Interactions of major and minor histocompatibility antigens in the graft-versus-host reaction.

The greater severity of the graft-versus-host (GVH) reaction induced by grafting C57BL/6(B6) lymphoid or bone marrow cells to irradiated (B6 x DBA/2)F1 recipients, as compared to that induced in H-2-identical (B6 x BALB/c)F1 recipients, has been shown to arise from a synergistic effect of H-2d and DBA/2 minor histocompatibility antigens (MiHAs), and not from a difference in the intensity of genetic resistance to B6 cell grafts exhibited by the two F1s. Furthermore, detection of such synergistic effects depends upon choice of an appropriate assay system; GVH splenomegaly results cannot be used to predict the outcome of a systemic GVH reaction.

Alloimmunization-activated suppressor cells. II. In vitro activity of suppressor cells implicated in the abrogation of lethal graft-versus-host reaction.

Incompatibility for DBA/2 (D2) minor histocompatibility antigens (MiHA) alone leads to a severe lethal graft-versus-host reaction (GVHR) in irradiated (D2 X B10.D2)F1 mice receiving a bone-marrow-plus-spleen-cell graft from B10.D2 donors. This mortality is abrogated when the donors are preimmunized simultaneously against specific D2 MiHA and unrelated H-2 antigens three days before grafting. Results presented here demonstrate that spleen cells from such preimmunized donors, which are able to diminish the intensity of the GVHR developed by normal cells, exhibit the following properties: (1) reduced proliferative response to D2 MiHA in one-way MLC; (2) radioresistant suppressive effect on the proliferative responses of both normal and specifically primed B10.D2 cells; (3) inability to lyse D2 target cells even after in vitro boosting, implying that the suppressive effect detected in vitro is not due to removal of the stimulating antigens from the culture; and (4) inability to suppress the development of an anti-MiHA cytolytic response by specifically primed B10.D2 cells, despite a pronounced suppressive effect on their proliferation. Taken together with the GVHR observations, these results suggest that simultaneous immunization against specific MiHA and unrelated H-2 antigens activates, in the spleens of treated donors, suppressor cells that can inhibit the immune response at the recognition phase, and probably also at an afferent, but not efferent, stage of cytotoxic effector-cell differentiation.

Graft-versus-host reaction. Influence of genetic background in donor-recipient pairs incompatible for major histocompatibility complex (MHC).

In two H-2b anti-H-2d but not in H-2b anti-H2k donor-recipient combinations, graft-versus-host reaction (GVHR) mortality was found to vary as a function of the host's genetic background; the same non-major histocompatibility complex genes and/or antigens which influence GVHR mortality do not influence the intensity of GVHR splenomegaly or the time of skin rejection. In contrast, the severity of GVHR mortality correlates with the intensity of stimulation in mixed lymphocyte culture. The roles of minor histocompatibility (H) antigens and Mls product are discussed.

Alloimmunization-activated suppressor cells. I: Abrogation of lethal graft-versus-host reaction directed against non-H-2 antigens.

Incompatibility for DBA/2 (D2) minor histocompatibility antigens (MiHA) alone leads to a severe lethal graft-versus-host reaction (GVHR) in adult (D2 X B10.D2)F1 recipients of B10.D2 bone marrow and spleen cells. In this genetic combination, mortality is completely abrogated by preimmunization of the graft donor against unrelated H-2b antigens and specific D2 MiHA a short time before grafting. Protection against GVHR mortality is elicited by immunizing the donors with a single transfusion of incompatible spleen cells or whole blood. Abrogation of GVHR mortality is due mainly to the immunization with specific MiHA, and only to a much lesser degree to the immunization with unrelated H-2 antigens; the protective effect induced by association of these two types of immunization, however, is significantly better than that elicited by either type of immunization alone. It is unlikely that this abrogation of GVHR mortality results from "dilution" of specifically reactive cells; rather, suppressor cells appear to be a contributing factor, because the preimmunization activates, in the donor spleen, suppressor cells capable of decreasing the severity of the GVHR developed against MiHA by normal cells. Histopathologic observations indicated that the lesions induced in various tissues after grafting of preimmunized donor cells were considerably less severe than those induced by grafting of normal donor cells. However, simultaneous immunization with specific MiHA and unrelated H-2 antigens may also exacerbate the GVHR, depending upon the conditions used for preimmunization; abrogation of GVHR mortality is favored by a single immunization with unrelated H-2b antigens and specific MiHA administered simultaneously a short time before grafting, whereas an acceleration of GVHR mortality is favored by long intervals and multiple immunizations. It is suggested that, depending upon the conditions used for the preimmunization, the allogeneic effect produced by stimulation with unrelated H-2 antigens may augment the response to MiHA or it may enhance the activation of suppressor cells that contribute to the abrogation of GVHR mortality.

Specific resistance to local graft-versus-host reaction in F1 hybrids pretreated intravenously with parent-strain spleen cells. Role of cytotoxic T lymphocytes directed against receptors for the major histocompatibility complex.

