Antibodies to the serine rich Entamoeba histolytica protein (SREHP) prevent amoebic liver abscess in severe combined immunodeficient (SCID) mice

Amoebic liver abscess caused by Entamoeba histolytica is a major cause of morbidity and mortality worldwide. We used mice with severe combined immunodeficiency (SCID mice) to study the role of antibody in protection from amoebic liver abscess, and to identify protective antigens of E. histolytica. Antisera to recombinant versions of two major surface antigens of E. histolytica, the serine rich E. histolytica protein (SREHP) and the 170 kDa adhesin were used in this study. We found that 100% of SCID mice passively immunized with antiserum to the recombinant SREHP molecule were protected from developing amoebic liver abscess after intrahepatic challenge with virulent E. histolytica trophozoites. In contrast, preimmune serum, antiserum to a portion of the 170 kDa adhesin, and antiserum to the trpE fusion partner of SREHP did not protect SCID mice from amoebic liver abscess. Our study demonstrates that antibodies to a recombinant version of the amoebic SREHP molecule can protect against amoebic liver abscess, and suggest the recombinant SREHP molecule should be considered as a possible vaccine candidate to prevent amoebic liver abscess.     

Hypoxia improves expansion potential of human cord blood-derived hematopoietic stem cells and marrow repopulation efficiency

Objectives: In bone marrow, hematopoietic stem cells (HSCs) reside in the most hypoxic endosteum niche, whereas the proliferating progenitors are located near the relatively oxygen‐rich vascular region. High oxygen tension is potentially detrimental to HSCs. The objective of this investigation was to compare cellular, functional, and molecular responses of human umbilical cord blood (UCB)‐derived hematopoietic stem and progenitor cells in culture under hypoxic and normoxic conditions. Methods: CD133‐enriched UCB cells were cultured in growth factor containing serum‐free and serum‐supplemented medium under 5% O₂ (hypoxia) or 21% O₂ (normoxia) for 10 d. The phenotypes of expanded cells were analyzed by flow cytometry and the engraftability by SCID‐repopulation assay. The expression of hypoxia‐inducible factor (HIF)‐1α and some of its target genes was analyzed by real‐time RT‐PCR. Results: In hypoxic culture, CD34⁺ CD38^? cells were expanded about 27‐fold, which was significantly (P < 0.01) higher than that obtained in normoxic culture. Serum‐free culture did not support the growth of cells in the presence of 21% O₂. Myeloid colony‐forming potential of cells was significantly (P < 0.05) increased in 5% O₂ compared with 21% O₂ culture. SCID‐repopulation efficiency seems to be better preserved in the cells cultured under hypoxic conditions. Hypoxia significantly (P < 0.05) induced the expression of HIF‐1α, vascular endothelial growth factor (VEGF), and ABCG2 genes and also upregulated CXCR4 receptor expression. Conclusions: Low oxygen tension enhanced the proliferation of UCB‐derived HSC/progenitor cells and maintenance of SCID‐repopulating cells than normoxia. These expanded cells are expected to be beneficial in the patients who lack human leukocyte antigen (HLA)‐matched donors.     

Comparison of human lung cancer/SCID mouse tumor xenografts and cell culture growth with patient clinical outcomes

