Immunological reactions to neural grafts in the central nervous system

Immunological rejection is a lasting, although highly variable, threat to allo- and xenogeneic neural tissue grafted to the CNS of rodents, monkeys and man. One major determinant for rejection of intracerebral CNS grafts appears to be induction of major histocompatibility complex (MHC) antigens on the donor CNS cells. We have previously examined the cellular immune response against neural mouse xenografts undergoing rejection in the adult rat brain. In this study we focus on the astro- and microglial reactions within and around the graft, and the potential of individual host rat and donor mouse brain cells to express MHC antigens. Previous light microscopical observations of expression of rat MHC antigen class I by endothelial cells, microglial cells, and invading leukocytes were extended to the ultrastructural level and found to include a few astrocytes. Rat and mouse MHC antigen class II was only detected on leukocytes and activated microglial cells. The findings imply that within grafts of brain or spinal cord tissue donor astrocytes, microglial cells and endothelial cells can be induced to act as target cells for class I specific host T cytotoxic cells, while only (graft and host) microglial cells can be induced to express MHC antigen class II and present antigen to sensitized (and possibly also resting) host T helper cells.     

BN rats do not reject F344 brain allografts even after systemic sensitization

Embryonic brain tissue allografts under many circumstances survive transplantation into the brain. It is generally believed that such grafts will not survive if the host animal is systemically sensitized, by skin grafting or other means, to major histocompatibility complex (MHC) antigens of the donor animal. We have found that F344 brain grafts survive in BN hosts even when the host is systemically sensitized to F344 tissue. Embryonic cerebral neocortex from F344 donors was transplanted into BN host rats (n = 95). Subsequently, the host rats were systemically sensitized with donor skin (n = 25), brain tissue (n = 41), or spleen cells (n = 6) and compared with a control group of rats consisting of allografts with no sensitization or sham procedures (n = 23). Rejection of the transplants in BN rat hosts was not provoked by any of the sensitization methods tested. Minor immunological responses that did not result in rejection were, however, present in many host animals. We did not observe infiltration of W3/13+ T cells and OX8+ cytotoxic lymphocytes in any of the groups. Nevertheless, substantial infiltrations of OX6+ antigen-presenting cells and W3/25+ helper T cells were present. There was also an extensive enhancement of MHC class I immunoreactivity in parts of the grafted tissue developing within the third ventricle, but not for the same type of graft in the lateral ventricle. This increase of MHC class I expression was not accompanied by infiltration of cytotoxic T cells. Our findings thus suggest that neural graft rejection depends on general genetic susceptibility to immune reactions, particularly experimental allergic encephalomyelitis and not only on disparity between donor and host antigens encoded by the MHC. Moreover, enhancement of MHC class I and class II expression within transplanted tissue does not predict graft rejection.     

Survival of intrastriatal xenografts of ventral mesencephalic dopamine neurons from MHC-deficient mice to adult rats

Previous studies of neural xenografts have used immunosuppressive agents to prevent graft rejection. In the present study we have examined the survival of mouse dopamine neurons lacking either MHC class I or MHC class II molecules transplanted into rat brains and the host immune and inflammatory responses against the xenografts. Survival of neural grafts was immunocytochemically determined at 4 days, 2 weeks, and 6 weeks after transplantation by counting tyrosine hydroxylase (TH)-positive cells in the graft areas. In addition, the host immune and inflammatory responses against neural xenografts were evaluated by semiquantitatively rating MHC class I and class II antigen expression, accumulation of macrophages and activated microglia, and infiltration of CD4- and CD8-positive T-lymphocytes. For the negative controls, the mean number of TH-positive cells in rats that received wild-type mouse tissue progressively decreased at various time periods following transplantation. In contrast, intrastriatal grafting of either MHC class I or MHC class II antigen-depleted neural xenografts resulted in a prolonged survival and were comparable to cyclosporin A-treated rats that had received wild-type mouse tissue. These results indicate that genetically modified donor tissue lacking MHC molecules can be used to prevent neural xenograft rejection.     

