Optical projection tomography implemented for accessibility and low cost (OPTImAL).

Optical projection tomography (OPT) is a three-dimensional mesoscopic imaging modality that can use absorption or fluorescence contrast, and is widely applied to fixed and live samples in the mm-cm scale. For fluorescence OPT, we present OPT implemented for accessibility and low cost, an open-source research-grade implementation of modular OPT hardware and software that has been designed to be widely accessible by using low-cost components, including light-emitting diode (LED) excitation and cooled complementary metal-oxide-semiconductor (CMOS) cameras. Both the hardware and software are modular and flexible in their implementation, enabling rapid switching between sample size scales and supporting compressive sensing to reconstruct images from undersampled sparse OPT data, e.g. to facilitate rapid imaging with low photobleaching/phototoxicity. We also explore a simple implementation of focal scanning OPT to achieve higher resolution, which entails the use of a fan-beam geometry reconstruction method to account for variation in magnification. This article is part of the Theo Murphy meeting issue 'Open, reproducible hardware for microscopy'.

Cytokine gene transcription in vascularised organ grafts: analysis using semiquantitative polymerase chain reaction.

Cytokine gene transcription has been analyzed by direct analysis of RNA obtained from mouse heterotopic cardiac transplants. The level of expression of the cytokine genes was assessed using semiquantitative polymerase chain reaction (PCR). Expression of the cytokines investigated fell into three groups. The first group included interleukin 1 beta (IL-1 beta), IL-5, IL-6, and interferon gamma (IFN gamma). These genes were expressed in normal heart tissue at low level and were upregulated following both syngeneic and allogeneic transplantation. Genes in the second group (IL-1 alpha, IL-3) were not expressed at detectable levels in normal heart but were induced following either syngeneic or allogeneic heart grafting. IL-2, IL-4, and tumor necrosis factor beta (IFN beta) comprised the third group and these cytokines were expressed only in allogeneic grafts after transplantation.

Specific cytotoxic T cells are found in the nonrejected kidneys of blood-transfused rats.

Preoperative, donor-specific blood transfusion leads to indefinite survival of rat renal allografts in the strain combinations used. 51Cr-release assays have shown that the level of specific cytotoxic effector activity in the grafts of transfused (nonrejected kidney) animals is very high and may equal or exceed that seen in the grafts of untreated (rejected kidney) recipients. Such cytotoxicity demonstrates specificity for the alloantigens of the kidney, is T cell-mediated, and may persist within the transplant.

Administration of recombinant interleukin 2 in vivo induces a polyclonal IgM response.

We studied the potential immunoenhancing effects of high doses of rIL-2 on murine T and B cell functions in vivo. Injection of rIL-2 caused a threefold or more increase in the frequencies of antigen-specific proliferative T cells, suggesting that rIL-2 initiated a polyclonal T cell response. In primary and secondary humoral immune responses, administration of rIL-2 in vivo selectively enhanced the production of IgM antibodies, whereas the IgG response was unaffected. Coadministration of rIL-2 with antigen failed to induce an isotype switch from IgM to IgG in genetically low-responding mice. Interestingly, in mice treated with rIL-2 alone (in the absence of exogenous antigen), polyclonal IgM production was induced. Polyclonal IgM production of lesser magnitude was found when mice were immunized with specific antigen in the absence of exogenous rIL-2, suggesting that local IL-2 concentrations in a primary immune response might be sufficient to elicit a polyclonal IgM response.

The specificity of rejection and the absence of susceptibility of pancreatic islet beta cells to nonspecific immune destruction in mixed strain islets grafted beneath the renal capsule in the rat.