Pretreatment of B6D2F1 hybrids by injection of B6 spleen cells by subcutaneous or intravenous routes induces specific resistance to the local graft versus host reaction provoked by s.c. engraftment of B6 spleen cells. This resistance has been attributed to the presence in the pretreated F1 hybrids of cytotoxic T lymphocytes directed against receptors that recognize the D2 alloantigens (anti-D2-receptor CTL). However, this hypothesis would seem to be challenged, at least partially, by our previously published results showing that a) when tested before induction of GVHR, the anti-D2-receptor CTL are detectable in F1 hybrids pretreated only by the s.c. route but not by the i.v. route; and b) specific resistance to GVHR observed in i.v.-pretreated F1 hybrids is mediated by a nylon-adherent, Thy-1-, radioresistant (2000 rads) suppressor cell of B6 origin that does not manifest any anti-D2-receptor CTL activity. However, these results did not allow us to exclude the possibility of the presence, in the i.v.-pretreated F1 hybrids, of anti-D2-receptor precursor CTL that could be reactivated during the GVHR by the D2-receptors expressed on the proliferating clone of grafted B6 cells, then differentiate to the receptor-specific CTL effectors that control the development of the GVHR. That is why we have studied in the present work the CTL activity developed against D2-receptors after induction of GVHR in either normal or resistant F1 hybrids. Our results show that F1 hybrids protected against GVHR by i.v. pretreatment with B6 cells or by a transfer of nylon-adherent spleen cells from i.v.-pretreated syngeneic F1 mice do not manifest enhanced anti-D2-receptor CTL activity. When considered along with our previous observations, these results favor our hypothesis that anti-D2-receptor CTL are not involved in the specific resistance to GVHR observed in the i.v.-pretreated F1 hybrids.

Lethal graft-versus-host reaction against non-H-2 antigens. I. Prevention of GVH-associated immunodeficiency by preimmunizing the donor against host-specific non-H-2 antigens.

Injection of B10.D2 cells into irradiated H-2d compatible (DBA/2xB10.D2)F1 recipients provokes a lethal GVH that can be abrogated by donor preimmunization against host-specific DBA/2 non-H-2 antigens. To study the possible relationship between the observed protection and restoration of immune responsiveness, we compared spleen cellularity, selected T and B cell functions, and NK activity in GVH and protected mice during the 1st month after grafting. Normal and isografted mice served as controls. GVH was found to be characterized by an early stimulation phase associated with splenomegaly and increased percentages (but not numbers) of Lyt-2+ and L3T4+ cells, followed by profound aplasia and abrogation of IL-2 production. Response to a B cell mitogen (LPS) is depressed, and cells from GVH mice exert a strong suppressive effect on the LPS and PHA responsiveness of normal cells. Suppression appears to be mediated by a radioresistant, nylon nonadherent, asialo GM1 negative cell expressing a low level of Thy-1 antigen. In contrast, protection correlates with progressive restoration of spleen cellularity and LPS responsiveness, with decreased but clearly detectable IL-2 production, and transient nonspecific suppressor activity. The immune status of protected mice resembles that of isografted controls. No correlation was found between mortality (or protection) and either PHA responsiveness, which remained depressed in all grafted mice throughout the observation period, or NK activity, which was strongly depressed in both GVH and protected mice. In conclusion, protection correlates with the disappearance of nonspecific suppressor cells and the restoration of cellularity and certain nonspecific immune functions. Donor immunization against host-specific non-H-2 antigens, which protects against mortality, also protects against GVH-associated immune deficiency.

Effectiveness of murine leukemia chemotherapy according to the immune state: reconsideration of correlations between chemotherapy, tumour cell killing, and survival time.

Cyclophosphamide (CPM) chemotherapy (134 mg/kg) of L1210 leukemia is less efficient in mice previously immunodepressed by antithymocyte serum (ATS) than in non-ATS pretreated mice. On the other hand, administration of a higher dose of CPM (403 mg/kg), which kills a greater number of leukemic cells but induces an immunodepression, according to the skin graft test, results in a shorter survival time than does the administration of a lower dose of CPM (134 mg/kg), capable of killing fewer leukemic cells but not inducing such an immunodepression. Thus, it appears that: (1) the antileukemic effect of the same dose of a chemotherapeutic drug is less efficient in immunodepressed than in nonimmunodepressed hosts, and (2) calculation of the number of neoplastic cells killed by a given chemotherapy by extrapolation from the survival time may lead to erroneous conclusions.

Interspersion of cyclophosphamide and BCG in the treatment of L1210 leukemia and Lewis Tumor.

The therapeutic value of interspersing cyclophosphamide (CPM) chemotherapy and BCG immunotherapy was investigated in two tumor models: L1210 leukemia and Lewis solid tumor (LLT). In the case of L1210 leukemia, the antileukemic effect of CPM was enhanced by subsequent BCG administration where a single cycle of combined treatment was applied; treatment by repeated doses of CPM interspersed with BCG was no more effective than CPM chemotherapy alone. In the case of LLT tumor, the effect of one cycle of combined CPM-BCG treatment was not different from CPM administered alone but treatment by repeated doses of CPM interspersed with BCG immunotherapy was less effective than CPM chemotherapy alone. These results indicate that, while the effect of BCG immunotherapy may be favorable or nil when BCG is applied after cell-reducing chemotherapy, it may be nil or unfavorable when applied repeatedly in interspersed chemoimmunotherapy treatments.