Leukemic cell growth in SCID mice has been reported as a predictor of disease relapse. However, there is a paucity of literature regarding xenograft growth and clinical outcomes in non-small cell lung cancer (NSCLC). Seventy-nine specimens from patients with NSCLC were either subcutaneously implanted into SCID mice and/or placed in tissue culture. Retrospective chart review was correlated with stage, histology, necrosis, disease-free interval, and survival. Tumor xenografts were successfully established with 17 of 37 (46%) tumor biopsy tissues. Thirteen of 59 (22%) specimens grew in cell culture. Patients whose tumors grew in SCID mice had no difference in survival compared to those with no growth (n=20, p=0.42). Median survival was 36 months in 13 patients whose tumors grew in cell culture compared to 39 months in 46 patients without growth. Eight of 12 (67%) patients with metastasis showed SCID/human xenograft growth, whereas nine of 25 (36%) without metastases did so (p=0.08). Growth of tumor cells in vitro occurred in 11 of 31 (35%) adenocarcinomas, one of 25 (4%) squamous cell carcinomas, and one of three (33%) large cell carcinomas (p=0.02). Well or moderately differentiated tumors grew in cell culture in only two of 22 (9%), whereas poorly or undifferentiated tumors grew in 11 of 32 (34%) cases (p=0.03). We conclude that neither the ability of a tumor to engraft and grow in SCID mice nor its ability to grow in vitro in cell culture is a reliable predictor of disease outcome or survival in patients with NSCLC. The ability to propagate tumors in vitro appears to be more dependent upon the histological type of tumor and its degree of differentiation.     

The SCID mouse mutant: definition and potential use as a model for immune and hematological disorders

Mice homozygous for a SCID mutation (SCID mice) are severely deficient in T and B lymphocytes. The absence of effector T and B cells has encouraged investigators to attempt engraftement of SCID mice with human fetal tissues, mature lymphocytes, hematopoietic progenitors and tumors. SCID mice can be reconstituted with human lymphocytes and are of interest for studying normal and abnormal lymphocyte development and function. SCID mice are also providing an in vivo model of infectious diseases. In addition, SCID mice readily support normal and pathologic human hematopoiesis differentiation and is useful for testing innovative hematological disease therapy. SCID mice with a fully functionnal human immune or hematopoietic system therefore seem to be extremely valuable for biomedical research.     

Mechanisms of innate and acquired resistance to Cryptosporidium parvum infection in SCID mice

SCID mice, which lack T and B cells, were used as hosts to investigate the nature of both T cell-independent and T-cell-dependent immune responses to infection with Cryptosporidium parvum. We found previously that SCID mice developed chronic infections in which the level of oocyst excretion was low up to about eight weeks post-infection but then increased significantly to cause morbidity and death after 13 weeks. In the present study, weekly administration of an anti-IFN-γ monoclonal antibody (MoAb) resulted in a shortened prepatent time, significant increase in oocyst excretion and early onset of disease and death. These results suggested an immunologically mediated resistance to C. parvum in the SCID host which required the production of IFN-γ. Attempts to demonstrate a role for TNF in nonspecific immunity were unsuccessful as injection of mice at weekly intervals with an anti-TNF MoAb failed to alter the course of infection. In contrast to the chronic infection observed in the mice above, SCID mice reconstituted with spleen cells from naïve BALB/c mice were able to recover. Depletion of CD4⁺ cells from the donor population abrogated this protective effect. Mice receiving spleen cells depleted of CD8⁺ cells were able to recover but the patent infection was prolonged compared with those obtained in mice receiving unfractionated cells. These results demonstrate that CD4⁺ cells are necessary for the development of immunity to C. parvum infection in reconstituted SCID mice, but, in addition, that CD8⁺ cells also make a significant contribution to this immunity.     

Evaluation of TCR Vβ subfamily T cell expansion in NOD/SCID mice transplanted with human cord blood hematopoietic stem cells

