ATIR101 administered after T-cell-depleted haploidentical HSCT reduces NRM and improves overall survival in acute leukemia

Abstract

Overcoming graft-versus-host disease (GvHD) without increasing relapse and severe infections is a major challenge after allogeneic hematopoietic stem-cell transplantation (HSCT). ATIR101 is a haploidentical, naïve cell-enriched T-cell product, depleted of recipient-alloreactive T cells to minimize the risk of GvHD and provide graft-versus-infection and -leukemia activity. Safety and efficacy of ATIR101 administered after T-cell-depleted haploidentical HSCT (TCD-haplo + ATIR101) without posttransplant immunosuppressors were evaluated in a Phase 2, multicenter study of 23 patients with acute leukemia and compared with an observational cohort undergoing TCD-haplo alone (n = 35), matched unrelated donor (MUD; n = 64), mismatched unrelated donor (MMUD; n = 37), and umbilical cord blood (UCB; n = 22) HSCT. The primary endpoint, 6-month non-relapse mortality (NRM), was 13% with TCD-haplo + ATIR101. One year post HSCT, TCD-haplo + ATIR101 resulted in lower NRM versus TCD-haplo alone (P = 0.008). GvHD-free, relapse-free survival (GRFS) was higher with TCD-haplo + ATIR101 versus MMUD and UCB (both P < 0.03; 1-year rates: 56.5%, 27.0%, and 22.7%, respectively) and was not statistically different from MUD (1 year: 40.6%). ATIR101 grafts with high third-party reactivity were associated with fewer clinically relevant viral infections. Results suggest that haploidentical, selective donor-cell depletion may eliminate requirements for posttransplant immunosuppressors without increasing GvHD risk, with similar GRFS to MUD. Following these results, a randomized Phase 3 trial versus posttransplant cyclophosphamide had been initiated.

Fig. 1. ATIR101 characterization and infusion.

a Schematic overview of the treatment of patients with ATIR101. Donor and patient PBMCs, as well as donor plasma, are obtained for production of ATIR101. The same donor is thereafter treated with G-CSF to mobilize stem cells and collect the graft. Patients then undergo myeloablative conditioning including ATG followed by HSCT with the CD34⁺-selected graft. ATIR101 infusion was planned for 28–32 days post HSCT. Patients do not receive posttransplant immunosuppression. b Schematic overview of the manufacturing process of ATIR101. Donor and patient lymphocytes are collected via apheresis and isolated over density gradient. Patient lymphocytes only are then irradiated and cultured together with donor lymphocytes for 4 days. During this period, donor anti-host alloreactive T cells are activated due to the presence of “foreign” HLAs on the patient’s cells. Next, 4,5-dibromorhodamine methyl ester (TH9402) is added to the culture. TH9402 is selectively retained in activated cells due to low P-glycoprotein activity responsible for its extrusion into the outside environment. After exposure to light, the dye becomes activated and a source of the reactive oxygen species, which, at high concentrations, leads to cell apoptosis. The remaining cells are infused into the patient (ATIR101). Adapted from figure available at: https://www.kiadis.com/products-and-technology/ (accessed May 2019). c CFSE-based proliferation assay to calculate the T-cell proliferation index in response to various stimuli. Untreated donor PBMCs (black bars) and ATIR101 cells (white bars) were stimulated with (1) irradiated autologous donor PBMCs to determine baseline proliferation by adding cells that may provide a “feeder effect”; (2) irradiated recipient PBMCs to determine recipient-specific activity; (3) irradiated third-party cells to determine activity against unrelated HLA; (4) anti-CD3/CD28 beads to determine overall proliferative capacity of T cells. Data are presented as mean ± standard error of the mean. d T-cell proliferation index of individual donor PBMCs and corresponding ATIR101 cells upon exposure to irradiated recipient T cells (left) and third-party (right) cells. e Mean proportion (± standard error of the mean) of T cells, monocytes, NK cells, and B cells in ATIR101 (white bars) compared with donor PBMCs (black bars) by flow cytometry. f Mean absolute number (± standard error of the mean) of viable T cells in the starting volume of donor PBMCs by flow cytometry and a theoretical equivalent volume of ATIR101. Pie charts: mean proportion (%) of CD4⁺ and CD8⁺ naïve (black), central memory (striped), effector memory (gray), and effector (dots) T cells and the average CD4:CD8 ratio (standard deviation) of donor PBMCs and ATIR101 by flow cytometry. g Mean absolute number (± standard error of the mean) of CD4⁺ and CD8⁺ naïve, CM, EM, and effector T cells. The figure shows absolute number of each cell type infused within a 2 × 10⁶ CD3⁺ cells/kg dose of ATIR101 (white bars) and within a representative equivalent sample of 2 × 10⁶ CD3⁺ cells/kg of donor PBMCs (black bars). *P < 0.05, **P < 0.01, ***P < 0.001 for ATIR101 compared with donor PBMCs. ATG anti-thymocyte globulin, CFSE carboxyfluorescein succinimidyl ester, CM central memory, EM effector memory, G-CSF granulocyte colony-stimulating factor, GvHD graft-versus-host disease, HLA human leukocyte antigen, HSCT hematopoietic stem-cell transplantation, NK natural killer, N.S. not significant, PBMC peripheral blood mononuclear cell.

