Peripheral tolerance to alloantigen results from altered regulation of the interleukin 2 pathway

Chimerism and tolerance to host and donor in severe combined immunodeficiencies transplanted with fetal liver stem cells

We have studied the peripheral T cell repertoire of two patients with severe combined immunodeficiency who were successfully treated with human histocompatibility leukocyte antigen (HLA)-mismatched fetal liver stem cell transplantation. The patients presented a split chimerism. T cells were of donor origin, whereas the B cells/monocytes were of the host phenotype. Interestingly, the natural killer (NK) cells in one patient were donor derived and in the other patient of host origin. The NK cells were functional but did not have antihost or donor reactivity. Despite the HLA mismatch between donor and host cells, complete tolerance was achieved in vivo, and a specific unresponsiveness of peripheral blood mononuclear cells from both patients toward the host cells was demonstrated in vitro. Nevertheless, we could isolate T cell receptor (TCR)alpha beta, CD4+ or CD8+, T cell clones specifically reacting with HLA class I and II molecules of the host. The CD4+ host-reactive T cell clones from both patients produced interleukins 2 and 5, interferon-gamma, granulocyte/macrophage colony-stimulating factor but are specifically defective in interleukin 4 production. The frequencies of CD8+ host-reactive T cells were high, and were in the same range as those observed for CD8+ alloreactive T cells. In contrast, no donor-reactive CD8+ T cells or host or donor-reactive TCR gamma delta + T cells were detected. These data indicate that, after fetal stem cell transplantation, donor-reactive, but not host-reactive cells, are deleted from the T cell repertoire. Therefore, a peripheral mechanism of suppression or clonal anergy, rather than clonal deletion, is involved in maintaining in vivo tolerance toward the host.

Analysis of activated T cell infiltrates in rat renal allografts by gamma camera imaging after injection of 123iodine-interleukin 2

Activated T cells bearing receptors for interleukin 2 (IL-2) play an important role in immunity and in immunopathological processes such as allograft rejection. In order to investigate the presence of activated T cells in lymphocytic infiltrates in transplanted kidneys, we investigated the uptake and retention of radioactivity after an intravenous injection of radioiodinated IL-2 in experimentally transplanted rats. IL-2 was enzyme radiolabelled with 123iodine using a glucose oxidase/lactoperoxidase method and shown to retain specific binding on an IL-2 receptor positive cell line, C58E6. To examine the kinetics of 123iodine-interleukin 2 (123I-IL-2) uptake in vivo, animals that had been transplanted five days previously with allogeneic or syngeneic grafts were injected with 123I-IL-2 and then imaged using an external gamma camera. Radioactivity was measured at time points up to 240 min after intravenous injection of 123I-IL-2. Four groups of animals were examined: allogeneic grafts (n = 7); syngeneic grafts (n = 6); ischaemic native kidneys (n = 5) all following injection with 123I-IL-2; and allogeneic transplants (n = 5) after injection of 123I-lactalbumin, an irrelevant molecule of similar molecular weight to IL-2. The peak radioactivity after injection was measured and the amount of radioactivity retained in the graft at increasing time intervals after injection was expressed as a function of initial peak radioactivity. At four hours after injection of 123I-IL-2, mean retention of activity by rejecting grafts was 77(+/- 2.68)% of peak activity, compared to 45(+/- 6.38)% in syngeneic controls (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved survival from potentially lethal graft-vs.-host disease by donor pretreatment with a recipient-specific blood transfusion. II. Evidence for a principal role of the CD4+ T cell subset

Pretreatment of prospective donors of hemopoietic cells with a single recipient-specific blood transfusion can significantly decrease the morbidity and mortality of potentially lethal graft-vs.-host disease (GVHD) in lethally irradiated, allogeneically reconstituted mice. In a previous report we described the requirements for induction of this blood transfusion effect. In the present study we addressed in particular the mechanism underlying this effect. The beneficial effect of blood transfusion appeared to be due to the white blood cell population in the transfused blood. X-irradiation (20 Gy) of the blood prior to transfusion did not abrogate the effect, which makes a veto cell mechanism unlikely. The blood transfusion effect in this model appeared to be mediated by the CD4+ T cell subset, since purified CD4+ spleen cells from transfused donors caused considerably less morbidity and mortality than naive CD4+ spleen cells. Apparently CD8+ cells were not involved, because their absence did not affect the beneficial effect. This observation was further confirmed by the finding that treatment of recipient mice that were reconstituted with spleen cells from transfused donors with anti-CD8 monoclonal antibody (mAb) did not abrogate the blood transfusion effect. Interestingly, the blood transfusion effect was enhanced by administration of anti-CD4 mAb to the recipients. The anti-CD4 mAb might impair the interaction between T cells and antigen-presenting cells, resulting in functional inactivation.

