Cell-mediated Attack Research Articles

Prospects of gene therapy for genetic skeletal muscle disease

Skeletal muscle cells are suitable for direct gene transfer which is the basis of somatic cell gene therapy that is potentially applicable to several genetic muscle diseases. Thus far, the most extensive preclinical gene therapy research focused on Duchenne muscular dystrophy (DMD) in which progressive muscle fiber necrosis and loss is caused by the deficiency of a surface membrane-associated cytoskeletal protein, dystrophin. A truncated version of the dystrophin cDNA driven by a constitutive promoter was delivered by a human adenovirus vector into muscles of genetically dystrophin-deficient (mdx) mice. As a result, a high percentage of the muscle fibers in the injected muscles showed sarcolemmal dystrophin. Transduction efficiency was significantly higher if the adenoviral recombinants were introduced at an early age vs adult animals. Even the truncated dystrophin could protect transduced fibers from necrosis. The initial high transduction efficiency rapidly declined due to a CD8 + T cell-mediated attack by the host immune system triggered by adenoviral elements. Application of safe and efficacious gene therapy for DMD must await solutions to this and other problems by the appropriate preclinical studies in the murine and canine models of dystrophin deficiency.

Imogen 38: a novel 38-kD islet mitochondrial autoantigen recognized by T cells from a newly diagnosed type 1 diabetic patient.

Cell-mediated autoimmune attack directed against islet proteins of approximately 38 kD in size has been associated with type 1 diabetes. A novel murine cDNA encoding an antigen of this size was cloned using a screening procedure based on the proliferative response of a human diabetic T cell clone (1C6) to a recombinant antigen epitope library. Membrane preparations from COS 7 cells transfected with the full-length 1,267-bp cDNA elicited a proliferative response from the reporter T cells comparable to that of the defined peptide epitope and native insulinoma antigen. In vitro translation and transfection experiments suggested that the protein is initially synthesized as a 44-kD protein and then processed to the native 38-kD form through the proteolytic removal of a 54-aa NH2-terminal mitochondrial targeting sequence. Differential centrifugation, Percoll density gradient centrifugation, and immunofluorescence studies confirmed localization of the antigen to mitochondria. Northern blot, Western blot, and 1C6 T cell proliferation assays showed that, although imogen 38 was more highly expressed in beta cell than alpha cell lines, it was also present in other tissues. It is concluded that imogen 38 may be a target for bystander autoimmune attack in diabetes rather than a primary autoantigen.

Towards a strategy of universally efficacious vaccination against pathogens uniquely susceptible to cell-mediated attack

Infection by some intracellular parasites is contained only by cell-mediated immunity, and yet antibody is produced at the expense of the cell-mediated response upon natural infection, leading to chronic or fatal disease. Effective vaccination must therefore generate an immunological imprint ensuring a strong and stable cell-mediated response upon infection. Such diseases include leprosy, tuberculosis, the leishmaniasis and AIDS ( Kaplan and Cohn (1986) Int. Rev. Exp. Pathol. 28, 45–78; Surcel et al. (1994) Immunology 81, 171–176; Pearson et al. (1983) Rev. Infect. Dis. 5, 907–927; Clerici and Shearer (1993) Immunol. Today 14, 107–111). BALB/C mice are susceptible to Leishmania major, a protozoan that causes cutaneous leishmaniasis in man, by the criterion that substantial infection results in antibody production and progressive disease ( Locksley and Scott (1991) Immunoparasitology Today, A58–A61; J.N. Menon and P.A. Bretscher, unpublished data). Infection of BALB/C mice with very few parasites results in an exclusive cell-mediated, Thl-like response and resistance to an ordinarily pathogenic, high dose challenge. This resistance is associated with a strong and stable cell-mediated response ( Bretscher et al. (1992) Science 257, 539–542; J.N. Menon and P.A. Bretscher, unpublished data). The generation of this Thl imprint by low dose infection has been achieved with three very different strains of the parasite. There is a similar dependency of susceptibility and resistance on relative parasite dose in ‘susceptible’ and ‘resistant’ mice and in mice of ‘intermediate susceptibility’. For example, ‘resistant’ mice are resistant to substantial infection but succumb to infection with very high doses of parasites. We therefore propose that infection of a genetically diverse population with a very low dose of viable parasites, that does not induce antibody in any individual, will either induce cell-mediated immunity and contain the parasite, or the parasite will grow until it reaches the threshold required to induce cell-mediated immunity, thereby generating the required imprint. Low dose infection may thus constitute universally efficacious vaccination. The pertinence of these observations to improving the efficacy of BCG vaccination against tuberculosis is discussed.

