Phenotype, specificity, and function of T cell subsets and T cell interactions involved in skin allograft rejection

Alloantigen-specific regulation of cytotoxic T cell responses is mediated through the induction of clonal anergy of CD8+ T cells

Priming mice with an alloantigen before immunization with this same alloantigen presented in association with a second one on an F1 stimulator cell inhibits the induction of cytotoxic response directed against the second alloantigen. This inhibition is associated with the induction of a strong cytotoxic T lymphocyte (CTL) response against the first priming alloantigen. For example, a specific suppression of anti-H-2b CTL responses could be induced in C3H/He mice (H-2k) by priming them with H-2d spleen cells before immunization with F1 (H-2dxb) spleen cells. In the present study, we have analyzed the mechanisms underlying this specific suppression of CTL responses. We have demonstrated that the reduction of H-2b-specific CTL responses is reflected by a decrease in the frequency of effector cells specific for H-2b antigen. However, there was no difference in the frequencies of precursor CTL in control and suppressed mice excluding clonal deletion as the mechanism maintaining low responsiveness. Co-culture experiments have shown that the suppression of anti-H-2b CTL responses was not due to suppressor cells but to the failure of CD8+ T cells of suppressed mice to collaborate with normal helper CD4+ T cells. The suppression was therefore ascribed to a functional impairment (clonal anergy) of the CD8+ T cell subset.

Processed MHC class I alloantigen as the stimulus for CD4+ T-cell dependent antibody-mediated graft rejection

The traditional view of graft rejection is one of direct recognition of allogeneic MHC molecules by effector T cells, the phenotype of which may be predicted by the nature of the MHC disparity. In this article, Andrew Bradley and colleagues discuss recent evidence that suggests this view may be an oversimplification, and argue that additional effector mechanisms, such as alloantibody, need to be reconsidered.

What are minor histocompatibility loci? A new look at an old question

In this article, Derry Roopenian relates the traditional view of minor histocompatibility (H) loci to recent advances in understanding of the tissue rejection process and the molecular nature of minor histocompatibility antigens. He proposes that minor H loci can be subdivided by the ability of their products to stimulate different T-cell subsets and discusses the implications of this concept in terms of the origins and behavior of minor H loci and their antigens, tumor immunology and autoimmunity.

Comparison of the humoral and cytotoxic T-lymphocyte response to individual HLA class I alloantigens in highly immunized patients

In order to investigate the correlation between activation of cytotoxic T-lymphocyte precursor (CTLp) and the formation of antibodies to alloantigens, we studied 21 highly sensitized patients waiting for a kidney transplantation. Both antibody reactivity and CTLp frequencies of these patients were determined against 88 individual HLA class I alloantigens. A high or low CTLp frequency against a certain HLA-A or -B alloantigen was not correlated with the presence or absence of the antibodies to that antigen. Mismatched antigens, towards which the patient had not formed antibodies, can induce either a higher or a lower frequency of CTLp compared to mismatches towards which the patients had formed antibodies. The possible implications of this lack of correlation between the T- and B-cell allorepertoires with regard to donor selection for (highly immunized) patients is discussed.

Differential involvement of CD4+ cells in mediating skin graft rejection against different amounts of transgenic H-2K(b) antigen

Differential involvement of CD4+ cells in mediating class I-disparate skin graft rejection was investigated using quantitatively different Kb transgenic mice as donors under conditions in which CD8+ cells were blocked in vivo by administration of anti-CD8 monoclonal antibody (mAb). Tg.H-2Kb-1 and -2 are C3H transgenic mice with 14 and 4 copies, respectively, of the H-2Kb gene. Cell surface expression of Kb antigen and the Kb antigenicity of skin for eliciting graft rejection with homozygous and heterozygous transgenic mice were correlated with the copy number. In vivo administration of anti-Lyt-2.1 (CD8) mAb markedly prolonged survival of heterozygous and homozygous C3H Tg.H-2Kb-2 skin grafted onto C3H mice, but prolonged survival of heterozygous Tg.H-2Kb-1 skin grafts much less and did not prolong survival of homozygous Tg.H-2Kb-1 grafts. Administration of anti-L3T4 (CD4) mAb alone did not have any effect on skin graft rejection. Administration of anti-L3T4 (CD4) mAb with anti-Lyt-2.1 (CD8) mAb blocked rejection in all combinations. These findings indicate that a quantitative difference of class I antigen caused differential activation of CD4+ cells under conditions in which CD8+ cells were blocked.

