Although stem cell mobilization has been performed for more than 20 years, little is known about the effects of mobilizing agents on apheresis composition and the impact of graft cell subsets on patients' outcome. With the increasing use of plerixafor and the inclusion of poor mobilizers in autologous transplant procedures, new parameters other than CD34 + stem cell dose are emerging; plerixafor seems to mobilize more primitive CD34 + /CD38 − stem cells compared with G-CSF, but their correlation with stable hematopoietic engraftment is still obscure. Immune recovery is as crucial as hematopoietic reconstitution, and higher T and natural killer cells infused within the graft have been correlated with better outcome in autologous transplant; recent studies showed increased mobilization of immune effectors with plerixafor compared with G-CSF, but further data are needed to clarify the clinical impact of these findings. In the allogeneic setting, much evidence suggests that mobilized T-cell alloreactivity is tempered by G-CSF, probably with the mediation of dendritic cells, even though no clear correlation with GVL and GVHD has been found. Plerixafor is not approved in healthy donors yet; early data suggest it might mobilize a GVHD protective balance of immune effectors, but further studies are needed to define its role in allogeneic transplant.

Allogeneic stem cell transplantation (SCT) is curative treatment in patients with acute leukemia and myelodysplastic syndrome. However, recurrent disease is the major cause of treatment failure. Isolated extramedullary relapse (iEMR) after SCT is relatively rare and not well characterized. We performed a retrospective analysis of 566 consecutive patients with acute myeloid leukemia (n = 446) and acute lymphoblastic leukemia (ALL; n = 120) after SCT to study the incidence, risk factors, treatment options, and outcome of iEMR. The 5-year cumulative incidence of bone marrow relapse (BMR) and iEMR was 41.0% and 5.8%, respectively. iEMR occurred significantly later than BMR at 10 and 4 months, respectively (P < .001). Diagnosis of ALL (HR, 2.6; P = .05), poor cytogenetics (HR, 2.1; P = .06), and prior extramedullary disease (HR, 3.8; P = .002) were independent factors predicting iEMR. Acute and chronic graft-versus-host disease (GVHD) reduced the risk of BMR but did not protect against iEMR. Most patients with iEMR received systemic treatment combined with local radiation and donor lymphocyte infusions when feasible. The 3-year survival after relapse was 8.5% and 30.1% after BMR and iEMR, respectively (P = .002). Patients with a first iEMR continued to have recurrent EMRs, and only a minority progressed to BMR. Second iEMR was also common after first BMR and associated with longer survival than second BMR. iEMR is more frequent in patients with ALL and prior extramedullary disease. It occurs later than BMR and more commonly in patients with chronic GVHD, suggesting less effective graft-versus-leukemia effect in extramedullary sites. Second iEMR is common after a first iEMR but also after a first BMR. Long-term survival is feasible with aggressive treatment.

Background Limited data is available to guide the choice of the conditioning regimen for patients with acute myeloid leukemia (AML) undergoing transplant with persistent disease. Methods We retrospectively compared outcome of fludarabine-treosulfan (FT), thiotepa-busulfan-fludarabine (TBF), and sequential fludarabine, intermediate dose Ara-C, amsacrine, total body irradiation/busulfan, cyclophosphamide (FLAMSA) conditioning in patients with refractory or relapsed AML. Results Complete remission rates at day 100 were 92%, 80%, and 88% for FT, TBF, and FLAMSA, respectively ( p = 0.13). Non-relapse mortality, incidence of relapse, acute (a) and chronic (c) graft-versus-host disease (GVHD) rates did not differ between the three groups. Overall survival at 2 years was 37% for FT, 24% for TBF, and 34% for FLAMSA ( p = 0.10). Independent prognostic factors for survival were Karnofsky performance score and patient CMV serology ( p = 0.01; p = 0.02), while survival was not affected by age at transplant. The use of anti-thymocyte globulin (ATG) was associated with reduced risk of grade III–IV aGVHD ( p = 0.02) and cGVHD ( p = 0.006), with no influence on relapse. Conclusions In conclusion, FT, TBF, and FLAMSA regimens provided similar outcome in patients undergoing transplant with active AML. Survival was determined by patient characteristics as Karnofsky performance score and CMV serology, however was not affected by age at transplant. ATG appears able to reduce the incidence of acute and chronic GVHD without influencing relapse risk. Electronic supplementary material The online version of this article (10.1186/s13045-019-0727-4) contains supplementary material, which is available to authorized users.