose escalation every 4 weeks based on clinical need. <h3>Results</h3> All donors collected successfully in one attempt. Following CD45RA-depletion, median residual T cell dose was 45 × 10⁶/kg and CD45RA-positive T cell dose was <0.001 × 10⁶/kg (>3.9 log depletion), allowing multiple doses to be stored for future use (Figure 1). Twelve patients received a total of 29 DLIs (median infusions=2, range 1–5; Figure 2). Indications for DLI included detectible leukemia (6), mixed chimerism (6), and lymphopenia/viral infection (3); 3 recipients had multiple indications. First DLI was infused a median of 101.5 days post-HCT (range 41-356). Twenty-three doses had no detectible CD45RA-positive T cells (<0.001 × 10⁶/kg) and 6 contained 0.001-0.002 × 10⁶ CD45RA-positive T cells/kg. No infusion related acute adverse events occurred. One patient developed acute GVHD (clinical grade IV, stage 3 skin/stage 4 gut), 21 days post-DLI (dose=1 × 10⁵ T cells/kg). After DLI, the majority of patients showed some clinical response (chimerism improvement/stability, decreased viral load, and/or rise in peripheral CD3 count). Eradication of detectable leukemia however was not successful, with all 6 patients eventually having disease progression (1 rapid progression; 5 frank relapse 2–6 months after first DLI). With median length of follow-up after last DLI of 243 days (range 20-924), no patients have developed chronic GVHD. <h3>Discussion</h3> CD45RA-depletion is feasible and effective in removing naïve donor T-cells. Haploidentical CD45RA-depleted DLIs were well tolerated and associated with low incidence of acute GVHD, even with T-cell doses as high as 10 × 10⁶/kg. The majority of patients showed clinical benefit from DLI, with the exception of leukemia disease control. We are currently further investigating the efficacy and safety of CD45RA-depleted DLI as part of a prospective clinical haploidentical HCT trial.