T cell requirements for the rejection of renal allografts bearing an isolated class I MHC disparity

This study has examined the cellular and humoral responses underlying the rejection of rat renal allografts bearing an isolated RT1Aa class I MHC disparity. RT1Aa disparate kidneys were rejected promptly by high responder RT1u but not by low responder RT1c recipients (median survival time 10 d and greater than 100 d, respectively). The magnitude and phenotype of the cellular infiltrate were similar in rejecting and nonrejecting RT1Aa disparate kidneys. Paradoxically, graft infiltrating cells and spleen cells from RT1u recipients showed minimal ability to lyse donor strain lymphoblasts in vitro, whereas effector cells from RT1c recipients showed modest levels of cytotoxicity. Injection of RT1u rats with MRC OX8 mAb was highly effective at selectively depleting CD8+ cells from graft recipients but had no effect in prolonging the survival of RT1Aa disparate grafts despite the complete absence of CD8+ cells from the graft infiltrate, which included numerous CD4+ T cells and macrophages. RT1u, but not RT1c, recipients mounted a strong alloantibody response against RT1Aa disparate kidneys. Immune serum obtained from RT1u recipients that had rejected a RT1Aa disparate graft was able, when injected into cyclosporin-treated RT1u recipients, to restore their ability to reject a RT1Aa, but not a third-party RT1c, kidney. These results suggest that CD8+ cells in general and CD8+ cytotoxic effector cells in particular are unnecessary for the rapid rejection of RT1Aa class I disparate kidney grafts by high responder RT1u recipients. By implication, CD4+ T cells alone are sufficient to cause prompt rejection of such grafts and they may do so by providing T cell help for the generation of alloantibody.

Antigen-presenting cells for CD8+ T cells

Evidence is presented that a wide variety of cell types are capable of presenting class I alloantigens to purified unprimed CD8+ cells in the absence of added help. These cells include dendritic cells, a population of Ia- Thy 1- cells in spleen, peritoneal exudate cells and one of three T-tumor lines. Some cell types, e.g. T-blast cells and overnight-adherent peritoneal exudate cells (OA-PEC) only expressed antigen-presenting cell (APC) function in the presence of added lymphokines. Stimulation of OA-PEC with small concentrations of lipopolysaccharide or treatment of T-blast cells with neuraminidase (N'dase) strongly enhanced the APC function of these cells and led to helper-independent responses. N'dase treatment of small resting T stimulators caused partial restoration of APC function: strong responses were observed but only in the presence of exogenous lymphokines. Studies with T-tumor lines preincubated with IFN-gamma suggested that APC function correlates closely with antigen (class I) expression. Collectively, the data support the view that APC function depends upon a multiplicity of factors including antigen density, the level of accessory (adhesion) molecules and net surface charge. It is suggested that the potency of APC function is largely a reflection of the overall avidity of T-APC interaction: high-avidity binding leads to helper-independent responses whereas weaker binding results in helper-dependent responses.

Cultured rat kidney parenchymal components are damaged by cytotoxic lymphocytes produced in MLC

Donor-specific cytotoxic lymphocytes (CTL) can be recovered from rejecting allografts both in animal models and in humans. These allograft infiltrating CTL expressing specific cytotoxicity to relevant MHC-restricted target cells in vitro most likely constitute the major effector arm during rejection. Effector cells with similar phenotype, specificity and function can be produced in mixed lymphocyte cultures (MLC). Despite the pivotal importance of CTL in allograft rejection, there is limited information about the susceptibility of different parenchymal graft cells to CTL-mediated damage. We used cultured rat glomerular epithelial cells (GEPC), glomerular mesangial cells (GMC), tubular cells (TC) and heart endothelial cells (HEC) as distinct parenchymal target components in 4 h Chromium release assays. All of these graft components were damaged by CTL produced in 6-day MLC (specific release: 10-25%). Three-day gamma-interferon (IFN-G) treatment enhanced MHC class I and II surface expression on all our targets and increased their susceptibility for CTL-mediated lysis in our experiments (specific release: 20-60%).

T cell reactivity to MHC molecules: immunity versus tolerance

The specificity of mature CD8+ and CD4+ T lymphocytes is controlled by major histocompatibility complex (MHC) class I and class II molecules, respectively. The MHC class specificity of T cells is stringent in many assays, but is less evident when cells are supplemented with exogenous lymphokines. The repertoire of T cells is shaped through contact with MHC molecules in the thymus and involves a complex process of positive selection and negative selection (tolerance). Tolerance of immature T cells to MHC molecules can reflect either clonal deletion or anergy and results from intrathymic contact with several cell types, including epithelial cells and cells with antigen-presenting function. Unlike immature T cells, mature T cells are relatively resistant to tolerance induction. In certain situations partial unresponsiveness of mature T cells can be achieved by exposing T cells to foreign MHC molecules expressed on atypical antigen-presenting cells. Tolerance is rarely complete, however, and the precise requirements for tolerizing mature T cells are still unclear.

Immune surveillance: both CD3+ CD4+ and CD3+ CD8+ T cells control in vivo growth of P815 mastocytoma