The role of human leucocyte antigen genes in the development of malignant disease

Introduction The human leucocyte antigen (HLA) class I and in particular class II genes play a major role in regulating the immune response. The extensive polymorphism of these genes has been characterised by a series of international histocompatibility workshops undertaken during the past 31 years, with the current (Twelfth) workshop due to conclude in St Malo in June 1996. Many studies, both within and without these workshops, have revealed significant associations between particular polymorphisms of the HLA class I and especially class II genes and predisposition to a large number ofbenign, immune system mediated diseases including rheumatoid arthritis,' coeliac disease,2 insulin dependent diabetes,3 multiple sclerosis,4 Graves's disease,5 and IgE responsiveness to various pollen and animal dander allergens.6 HLA class II allelic associations have also been detected in other benign conditions with no obvious immunological component, such as narcolepsy.7 However, the first HLA and disease association to be reported in 1967 was between the HLA class I B35, B5 and B18 group of alleles (then known as 4C) and a malignant condition-Hodgkin's disease.8 Nevertheless, until recent years there has been comparatively little interest in HLA genetic polymorphism and predisposition to malignant diseases. This has now changed, particularly since the advent of accurate, high resolution DNA based methods for analysis ofHLA polymorphism. A small but growing literature now exists relating HLA class II polymorphism and predisposition to a number of malignancies. In addition, downregulation of HLA class I expression on tumour cells would seem to be a frequent route by which tumour cells escape from T cell mediated attack. These more recent findings will be outlined below.

IMMUNE MANIFESTATIONS OF INFLAMMATORY MUSCLE DISEASE

Evidence of autoimmune muscle injury and of systemic autoimmunity is seen in PM and DM. In typical PM, a cell-mediated attack on muscle fibers by CD8+ cytotoxic T cells predominates, directed at an unknown antigen. In DM, vascular injury is prominent, with loss of muscle capillaries and ischemic muscle damage, apparently mediated by local complement activation in small muscle vessels. Although humoral immunity seems more important in the pathogenesis of DM, serum autoantibodies are commonly found in both forms. About one third of patients have MSAs, whereas others have less specific antibodies such as anti-U1RNP, often associated with overlap syndromes involving myositis. MSAs are mutually exclusive and define characteristic clinical subgroups. Antibodies to five of the aminoacyl-tRNA synthetases are each associated with an "antisynthetase syndrome" marked by myositis, ILD, arthritis, and other features, but individual patients have only a single antisynthetase. Rare autoantibodies to certain translation factors may be associated with a similar syndrome. Anti-SRP is commonly associated with severe, acute, resistant myositis, whereas anti-Mi-2, the only MSA directed at a nuclear protein, is specifically associated with DM. Patients with anti-PM-Scl commonly have an overlap syndrome of PM/DM and SSc. Recent studies have recognized other antibodies in PM and DM, including antibody to endothelial cells, heat shock proteins, and, in a high proportion of patients, a 56-kd component of a ribonucleoprotein particle. The MSAs and their antigens are being characterized in detail. To date, data suggest similarity of predominant epitopes between different patients and a tendency toward conformational epitopes. It is not known if the recognized autoantibodies participate in tissue injury or pathogenetic processes, but production of the MSAs appears to be linked to etiologic factors and can be a clue to understanding the disease. Although these autoimmune responses are becoming better defined, the inciting events leading to generation of these responses and development of PM and DM remain unknown.

Humoral immunity in polymyositis/dermatomyositis.

