The role of antibodies in the rejection and enhancement of organ allografts.?7318

Transplant Tolerance, Not Only Clonal Deletion

The quest to understand how allogeneic transplanted tissue is not rejected and how tolerance is induced led to fundamental concepts in immunology. First, we review the research that led to the Clonal Deletion theory in the late 1950s that has since dominated the field of immunology and transplantation. At that time many basic mechanisms of immune response were unknown, including the role of lymphocytes and T cells in rejection. These original observations are reassessed by considering T regulatory cells that are produced by thymus of neonates to prevent autoimmunity. Second, we review "operational tolerance" induced in adult rodents and larger animals such as pigs. This can occur spontaneously especially with liver allografts, but also can develop after short courses of a variety of rejection inhibiting therapies. Over time these animals develop alloantigen specific tolerance to the graft but retain the capacity to reject third-party grafts. These animals have a "split tolerance" as peripheral lymphocytes from these animals respond to donor alloantigen in graft versus host assays and in mixed lymphocyte cultures, indicating there is no clonal deletion. Investigation of this phenomenon excludes many mechanisms, including anti-donor antibody blocking rejection as well as anti-idiotypic responses mediated by antibody or T cells. This split tolerance is transferred to a second immune-depleted host by T cells that retain the capacity to effect rejection of third-party grafts by the same host. Third, we review research on alloantigen specific inhibitory T cells that led to the first identification of the CD4+CD25+T regulatory cell. The key role of T cell derived cytokines, other than IL-2, in promoting survival and expansion of antigen specific T regulatory cells that mediate transplant tolerance is reviewed. The precise methods for inducing and diagnosing operational tolerance remain to be defined, but antigen specific T regulatory cells are key mediators.

Non-canonical B cell functions in transplantation

B cells are differentiated to recognize antigen and respond by producing antibodies. These activities, governed by recognition of ancillary signals, defend the individual against microorganisms and the products of microorganisms and constitute the canonical function of B cells. Despite the unique differentiation (e.g. recombination and mutation of immunoglobulin gene segments) toward this canonical function, B cells can provide other, "non-canonical" functions, such as facilitating of lymphoid organogenesis and remodeling and fashioning T cell repertoires and modifying T cell responses. Some non-canonical functions are exerted by antibodies, but most are mediated by other products and/or direct actions of B cells. The diverse set of non-canonical functions makes the B cell as much as any cell a central organizer of innate and adaptive immunity. However, the diverse products and actions also confound efforts to weigh the importance of individual non-canonical B cell functions. Here we shall describe the non-canonical functions of B cells and offer our perspective on how those functions converge in the development and governance of immunity, particularly immunity to transplants, and hurdles to advancing understanding of B cell functions in transplantation.

Accommodation in ABO-incompatible organ transplants

Accommodation refers to a condition in which a transplant (or any tissue) appears to resist immune-mediated injury and loss of function. Accommodation was discovered and has been explored most thoroughly in ABO-incompatible kidney transplantation. In this setting, kidney transplants bearing blood group A or B antigens often are found to function normally in recipients who lack and hence produce antibodies directed against the corresponding antigens. Whether accommodation is owed to changes in anti-blood group antibodies, changes in antigen or a change in the response of the transplant to antibody binding are critically reviewed and a new working model that allows for the kinetics of development of accommodation is put forth. Regardless of how accommodation develops, observations on the fate of ABO-incompatible transplants offer lessons applicable more broadly in transplantation and in other fields.

Tissue-specific and tissue-restricted histocompatibility antigens

Strictly defined, tissue-specific antigens are antigens characteristic of one particular tissue or cell. They are usually associated with autoimmunity and are remarkably homologous between species. In contrast, histocompatibility (H) antigens reflect polymorphism within species - they are alloantigens - and class-I major H complex (MHC) antigens - at least mouse H-2D and H-2 K and human HLA-A and -B, the commonest targets of acute allograft rejection - are widely distributed in the body; class-II MHC antigens - mouse Ia and human DR - have a much more limited distribution, being expressed primarily on B lymphocytes and on macrophages and other cells involved in antigen presentation and immune activation. This review is devoted to H antigens other than class-IIMHC antigens with limited if not highly specific, tissue distribution. Some of these antigens are classic tissue-specific antigens, others are alloantigens with limited tissue expression. Much of the evidence that they evoke immune responses that damage or destroy transplanted tissue is incomplete or circumstantial, but some is convincing and includes the immunogenetic characterization of new antigen systems that may have to be reckoned with clinically, especially when dealing with HLA-matched transplants.