The aim of this study was to examine whether a spontaneous immune response controls neoplastic growth in P815-bearing DBA/2 mice, and to characterize the cells involved in tumor resistance in vivo. Several cell lineages such as T-cell-receptor (TcR)-bearing T cells, NK cells and macrophages mediate some anti-tumor activity in vitro. P815 was chosen as a model because it is weakly immunogenic and is a good target both for tumor-specific, MHC-restricted CTL-mediated lysis and for MHC-unrestricted lysis exerted by long-term cultured lymphocytes or activated macrophages. Since most "NK-like activity" in freshly isolated populations appears to be associated with CD3- cells, whereas antigen-specific, MHC-restricted T cells mostly express CD3 determinants, CD3 was a good marker for evaluating the role of T cells and "NK" cells in tumor resistance in vivo. The survival of anti-CD3-treated animals that were inoculated with tumor cells was strongly reduced (mean survival time: 17 days vs. 40 days for the control group) and was associated with increased tumor growth rate. We followed the same approach to define the T-cell subset(s) that mediate(s) this immune response. Both CD4+ and CD8+ T cells were required for induction of immune control on neoplastic growth. The approach used has revealed the important role of CD4+ T cells in immune responses that control in vivo growth of a class-I-positive, class-II-negative tumor and suggests that these cells may play a central role in tumor resistance. Since CD4+ cells are activated by soluble, exogenous proteins, this finding may have important implications for immunotherapy.

In vivo induction of antigen-specific transplantation tolerance to Qa1a by exposure to alloantigen in the absence of T-cell help

A goal of transplantation immunology is to be able to induce antigen-specific tolerance in transplant recipients. In the present study we describe an in vivo model of antigen-specific transplantation tolerance to skin allografts using mice congenic at Qa1, a ubiquitously expressed class I-like molecule encoded to the right of H-2D. B6 mice are deficient in Qa1a-specific T-helper cells and only reject Qa1a disparate tail skin grafts when a second graft expressing additional helper determinants is also present. We report that animals initially engrafted with Qa1a disparate skin, in the absence of any source of additional help, are rendered tolerant to Qa1a disparate skin allografts despite the subsequent presence of inducer skin grafts expressing additional helper allodeterminants. The nonresponsive state is Qa1a-specific, because HY-bearing inducer grafts are rejected normally. In vitro, Qa1a-tolerant animals are specifically unable to generate anti-Qa1a T-killer cells, which provides the cellular basis for their failure in vivo to reject Qa1a skin allografts. Thus, initial exposure to Qa1a allodeterminants, in the absence of T-cell help, leads to a state of Qa1a-specific transplantation tolerance. This study suggests that antigen-specific transplantation tolerance may be induced by exposing naive T-killer cells to tissue alloantigens under conditions in which T-cell help is not generated.

Allograft rejection in athymic nude rats by transferred T-cell subsets. I. The response of naive CD4+ and CD8+ thoracic duct lymphocytes to complete allogeneic incompatibilities

PVG.rnu/rnu nude rats were pre-grafted with two allogeneic skin grafts, AO(RTlu) and BN(RTln), 6-14 days in advance of cell transfer. Cellular requirements for rejection were established by transferring graded numbers of B cell-depleted (Ig-) thoracic duct lymphocytes (TDL) or purified W3/25+ (CD4+) or OX8+ (CD8+) TDL subsets. Allografts were rejected by 10(5) to 5 x 10(6) Ig- TDL in a dose-dependent fashion. A similar dose-response relationship was found by transferring 5 x 10(5) to 5 x 10(6) Ig- OX8- TDL (purified by depletion of B cells and OX8+ cells). Larger numbers of Ig- OX8- TDL (10-30 x 10(6)) did not significantly accelerate rejection. W3/25+ TDL alone (10(5)), highly purified by fluorescence-activated cell sorting (FACS), were sufficient to induce allograft rejection in this athymic nude rat model. In contrast, 10 times more FACS purified OX8+ TDL (10(6)) were unable to initiate skin graft rejection despite the complete class I and class II MHC incompatibilities. Furthermore, the addition of 10(6) OX8+ cells did not accelerate or retard the rejection induced by 10(5) W3/25+ cells alone. Pre-grafted nude recipients, irradiated (500 R) 2 hr before W3/25+ TDL injection, in order to eliminate putative nude T cells, rejected allografts on the same day as unirradiated controls. We conclude that when confronted with complete MHC disparities, CD4+ T cells are necessary and sufficient to induce skin allograft rejection whereas CD8+ T cells do not appear to contribute.

Tumour-induced immunity to H-Y-disparate skin grafts without concomitant priming of CTL

A tumour, ET-5, arising as a subcutaneous mass in a C57BL/6 male mouse after treatment with a mutagen, has been found to elicit immunity to H-Y antigen in B6 female mice that have rejected the tumour. Anti-H-Y immunity is demonstrable in vivo by accelerated rejection of male skin grafts, and by the ability of spleen cells from ET-5-primed female mice to transfer immunity against H-Y antigen to immunodeficient hosts given indicator male skin grafts. However, spleen cells from ET-5-immune female mice fail to generate CTL specific for H-Y antigen when co-cultured with male stimulator cells in vitro. This finding implies that the generation of H-Y-specific immunity in vivo can occur in the absence of priming of CTL, and thus calls into question the necessity for CTL participation in H-Y-disparate tumour graft rejection.

