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Mixed chimerism (MC), a persistent or increasing number of host cells after allogeneic hematopoietic stem cell transplantation (HSCT), is a predictor of disease relapse. Donor lymphocyte infusions (DLI) have the potential to enhance the graft-versus-malignancy (GVM) effect, reducing the risk of relapse in patients with MC. Hence, in addition to utilizing DLI in the relapsed setting, there is a motivation to pursue pre-emptive DLI for patients in complete remissions after HSCT. To assess the safety and efficacy of DLI, records of 86 patients who received DLI between 2003 and 2015 at a single institution were studied retrospectively. Patients who received DLI included 50 patients with relapsed/residual (RR) disease, 29 patients with emerging MC without detectable disease, and 7 patients in an "other" cohort who had neither RR disease nor emerging MC after HSCT. DLI were administered using a dose-escalation protocol. After DLI, 93% of MC patients converted to full donor chimerism (FDC). Nonrelapsed patients (MC and other) reported high overall survival (OS) at 1 and 5 years (83% at 1 year, 70% at 5 years for MC; 86% at 1 year, 69% at 5 years for other) and was statistically superior to 5-year OS for RR patients (nonrelapsed 69% versus RR 28%; P = .00032). Improved survival correlated with successful conversion to FDC after DLI for RR and MC cohorts: 71% 2-year OS for patients converted to FDC versus 13% for patients who failed to achieve FDC (P < .0001). DLI for nonrelapsed patients was associated with a superior 5-year progression-free survival (PFS) of 71% compared with 18% 5-year PFS in the RR group (P < .0001). Relapse/progressive disease was the most frequent cause of death (41%). Seven MC (24%), 2 other (29%), and 39 RR patients (78%) relapsed or did not respond after DLI. Overall, 6 patients (7%) died of graft-versus-host disease after DLI. Our results demonstrate a successful dose-escalation approach for nonrelapsed patients that correlated with high survival and a high rate of achieving FDC in MC and RR populations. DLI remain a viable option to boost the GVM effect in the relapsed setting and may pre-emptively protect against relapse in MC populations after HSCT.

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