Kinetics of Chimerism and Early Immune Recovery in Patients Receiving Unmodified Peripheral Blood Allogeneic Grafts Followed By Post-HSCT High Dose Cyclophosphamide for Gvhd Prophylaxis

Background: Recent studies have shown the intravenous administration of high-dose cyclophosphamide (CY) in the early post-transplant period to be a strategy for GvHD prophylaxis in patients with hematologic malignancies who receive allogeneic marrow grafts from alternative donors. We evaluated the outcomes of patients who received HPC-Apheresis products to compare the impact of post- transplant CY on neutrophil engraftment, hematopoietic chimerism, and early immune reconstitution in patients who received post-HSCT CY following haplo-identical (HAP), matched unrelated donor (MUD), and mismatched unrelated donor (mMUD) grafts vs. with conventional matched related donor (MRD) graft recipients. 

Methods and Results: We transplanted 44 patients (median age, 49 years; range, 20-72 years) with advanced hematologic malignancies n=8 (HAP); 14 (MRD); 17 (MUD); 5 (mMUD). All patients received conditioning regimens based on busulfan or total body irradiation (TBI). High-dose CY (50 mg/kg/day) was administered on days 3 and 4 following HAP and on day 3 following MUD transplant. Peripheral blood lymphocyte reconstitution and quantitative T-cell and myeloid specific donor chimerism (STR) status was assessed on post-HSCT days 30 and 60. Mean time to ANC 500 was 12.5 days for MRD, mMUD and MUD graft recipients.  HAP recipients took slightly longer at 15.2 days but not significantly different from others. Day +30 median CD3/CD15 chimerism was 82.3+12.4/99.8+0.5 for MRD; 86.7+16.0/97.6+2.2 for MUD; 87.6+15.3/99.8+0.4 for mMUD; and 98.8+1.8/99.2+1.2 for HAP. Day +30 HAP CD3 chimerism was significantly improved over MRD (p<0.001) but not over MUD or mMUD. CD15 chimerism did not differ between groups. Of 30 patients that received CY, 18(60%) and 27(90%) achieved full (>95%) donor CD3+ and CD15+chimerism by day +30, respectively vs. 1 (7%) and 12 (86%) in 16 patients who underwent MRD transplants. Day +30 total T cell recovery was significantly faster in MRD than CY-treated recipients (p=0.015) due principally to more robust CD8+ T cell recovery. CD4 T cell recovery remained incomplete in all groups through day +100.  Recovery of γδ T cells did not differ between groups. Regulatory T cells are virtually absent.  NK cells recover to normal numbers at day +28 in all groups.

Conclusions: Recipients of HAP, MUD and mMUD grafts who received post-HSCT CY show similar engraftment kinetics as those who receive MRD grafts with standard immunosuppression. T-cell engraftment appears to follow myeloid engraftment in those who received post-transplant CY and is generally earlier by day 30 than in MSD graft recipients, although CD3+CD8+ recovery is greater in MRD recipients than others.  Taken together, HPC-Apheresis is a reasonable alternative donor graft source when accompanied by post-HSCT CY-based GvHD prophylaxis.