Testicular immune cell populations and macrophage polarisation in adult male mice and the influence of altered activin A levels

Detailed morphological characterization of testicular leukocytes in the adult CX₃CR₁^gfp/+ transgenic mouse identified two distinct CX₃CR₁⁺ mononuclear phagocyte (macrophage and dendritic cell) populations: stellate/dendriform cells opposed to the seminiferous tubules (peritubular), and polygonal cells associated with Leydig cells (interstitial). Using confocal microscopy combined with stereological enumeration of CX₃CR₁^gfp/+ cells established that there were twice as many interstitial cells (68%) as peritubular cells (32%). Flow cytometric analyses of interstitial cells from mechanically-dissociated testes identified multiple mononuclear phagocyte subsets based on surface marker expression (CX₃CR₁, F4/80, CD11c). These cells comprised 80% of total intratesticular leukocytes, as identified by CD45 expression. The remaining leukocytes were CD3⁺ (T lymphocytes) and NK1.1⁺ (natural killer cells). Functional phenotype assessment using CD206 (an anti-inflammatory/M2 marker) and MHC class II (an activation marker) identified a potentially tolerogenic CD206⁺MHCII⁺ sub-population (12% of total CD45⁺ cells). Rare testicular subsets of CX₃CR₁⁺CD11c⁺F4/80⁺ (4.3%) mononuclear phagocytes and CD3⁺NK1.1⁺ (3.1%) lymphocytes were also identified for the first time. In order to examine the potential for the immunoregulatory cytokine, activin A to modulate testicular immune cell populations, testes from adult mice with reduced activin A (Inhba^+/-) or elevated activin A (Inha^+/-) were assessed using flow cytometry. Although the proportion of F4/80⁺CD11b⁺ leukocytes (macrophages) was not affected, the frequency of CD206⁺MHCII⁺cells was significantly lower and CD206⁺MHCII^- correspondingly higher in Inha^+/- testes. This shift in expression of MHCII in CD206⁺ macrophages indicates that changes in circulating and/or local activin A influence resident macrophage activation and phenotype and, therefore, the immunological environment of the testis.

An in vitro model demonstrates the potential of neoplastic human germ cells to influence the tumour microenvironment

Testicular germ cell tumours (TGCT) typically contain high numbers of infiltrating immune cells, yet the functional nature and consequences of interactions between GCNIS (germ cell neoplasia in situ) or seminoma cells and immune cells remain unknown. A co-culture model using the seminoma-derived TCam-2 cell line and peripheral blood mononuclear cells (PBMC, n = 7 healthy donors) was established to investigate how tumour and immune cells each contribute to the cytokine microenvironment associated with TGCT. Three different co-culture approaches were employed: direct contact during culture to simulate in situ cellular interactions occurring within seminomas (n = 9); indirect contact using well inserts to mimic GCNIS, in which a basement membrane separates the neoplastic germ cells and immune cells (n = 3); and PBMC stimulation prior to direct contact during culture to overcome the potential lack of immune cell activation (n = 3). Transcript levels for key cytokines in PBMC and TCam-2 cell fractions were determined using RT-qPCR. TCam-2 cell fractions showed an immediate increase (within 24 h) in several cytokine mRNAs after direct contact with PBMC, whereas immune cell fractions did not. The high levels of interleukin-6 (IL6) mRNA and protein associated with TCam-2 cells implicate this cytokine as important to seminoma physiology. Use of PBMCs from different donors revealed a robust, repeatable pattern of changes in TCam-2 and PBMC cytokine mRNAs, independent of potential inter-donor variation in immune cell responsiveness. This in vitro model recapitulated previous data from clinical TGCT biopsies, revealing similar cytokine expression profiles and indicating its suitability for exploring the in vivo circumstances of TGCT. Despite the limitations of using a cell line to mimic in vivo events, these results indicate how neoplastic germ cells can directly shape the surrounding tumour microenvironment, including by influencing local immune responses. IL6 production by seminoma cells may be a practical target for early diagnosis and/or treatment of TGCT.

Long-term controlled normoglycemia in diabetic non-human primates after transplantation with hCD46 transgenic porcine islets

Xenotransplantation of porcine islets into diabetic non-human primates is characterized by (i) an initial massive graft loss possibly due to the instant blood-mediated inflammatory reaction and (ii) the requirement of intensive, clinically unfriendly immunosuppressive therapy. We investigated whether the transgenic expression of a human complement-regulatory protein (hCD46) on porcine islets would improve the outcome of islet xenotransplantation in streptozotocin-induced diabetic Cynomolgus monkeys. Immunosuppression consisted of thymoglobulin, anti-CD154 mAb for costimulation blockade, and mycophenolate mofetil. Following the transplantation of islets from wild-type pigs (n = 2) or from 1,3-galactosyltransferase gene-knockout pigs (n = 2), islets survived for a maximum of only 46 days, as evidenced by return to hyperglycemia and the need for exogenous insulin therapy. The transplantation of islets from hCD46 pigs resulted in graft survival and insulin-independent normoglycemia in four of five monkeys for the 3 months follow-up of the experiment. One normalized recipient, selected at random, was followed for >12 months. Inhibition of complement activation by the expression of hCD46 on the pig islets did not substantially reduce the initial loss of islet mass, rather was effective in limiting antibody-mediated rejection. This resulted in a reduced need for immunosuppression to preserve a sufficient islet mass to maintain normoglycemia long-term.