Specific unresponsiveness in rats with prolonged cardiac allograft survival after treatment with cyclosporine. III. Further characterization of the CD4+ suppressor cell and its mechanisms of action

The cellular basis of the specific unresponsiveness that develops in DA rats treated with cyclosporine (CSA) for 10 d after grafting a PVG heart was examined using an adoptive transfer assay. CD4+ cells from rats with long survival grafts specifically lack the capacity to restore PVG heart graft rejection, and can also inhibit the capacity of naive T cells to restore rejection, while in the first few weeks post-transplant, both CD4+ and CD8+ T cells from CSA-treated hosts have the capacity to effect PVG graft rejection. In this study, we demonstrated the CD4+ suppressor cells also had the capacity to inhibit restoration of rejection by CD4+ cells from CSA-treated DA rats recently transplanted with PVG hearts, and from rats sensitized to third party, but not from those specifically sensitized to PVG. They also inhibited the capacity of both naive CD8+ and sensitized CD8+ cells to effect rejection. These results showed that the CD4+ suppressor cell was capable of overriding the capacity to effect rejection of the CD4+ cell and activated CD8+ cells that were present in the CSA-treated host shortly after transplantation. The failure of naive CD8+ cells to augment suppression and the capacity of CD4+ suppressor cells to transfer unresponsiveness to irradiated hosts in which regeneration of CD8+ cells was abolished by thymectomy suggested that it was the CD4+ cell alone that mediated suppression. However, the failure of CD4+ suppressor cells to reinduce unresponsiveness in irradiated hosts whose CD8+ cells had been depleted by therapy with the mAb MRC Ox8 showed that a radioresistant CD8+ cell was required to reestablish the state of specific unresponsiveness. The induction of CD4+ suppressor cells in thymectomized hosts suggested that these cells were derived from long-lived CD4+ lymphocytes. However, their sensitivity to cyclophosphamide and their loss of suppressor function both after removal of the graft and after 3 d in culture demonstrated that the suppressor cell itself had a short lifespan. The CD4+ suppressor was shown to be MRC Ox22+ (CD45R+), MRC Ox17+ (MHC class II), and MRC Ox39+ (CD25, IL-2-R). These studies demonstrated the CD4+ suppressive cell identified in rats with specific unresponsiveness induced by CSA therapy had many features of the suppressor inducer cell identified in in vitro studies of the alloimmune response.(ABSTRACT TRUNCATED AT 400 WORDS)

Complexity at the mouse minor histocompatibility locus H-4

The fine immunogenetics of the chromosome 7 mouse minor histocompatibility (H) locus H-4 was investigated. Both class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) and class II MHC-restricted "helper" T cells (TH) specifically reactive with H-4 antigens were isolated as clones and were used as genetic probes for classical backcross segregation analysis. Results of a four point cross indicated that the H-4 locus was actually comprised of two genes, that have been designated H-46 and H-47. The former encodes antigens recognized by the TH and the latter encodes antigens recognized by the CTL. Moreover, these two genes could be separated from the gene pink-eyed dilution (p) which was found to be "sandwiched" between them. The functional significance of a minor H congenic strain differing by both TH-defined H-46 and CTL-defined H-47 was addressed using F1 complementation tests. Such studies indicated that immune responses against H-46 antigens was required for generation of H-47-specific CTL. Altogether, these results suggest selective presentation of different minor H gene products by class I or class II MHC proteins and that the minor H "locus" H-4 may have necessarily included both TH and CTL-defined genes because of requisite TH-CTL collaboration.

Responses against antigens encoded by the H-3 histocompatibility locus: antigens stimulating class I MHC- and class II MHC-restricted T cells are encoded by separate genes

The purpose of this work was to study the genetic basis of histocompatibility antigens encoded by the mouse minor histocompatibility (H) locus H-3. Both class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) and class II MHC-restricted helper T cells (TH) specific for antigens encoded by genes within the H-3 locus were isolated and analyzed. Typing a number of mouse strains for expression of antigens recognized by these TH and CTL suggested that there was a different strain distribution pattern of expression of the antigens recognized by TH compared with those recognized by CTL. Separation of the genes whose products stimulate TH from those whose products stimulate CTL was suggested by: (1) analysis of the strain B10.FS(92NX)/Grf that has undergone recombination within the H-3 region; (2) genetic segregation studies of (B10.UW-H-3b/Sn x C57BL/10Sn)F2 mice; and (3) F1 complementation studies in which CTL specific for products of the TH-defined gene(s) could not be detected, even in the absence of immune responses to products of the CTL-defined genes. Taken together, these data suggest that in addition to two genes (B2m and Cd-1) within the H-3 region whose products typically stimulate class I MHC-restricted CTL, there is at least one additional gene whose product selectively stimulates class II MHC-restricted TH. This new gene is located telomeric from the CTL-defined genes and between the loci we and un on chromosome 2. These data demonstrate a novel degree of complexity of the H-3 "locus" and suggest selective presentation of minor H gene products in the context of class I or class II MHC proteins.

