Idiotypic manipulation of the immune response to transplantation antigens

Thymic microchimerism correlates with the outcome of tolerance-inducing protocols for solid organ transplantation

This study found that pretransplant infusion of donor peripheral blood leukocytes, either total leukocytes (peripheral blood leukocytes) or peripheral blood mononuclear cells (PBMC), under appropriate immunomodulating conditions was more effective than donor bone marrow (BM) in prolonging the survival of rats that received kidney grafts. A higher percentage of MHCII(+) cells was found in donor PBMC than in BM cells, and depletion of MHCII(+) cells from donor PBMC abolished their tolerogenic potential. By the analysis of microchimerism in rats infused with donor cells and killed at different time points thereafter, the better tolerogenic potential of leukocyte infusion related to a higher capability of these cells to engraft the recipient thymus. PCR analysis on OX6-immunopurified cells revealed the presence of donor MHCII(+) cells in the thymus of these animals. The role of intrathymic microchimerism was reinforced by findings that thymectomy at the time of transplant prevented tolerance induction by donor leukocytes. Donor DNA was found in the thymus of most long-term graft animals that survived, but in none of those that rejected their grafts. The presence of intrathymic microchimerism correlated with graft survival, and microchimerism in other tissues was irrelevant. PCR analysis of DNA from thymic cell subpopulations revealed the presence of donor MHCII(+) cells in the thymus of long-term surviving animals. Thus, in rats, donor leukocyte infusion is better than donor BM for inducing graft tolerance, defined by long-term graft survival, donor-specific T cell hyporesponsiveness, and reduced interferon gamma production. This effect appears to occur through migration of donor MHCII(+) cells in the host thymus.

The effects of chimeric cells following donor bone marrow infusions as detected by PCR-flow assays in kidney transplant recipients

40 recipients of first cadaver kidney transplants were given perioperative donor vertebral bone marrow infusions (DBMC), compared with 100 controls who did not receive donor bone marrow. The immunosuppressive regimen included OKT3, Tacrolimus, and steroid maintenance therapy, and, in some patients, newly introduced mycophenolate mofetil. This report describes the 24-mo actuarial follow-up and several immunological monitoring studies including sequential measurements of donor bone marrow lineage subset chimerism by the recently reported PCR-flow assay. This is a sensitive in situ PCR detection system for donor versus recipient histocompatibility genes as well as cell surface CD epitope markers using flow cytometry. The results indicate (a) the stabilization of the donor CD3+ and CD34+ cells in recipient peripheral blood at levels below 1% between 6 mo and 1 yr postoperatively, with a 10-fold higher level of donor cell chimerism of these lineages in recipient iliac crest marrow; (b) significantly lower levels of chimerism in peripheral blood up to 6 mo postoperatively in patients who had early acute (reversible) rejection episodes compared with those who did not; (c) a higher degree of chimerism seen in patients who were class II MHC HLA DR identical with their donors; (d) the identification of a high proportion of the donor bone marrow derived CD3 dimly staining subset of T cells (to which regulatory functions have been ascribed) in recipient peripheral blood and especially in recipient bone marrow; and (e) an unexpectedly increased susceptibility to clinically significant infections (primarily viral), and even death in the DBMC-infused group, compared with controls, but no graft losses because of rejection in the DBMC-infused group. Mixed lymphocyte culture assays showed a trend toward a greater number of nonspecifically low reactors in the DBMC group, as well as a greater number of nonspecifically high reactors in the controls (P = 0.058). The autologous mixed lymphocyte reaction also indicated a trend towards nonspecific immune activation in the DBMC group. Finally, anti-cytomegaloviral IgG antibody reactivity was significantly inhibited in the DBMC group 4-6 mo postoperatively (P = < 0.05). In the controls, there were no donor cell lineages detected by PCR-flow in the peripheral blood. These rather unexpected findings, indicating a more depressed cellular and humoral immune capacity in the DBMC cadaver kidney transplant recipients in this relatively early follow-up period, are discussed relevant to chimerism, MHC restriction, and suppressor activity brought about by specialized DBMC subsets, which still need to be defined.

