Clonal expansion of CD8(+) T cells reflects graft-versus-leukemia activity and precedes durable remission following DLI

Donor lymphocyte infusion (DLI) is a standard of care for relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation. Currently it is poorly understood how and when CD8(+) αβ T cells exert graft-versus-leukemia (GVL) activity after DLI. Also, there is no reliable biomarker to monitor GVL activity of the infused CD8(+) T cells. Therefore, we analyzed the dynamics of CD8(+) αβ T-cell clones in patients with DLI. In this prospective clinical study of 29 patients, we performed deep T-cell receptor β (TRB ) sequencing of sorted CD8(+) αβ T cells to track patients’ repertoire changes in response to DLI. Upon first occurrence of GVL, longitudinal analyses revealed a preferential expansion of distinct CD8(+) TRB clones (n = 14). This did not occur in samples of patients without signs of GVL (n = 11). Importantly, early repertoire changes 15 days after DLI predicted durable remission for the 36-month study follow-up. Furthermore, absence of clonal outgrowth of the CD8(+) TRB repertoire after DLI was an early biomarker that predicted relapse at a median time of 11.2 months ahead of actual diagnosis. Additionally, unbiased sample analysis regardless of the clinical outcome revealed that patients with decreasing CD8(+) TRB diversity at day 15 after DLI (n = 13) had a lower relapse incidence (P = .0040) compared with patients without clonal expansion (n = 6). In conclusion, CD8(+) TRB analysis may provide a reliable tool for predicting the efficacy of DLI and holds the potential to identify patients at risk for progression and relapse after DLI.