Examination of the T cell receptor (TCR) gene repertoire is important in the analysis of the immune status of models, because clonal expansion of T cells permits the identification of specific antigen responses of T cells. Little is known about T-cell immunity in the humanized NOD/SCID mouse model. TCR Vβ repertoire usage and clonality were analyzed to investigate the distribution and clonal expansion of TCR Vβ subfamily T cells in NOD/SCID mice transplanted with human cord blood (CB) hematopoietic stem cells. The NOD/SCID mice were sublethally irradiated (⁶⁰Co, 300cGy) to eliminate residual innate immunity in the host. The experimental mice were transplanted intravenously with CB CD34⁺ cells sorted by MACS. After 6 weeks, RNA was obtained from peripheral blood, bone marrow and thymus of the study animals. The gene expression and clonality of the TCR Vβ repertoire were determined by RT-PCR and GeneScan techniques. A restricted range of TCR Vβ usage was exhibited in the bone marrow of mice, which included TCR Vβ 1, 2, 9, 13 and 19. Further, oligoclonal expression of some TCR Vβ subfamilies (Vβ9, 13, 19) was identified by GeneScan technique. To investigate the reason for oligoclonal expansion of the TCR Vβ subfamily T cells from CB in mouse models, the T-cell culture with tissue-antigen of NOD/SCID mouse was performed in vitro. The cells from peripheral blood mononuclear cells and bone marrow, spleen, thymus in NOD/SCID mice were frozen and thawed, and used as tissue-antigen. CB mononuclear cells were separately cultured with the component from those murine cells for 15–20 days. Oligoclonal expression or oligoclonal trend of some TCR Vβ subfamilies (Vβ10, 11 and Vβ2, 15, 16, 19) was detected in T cells after stimulation with tissue-antigen of NOD/SCID mouse. Interestingly, a similar clonal expansion of the TCR Vβ11 subfamily was found in T cells cultured with peripheral blood, bone marrow and spleen respectively. The TCR Vβ subfamily T cells could be reconstituted in humanized NOD/SCID mouse transplanted with CD34⁺ cells from CB. The restricted expression and clonal expansion of some CB T cell clones may be induced by tissue-antigens of NOD/SCID mice.     

Pulmonary diseases in children with severe combined immune deficiency and DiGeorge syndrome

Pulmonary disease is a common presenting feature and complication of T-cell immunodeficiency. We retrospectively reviewed 15 children with severe combined immune deficiency (SCID) and 19 children with DiGeorge syndrome at the time of their first presentation to the Royal Children's Hospital in the 15-year period from 1981 to 1995. In children with SCID, pulmonary disease was a common (67%) presenting feature and the organisms identified were Pneumocystis carinii (PCP) (n = 7), bacteria (n = 4), viruses (n = 3), and a fungus (n = 1). Late pulmonary complications included lower respiratory tract infections, bronchiolitis obliterans, and lymphointerstitial pneumonitis. Pulmonary infections were common (17 occasions) and the organisms identified were bacteria (n = 7), viruses (n = 6), fungi (n = 3), and Mycobacterium tuberculosis (n = 1). Pulmonary complications were responsible for 5 of 9 deaths. PCP was not identified as a late complication in any child, presumably as a result of effective prophylactic therapy. Although pulmonary disease was not a major presenting feature in children with DiGeorge syndrome, pulmonary complications were common. These included recurrent bacterial and viral infections and bronchomalacia, which complicated management and predisposed to morbidity and mortality, even in those without a T-cell defect. We conclude that pulmonary disease is a common manifestation in children with SCID and DiGeorge syndrome. Pediatr. Pulmonol. 1997; 24:324–330. © 1997 Wiley-Liss, Inc.     

Antibody-dependent neutrophil-mediated parasite killing in non-lethal rodent malaria

The effects of administrating recombinant human granulocyte colony-stimulating factor (rhG-CSF) and passively transferring immune serum on infection with an attenuated variant of Plasmodium berghei XAT (Pb XAT), in severe combined immunodeficiency (SCID) mice were examined. In immune competent (C.B-17) mice, the attenuated parasite infection was inevitably self-resolving and degenerating forms inside erythrocytes appeared, coinciding with the drop in parasitaemia, whereas SCID mice were unable to control parasite growth and all the mice died. Continuous administration with rhG-CSF caused neutrophilic granulocytosis in both SCID and C.B-17 mice. The effect of rhG-CSF on the infection in C.B-17 mice was to suppress the course of the parasitaemia at an early phase whereas it had no effect in SCID mice. When immune serum was transferred on the day of infection, the prepatent period was prolonged two days in both SCID and C.B-17 mice. When administration with rhG-CSF was combined with transfer of immune serum, SCID mice showed four days delay in patency and degenerating parasites were seen during the course of parasitaemia, although the infection was ultimately fatal. C.B-17 mice similarly treated showed a seven day delay in the onset of the patent parasitaemia which was of a lesser magnitude and shorter in duration compared with control mice. On the other hand, when C.B-17 mice were splenectomized three weeks before infection and then treated with rhG-CSF and immune serum, no degenerating parasites were seen during the infection and all mice died with high parasitaemias. These results show that antibody-dependent neutrophil-mediated parasite killing may occur in the spleen of mice infected with P. berghei XAT.     