Human CD4 "internal antigen" mimicry by anti-idiotypic monoclonal antibodies

Of 1019 hybridomas generated from a BALB/c mouse immunized with the syngeneic anti-CD4 monoclonal antibody HP2/6, 3 were found to secrete anti-idiotypic antibodies. Detailed analysis of anti-idiotypic monoclonal antibodies F16-10F6, F16-14D6 and F16-16D7 showed they recognize idiotope(s) not expressed by any of the anti-CD4 monoclonal antibodies tested, including those which inhibit the binding of HP2/6 to CD4 antigen. The idiotope recognized by the three anti-idiotypic antibodies are within (or closely related to) the antigen combining site of the immunizing antibody and distinct and spatially distant from the idiotope defined by monoclonal antibody F11-2302 which was previously shown to be outside the antigen combining site of HP2/6. Although F16-14D6 and F16-16D7 are indistinguishable in isotype, binding titer to idiotopes, fine specificity on a panel of monoclonal antibodies, relation to the combining site and competitive binding, it is likely that they are structurally different and recognize two distinct combining site-related idiotopes on HP2/6, as they display different spectrotypes and induce anti-anti-idiotypic (Ab3) immune sera with different specificities. Analysis of the fine specificity of the two Ab3 immune sera suggest they share idiotopes with HP2/6 and contain antibodies reacting with CD4 antigen. Among the latter, those induced with F16-14D6 display a different CD4 epitope specificity than HP2/6. Hence, anti-idiotypic antibodies F16-14D6 and F16-16D7 behave as "network antigen" for human CD4; idiotope-triggered antibody cascade may have a role in changing the specificities of antibody.

Immunomodulation of kidney and heart transplants by anti-idiotypic antibodies

To explore the possibility that circulating HLA antigens from the graft and anti-anti-HLA (anti-idiotypic) antibodies influence the long-term survival of renal and cardiac allografts, analysis of 330 renal allograft recipients and 174 recipients of cardiac allografts was conducted. Anti-donor-HLA antibodies (Ab1) present before or after transplantation are associated with graft failure, whereas irrelevant anti-HLA antibodies had no impact on actuarial graft survival. Ab1 may be uncovered by dissociation of immune complexes and depletion of soluble antigens with monoclonal antibody-coated magnetic beads. Of the 421 sera tested from 65 heart recipients, 97 showed Ab1 before depletion and 178 after depletion; similar rise in positive sera was seen in 39 renal transplant recipients. Three distinct patterns of appearance of Ab1 and Ab2 (anti-Ab1 antibody) were recognized. Patients with cyclic variations of Ab1 in association with Ab2 had 100% graft survival, whereas patients with cyclic variations of Ab1 but no detectable Ab2 had 2-year graft survival of 36% for kidneys and 71% for hearts. Presence of Ab1 in all sera after transplantation led to 47% and 56% 2-year renal and heart allograft survival, respectively.

Influence of antiidiotypic antibody activity on renal transplant outcome

The presence of cytotoxic HLA antibodies (Ab1) against donor lymphocytes in pretransplant sera is almost always associated with rapid rejection of the renal transplant. We have investigated the possibility that antiidiotypic antibodies (Ab2) to cytotoxic HLA antibodies might modulate the immune response and favorably influence renal allograft outcome. The role of antibodies (Ab3) which potentiate the cytotoxic effect of Ab1 was also studied. Pretransplant sera from 63 patients were tested for inhibitory or potentiating activity in the short antiidiotypic assay. Inhibitory activity was detected in 30 patients and in 28 the transplant survived more than a year. Of patients without antibody activity 11 of 17 had grafts surviving more than one year, and of those showing potentiating activity 11 of 16 were functioning at a year. The difference in transplant survival between the first group and the other two groups was statistically significant (P less than 0.05). There was no significant difference in survival rates between the latter two groups. Potentiating activity is therefore not an independent predictor of transplant failure, whereas the presence of antiidiotypic antibody activity did correlate with improved allograft survival.

Structure and specificity of a class II MHC alloreactive gamma delta T cell receptor heterodimer

Two distinct CD3-associated T cell receptors (TCR alpha beta and TCR gamma delta) are expressed in a mutually exclusive fashion on separate subsets of T lymphocytes. While the specificity of the TCR alpha beta repertoire for major histocompatibility complex (MHC) antigens is well established, the diversity of expressed gamma delta receptors and the ligands they recognize are less well understood. An alloreactive CD3+CD4-CD8- T cell line specific for murine class II MHC (Ia) antigens encoded in the I-E subregion of the H-2 gene complex was identified, and the primary structure of its gamma delta receptor heterodimer was characterized. In contrast to a TCR alpha beta-expressing alloreactive T cell line selected for similar specificity, the TCR gamma delta line displayed broad cross-reactivity for multiple distinct I-E-encoded allogeneic Ia molecules.