Autoantibodies are found in most patients with polymyositis (PM) or dermatomyositis (DM) and 35-40% of these patients have myositis-specific antibodies. Twenty-five to thirty percent have anti-aminoacyl-tRNA synthetases, of which anti-Jo-1, directed at histidyl-tRNA synthetase, is by far the most common. Patients with anti-synthetases have a high frequency of myositis, interstitial lung disease, Raynaud's phenomenon, and other features constituting an "anti-synthetase syndrome." Anti-synthetases tend to react with conformational epitopes and to inhibit enzymatic activity, suggesting reaction with conserved regions. Sera with antibodies to alanyl-tRNA synthetase (anti-PL-12) also have antibodies to tRNA(ala), whereas most sera with other anti-synthetases do not react directly with tRNA. Production of the antibodies appears to be antigen-driven, and is influenced by HLA genes, although an initiating factor, possibly a viral infection, may be important. Antibodies to other cytoplasmic antigens, most notably the signal recognition particle (anti-SRP), are seen in a small percentage of patients. Patients with anti-SRP do not tend to develop the anti-synthetase syndrome, but may have very severe disease. Antibodies to the nuclear antigen Mi-2 are also specific for myositis, and are strongly associated with DM. Several autoantibodies, including anti-PM-Scl, anti-Ku, and anti-U1 and U2 RNP, have been associated with scleroderma-PM overlap. The role of humoral immunity in the myositis of PM and DM has not yet been clarified. Capillary loss and ischemic damage are important in DM, and seem to be mediated by humoral mechanisms, whereas cell-mediated attack on muscle fibers is important in PM. The mechanism of skin injury in cutaneous lesions is not known, but antibody deposition is inconsistent and uncommon. Whether the myositis-specific antibodies are involved in disease pathogenesis is not yet known, although there is no direct evidence for this. An understanding of the reasons for production of these antibodies, however, should provide insight into the etiology and pathogenesis of PM and DM.

An hypothesis to explain why cell-mediated immunity alone can contain infections by certain intracellular parasites and how immune class regulation of the response against such parasites can be subverted.

Cells with a low density of parasite-specific antigens on their surface are postulated to be susceptible to a cell-mediated attack but not to effector mechanisms normally activated following the binding of specific antibody to the infected cell. It is further postulated that such infected cells normally induce a cell-mediated response, and that cells infected with slow-growing intracellular parasites have a low density of parasite-specific antigens on their surface. Despite these general postulates, cell-mediated immunity is not invariably induced following natural infection by certain slow-growing parasites, such as those responsible for leprosy, tuberculosis, and the leishmaniases, and antibody can be induced that is exclusive of a strong, cell-mediated response. It is proposed that certain events in such cases subvert the normal regulatory processes that control the class of immunity induced. In these cases, the parasite-infected cells, bearing a low representation of parasite antigens, induce antibody even though they are not susceptible to antibody-dependent effector mechanisms, and so they are not eliminated. In this case, chronic infection and uncontrolled growth of the parasite occurs, often with fatal consequences.

Delayed type hypersensitivity is abnormal in patients with lichen planus

Lichen planus is characterized by the histological features of a cell-mediated attack on the epidermis. To see whether there is any defect in cutaneous immunity in non-lesional skin, we measured the response to a contact sensitizer in 17 patients with lichen planus and 27 control subjects. Sensitization was induced with 30 micrograms dinitrochlorobenzene applied to the thigh. The subjects were challenged 4 weeks later with three doses of dinitrochlorobenzene (8.8, 12.5 and 17.7 micrograms), and responses were quantified with calipers as the change in skinfold thickness at 48 h. Patients with lichen planus were significantly less responsive with smaller reactions at all challenge doses. These abnormalities suggest that the skin is abnormal in areas unaffected by the rash, and raise the possibility that there may be a primary defect in the cutaneous immune system in lichen planus.

Loss of epidermal integrity by T cell-mediated attack induces long term local resistance to subsequent attack. II. Thymus dependency in the induction of the resistance.

Our previous study showed that in cutaneous graft-vs-host disease (GVHD) induced by intradermal injection of autoreactive T cells the epidermal structures spontaneously recovered from the destruction became resistant to the subsequent attempts to induce the cutaneous GVHD and that the resistance correlated well with a 30-fold increase in the number of Thy-1+ epidermal cells (Thy-1+EC). We show that the resistance to the cutaneous GVHD was never induced in athymic nude mice and adult thymectomy lethal radiation and bone marrow reconstitution (ATXBM) mice under the same conditions, indicating that the induction of the resistance is dependent on the presence of thymus. A great increase in the number of Thy-1+EC was similarly observed in the epidermis of the athymic nude and ATXBM mice that spontaneously recovered from the cutaneous GVHD and that remained susceptible to the induction of the cutaneous GVHD. However, the results with B10Thy-1.1----B6 radiation chimeras clearly demonstrate that the vast majority of the increased Thy-1+EC found in the "susceptible" epidermis of the ATXBM mice were of donor bone marrow origin and there was no increase in the number of host-derived Thy-1+EC, whereas in the "resistant" epidermis of the XBM mice both Thy-1+EC populations were equally increased. The overall results indicate that the expansion of Thy-1+EC that mature in the thymus is crucial to the induction of the resistance, although the migration of bone marrow-derived Thy-1+EC precursors to the epidermis occurs quite independently of the presence of thymus.