Effect of prolonged monoclonal antibody administration on cardiac allograft survival in the rat

After heterotopic cardiac transplantation in the rat, monoclonal antibodies (MoAb) specific for rat T-cell subsets were administered until rejection. Across combined major histocompatibility complex (MHC) and non-MHC differences (WF to Lew) and isolated non-MHC differences (WF to Lew.1W) cardiac allografts were rapidly rejected in unmodified hosts (7.7 +/- 1.0 days and 12.2 +/- 0.8 days respectively). Across combined MHC and non-MHC differences, administration of MoAb OX-19 (pan T-cell) on days -1, 0, and 1 (where day 0 was the day of transplantation) and alternate days thereafter until rejection significantly prolonged allograft survival (28.5 +/- 10.2 days, P less than 0.01). Administration of MoAb W3/25 (helper T cell) and MoAb OX-39 (interleukin 2 (IL-2) receptor) prolonged allograft survival (11.3 +/- 2.6 days, P less than 0.05 and 13.3 +/- 2.0 days, P less than 0.01 respectively), whereas MoAb OX-8 (cytotoxic/suppressor T cell) administration had no effect on allograft survival. In contrast, across non-MHC differences (WF to Lew.1W) administration of MoAb OX-8 markedly prolonged allograft survival (85, greater than 100 x 3 days) whereas MoAb W3/25 administration had no effect. The effect of MoAb administration on lymphocyte subsets at rejection was assessed by flow cytometry. The relationship between depletion of targeted T-cell subsets and graft survival was variable. Across both combined MHC and non-MHC and isolated non-MHC differences MoAb OX-8 administration resulted in a marked reduction of OX-8+ cells at rejection with no prolongation of graft survival in the former and indefinite graft survival in the latter. In contrast, OX-19 administration resulted in prolonged graft survival but at rejection there were significant numbers of OX-19+ cells present. Administration of MoAb W3/25 failed to affect a significant reduction in W3/25+ cells, but allograft survival was nonetheless prolonged.

In vivo use of monoclonal antibodies against murine T cell antigens

Experiments were performed seeking conditions for the optimum use of anti-T cell monoclonal antibodies in vivo in mice. Anti-L3T4 (CD4) and anti-Lyt2 (CD8) antibodies of different subclasses (IgG2b, IgG2a, and IgM) and species (rat or mouse) were used. The results showed that (i) intraperitoneal compared to intravenous administration of the different antibodies achieved the same serum levels whether in the presence or absence of the recipient's thymus; (ii) repeated treatment with a rat IgM anti-L3T4 or a rat IgG2b anti-Lyt2 antibody was followed by inability to detect serum levels of each antibody; (iii) in vivo treatment with these antibodies caused target cell lysis, target antigen masking without cell destruction, or target antigen modulation without cell destruction and the particular effect of a given antibody could not be predicted by its isotype or specificity; (iv) neither the C5 component of complement nor antibody-dependent cell-mediated cytotoxicity mediated the action of GK1.5 antibody in vivo; (v) dose-response curves of in vivo potency of a given antibody could not be predicted by in vitro assays; (vi) thymocytes were depleted by monoclonal antibody treatment by using 1000-fold more antibody than needed to deplete peripheral lymphocytes; (vii) the rate of return of target T cells after depletion in nonthymectomized mice depended on the dose of the antibody; and (viii) thymectomy prolonged the effect of most, but not all antibodies. In thymectomized mice, CD8+ cells remained almost undetectable for prolonged periods of time after depletion while CD4+ cells returned to approximately 30% of their original level and remained constant over time after initial complete depletion. These results provide useful data for the effective use of monoclonal anti-T cell antibodies in mice. They stress the difficulty of predicting the in vivo effects of monoclonal antibodies without actually testing them in vivo. They include new insights into mechanisms of action of monoclonal antibodies and the role of thymectomy in prolonging their effect. They describe the unrecognized ability of antibodies to deplete thymocytes.

T cell subsets mediating lethal graft versus host disease: demonstration that synergy between CD4+ and CD8+ T cells is the predominant mechanism in low responder rat strains

T cell subsets from rat strains that have been characterized as high and low responders to alloantigen were examined for their capacity to mediate lethal graft versus host disease (GVHD) across strain combinations incompatible for class I, class II, and non-MHC antigens. Inocula of 5 X 10(7) lymph node and spleen cells (LC) from low responder DA (RT1a) and high responder W/F (RT1u) strains caused lethal GVHD in (W/F X DA)F1 hybrids given 6 Gy whole body irradiation. W/F CD4+ (W3/25+) cells (2 X 10(7], equal to the number in 5 X 10(7) LC mediated lethal GVHD but 10(8) DA CD4+ cells were required to cause lethal GVHD. CD8+ (MRC OX8+) cells (5 X 10(7] from W/F rats alone caused lethal GVHD but those from DA rats could not. Mixtures of CD4+ and CD8+ DA T cells, equivalent to the number in 5 X 10(7) LC, did mediate lethal GVHD, demonstrating that synergy between the subsets was the predominant mechanism with DA cells. These results suggest that differences in alloreactivity between the strains tested may be due to alternate requirements for the alloactivation of T cell subsets; the high responder subsets being self-sufficient and the low responder subsets being dependent upon each other.

