ALTERATION OF THE HOMOGRAFT RESPONSE BY ANTIMETABOLITES *

A Review of Cyclophosphamide-Induced Transplantation Tolerance in Mice and Its Relationship With the HLA-Haploidentical Bone Marrow Transplantation/Post-Transplantation Cyclophosphamide Platform

The bone marrow transplantation (BMT) between haplo-identical combinations (haploBMT) could cause unacceptable bone marrow graft rejection and graft-versus-host disease (GVHD). To cross such barriers, Johns Hopkins platform consisting of haploBMT followed by post-transplantation (PT) cyclophosphamide (Cy) has been used. Although the central mechanism of the Johns Hopkins regimen is Cy-induced tolerance with bone marrow cells (BMC) followed by Cy on days 3 and 4, the mechanisms of Cy-induced tolerance may not be well understood. Here, I review our studies in pursuing skin-tolerance from minor histocompatibility (H) antigen disparity to xenogeneic antigen disparity through fully allogeneic antigen disparity. To overcome fully allogeneic antigen barriers or xenogeneic barriers for skin grafting, pretreatment of the recipients with monoclonal antibodies (mAb) against T cells before cell injection was required. In the cells-followed-by-Cy system providing successful skin tolerance, five mechanisms were identified using the correlation between super-antigens and T-cell receptor (TCR) Vβ segments mainly in the H-2-identical murine combinations. Those consist of: 1) clonal destruction of antigen-stimulated-thus-proliferating mature T cells with Cy; 2) peripheral clonal deletion associated with immediate peripheral chimerism; 3) intrathymic clonal deletion associated with intrathymic chimerism; 4) delayed generation of suppressor T (Ts) cells; and 5) delayed generation of clonal anergy. These five mechanisms are insufficient to induce tolerance when the donor-recipient combinations are disparate in MHC antigens plus minor H antigens as is seen in haploBMT. Clonal destruction is incomplete when the antigenic disparity is too strong to establish intrathymic mixed chimerism. Although this incomplete clonal destruction leaves the less-proliferative, antigen-stimulated T cells behind, these cells may confer graft-versus-leukemia (GVL) effects after haploBMT/PTCy.

SUPPRESSION OF ANTIBODY SYNTHESIS AND PROLONGATION OF HOMOGRAFT SURVIVAL BY CHLORAMPHENICOL

Chloramphenicol suppresses primary antibody synthesis in vivo without affecting the ability to develop a normal anamnestic response. Chloramphenicol also prolongs homograft survival in rabbits. The survival of homografts is related to the duration as well as to the amount of chloramphenicol administered. The mechanism of action of chloramphenicol in suppressing immune responses is correlated with its ability to inhibit protein synthesis in proliferating mammalian cells. These observations suggest that the inhibitory effect of chloramphenicol on protein synthesis may be applicable to mammalian cells in vivo as well as to cell-free systems and to intact mammalian cells in vivo.

Induction of permanent mixed chimerism and skin allograft tolerance across fully MHC-mismatched barriers by the additional myelosuppressive treatments in mice primed with allogeneic spleen cells followed by cyclophosphamide

A pure method of drug (cyclophosphamide plus busulfan)-induced skin allograft tolerance in mice that can regularly overcome fully H-2-mismatched barriers in mice has been established. The components of the method are i.v. administration of 1 x 108 allogeneic spleen cells on day 0, i.p. injection of 200 mg/kg CP and 25 mg/kg busulfan on day 2, and i.v. injection of T cell-depleted 1 x 107 bone marrow cells from the same donor on day 3. Recipient B10 (H-2b; IE-) mice prepared with this conditioning developed donor-specific tolerance, and long-lasting survival of skin allografts was shown in almost of the recipient mice. In the tolerant B10 mice prepared with new conditioning, stable multilineage mixed chimerism was observed permanently, and IE-reactive Vbeta11+ T cells were reduced in periphery as seen in untreated B10.D2 (H-2d; IE+) mice. The specific tolerant state was confirmed by the specific abrogation against donor Ag in the assays of CTL activity and MLR and donor-specific acceptance in the second skin grafting. These results demonstrated that the limitation of standard protocol of cyclophosphamide-induced tolerance, which have been reported by us since 1984, can be overcome by the additional treatments with the myelosuppressive drug busulfan, followed by 1 x 107 T cell-depleted bone marrow cells. To our knowledge, this is the first report to induce allograft tolerance with a short course of the Ag plus immunosuppressive drug treatment without any kind of mAbs (pure drug-induced tolerance).

The effect of aminomethylpteroylglutamic acid on the development of skin hypersensitivity and on antibody formation in guinea pigs

1. In guinea pigs, aminomethylpteroylglutamic acid (methotrexate) is capable of blocking the development of delayed skin hypersensitivity, the primary antibody response, and the specific febrile response to ovalbumin and diphtheria toxoid. The primary antibody response is more easily inhibited than is the development of delayed skin hypersensitivity. 2. The effect of methotrexate on immunologic responses depended upon the dose of methotrexate employed and the strength of the antigenic stimulus.

Fractionated dosing of cyclophosphamide for establishing long-lasting skin allograft survival, stable mixed chimerism, and intrathymic clonal deletion in mice primed with allogeneic spleen cells

BACKGROUND

Injection of allo-spleen cells (SC) followed by a single dose of cyclophosphamide (CP) can induce tolerance of tumor and/or skin allografts in mice. To minimize the damage caused by CP, fractionation of CP that can establish long-lasting skin graft survival, stable mixed chimerism, and intrathymic clonal deletion in the host was investigated in the present study.