A novel cDNA-uPA/SCID/Rag2−/−/Jak3−/− mouse model for hepatitis virus infection and reconstruction of human immune system

Although human hepatocyte-transplanted immunodeficient mice support infection with hepatitis viruses, these mice fail to develop viral hepatitis due to the lack of an adaptive immune system. In this study, we generated new immunodeficiency cDNA-urokinase-type plasminogen activator (uPA)/SCID/Rag2^−/−/Jak3^−/− mice and established a mouse model with both a humanized liver and immune system. Transplantation of human hepatocytes with human leukocyte antigen (HLA)-A24 resulted in establishment of a highly replaced liver in cDNA-uPA/SCID/Rag2^−/−/Jak3^−/− mice. These mice were successfully infected with hepatitis B virus (HBV) and hepatitis C virus (HCV) for a prolonged period and facilitate analysis of the effect of anti-HCV drugs. Administration of peripheral blood mononuclear cells (PBMCs) obtained from an HLA-A24 donor resulted in establishment of 22.6%–81.3% human CD45-positive mononuclear cell chimerism in liver-infiltrating cells without causing graft-versus-host disease in cDNA-uPA/SCID/Rag2^−/−/Jak3^−/− mice without human hepatocyte transplantation. When mice were transplanted with human hepatocytes and then administered HLA-A24-positive human PBMCs, an alloimmune response between transplanted human hepatocytes and PBMCs occurred, with production of transplanted hepatocyte-specific anti-HLA antibody. In conclusion, we succeeded in establishing a humanized liver/immune system characterized by an allo-reaction between transplanted human immune cells and human liver using a novel cDNA-uPA/SCID/Rag2^−/−/Jak3^−/− mouse. This mouse model can be used to generate a chronic hepatitis mouse model with a human immune system with application not only to hepatitis virus virology but also to investigation of the pathology of post-transplantation liver rejection.     

Minisatellite instability in severe combined immunodeficiency mouse cells

We have recently found that okadaic acid, which shows strong inhibitory activity on protein serine/threonine phosphatases and tumor-promoting activity in vivo and in vitro, induces minisatellite mutation (MSM). Human tumors and chemically induced counterparts in experimental animals are also sometimes associated with MSM. In the present study, we demonstrated minisatellite (MS) instability in severe combined immunodeficiency (SCID) cells in which the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is impaired. Cells from a SCID fibroblast cell line transformed by simian virus 40 large tumor antigen, SC3VA2, and from an embryonal SCID fibroblast cell line, SC1K, were cloned and propagated to 10⁷ to 10⁸ cells, and then subjected to subcloning. After propagation of each subclone to 10⁷ to 10⁸ cells, DNA samples were digested with HinfI and analyzed by Southern blotting using the Pc-1 MS sequence as a probe. Under low-stringency conditions, about 40 MS bands were detected, with 45% ± 6% and 37% ± 3% of SC3VA2 and SC1K cells, respectively, having MSM. In contrast, cells from the RD13B2 cell line, which was established from SCVA2 by introducing human chromosome 8q fragments, on which DNA-PKcs is known to reside, to complement the SCID phenotype, showed a very low frequency of MSM (3% ± 3%). The high frequencies of MSM in SC3VA2 and SC1K were significant, with no difference between the two. The present study clearly demonstrates that MS instability exists in SCID fibroblasts, suggesting that DNA-PKcs might be involved in the stable maintenance of MS sequences in the genome.     