The specificity of rejection of isolated pancreatic islets was examined in the rat using a quantitative model in which syngeneic (DA) or a mixture of syngeneic and allogeneic (DA and LEW or PVG) islets were implanted beneath the capsule of the kidney of nondiabetic normal rats (DA). 3 wk after transplantation total insulin extraction assays of the kidney with its islet implant together with immunohistological examination of the site of transplantation for evidence of syngeneic or allogeneic tissue demonstrated the total destruction of allogeneic islets without any evidence of damage to syngeneic islets either distant or in immediate proximity to allogeneic islets. Pancreatic islets, and especially beta cells, appear to be particularly vulnerable to the effector arm of both autoimmune and alloimmune responses, a vulnerability that has been attributed to the cytotoxic effects of lymphokines, notably IL-1, released in both autoimmune and alloimmune responses. The experiments reported here demonstrate not only the exquisite specificity of the allograft reaction but are not compatible with a hypothesis that B cells within an intact islet are nonspecifically susceptible to destruction by lymphokines.

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

Tolerance to alloantigen may be induced in rats by administration of blood followed by transplantation of a renal allograft. The mechanism of this tolerance was investigated by directly analyzing the functional activity of graft-infiltrating cells. We have previously shown cytotoxic T lymphocyte infiltration of, and major histocompatibility complex induction on, grafts of tolerant animals. We now report that cells isolated from the grafts of tolerant rats show a reduced expression of the p55 interleukin 2 receptor (IL-2R) chain on the cell surface compared with that seen on the cells of untreated animals. Scatchard analysis further reveals low expression of high affinity IL-2R. This is due to reduced transcription of both IL-2R alpha and beta chain mRNAs and results in a reduced ability of cells to proliferate in response to IL-2. Cells isolated from tolerant animals are unable to make biologically active IL-2 in culture, whereas cells from untreated animals make high levels. This is not reflected at the mRNA level as the IL-2 gene is induced in both tolerant and untreated animals to similar levels. The induction of tolerance is abrogated by administration of recombinant IL-2 to animals at the time of transplantation. Thus, we conclude that an altered regulation of the IL-2 pathway results in tolerance in these alloantigen-treated and transplanted animals.

Specific tolerance to neural allografts induced with an antibody to the interleukin 2 receptor.

Despite considerable evidence documenting the central nervous system as a site of immunological privilege, immune responses do occur within the brain and neural allografts between major histocompatibility complexes (MHC) and minor antigen incompatible rat strains may be rejected. The survival of completely MHC incompatible neural allografts has been found to be prolonged indefinitely after administration of a monoclonal antibody (mAb) to the interleukin 2 receptor (IL-2R) for 10 d after transplantation. Here we present evidence that rats with long-term surviving lateral ventricular neural allografts, after anti-IL-2R treatment, accept subsequent neural allografts from the same donor strain, placed in a peripheral nonprivileged site, but rapidly reject third-party grafts. Thus, treatment with a mAb to the p55 chain of the IL-2R has resulted in the specific acceptance of second grafts of fully allogeneic neural tissue. These results suggest that ongoing interaction between elements of the host immune system and alloantigen within the brain maintains the tolerant state and furthermore, that interruption of signaling through the IL-2R may be important in allospecific tolerance induction.

Cytokines as mediators of organ graft rejection and tolerance.

The analysis of cytokines following organ transplantation continues to flourish as a major area of investigation for transplant biologists. Over the past year many papers have reported the use of both molecular and antibody-based tools to dissect the expression of cytokines during graft rejection in both experimental and clinical transplantation. Further, how the expression of cytokines is altered during the induction of tolerance has been investigated by several groups.

Cytokines and transplantation: Th1/Th2 regulation of the immune response to solid organ transplants in the adult.

It has been very tempting to accept the suggestion that the route to rejection or tolerance of organ transplants is determined by T-helper type 1 and type 2 cells, respectively. Much of the data used to support this idea, however, is indirect and therefore cannot be used to imply a causal role for either population as suggested. Recent experiments have been aimed at further expanding knowledge in this area and conclude that the expansion of neither population alone inevitably results in graft damage or tolerance.

Notch signalling and voltage-gated Na+ channel activity in human prostate cancer cells: independent modulation of in vitro motility.