Human dendritic cells pulsed with specific lipopeptides stimulate autologous antigen-specific T cells without the addition of exogenous maturation factors

Serum-free culture conditions to generate immature human monocyte-derived DC (Mo-DC) were optimized, and the parameters that influence their maturation after exposure to lipopeptides containing CD4(+) and CD8(+) T-cell epitopes were examined. The lipopeptides contained a single CD4(+) helper T-cell epitopes, one of a number of human leucocyte antigen (HLA)-A2-restricted cytotoxic T-cell epitope and the lipid Pam2Cys. To ensure complete maturation of the Mo-DC, we examined (i) the optimal lipopeptide concentration, (ii) the optimal Mo-DC density and (iii) the appropriate period of exposure of the Mo-DC to the lipopeptides. The results showed that a high dose of lipopeptide (30 microm) was no more efficient at upregulating maturation markers on Mo-DC than a low dose (6 microm). There was an inverse relationship between Mo-DC concentration and the mean fluorescence intensity of maturation markers. In addition, at the higher cell concentrations, the chemotactic capacity of the Mo-DC towards a cognate ligand, CCL21, was reduced. Thus, high cell concentrations during lipopeptide exposure were detrimental to Mo-DC maturation and function. The duration of exposure of Mo-DC to the lipopeptides had little effect on phenotype, although Mo-DC exposed to lipopeptides for 48 rather than 4 h showed an increased ability to stimulate autologous peripheral blood mononuclear cells to release interferon-gamma in the absence of exogenous maturation factors. These findings reveal conditions for generating mature antigen-loaded DC suitable for targeted immunotherapy.

Durable clinical responses in patients (pts) with ovarian carcinoma treated on a phase II trial of autologous dendritic cells (DC) pulsed with MUC1

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Background: Mucin 1 (MUC1) is a glycoprotein highly expressed by ovarian carcinoma and is thus a potential antigen for immunotherapy. Following successful phase I results (Loveland et al. Clin Can Res 2006; 12:869), using DC pulsed with mannan-MUC1 fusion protein (DC-MFP), we report a phase II trial in similarly treated pts with ovarian carcinoma. Methods: Eligibility: incurable disease; age = 18 yrs; PS 0–2; no autoimmune disorders; rising CA125 levels (= 25% in 1 mth, confirmed). The primary endpoint was CA125 response (major = 50%, minor = 25%, each confirmed at = 4 wk) or stabilisation (= 3 mths). PBMC were collected by leukapheresis, cultured with IL-4 and GM-CSF to generate DC, and pulsed with MFP on d5. DC were reinjected on d6 as 8 i.d. injections (each 5x106), given 4-weekly × 3, then 10- weekly to 12 mths. Excess cells were cryopreserved for subsequent injections. Results: 28 pts were recruited, with all evaluable for toxicity and 21 for efficacy (received = 3 vaccinations). Characteristics were: serous histology 24 (86%) pts; median age 58 yrs (34–78); PS 0–1 27 (96%) pts; prior systemic therapy (all pts platinum-treated) 1 line 5 pts, 2 line 4 pts, 3 line 10 pts, = 4 lines 9 pts. Leukapheresis was generally required only 6-monthly. Following ex vivo culture, the proportion of CD86+ cells ranged from 40 - 85%. There was no grade = 3 therapy-related toxicity. Of 21 pts, 4 (19%) showed CA125 response or stabilisation. 2 pts had major response: 1 pt with 4 previous lines of systemic therapy (DC-MFP response duration 12+ mths) and 1 pt treated second line (duration 14 mths). One pt had stable disease of 7 mths duration which included 10 wks classified as minor response and one pt, treated fifth-line, had stable disease for 5 mths. An additional pt, treated fourth-line, had >25% CA125 reduction which was not confirmed by repeat CA125. CT scan results were generally concordant with CA125 status. No relationship was seen between clinical benefit and HLA type. 88% of tumours were MUC1+ on IHC. Conclusions: Study treatment was well tolerated and acceptable to pts. There was clear evidence of clinical benefit, including pts who were heavily pre-treated. This approach warrants further study in ovarian carcinoma. Supported by grants from PrimaBiomed Ltd.

No significant financial relationships to disclose.

Genetic engineering for xenotransplantation

Xenotransplantation is being pursued vigorously to solve the shortage of allogeneic donor organs. Experimental studies of the major xenoantigen (Gal) and of complement regulation enable model xenografts to survive hyperacute rejection. When the Gal antigen is removed or reduced and complement activation is controlled, the major barriers to xenograft survival include unregulated coagulation within the graft and cellular reactions involving macrophages, neutrophils, natural killer (NK) cells, and T lymphocytes. Unlike allografts, where specific immune responses are the sole barrier to graft survival, molecular differences between xenograft and recipient that affect normal receptor-ligand interactions (largely active at the cell surface and which may not be immunogenic), are also involved in xenograft failure. Transgenic strategies provide the best options to control antigen expression, complement activation, and coagulation. Although the Gal antigen can be eliminated by gene knockout in mice, that outcome has only become a possibility in pigs due to the recent cloning of pigs after nuclear transfer. Instead, the use of transgenic glycosyl transferase enzymes and glycosidases, which generate alternative terminal carbohydrates on glycolipids and glycoproteins, has reduced antigen in experimental models. As a result, novel strategies are being tested to seek the most effective solution. Transgenic pigs expressing human complement-regulating proteins (DAF/CD55, MCP/CD46, or CD59) have revealed that disordered regulation of the coagulation system requires attention. There will undoubtedly be other molecular incompatibilities that need addressing. Xenotransplantation, however, offers hope as a therapeutic solution and provides much information about homeostatic mechanisms.

A therapeutic human anti-idiotypic antibody mimics CD55 in three distinct regions

The human anti-idiotypic antibody 105AD7 was isolated from a colorectal cancer patient receiving the anti-tumor antibody 791T/36 for radioimmuno-scintigraphy of liver metastases. We have mapped the binding site of 791T/36 to the first two small consensus repeat (SCR) domains of the complement regulatory protein (CD55) that is overexpressed by a wide range of solid tumors. Cloning of both antigen and anti-idiotype has identified the molecular basis of their mimicry. Amino acid homology has been identified between three complementarity-determining regions of 105AD7 and three regions of CD55 within the first two SCR domains. 791T/36 and anti-anti-idiotypic (Ab3) polyclonal antibodies raised against 105AD7 showed specific binding to these peptides. The antibodies were also found to bind synergistically to combinations of these peptides, indicating cooperativity between the peptides in stabilizing antibody binding. This also implies that the contact face on both CD55 antigen and 105AD7 is generated by the cooperation of several peptides positioned on two domains in each protein. Thus a human monoclonal anti-idiotypic antibody generated by a cancer patient is able to show both amino acid and structural homology with the complement regulatory protein CD55. These findings help identify the mechanism by which a human anti-idiotypic antibody is able to mimic a tumor-associated antigen and stimulate anti-tumor B and T cell responses.