Glial cell transplants that are subsequently rejected can be used to influence regeneration of glial cell environments in the CNS

Transplantation of glial cells into demyelinating lesions in CNS offers an experimental approach which allows investigation of the complex interactions that occur between CNS glia, Schwann cells, and axons during remyelination and repair. Earlier studies have shown that (1) transplanted astrocytes are able to prevent Schwann cells from participating in CNS remyelination, but that they are only able to do so with the cooperation of cells of the oligodendrocyte lineage, and (2) transplanted mouse oligodendrocytes can remyelinate rat axons provided their rejection is controlled by immunosuppression. On the basis of these observations, we have been able to prevent the Schwann cell remyelination that normally follows ethidium bromide demyelination in the rat spinal cord by co-transplanting isogeneic astrocytes with a potentially rejectable population of mouse oligodendrocyte lineage cells. Since male mouse cells were used it was possible to demonstrate their presence in immunosuppressed recipients using a mouse Y-chromosome probe by in situ hydridisation. When myelinating mouse cells were rejected by removal of immunosuppression, the demyelinated axons were remyelinated by host oligodendrocytes rather than Schwann cells, whose entry was prevented by the persistence of the transplanted isogeneic astrocytes. The oligodendrocyte remyelination was extensive and rapid, indicating that the inflammation associated with cell rejection did not impede repair. If this host oligodendrocyte remyelination was prevented by local X-irradiation, the lesion consisted of demyelinated axons surrounded by processes from the transplanted astrocytes. By this approach, it was possible to create an environment which resembled the chronic plaques of multiple sclerosis. Thus, these experiments demonstrate that in appropriate circumstances the temporary presence of a population of glial cells can alter the outcome of damage to the CNS. © 1995 Wiley-Liss, Inc.     

Glucocorticoids and central nervous system inflammation

Glucocorticoids (GCs) are well known for their anti-inflammatory and immunosuppressive properties in the periphery and are therefore widely and successfully used in the treatment of autoimmune diseases, chronic inflammation, or transplant rejection. This led to the assumption that GCs are uniformly anti-inflammatory in the periphery and the central nervous system (CNS). As a consequence, GCs are also used in the treatment of CNS inflammation. There is abundant evidence that an inflammatory reaction is mounted within the CNS following trauma, stroke, infection, and seizure, which can augment the brain damage. However an increasing number of studies indicate that the concept of GCs being universally immunosuppressive might be oversimplified. This article provides a review of the current literature, showing that under certain circumstances GCs might fail to have anti-inflammatory effects and sometimes even enhance inflammation.     

Mesenchymal Stem Cells Form 3D Clusters Following Intraventricular Transplantation

Mesenchymal stem cells (MSCs) are regarded as an immune privileged cell type with numerous regeneration-promoting effects. The in vivo behavior of MSC and underlying mechanisms leading to their regenerative effects are largely unknown. The aims of this study were to comparatively investigate the in vivo behavior of canine (cMSC), human (hMSC), and murine MSC (mMSC) following intra-cerebroventricular transplantation. At 7 days post transplantation (dpt), clusters of cMSC, hMSC, and mMSC were detected within the ventricular system. At 49 dpt, cMSC-transplanted mice showed clusters mostly consisting of extracellular matrix lacking transplanted MSC. Similarly, hMSC-transplanted mice lacked MSC clusters at 49 dpt. Xenogeneic MSC transplantation was associated with a local T lymphocyte-dominated immune reaction at both time points. Interestingly, no associated inflammation was observed following syngeneic mMSC transplantation. In conclusion, transplanted MSC formed intraventricular cell clusters and exhibited a short life span in vivo. Xenogeneically in contrast to syngeneically transplanted MSC triggered a T cell-mediated graft rejection indicating that MSCs are not as immune privileged as previously assumed. However, MSC may mediate their effects by a “hit and run” mechanism and future studies will show whether syngeneically or xenogeneically transplanted MSCs exert better therapeutic effects in animals with CNS disease.     

