Inhibition of antiskin allograft immunity by infusions with syngeneic photoinactivated effector lymphocytes

Induction of tolerance for skin allotransplantation requires selective suppression of the host response to foreign histo-compatibility antigens. This report describes a new approach that employs pretreatment of effector cells with 8-methoxy-psoralen (8-MOP) and ultraviolet A light (UVA) to render the effector cells of graft rejection immunogenic for the syngeneic recipient. Reinfusion of photodamaged cells resulted in an immunosuppressive host response that permitted prolonged retention of histoincompatible skin grafts and specifically inhibited in vitro and in vivo responses that correlate with allograft rejection. Eight days after BALB/c mice received CBA/j skin grafts, their splenocytes served as a source of alloreactive effector cells. The splenocytes were treated with 100 ng/ml8-MOP and 1 J/cm² UVA before reinfusion into naive BALB/c recipients. Recipient mice were tested for tolerance to alloantigens in mixed leukocyte culture (MLC), cytotoxicity (CTL), delayed type hypersensitivity assays (DTH), and challenge with a fresh CBA/j graft. Splenocytes from BALB/c recipients of photoinactivated splenocytes containing the effector cells of CBA/j alloantigen rejection proliferated poorly in MLC and generated lower cytotoxic T cell responses to CBA/j alloantigens in comparison with sensitized and naive controls. Splenocytes from these hyporesponsive mice suppressed the MLC and CTL response to alloantigen from sensitized and naive BALB/c mice. In vivo the DTH response was specifically suppressed to the relevant alloantigen in comparison with controls. Moreover, BALB/c mice treated in this fashion retained a CBA/j skin graft for up to 42 d posttransplantation without visual evidence of rejection. These results indicate that the in vivo and in vitro response to alloantigen can be attenuated by pretreating the host with photoinactivated splenocytes containing the effector cells of alloantigen rejection.