Inhibition of hyperacute transplant rejection by soluble proteins with the functional domains of CD46 and FcgammaRII

BACKGROUND

Recombinant soluble forms of complement regulatory molecules, including the human complement regulatory protein CD46 (rsCD46), have been shown to inhibit hyperacute transplant rejection (HAR) and protect against complement-mediated inflammatory tissue damage. Similarly, recombinant soluble forms of the immunoglobulin receptor FcgammaRII (rsFcgammaRII) can attenuate antibody-mediated inflammatory responses. We have produced and tested the function of novel recombinant chimeric proteins that incorporate the functional domains of both CD46 (membrane cofactor protein, MCP) and the low affinity human IgG receptor FcgammaRII (CD32).

METHODS

Two recombinant soluble chimeric proteins (CD46:FcR and FcR:CD46) were designed and produced using a human cell expression system. Their ability to protect cells against complement-mediated lysis (through the CD46 domain) and bind human IgG (through the Fc receptor domain) was assessed in vitro. They were also tested in vivo in the rat reverse passive Arthus reaction and a murine model of hyperacute cardiac transplant rejection.

RESULTS

In vitro, the functional domains of the chimeric proteins each retained their activity. In vivo, the serum half-life of the recombinant chimeric proteins in mice was more than either rsCD46 or rsFcgammaRII. In the rat reverse passive Arthus reaction, intradermal injection of each recombinant protein substantially reduced inflammatory skin edema (>50%) and polymorphonuclear neutrophil infiltration (>90%). In the hyperacute rejection model, i.v. treatment with FcR:CD46 prevented complement-mediated rejection, macroscopic bruising, edema, and thrombosis more effectively than rsCD46.

CONCLUSIONS

CD46/FcgammaRII bifunctional proteins have an improved ability to control complement-mediated hyperacute graft rejection and have therapeutic potential in other conditions involving antibody-mediated inflammation.

Current and future prospects for xenotransplantation

The transplantation of organs and tissues between animal species, or xenotransplantation, is the focus of a growing field of research, owing primarily to the increasing shortage of allogeneic donor organs. The pig stands out as the most suitable donor animal for humans; however, xenografts (e.g. pig organs) used for human transplantation are normally destroyed by the host within minutes by hyperacute xenograft rejection. An improved understanding of the immune recognition and rejection of xenografts has resulted in new therapies that can partially overcome hyperacute rejection (HAR), delayed xenograft rejection (DXR) or acute vascular xenograft rejection. Strategies to diminish immunogenicity following xenotransplantation can be divided into two approaches: those directed at the recipient (e.g. antibodies or complement depletion or inhibition and tolerance induction) and those directed at the donor (e.g. transgenic modifications to express human complement-regulatory proteins or removal or displacement of alphaGal epitopes). DXR is likely to be controlled by transgenic inhibition of endothelial cell activation (e.g. inhibition of NF-kappaB). Transgenic pigs required for xenotransplantation will soon be generated at a greater efficiency and precision using nuclear transfer and cloning when compared to pronuclear injection. Of greater significance is that nuclear transfer offers the ability to target gene insertion selectively to specific gene loci and to delete specific genes in the pig. Experimental pig-to-primate organ xenotransplantation is currently under way, and results show increased transplant function from minutes to days and weeks. The final therapeutic regimen that allows survival of a discordant xenograft is likely to involve a combination of 'modified' functional genes in the donor organ, the development of immunological tolerance to pig antigens and administration of novel therapeutic agents, including immunosuppressants, that can control natural killer (NK) cell and monocyte mediated responses.

Autoreactive cytotoxic T cells in mice are induced by immunization with a conserved mitochondrial enzyme in Freund's complete adjuvant

Standard methods to generate autoimmune reactions in mice, by immunization with antigens emulsified with adjuvants, stimulate strong helper (CD4) T-cell and antibody responses but are not reported to induce cytolytic CD8 T cells. The aim of this study was to assess whether specific autoreactive CD8 T cells could be readily generated after immunization with a 'weak' autoantigen in adjuvant. Mice were immunized intraperitoneally three times with the E3 subunit of the mitochondrial 2-oxoacid dehydrogenase enzyme complexes (dihydrolipoamide dehydrogenase) emulsified with Freund's complete adjuvant. Splenic and lymph node lymphocytes were harvested after 14 days for in vitro functional studies. T lymphocytes were tested for proliferative responses and cytotoxicity against antigen-loaded isogeneic target cells. An autoreactive cytolytic T lymphocyte (CTL) response was detectable only after the in vitro restimulation of lymphocytes with E3 antigen-loaded syngeneic splenocytes. These CTL were identified as H-2-restricted CD8+ T cells. A proliferative response to E3 was demonstrable against antigen-pulsed syngeneic splenocytes. Immunized mice also generated strong antibody responses to E3. Liver histology showed portal infiltrates interpreted as a response of the liver to a non-specific immunological stimulus. It is concluded that autoreactive cytolytic T cells can be generated experimentally upon appropriate stimulation of the immune system, and can be identified in vitro upon release from the controlling mechanisms that are likely to regulate them in vivo.

Transgenic expression of a CD46 (membrane cofactor protein) minigene: studies of xenotransplantation and measles virus infection

CD46 (membrane cofactor protein) is a human cell-surface regulator of activated complement and a receptor for the measles virus. A CD46 transgenic mouse line with an expression pattern similar to that of human tissues has been produced, to develop an animal model of (i) the control of complement activation by complement regulators in hyperacute rejection of xenografts, and (ii) measles virus infection. The mouse line was made using a CD46 minigene that includes promoter sequence and the first two introns of genomic CD46, which was coinjected into mouse ova with chicken lysozyme matrix attachment region DNA. A high level of CD46 expression in homozygotic transgenic mice was obtained with spleen cells having approximately 75% of the level found on human peripheral blood mononuclear cells. CD46 was detected in all tissues examined by immunohistochemistry, radioimmunoassay and Western blotting, showing that these mice were suitable for transplantation and measles virus infection studies. It also indicated that the transgene included the important regulatory elements of the CD46 promoter. Transgenic spleen cells were significantly protected in vitro from human complement activated by either the classical or alternative pathways and from alternative pathway rat complement. Furthermore, transgenic mouse hearts transplanted to rats regulated complement deposition in an in vivo model of antibody-dependent hyperacute xenograft rejection. Similar to human lymphocytes, transgenic lymphoblasts could be infected in vitro with measles virus; infected cells expressed viral proteins and produced infectious viral particles. The data demonstrate the suitability of this minigene for obtaining high-level CD46 expression sufficient for enhanced resistance of transgenic cells to complement attack and for obtaining wide tissue distribution of CD46, analogous to human tissues and, therefore, useful for comparative studies.

