Improved Overall Survival, Relapse-Free-Survival, and Less Graft-vs.-Host-Disease in Patients With High Immune Reconstitution of TCR Gamma Delta Cells 2 Months After Allogeneic Stem Cell Transplantation

Abstract

T-cell receptor (TCR) γδ cells are perceived as innate-like effector cells with the possibility of mediating graft-vs. -tumor (GVT) without causing graft-vs.-host disease (GVHD) in the setting of hematopoietic allogeneic stem cell transplantation (HSCT). We conducted a prospective study to assess the clinical impact of TCR γδ cell immune reconstitution on overall survival, relapse-free-survival, relapse and GVHD. The impact of CD3, CD4, and CD8 T cells together with NK cells including subtypes were analyzed in parallel. A total of 108 patients with hematological malignancies transplanted with HLA-matched, T cell replete stem cell grafts were included for analyses of absolute concentrations of CD3, CD4, and CD8 positive T cells and NK cells together with a multi-color flow cytometry panel with staining for TCRαβ, TCRγδ, Vδ1, Vδ2, CD3, CD4, CD8, HLA-DR, CD196, CD45RO, CD45RA, CD16, CD56, CD337, and CD314 at 28, 56, 91, 180, and 365 days after transplantation. Immune reconstitution data including subsets and differentiation markers of T and NK cells during the first year after transplantation was provided. Patients with TCR γδ cell concentrations above the median value of 21 (0-416) × 10⁶ cells/L 56 days after transplantation had significantly improved overall survival (p = 0.001) and relapse-free survival (p = 0.007) compared to patients with concentrations below this value. When day 56 cell subset concentrations were included as continuous variables, TCR γδ cells were the only T cell subsets with a significant impact on OS and RFS; the impact of TCR γδ cells remained statistically significant in multivariate analyses adjusted for pre-transplant risk factors. The risk of death from relapse was significantly decreased in patients with high concentrations of TCR γδ cells 56 days after transplantation (p = 0.003). Also, the risk of acute GVHD was significantly lower in patients with day 28 TCR γδ cell concentrations above the median of 18 × 10⁶ cells/L compared to patients with low concentrations (p = 0.01). These results suggest a protective role of TCR γδ cells in relapse and GVHD and encourage further research in developing adaptive TCR γδ cell therapy for improving outcomes after HSCT.

Keywords: allogeneic stem cell transplantation; cell therapy; gamma delta (γδ) T cells; innate immunology; transplant immunology.

Figure 1

Concentrations of TCR γδ cells and Vδ1 and Vδ2 subsets during the first year after transplantation. Patient numbers day 28 n = 106, day 56 n = 104, day 91 n = 99, day 180 n = 86, day 365 n = 66 (values from one patient with day 180 TCR γδ cell concentrations of 632 mio/L and Vδ2 concentration of 570 mio/L are not included in the figure).

Figure 2

Distribution of TCR γδ T cell subsets (Vδ1, Vδ2, nonVδ1-nonVδ) during the first year after transplantation. Each compartment is constructed by the use of median percentages. Patient numbers day 28 n = 106, day 56 n = 104, day 91 n = 99, day 180 n = 86, day 365 n = 66.

Figure 3

Differentiation subsets in (A) the TCR γδ compartment (B) the CD4 compartment, and (C) the CD8 compartment during the first year after transplantation. The fractions are constructed with the use of median percentages. Patient numbers day 28 n = 106, day 56 n = 104, day 91 n = 99, day 180 n = 86, day 365 n = 66. CM, central memory; EM, effector memory.

Figure 4

Estimated (A) overall survival (p = 0.001) and (B) relapse-free survival (p = 0.007) in patients with high vs. low concentrations (median 21 × 10⁶/L) of TCR γδ cells 56 days after transplantation, n = 104.

Figure 5

Cumulative incidence (Gray's test for competing risk) of death from relapse with death from transplant-related-mortality as a competing event in patients with high vs. low (A) concentrations of TCR γδ cells (median 21 × 10⁶/L), p = 0.003, and (B) TCR γδ cell fraction of the total CD3 T cell concentration (median 4.5%), p = 0.02, 56 days after transplantation, n = 104.

Figure 6

Cumulative incidence (Gray's test for competing risk) of acute GVHD with death as competing event in patients with high vs. low (A) concentrations of TCR γδ cells (median 18 × 10⁶/L), p = 0.01, and (B) TCR γδ cell fraction of the total CD3 T cell concentration (median 4.6%), p < 0.001, 28 days after transplantation, n = 97. Patients diagnosed with acute GVHD before their respective day 28 sample were excluded.

Figure 7

(A) Distribution of patients with high vs. low concentrations (median 7.9 × 106/L) of TCR Vδ1 cells 1 year post-transplant according to CMV infection, p = 0.004, n = 66, and (B) distribution of patients with high vs. low concentrations (median 1.5 × 10⁶/L) of TCR Vδ1 cells 28 days post-transplant according to donor serological CMV status, p = 0.006, n = 106.

Figure 8

Possible mechanism for tumor antigen recognition and effector functions by TCR γδ cells. Adapted from Minculescu and Sengeloev (10).