The roles of CD8+ and CD4+ cells in tumor rejection

In vivo administrations of anti-Lyt-2.2 (CD8) mAb and anti-L3T4 (CD4) mAb selectively eliminated CD8+ cells and CD4+ cells, respectively. The relative potencies of CD8+ cells and CD4+ cells and their roles in primary tumor rejections were studied by investigating the effects of these mAbs on tumor growth. CD8+ cells were themselves fully capable of mediating rejection in 5 different tumor rejection systems: two radiation leukemia virus (RadLV)-induced leukemias, B6RV2 and BALBRVD, a radiation-induced leukemia BALBRL male 1, and a plasmacytoma BALBMOPC-70A in CB6F1 mice, and a Friend virus-induced leukemia B6FBL-3 in B6 mice. On the other hand, CD4+ cells were capable of resisting tumor growth of B6FBL-3, but not of the other four tumors. Furthermore, for efficient rejection of CB6F1UV female 1 sarcoma by CB6F1 mice, synergy of CD8+ and CD4+ cells was necessary. Blocking of UV female 1 rejection was abrogated by delayed administration of anti-L3T4 (CD4) mAb but not anti-Lyt-2.2 (CD8) mAb, indicating the involvement of CD4+ cells in only the initial phase of rejection.

Cellular requirements for renal allograft rejection in the athymic nude rat

This study has examined the ability of adoptively transferred CD4+ and CD8+ T cells to mediate rejection of a fully allogeneic DA renal graft in the PVG nude rat. Transfer, at the time of transplantation, of naive CD4+ T cells caused rapid graft rejection and primed CD4+ cells were several times more potent. In contrast, naive or specifically sensitized CD8+ cells were entirely ineffective at mediating renal allograft rejection. Whereas nonrejecting grafts showed only a mild cellular infiltrate, rejecting grafts in CD4+ reconstituted animals showed a substantial infiltrate and many of the infiltrating cells had a phenotype (MRC OX8+, MRC OX19-), consistent with NK cells. Experiments using a mAb (HIS 41) against an allotypic determinant of the leukocyte common antigen confirmed that the majority (greater than 80%) of the cellular infiltrate in rejecting grafts derived from the host rather than from the CD4+ inoculum. Infiltrating mononuclear cells, obtained from rejecting allografts 7 d after transplantation in CD4+-injected PVG nude hosts, showed high levels of in vitro cytotoxicity against not only kidney donor strain Con A blasts but also third-party allogeneic Con A blasts, as well as against both NK and LAK susceptible targets. When splenocytes from nontransplanted nude PVG rats were tested in vitro they also demonstrated high levels of lytic activity against both NK and LAK susceptible targets as well as allogeneic Con A blasts, which were not susceptible to lysis by spleen cells from euthymic rats. These findings suggest that injected CD4+ cells may cause renal allograft rejection by the recruitment of extrathymically derived, widely alloreactive cells into the kidney in this model of graft rejection.

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 histocompatibility 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/ml 8-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.

Effect of elimination of OX-19+ and OX-8+ T-cell subsets upon pancreatic allograft survival

Depletion of T cell subsets with monoclonal antibody (mAb) permits analysis of cellular events mediating allograft destruction. Mab OX-19 and mAb OX-8 were used singly and in combination together with a short pretransplant course of cyclosporine A (CsA) to deplete OX-19+ cells (all T cells) and OX-8+ cells (cytotoxic/suppressor and NK cells), respectively, in diabetic Lewis (Lew) recipients of a Wistar Furth (WF) pancreatic allograft. Depletion of lymph node T cell subsets was assessed at rejection (blood sugar greater than 250 mg/dl) by flow cytometry. Untreated Lew recipients (Group 1) rapidly rejected their allograft (11.5 +/- 2.5 days). MAb OX-19 administration on the day prior to surgery (Day -1), on the day of surgery (Day 0), and alternate days thereafter until rejection (Group 2) prolonged graft survival (15.0 +/- 1.6 days, P less than 0.05). MAb OX-19 administration on alternate days beginning 14 days prior to transplantation (Day -14) until rejection (Group 3) further prolonged graft survival (22.6 +/- 3.4 days, P less than 0.01). At rejection large numbers of OX-19+ cells were present in both groups. Administration of mAb OX-8 alone (Group 4) failed to prolong graft survival despite marked depletion of OX-8+ cells at rejection. Administration of mAb OX-19 from Day -14 together with CsA (15 mg/kg) from Days -14 to -8 inclusive (Group 5) resulted in a marked and sustained depletion of OX-19+ cells at rejection but only a modest prolongation of graft survival (27.6 +/- 6.0 days, P = 0.11). CsA alone from Days -14 to -8 failed to prolong graft survival.(ABSTRACT TRUNCATED AT 250 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)

Antigen-presenting cells for unprimed T cells

The triggering requirements of T cells differ for primed and unprimed cells: primed T cells can be triggered to produce lymphokines without viable antigen-presenting cells (APCs), apparently by crosslinking the T-cell receptor (TCR). Unprimed T cells do, however, require viable APCs and here Jonathan Sprent and Mary Schaefer review what type of cells can carry out this function, with particular reference to APCs for unprimed CD8+ cells.

