Allogeneic peripheral blood stem cell transplantation results in less alteration of early T cell compartment homeostasis than bone marrow transplantation

Since low T cell counts evaluated 1 month after allogeneic bone marrow tran splantation (BMT) are associated with an increased risk of leukemia relapse (Powles et al., Blood 1998; 91: 3181-3486), we compared, in a randomized m ulticentric clinical study, the peripheral blood cells obtained 30 days aft er allogeneic BMT vs allogeneic G-CSF-mobilized peripheral blood stem cell transplantation (BCT) in an HLA-identical setting. T cell counts were highe r 30 days after BCT (718 +/- 142 cells/mul, n = 20) than after BMT (271 +/- 53 cells/mul, n = 26, P = 0.006). However, T cells were less activated aft er BCT than after BMT, as demonstrated by a lower expression level of CD25 and a lower percentage of HLA-DR+ and CD95(+) T cells. Furthermore, CD4(+), CD8(+) and CD45RA(+) post-BCT T cell counts correlated with the number of cells infused,vith the PBSC graft, while such a correlation was not observe d between post-BMT counts and BM graft cell numbers, suggesting that the in tensity of post-transplant peripheral lymphoid expansion and/or deletion di ffered between BCT and BMT. A comparison of the input of T cells expressing different CD45 isoforms with the post-transplant cell recovery further con firmed that, within the CD4+ T cell subset, post-transplant expansions occu rred at a higher level after BMT than after BCT, affecting mainly the CD4CD45RO(+) subset. Altogether, our data demonstrate for the first time in a randomized setting that homeostasis of the T cell pool is less altered earl y after BCT than after BMT. This may have a strong impact on the graft-vers us-leukemia (GVL) effect and subsequent relapse rate.