Translation is enhanced after silent nucleotide substitutions in A+T- rich sequences of the coding region of CD46 cDNA

Specific sequences in the coding region of CD46 (membrane cofactor protein) transcripts have been shown to have a marked effect on translation. Two A+T-rich regions of CD46 cDNA were altered by mutation without changing the CD46 amino acid sequence (silent nucleotide substitution). In one region, the A+T content was reduced from 78% to 55% and in the other a putative polyadenylation addition sequence was disrupted. In each example, mutated sequences transfected into COS-7 cells produced significantly more soluble or cell surface protein (up to a 20-fold increase) than wild-type sequences. The amount of cellular plasmid DNA and CD46 mRNA was not increased, suggesting that the effect was not due to increased transfection efficiency, or transcript synthesis or stability. Biosynthetically labelled transfected cells showed an increase in translation rate but cell-free in vitro translation studies demonstrated that wild-type and mutated transcripts were translated with similar efficiency. The data show that translation of CD46 is affected by specific mRNA coding sequences, 400-540 bases from the initiation codon, and suggest that these sequences require the structural integrity of the cell to exert their effect.

Engineering of recombinant soluble CD46: an inhibitor of complement activation

Human CD46 (membrane cofactor protein) is a type 1 glycoprotein that functions to protect autologous cells from complement-mediated damage by binding C3b and C4b for their factor I-mediated cleavage. We now describe the production and function of recombinant soluble CD46 (rsCD46), which was produced as a truncated form by mutagenesis using the splice overlap extension polymerase chain reaction, by inserting a translational stop codon into the CD46 cDNA at the junction of the transmembrane and extracellular domains. After transfection of an expression construct into 293-EBNA (Epstein-Barr nuclear antigen)-transformed cells, secretion of rsCD46 protein was detected by immunoradiometric assay using monoclonal antibodies. Following a single-step immunoaffinity purification, the protein resolved as a single band of approximately 56,000 MW on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified rsCD46 (51 micrograms/ml) protected Chinese hamster ovary (CHO) cells from lysis initiated by a high titre rabbit anti-CHO antibody and complement from rabbit or human. The protection was specifically mediated by rsCD46 because the monoclonal antibody M177, which blocks interaction between CD46 and C3b/C4b, abrogated the protection. The results demonstrate that rsCD46 is effective as a fluid-phase regulator of complement activation on cell surfaces, even when initiated by the classical complement pathway. The in vivo efficacy of rsCD46 was investigated using a mouse heart to rat xenograft model. Administration of a bolus injection of rsCD46 was effective at delaying hyperacute graft rejection. These data suggest that rsCD46 may have a role as a therapeutic agent.

A functional analysis of recombinant soluble CD46 in vivo and a comparison with recombinant soluble forms of CD55 and CD35 in vitro

The human cell surface complement regulatory proteins CD46 (MCP), CD55 (DAF) and CD35 (CR1) protect autologous cells from complement-mediated damage by inhibiting C3 and C5 convertases. This regulatory potential has previously been exploited in the treatment of some models of inflammatory injury by the generation of recombinant soluble (rs) proteins, such as rsCD55 and rsCD35 . More recently, we have shown that rsCD46 inhibits complement activation in the fluid phase. In this report, the ability of rsCD46, rsD55 and rsCD35 to regulate human complement activation mediated by the classical pathway in vitro was clearly demonstrated by all three soluble proteins; however, rsCD35 was a more effective inhibitor than either rsCD46 or rsCD55. A combination of rsCD46+ rsCD55 was more potent than either of these proteins alone. Cell lysis via alternative pathway activation in vitro was efficiently regulated by rsCD46 and rsCD35 to a similar extent, whereas rsCD55 was not effective. Assays of rsCD46 in vivo have previously not been possible due to difficulties in expressing sufficient quantities of protein. This limitation has been overcome and now we report the ability of rsCD46 to inhibit immune complex-mediated inflammation in a rat using the reverse passive Arthus reaction model. Administration of rsCD46 significantly reduced the size of lesion, and histological examination showed a reduction in inflammatory infiltrate and edema. These data suggest that rsCD46, in addition to rsCd55 and rsCD35, may be useful a therapeutic agent.

CTL in mice immunized with human mucin 1 are MHC-restricted

CTLs that recognize tumor Ags have been described in mice and humans, particularly for melanoma. These CTLs are CD8+, which is MHC-restricted. In contrast, in human carcinomas of the breast, pancreas, or ovary, and in multiple myeloma, CD8+ CTLs have been described that lyse targets expressing human MUC1 in a non-MHC-restricted manner. On the basis of these observations, we immunized mice with conjugates of mannan-human fusion protein, human mucin 1 (MUC1), which produced CD8+ CTLs. In contrast to the human anti-MUC1 CTLs found in cancer patients, the murine anti-MUC1 CTLs were clearly MHC-restricted, e.g., in inbred mice of the H-2-b, d, k, s, or z haplotypes; the H-2 restriction was also confirmed in H-2 congenic strains. Tests of H-2 recombinant strains demonstrated that MUC1 peptides were able to associate with D or K class I molecules of the b, d, or k haplotypes. Mice lacking MHC-class I molecules made weak CTL responses that were H-2Db-restricted, and in the class I H-2Kbm1 mutant strain, CTL restriction was also shown. Finally, cold target inhibition studies demonstrated that Kb and Db are recognized similarly, but Kk is less well recognized. Thus, anti-MUC1 CTLs induced by immunization of mice are different from those obtained from patients. The immunization of cancer patients with MUC1 peptides is now undergoing clinical trials and it will be of interest to observe whether the CTLs induced are HLA-restricted, not restricted, or whether both types of CTLs are produced.