Loss of epidermal integrity by T cell-mediated attack induces long-term local resistance to subsequent attack. I. Induction of resistance correlates with increases in Thy-1+ epidermal cell numbers.

The cutaneous graft-versus-host disease (GVHD) lesions induced by intradermal injection of cloned autoreactive T cells have been shown to subside rapidly and the epidermis returns to normal 2 wk after injection. Those mice that had spontaneously recovered from the cutaneous GVHD became resistant to subsequent attempts to induce the cutaneous GVHD by the T cells while maintaining their activity to mount delayed-type hypersensitivity (DTH) responses and to induce the enlargement of the popliteal lymph nodes (PLN). The resistance appeared to be restricted to the epidermal structures of the injection sites, suggesting the involvement of locally acting suppression mechanisms. This local resistance was not specific for the clonotype used for the induction of the resistance. A loss of the epidermal integrity by an attack of T cells capable of producing cutaneous GVHD was a prerequisite for the induction of the resistance. By up to at least 8 mo after injection of the T cells, no mice became susceptible to the cutaneous GVHD again, provided that the T cells were injected into the same footpad sites that had initially received the T cells. This resistance correlated well with the great increase (20-30-fold) in Thy-1+ EC number. The great increase in the number of Thy-1+ EC following destruction of epidermal structures may be important in protecting the epidermal integrity from an additional attack by T cells.

Distinct restriction of complement- and cell-mediated lysis.

Complement- and cell-mediated killing utilize related effector proteins (C8/C9 and perforin, respectively), suggesting that proteins which protect cells against complement- and cell-mediated attack may also be similar. In homologous complement-mediated killing two protective proteins, which are anchored to the cell membrane by phosphatidylinositol glycan (PIG) tails, are known. To study whether similar PIG-tailed proteins protect against lymphocyte-mediated killing, nucleated cell lines with a mutation in the biosynthesis of the PIG anchor were used. It was found that PIG-tailed membrane proteins restrict homologous complement-mediated lysis but not three different types of cell-mediated killing or lysis by purified perforin. Furthermore, E from patients with an acquired defect in PIG tail biosynthesis did not differ from normal E in sensitivity to antibody-dependent cell-mediated cytotoxicity, in spite of their increased sensitivity to human C8 and C9.

Role of membrane lipids in the immunological killing of tumor cells: I. Target cell lipids.

The metabolic and physical properties of tumor cells that are associated with their ability to resist or escape from immune attack have been investigated. The susceptibility of P815 murine mastocytoma cells to immune killing can be modulated. Culturing the cells with adriamycin or with hydrocortisone increases or decreases, respectively, the sensitivity of the cells to killing by antibody (Ab) plus complement (C); in addition, culturing the cells with mitomycin C or hydrocortisone increases or decreases, respectively, the sensitivity of the cells to killing by cytotoxic T lymphocytes (CTL). The susceptibility of the cells to Ab-C killing correlates with the ability of the cells to synthesize complex cellular lipids, but not DNA, RNA, protein, or carbohydrate. Further, tumor cells rendered sensitive to Ab-C killing by adriamycin are decreased in total lipid content and in their cholesterol/phospholipid mole ratio; hydrocortisone-treated resistant cells showed the opposite effects. The ability of tumor cells to resist CTL killing did not correlate with their total cellular lipid synthesis, but did correlate with the synthesis and composition of specific cellular phospholipids. In addition, tumor cells increased in sensitivity to Ab-C killing exhibited an increase in cell surface membrane fluidity, whereas cells increased in susceptibility to CTL attack showed an increase in their net negative cell surface charge density. These data show certain unique chemical and physical properties of tumor cells to be of fundamental importance for their ability to resist either humoral or cell-mediated immunologic attack; modulation of one or another of these cellular properties results in a change in the cells' susceptibility to immune killing by antibody plus C or by cytotoxic T lymphocytes.

