Addition of treosulfan to a nonmyeloablative conditioning regimen results in enhanced chimerism and immunologic tolerance in an experimental allogeneic bone marrow transplant model

Abstract

Treosulfan (L-threitol-1,4-bismethanesulfonate) is an alkylating agent with routine clinical application in the treatment of ovarian cancer. In this murine study we show that this drug also has the ability to deplete primitive hematopoietic stem cells in a dose-dependent manner as determined by the cobblestone area-forming cell assay and is similar to its parent compound busulfan. Because busulfan is frequently used as part of the conditioning regimen before stem cell transplantation, we investigated an alternative nonmyeloablative protocol in an allogeneic bone marrow transplantation model in which low-dose treosulfan was added to an immune-suppressive regimen consisting of T cell-depleting antibodies, fludarabine, and thymic irradiation. Although this treatment protocol produced minimal myelosuppression, the addition of treosulfan proved to be important for allowing stable multilineage and mixed chimerism in C57BL/6 recipients of major histocompatibility complex-mismatched B10.A bone marrow without evidence of graft-versus-host disease. Donor lymphocyte infusion performed at 10 weeks after bone marrow transplantation had the effect of transforming the state of mixed chimerism to full donor-type cells, again without evidence of graft-versus-host disease. Donor-specific immunologic tolerance in the mixed chimeric animals was indicated by the acceptance of donor-type and rejection of third-party skin grafts. Thus, low-dose treosulfan may be considered as a useful component of a truly nonmyeloablative conditioning protocol in providing for mixed hematopoietic chimerism and, consequently, in establishing a platform for adoptive immunotherapy.

Treosulfan-based conditioning before hematopoietic SCT: more than a BU look-alike

“…It is effective against different types of malignant cells and it is cytotoxic to committed and more immature hematopoietic progenitors. 25 It is easily administered and converted to the active form by nonenzymatic activation. 5 It has myeloablative and immunosuppressive characteristics, but is associated with limited non-hematological toxicity.…”

“…20,24 Treosulfan has a broad anti-stem-cell effect against both primitive and committed stem cells. 25,26 In contrast to BU, which preferentially depletes primitive stem cells, treosulfan was found to deplete committed progenitors as well as primitive stem cells in vitro. 26 In addition, agar colony assays demonstrated that the stem cell toxicity of treosulfan is superior to that achieved by BU or CY.…”

“…48 We assumed that the reason for earlier and therefore more prolonged neutropenia compared with BU was the preferential depletion of primitive stem cells by BU, whereas treosulfan was found to deplete committed progenitors as well as primitive stem cells in vitro. 25,26 In their earlier report, Casper et al 40 showed that complete donor chimerism, defined as more than 95% donor cells in the BM, was reached on day 14 by 70% of the patients and on day 28 by 81%; 2 patients had complete donor chimerism when first tested on day 56 and 1 patient had reached complete chimerism by day 56. Other studies showed similar or better results.…”

GVHD after chemotherapy conditioning in allogeneic transplanted mice

“…30,31 Thus the lack of donor alloreactivity against host residual cells and/or the high dose of BU may explain the lack of need of CY. In our previous studies, 32,33 we have shown that similar myeloablative effects of BU were obtained after the administration of BU as i.v.…”

Reduced-toxicity conditioning with fludarabine and treosulfan prior to allogeneic stem cell transplantation in multiple myeloma

“…10,15,29 The stable engraftment and high rate of early complete chimerism achieved in our patient collective indicate that the conditioning agents fludarabine and treosulfan possess pronounced stem cell toxicity as well as immunosuppressive features, which have both been recently attributed to treosulfan in in vitro studies and rodent models. [30][31][32][33][34][35] In contrast to busulfan, which preferentially depletes primitive stem cells, treosulfan was found to deplete committed progenitors as well as primitive stem cells in vitro. 31 In addition, agar colony assays demonstrated that the stem cell toxicity of treosulfan is superior to that achieved by busulfan or cyclophosphamide.…”