This study tested the possible functional relationship of two signalling mechanisms shown previously to be involved in human prostate cancer (PCa), Notch and voltage-gated sodium channel. Notch1 and Notch2 were differentially expressed in PCa cell lines of varying metastatic potential (LNCaP, PC-3, PC-3M) in comparison to a normal prostate cell line (PNT2), whereas Notch3 and Notch4 were not expressed. The Notch ligand Jagged1, but not Jagged2, was increased in all cell lines, whereas the Notch downstream target Deltex was not expressed. In comparison to the LNCaP cell line, Hes1, another downstream target, showed elevated expression in the metastatic PC-3 and PC-3M cells and promoted lateral motility. In contrast, the Notch ligand Delta-like1 (Dll1) levels were higher in LNCaP compared with PC-3 and PC-3M cells. Importantly, decreasing Dll1 expression increased the lateral motility of PC-3 cells, whereas blocking voltage-gated Na(+) channel activity with tetrodotoxin decreased motility. However, the effect of Dll1 was independent of Notch signalling through Hes1 and voltage-gated Na(+) channel expression/activity.

In situ expression of soluble B7-1 in the context of oncolytic herpes simplex virus induces potent antitumor immunity.

In vivo delivery of immunomodulatory genes is a promising strategy for solid tumor vaccination. A drawback is that it necessitates induction of a large effect from transgene expression in a small percentage of tumor cells. Although the B7 family is known to be the most potent of the costimulatory molecules, gene transduction of B7 alone has not been effective in inducing antitumor immunity in nonimmunogenic tumors by ex vivo methods, much less in vivo. We have developed a novel approach where a gene encoding soluble B7-1, a fusion protein of the extracellular domain of murine B7-1 and the Fc portion of human IgG1, is delivered to tumor cells in vivo in the context of an oncolytic replication-competent herpes simplex virus, and the gene product is secreted by tumor cells rather than expressed on the cell surface. Defective herpes simplex virus vectors containing the B7-1-immunoglobulin (B7-1-Ig) fusion transgene (dvB7Ig) were generated using G207 as a helper virus and tested in the poorly immunogenic murine neuroblastoma, Neuro2a, in syngeneic A/J mice. Intraneoplastic inoculation of dvB7Ig/G207 at a low titer successfully inhibited the growth of established s.c. tumors, despite the expression of B7-1-Ig being detected in only 1% or fewer of tumor cells at the inoculation site, and prolonged the survival of mice bearing intracerebral tumors. Immunohistochemistry of dvB7Ig/G207-inoculated tumors revealed a significant increase in CD4+ and CD8+ T-cell infiltration compared with control tumors inoculated with defective vector expressing alkaline phosphatase (dvAP/G207). The antitumor effect of dvB7Ig/G207 was not manifested in athymic mice. In vivo depletion of immune cell subsets in A/J mice further revealed that CD8+ T cells, but not CD4+ T cells, were required. Animals cured of their tumors by dvB7Ig/G207 treatment were protected against rechallenge with a lethal dose of Neuro2a cells but not SaI/N cells. The results demonstrate that the use of soluble B7-1 for immune gene therapy is a potent and clinically applicable means of in situ cancer vaccination.

Enumeration of human alloreactive helper T lymphocyte precursor frequencies by limiting dilution analysis of interleukin-2 production.

We describe a limiting dilution assay for the enumeration of alloreactive interleukin-2 (IL-2) producing helper T lymphocyte precursors (HTLp). In place of the commonly used CTLL cell line, we have employed concanvalin A (ConA) stimulated rat thymocytes as IL-2 responsive indicator cells in a proliferation assay to detect IL-2 levels in limiting dilution microculture supernatants. The proliferation of ConA stimulated thymocytes induced by either recombinant IL-2 or culture supernatants could be blocked by co-incubation with a monoclonal antibody against the rat IL-2 receptor alpha chain, demonstrating the specificity of the response. Our investigations of alloantigen-induced IL-2 production show that (i) a minimum stimulator cell irradiation dose of 50-60 Gy is required to prevent backstimulation of microcultures; (ii) frequencies of alloreactive HTLp are significantly associated with HLA-DR antigen matching between responder and stimulator; (iii) HTLp frequencies detected in assays using B lymphoblastoid cell line stimulators are significantly higher than in assays employing peripheral blood lymphocyte stimulators but possibly reflect a degree of non-specific activation; and (iv) allosensitized responders exhibit altered kinetics of IL-2 production which may permit discrimination between sensitized and naive individuals. Our results both confirm and extend previous reports concerning such features of the alloresponse in humans and demonstrate that ConA stimulated thymocytes are a suitable alternative to CTLL as IL-2 responsive indicator cells in limiting dilution assays for HTLp analysis.