An Ly-like specificity with extensive nonlymphoid expression

The characteristics of a strong mouse alloantigen with renal, bone marrow, and lymphoid expression were studied. This antigen is probably identical to that currently designated Ly-6.2. It was defined by the high-titered (1:1000) cytotoxic activity of three different antisera against peripheral lymphocyte target cells from DBA/2, DBA/1, and a variety of other strains. In the F(2) and four backcross generations the genetic control of this specificity segregated as a single autosomal dominant gene. In lymphoid tissues the predominant expression was on T cells but 10-30% of B cells were lysed by these antisera. The specificity was expressed strongly in kidney, as shown by sequential absorption, in amounts equal to or greater than the amount in lymphoid tissues. Comparison to the rate of absorption of H-2 by kidney indicated that this antigen may be expressed in amounts comparable to an H-2 antigen in kidney. Immunization with kidney tissue resulted in a strong cytotoxic antibody response. The number of bone marrow cells expressing this antigen (40-50%) was well beyond what could be accounted for by T lymphocytes in bone marrow. In addition, a nonlymphoid tumor, the P815Y mastocytoma, was positive by cytotoxicity and by absorption. The extensive nonlymphoid expression and antigenic strength of Ly-6.2 raises the possibility that this serologically defined lymphocyte alloantigen will have histocompatibility effects when allografts of the appropriate tissues are examined.

The role of B cells in solid organ transplantation

The role of antibodies in chronic injury to organ transplants has been suggested for many years, but recently emphasized by new data. We have observed that when immunosuppressive potency decreases either by intentional weaning of maintenance agents or due to homeostatic repopulation after immune cell depletion, the threshold of B cell activation may be lowered. In human transplant recipients the result may be donor-specific antibody, C4d+ injury, and chronic rejection. This scenario has precise parallels in a rhesus monkey renal allograft model in which T cells are depleted with CD3 immunotoxin, or in a CD52-T cell transgenic mouse model using alemtuzumab to deplete T cells. Such animal models may be useful for the testing of therapeutic strategies to prevent DSA. We agree with others who suggest that weaning of immunosuppression may place transplant recipients at risk of chronic antibody-mediated rejection, and that strategies to prevent this scenario are needed if we are to improve long-term graft and patient outcomes in transplantation. We believe that animal models will play a crucial role in defining the pathophysiology of antibody-mediated rejection and in developing effective therapies to prevent graft injury. Two such animal models are described herein.

Donor specific antibodies after transplantation

The detection of donor-specific antibodies after organ transplantation might provide an incisive way to monitor allo-specific immunity and predict graft outcome. Still, the availability of new assays for these antibodies prompts us to pose some questions about results that might be observed. These questions include whether the antibodies detected in the blood are a sensitive measure of alloimmunity, whether the detected antibodies are truly specific for the donor and whether they are noxious for the graft. Here, we explain why answers to these questions might interest the basic scientist and clinician.

Antibody-mediated rejection: emergence of animal models to answer clinical questions

Decades of experiments in small animals had tipped the balance of opinion away from antibodies as a cause of transplant rejection. However, clinical experience, especially with sensitized patients, has convinced basic immunologists of the need to develop models to investigate mechanisms underlying antibody-mediated rejection (AMR). This resurgent interest has resulted in several new rodent models to investigate antibody-mediated mechanisms of heart and renal allograft injury, but satisfactory models of chronic AMR remain more elusive. Nevertheless, these new studies have begun to reveal many insights into the molecular and pathological sequelae of antibody binding to the allograft endothelium. In addition, complement-independent and complement-dependent effects of antibodies on endothelial cells have been identified in vitro. As small animal models become better defined, it is anticipated that they will be more widely used to answer further questions concerning mechanisms of antibody-mediated tissue injury as well as to design therapeutic interventions.