A randomized trial of depression assessment intervention in home health care

OBJECTIVES: To determine whether an educational intervention would improve depression assessment and appropriate referral. Secondary analyses tested whether referral led to depression improvement. DESIGN: Training in the Assessment of Depression (TRIAD) was a three‐group, nurse‐randomized trial. Researchers interviewed randomly selected patients at baseline and 8 weeks. SETTING: Three certified home healthcare agencies in Westchester County, New York. PARTICIPANTS: Fifty‐three medical/surgical nurses were randomized within agency to three intervention groups: full, minimal, or control. Research contact with nurses' patients (aged >65; N=477) yielded 256 (53.7%) enrolled subjects, 84 (17.6%) ineligibles, and 120 (25.2%) refusals; 233 of the 256 (87.1%) enrolled patients completed follow‐up interviews. INTERVENTION: Nurse training in clinically meaningful use of depression sections of Medicare's mandatory Outcome and Assessment Information Set (OASIS). MEASUREMENTS: Nurse‐assessed mood or anhedonia (OASIS) versus research assessments using the Structured Clinical Interview for Axis I Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Disorders (SCID); referrals for mental health evaluation (agency records), and depression severity (24‐item Hamilton Depression Rating Scale; HDRS). RESULTS: Referral rates for patients with (SCID) depressed mood or anhedonia (n=75) varied according to nurse group: 50.0% full intervention, 18.5% minimal, 21.4% control (P=.047). Rates for nondepressed patients (n=180) did not differ (4.9%, 2.0%, 5.8%, respectively; P=.60). In patients with major or minor depression (n=37), referral was associated with symptom improvement. Change in HDRS was 5 points greater in referred patients than others (P=.04). Concordance between OASIS and SCID did not differ between intervention groups. CONCLUSION: TRIAD showed that training nurses to assess for depression using an approach developed in partnership with home healthcare agencies led to appropriate referral and care for depressed patients.     

The DNA damage response in DNA-dependent protein kinase-deficient SCID mouse cells: Replication protein A hyperphosphorylation and p53 induction

Severe combined immunodeficient (SCID) mice display an increased sensitivity to ionizing radiation compared with the parental, C.B-17, strain due to a deficiency in DNA double-strand break repair. The catalytic subunit of DNA-dependent protein kinase (DNA-PK_CS) has previously been identified as a strong candidate for the SCID gene. DNA-PK phosphorylates many proteins in vitro, including p53 and replication protein A (RPA), two proteins involved in the response of cells to DNA damage. To determine whether p53 and RPA are also substrates of DNA-PK in vivo following DNA damage, we compared the response of SCID and MO59J (human DNA-PK_cs-deficient glioblastoma) cells with their respective wild-type parents following ionizing radiation. Our findings indicate that (i) p53 levels are increased in SCID cells following ionizing radiation, and (ii) RPA p34 is hyperphosphorylated in both SCID cells and MO59J cells following ionizing radiation. The hyperphosphorylation of RPA p34 in vivo is concordant with a decrease in the binding of RPA to single-stranded DNA in crude extracts derived from both C.B-17 and SCID cells. These results suggest that DNA-PK is not the only kinase capable of phosphorylating RPA. We conclude that the DNA damage response involving p53 and RPA is not associated with the defect in DNA repair in SCID cells and that the physiological substrate(s) for DNA-PK essential for DNA repair has not yet been identified.     