Spontaneous acceptance of liver allografts in the rat. Analysis of the immune response.

In a model of arterialized rat liver transplantation, the biological indicators of liver dysfunction and the phenotype and in vitro function of graft-infiltrating cells have been compared in rejected (DA-to-Lew) and spontaneously accepted (Lew-to-DA) grafts, 2-8 days after grafting. Recipients of rejected and nonrejected allografts had, during this time, similar loss in body weight and plasma levels of transaminase. The markers of cholestasis, however, increased from days 3 and 4 onward in the recipients of rejected grafts, but remained low and similar in the recipients of nonrejected allografts and those of syngeneic grafts. From days 2 to 6 the phenotype, IL-2 responsiveness, and donor-specific cytotoxic potential of the leukocytes infiltrating rejected and nonrejected allografts were comparable. On days 7 and 8, although the proportion of T cell subpopulations was identical in both combinations, activated CD4+ graft-infiltrating cells were reduced in the nonrejected grafts. Also at this time, donor-specific cytotoxic cells were no longer detected in nonrejected grafts, whereas activity had reached a peak in the rejected grafts. These results suggest that liver grafts in both the LEW-->DA (grafts not rejected) and DA-->LEW (grafts rejected) strain combinations undergo tissue damage, but that the type of damage differs between the two combinations. Specifically, cholestasis was only observed in grafts that would subsequently be rejected. The difference in graft damage occurred at a very early time point (3 or 4 days after grafting), at which time neither the intensity nor phenotype of the graft infiltrate, its IL-2 responsiveness, or its cytotoxic potential varied between the two combinations. Thus, a lack of immune reactivity, as assessed by these parameters, does appear not to be responsible for spontaneous acceptance of liver transplants in the LEW-->DA strain combination.

Lack of correlation between the induction of donor class I and class II major histocompatibility complex antigens and graft rejection.

The induction of donor major histocompatibility complex (MHC) antigens on nonrejected and rejected rat renal allografts was compared at various times after transplantation in two strain combinations, DA-to-PVG and LEW-to-DA. Graft rejection was prevented by preoperative donor-specific blood transfusion (DST). Quantitative absorption analysis and immunohistology were performed using monoclonal antibodies specific for donor class I and class II MHC antigens. A significant increase in the expression of donor MHC antigens, both class I and class II, was demonstrated on nonrejected as well as rejected kidneys after transplantation. A kinetic analysis showed that induction of donor class I antigens was accelerated on the nonrejected grafts, and by day 5 the nonrejected kidneys showed increased expression of class I antigen when compared with the rejected grafts (a 37- vs. a 25-fold increase in expression). Increased expression of donor class I antigens persisted on the nonrejected grafts and was still detectable on long-term-surviving kidneys, 50 days after transplantation. The magnitude of class II antigen induction was similar on both rejected and nonrejected grafts (8-fold by 5 days after transplantation). Immunohistology demonstrated that class I and class II antigens were induced on identical structures in the kidney in both situations. In particular the vessel endothelia, which do not express class II antigens in normal kidney, become strongly positive in both rejected and nonrejected grafts 5 days after transplantation. Although renal allograft rejection is completely suppressed in rats given a single donor-specific blood transfusion before transplantation, graft survival cannot be explained by the lack of induction of donor MHC antigens. Donor MHC antigens are induced on these nonrejected kidney grafts, and therefore they could act as target molecules for the effector cells that mediate graft destruction. Thus the induction of donor MHC antigens on tissue allografts should not be considered as indicative of a rejection response resulting in graft destruction.

The immune response following small bowel transplantation: I. An unusual pattern of cytokine expression.