Relationship between cell-mediated and humoral immune attack on tumor cells: II. The role of cellular lipid metabolism and cell surface charge in the outcome of immune attack

Treatment of P815 tumor cells with adriamycin increased their sensitivity to killing by anti-P815 antibody plus C, but not by allogeneic P815-sensitized spleen cells. Conversely, mitomycin C treatment enhanced the cells' sensitivity to cell-mediated, but not antibody-C, killing. Hydrocortisone, but not epinephrine, was effective in increasing the resistance of the cells to killing by both antibody-C and cell-mediated attack systems. The ability of the tumor cells to resist antibody-C killing correlated with their ability to incorporate fatty acid into complex cellular lipid; no such correlation was found between the cellular lipid synthesis and tumor cell susceptibility to cell-mediated killing. Drug or hormone-treated tumor cells exhibited unique changes in cellular lipid synthesis and composition and in cell surface physical properties that correlated with their susceptibility to antibody-C or cell-mediated attack. Cells increased in their sensitivity to antibody-C killing exhibited a decreased cholesterol:phospholipid mole ratio. In contrast, cells rendered more sensitive to cell-mediated killing exhibited an increase in polar phospholipid content and a measurable decrease in net negative cell surface charge density. These data implicate unique chemical and/or physical properties of tumor cells to be of fundamental importance for their ability to resist either humoral or cell-mediated immunologic attack; modulation of one or another of these cellular properties results in a change in the cells' susceptibility to immune killing by antibody plus C or by cytotoxic T lymphocytes.

COELIAC DISEASE: A GRAFT-VERSUS-HOST-LIKE REACTION LOCALISED TO THE SMALL BOWEL WALL?

In coeliac disease, gluten, or one of its fractions, combines with a gut-wall macrophage or lymphocyte to form a lymphoid cell which is recognised by the host as foreign. It is proposed that this cell, rather than being eliminated as the target of a cell-mediated attack by the host, becomes autonomous and initiates a graft-versus-host (GVH)-like reaction. The reaction is largely confined to the gut wall and its associated lymphoid tissue. The severe cachexy and the peripheral lymph-node and splenic atrophy may be explained as features of chronic GVH disease or a "runting" syndrome. Untreated coeliac disease may lead to lymphomatous transformation indistinguishable from the lymphoma of experimental chronic GVH disease.

Relationship between cell-mediated and humoral immune attack on tumor cells: I. Drug and hormone effects on susceptibility to killing and macromolecular synthesis

The effect of metabolic inhibitors and hormones on the susceptibility of P815 murine mastocytoma cells to antibody-C and cell-mediated killing, and on the ability of the cells to synthesize DNA, RNA, protein, carbohydrate, and lipid was tested. Pretreatment of the cells with adriamycin, actinomycin D, and puromycin increased the sensitivity of the cells to killing by rabbit anti-P815 antibody plus guinea pig C, but not by allogeneic P815-sensitized spleen cells. Conversely, mitomycin C treatment enhanced the cells' sensitivity to cell-mediated, but not antibody-C, killing. Insulin and hydrocortisone, but not epinephrine, were effective in decreasing the susceptibility of the cells to killing by both antibody-C and cell-mediated attack systems. The kinetics of the drug-induced increase and the hormone-induced decrease in susceptibility of the cells to antibody-C killing correlated with a decrease and increase, respectively, in the ability of the cells to incorporate fatty acid into complex cellular lipid. No such correlation was found between cellular lipid synthesis and tumor cell susceptibility to cell-mediated killing. The ability of the cells to resist either form of immune attack was not dependent on the ability of the cells to synthesize DNA, RNA, protein, or complex carbohydrate. These results suggest that the susceptibility of these tumor cells to antibody-C vs cell-mediated killing may be linked to different metabolic properties of the cells, and may reflect differences in the mechanisms of humoral vs cellular immune attack.

Participation of three major glycoprotein antigens of herpes simplex virus type 1 early in the infectious cycle as determined by antibody-dependent cell-mediated cytotoxicity.

Tissue culture cells infected with herpes simplex virus type 1 synthesize three major glycoprotein antigens (Ag-11, Ag-8, and Ag-6), which have been characterized by crossed immunoelectrophoresis. The three viral antigens have been identified as a mixture of gA and gB (Ag-11), gD (Ag-8), and gC (Ag-6). Recent findings have shown that antibodies directed to each of the three antigens individually are able to mediate antibody-dependent cell-mediated cytotoxicity when tissue culture cells late in the infectious cycle (18 h postinfection) are used. In this work, antibody-dependent cell-mediated cytotoxicity was applied to study the time postinfection at which the individual viral antigens first made their appearance at the cell surface. All three viral antigens (Ag-11, Ag-8, and Ag-6) could be demonstrated as newly synthesized from 3 to 4 h postinfection, and the quantities of the antigens at the surfaces of the infected cells increased with time postinfection. The use of cycloheximide and ultraviolet-inactivated virus demonstrated that input virus could be detected by antibody-dependent cell-mediated cytotoxicity during the first 2 h postinfection, but the cytotoxicity caused by input virus remained constant with time postinfection. In conclusion, these observations demonstrate the participation of individual herpes simplex virus surface antigens in antibody-dependent cell-mediated cytotoxicity attack on cells early in infection.