Immunologic consequences of multiple, high-dose administration of allogeneic mesenchymal stem cells to baboons

Mesenchymal stem cells (MSCs) express low immunogenicity and demonstrate immunomodulatory properties in vitro that may safely allow their transplantation into unrelated immunocompetent recipients without the use of pharmacologic immunosuppression. To test this hypothesis, three groups of baboons (three animals per group) were injected as follows: group 1 animals were injected with vehicle; group 2 animals were injected IV with DiI-labeled MSCs (5 x 106 MSCs/kg body weight) followed 6 weeks later by IM injections of DiO-labeled MSCs (5 x 10(6) MSCs/kg) from the same donor; and group 3 animals were treated similarly as group 2 except that MSCs were derived from two different donors. Muscle biopsies, performed 4 weeks after the second injection of MSCs, showed persistence of DiO-labeled MSCs in 50% of the recipients. Blood was drawn at intervals for evaluation of basic immune parameters (Con A mitogen responsiveness, PBMC phenotyping, immunoglobulin levels), and to determine T-cell and alloantibody responses to donor alloantigens. Host T-cell responses to donor alloantigens were decreased in the majority of recipients without suppressing the overall T-cell response to Con A, or affecting basic parameters of the immune system. All recipient baboons produced alloantibodies that reacted with donor PBMCs. Two of six animals produced alloantibodies that reacted with MSCs. We conclude that multiple administrations of high doses of allogeneic MSCs affected alloreactive immune responses without compromising the overall immune system of recipient baboons. The induction of host T-cell hyporesponsiveness to donor alloantigens may facilitate MSC survival.

Pretransplant blood transfusion without additional immunotherapy generates CD25+CD4+ regulatory T cells: a potential explanation for the blood-transfusion effect

BACKGROUND

Preoperative blood transfusion has had a significant historic impact on graft outcome in clinical kidney transplantation, and the effect has been widely replicated in many experimental transplant models. Although the mechanisms underlying the blood-transfusion effect are poorly understood, one possibility is that preexposure to alloantigen results in the induction of regulatory cells with the capacity to control the effector arm of the immune response.

METHODS

Recent studies in autoimmune models have shown that T cells with regulatory function can be isolated from unmanipulated animals on the basis of CD25 expression, and we have recently shown that pretreatment of recipient mice with donor alloantigen combined with anti-CD4 antibody therapy generates CD25+CD4+ T cells that can prevent graft rejection. We therefore used this sensitive adoptive transfer mouse model to ask whether blood transfusion in the absence of any other treatment can also lead to the generation of alloreactive CD25+CD4+ regulatory T cells.

RESULTS

Although a single donor-specific transfusion (DST) fails to induce dominant regulation, we demonstrate that pretreatment with multiple DSTs generates CD25+CD4+ T cells that are as effective as those that result from blood transfusion under anti-CD4 antibody cover. More importantly, our results show that these cells also develop following multiple transfusions of unrelated (random) blood.

CONCLUSION

These results provide a basis for understanding the blood-transfusion effect in transplantation and, by providing a link between naturally occurring regulatory cells and those induced by alloantigen, may shed new light on the fundamental basis of the effect itself.

ABO-incompatible liver transplantation with no immunological graft losses using total plasma exchange, splenectomy, and quadruple immunosuppression: evidence for accommodation

ABO-incompatible liver transplants (LTX) have been associated with a high risk of antibody-mediated rejection, poor patient and graft survival, and a high risk of vascular thrombosis and ischemic bile duct complications. We used pretransplantation and posttransplantation double-volume total plasma exchange (TPE), splenectomy, and quadruple immunosuppression (cyclophosphamide or mycophenolate mofetil, prednisone, cyclosporine or tacrolimus, and OKT3 induction) in 14 patients receiving ABO-incompatible LTX between June 1992 and February 2001: A(1) to O (seven), B to O (two), B to A (two), A to B (one), AB to A (one), and AB to O (one). Actuarial 1- and 5-year patient and graft survival rates are 71.4% and 61.2 % and 71.4% and 61.2%, respectively, with a mean follow-up of 62.9 +/- 39.4 months. Ten acute cellular rejections occurred, and the mean time to the first episode was 62 +/- 33 days. All were steroid sensitive. No antibody-mediated rejection or vascular thromboses occurred. Pretransplantation pre-TPE immunoglobulin (Ig) G mean isohemagglutinin titers were 262 +/- 326, compared with pretransplantation post-TPE titers of 65 +/- 103 (P =.04). Eight of nine patients with measurable titers before and after TPE achieved a reduction in titers. The mean number of posttransplantation TPE was 5.5 +/- 4.1 (range, 0 to 12), and the last TPE was on postoperative day 9.4 +/- 5.3. IgG isohemagglutinin titers 2 weeks posttransplantation had increased to 153 +/- 309 (P =.03 compared with pretransplantation pre-TPE IgG). ABO-incompatible liver transplantations can be performed with acceptable patient and graft survival rates with a low risk of antibody-mediated rejection with a combination of TPE, splenectomy, and quadruple immunosuppression. Recovery of isohemagglutinin antibody levels without humoral rejection suggests that accommodation may be the protective mechanism preventing late antibody-mediated rejection.