Acute cell mediated graft rejection is frequently associated with an immune response dominated by cytokines like IL-2 and IFNgamma. While small bowel grafts are rejected acutely, there is little information on the type of immune response generated following transplantation and, in particular, whether the cytokine profile resembles that seen during the rejection of other solid organ grafts. In this paper we compare the expression of cytokines in isolated gut tissue following experimental small bowel transplantation with that in heart grafts. Heterotopic small bowel (n=32) and cardiac (n=32) transplants were performed using the following rat strain combinations: syngeneic Lewis (Lew) > Lew (n=8), blood group D Agouti (DA) > Lew (n=8) and allogeneic Lew > DA (n=8), DA > Lew (n=8). Two rats from each group were sacrificed at 1, 3, 5, or 7 days after transplantation. RNA was prepared separately from gut wall, after removing the Peyer's patches (PPs) and mesenteric lymph nodes (MLNs) and from heart. Cytokine (IL-1alpha, IL-2, IL-4, IL-6, IL-10 and IFNgamma) transcripts were analyzed using semiquantitative RT-PCR. Most notably, transcripts of only a single cytokine, IFNgamma, became progressively elevated with time in the rejecting small bowel grafts. This is in marked contrast to the findings presented here for rat cardiac grafts in which transcripts of all cytokines tested show an increase with rejection. This significant and steady increase in IFNgamma expression occurred before there was any clinical or histological evidence of rejection. These data demonstrate that the mechanisms of rejection in small bowel and other solid organ grafts are likely to be different. Further, the unique rise in IFNgamma expression in the gut wall may be a valuable and early indicator of graft rejection.

The immune response following small bowel transplantation. II. A very early cytokine response in the gut-associated lymphoid tissue.

The small bowel has a unique amount of closely associated lymphoid tissue in the form of mesenteric lymph nodes (MLNs) and Peyer's patches (PPs). It is rather unclear how this may affect the immune response to transplants involving small bowel. It is clear, however, that host-derived leukocytes infiltrate this lymphoid tissue very rapidly after transplantation of small bowel, which suggests the possibility of an early immune response within this compartment. To investigate this possibility, we analyzed, using a semiquantitative reverse transcriptase-polymerase chain reaction, the level of cytokine transcripts within isolated MLNs and PPs for the first 7 days after small bowel transplantation. Heterotopic small bowel (n=32) transplants were performed using the following rat strain combinations: syngeneic Lewis (Lew)-->Lew (n=8), blood group D Agouti (DA)-->DA (n=8), allogeneic Lew-->DA (n=8), and allogeneic DA-->Lew (n=8). Two rats from each group were killed at 1, 3, 5, and 7 days after transplantation. RNA was prepared separately from PPs and MLNs before analysis of transcripts for interleukin (IL) 2, IL-4, IL-10, IL-6, IL-1alpha, and interferon (IFN) gamma. No increase in transcripts for IL-2 or IL-10 was observed in either PPs or MLNs of syngeneic grafts. A small rise in IL-6, IL-1alpha, and IFN-gamma transcripts was seen in MLNs and IFN-gamma transcripts in PPs of syngeneic grafts. In contrast, in allografts an extremely early increase in cytokine transcripts was observed; all cytokine transcripts tested were elevated within the first 24 hr after transplantation. Indeed, the peak response of both IL-2 and IL-10 occurred within 1 to 3 days after grafting. This early immune response in the lymphoid tissue may not be controlled by immunosuppression delivered only at the time of transplantation, and therefore may be responsible for the difficulty in achieving adequate immunosuppression in small bowel transplantation.

Cytokine gene expression in pancreatic islet grafts in the rat.

We examined the production of cytokine message in allogeneic and syngeneic rat pancreatic islet grafts using specific primers and polymerase chain reaction. Freshly isolated islet preparations contained transcripts for interleukin (IL)-1alpha, IL-6, IL-10, and interferon-gamma (IFN-gamma) but not for IL-2. IL-1alpha in allogeneic grafts showed increased and consistently high expression from 1 to 7 days after transplantation, but the level in syngeneic grafts fell quickly to pretransplant levels. IL-2 and IFN-gamma transcripts were found in allogeneic grafts at 1, 3, 5, and 7 days after transplantation with a peak at day 5, but these cytokines were almost absent from syngeneic grafts. The peak of IL-6 expression was 1 day after transplantation in both syngeneic and allogeneic grafts, and then the level fell quickly. IL-10 was produced at approximately the same high level at all time points in both syngeneic and allogeneic grafts. The results show that freshly isolated islet preparations contain IL-1alpha, IL-6, IL-10, and IFN-gamma transcripts at the time of transplantation. The initial production of cytokines in islet grafts, especially IL-1, may explain phenomena such as graft nonfunction, rapid rejection, and lack of response to immunosuppression.

