Allogeneic peripheral blood stem cell transplantation with CD34+-cell selection and delayed T-cell add-back in adults. Results of a single center pilot study

Servei d'Hematologia Clinica, Hospital de la Santa Creu i Sant Pau, Av. Sant Antoni M feminine Claret, 167, 08025 Barcelona, Spain. rmartino@hsp.santpau.es

BACKGROUND AND OBJECTIVES: Allogeneic peripheral blood stem cell transplantation with CD34+ cell-selection (CD34+-PBSCT) allows rapid hematologic engraftment with a reduction in graft-versus-host disease (GVHD), although concerns exist regarding the increased risk of tumor relapse associated with T-cell depletion of the graft. Delayed T-cell add-back (TCAB) after such transplants may restore the graft-versus-tumor effect while achieving a reduced early transplant-related mortality due to less GVHD in a group of patients at high risk of early death (i.e., age >= 45 years). DESIGN AND METHODS: Ten patients 45 years of age or older with hematologic malignancies received a CD34+-PBSCT and cyclosporin A (CyA) to prevent acute GVHD, followed by a planned delayed donor TCAB of 107 T-cells/kg to restore the graft-versus-tumor effect. The infused graft included a median of 6.3x106 CD34+ cells/kg and 4.4x104 CD3+ cells/kg. RESULTS: Engraftment was prompt in all cases. Four patients developed acute GVHD after the CD34+-PBSCT and/or chronic GVHD after CyA withdrawal and did not proceed to TCAB, and two patients died early before the planned TCAB. Four patients proceeded to TCAB at a median of day +104 after CD34+-PBSCT (+92 to +150). Two of these patients developed acute GVHD grades I-II (IBMTR Index B) after TCAB and all four developed chronic GVHD, which was extensive in two. With a median follow-up of 611 days (range 499-847) after transplant in the seven survivors, there have been no disease progressions, and all patients show a pattern of complete donor chimerism in bone marrow and peripheral blood. INTERPRETATIONS AND CONCLUSIONS: The results of our pilot study suggest that this protocol produces an acceptable transplant-related morbidity and mortality in patients 45 years and older. However, there may be benefit in infusing CD34+-selected PBSCT with even lower T-cell contents and further delaying the TCAB.