Prolonged survival of corneal allografts incubated in alloantibody fragments

BACKGROUND

In this study, we determined the binding characteristics of F(ab')2 alloantibody fragments to corneal antigens and assessed the capacity of these antibody fragments to protect corneal allografts from immune attack.

METHODS

Goat anti-rabbit alloantibodies were pepsin-digested and labeled with 125I, and the time course of association and dissociation of the F(ab')2 fragments was determined. Corneal allografts were incubated in unlabeled F(ab')2 fragments and transplanted into allogeneic recipients, and the graft survival times were recorded.

RESULTS

Binding of radiolabeled F(ab')2 fragments to rabbit cornea cells reached a maximum at 12 hr. At 32 degrees C (rabbit corneal temperature), the radiolabel eluted rapidly from the cornea, reaching baseline at 72 hr. At 4 degrees C (corneal graft storage temperature), significant amounts remained associated with the cornea at 96 hr. Mean survival time for grafts incubated in F(ab')2 anti-rabbit fragments was significantly greater than that of grafts incubated in nonimmune F(ab')2 fragments. Three of the corneal allografts incubated in goat F(ab')2 anti-rabbit fragments survived for 100 days, whereas the longest surviving control allograft incubated in goat F(ab')2 nonimmune fragments was rejected on day 24. Preincubation of corneas in unlabeled, immune F(ab')2 fragments followed by incubation in radiolabeled, immune F(ab')2 fragments suggested that antigen masking was not a factor in the prolongation of graft survival.

CONCLUSION

Based on the binding and release kinetics and the graft survival times, it appears that the protective effect of immune F(ab')2 fragments extends well beyond the binding interval of the antibody fragments to corneal cell membranes.

T cell-dependent acceleration of chemoattractant cytokine gene expression during secondary rejection of allogeneic skin grafts

Chemoattractant cytokines, chemokines, are likely to play a critical role in directing leukocytes to graft sites and in amplifying intragraft inflammation during rejection. Since second-set graft rejection occurs at an accelerated rate, we hypothesized that chemokine genes would be expressed earlier during secondary allograft rejection than during rejection of primary allografts. We have tested this hypothesis by using Northern blot analysis to compare intragraft expression levels of genes encoding interleukin (IL) 1beta and six chemokines during rejection of C57BL/6 skin grafts on naive and C57BL/6-sensitized BALB/c recipients. Expression levels of IL-1beta, interferon-gamma inducible protein, macrophage inflammatory protein-1 (MIP-1) alpha, and MIP-1beta genes were 10- to 17-fold higher on day 5 after transplantation in C57BL/6 grafts on C57BL/6-presensitized recipients than in C57BL/6 grafts on unprimed recipients. Intragraft expression of the chemokines regulated upon activation, normal T cell expressed and secreted (RANTES), during primary C57BL/6 graft rejection was virtually undetectable at day 7 after primary transplantation, but was expressed at high levels by day 5 after secondary transplantation. In third-party CBA/Ca allografts on unsensitized and C57BL/6-presensitized BALB/c mice, similar levels of IL-1beta, MIP-1alpha, and MIP-1beta expression were observed. High levels of RANTES and interferon-gamma inducible protein expression, however, were observed at day 5 after transplantation in CBA/Ca grafts on C57BL/6-presensitized recipients and correlated with accelerated rejection of the third-party grafts. Although T cells from C57BL/6-presensitized recipients did not express increased reactivity to CBA/Ca stimulator cells in vitro, serum antibodies from these recipients demonstrated reactivity to cells from CBA/Ca and A/J mice. When compared with transfer of unprimed cells, transfer of C57BL/6-primed lymphoid cells to sublethally irradiated BALB/c mice engrafted with C57BL/6 grafts resulted in increased intragraft proinflammatory cytokine gene expression. Deletion of T cells before transfer abrogated the increased intragraft expression of proinflammatory cytokine genes. Collectively, these results indicate that the accelerated expression of chemokine genes during second-set rejection of allogeneic skin grafts is mediated by immune T cells.