MHC antigen expression and cellular response in spontaneous and induced rejection of intracerebral neural xenografts in neonatal rats

Fetal mouse retinae transplanted to the mesencephalon of neonatal rats generally survive for prolonged periods of time without immune suppression suggesting that such grafts enjoy a degree of immunological privilege. A small, but consistent percentage of these transplants, however, ultimately undergo spontaneous rejection. In addition, rejection can be induced by (1) systemically sensitizing the host to the donor antigens by placing a mouse skin graft or (2) producing a local degenerative process adjacent to the graft by removing the host eye contralateral to the side of the retinal transplant. To elucidate the immunological events that underly spontaneous and induced rejection in this system, we examined the distribution of lymphocytes, astrocytes, microglia, and cells expressing major histocompatibility complex (MHC) antigens in unrejected grafts, in transplants showing spontaneous rejection, and in grafts undergoing induced rejection. In unrejected grafts, increased astrocytic and microglial staining was seen around the photoreceptor layer of the graft and at the graft-host interface, but no lymphocytes and only occasional cells expressing MHC antigens were detected. In contrast, spontaneously rejecting grafts showed widespread MHC, lymphocytic, astrocytic, and microglial immunoreactivity that extended well beyond the limits of the transplant into the surrounding host brain. Skin graft-induced rejection produced a temporally consistent, comparatively localized enhancement of astrocytic, microglial and MHC immunoreactivity and infiltration of lymphocytes. Four to five days after skin grafting, before neural graft rejection was detectable histologically, MHC immunoreactivity was demonstrated within the transplant coinciding with the presence of small numbers of lymphocytes and an increase in microglial staining. By 8 days, grafts had undergone profound necrosis. Intense astrocytosis, microglial staining, MHC immunoreactivity, and perivascular lymphocytic cuffing were present within the graft and at the graft-host interface. With longer survival times, several of these changes were also detected within the visual pathways, suggesting that the regions to which the graft projected were also involved, though in a delayed fashion. After eye removal, the temporal pattern of rejection was more protracted and considerably less uniform than that seen after skin grafting. At 7 days, prominent microglial, astrocytic, and MHC immunoreactivity was seen in the area of distribution of the host optic axons within the superior colliculus and to a lesser extent around the graft itself, however, no infiltration of lymphocytes was detected. With longer survival times, an increasing percentage of grafts showed signs of overt rejection with perivascular cuffing by lymphocytes; however, even at 21 days, a small number of grafts remained free of lymphocytic infiltration, despite the presence of intense MHC, astrocytic, and microglial staining. We conclude that the different rejection models studied may involve fundamentally different triggers of the host immune system, but that in each case MHC expression may be the precedent step to graft rejection.     

Kidney transplantation and liaison psychiatry, part II: A case of dissociative identity disorder

Abstract  The authors examined the case of an adolescent patient with dissociative identity disorder secondary to psychological shock of a transplant rejection response. Psychiatric symptoms consisted ot three components: visual hallucinations and delusions as a psychological defense against the anxiety of a transplant rejection; appearance of three personalities including proper self, the dead child (donor), and a prophet with strong predicting power; and a twilight state. These psychiatric symptoms may have been related to two psychological factors; immature personality characteristics formed during hemodialysis, and post-traumatic stress caused by a chronic rejection reaction from the patient's first transplant.     

Heterotopic brain transplants in the study of experimental allergic encephalomyelitis

A heterotopic transplant paradigm was developed for its potential usefulness in dissecting genetically determined immune and central nervous system (CNS) components in the induction of experimental allergic encephalomyelitis (EAE). EAE is a cell-mediated, organ-specific, autoimmune disease producing inflammatory demyelination in the CNS. Susceptibility to EAE is determined by multiple genes and reflects both immune competence and target tissue responses. Syngeneic fetal CNS was heterotopically transplanted into the anterior chamber of the eye or beneath the capsule of the kidney of adult SJL or (SJL X BALB/c)F1 mice. Transplants usually survived better in the eye than the kidney. Six to eight weeks after transplantation, some mice were immunized for EAE. Immunized mice developed clinical and pathological signs of EAE in 12 to 15 days. The placement of CNS tissue into the eye or kidney prior to immunization did not suppress induction of EAE. Transplants in either location, in immunized mice, manifested perivascular inflammation and demyelination similar to that seen in the host CNS. However, transplants in mice not immunized for EAE, but maintained an equal time period after transplantation, did not demonstrate these features. The ability to produce the specific pathologic lesions of EAE in CNS tissue transplanted outside the CNS allows the design of studies of the tissue localization of genetic restrictions to development of EAE.     