A protective NOD islet-infiltrating CD8+ T cell clone, I.S. 2.15, has in vitro immunosuppressive properties

Type 1, insulin-dependent diabetes mellitus (IDDM) appears to result from a T cell-dependent destruction of insulin-producing pancreatic beta cells. In non-obese diabetic (NOD) mice and in other rodent models of human IDDM, final expression of disease may be controlled by protective, as well as, destructive T cell influences. Previously, a CD8+ T cell clone, I.S. 2.15, was isolated directly from islets of disease-resistant male NOD mice. Upon transfer to young NOD recipients, the non-cytolytic I.S. 21.5 T cell clone, confers in vivo protection from two forms of accelerated IDDM. The present study demonstrates that I.S. 2.15 T cells induce in vitro immunosuppression. The suppressive effects of I.S. 2.15 T cells are mediated through soluble factor(s) and are independent of T cell activation, cell contact, antigen specificity or the major histocompatibility complex (MHC). By polymerase chain reaction (PCR), I.S. 2.15 T cells contain mRNA species encoding for the potentially immunosuppressive cytokines, interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). The T cell suppressive effects engendered by I.S. 2.15 T cells closely mimic those observed with TGF-beta. Moreover, I.S. 2.15-induced immunosuppression correlates with intracellular levels of TGF-beta mRNA. These results establish that immunoregulatory T cells are present within islets in IDDM-resistant NOD mice and may impact on final disease expression through the production of soluble mediator(s).

Extrathymic T-cell selection

The T-cell repertoire is formed during T lymphocyte maturation in the thymus. There is, however, increasing evidence that there are additions to, and modifications of, this repertoire by extrathymic events. Most importantly, mature peripheral T cells are not only susceptible to activation signals but also to tolerance induction upon encounter of extrathymic antigen. An understanding of these inactivation processes should result in strategies for specific immunosuppression in organ transplantation and autoimmune diseases.

A monoclonal antibody to the interleukin-2 receptor enhances the survival of neural allografts: a time-course study

A time-course study of the survival and immunological characteristics of rat neural allografts was undertaken in animals treated with a murine monoclonal antibody to the alpha-chain (p55) of the rat interleukin-2 receptor. This antibody, NDS 63, was administered for ten days following grafting beginning on the day of operation. Inbred rat strains differing at both major and minor histocompatibility loci were selected as donor and host. Furthermore, the recipient strain displayed a high responder major histocompatibility complex haplotype. All grafts were placed in the lateral ventricle. Comparison was drawn between NDS 63-treated recipients and two groups of controls; an untreated group and a second group treated with the monoclonal antibody NDS 66, directed at a second epitope on the alpha-chain of the interleukin-2 receptor, which has been shown to be ineffective in competing with interleukin-2 for binding. Immunocytochemical analysis of the transplants was performed at several time-points up to 150 days following grafting. Grafts of NDS 63-treated recipients exhibited 100% survival with minimal induction of major histocompatibility complex antigens (both class I and class II) and negligible leukocyte infiltration at all time-points studied. In contrast grafts from both groups of controls showed evidence of a chronic immune response with most grafts undergoing rejection as shown by markedly elevated major histocompatibility complex antigen expression accompanied by specific immune cell infiltration. This was a protracted process with several grafts undergoing complete rejection by 60 days and a majority, but not all, by 150 days after transplantation. It is concluded that NDS 63, a monoclonal antibody to the interleukin-2 receptor, may diminish the immune response to transplanted allogeneic neural tissue and thereby enhance its prospects for long-term survival.

Transplantation tolerance in heart transplant recipients as demonstrated by unresponsiveness in cell-mediated lympholysis

Transplantation tolerance or adaptation to an allograft is associated with unresponsiveness to donor-specific transplantation antigens measured in in vitro cell-mediated lympholysis (CML). We here demonstrate in a longitudinal follow-up that CML nonreactivity develops in seven of ten patients following heart transplantation. The first manifestation of this nonreactivity manifested between 3 and 27 months after transplantation. CML nonreactivity correlated with time after transplantation and the percentage of activated lymphocytes in peripheral blood. CML nonreactivity was also associated with good graft function, i.e., in condition of nonresponsiveness patients did not manifest acute rejection. The only exception was seen in one patient in whom the immunosuppressive therapy was strongly reduced. A more detailed evaluation of this patient indicated that the underlying mechanism for CML nonreactivity is clonal anergy or active suppression of the alloreactive cells.