Cellular mechanisms of adaptation of grafts to antibody

New, more effective, strategies of immunosuppression, including those recently designed to induce durable T cell tolerance (by grafting allogeneic or xenogeneic haematopoietic cells into T lymphocyte-depleted recipients), leave humoral rejection as the main barrier to transplantation of vascularized organs between different species. Recent experimental work indicates that hyperacute rejection can be prevented by manipulations of antibodies and complement. In this paper, we review the mechanisms governing the interaction of antibodies with cell surface antigens in vitro and in vivo, and their cellular consequences. Evidence is presented that, in appropriate conditions, antibodies can protect by effecting modification of graft antigenicity (adaptation or accommodation).

Intrathymic injection of donor alloantigens induces donor-specific vascularized allograft tolerance without immunosuppression

The induction of donor-specific tolerance could prevent the side effects of immunosuppression while improving allograft survival. Male adult Buffalo (RT1b) rats underwent an intrathymic (IT), portal venous (PV), intrasplenic (IS), or subcutaneous (SQ) injection of 25 x 10(6) major histocompatibility complex (MHC) mismatched Lewis (RT1(1)), UV-B-irradiated Lewis (RT1(1)), ACI (RT1a), or syngeneic Buffalo (RT1b) splenocytes. At the completion of the donor alloantigen injection, 1 mL rabbit anti-rat lymphocyte serum (ALS) was administered intraperitoneally to the Buffalo recipients, and 21 days later a heterotopic Lewis or ACI heart was transplanted. Intrathymic injection of donor alloantigen induced a donor-specific tolerance that allowed the cardiac allograft to survive indefinitely (mean survival time [MST] > 140.7 days) in 84% of the recipients without further immunosuppression, whereas groups receiving antigen injections at other sites (PV, IS, and SQ) plus ALS rejected cardiac allografts in normal fashion (MST approximately 8.0 days). Buffalo recipient rats with long-term surviving Lewis cardiac allografts after Lewis IT injection and ALS subsequently rejected a heterotopic third-party ACI cardiac allograft in normal fashion (MST approximately 7 days), whereas a second Lewis cardiac allograft was not rejected (MST > 116 days). Microchimerism is unlikely because Lewis allograft survival was also prolonged (MST > 38.7 days) in rats receiving UV-B-irradiated splenocytes IT, which cannot proliferate. Survival of Lewis renal allografts was also prolonged, but not indefinitely, in Buffalo recipients possessing a long-term surviving Lewis cardiac allograft (MST approximately 17.6 days versus 7 days for control). This model emphasizes the potential role of exposure of immature thymocytes to foreign donor alloantigens during maturation in the thymic environment for the development of unresponsiveness to an MHC-mismatched donor-specific vascularized allograft.

Intestinal graft versus host disease

An ileocolectomy specimen was examined from a patient with graft versus host disease (GvHD). In addition to the characteristic histological features of this condition, both the small and the large intestine showed extensive destruction of mucosal tissue with survival of clusters of enterochromaffin cells. This appearance has previously been described only in the large bowel. Endocrine cells seem to be less vulnerable to the effects of GvHD than epithelial cells, resulting in their being spared, which is not seen in other types of crypt destruction.

Mechanisms maintaining enhancement of allografts. I. Demonstration of a specific suppressor cell

DA rats treated with hyperimmune anti-PVG serum and grafted with (DA X PVG)F1 heart grafts in which graft survival was prolonged for greater than 75 d were used to examine the cellular mechanisms that maintain the state of specific unresponsiveness found in these animals. The capacity of lymphocytes from these animals to effect or inhibit graft rejection on adoptive transfer to irradiated heart-grafted hosts was tested. Spleen cell populations and the T cell subpopulation separated from spleen cells in vitro failed to restore rejection of PVG heart grafts in irradiated DA recipients but restored third party Lew graft rejection. Whole spleen cells had the capacity to suppress the ability of normal DA LNC to cause graft rejection, but T cells from spleen only delayed the restoration of rejection. LNC and recirculating T cells from rats with enhanced grafts adoptively restored PVG rejection, however. These studies show that the state of specific unresponsiveness that follows the induction of passive enhancement is dependent in part upon active suppression, which is induced or mediated by T lymphocytes. The recirculating pool of lymphocytes in these animals is not depleted of specific alloreactive cells with the capacity to initiate and effect rejection. Thus, these animals' unresponsiveness is not like that found in transplantation tolerance induced in neonatal rats, but is, in part, due to a suppressor response that can inhibit normal alloreactive cells' capacity to initiate and effect rejection.