Xenotransplantation for CNS repair: immunological barriers and strategies to overcome them

Neural transplantation holds promise for focal CNS repair. Owing to the shortage of human donor material, which is derived from aborted embryos, and ethical concerns over its use, animal donor tissue is now considered an appropriate alternative. In the USA, individuals suffering from Parkinson's disease, Huntington's disease, focal epilepsy or stroke have already received neural grafts from pig embryos. However, in animal models, neural tissue transplanted between species is usually promptly rejected, even when implanted in the brain. Some of the immunological mechanisms that underlie neural xenograft rejection have recently been elucidated, but others remain to be determined and controlled before individuals with neurological disorders can benefit from xenotransplantation.     

Immune problems in central nervous system cell therapy

Transplantation of cells and tissues to the mammalian brain and CNS has revived the interest in the immunological status of brain and its response to grafted tissue. The previously held view that the brain was an absolute “immunologically privileged site” allowing indefinite survival without rejection of grafts of cells has proven to be wrong. Thus, the brain should be regarded as a site where immune responses can occur, albeit in a modified form, and under certain circumstances these are as vigorous as those seen in other peripheral sites. Clinical cell transplant trials have now been performed in Parkinson’s disease, Huntington’s disease, demyelinating diseases, retinal disorders, stroke, epilepsy, and even deafness, and normally are designed as cell replacement strategies, although implantation of genetically modified cells for supplementation of growth factors has also been tried. In addition, some disorders of the CNS for which cell therapies are being considered have an immunological basis, such as multiple sclerosis, which further complicates the situation. Embryonic neural tissue allografted into the CNS of animals and patients with neurodegenerative conditions survives, makes and receives synapses, and ameliorates behavioral deficits. The use of aborted human tissue is logistically and ethically complicated, which has lead to the search for alternative sources of cells, including xenogeneic tissue, genetically modified cells, and stem cells, all of which can and will induce some level of immune reaction. We review some of the immunological factors involved in transplantation of cells to CNS.     

Patterns of immune rejection of mouse neocortex transplanted into neonatal rat brain, and effects of host immunosuppression

We studied the histological and immunological characteristics of graft rejection in the rodent central nervous system (CNS) using embryonic mouse neocortex transplanted into the CNS of neonatal rats. Grafts from animals aged 8-145 days (n = 210) were examined using standard histological techniques for demonstrating cell morphology and fiber projections. Immunohistochemical techniques were used to identify graft projections into the host CNS. The incidence of graft rejection was 18% for animals between 18 and 30 days of age, but increased abruptly to 73% for animals older than 30 days. No graft rejection was seen in animals younger than 18 days. In a smaller group of xenograft recipient rats sacrificed at specific time points before and after one month of age, detailed immunohistochemical studies were performed to correlate the histological appearance of the graft with the level of major histocompatibility complex (MHC) class I and II immunoreactivity, and microglial, astrocytic and lymphocytic staining within the graft and host brain. Evidence of mild rejection as manifested by the appearance of scattered lymphocytes within the graft coincided with the development of Class I and II immunoreactivity within the graft and at the graft-host interface, which was demonstrated in some animals as early as 24 days. At 29 days of age, rejecting grafts showed diffuse MHC expression within the graft and at the graft-host interface; in contrast, unrejected grafts failed to show MHC immunoreactivity. Thirty-four day-old grafts often showed severe rejection with perivascular lymphocytic cuffing within the graft and in host parenchyma remote from the graft associated with increased MHC immunoreactivity within the host brain. In grafts older than 34 days there was frequently a violent rejection reaction with disruption of the cytoarchitecture of the graft and surrounding host tissues, and widespread MHC antigen expression. Immunosuppression with cyclosporin A was effective in avoiding rejection. The high incidence of rejection with neocortical xenografts is in striking contrast to the much lower incidence seen with retinal xenografts. This suggests that there are immunological features unique to neocortex which incite host recognition and rejection.     