CTL in mice immunized with human mucin 1 are MHC-restricted

CTLs that recognize tumor Ags have been described in mice and humans, particularly for melanoma. These CTLs are CD8+, which is MHC-restricted. In contrast, in human carcinomas of the breast, pancreas, or ovary, and in multiple myeloma, CD8+ CTLs have been described that lyse targets expressing human MUC1 in a non-MHC-restricted manner. On the basis of these observations, we immunized mice with conjugates of mannan-human fusion protein, human mucin 1 (MUC1), which produced CD8+ CTLs. In contrast to the human anti-MUC1 CTLs found in cancer patients, the murine anti-MUC1 CTLs were clearly MHC-restricted, e.g., in inbred mice of the H-2-b, d, k, s, or z haplotypes; the H-2 restriction was also confirmed in H-2 congenic strains. Tests of H-2 recombinant strains demonstrated that MUC1 peptides were able to associate with D or K class I molecules of the b, d, or k haplotypes. Mice lacking MHC-class I molecules made weak CTL responses that were H-2Db-restricted, and in the class I H-2Kbm1 mutant strain, CTL restriction was also shown. Finally, cold target inhibition studies demonstrated that Kb and Db are recognized similarly, but Kk is less well recognized. Thus, anti-MUC1 CTLs induced by immunization of mice are different from those obtained from patients. The immunization of cancer patients with MUC1 peptides is now undergoing clinical trials and it will be of interest to observe whether the CTLs induced are HLA-restricted, not restricted, or whether both types of CTLs are produced.

Oxidative/reductive conjugation of mannan to antigen selects for T1 or T2 immune responses

The induction of CD8+ cytotoxic T lymphocytes (CTLs) is desirable for immunization against many diseases, and recombinant-synthetic peptide antigens are now favored agents to use. However, a major problem is how to induce CTLs, which requires a T1-type response to such synthetic antigens. We report that T1-type (generating high CTL, low antibody) or T2-type (the reciprocal) responses can be induced by conjugation of the antigen to the carbohydrate polymer mannan: T1 responses are selected by using oxidizing conditions; T2 responses are selected by using reducing conditions for the conjugation. Using human MUC1 as a model antigen in mice, immunization with oxidized mannan-MUC1 fusion protein (ox-M-FP) led to complete tumor protection (challenge up to 5 x 10(7) MUC1+ tumor cells), CTLs, and a high CTL precursor (CTLp) frequency (1/6900), whereas immunization with reduced mannan-MUC1 FP (red-M-FP) led to poor protection after challenge with only 10(6) MUC1+ tumor cells, no CTLs, and a low CTLp frequency (1/87,800). Ox-M-FP selects for a T1 response (mediated here by CD8+ cells) with high interferon gamma (IFN-gamma) secretion, no interleukin 4 (IL-4), and a predominant IgG2a antibody response; red-M-FP selects for a T2-type response with IL-4 production and a high predominant IgG1 antibody response but no IFN-gamma.

Hepatic portal infiltrates in mice immunized with syngeneic lymphoid cells: connotations for models of autoimmune liver disease

The aim of this study was to investigate liver histology in mice after immunization with the conserved self molecule dihydrolipoamide dehydrogenase, E3, a subunit of the mitochondrial 2-OADC enzyme family identified as the M2 autoantigen in the liver disease, primary biliary cirrhosis. Mice were immunized by a novel procedure. The autoantigen E3 was introduced by pinocytosis into hypertonically treated syngeneic lymphoid cells to facilitate intracellular antigen processing and presentation and the generation of a cytolytic T cell response. Liver sections were examined and scored for evidence of an inflammatory response by two independent procedures: standard microscopy with visual scoring, and automated scanning with computerized scoring. There was a close correlation between read-outs of liver histology by standard microscopy and automated scanning, using the index of mononuclear cellular infiltrations in hepatic portal tracts. Such infiltrates were prominent in the immunized mice, but, unexpectedly, the degree of infiltration was similar in mice injected with autoantigen (E3)-loaded syngeneic cells, or syngeneic cells treated only with hypertonic medium. The equivalent changes in the liver with the experimental and control protocol is indicative of the reactivity of the liver to any provocative immune stimulus, and is cautionary for protocols designed for the induction of autoimmune liver disease in experimental animals.

Gal alpha(1,3)Gal is the major xenoepitope expressed on pig endothelial cells recognized by naturally occurring cytotoxic human antibodies

Hyperacute rejection, mediated by natural antibody, is the major barrier to xenotransplantation. The studies reported herein were aimed at evaluating antibody-mediated cytotoxicity and the role of the Gal alpha(1,3)Gal epitope, which we had previously demonstrated was the major epitope of pig cells detected by naturally occurring human antibodies. Also, we had shown that this epitope could be induced in non-expressing cells by the transfection of a cDNA clone encoding alpha(1,3)galactosyl transferase, the enzyme that produces this epitope. The importance of the Gal alpha(1,3)Gal epitope was supported by (1) sugar inhibition studies; (2) complete absorption of cytotoxic antibodies by melibiose-sepharose columns; and (3) the ability of normal human serum to lyse COS cells after transfection with a cDNA clone encoding alpha(1,3)galactosyl transferase. These findings strongly suggest that the majority of cytotoxic human antibodies that would recognize a xenogeneic graft are directed to the Gal alpha(1,3)Gal epitope.

Upregulation of complement regulators MCP (CD46), DAF (CD55) and protectin (CD59) in arthritic joint disease

CD46, CD55 and CD59 are cell surface glycoproteins which are widely distributed on normal tissue, where they function in the prevention of complement-mediated damage. In this study we have investigated the altered expression of these molecules under inflammatory conditions both in vitro and in vivo. By using immunocytochemical techniques we demonstrated marked but disparate upregulation of these molecules in IL1-treated cartilage and in diseased cartilage from arthritic joints compared to normal cartilage in both humans and pigs. Expression of these proteins was restricted to the chondrocyte surface, and was also demonstrated on isolated chondrocytes grown in monolayer culture and stimulated with IL1. It is suggested that the elevated levels of these regulatory proteins may be necessary to ameliorate the multiple damaging effects of the inflammatory processes associated with destructive joint diseases.