Effects of placental extracts on the immune response to histocompatibility antigens: class deviation of alloantibody response and allograft enhancement

Placental extracts obtained from CBA (H-2k) mice during syngeneic (CBA female X CBA male) pregnancy were evaluated for their capacity to deviate the immune reaction of CBA mice toward A/J(H-2a) immunizing spleen cells, as tested by alloantibody subclass formation and Sa 1 allograft accelerated rejection-or enhancement. The immunomodulatory activity appeared to be located in the soluble and in the insoluble extracts of placenta. The sodium deoxycholate (SDO) solubilized proteinic material, fractionated on Concanavalin A [Con A] and injected to CBA mice simultaneously with A/J spleen cells caused a suppression of the hemagglutinating titer and C-mediated cytotoxicity (IgG2). However, it also favoured antibody-mediated mast cell degranulation (IgG1) and Sa 1 allograft enhancement. The presence and role of IgG1 antibodies in both tumor enhancement and gestation has been described. It is concluded that placenta contains Con A-binding glycoproteins which are located in the membranes and released in soluble form. They exert their immunomodulatory effect in a way which might help the successful outcome of pregnancy as it helps to enhance the development of allografted sarcoma.

Maternal antipaternal immunity in couples predisposed to repeated pregnancy losses

Maternal antipaternal immunity was compared between a group of 12 couples with normal reproductive histories and a group of 13 couples with obstetrical histories of more than one consecutive stillbirth or repeated pregnancy loss subsequent to having had successfully carried to term. Couples were studied for maternal-paternal HLA antigen sharing and for maternal antihusband immunity in tests detecting both complement dependent and independent antibodies as well as in an assay measuring direct cell-mediated cytotoxicity. There was no significant difference in the proportion of HLA antigen sharing between these two groups; however, the women in the pregnancy loss group demonstrated significantly more antipaternal immunity than their normal childbearing counterparts and more than previously described for aborting couples who share HLA antigens. Screening of the cytotoxic sera on a well characterized cell panel failed to reveal alloreactivity patterns consistent with paternal HLA antigen profiles. These data demonstrate that certain women who suffer recurrent pregnancy losses can mount vigorous immune responses to paternal lymphocyte antigens. We propose that the appearance of such lymphocytotoxins represents inappropriate maternal immune responses to fetal extraembryonic antigens that may subsequently result in fetal demise.

Effects of immunization of mothers on the immune reaction of their offspring: inhibition of immune responses of offspring caused by antibody imported through the milk

Effects of immunization of pregnant AKR mice with nucleated chicken erythrocytes (CRBC) on immune responses of their offspring were examined. Antigen-specific reduction of generation of cytotoxicity and plaque forming cells (PFC) was demonstrated in the offspring at 8 weeks after birth, and lasted for 15 weeks. Cross-fostering experiments and cell transfer experiments showed that such suppression would be induced by antibody contained in the milk of immunized mothers rather than suppressor cells. Activities to enhance opsonization and to mediate antibody-dependent cell-mediated cytotoxicity (ADCC) were demonstrated in the serum of such offspring before challenge with CRBC. Delayed footpad reaction (DFR) was maintained at the normal level in such offspring of immunized mice.

Immunology of renal transplantation rejection

Recent studies into the mechanisms of graft rejection have highlighted the complexity of this response. Although current immunosuppressive treatments are crude, laboratory observations on the mechanisms of graft rejection have already led to various techniques which may assist in the early diagnosis of rejection, in the prognosis of a rejection episode, and in the development of more specific therapy to prevent and treat rejection. Already, the monitoring of T-cell subsets in blood and graft infiltrates is of considerable help. These observations may lead to the advent of more specific and subtle immunosuppressive therapy, such as the use of monoclonal antibodies directed against T-cell subsets. In the long term, the induction of states of specific unresponsiveness to the graft holds great promise, as do the development of techniques to assess adequacy of immunosuppression and to detect the presence of specific unresponsiveness.

Allogeneic tumor rejection induced by the intravenous injection of Lyt-2+ cytolytic T lymphocyte clones

The in vivo activity of murine Lyt-2+ cytolytic T lymphocyte clones was assessed in a tumor allograft model system. Mice that had been sublethally irradiated 16 h previously were injected intraperitoneally with 131I-IUdR-labeled tumor cells. Simultaneously, various doses of four cytolytic T cell clones were injected intravenously and the mice monitored for tumor cell elimination by whole-body counting tecniques. These four clones had been selected on the basis of their ability to proliferate in response to alloantigens in the absence of added T cell growth factor(s). With two of the four clones tested, rapid elimination of tumor cells within the peritoneal cavity was observed, as early as 48 h after intravenous injection of the cloned T cells.

