The effects of rapamycin and cyclosporin a on tolerance induction through bone marrow transplantation with costimulation blockade

Abstract

Background: To increase the clinical applicability of a recently developed tolerance protocol using BMT with costimulation blockade, we evaluated the effects of the concomitant use of rapamycin and cyclosporin A (CsA). Methods: C57BL/6 mice (I-E-) received total body irradiation (3Gy, d0), 20x10*6 bone marrow cells from Balb/c donors (I-E ; d1), an anti-CD154 mAb (d1) and CTLA4Ig (d3). One group was treated in addition with rapamycin (0.2 mg/kg/d; d1-d29), and one with CsA (20 mg/kg/d; d1-d29). Results: All mice receiving the standard protocol (n 5, control group) and all mice receiving additional rapamycin (n 6) developed substantial multi-lineage chimerism ( 15% at wk 6), which was sustained throughout the observation period (currently 6 mo). Mice receiving additional CsA (n 6) also developed early chimerism ( 15% at wk 6), but 3 mice lost chimerism by 10 weeks post BMT, and only 2 of 5 mice demonstrated chimerism 6 months post BMT (1 mouse with declining chimerism was sacrificed at 5 mo). Rapamycin had no significant effect on early deletion (wk 1) of Vbeta11 CD4 cells (3.40 0.41% vs. 2.59 0.71% for the control group; p 0.05) or Vbeta5 CD4 cells (0.92 0.20% vs. 1.09 0.19%; p 0.1). CsA, in contrast, blocked deletion of Vb11 CD4 cells (4.28 0.42%; p 0.005 vs. control group) and Vb5 CD4 cells (1.62 0.14%; p 0.005 vs. control group) at wk 1. Levels of Vb11 and Vb5 T cells were also significantly higher in CsA mice at wk 8 compared to the controls. Rapamycin had no negative effect on donor skin graft survival ( 120 days in 6 of 6 mice; control group: 120 days in 3 of 5 mice), while 5 of 6 mice receiving CsA lost their donor graft within 21 days. Conclusions: In a model employing BMT plus anti-CD154 and CTLA4Ig without cytotoxic T cell antibodies, CsA blocked early deletion, allowed BM engraftment but led to a late loss of chimerism and may have impaired tolerance induction. Rapamycin did not impair chimerism, peripheral deletion or tolerance induction and is thus a potential candidate to be used clinically in this tolerance protocol. 279