Polymorphic expression of CD46 protein isoforms due to tissue-specific RNA splicing

CD46 is a member of the regulators of complement activation (RCA) family and serves to protect autologous cells from complement mediated lysis. The CD46 gene consists of 14 exons and extensive RNA splicing produces protein isoforms of different molecular weight. Predominant protein isoforms of 66 and 56 kDa arise from splicing in or out of exon 8 which encodes a region rich in serine, threonine and proline residues known to be heavily O-glycosylated. An inherited allelic polymorphism controls the relative expression of these isoforms in PBL and other tissues. This study has analysed an independent and overriding tissue specific regulation of CD46 splicing. Salivary gland and kidney produce RNA transcripts that preferentially include exon 8, giving rise to the 66 kDa protein species, while exon 8 is spliced out in brain tissue to give the 56 kDa protein. The cytoplasmic tail of CD46 is encoded by either exon 13 (CYT 1) or exon 14 (CYT 2). There is a preferential deletion of exon 13 from transcripts in salivary gland, kidney and brain to encode a protein containing cytoplasmic tail CYT 2. This preferential production of the CYT 2 tail is contrary to that seen on peripheral blood lymphocytes where equivalent expression of both CYT 1 and CYT 2 is observed. Our results suggest that while the splicing of exons within most cells is controlled by nucleotide sequences within or close to the CD46 gene (i.e. cis-regulation), splicing in tissues such as salivary gland, kidney and brain is regulated by trans-splicing factors encoded by another gene(s).

Identification and quantification of complement regulator CD46 on normal human tissues

CD46 is a cell-surface regulatory molecule that prevents lysis of autologous human cells by activated complement. It has been well characterized on leucocytes, reproductive cells and various cultured cell lines and is considered to be ubiquitously expressed. We now extend these analyses and describe CD46 in a variety of different human tissues. Strong expression was observed by immunohistology on epithelial cells lining exocrine ducts and glands, such as salivary gland and pancreas and on kidney tubules and glomerular epithelium. Quantitative tissue expression was measured by radioimmunoassay and confirmed histological observations. Thus, CD46 is highly expressed on cells in contact with extracellular fluids thought not to contain large quantities of complement but which may still be subjected to complement attack thereby necessitating the presence of complement regulators to prevent non-specific destruction of cells.

Different membrane cofactor protein (CD46) isoforms protect transfected cells against antibody and complement mediated lysis

The need for organ transplantation, especially of kidneys, exceeds the availability of human donors and the possibility of xenotransplantation from suitable animals is now being addressed. The immediate barrier to success is hyperacute graft rejection, resulting from naturally occurring xenoreactive antibodies and the activation of complement. It is proposed that the intensity of the hyperacute response can be reduced by providing additional regulatory molecules to limit activation of the complement cascade, initially as transfected gene products in cultured cells as an in vitro model and eventually as a transgene in potential donor animals, such as pigs. Limiting the activity of C3b reduces the production of the C3a, C4a and C5a anaphylotoxins, thus curtailing not only the immediate C3b-mediated lytic pathway but also the later effects of a cellular inflammatory response including endothelial and platelet cell activation. To develop and assess the first part of this strategy, we have transfected several cDNA's encoding isoforms of CD46 (membrane cofactor protein). At least four different CD46 isoforms are commonly expressed in almost all human cells, and we have compared two of these and a third form to determine if they mediate different functions. After transfection, CD46-expressing CHO-K1 cells were selected with methionine sulphoximine and identified using monoclonal antibodies. Transfectants with suitable CD46 expression were assayed for primary CD46 function using a lysis assay dependent on the reaction of antibody and complement. In this in vitro model of hyperacute rejection, normal human sera containing natural xenoreactive antibodies were shown to lyse CHO cells, but only in the presence of complement.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoreactive MHC-restricted cytotoxic cells in BALB/c mice after novel immunisation with a conserved mammalian autoantigen

We investigated whether a novel immunisation scheme using an endogenous protein could stimulate an autoreactive cytolytic response. The protein selected was porcine dihydrolipoamide dehydrogenase, the E3 component of the mitochondrial 2-OADC enzyme family, because it is structurally conserved in mammals and ubiquitously expressed. Recombinant insulin was used as an alternative antigen. Female BALB/c mice were injected with adjuvant-free syngeneic lymphoid cells that had been exposed to E3 in hypertonic medium to facilitate its pinocytosis and were given two booster injections. Effector lymphoid cells from immunised mice were cultured in vitro with irradiated syngeneic cells that had been treated with hypertonic medium, either with or without antigen. Cytolytic effector cells were detected that lysed isogeneic and not allogeneic target cells, but only from mice immunised with E3. This experimental system provides a new model for the early stages of the development of autoimmunity.

Differing epitope selection of experimentally-induced and natural antibodies to a disease-specific autoantigen, the E2 subunit of pyruvate dehydrogenase complex (PDC-E2)

Naturally-occurring autoantibodies to a family of mitochondrial enzymes, the 2-oxoacid dehydrogenase complexes (2-OADC), characterize the human liver disease primary biliary cirrhosis. The immunodominant epitope for these autoantibodies is associated with the lipoyl-binding domain of the E2 subunit of the enzymes. The reactivity of these disease-associated autoantibodies was compared with that of antibodies raised in rats and rabbits, by immunization with various preparations derived from the 2-OADC enzymes, using immunization protocols that have successfully induced various organ-specific autoimmune diseases in animals. The immunogens included the intact pyruvate dehydrogenase complex (PDC) from bovine heart, human recombinant PDC-E2, and short synthetic peptides representing the immunodominant lipoic acid binding sequences of the 2-OADC enzymes. The techniques for antibody analysis included immunofluorescence, immunoblotting on mitochondrial extracts, ELISAs using entire PDC, PDC-E2, or synthetic peptides, epitope mapping by peptide scanning on overlapping octameric peptides representing the human PDC-E2 sequence, affinity purification on PDC-E2, and inhibition in vitro by sera of the catalytic function of PDC. Experimental immunization did not elicit any evidence of autoimmune disease. Moreover, the experimentally-induced antibodies in striking contrast to the natural autoantibodies showed preferential reactivity with PDC-E2 rather than with intact PDC, failed to inhibit in vitro the catalytic function of PDC, and, on peptide scanning, reacted with discrete epitopes, but at sites other than the lipoyl-binding region of PDC-E2. Our data indicate that 'multisystem' autoimmune diseases including primary biliary cirrhosis may not be elicitable experimentally because a critical disease-relevant autoepitope is not engaged by the immune system.

