The Effect of Donor Lymphocyte Infusion Dose on the Occurrence of Severe Life-Threatening Acute Graft-Versus-Host Disease Early after Reduced Intensity Conditioning T Cell Depleted Stem Cell Transplantation.
Authors: Von Dem Borne Peter A. , Starrenburg C.W.J. Ingrid , Beaumont M. Floor , Halkes Stijn J.M. , Marijt Erik W.A. , Falkenburg J.H. Frederik , Willemze Roelof 
Published: April 2020

Abstract
Donor lymphocyte infusion (DLI) after allogeneic stem cell transplantation (SCT) is an effective form of immunotherapy for hematological malignancies. The positive effects of DLI can be offset by the development of acute Graft-versus-Host-Disease (aGvHD), resulting in significant morbidity and mortality. To reduce the incidence of severe aGvHD, DLI can be administered in escalating doses starting with a low dose at a safe time point after SCT (i.e. 6 months). To prevent early disease relapse it would be preferable to administer DLI at an earlier time point after transplantation. However, only limited data exist on the dose that can be safely and effectively used early after SCT. Furthermore, after reduced intensity conditioning (RIC) SCT, potent immune response inducing antigen presenting cells of the patient remain present for months, potentially increasing the risk for GvHD after early DLI administration. To investigate if a time dependent DLI dose - GvHD response curve exists, we retrospectively analyzed the incidence of acute GvHD in 68 patients receiving a first DLI after RIC SCT both with related (n=44) and unrelated donors (n=24) for diverse indications (AML, ALL, NHL, myeloma, CLL, CML, solid tumors). A RIC regimen was used consisting of fludarabine, busulphan and horse ATG together with donor T cell depletion using alemtuzumab in vitro added to the graft prior to infusion. This regimen induces hardly any GvHD after SCT and DLI could be administered in escalating doses to most patients, either for persisting patient chimerism in the bone marrow or for progressive disease. The study group consisted of 38 male and 30 female patients (median age 55 years, range 34–66). Out of the 68 patients 7 were not evaluable due to non-GvHD related death within 3 months after DLI. Patients transplanted with a related donor (n=40) received a median of 5 x 10E6/kg CD3+ cells (range 0.3–5) at a median time point of 6.4 months (range 3.1–13) after SCT, and those transplanted with an unrelated donor (n=21) a median of 1.5 x 10E6/kg CD3+ cells (range 0.1–2.5) at a median time point of 6.9 months (range 3.1–9.7) after SCT. aGvHD was observed in 57% of evaluable patients (34% grade 1–2 and 23% grade 3–4). Analysis showed a difference in incidence of and mortality due to aGvHD between patients who received DLI before and after 5 months after SCT. Eight of 46 patients to whom DLI was administered more than 5 months after SCT developed grade 3–4 aGvHD (17%), of which 3 patients died from causes related to the GvHD (7%). Six of 11 patients who received DLI before 5 months after SCT in moderately high doses (1–5 x 10E6/kg CD3+ cells in related patients, 0.5–1.5 x 10E6/kg CD3+ cells in unrelated patients) developed grade 3–4 aGvHD (55%), of which 5 patients died from causes related to the GvHD (45%). Based on these data the subsequent patients were given lower DLI dosages. Thus, the next 4 patients received DLI at a dose of 0.1–0.3 x 10E6/kg CD3+ cells at 3.1 to 4.4 months after SCT. They developed no or only mild (grade 1) aGvHD. One of these patients transplanted for aplastic anemia received DLI for decreasing donor bone marrow chimerism (62% to 17%), after which the graft was successfully retained (stable 64% donor chimerism). Two patients received DLI for high risk disease (biphenotypic AML and refractory aggressive NHL) and are still alive 1 year after DLI. In the patient with biphenotypic AML donor bone marrow chimerism increased after DLI from 98 to 100%, and in the patient with NHL from 97% to 99%. The remaining patient was given DLI for a rapid rejection without any response. In conclusion, in patients transplanted with a T cell depleted RIC regimen, DLI can be administered safely more than 5 months after SCT with limited risk of life-threatening grade 3-4 GvHD. Before 5 months DLI results in a high incidence of severe aGvHD and GvHD related mortality. DLI may be safely administered in very low doses (&lt; 0.5 x 10E6/kg CD3+ cells) early after SCT, retaining a positive effect on donor bone marrow chimerism.