Inhibition of antiskin allograft immunity induced by infusions with photoinactivated effector T lymphocytes (PET cells)

Induction of tolerance for skin allotransplantation requires selective suppression of the host response to foreign histocompatibility antigens. This report describes a new approach which employs pre-treatment with 8-methoxypsoralen (8-MOP) and ultraviolet A light (UVA) to render the effector cells of graft rejection immunogenic for the syngeneic recipient. Eight days after BALB/c mice received CBA/j skin grafts, their splenocytes were treated with 100 ng/ml 8-MOP and 1 J/cm2 UVA prior to 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 and 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. BALB/c mice treated in this fashion retained a CBA/j skin graft for up to 42 days post-transplantation without visual evidence of rejection. These results showed that reinfusion of photoinactivated effector cells resulted in an immunosuppressive host response which specifically inhibited in vitro and in vivo responses that correlate with allograft rejection and permitted prolonged retention of histoincompatible skin grafts.

Evidence that the effector mechanism of skin allograft rejection is antigen-specific

In vivo rejection responses are initiated by specific T-cell recognition of foreign histocompatibility antigens expressed by tissue allografts, but it is not certain if the effector mechanism mediating the actual tissue injury is also antigen-specific. To directly assess the specificity of the effector phase of in vivo rejection responses, we constructed B6 in equilibrium with A/J allophenic mice that are genetic mosaics whose individual cells express either H-2b or H-2a histocompatibility antigens but not both. Trunk skin from B6 in equilibrium with A/J allophenic mice was grafted onto immunoincompetent H-2b nude mice and allowed to heal and regrow hair that was both black and white, reflecting the genetic mosaicism of the allophenic grafts. One month after engraftment, the H-2b nude animals were reconstituted with syngeneic H-2b T cells reactive against H-2a allodeterminants. An obvious rejection response ensued involving antigen-nonspecific inflammatory destruction of the epidermis and complete hair loss. Despite the intensity of the nonspecific inflammatory response, the allophenic skin grafts survived. Importantly, the allophenic grafts regrew hair and the predominant color of that hair was black, providing visual proof that syngeneic B6 melanocytes and hair follicle cells had not been destroyed. Thus, these results demonstrate that although the intense inflammatory component of skin graft rejection responses is capable of damaging superficial epidermal cells nonspecifically, it does not cause rejection of skin allografts. Rather, rejection of skin allografts is mediated by antigen-specific effector T cells that assess individual cells within the dermis of the graft for expression of foreign histocompatibility antigens.

Evidence for involvement of dual-function T cells in rejection of MHC class I disparate skin grafts. Assessment of MHC class I alloantigens as in vivo helper determinants

The present study further characterizes the cellular mechanisms involved in the in vivo rejection of MHC class I-disparate skin allografts. Previously, we demonstrated that class I-specific rejection responses could result from collaborations between distinct populations of lymphokine-secreting T helper (Th) and lymphokine-responsive T effector (Teff) cells. In the present study, we have assessed the possibility that class I-specific rejection responses could also result from a second cellular mechanism involving a single population of dual-function Th/Teff cells that would not have any further requirement for cell-cell collaboration. Our experimental strategy was to determine the ability of MHC class I-allospecific T cells, in response to class I allodeterminants expressed on skin grafts, to provide help in vivo for activation of helper-dependent Teff cells. We found that class I anti-Kbm1-allospecific T cells would reject bm1 skin allografts, but would not generate help for the activation of helper-dependent effector cells that were specific for third-party skin allografts (e.g., grafts expressing Kbm6, Qa1a, or H-Y allodeterminants). This failure of anti-Kbm1 T cells to provide help in response to bm1 skin allografts was not due to an inability of lymphokine-secreting anti-Kbm1 Th cells to recognize and respond in vivo to Kbm1 allodeterminants expressed on skin, since lymphokine-secreting anti-Kbm1 Th cells were specifically primed in animals engrafted with bm1 skin allografts. Nor was any evidence found that this failure was due to active suppression of anti-Kbm1 helper activity. Rather, we found that anti-Kbm1 T cells consumed nearly all of the helper factors they secreted. Taken together, these results are most consistent with the in vivo activity of dual-function Th/Teff cells that consume the lymphokines they secrete. Thus, this study demonstrates that MHC class I-disparate skin allografts can be rejected by two mechanisms, depending on the ability of the allospecific Teff cell to secrete helper lymphokines. MHC class I-disparate grafts can be rejected by (a) class I-allospecific Teff cells that are unable to produce lymphokine but are responsive to exogenous T cell help; and (b) class I-allospecific dual-function Th/Teff cells that are able to both produce and consume soluble lymphokine.

