Drug-induced in vitro tolerance to allogeneic antigens. II. Further analysis of in vitro-tolerized spleen cells in a fully allogeneic murine combination

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.

Improving immune reconstitution while preventing graft-versus-host disease in allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematologic malignancies or inherited disorders. Ex vivo T-cell depletion (TCD) of the graft and post-transplantation immunosuppression efficiently prevent the development of graft-versus-host disease (GVHD). However, the consequence of these nonspecific approaches is a long-lasting immunodeficiency associated with increased disease relapse, graft rejection, and reactivation of viral infections. Donor lymphocyte infusion, to treat leukemic relapse after allogeneic HSCT, can cause severe GVHD. Several strategies are being optimized to specifically inactivate anti-host T cells while preserving antileukemic or antimicrobial immunocompetence, based on ex vivo or in vivo elimination of anti-host T cells or on the modulation of their anti-host activity.

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.

Donor-specific prolongation of rat skin graft survival induced by rat-donor cells and cyclophosphamide under coadministration of monoclonal antibodies against T cell receptor alpha beta and natural killer cells in mice

Because of the recent interest in human xenotransplantation, we investigated the possibility of inducing tolerance in a xenogeneic combination using cyclophosphamide (CP). Donor-specific prolongation of xenogeneic Fisher 344 (F344) rat skin graft survival for up to 60 days was induced in C57BL/6 (B6) mice by giving F344 bone marrow cells and spleen cells on day 0, CP on day 2, and monoclonal antibodies against murine TCR-alpha beta and NK1.1 on days--1 and 3. The inoculation of the xenogeneic cells brought accelerated repopulation of TCR-alpha beta+ T cells, even under the administration of anti-TCR-alpha beta mAb. The quick increase of the host TCR-alpha beta+ T cells caused by the xenogeneic cell injection was deeply suppressed by CP. Mixed lymphocyte reaction, CTL activity, and antibody production against donor F344 were profoundly suppressed for 50 days. Mixed xenogeneic chimerism was observed for 1 month after the inoculation of donor cells in the spleen and peripheral blood of the recipient B6 mice, but was never observed in the thymus. Moreover, when irradiated F344 cells were used in place of viable cells, chimerism was never detected and graft survival was only slightly prolonged. Clonal deletion of V beta 5- or V beta 11-bearing murine T cells was not observed on day 50 in the thymus or spleen of the recipient B6 mice. These results suggest that treatment with viable xenogeneic donor cells, CP, and mAbs against T and NK cells can induce a temporary peripheral mixed chimerism and donor-specific prolongation of xenogeneic skin graft survival. The destruction with CP of T and B cells that are xenoreactive and thus proliferating after antigen stimulation, followed by mechanism other than intrathymic clonal deletion, may be the mechanism of the hyporesponsiveness in the present system.

Alloreactivity against IE-encoded antigens: evidence of the discrepancy between graft rejection and reactivity of IE-reactive T cells

Participation of IE antigens (Ag) in immune response as the transplantation Ag was examined. IE- B10.A(4R)(4R; Kk, IAk, IE-, Db) mice could not reject skin graft from IE Ag alone-disparate B10.A(2R) (2R; Kk, IAk, IEk, Db) mice despite intravenous (iv) injection of 2R spleen cells (SC) before or after skin grafting, indicating that graft rejection could not be caused across IE Ag-barrier alone. Furthermore, 4R SC could not induce lethal graft-versus-host disease (GVHD) in supralethally (950 rad) irradiated 2R mice. On the other hand, infiltration of lymphoid cells was observed at the site of transplanted 2R skin in 4R mice. SC of 4R mice unprimed or primed with 2R skin or 2R SC showed the capability to proliferate in vitro in response to 2R Ag. In immunofluorescence analysis of lymph node cells (LNC) of 4R mice injected iv with 2R SC 7 days earlier, IE-reactive CD4+Vbeta 11+ T cells did not change in number, but slightly increased the expression of interleukin-2 receptor (IL-2R). In 2R mice irradiated with 670 rad and injected iv with 4R SC 7 days earlier, 4R-derived CD4+V beta 11+ T cells proliferated, changed to blastoid form, and showed a markedly increased expression of IL-2R. To further investigate the influence of IE alloantigens on transplantation immunity, IL-2 production and anti-class I CTL activity were assayed. The 4R SC capable of recognizing IEk and Dk Ag of B10.BR (Kk, IAk, IEk, Dk) generated levels of both IL-2 and CTL activities higher than those of 2R SC capable of recognizing Dk Ag alone. These results strongly suggest that IE alloantigens indirectly act as the transplantation Ag by the stimulation of IE-reactive CD4+ helper T cells resulting in the differentiation of class I-restricted CD8+ T cells.