Immunosuppression induced by hepatic portal venous immunization spares reactivity in IL-4 producing T lymphocytes

Immunization of naive or specifically primed C3H/HEJ with irradiated B10.BR spleen cells via the hepatic portal vein leads to an antigen specific decrease in the proliferative and cytotoxic response to B10.BR antigen assayed in vitro (and to increased graft survival of B10.BR grafts in vivo). This effect seems to be mediated in the main by a decrease in IL-2 production from CD4+ T lymphocytes of mice given antigen by the portal route, which is in turn caused by a decreased precursor frequency of IL-2-producing cells. No clear decrease in IL-4 production was seen. Hepatic APC isolated from mice receiving antigen via the portal vein were unable to induce IL-2 production from a C3H/HEJ anti-B10.BR cell line in vitro, in contrast to splenic APC derived from the same mice. Even when antigen was given by conventional (systemic) intravenous routes (in this case via the lateral tail vein) hepatic APC isolated from those mice were unable to stimulate IL-2 production from this cell line. Furthermore, 24 h exposure of a cell line to antigen pulsed hepatic APC left those cells refractory to a subsequent restimulation with antigen presented by splenic APC. Spleen lymphoid cells from primed mice challenged in vivo with B10.BR liver cells (i.v.) were similarly unable to produce IL-2 on rechallenge in vitro with irradiated B10.BR spleen cells, though no defect was seen if in vivo challenge was with B10.BR spleen cells. These data imply that presentation of multiple minor cell surface antigens by hepatic APC leads to specific anergization of IL-2 producing T cells, in a fashion which seems to be distinct from that previously reported as due to 'veto-like' activity.

Inflammation but not autoimmunity occurs in transgenic mice expressing constitutive levels of interleukin-2 in islet beta cells

Transgenic mice expressing murine interleukin (IL)-2 constitutively in islet beta cells were generated (RIP-IL-2 mice). They died at an early age, when higher levels of IL-2 were produced, because of a predominant macrophage inflammatory response that destroyed the exocrine pancreas. Animals with lower levels of IL-2 survived and had islets that became increasingly infiltrated with lymphocytes over time. However, in spite of the presence of impressive peri- and intra-islet infiltrates, autoimmunity to islet antigens was not seen. Autoimmunity was also not induced to extrathymic H-2Kb molecules known to induce tolerance by a peripheral mechanism when the RIP-IL-2 mice were mated to other mice expressing H-2Kb in islet beta cells (RIP-Kb mice). Apparently, IL-2 can act only on activated T cells and is unable to reverse tolerance in T cells that have been made unresponsive through inappropriate presentation of antigen.

Acute rejection in heart transplant patients is associated with the presence of committed donor-specific cytotoxic lymphocytes in the graft but not in the blood

In vivo-activated, committed donor-specific cytotoxic lymphocytes (cCTL) can be propagated and expanded from endomyocardial biopsies (EMB) in IL-2-enriched medium especially during an acute rejection episode. We report here our efforts to detect these cCTL by the same technique in peripheral blood at the moment of rejection and when no rejection was diagnosed. During or just before rejection, significantly less frequent (P less than 0.01) donor reactive cCTL were found in PBL samples (two out of 20) than in the simultaneously taken EMB samples (13 out of 19). Donor B-LCL and/or third-party B-LCL were lysed by 15 PBL samples. Inhibition studies revealed that this lysis was due to LAK-like cytotoxicity. The results show that peripheral blood does not reflect intra-graft events, which is probably the reason for the irreproducible results of diagnosis of rejection by monitoring immunological parameters in the peripheral blood.

Polymerase chain reaction for detection of cytokine gene expression

A powerful method to amplify reverse-transcribed RNA, the polymerase chain reaction can be used to measure cytokine gene transcription in a small number of cells, or in cases where there is low mRNA copy number. This technique may be used to obtain qualitative or quantitative determinations of cytokine gene expression. In this review we discuss the various strategies recently described for the evaluation of cytokine expression using the polymerase chain reaction.

