Effect of Differences in Immunological Reconstitution By Donor Age and Recipient Age on the Incidence of Chronic Graft-Versus-Host Disease

Background: Development of chronic graft-versus-host disease (cGVHD) has been reported to be associated with donor age and recipient age. We hypothesized that differences in post-transplantation immunological reconstitution depending on donor age and recipient age might be responsible for the incidence of cGVHD. Redevelopment of regulatory T (Treg) cell expansion and cytokine production was investigated over time according to donor age and recipient age at the time of transplantation after allogeneic hematopoietic cell transplantation (HCT).

Methods: The subjects were 39 consecutive patients who underwent HCT for different hematologic diseases at our hospital between December 2008 and December 2021 and survived for more than 3 years after HCT without cGVHD. The patients were classified into younger (age ≤59, n=23) and older (age ≥60, n=16) groups. The donor source was divided into subgroups based on use of cord blood or an adult donor: cord blood (younger, n=5; older, n=8) and adult donor (younger, n=18; older, n=8). Peripheral blood was drawn from all patients on day 200 and at 24 and 36 months after HCT. Analysis of Treg, T, B, and NK cells was performed using flow cytometry. T cells were isolated using EasySep kits and cultured at 37℃ in 5% CO ₂ in air for 4 days with 10% heat-inactivated fetal calf serum as controls, interleukin-2 (IL-2) and transforming growth factor-β1 (TGFβ1) as samples, or concanavalin A (ConA) (10 µg/ml) at a density of 1×10 ⁶ cells/ml. Treg cells were analyzed by flow cytometry and ConA-stimulated culture supernatants were tested for concentrations of IL-4, IL-5, IL-6, IL-10, IL-13, TGFβ1, tumor necrosis factor α (TNFα) and interferon-γ (IFNγ).

Results: The results for patients who underwent HCT at our institution during the same observation period as this study suggested that donor source and patient age may be involved in development of cGVHD (p=0.032, p=0.015, respectively). In younger patients, CD4/8 in peripheral blood showed a tendency to increase over time after transplantation: 0.91±1.0 at 200 days, 0.54±0.29 at 2 years, and 1.32±0.57 at 3 years (R=0.308, p=0.072); and young patients after cord blood transplantation showed a marked improvement: 0.30±0 at 200 days, 0.59±0.18 at 2 years, and 1.84±0.27 at 3 years (R=0.913, p=0.0016). Percentages of Treg cells in peripheral blood and stimulated cultures were positively correlated in younger (R=0.349, p=0.043) and older (R=0.381, p=0.029) patients. The percentage, absolute number, and amplification rate of Treg cells in stimulation culture of T cells from younger patients (6.37±4.02%, 3759.4±1963.3 /mL, 12.4±11.5 times) at 200 days after transplantation were significantly higher than those for older patients (3.04±1.48%, 1783.9±1152.0 /mL, 5.4±3.7 times) (p=0.027, p=0.003, p=0.023). Post-transplant Treg cell expansion rates in younger cord blood transplant recipients significantly increased by 2.4±0 times at 200 days, 2.8±0.6 times at 2 years, and 5.8±2.1 times at 3 years (R=0.711, p=0.046). Regarding cytokine production, IL-5 in stimulation culture from younger patients showed a tendency to increase over time: 4.75±8.89 pg/mL at 200 days, 20.04±27.20 pg/mL at 2 years, and 59.51±104.93 pg/mL at 3 years (R=0.294, p=0.087).

Conclusions: T cell reconstitution and cytokine production tended to increase over time after transplantation in younger patients. The ability to reconstitute Treg cells was higher in younger patients early after transplantation and increased over time in young cord blood transplant recipients. These factors may account for the high incidence of cGVHD in older transplant recipients from adult donors, although the number of cases in the study is limited and the data are preliminary.