Pancreatic tumor growth is regulated by the balance between positive and negative modulators of angiogenesis

There is increasing evidence for the implication of tumor-derived angiogenic and anti-angiogenic factors in controlling tumor growth in vivo. In this study, we documented the production of inhibitors of angiogenesis by pancreatic cancer cells and examined how changes in the balance between pro- and anti-angiogenic factors regulate tumor growth in vivo. The human pancreatic cancer cell line Hs-776T (HS-W) produces slow-growing tumors in SCID mice. Cells of a variant form (HS-R) of Hs-776T produced faster-growing tumors compared to HS-W. Characterization of HS-W and HS-R cells in vitro showed similar proliferation rates and production of the angiogenic factors vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Analyzes of anti-angiogenic factors showed comparable levels of angiostatin and thrombospondin 1 and 2, but endostatin was only detected in conditioned media of HS-W cells and was absent in HS-R. Cell proliferation was similar in both tumor types in vivo, whereas HS-W tumors demonstrated increased apoptosis with a high percentage of apoptotic endothelial cells (EC). Subsequently, VEGF was over-expressed in Hs-776T cells (HS-VF), resulting in rapidly growing tumors and lowering tumor and EC apoptosis. Collectively, our study confirms that tumor growth is dependent on its ability to increase the angiogenic stimulus or to reduce the amounts of endogenous anti-angiogenic factors.     

Newborn Screening for Severe Combined Immunodeficiency

Purpose of Review

This review provides a brief history of newborn screening (NBS) for severe combined immunodeficiency (SCID), discusses the theoretical basis for the T cell receptor excision circle (TREC) assay, highlights the results of recent studies using the TREC, and provides practical advice for the evaluation of infants with an abnormal TREC assay.

Recent Findings

Currently, all but three states perform NBS for SCID in the USA. NBS using the TREC assay is highly sensitive in identifying infants with SCID and may also identify infants with T cell lymphopenia due to other causes such as congenital syndromes, multiple congenital anamolies, and some combined immunodeficiencies.

Summary

Regardless of the genetic etiology, all forms of SCID are characterized by a severe deficiency of naïve T cells. TRECs are a biomarker of newly formed, naïve T cells that have recently left the thymus. Consequently, the TREC assay identifies infants with SCID and other causes of severe T cell lymphopenia.

     

Tumorigenicity of human T-cell leukemia virus type I-infected cell lines in severe combined immunodeficient mice and characterization of the cells proliferating in vivo

The mechanism involved in leukemogenesis and neoplastic cell growth of adult T-cell leukemia (ATL) still remains unclear. We examined the tumorigenicity of human T-cell leukemia virus type I (HTLV-I)-infected cell lines in an in vivo cell proliferation model using severe combined immunodeficient (SCID) mice. Eleven HTLV-I-infected cell lines were injected into SCID mice and we found that 4 of them were capable of proliferating in SCID mice. Three of four transplantable cell lines are derived from the leukemic cell clone and 6 of 6 HTLV-I-infected cell lines of nonleukemic cell origin could not engraft in SCID mice. Interestingly, it was shown that some HTLV-I-infected and interleukin-2 (IL-2)-dependent cell lines could successfully engraft in SCID mice. The expression of IL-2 mRNA was not detected in these cell lines growing either in vivo or in vitro. HTLV-I viral products were not detected in 3 of 4 transplantable cell lines proliferating in vivo. Peripheral blood T cells immortalized by introduction of tax gene of HTLV-I were found to have no tumorigenic potential in SCID mice. These data suggest that (1) HTLV-I-infected cell lines of nonleukemic cell origin do not have enough leukemogenic changes to acquire the tumorigenic potential in SCID mice; (2) the IL-2 autocrine mechanism is not directly involved in the tumor cell growth; (3) viral gene expression is not needed for the maintenance of neoplastic cell growth; and (4) the expression of tax gene is not sufficient for the neoplastic cell growth in vivo.     