Development of fetal retina,tectum, and cortex transplanted to the superior colliculus of adult rats

Earlier studies showed that embryonic retina, cortex, or tectum transplanted adjacent to the superior colliculus of newborn host rats differentiated many of the histological features appropriate for the donor region and developed interconnections with the host nervous system. In the study presented here, the same regions were transplanted to the brain of adult host rats and the development of these transplants was compared to those into newborn hosts. Retina, rostral tectum, or occipital cortex was dissected from donor rat embryos on gestational day 14 or 15. A portion of cortex was aspirated in 2-;menth-old host rats to expose the right superior colliculus, and one of the donor tissues was placed adjacent to the colliculus in each host. Two to 4 months after transplantation, transplant histology and neuronal interconnections between the transplant and host nervous system were studied by using Nissl and neurofibrillar stains and ³H-proline and HRP tract tracing techniques. Four main points can be drawn from these results. First, 80% of the transplants survived in adult hosts –a percentage comparable to that found in newborn hosts. Second, each of the types of tissues transplanted differentiated histological characteristics appropriate for its site of origin, although the degree of differentiation was always much less than in transplants to newborns. Third, the transplants developed only relatively local projections into the host cortex and superior colliculus. This contrasts with the extensive projections found from the transplants into the brain of newborn hosts. Fourth, no definitive projections from the host retina or brain were identified to any of the transplants into adults, whereas both cortical and tectal transplants into newborns received projections from the host.     

Human fetal neural precursor cells can up-regulate MHC class I and class II expression and elicit CD4 and CD8 T cell proliferation

The use of allogeneic fetal neural precursor cells (NPCs) as a cell replacement therapy in neurodegenerative disorders holds great promise. However, previous studies concerning the possibility of alloimmune rejection of the transplanted cells have been inconclusive. Here, we used flow cytometry to quantify the expression of major histocompatibility complex (MHC) molecules by human NPCs, obtained from the cortex or ventral mesencephalon of fetuses with gestational ages between 7 and 11 weeks. MHC class I was undetectable on the surface of freshly isolated primary fetal tissue from either location, but increased over time in proliferating NPC cultures; after 7days in vitro, MHC class I was detectable on most cells. Following differentiation, MHC class I expression persisted on non-neuronal cells. MHC class II levels remained low at all time points but were inducible by pro-inflammatory cytokines, whereas the co-stimulatory molecules, CD80 and CD86, remained undetectable. Nonetheless, CD4+ and CD8+ T cells proliferated when peripheral blood mononuclear cells (PBMCs) were cultured with allogeneic NPCs. Weaker responses were obtained when NPCs were co-cultured with purified allogeneic responder T cells, suggesting that indirect allorecognition contributed significantly to PBMC responses. In conclusion, differentiating human NPCs are immunogenic in vitro, suggesting that they may trigger immune rejection unless transplant recipients are immunosuppressed.     

Migration patterns of donor astrocytes after reciprocal striatum-cerebellum transplantation into newborn hosts.

Fragments of striatum or cerebellum from E 25 rabbit embryo were implanted into either the striatum or the mesencephalon of newborn mice. Implanted rabbit astrocytes were selectively identified by monoclonal antibodies to the GFAP which are unable to combine with mouse GFAP. Previous investigations had shown that xenogenic astrocytes have the capacity to migrate in host CNS. The purpose of this study was to compare the patterns of migration of transplant-derived astroglial cells according to the topographic origin of the transplant and location of the grafting site. We found that the migration pattern of the grafted cells from any of both selected sites of implantation was independent from the topographic origin of the transplant. The routes as well as the distances of migration were similar after homo- or heterotopic transplantation. We conclude that astroglial cells or their precursors do not express information which would direct them to move specifically toward a defined region in the host brain according to the region of origin in the donor.     