METHODS

Allo-SC (10(8)) were given intravenously on day 0. CP at 200 mg/kg was given intraperitoneally on day 2 in a single dose (CP 200x1 group). CP at 100, 66, 50, 40, and 33 mg/kg was given daily from day 1 through days 2, 3, 4, 5 and 6, respectively, in the fractionated doses (CP 100x2, 66x3, 50x4, 40x5, and 33x6 groups; total dose=200 mg/kg). Allografting was performed on day 14.

RESULTS

In a fully allogeneic combination of C57BL/6 (H2b)-->AKR (H2k, Mls-1a), an EL-4 tumor (H2b) was specifically accepted to kill the AKR mice in all of the SC+CP 200x1, 100x2, 66x3, 50x4, 40x5, and 33x6 groups (n=6), but C57BL/6 skin graft survival was not prolonged in any of the tumor-tolerant groups. In an H2-identical combination of AKR-->C3H (H2k, Mls-1b), AKR skin graft survival was prolonged remarkably (80-90 days) in the SC+CP 200x1, 100x2, and 66x3 groups (n=5-11), but was prolonged moderately (20-60 days) in the SC+CP 50x4 and 40x5 groups. In both of the SC+CP 200x1 and 66x3 groups in the AKR-->C3H combination, mixed chimerism was maintained for as long as 100 days after tolerance induction in both the spleen and thymus, associated with intrathymic clonal deletion of Vbeta6+ T cells. The decreases in leukocyte count, hemoglobin level, spleen weight, SC count, and body weight were significantly smaller in the SC+CP 66x3 group than in the SC+CP 200x1 group.

CONCLUSIONS

Fractionated CP is effective in ameliorating the compromised state induced by a single dose of CP. To induce a long-lasting skin allograft survival associated with stable mixed chimerism and intrathymic clonal deletion in an H2-identical combination, 200 mg/kg of CP can be divided into three or fewer fractions.

Cyclophosphamide-induced immunological tolerance: an overview

A cyclophosphamide (CP)-induced tolerance system in mice that primarily consists of donor cell injection followed by CP-treatment was found useful for inducing a long-lasting allo- or xeno-tolerance to various solid organs. In the cells-followed-by-CP system, the sequential mechanisms of tolerance were clarified using the specific correlation between superantigens and certain T cell receptor (TCR) V beta segments. Those include the clonal destruction of antigen-stimulated mature T cells, the peripheral clonal deletion associated with peripheral chimerism, the intrathymic clonal deletion associated with intrathymic chimerism, and the clonal anergy. The generation of suppressor T cells was another important mechanism of tolerance in the late stage. Special care was taken to overcome the " hard" barriers of allo- or xeno-combinations by reducing the "split tolerance" produced through the clonal destruction mechanism. For this purpose, the tolerogen, antimitotic drugs, their doses, timing, route of administration, combined immunosuppressants, and supportive treatment were all crucial for successful induction of a long-lasting skin tolerance. This system may be applicable to human transplantation.

Effects of DL-alpha-difluoromethylornithine, 4-deoxypyridoxine and methylglyoxal bis(guanylhydrazone) on allograft prolongation

DL-alpha-difluoromethylornithine (DFMO), 4-deoxypyridoxine (4-DOP), and methylglyoxal bis (guanylhydrazone) (MGBG) were tested as inhibitors of acute skin graft rejection. Proximal full thickness tail skins were exchanged between C57BL/6 and Balb/C mice. Distal autografts were placed to monitor healing. Inhibitors were given singly or in combination, either orally or by injection, in various schedules to 10 groups of mice. Compared to controls, singly treated mice had significant mean prolongation of allografts ranging from 126% to 141%. Likewise, DFMO plus MGBG extended mean time of complete rejection ranging from 172% to 206%. Autografts remained intact. Some grafts persisted after discontinued immunosuppression. Complete rejection was preceded by a decline in vascularity of the graft bed and/or gradual replacement by host tissue. Graft protection in such stringent circumstances i.e., the use of skin in strains with complete histoincompatibility at the H-2 MHC loci, clearly indicate the anti-rejection effects of polyamine synthesis inhibitors. Moreover, primary and secondary effects of DFMO establish the critical role of polyamine pathway activation in acute rejection. In doses and schedules used, toxicity was encountered when DFMO and 4-DOP were used in combination and when increased amounts of MGBG were administered.

Activity of various immunosuppressive drugs on tuberculin hypersensitivity reaction in chickens

Drug induced immunosuppression of chicken immune response was studied in F1 hybrids of the CB and IC inbred lines. In tuberculin reaction complete inhibition of wattle swelling was induced by the administration of methotrexate, colcemid (1 mg/KBW), and 6-mercaptopurine. The cellular infiltration was substantially reduced in these cases. Cyclophosphamide and colcemid (0.1 mg/KBW) reduced partially the wattle swelling but had no apparent effect on the cellular infiltration. Acetinomycin D did not affect in measurable degree the wattle swelling. The histologic picture was in this case the same as in the control animals. The same drug administration schedule had less pronounced effect on anti-HSA antibody production. No anti-HSA antibody was found after the 500 mg/animal doses of 6-mercaptopurine. Significant reduction of anti-HSA titres was found after 50 mg/animal doses of 6-mercaptopurine, colcemid (1 mg/KBW), 25 MG/KBW or cyclophosphamide and after the methotrexate treatment.

Suppression of the immune response

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