Defective T-cell stimulatory pathways in patients after allogeneic bone marrow transplantation (BMT) in man

Impact of early NK cell recovery on development of GvHD and CMV reactivation in dose-reduced regimen prior to allogeneic PBSCT

Dose-reduced allogeneic peripheral blood stem cell transplantation (PBSCT) is a therapeutic approach for patients with haematological malignancies who are not eligible for conventional allogeneic PBSCT. We analysed early development of lymphocyte subpopulations and the occurrence of cytomegalovirus (CMV) reactivation and acute graft-versus-host reaction (GvHD) in patients undergoing the protocol according to Slavin vs conventionally treated patients. Lymphocyte status prior to conditioning and at day +30 after allogeneic PBSCT was determined in 24 out of 51 patients who received conventional allogeneic PBSCT (eg cyclophosphamide plus total body irradiation) and compared with 27 patients being treated according to the Slavin protocol (fludarabine, busulphan and ATG). There is a significant delay in CD4 (T helper) cell development and consecutive lower CD4/CD8 ratios and a better reconstitution of CD8 (T cytotoxic) and NK (natural killer) cells after the Slavin protocol. Patients undergoing this protocol and no, or only grade I, acute GvHD show an even better NK cell reconstitution compared to patients with grade II-IV GvHD. A low CD4/CD8 ratio represents a CMV risk factor only in conventionally treated patients with grade 0-I GvHD, while after preparative regimen according to the Slavin protocol, the NK/CD8 ratio might be a marker for the prediction of CMV reactivation in addition to CMV risk status.

Immune reconstitution following allogeneic stem cell transplantation in recipients conditioned by low intensity vs myeloablative regimen

We have investigated the immune status of patients with hematologic malignancies treated with a low intensity conditioning in preparation for allogeneic stem cell transplantation. Conditioning consisted of fludarabine, anti-T lymphocyte globulin and low-dose busulfan, followed by infusion of allogeneic blood stem cells. This protocol resulted in rapid engraftment and complete replacement of host with donor hematopoietic cells. Immunological parameters of these patients were compared to those patients who were conditioned by an aggressive myeloablative regimen. Distribution of cell surface markers of lymphocyte subsets from both groups of patients was similar, but different from that of normal control cells. Reduced intensity or non-myeloablative conditioning prior to allogeneic stem cell transplantation (NST), hardly lowered the normal T cell-dependent mitogenic response even during the early period following transplant, while the myeloablative treatments resulted in a suppressed mitogenic reaction and in slow immune recovery. Reactivity of non-MHC restricted cytotoxic T cells was also at a normal level in patients who were treated with NST. We conclude that stem cell engraftment following reduced conditioning may result in early reconstitution of immune responses assessed in vitro. We hypothesize that clinical application of NST may lead to faster development of effective immune responses against residual host-type malignant and abnormal non-malignant hematopoietic cells, although the role of fludarabine on post-transplant infections remains to be investigated in a larger cohort of patients.