Induction of tolerance across major barriers using a two-step method with genetic analysis of tolerance induction

Using a murine skin allograft tolerance induction system that consists of intravenous injection of 1 x 10(8) allogeneic spleen cells followed by intraperitoneal (i.p.) injection of 200 mg/kg cyclophosphamide (CP) 2 days later, sensitivity to tolerance induction was examined across various histocompatibility (H) barriers. Although each group of class I, class II or multiminor H antigens was not by itself a prohibitively strong barrier, resistance to tolerance induction increased when the three types of barriers were combined in various ways. When the donor-recipient combinations were disparate at the entire spectrum of both H-2 plus non H-2 antigens (fully allogeneic), profound tolerance to skin allografts was not induced by this method in any of the combinations examined. Based on these results, induction of tolerance across fully allogeneic barriers was attempted in C57BL/10SnJ (B10; H-2b) mice against C3H/HeSnJ (C3H; H-2k) strain by addressing the 11 barriers as two separate challenges. B10 mice were first given B10.BR/SgSnJ (B10.BR; H-2k) spleen cells plus CP to make them tolerant to the H-2k component represented among C3H antigens, and then later were given C3H spleen cells plus CP to establish a tolerant state to the remainder of the disparate antigens of the C3H donors. After these two separate manipulations, C3H skin was accepted in the B10 mice, and normal hair growth was observed in the grafted C3H skin. By contrast, B10 mice given C3H spleen cells plus CP and then again another injection of C3H spleen cells plus CP were not rendered tolerant to C3H skin. In B10 mice, tolerance to C3H induced with B10.BR spleen cells plus CP and then C3H spleen cells plus CP was specific to C3H, and the tolerant B10 mice rejected third-party skin from DBA/2J (DBA; H-2d) strain in a normal fashion. In transfer experiments, the mechanism of tolerance was found to be based largely on reduction of the effector cells rather than on a mechanism involving active suppression. Assays for chimerism revealed that maintaining the tolerant state required persistence of cells of donor origin. These data indicate that in a primary immune response to a certain dose of allogeneic cells (tolerogen), the existence of a relatively large proportion of potentially reactive clones in the host may trigger proliferation of only a part of the population and some of the potentially reactive cells may differentiate rapidly without a prolonged period of proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-lasting skin allograft tolerance in adult mice induced across fully allogeneic (multimajor H-2 plus multiminor histocompatibility) antigen barriers by a tolerance-inducing method using cyclophosphamide

A new method of cyclophosphamide (CP)-induced skin allograft tolerance in mice that can regularly overcome fully allogeneic (major H-2 plus non-H-2) antigen barriers in mice has been established. The components of the method are intravenous or intraperitoneal administration of 50-100 micrograms of anti-Thy-1.2 mAb on day -1, intravenous injection of 90 x 10(6) allogeneic spleen cells mixed with 30 x 10(6) allogeneic bone marrow cells from the same donor on day 0, and intraperitoneal injection of 200 mg/kg CP on day 2. In each of four fully allogeneic donor----recipient combinations, including C3H/HeJ (C3H; H-2k)----C57BL/6J(B6; H-2b), B6----C3H, BALB/cByJ (BALB; H-2d)----B6, and BALB----C3H, long-lasting survival of skin allografts was induced in most of the recipient mice. The specific tolerant state induced was dependent on the doses of the antibody and bone marrow cells used. The optimal timing of CP treatment to induce tolerance was found to be 1-3 d after the stimulating cell injection. Treatment with the anti-Thy-1.2 antibody together with CP on day 2 after the cell injection on day 0 also induced profound tolerance. In the B6 mice made tolerant of C3H with antibody, C3H spleen cells plus C3H bone marrow cells, and then CP, a minimal degree of stable mixed chimerism was established and the antitolerogen (C3H) immune responses examined here, including delayed footpad reaction (DFR), CTL activity, and capacity for antibody production against donor-strain antigens were abrogated in a tolerogen-specific manner. From cell transfer experiments, the mechanism of tolerance could be largely attributed to reduction of effector T cells reactive against the tolerogen, and strong suppressive influences that might prolong skin allograft survival directly were not detected in the tolerant mice. Moreover, pretreatment with anti-Thy-1.2 antibody or anti-L3T4 (CD4) antibody was more effective than pretreatment with anti-Lyt-1 (CD5) antibody or anti-Lyt-2 (CD8) antibody as an initial step in tolerance induction. These results suggest that permanent tolerance to fully allogeneic skin grafts may be induced because antibody given before the stimulating cell injection reduces the number of reactive T cells in the recipient mice. This antibody treatment may facilitate an antigen-stimulated destruction of responding and thus proliferating cells with CP by preventing a possibly less proliferative, more rapid maturation of reactive T cells or by destroying residual effector T cells.(ABSTRACT TRUNCATED AT 400 WORDS)