Post-thymic tolerance to self antigens

There is now convincing evidence for the imposition of self-tolerance by means of the clonal deletion of self-reactive T cells operating within the thymus. Since not all self components may be encountered there, the question must be asked whether tolerance can occur post-thymically. To test this, we have used transgenic technology to direct expression of a known 'non-self' gene, H-2Kb, to the insulin producing beta cells of the pancreas of mice. H-2Kb-bearing skin, but not skin from other mouse strains, failed to be rejected by the 'RIP-Kb' transgenic mice indicating specific tolerance. Following in vitro stimulation, their spleen cells could not kill H-2Kb-bearing targets, but could respond to third party targets. Their reactivity to H-2Kb was restored by providing them with IL-2. Two hypotheses could account for the above: tolerance results either from the deletion or functional silencing of high affinity effector cytotoxic cells or of regulatory, IL-2-producing helper T cells. Since it is difficult to distinguish between these, we have produced a second series of transgenic mice with rearranged T cell receptor (TCR) genes encoding an anti-H-2Kb TCR, and obtained 'double transgenic' offspring by mating these mice with RIP-Kb mice. The TCR utilized the V beta 11 segment which can be detected by a monoclonal antibody. Although the double transgenic mice were tolerant of H-2Kb, there was no evidence of deletion of anti-H-2Kb T cells. It seems, therefore, that a non-deletional mechanism operates to induce post-thymic tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Ly-1 B (B-1) cells are the main source of B cell-derived interleukin 10

We have previously reported (O'Garra, A. et al., Int. Immunol. 1990, 2:821) that murine B lymphomas and purified normal peritoneal B cells produce interleukin (IL) 10. We now show that this production of IL 10 B cells correlates with the presence of Ly-1 (B-1) B cells, in both normal and diseased mice. Using a semi-quantitative modification of the polymerase chain reaction, we show that IL 10 expression is detectable in peritoneal B cells but only becomes apparent in splenic B cells of aged mice of which a high proportion are Ly-1+. Furthermore, the expression of IL 10 is constitutive in splenic B cells from mice carrying the Ly-1+ BCL1 lymphoma. Since IL 10 is a potent regulator of in vitro immune function, its production by Ly-1 lineage B (B-1) cells raises the possibility that this subset of B cells may regulate their own development and/or the function of other immunocompetent cells.

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.

T-cell growth factors and the treatment of patients with cancer

T-cell maturation has traditionally been felt to occur primarily within the thymus but it is now clear that dynamic processes in the periphery govern many functions such as T-cell activation, proliferation, tolerization, and migration into peripheral tissues. Four T-cell growth factors have now been identified. These include: interleukin-2 (IL-2), IL-4, IL-7, and a potent cofactor recently described, IL-10. These factors are believed to work synergistically in the fine regulation of the lymphoid pool. Both IL-2 and IL-4 have entered clinical trials with significant responses in the IL-2-based regimens of up to 40 to 50% in certain tumors. IL-7 and IL-10 are in preclinical studies. Although IL-2, IL-4, and IL-7 have been shown to induce lymphokine-activated killer cell activity from sensitive precursors, such studies have yet to be performed with IL-10.

The role of cell division in the induction of clonal anergy

The interaction of antigen with lymphocyte antigen receptors can result in either clonal expansion or unresponsiveness (anergy). In 1970, Bretscher and Cohn proposed a two-signal model of lymphocyte activation to explain this paradox: antigen receptor occupancy alone could induce unresponsiveness whereas antigen receptor occupancy plus a costimulatory signal could induce immunity. Here, Marc Jenkins reviews in vitro and in vivo manifestations of clonal anergy and evaluates the ability of the two-signal model to explain these phenomena.

Cytokines and Ly-1 (B1) B cells

In an attempt to elucidate the possible role of cytokines in autocrine growth of Ly-1+B cells, and the role of this subset of B cells in immune regulation, both in normal and diseased hosts, we have performed a systematic analysis of cytokine production by a series of mouse Ly-1+B lymphomas, as well as normal peritoneal Ly-1+ and conventional B cells. The lymphomas all express TGF-beta, and some express IL-3 and IL-4. We observed that both the lymphomas and the peritoneal cells produce TNF-alpha, TNF-beta and IL-6. Another cytokine, IL-10, is produced predominantly by peritoneal Ly-1+B cells from healthy mice and by Ly-1+ B lymphomas, but not by conventional B cells. As IL-10 regulates the production of monokines and a subset of T-cell derived cytokines, our results suggest a broad immunoregulatory role for Ly-1 B cells. To complement these studies we have also examined the responses of Ly-1 B cells to mitogens and cytokines previously shown to stimulate conventional B cells. In summary, Ly-1 B cells, in contrast to conventional B cells do not respond to anti-Ig antibodies, even in the presence of IL-4. They do respond to LPS, and this response is preferentially enhanced by IL-5, and marginally enhanced by IL-3. Surprisingly LPS-induced proliferation of peritoneal B cells is inhibited by IL-6 and to a greater extent by IL-10. Whether this inhibition is a result of differentiation into Ig secreting cells is currently being evaluated. We discuss our findings in terms of the potential of Ly-1 B cells to regulate their own development and the immunocompetence of other cells.