Patterns of graft infiltration and cytokine gene expression during the first 10 days of kidney transplantation.

Understanding of the events preceding acute cellular rejection of kidney transplants would be useful in the development of immunosuppressive strategies to prevent rejection. Information about these events in humans has been scarce, because of the lack of early, serial, biopsy samples. We took daily fine needle aspirates from kidney allografts for the first 10 days after transplant. Samples were analyzed by morphological cytology of graft-infiltrating cells, and reverse transcriptase-polymerase chain reaction for detection of interleukin (IL)-2, IL-4, IL-6, IL-10, and gamma-interferon gene expression. During the first 4 days, all of the grafts developed a low-grade monocyte-rich mononuclear cell infiltrate, accompanied by IL-10 gene expression. Thereafter, the infiltrates either remained stable or intensified. Of the 13 grafts with dense infiltrates, seven developed graft dysfunction. The remaining six did not, despite significant interstitial infiltrates. Both rejecting and nonrejecting dense infiltrates were associated with a biphasic pattern of IL-2 and gamma-interferon gene expression, preceding and accompanying lymphocytic graft infiltration. Grafts that did not develop dense infiltrates had no detectable IL-2 or gamma-interferon gene expression and did not suffer cellular rejection during the study period. The development of both rejecting and nonrejecting infiltrates was strongly associated with DR mismatches between donor and recipient. IL-2 and gamma-interferon gene expression are necessary, but not sufficient, for the development of acute cellular rejection in the first 10 days of kidney transplantation, and are more closely associated with the period leading up to rejection than with the period of graft dysfunction.

Effect of one-HLA-haplotype-matched and HLA-mismatched blood transfusions on recipient T lymphocyte allorepertoires.

BACKGROUND: Pretransplant blood transfusion has a well-known beneficial effect on posttransplant graft survival. Recently, it has been proposed that the clinical benefit of transfusion is due to HLA-DR antigen sharing between the blood donor(s) and the recipient. Immunological studies have suggested that this might result from a functional deletion of donor-reactive cytotoxic T lymphocytes. METHODS: We investigated frequencies of alloreactive lymphocyte precursors with cytotoxic or interleukin-2-producing helper function by limiting dilution analysis in 10 renal dialysis patients before and after transfusion with fresh, allogeneic whole blood. Five patients received blood transfusions from donors matched for one HLA haplotype (or one HLA-B-DR antigen) and the other five patients received blood from fully HLA-mismatched donors. RESULTS: Contrary to some previous reports, frequency analysis of cytotoxic T lymphocyte precursors revealed no significant differences between the two treatment groups in terms of development of blood donor-specific hyporesponsiveness after transfusion. Split-well analysis of cytotoxic T lymphocyte precursors reactive with single-mismatched HLA antigens demonstrated that the effects of transfusion on alloreactive specificity are complex and may vary depending on the particular antigens mismatched between the recipient and blood donor. Analysis of donor-specific helper T lymphocyte precursor frequencies revealed a significant decrease of interleukin-2-producing cells 3 months after transfusion in the total patient population. This effect was most prominent in the recipients of HLA-mismatched blood, but it also exhibited some degree of nonspecificity, as frequencies of third-party reactive helper T lymphocyte precursors were also significantly reduced. CONCLUSIONS: Our overall results suggest that the degree of HLA matching between blood donor and recipient does not greatly influence the effect of blood transfusion on the T lymphocyte allorepertoire. The apparent induced down-regulation of helper T lymphocyte activity may play a role in the reported immunosuppressive effects of allogeneic blood transfusion.

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.