Polysaccharide antibody responses are impaired post bone marrow transplantation for severe combined immunodeficiency,but not other primary immunodeficiencies

Established treatment of severe combined immunodeficiencies (SCID) and other primary immunodeficiencies (PID) is bone marrow transplantation (BMT). Normal lymphocyte numbers and protein antigen responses are present within 2 years of BMT, polysaccharide antibody responses appear last. Streptococcus pneumoniae infection causes significant morbidity and mortality post-BMT. Previous studies have shown good protein antigen responses post-BMT for SCID and PID, but had not examined the polysaccharide responses. We retrospectively analysed pneumococcal polysaccharide (PPS) responses in our patient series.In total, 22 SCID and 12 non-SCID PID were evaluated, all >2 years post BMT: 17 SCID, 12 PID received chemotherapy conditioning; 17 SCID, three PID had T-cell depleted (TCD) BMT, others had nonconditioned whole marrow BMT. All had normal Haemophilus influenza B and tetanus antibody responses. Of 22 SCID, 13 vs 11/12 PID responded to PPS vaccine (P=0.05). There was no association with donor age, GvHD, B-cell chimerism, or IgG2 level. Fewer TCD marrow recipients responded to PPS (P=0.04). Analysis of the SCID group showed no association of PPS response with type of marrow received. This is the first study to specifically examine PPS antibody responses following SCID and PID BMT. Pneumococcal conjugate vaccine antibody responses should be examined in these children.     

Hepatocellular carcinoma xenograft supports HCV replication: a mouse model for evaluating antivirals

AIM: To develop a hepatocellular carcinoma (HCC) xenograft model for studying hepatitis C virus (HCV) replication in a mice, and antiviral treatment.METHODS: We developed a stable S3-green fluorescence protein (GFP) cell line that replicated the GFP-tagged HCV sub-genomic RNA derived from a highly efficient JFH1 virus. S3-GFP replicon cell line was injected subcutaneously into γ-irradiated SCID mice. We showed that the S3-GFP replicon cell line formed human HCC xenografts in SCID mice. Cells were isolated f...     

Effect of FK-506 on xenografted human Graves' thyroid tissue in severe combined immunodeficient mice

OBJECTIVE We studied the macrolide antibiotic FK-506, an immunosuppressive agent, in an attempt to ameliorate the lesion of autoimmune thyroid disease in human thyroid tissue xenografted into severe combined immunodeficient (SCID) mice. It was not felt appropriate to employ this agent directly in patients with autoimmune thyroid disease because adequate therapeutic modalities are available and the introduction of new, experimental agents could not be justified. Moreover, the study of the tissue before and after treatment could not have been undertaken directly in patients. DESIGN Human thyroid xenografts from four patients with Graves' disease and two normal persons were xenografted into SCID mice. Two weeks after xenograft-ing, human immunoglobulin G (IgG) was detectable in all SCID mice xenografted with Graves' thyroid tissue. Mice were divided into two groups with human IgG levels similar to each other. Mice in the first group were treated with FK-506 daily for 6 weeks; mice in the second (similar) group were given phosphate-buffered saline (PBS) only (control group). MEASUREMENTS Blood samples were taken every 2 weeks from the tail veins for human IgG, thyroid stimulating antibody, thyroperoxidase antibodies, thyroglobulin antibodies, and interferon-gamma (IFN-7). After 8 weeks treatment, animals were sacrificed; thyroid tissue was examined histologically and for thyrocyte HLA-DR expression. FK-506 was also added to thyrocytes in in-vitro tissue culture conditions. RESULTS After 4–6 weeks of FK-506 therapy, human IgG, all thyroid antibodies and IFN-7 were suppressed, while the levels remained elevated in the control group. Lymphocytic infiltration virtually disappeared in the human thyroid tissue of the FK-506-treated mice and thyrocyte HLA-DR expression markedly declined; in the control mice, lymphocytic infiltration remained heavy and HLA-DR expression remained high. On the other hand, FK-506 added directly to thyrocytes in vitro (without lymphocytes) did not reduce thyrocyte HLA-DR expression. CONCLUSIONS FK-506 appears to suppress the activation of intrathyroidal lymphocytes, but not thyrocytes. From these observations, it is concluded that this agent, by its action on intrathyroidal lymphocytes, is able to ameliorate the immunologically mediated histological and serological disturbance in human autoimmune thyroid disease, at least under these circumstances.