Combinations of anti-LFA-1, everolimus, anti-CD40 ligand, and allogeneic bone marrow induce central transplantation tolerance through hemopoietic chimerism, including protection from chronic heart allograft rejection

Central transplantation tolerance through hemopoietic chimerism initially requires inhibition of allogeneic stem cell or bone marrow (BM) rejection, as previously achieved in murine models by combinations of T cell costimulation blockade. We have evaluated LFA-1 blockade as part of regimens to support mixed hemopoietic chimerism development upon fully allogeneic BALB/c BM transfer to nonirradiated busulfan-treated B6 recipient mice. Combining anti-LFA-1 with anti-CD40 ligand (CD40L) induced high incidences and levels of stable multilineage hemopoietic chimerism comparable to chimerism achieved with anti-CD40L and everolimus (40-O-(2-hydroxyethyl)-rapamycin) under conditions where neither Ab alone was effective. The combination of anti-LFA-1 with everolimus also resulted in high levels of chimerism, albeit with a lower incidence of stability. Inhibition of acute allograft rejection critically depended on chimerism stability, even if maintained at very low levels around 1%, as was the case for some recipients without busulfan conditioning. Chimerism stability correlated with a significant donor BM-dependent loss of host-derived Vbeta11(+) T cells 3 mo after BM transplantation (Tx). Combinations of anti-CD40L with anti-LFA-1 or everolimus also prevented acute rejection of skin allografts transplanted before established chimerism, albeit not independently of allospecific BMTx. All skin and heart allografts transplanted to stable chimeras 3 and 5 mo after BMTx, respectively, were protected from acute rejection. Moreover, this included prevention of heart allograft vascular intimal thickening ("chronic rejection").