Donor Lymphocyte Infusion in Patients with Thalassemia Major Who Have Mixed Chimerism Following Allogeneic Stem Cell Transplant

Allogeneic stem cell transplantation (HSCT) is the only curative option for patients with thalassemia major (BTM). HSCT in BTM is associated with increased risk of graft rejection. Some patients do not achieve full donor chimerism after transplant despite hematopoietic engraftment. Early post transplant mixed chimerism (MC) is a known predictor of secondary graft rejection. Data is limited on the role of donor lymphocyte infusion (DLI) to prevent secondary graft rejection following detection of early MC in BTM. We report our experience with DLI in BTM patients who had developed progressive worsening early MC after HSCT.

All patients with BTM who underwent HSCT at our centre between September 1994 and December 2013 were included in the analysis. During this period, 406 patients underwent HSCT for BTM. Median age was 8 years (range: 1 - 25) and 247 were males (60.8 %). Conditioning regimen was busulphan based in 274 (67.5%) or treosulfan based in 132 (32.5%). The graft source was BM in 305 (75.1%) and PBSC in 101 (24.9%) etc. Median CD34 stem cell dose was 9.24x10⁶/kg (range: 2.1- 33). GVHD prophylaxis consisted of CSA and short course MTX.

Patients who engrafted underwent chimerism analysis of peripheral blood at day 28 and between days 60-90. Subsequently chimerism analysis was done at the discretion of the treating physician. Chimerism analysis was done by qualitative and quantitative methods up to 2007 and by quantitative method from 2007.

MC was defined by >5% recipient cells at any time point post transplant. The severity of MC was determined as per previously published criteria (level I= < 10%, level II = 10-25 %, level III = >25 %). In patients who developed MC, immunosuppression was tapered and stopped and chimerism monitored. Cyclosporine was tapered by approximately 30% every 2 weeks until there was stable MC or complete donor chimerism. If progressive loss of donor chimerism leading to level II or III MC occured on two consecutive occasions with a concurrent drop in hemoglobin despite stopping immunosuppression and in the absence of GVHD, DLI was given. Patients should have had at least 10% donor chimerism in order to have a DLI.

There were 109 (41.6 %, out of 262 patients in whom chimerism was done) patients who developed MC. Of these, 35 (32.1%) developed progressively worsening MC and drop in hemoglobin despite tapering of immunosuppression (91% of these were within day 60). Of these 35 patients, 23 (65.7%) received DLI while 12 developed anemia requiring transfusion (4continued to be on blood transfusion and 8 underwent a second transplant).

Among 23 patients who received DLI, 9 (39.1%) showed response (rise in Hb with CC or stable MC) while 14 (60.9%) failed to show any response. The median time to show response was 28 (8-192) days and the median time to peak response was 44 (23-442) days. The 14 patients who did not show any response developed anemia requiring transfusion (11 continued to be on blood transfusion while 3 underwent a second transplant). While 80% of those with level II chimerism responded to DLI, only 31.2% of those with level III chimerism showed a response (summarized in Table 1).

DLI was well tolerated by the majority of the patients. However, 7 (30.4%) patients developed cytopenia. While 6 of these had level III chimerism at the time of DLI, 1 had level II chimerism. Two patients developed Grade IV cytopenia. Grade 2 acute GVHD developed in 3 (13%; liver=2, gut=1) which responded to immunosuppressive treatment. Chronic GVHD developed in 2 (8.7%: extensive=1). There was no mortality related to DLI.

DLI helped close to 40% patients achieve either complete donor chimerism or stable MC who otherwise might have required a second stem cell transplant with minimal risk. There was a trend to suggest that early administration of DLI at level II MC was superior to DLI administered at level III.