Induction of peripheral tolerance to class I major histocompatibility complex (MHC) alloantigens in adult mice: transfused class I MHC-incompatible splenocytes veto clonal responses of antigen-reactive Lyt-2+ T cells.

Abstract

SummaryThe efficacy and the mode ofaction of pretransplant transfusion with class I major histocompatibility complex (MHC)-disparate splenocytes in establishing a state of peripheral tolerance in adult mice is analyzed. Adult mice injected intravenously with a critical number of N5 x 10' allogenic splenocytes accept skin grafts and develop chimerism in the peripheral lymphatic tissues, but not in thymus and bone marrow. In parallel, a split tolerance evolves : the frequency of class I MHC-reactive Lyt-2+ cytotoxic T lymphocyte precursor (CTIrp)-and interleukin 2 (IIr2)-producing T cells falls off in the peripheral lymphoid tissue, but remains unaltered intrathymically. In particular, high affinity CTLp become clonally undetectable . In vivo generation of tolerant cells is cyclosporin A resistant, but dependent on recipient L3T4+ T cells. Loss of Lyt-2+ CTIrpand IL-2-producing T cell precursors is not due to active suppression, but is caused by clonal anergy. Donor-derived chimeric cells positively selected 7 d after intravenous transfusion exhibit in vitro the hallmarks of veto cells, i.e., paralyze CTLp reactive to donor-type class I MHC alloantigens . We conclude that the peripheral (split) tolerance induced in vivo by pretransplant transfusion operates because donor-type cells develop in vivo efficiently into "veto cells;' which in turn induce a state of clonal anergy within antigen-reactive Lyt-2+ T lymphocytes.A prime aim in transplantation immunology is to define gentle methods able to convert immune reactivity to transplantation antigens into a state of immune unresponsiveness. This conversion is successful in neonates: introduction of foreign antigens into a developing immune system prevents the system from responding further on to these antigens (1, 2). Recent evidence indicates that both in natural tolerance and in experimentally induced neonatal unresponsiveness maturing antigen-reactive thymocytes become either clonally deleted (3-8) or at least clonally silenced (9-11) .Induction of unresponsiveness in a mature peripheral T cell pool meets difficulties : receptor occupancy by antigens primarily induces sensitization rather than tolerization (12)(13)(14) . Therefore, most strategies attempt first to reduce the pool of immunocompetent peripheral T lymphocytes, and thereafter to induce unresponsiveness by exposing the regenerating (neonatal) immune system to antigen . In the first step, rather invasive techniques are used, such as whole body (15, 16) or total lymphoid irradiation (17), systemic application of antiproliferative drugs (18,19), or a combination of either of these methods.Evaluation of pretransplant transfusion effects have indicated that intravenous confrontation with allogeneic cells may induce specific immunosuppression rather than sensitization (20)(21)(22)(23)(24)(25)(26)(27)(28) Miller, Bevan, pioneered the veto cell concept . Accordingly, unlinked to the specificity of their own antigen receptor, veto cells paralyze in vitro the response of T cells reacting to antigens displayed by ...

Inhibition of cytotoxic alloreactivity by human allogeneic mononuclear cells: evidence for veto function of CD2+ cells

“…Aliquots of effector cells after panning and counting were transferred into 96‐well round‐bottom microtitre plates (10 4 cells/well). After addition of [ 3 H]thymidine (0·5 μCi/well, 5 Ci/mmol; NEN, Dreieich, Germany) plates were incubated for 8 hr under standard conditions in a final volume of 200 μl/well. Cells were than harvested with an automatic cell harvester (Pharmacia LKB, Uppsala, Sweden).…”

“…In vivo data from animal models of organ transplantation suggest that application of allogeneic leucocyte cells may – under certain conditions – lead to a down‐regulation of the alloresponse and may contribute to tolerance induction. 1–4 The imm_unological mechanisms by which these allogeneic cells down‐regulate the alloresponse, however, are not entirely clear. The relevant mechanisms seem to vary considerably between different models, and allospecific as well as non‐specific suppressive effects have been observed.…”

Immune regulatory activity of CD34+ progenitor cells: evidence for a deletion-based mechanism mediated by TNF-α

“…A neutralizing anti-HLA class I antibody served as a positive control, in line with early observations that the veto activity is dependent on class I triggering. [17][18][19] The critical control for each experiment is the specificity control-namely, the inhibition of antidonor response in the absence of inhibition of anti-third-party response. Table 2 summarizes the results of different experiments in which the potential of several regulatory agents to neutralize the regulatory activity of donor CD34 ϩ cells toward antidonor CTL-p was tested.…”

Correlation between lymphocyte-induced donor-specific tolerance and donor cell recirculation.

“…phoid cells can produce a donor-specific reduction in the ability of the mice to proliferate (1), generate CTL (2-6), and generate Th (7) in a subsequent MLR, and can also enhance survival of a graft syngeneic to the lymphoid cell donor (6,(8)(9)(10). One possible explanation is that the injected donor lymphoid cells act as deletional APC or veto cells (11)(12)(13)(14)(15) and produce fimctional deletion rather than activation of host lymphocytes that recognize them (3)(4)(5)(6)(7)(8). However, if this hypothesis is correct, an explanation for the following must be found.…”