Transplantation tolerance

New experimental protocols for the induction of transplantation tolerance continue to be developed. In the past year, encouraging data have been reported from a clinical trial using a protocol specifically designed to induce tolerance to the histocompatibility antigens of the kidney donor. Progress has also been made in our understanding of the mechanisms responsible for the induction and maintenance of tolerance to alloantigens in vivo; it is becoming increasingly clear that more than one mechanism can be involved, particularly at different phases in the response.

Molecular cloning of cDNAs for the rat interleukin 2 receptor alpha and beta chain genes: differentially regulated gene activity in response to mitogenic stimulation

We have isolated, by transient expression and screening using an oligonucleotide probe, cDNA clones encoding the rat interleukin 2 receptor (IL 2R) alpha and beta chains, respectively. Both chains are approximately 60% identical at the amino acid level to their human counterparts. In common with the human and mouse IL 2R beta chains, the rat beta chain is a member of the cytokine receptor family. The rat IL 2R beta chain contains no conventional signal transduction machinery and, like the mouse IL 2R beta chain, has a significant number of deletions in its cytoplasmic tail in comparison to the human protein. Northern analysis indicates that the rat beta chain message is constitutively transcribed in normal resting lymphocytes, whereas the alpha chain message is absent. Transcription of both chains of the receptor is up-regulated by cellular activation. However, kinetic studies have shown that whereas alpha chain message is rapidly induced, and can be detected 5 h after the addition of phytohemagglutinin, levels of beta chain mRNA increase at a much later time point and are not seen to rise until approximately 24 h after the addition of mitogen. These data suggest that the expression of high-affinity IL 2R is controlled by factors which influence transcription of both the alpha and the beta chain genes.

A transgenic approach to the study of peripheral T-cell tolerance

There is now convincing evidence for the imposition of self tolerance by means of the clonal deletion of self-reactive T cells operating within the thymus. Since not all self components may be encountered there, the question must be asked whether tolerance can occur post-thymically. To test this, we and other investigators have used transgenic technology to direct expression of a known "nonself" gene to a given extrathymic tissue. No lymphocytic infiltration was ever seen in transgene-expressing tissues, even if the mice were given normal syngeneic (nontransgenic) spleen cells intravenously or were stimulated with H-2Kb spleen cells. Infiltration did, however, occur in irradiated transgenic recipients of H-2Kb immune spleen cells. In MET-Kb mice, this infiltrate diminished with time, raising the possibility that peripheral tolerance may even have been induced in immune cells. H-2Kb-bearing skin was accepted in young RIP-Kb mice but rejected in older mice, which had lost more than 75% of their beta cells as a result of the overexpression of H-2Kb. This loss of tolerance thus occurred when the concentration of the tolerogen, H-2Kb, fell below some critical threshold. Following in vitro stimulation, spleen cells from young RIP-Kb mice could not kill H-2Kb-bearing targets, but could respond to third party targets. Thymus cells, on the other hand, could be stimulated to kill both targets, clearly indicating that tolerance was not imposed intrathymically. Spleen cells from older RIP-Kb mice (those that had lost most of their beta cells) killed both targets, which is in agreement with the in vivo data. Reactivity to H-2Kb was restored to young spleen cells by providing them with IL-2. Two hypotheses were proposed to account for the above findings: tolerance results either from the deletion or functional silencing of high-affinity effector cells or of regulatory, IL-2-producing helper T cells. As it is difficult to distinguish between these, we have produced a second series of transgenic mice (F3+) with rearranged TCR genes encoding an anti-H-2Kb TCR and derived "double-transgenic" (F3+RIP+) offspring by mating these mice with RIP-Kb mice. The transgenic TCR utilized the V beta 11 segment which can be detected by a monoclonal antibody. There were in the thymus very few CD4+ and very few CD4+8+ cells in both F3+ and F3+RIP+ mice and, in the double-transgenic mice, there was no evidence of deletion of CD8+V beta 11+ cells in the periphery although they showed tolerance to H-2Kb-bearing skin.(ABSTRACT TRUNCATED AT 400 WORDS)