Validation of the MTT dye assay for enumeration of cells in proliferative and antiproliferative assays

Increasing use is being made of colorimetric assays to quantitate viable cells, e.g., the cellular reduction of the tetrazolium salt, MTT, to formazan by mitochondrial succinate dehydrogenase. We validated this assay for cell proliferation in mixed lymphocyte cultures as compared with 3H-thymidine uptake, and for inhibition of cell proliferation induced by interferon with results compared by direct cell counting. We also found that cells do not, as previously assumed, require functional mitochondria: there were no differences in formazan production by normal cells or respiratory defective cells in which mitochondria had been poisoned by the nucleic acid toxin, ethidium bromide. The high reproducibility of MTT metabolism by lymphoblasts and various cultured cell lines establishes the reliability and versatility of this method for quantitating cell numbers.

T-cell tolerance induced in nude mice grafted with thymic epithelium

This study investigated the ability of foetal thymic epithelium prepared by 24 degrees culture (24 degrees-TE) or treatment with deoxyguanosine (dGuo-TE), to induce tolerance in nude mice. Thymic chimeras were constructed in which the thymic epithelium differed from the host at both major histocompatibility complex (MHC) antigens and multiple minor histocompatibility antigens (mHa), or at mHa only. Peripheral CTL from nude mice receiving dGuo-TE disparate for mHa, or both MHC antigens and mHa, were uniformly tolerant of thymic mHa. CTL from nude mice grafted with 24 degrees-TE or dGuo-TE were tolerant of host MHC antigens, but the two treatments differed in the efficiency with which they induced tolerance to thymic MHC antigens. CTL responses specific for thymic MHC antigens could be generated in vitro from dGuo-TE grafted mice but not from those receiving 24 degrees-TE. The addition of concanavalin A (Con A) supernatant had no effect on the CTL tolerance observed in 24 degrees-TE grafted mice, suggesting that the lack of CTL responses was not due to tolerance in MHC class II restricted 'helper' cells. However, CTL responses against the thymic MHC antigens of dGuo-TE grafted mice displayed high sensitivity to blocking by anti-CD8 antibodies, indicating that these CTL were of low affinity. These results suggest that 24 degrees-TE induces tolerance in most thymic MHC-specific CTL precursors, whereas dGuo-TE induces tolerance only in CTL with high affinity for thymic MHC antigens. Therefore, 24 degrees-TE and dGuo-TE are both capable of inducing CTL tolerance, consistent with the previously reported acceptance of thymic donor-type skin grafts by nude recipients of dGuo-TE treatment. We conclude that MHC class I molecules on thymic epithelium play a role in negative selection of the developing T-cell repertoire.

Autoantibody against dihydrolipoamide dehydrogenase, the E3 subunit of the 2-oxoacid dehydrogenase complexes: significance for primary biliary cirrhosis

Autoantibodies in primary biliary cirrhosis recognize mitochondrial 2-oxacid dehydrogenase complexes, particularly the E2 subunits. Reactivity with the E3 subunit, common to each of the enzyme complexes, was sought by immunoblotting, with sera screened at 1:100 instead of the conventional 1:1,000 dilution. This was found in 11 of 29 sera from patients with primary biliary cirrhosis but also in 10 of 40 sera from normal subjects. Two-dimensional immunoblotting and immunoblotting on purified enzymes established that the reactivity was actually with E3 rather than with another component of the 2-oxoacid enzymes of similar molecular weight. Purified antibodies to E3 eluted from an affinity column did not cross-react with other components of the 2-oxoacid enzyme complexes. The antibodies to E3 did not react with the Escherichia coli or yeast E3 subunits, suggesting that they are not stimulated by immune responses against microorganisms. Thus the proposal that reactivity to the shared E3 subunit of the 2-oxoacid enzyme complexes could initiate primary biliary cirrhosis is not reflected at the antibody level.

Characterization of the spontaneous mutant H-2Kbm29 indicates that gene conversion in H-2 occurs at a higher frequency than detected by skin grafting

A spontaneous mutation of H-2Kb, Kbm29, was discovered among the progeny of F1 hybrid parents. Unlike other characterized spontaneous class I variants, this mutant was detected with the use of antibody, rather than tissue grafting. Although Kbm29 is serologically indistinguishable from the previously described mutant molecule Kbm3, it is identical to the parental Kb by skin grafting and CTL assays. A full length cDNA of Kbm29 was amplified by polymerase chain reaction with locus-specific primers, cloned, and sequenced. Two nucleotides were found to be mutated, resulting in a single amino acid change (Lys----Ala) at amino acid 89 of the mature glycoprotein. This is consistent with the observed serologic changes, as the same amino acid substitution is responsible for the serologic profile of Kbm3. The occurrence of a mutation which is not detectable by the methods normally used to screen for H-2 mutants provides evidence that the high spontaneous rate of structural mutation described for the Kb molecule is underestimated.

Characterization of the spontaneous mutant H-2Kbm29 indicates that gene conversion in H-2 occurs at a higher frequency than detected by skin grafting

A spontaneous mutation of H-2Kb, Kbm29, was discovered among the progeny of F1 hybrid parents. Unlike other characterized spontaneous class I variants, this mutant was detected with the use of antibody, rather than tissue grafting. Although Kbm29 is serologically indistinguishable from the previously described mutant molecule Kbm3, it is identical to the parental Kb by skin grafting and CTL assays. A full length cDNA of Kbm29 was amplified by polymerase chain reaction with locus-specific primers, cloned, and sequenced. Two nucleotides were found to be mutated, resulting in a single amino acid change (Lys----Ala) at amino acid 89 of the mature glycoprotein. This is consistent with the observed serologic changes, as the same amino acid substitution is responsible for the serologic profile of Kbm3. The occurrence of a mutation which is not detectable by the methods normally used to screen for H-2 mutants provides evidence that the high spontaneous rate of structural mutation described for the Kb molecule is underestimated.