Long-term survival of mouse corpus callosum grafts in neonatal rat recipients, and the effect of host sensitization.

Previous studies have suggested that the incidence of spontaneous rejection among immunogenetically mismatched neural transplants in neonatal recipients varies significantly depending on the cellular composition of the graft material. For example, neuron-rich grafts of embryonic mouse retina generally survive for extended periods without showing signs of rejection after implantation into neonatal rats, whereas cortical xenografts, which contain abundant glial and endothelial cells as well as neurons, typically undergo rejection 4-6 weeks after implantation. To determine whether the presence of donor glia is responsible for this high incidence of spontaneous rejection, we examined the fate of a non-neuronal graft material composed predominantly of xenogeneic glial cells (post-natal day 3, PD3, CD-1 mouse corpus callosum) implanted into the mesencephalon of PD1 Sprague-Dawley rats. The distribution and survival of donor astrocytes were assessed using a monoclonal antibody specific for a mouse astrocyte surface antigen, M2. Thirteen of 16 animals sacrificed within 2 months of implantation had detectable transplants. In these animals, M2-positive cells frequently migrated well away from body of the graft, clustering in large numbers in several characteristic regions of the host brain. Unlike cortical grafts of similar age, the vast majority (93%) of callosal transplants showed no histological signs of rejection or major histocompatibility complex antigen expression in and around the transplant-derived cells. As previously noted in the neonatal retinal transplant paradigm, however, well-integrated 1-month-old corpus callosum grafts could be induced to reject by appropriate sensitization of the host immune system, implying that the host was not immunologically tolerant to the foreign neural graft. With longer survival times in unsensitized hosts, a progressively smaller percentage of animals had detectable donor astrocytes (5 of 10 animals at 3 months postimplantation and 4 of 16 animals at 4 months); in those 9 animals with surviving grafts, only small numbers of M2-positive cells were seen within the graft bed and surrounding host brain. However, only 2 of the 26 "long-term" animals showed evidence of graft rejection. These results indicate that mouse astrocytes show characteristic patterns of migration into the host brain when implanted into neonatal rats; however, these xenogeneic cells have a limited duration of survival. The infrequency with which even subtle signs of spontaneous rejection were detected in animals that had received corpus callosum xenografts suggests that an immune-mediated process is unlikely to be responsible for the time-dependent elimination of the donor astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Transplantation of central nervous tissue

Studies of post-lesional reorganization of central nervous connections have shown that central nerve fibers respond to nearby denervation by sprouting and formation of new terminals. The connections in the central nervous system (CNS) are accordingly much more plastic than was thought for a long time. This has revived the interest in transplantation of central nervous tissue. In this study we present some historical data on CNS transplantation supplemented by recent results obtained in our laboratory. Pieces of hippocampal tissue from embryonic or early postnatal rats were transplanted to different parts of the brain of littermates or adult rats. About two-thirds of the transplants were recovered after survival times ranging from 4 d to 2 years, and their cytological organization and intrinsic connections were monitored by cell and fiber stains and histochemical methods (AChE staining and Timm sulphide silver method). Comparison with both a normal and a lesioned control material revealed that in most transplants the tissue had developed as it does when left in situ in the donor brain, but deprived of its major afferent connections. In several instances we found evidence of a major exchange of connections between the transplants and host brains. The conditions needed for this to occur appeared to involve growth stimulation of host brain fibers by transection (host to transplant) and denervation of host neuropil (transplant to host). In cases where these conditions are met, the use of transplants may have future implications in attempts to repair lesions in the central nervous systems.     

