CD6+ Donor Marrow T-Cell Depletion as the Sole Form of Graft-Versus-Host Disease Prophylaxis in Patients Undergoing Allogeneic Bone Marrow Transplant From Unrelated Donors

PURPOSE: The role of donor marrow T-cell depletion (TCD) in preventing graft-versus-host disease (GVHD) after transplantation of unrelated allogeneic marrow remains undefined. Because different TCD methodologies differ in the degree and specificity with which T cells are removed, it is likely that transplant outcomes would depend on which technique is used. Herein, we report results in the first 48 recipients of unrelated marrow using CD6+ TCD as the sole form of GVHD prophylaxis. PATIENTS AND METHODS: Median age of patients was 46 years (20 to 58 years). Donors were matched at A/B HLA loci. Ablation consisted of cyclophosphamide and fractionated total-body irradiation (TBI; 14 Gy). To facilitate engraftment, patients also received 7.5 Gy (22 patients) corrected or 4.5 Gy (26 patients) corrected of total lymphoid irradiation (TLI) before admission. No additional immune suppressive prophylaxis was administered. Granulocyte colony-stimulating factor was administered daily from day +1 to engraftment. RESULTS: All 48 patients demonstrated neutrophil engraftment. An absolute neutrophil count of 500 x 10(6)/L was achieved at a median of 12 days (range, 9 to 23 days). There were no cases of late graft failure. The number of CD34+ cells infused/kg was associated with speed of platelet and neutrophil recovery. The dose of TLI did not influence engraftment. Grades 2-4 acute GVHD occurred in 42% of patients (95% confidence interval CI, 0.28 to 0.57). Mortality at day 100 was 19%. There have been only five relapses. Estimated 2-year survival was 44% (95% CI, 0.28 to 0.59) for the entire group, 58% for patients less than 50 years of age. In multivariable analysis, age less than 50 years (P =.002), cytomegalovirus seronegative status (P =.04), and early disease status at bone marrow transplant (P =.05) were associated with superior survival. CONCLUSION: CD6+ TCD does not impede engraftment of unrelated bone marrow after low-dose TLI, cyclophosphamide, and TBI. CD6+ TCD as the sole form of GVHD prophylaxis results in an incidence of GVHD that compares favorably with many adult studies of unrelated transplantation using unmanipulated marrow and immune-suppressive medications, especially in light of the median age of our patients (46 years). Although event-free survival in patients less than 50 years of age is very encouraging, older patients experience frequent transplantation-related complications despite TCD.