Serial Lineage Chimerism Analysis Improves Early Diagnosis of Graft Failure after Allogeneic HSCT
Authors: Gómez-Centurión Ignacio , Kwon Mi , Balsalobre Pascual , Serrano David , Dorado Herrero Nieves , Solán Laura , Chicano Lavilla María , Carbonell Diego , Díez-Martín Jose Luis , Martínez-Laperche Carolina , Buño Ismael 
Published: October 2019

Abstract
Background: Graft failure (GF) is an unusual but threatening complication after allogeneic HSCT (allo-HSCT). Early diagnosis is crucial for therapeutic interventions to be effective. The monitoring of chimerism in peripheral blood (PB) and T lymphocytes (TL) has shown to contribute in the early detection of this complication. The objective of this study was to describe chimerism dynamics in patients who developed GF after allo-HSCT.
Methods: Nineteen patients out of 416 procedures were diagnosed with GF after allo-HSCT since 2003 in our center. Chimerism studies were performed by STR-PCR (AmpFLSTR™ SGM Plus™, Thermo Fisher) in PB and TL weekly since day +14. Patients were classified into three groups: primary GF (absence of neutrophil engraftment by day +28), secondary GF (development of severe cytopenias and progressive mixed chimerism (MC) after initial achievement of neutrophil engraftment), and incipient GF (development of increasing MC with non severe cytopenias) [1]. Relapse/progression was ruled out in all cases. [1] Díez-Martín et al. Bone Marrow Transplant. (2004) 33, 1037-1041.
Results: Seven patients were diagnosed with primary GF, 7 with secondary GF and 5 with incipient GF (Table 1). No evident causes of GF were detected in all primary GF cases. Chimerism analysis on day +14, +21 y +28 revealed persistent high percentages of recipient cells before GF were diagnosed, in PB and mainly and earlier in TL (Fig. 1A). Median time to salvage allo-HSCT was 45 days (range 35-77). Two patients were treated with donor lymphocytes infusion (DLI) and five with second allo-HSCT. Five patients achieved engraftment, and six achieved complete chimerism (CC). Six-months OS after salvage was 43%.
The 7 patients diagnosed with secondary GF had achieved initial neutrophil engraftment in a median of 17 days (range 13-28). Median time to GF after allo-HSCT was 75 days (range 39-108). Six of them developed CMV reactivation before GF. Chimerism analysis before and at diagnosis of secondary GF, showed persistent high percentages of recipient cells, with a trend towards increasing dynamics in PB and mainly in TL (Fig. 1B). Median time to salvage therapy was 35 days (range 8-817) after GF confirmation. One patient was treated with DLI and six with second allo-HSCT. Five patients achieved engraftment and CC. Six-months OS was 57%.
The 5 patients diagnosed with incipient GF showed persistent high percentages of recipient cells, with a trend towards increasing dynamics particularly in TL before and at diagnosis of GF (Fig. 1C). As salvage treatment, patients were treated with immunosuppression withdrawal followed by at least one DLI as salvage theraphy, in a median of 83 days (range 61-126) after allo-HSCT. All patients achieved CC in both PB and TL. Four patients developed grade II-IV GVHD. Six-months OS was 57%.
Conclusions: Patients with primary GF presented MC in serial chimerism analysis after allo-HSCT, with persistent high percentages of recipient cells particularly in TC. Patients with secondary and incipient GF showed increasing MC mainly in TC, before GF was established. Early T-cell chimerism dynamics may be the best predictor of GF, allowing early therapeutic interventions. In our experience, timely and individualized second allo-HSCT after GF may improve outcome after primary or secondary GF. On the other hand, early DLI could benefit patients with incipient GF.

Disclosures
No relevant conflicts of interest to declare.