H-2M3 encodes the MHC class I molecule presenting the maternally transmitted antigen of the mouse

Mta, the maternally transmitted antigen of mice, is a hydrophobic, N-formylated mitochondrial peptide, MTF, presented on the cell surface to cytotoxic T lymphocytes by a novel major histocompatibility complex class I molecule, encoded by H-2M3. We have cloned and sequenced two alleles of M3, which differ in their ability to present MTF despite greater than 99% identity in the coding regions. M3 is as divergent from classical, antigen-presenting H-2 molecules as from other class I genes of the Hmt and the Qa/Tla regions. Amino acids critical for folding of class I molecules are conserved in M3. Noncharged amino acids lining the peptide-binding groove and phenylalanine 171 may explain the unique interaction with MTF, and leucine 95 appears critical for immunological activity.

Maternally transmitted antigen of mice: a model transplantation antigen

Molecular identification proved Mta, the maternally transmitted antigen of mice, to be a model minor histocompatibility (H) antigen. It consists of a peptide, MTF, that is presented on the cell surface by an H-2 class-I molecule, HMT. MTF is derived from ND1, a mitochondrially encoded protein, and the amino-terminal N-formyl-methionine is essential for binding to HMT; conservative substitutions at the sixth residue causes MTF to be a minor H antigen. HMT is encoded by the M3 gene at the telomeric end of the H-2 complex. The peptide-binding site of HMT is hydrophobic, and allelic forms of the mature protein differ by only three amino acids. Homologues and analogues of the mouse Mta system have recently been identified in rats.

Some biochemical properties of human lymphoblastoid Namalwa cells grown anaerobically

Using cultured lymphoblastoid Namalwa cells, we have demonstrated that humans cells can be grown for long periods in the absence of oxygen. Such anaerobic growth occurs at the same rate as that of aerobic cultures, but is characterized by a strict dependence on pyruvate. Cells in anaerobic culture undergo a severe loss of mitochondrial cytochromes, that is reversible on reaeration. Anaerobically grown cells show a two-fold increase in glucose consumption, consistent with anaerobic glycolysis providing the source of ATP for cellular maintenance and growth. The requirement for pyruvate is explained by the necessity for these cells to re-oxidise NADH derived from metabolic reactions. Detailed study of anaerobically grown human cells provides a new framework for investigating tissues depleted in mitochondrial functions, as occurs in mitochondrial diseases and the ageing process.

IgG antibody and delayed-type hypersensitivity responses in nude mice grafted with thymic epithelium

This study compared the ability of foetal thymic epithelium depleted of lymphocytes and dendritic cells, by low temperature or deoxyguanosine (dGuo) treatment in organ culture, to reconstitute T-cell function in nude mice. It is shown that renal capsule grafts of either type could promote the development of functional T lymphocytes in the periphery, as judged by in vivo assays. Both syngeneic and allogeneic thymic epithelium endowed nude mice with the capacity to mount IgG antibody and delayed-type hypersensitivity (DTH) responses to the T-dependent antigen ovalbumin (OVA). Functional reconstitution was accompanied by the appearance of Thy-1-bearing cells in the spleens of thymic grafted nude mice. The results from allogeneically grafted recipients show that a substantial population of peripheral T cells was present that collaborated with B cells and other antigen-presenting cells (APC) which do not express major histocompatibility complex (MHC) molecules of the thymus donor haplotype.

Delayed-type hypersensitivity and allograft rejection in the mouse: correlation of effector cell phenotype

Delayed-type hypersensitivity (DTH) responses to alloantigens were found to correlate with both skin and tumour allograft rejection in 224 reconstituted ATXBM-CBA mice. Furthermore, DTH responses and allograft rejection were observed only in mice that had received Ly-1 cells. Depletion of Thy-1+ or Ly-1+ cells led to indefinite graft survival and the absence of DTH responses, whereas depletion of Ly-2+ cells led to rapid graft rejection and strong DTH responses. The same result was obtained with CBA mice responding to grafts of either C57BL/6 skin, the B16 melanoma, or the EL4 lymphoma; and for (CBA X A)F1 mice responding to H-2K region alloantigens of AQR skin grafts. Thus, DTH and allograft rejection are both mediated by a Ly-1 T cell and it is considered that these are two different manifestations of the same transplantation response.

Cells mediating graft rejection in the mouse. III. Ly-1+ precursor T cells generate skin graft rejection

Skin graft rejection in ATXBM CBA mice reconstituted with naive (nonsensitized) cells was shown to be mediated predominantly by Ly-1+2- effector T cells. Thus, after the treatment of the inoculum with the monoclonal anti-Ly-1.1 antibody and complement, C57BL/6 skin grafts survived indefinitely, whereas Ly-2 antibody depletion merely delayed the onset of rejection. This showed that a Ly-1+2- precursor cell rather than a Ly-1+2+ cell was the progenitor of the Ly-1+2- graft rejection effector cell. Nevertheless, another T cell subset augmented the rejection of ski grafts and it was concluded that LY-1,2,3+ cells also provided a pool of precursor cells. Thus, it appeared that both Ly-1+ and Ly-1,2,3+ cells can function as precursor cells for the effector cells, which, as shown previously, have the ly-1+ phenotype.

Cells mediating graft rejection in the mouse. IV. The Ly-5, 6, and 8 effector cell phenotype

Skin graft rejection was previously shown to be mediated by sensitized lymphocytes bearing the Thy-1+, Ly-1+2-3- cell surface phenotype and these cells were further characterized using antisera to the Ly-5, 6, and 7 specificities. By using an adoptive transfer system in which ATXBM mice (CBA/H) received sensitized cells treated with antiserum and complement, it was shown that the cells mediating skin graft rejection were of the Ly-5+6-7+ phenotype. Other studies have demonstrated that cytotoxic T cells are Ly-5+6+7-, whereas helper T cells are Ly-5+6-7+, so that the T cells-mediating graft rejection is again clearly distinguished from the cytotoxic T. cell. At this time, however, it is not possible to separate the T cells mediating helper T cell functions, delayed-type hypersensitivity (DTH), and allograft rejections.