Langerhans cell-containing epidermal cells are not cytotoxic in antibody-dependent- and mitogen-induced-cellular cytotoxicity

Langerhans cells (LC) constitute a small (2-6%) subpopulation of mammalian epidermal cells (EC) and are the only EC that bear Fc-IgG receptors and that share several other cell-surface characteristics and functional capabilities with cells of the monocyte-macrophage series. Since Fc-IgG receptor-positive macrophages are potent effector cells in antibody-dependent cellular cytotoxicity (ADCC), we determined whether LC-containing EC populations are also able to mediate ADCC. In the ADCC assay employed, BALB/c LC-containing EC at different effector/target cell ratios consistently failed to lyse bovine red blood cell (BRBC) targets which were either trinitrophenyl(TNP)-modified or not modified and reacted with an appropriate antibody: a purified rabbit IgG anti-BRBC, or a mouse or rabbit anti-TNP antiserum. In addition, LC-containing EC did not mediate mitogen-induced cellular cytotoxicity using purified phytohemagglutinin. BALB/c spleen cells, used as a positive control, gave substantial specific release in all experiments performed.

Specificities of antibodies eluted from human cadaveric renal allografts. Multiple mechanisms of renal allograft injury

The purpose of the present experiments was to evaluate the role of circulating antibodies in the rejection of human renal allografts and to study the apparent target(s) for antibody binding. Eluates obtained from surgical biopsy and nephrectomy specimens of rejecting, cadaveric human renal allografts were tested for antibodies directed to structural antigens of normal kidney and for cytotoxic antibody activity against mononuclear cell populations. By indirect immunofluorescence 23 of 35 eluates contained immunoglobulin that bound to normal kidney. Staining was in smooth muscle only in 10 patients, in smooth muscle and other structures such as tubular basement membranes, proximal cells, or brush border in 9 patients, and in structures other than smooth muscle in 4 patients. All 16 eluates tested contained antibodies cytotoxic for cells derived from a panel of normal volunteers. Six were cytotoxic to T cells and 10 to B cell and monocyte-enriched preparations. Absorption of eluates with pooled buffy coat cells, platelet concentrates and packed, cultured B cells removed antibodies reactive with vascular wall smooth muscle and endothelium, but not antibodies to tubular basement membranes, proximal or distal tubular cells, brush border, or other structures of kidney sections. Two of five eluates containing antikidney antibodies were found to bind to rat kidneys in vivo. These results suggest that circulating antibodies participate in cadaveric renal allograft destruction and demonstrate that they can be recovered directly from the allograft. Moreover, the data indicate that there are different antibody populations involved: some clearly directed to allo-specific differences and others that are apparently kidney-specific.

The brain and subarachnoid space as possible sites for endocrine tissue transplantation

Immunological rejection has been the major problem limiting the successful transplantation of tissue from one animal to another. Recent technological developments, combined with the use of the central nervous system as an immunologically privileged site, suggest that it might be possible to achieve long-term survival of hormone-secreting tissues, between two gentically dissimilar animals, if these tissues are transplanted to the brain and subarachnoid space of the host. The physiological parameters that should be considered in the clinical application of a transplant of this type are discussed.

Role of humoral presenitization in human renal transplant rejection

A prospective study of 31 cadaveric renal allograft recipients was performed to determine the significance of pretransplant presensitization undetected by the conventional microlymphocytotoxicity crossmatch. Donor-specific humoral presensitization revealed by the antibody-dependent cell-mediated cytotoxicity assay (ADCC) was associated with a high incidence of early graft rejection. Six-month graft survival was 20% in recipients with positive pretransplant ADCC and 75% in ADCC-negative recipients (P < 0.01). Among recipients highly presensitized to a random panel of HLA antigens, donor-specific humoral presensitization detected by chromium-51-release complement-dependent cytotoxicity (51Cr-CDC) was also highly correlated with accelerated rejection (P < 0.05). Pathologic study of the rejected allografts revealed antibody-mediated rejection vasculitis in all recipients. We conclude that humoral presensitization undetected by current conventional methods plays a cardinal role in early renal graft rejection and is a major factor responsible for low cadaveric renal transplant survival. This study suggests that use of the ADCC and 51Cr-CDC as routine adjunctive crossmatch procedures may contribute to improvement in renal transplant survival rates.