Potential role of anti-idiotype antibodies in active tumor immunotherapy

The tumor-specified cellular and humoral immunity induced by anti-idiotype antibodies (Ab2s) 2F10 and 3A4 has been studied. Ab2s were made against a monoclonal anti-L1210/GZL lymphoma, 11C1. They were screened for their ability to block 11C1 binding to tumor, induce tumor-specific DTH and CTL responses, and induce an anti-tumor humoral response. Two Ab2s, 2F10 and 3A4, which were found to have similar fine specificity and to induce similar cellular and humoral responses, were compared for their ability to elicit tumor-protective immunity. Interestingly, only preimmunization with the 2F10 Ab2 protected animals from live tumor challenge. The possible causes for this discriminatory biological effect induced by otherwise similar Ab2s are discussed.

Current concepts: immunology. Transplantation immunology

The MHC is of overwhelming importance in determining the fate of an allograft. Over the past 10 years, our understanding of the serology of this locus, its role in cellular immunity, its biochemistry, and most recently, its molecular biology has increased enormously. Genes for all the known loci, both Class I and Class II, have been cloned and sequenced, and their evolution and function are therefore now more amenable to investigation at the molecular level. Concomitantly, an understanding of the different populations of immune cells involved in the recognition of the antigens encoded by these loci has permitted a more precise immunologic description of the rejection response. It is now clear that recognition of both Class I and Class II allogeneic differences by both helper and cytotoxic T cells has an important role in graft rejection. The goal of transplantation biologists is to take advantage of this increased understanding in order to design new techniques for specifically modifying the immune response to MHC antigens and achieving specific tolerance. Some exciting approaches are already being studied, including specific modifications of both the antigen and the receptor arms of the immune response. It is hoped that these approaches will have new clinical applications in the near future.

Effect of antiidiotypic antibodies to HLA on graft survival in renal-allograft recipients

Although the presence in the recipient of preformed antibodies to HLA antigens in the kidney of a renal-transplant donor may be associated with early graft failure, such grafts are often well tolerated. We have investigated the possibility that anti-anti-HLA (antiidiotypic) antibodies influence the outcome of renal transplantation in recipients with a history of presensitization to their donor's HLA antigens. A retrospective analysis of 20 such cases showed that in 10 patients the transplanted kidney was rejected within one month, whereas in the remaining 10 the graft was tolerated for more than a year. Nine of the 10 patients in whom the graft was tolerated had anti-anti-HLA antibodies at the time of transplantation. Nine of the 10 patients in whom the graft was rejected had antibodies that potentiated, rather than blocked, the cytotoxic activity of anti-donor-HLA antibodies. These results suggest that patients with anti-anti-HLA antibodies specific for a potential donor can safely undergo transplantation, despite a prior history of anti-HLA antibodies. At the time of transplantation, patients who have antibodies that potentiate the cytotoxic activity of a historically positive serum are at high risk of graft rejection within a short period. Taking these considerations into account may improve the reliability of cross-matching in renal transplantation.

DNA antibody idiotypes: a review of their genetic, clinical, and immunopathologic features

The initial studies of anti-DNA antibody idiotypes we performed, along with those of our colleagues and other groups, focused on the narrow question of their relevance to lupus autoantibodies. The subsequent studies in this report have forced us to examine a much broader range of issues. It is evident that despite the great advances in understanding the structure and function of antibodies, lymphocytes, and receptors, our knowledge of many fundamental elements in autoimmune disease is woefully incomplete. We are still unsure whether the germ line gene sequences controlling antibody production have evolved solely in response to exposure to new foreign antigens. Alternatively, these antibodies (and the idiotypes they bear) may have developed largely in response to changes in the internal environment. Superficially, it can be argued that "self reactivity" associated with the clinical expression of a disease results from a combination of immunologic, genetic, hormonal, and environmental elements. For example, the expression of the 16/6 Id in an appropriate setting may have pathogenetic consequences for some individuals. However, our knowledge of the precise sequence of events that result in devastating disease for some but minimal disease for others is just one of the remaining mysteries.