An in vivo and in vitro analysis of systemic immune function in mice with histologic evidence of neural transplant rejection

Histologic and immunocytochemical analyses of fetal neocortical tissue transplanted to the lateral ventricle of inbred adult mice indicate that this tissue survives transplantation well if the donor and host are isogeneic. The major histocompatibility complex (MHC) of the mouse is known as the H-2 locus. H-2-incompatible neural transplants (allografts), unlike their H-2-identical counterpart (isografts), are characterized by the presence of T cells comprising both major T-cell subsets and macrophages, and by a marked increase in the expression of both class I and class II (Ia) MHC antigens. These findings suggest a recognition of H-2 alloantigens by the host's immune system followed by an appropriate effector response. We report here our attempts to demonstrate systemic host sensitization to alloantigens in mice bearing H-2-incompatible intraventricular neural transplants. We measured the time to rejection of orthotopic skin grafts subsequent to neural transplantation, splenocyte proliferative responses to alloantigens in mixed lymphocyte cultures (MLC), and class I-restricted antigen-specific cytolytic T lymphocyte (CTL) activity. No significant differences were found in any of these tests of host systemic sensitization between mice with allogeneic neural transplants and those with isogeneic transplants or control animals. We conclude that intraventricular neural transplants, while recognized and affected by cells of the host's immune system, do not elicit a detectable systemic sensitization to class I H-2 alloantigens. Rejection of neural transplants may depend on sensitization to class II H-2 alloantigens, to so-called minor histocompatibility antigens, or some combination thereof.     

Visualization of antigen-specific T cell activation in vivo in response to intracerebral administration of a xenopeptide

Allogeneic or xenogenic tissues exhibit prolonged survival when grafted into the brain parenchyma in comparison to grafting into peripheral sites. The brain, therefore, has long been considered an immunologically privileged site. However, the immunological privilege of the brain is not absolute, and it cannot shield neural xenografts from rejection. In our laboratory, we are interested in determining how to prevent neural xenograft rejection. To do so, we need to first understand how the immune system responds to CNS antigens leading to graft rejection. In order to monitor immune system responses to CNS antigens an adoptive transfer system was used to directly track CNS antigen-specific CD4(+) T cell responses in vivo. This would then allow us to monitor changes in the number, activation state, and anatomic distribution of antigen-specific cells. We have found that, after intracerebral injection of xeno peptide antigens with adjuvant, antigen-specific cells accumulated in the cervical lymph node, proliferated there for several days, and then disappeared slowly from the nodes. Interestingly, peptide antigens given intracerebrally also stimulated a strong antigen-specific CD4(+) T cell response. Moreover, cells remaining in the lymph node 8 days after antigen stimulation produce IL-2 with secondary antigenic challenge. Previous studies have shown that the administration of antigens without adjuvant in a monomeric form via either the intraperitoneal or intravenous route has failed to induce cell-mediated immunity and resulted in antigen-specific T cell unresponsiveness. Our findings demonstrate that antigen delivered intracerebrally can activate immune responses in a manner different than antigen delivered to peripheral sites outside of the CNS.     

肾移植中经移植肾动脉输注骨髓间充质干细胞3例报告

背景：骨髓间充质干细胞可诱导移植免疫耐受,目前其输注方式尚无定论,临床上主要为经外周静脉全身输注,仅有少量经大鼠原肾动脉输注骨髓间充质干细胞,发现其可在肾小球内驻留,并可减轻肾小球肾炎,但无经移植肾动脉输注骨髓间充质干细胞的临床病例报道。 目的：分析肾移植中经移植肾动脉输注骨髓间充质干细胞的可操作性。 方法：于2009-10/12对3例慢性肾功能不全、尿毒症期患者行亲属活体供肾移植,移植过程中在移植肾动脉吻合口固定一留置针,开放移植肾血流时,经移植肾动脉以输血器加压快速输注骨髓间充质干细胞,移植过程中、移植后3个月内密切观察可能发生的并发症及移植肾功能恢复情况。 结果与结论：3例患者骨髓间充质干细胞输注过程顺利,移植肾血流充盈良好,移植过程中、移植后未发生栓塞、感染、移植物抗宿主病等并发症,未发生移植肾排斥反应,移植肾功能恢复顺利。结果说明经移植肾动脉输注骨髓间充质干细胞具有临床可操作性,但异位分化、肿瘤等远期并发症尚需进一步观察。