Reactivity of Ly-2+ T cells against 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells: specificity, frequency of interleukin 2-producing Ly-2+ helper T cells and clonal segregation from Ly-2+ cytotoxic T lymphocytes

The in vitro reactivity of purified murine Ly-2+ and L3T4+ T cells towards 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells was analyzed. Both T cell subpopulations autonomously proliferated and produced interleukin 2. In either the Ly-2+ or L3T4+ T cell subset the frequencies of TNP-specific interleukin 2 (IL 2)-producing T lymphocyte precursors (IL 2 TL-p) were equally high (f = 1/400-1/1000). Clonally developing IL 2 TL of either T cell subset showed an exquisite antigen (TNP) specificity as shown by the split culture approach. TNP-specific Ly-2+ IL-2 TL used class I MHC (H-2Kk) gene products as major histocompatibility complex (MHC) restriction elements, while L3T4+ IL 2 TL proved to be class II MHC (H-2I-AkI-Ek) restricted. Clonal segregation analyses revealed that the majority of clonally developing TNP-reactive Ly-2+ TL segregated into either IL 2 TL-p or cytotoxic T lymphocyte presursors, i.e. both functions appear to be mutually exclusive. Less than 10% of the responding Ly-2+ T cells seemed to be bifunctional. These findings provide compelling evidence for the L3T4+ T cell-independent, autonomous reactivity of Ly-2+ T cells in MHC-restricted antigen-specific responses and suggest T-T cell interactions within the functional heterogenous Ly-2+ T cell population.

Clinical applications of monoclonal antibodies in renal allograft biopsies

This study details the use of immunoperoxidase stains by monoclonal antibodies of core renal biopsy tissue. Subset analysis by appropriate monoclonal antibody is discussed with particular reference to the amount of, role for, and morphologic place of the various infiltrating cells. The role of monoclonal antibody staining of interleukin 2 (IL-2) receptor bearing lymphocytes and HLA class II antigen positive cells is also discussed. It was concluded that immunoperoxidase marker studies can determine the cell types, identify their location and functional status. This might be potentially useful for prognosis and for diagnosis of rejection and cyclosporine toxicity.

Role of T cell subsets in lethal graft-versus-host disease (GVHD) directed to class I versus class II H-2 differences. I. L3T4+ cells can either augment or retard GVHD elicited by Lyt-2+ cells in class I different hosts

Detailed information was sought on the capacity of purified Lyt-2+ cells to mediate lethal graft-versus-host disease (GVHD) directed to class I H-2 differences. When B6 Lyt-2+ cells were transferred to irradiated class I-different (B6 x bm 1)F1 mice, three different patterns of lethal GVHD were observed. First, rapid death from hematopoietic failure occurred when Lyt-2+ cells were transferred together with host-type marrow cells; this form of GVHD probably reflected direct destruction of stem cells by Lyt-2+ cytotoxic cells. Second, a pattern of late-onset, chronic GVHD resulting in death only after 4-6 wk occurred when Lyt-2+ cells were supplemented with donor marrow. This syndrome developed in the apparent absence of L3T4+ cells and was observed with either high or low doses of Lyt-2+ cells and with either light or heavy irradiation of the host. Third, an acute form of GVHD resulted when Lyt-2+ cells plus donor marrow cells were supplemented with exogenous help, i.e., by adding small doses of donor L3T4+ cells or injecting the hosts with rIL-2. Although L3T4+ cells potentiated GVHD when injected in small doses, supplementing Lyt-2+ cells with large doses of L3T4+ cells paradoxically led to marked protection; symptoms of GVHD were mild and no deaths occurred.

The mode of recognition of tumor antigens by noncytolytic-type antitumor T cells: role of antigen-presenting cells and their surface class I and class II H-2 molecules

The present study investigated the role of antigen-presenting cells (APC) in the activation of noncytolytic T cells against tumor antigens. The noncytolytic-type T cells exerted their antitumor effect by producing gamma-interferon (IFN-gamma) and by activating macrophages as the ultimate effectors. The production of IFN-gamma by these noncytolytic T cells following the stimulation with tumor cells required the participation of Ia+ APC, since the depletion of APC from cultures of tumor-immunized spleen cells resulted in almost complete inhibition of the IFN-gamma production. Both L3T4+ and Lyt-2+ subsets of T cells were capable of producing IFN-gamma, and the requirement of APC for the production of IFN-gamma was the case irrespective of whether noncytolytic T cells were of L3T4+ or Lyt-2+ phenotype. More importantly, it was demonstrated that the production of IFN-gamma by L3T4+ and Lyt-2+ T cells was inhibited by addition of the respective anti-class II and anti-class I H-2 antibody to cultures. These results indicate that antitumor L3T4+ or Lyt-2+ noncytolytic T cells are activated for the IFN-gamma production by recognizing tumor antigens in the context of self-class II or -class I H-2 molecules on APC.

Recognition requirements for the activation, differentiation and function of T-helper cells specific for class I MHC alloantigens

The present review has focused on the specificity of the T-helper cell populations initiating MHC class I alloreactions. In contrast to conventional immune responses against soluble antigens, responses against membrane-bound class I alloantigens are initiated by two distinct antigen-specific T-helper cell populations that can be distinguished by their Lyt phenotype, MHC restriction specificity, antigen specificity, and requirement for thymically determined self-recognition. Alloresponses were shown to be a composite consisting of two distinct components: one mediated by L3T4+ Th cells and very similar to conventional self + X responses; and one mediated by Lyt2+ Th cells and unique to alloresponses against MHC class I antigens. As would befit an unusual Th cell population, the recognition/response spectrum of Lyt2+ Th cells was highly unusual and was found to be the basis for much of the uniqueness we attribute to immune alloreactions, including rapid rejection of tissue allografts in vivo.