Fig. 2. Immune reconstitution in the TCD-haplo + ATIR101 population (N = 23).

Absolute number of lymphocytes, T cells (CD3⁺, CD4⁺, and CD8⁺), B cells (CD19⁺), and NK cells (CD56⁺) as cells ×10⁹/L in individual patient samples to 24 months post HSCT. Line shows mean values. Arrow indicates time of ATIR101 infusion. HSCT hematopoietic stem-cell transplantation.

Fig. 3. Outcomes following TCD-haplo + ATIR101 (N = 23).

Kaplan–Meier plots are shown for OS (a), PFS (b), and GRFS (g). Cumulative incidence plots, taking into account competing risks, for RRM (c), NRM (d), acute GvHD Grade 2–4 and Grade 3–4 (e), and moderate/severe chronic GvHD (f). GRFS GvHD-free, relapse-free survival, GvHD graft-versus-host disease, HSCT hematopoietic stem-cell transplantation, NRM non-relapse mortality, OS overall survival, PFS progression-free survival, RRM relapse-related mortality.

Fig. 4. Cumulative incidence of NRM and Kaplan–Meier of GRFS for patients receiving TCD-haplo + ATIR101 (N = 23) and the control study TCD-haplo (N = 35), MUD (N = 64), MMUD (N = 37), and UCB (N = 22) populations.

a Cumulative incidence plot of NRM taking into account competing risk and (b) Kaplan–Meier of GRFS over 1 year, for TCD-haplo + ATIR101 (pink) and patients from the control study who received TCD-haplo (orange), MUD (brown), MMUD (green), or double UCB (blue). a Groups were compared using Gray’s test. b HR and their corresponding 95% CI are presented, and groups are compared using the log-rank test with Bonferroni correction for multiple comparisons. CI confidence interval, GRFS graft-versus-host disease-free, relapse-free survival, HR hazard ratio, HSCT hematopoietic stem-cell transplantation, MMUD mismatched unrelated donor, MUD matched unrelated donor, NRM non-relapse mortality, TCD-haplo T-cell-depleted haploidentical HSCT, UCB umbilical cord blood.

Fig. 5. Impact of donor and ATIR101 characteristics.

The characteristics of ATIR101 and donor PBMCs were evaluated for patients without viral infections or with Grade ≤2 viral infections (Grade 0–2; n = 14) and with Grade 3–5 viral infections (n = 9) within 1 year post ATIR101. a, c, e on the left show data using ATIR101 and b, d, f on the right show data using donor PBMCs. The mean proportion (%) of CD4⁺ and CD8⁺ naïve (black), central memory (striped), effector memory (grey), and effector (dots) T cells, and the average CD4:CD8 ratio, by flow cytometry is shown for ATIR101 (a) and donor PBMCs (b) according to the viral infection groups. T-cell PI of ATIR101 (c) or donor PBMCs (d) is shown for both viral infection groups, after stimulation with autologous irradiated donor cells, irradiated recipient T cells, third-party cells, and CD3/CD28 beads. Kaplan–Meier of time to Grade ≥3 viral infection for patients divided into those with “high” (>median PI; n = 11; circles) and “low” (≤median PI; n = 12; triangles) responsiveness to stimulation with third-party cells in ATIR101 (e) or donor PBMCs (d). Groups are compared using the log-rank test. Individual third-party reactivity is indicated for ATIR101 (g) and donor PBMCs (h). Correlation between T-cell PI for corresponding ATIR101 and donor PBMCs in response to stimulation with third-party cells is shown in i using Spearman’s correlation. Patients with Grade ≥3 viral infections are indicated in red. A patient with a Grade ≥3 viral infection with substantial third-party reactivity (in donor PBMCs and ATIR101) is indicated with a “1”. This patient was CMV positive and had a CMV-negative donor yielding a Grade 3 CMV infection. *P < 0.05. CMV cytomegalovirus, PBMC peripheral blood mononuclear cell, PI proliferation index.