Microchimerism, Donor Dendritic Cells, and Alloimmune Reactivity in Recipients of Flt3 Ligand-Mobilized Hemopoietic Cells: Modulation by Tacrolimus

Abstract

Flt3 ligand (FL) is a potent hemopoietic growth factor that strikingly enhances stem cells and dendritic cells (DC) in vivo. We examined the impact of infusing FL-mobilized bone marrow (BM) cells on microchimerism and anti-donor reactivity in normal and tacrolimus-immunosuppressed, noncytoablated allogeneic recipients. BM from B10 (H2b) mice given FL (10 μg/day; days 0–8; FL-BM) contained a 7-fold higher incidence of potentially tolerogenic immature CD11c+ DC (CD40low, CD80low, CD86low, MHC IIlow) that induced alloantigen-specific T cell hyporesponsiveness in vitro. C3H (H2k) mice received 50 × 106 normal or FL-BM cells (day 0) and tacrolimus (2 mg/kg/day; days 0–12). On day 15, enhanced numbers of donor (IAb+) cells were detected in the thymi and spleens of FL-BM recipients. Tacrolimus markedly enhanced microchimerism, which declined as a function of time. Ex vivo splenocyte proliferative and CTL responses and Th1 cytokine (IFN-γ) production in response to donor alloantigens were augmented by FL-BM infusion, but reduced by tacrolimus. Systemic infusion of purified FL-BM immature DC, equivalent in number to that in corresponding whole BM, confirmed their capacity to sensitize, rather than tolerize, recipient T cells in vivo. In vitro, tacrolimus suppressed GM-CSF-stimulated growth of myeloid DC from normal BM much more effectively than from FL-BM without affecting MHC class II or costimulatory molecule expression. Infusion of normal B10 BM cells at the time of transplant prolonged C3H heart allograft survival, whereas FL-BM cells did not. A therapeutic effect of tacrolimus on graft survival was observed in combination with normal, but not FL-BM cells. These findings suggest the need for alternative immunosuppressive strategies to calcineurin inhibition to enable the engraftment, survival, and immunomodulatory function of FL-enhanced, immature donor DC.

Flt3 ligand therapy for recipients of allogeneic bone marrow transplants expands host CD8α+ dendritic cells and reduces experimental acute graft-versus-host disease

“…11,38 This observation is consistent with recent findings that demonstrate the impaired allostimulatory capacity of DCs isolated from bone marrow of FL-treated mice, though that study suggested that the impaired function of FL DCs was probably a result of their immaturity. 11 In our experiments, however, FL DCs and control DCs displayed similar phenotypes. Freshly isolated splenic DCs express little MHC class II, CD80, or CD86, but these molecules are up-regulated in culture even without any additional stimuli.…”

“…4,5 Therefore, FL has been proposed as a means to boost protective immunity against several diseases including cancer and infectious agents. FL can augment immunologic responses, [6][7][8][9][10][11][12][13][14] but it can also induce tolerance. 15 Dendritic cells (DCs) are centrally involved in the initiation of T-cell-dependent immune responses.…”

Dendritic Cell Subset Ratio in Tolerant, Weaning and Non-Tolerant Liver Recipients Is Not Affected by Extent of Immunosuppression

“…Studies on the effects of CsA or tacrolimus on phenotypic maturation of DC have shown either no inhibition (31,39,40) or heterogeneous effects, depending on the maturation stimulus and the cell surface molecules analyzed (41,42). Moderate suppressive effects on IL12p70 and IFNa production have been reported (40,41), and tacrolimus-exposed DC has reduced T-cell-stimulating ability (31,40,43).…”

Induction of Allospecific Tolerance by Immature Dendritic Cells Genetically Modified to Express Soluble TNF Receptor

“…The observation of multilineage microchimerism in long-surviving recipients of organ allografts indicates that chimerism is an essential prerequisite for tolerance induction (54,55). Although passenger leukocytes were reported in the observation of chimerism in long-surviving recipients, donor hemopoietic cells and DC are also important in generation of microchimerism (56). Hence, the preservation of imDC tolerogenic potential and efforts to manipulate microchimerism using immunosuppressive therapy are promising approaches.…”