Immunological enhancement induced by gastrointestinal immunization of mice pretreated with cyclophosphamide

The present study suggests that pretreatment of mice with cyclophosphamide (CPA) not only suppresses the intestinal immune response to malignant ascites cells but alters the character of the response. Non-treated animals were sensitized by intestinal immunization while CPA-treated animals showed enhanced tumour growth. Sera from enhanced mice contained factors which at the tumor cell membrane were able to interfere with the binding of antibodies detectable by immunofluorescence technique. These factors might be immunoglobins with similarities to IgG, but bound to antigen they were undetectable by the fluorescence method. Enhanced mice were found to be immunologically hyporesponsive to the challenging tumor graft as evidenced by a delay in the immune response to the graft.

A long-lasting enhancing effect of anti-tuberculin antiserum on delayed-type hypersensitivity reaction in BCG-infected guinea pigs

Anti-tuberculin serum and anti-BCG immunoglobulins from immunized guinea pigs were transferred into recipient guinea pigs which had been infected with BCG. An enhancement of tuberculin skin reactivity was observed 7 and 35 days after transfer of homologous antiserum in comparison to a control group. This indicates a modulating effect of humoral factors, presumably specific antibodies on the expression of delayed-type hypersensitivity reaction after immunostimulation with BCG.

Enhancement of human kidney allografts by cold B-lymphocyte cytotoxins

The sera of 233 kidney transplant patients before transplantation were tested by cytotoxicity against a panel of B and T lymphocytes at 5 degrees C and 37 degrees C. The results divided the patients into four groups: those whose sera reacted with B lymphocytes at 5 degrees C; those reacting with B lymphocytes at 5 degrees C and 37 degrees C; those reacting with T lymphocytes at 37 degrees C; and those with no antibodies. The patients with pre-transplant antibodies reactive with B lymphocytes at 5 degrees C had a significantly higher kidney-transplant survival rate at 6 months (70%) and 1 year (65%) than patients who had no antibodies (47% and 46%, respectively). Patients with antibodies reactive at 37 degrees C had a 6-month survival-rate of 38% when reactive against B cells and 43% when reactive against T lymphocytes. The cold cytotoxins were IgM.

Association between treatment-resistant kidney-allograft rejection and post-transplant appearance of antibodies to donor B-lymphocyte alloantigens

In 18 kidney-allograft recipients the post-transplant appearance of antibodies to B-lymphocyte (DRw) alloantigens of the kidney donor was significantly associated with the rejection of the graft within 1 month of transplantation or the poor recovery of graft function, despite treatment for rejection. None of the 10 recipients whose grafts were accepted or whose renal function recovered well after treatment for rejection made antibodies to donor B-lymphocyte antigens after transplantation. DRw antigens are thus targets for the host's immune response to a graft and may be responsible for kidney rejection in patients who do not respond to rejection therapy.

The influence of embryonal bursectomy on benzpyrene-induced sarcoma of the chicken

160 chickens hormonally bursectomized before hatching, and 160 controls were twice given a dose of 10 mg 3,4-benzo(a)pyrene 2 weeks and 6 weeks after hatching. After 24 weeks the controls had developed muscle sarcomas at a significantly higher rate than the bursectomized animals (49.6--32.1%). The tumors were identified as malignant polymorphocellular rhabdomyosarcomas in light and electron microscopy. When the experiment was stopped after 27 weeks, the controls showed more tumors than the bursectomized chickens (65.1% versus 58.9%). The effect of bursectomy lies in a prolongation fo tumor latency. The frequency of metastases is equally decreased to a significant degree (41.7% versus 21.7%). These results are interpreted as an illustration of the disturbed equilibrium between the T and B cell responses.

Inhibiton of Fc-rosette formation by serum of patients with renal allograft rejection

A test which measures the inhibition of Fc-rosette formation by the patient's serum was used in a group of 23 renal allograft recipients. All 13 serum samples obtained during acute rejection and 2 of 3 obtained during chronic rejection showed strong inhibitory activity, suggesting that the test is of value in confirming the presence of rejection. Its value as a predictive test remains to be established. Preliminary experiments suggest that both immune complexes and alloantibodies contribute to the observed inhibition of Fc-rosette formation.