Cell-mediated lysis of lipid vesicles containing eye muscle protein: implications regarding pathogenesis of Graves ophthalmopathy.

We prepared artificial vesicles that are lysed upon cell-mediated immunological attack by human lymphocytes. These vesicles are made from a mixture of dimyristoyl lecithin, dipalmitoyl lecithin, and cholesterol, have eye muscle membrane protein (EMP) inserted into the bilayer wall, and contain intravesicular (99m)Tc marker. Injury to the vesicular membrane was assessed by measurement of (99m)Tc release. Thyroglobulin (Tg) and Tg-anti-Tg complex (TgA) bind to EMP-vesicles to an extent equal to or greater than to native eye muscle membranes in vitro; this binding requires the presence of normal human IgG. The role of Tg, TgA, IgG, and peripheral blood lymphocytes in altering membrane permeability was analyzed. Incubation of vesicles for up to 3 hr alone, with added IgG alone, or with further addition of Tg or TgA did not result in (99m)Tc release. Addition of lymphocytes from normal donors to the above four preparations showed release in the presence of TgA. Lymphocytes from each of eight patients with Graves ophthalmopathy caused release not only in the presence of TgA, but also in the presence of Tg. Separation of a patient's lymphocytes into high- and low-affinity rosette-formers (T and K cells, respectively) showed that cell-mediated vesicle lysis in the presence of TgA was greater with K cells than with T cells, while vesicle lysis in the presence of Tg was greater with T cells than with K cells. Vesicles made with inserted Tg but lacking EMP were not lysed by such T cells. Lymphocytes failed to induce permeability changes in vesicles containing other inserted proteins obtained from human nonextraocular muscle, liver, spleen, or adrenal, even if Tg or TgA were present. The results support the concept that muscle cell damage in Graves ophthalmopathy is immunological, cell-mediated, and of two types: (i) K lymphocytes reacting to immune complex, TgA, on the eye muscle cell surface (i.e., antibody-dependent cytotoxicity) and (ii) sensitized T lymphocytes reacting to Tg on the eye muscle cell surface. An antigenic role for EMP is possible, but has not been unequivocally proven.

Liposomes As Model Membrane Systems for Immune Attack

Abstract The interaction of human peripheral blood lymphocytes with liposomes containing DNP-aminocaproylphosphatidylethanolamine together with either egg yolk or dipalmitoylphosphatidylcholine has been investigated. When lymphocytes were incubated with liposomes at 37°C, the aqueous compartment (86Rb+) and the lipid portion (3H-lipid) of the liposomes became cell associated to an equivalent extent. At 0°C, however, the incorporation of 3H-lipid exceeded that of 86Rb+. Lymphocyte-liposome interactions were accompanied by the transfer of DNP to the surface of the lymphoid cell as measured by susceptibility to complement in the presence of anti-DNP antibody. Hapten transfer was not limited to liposome interactions with lymphocytes, but occurred also with other cells (e.g., Chang cells). Hapten transfer could also be demonstrated by susceptiblity to K cell-mediated lysis. These findings suggest that liposomes may prove to be a useful vehicle for the transfer of new antigenic determinants onto cell surfaces. The implications of these findings are discussed in the context of using liposomes as targets for cell-mediated cytotoxic attack.

Graft-versus-host disease impairs cerebellar growth.

Graft-versus-host disease impairs cerebellar growth.

Growth of human tumors in lethally irradiated mice reconstituted with syngeneic fetal liver cells

Transplantation into lethally irradiated mice of hematopoietic and lymphoid cells from immature donors which hypothetically will not mount a cell mediated attack against simultaneously inoculated human tumor cells has resulted in tumor engraftment and growth in long-term surviving radiation chimeras. Twenty-four hours after lethal irradiation, A or CBA mice were given iv injections of 2 X 10(7) fetal liver cells from syngeneic donors of 14, 16, or 18 days of embryonation and sc injections of 1, 3, or 6 X 10(6) human choriocarcinoma (C-1, C-2, and C-3) cells or human breast carcinoma (B-1) cells that had been maintained in culture. Palpable tumors greater than or equal to 5 mm were noted in 18/22 mice injected with C-1, 9/16 with C-2, 10/10 with C-3, and 18/30 with B-1. Tumors of 17 (31%) of mice remained palpable until death of the animal or until termination of the experiment 100 days post inoculation. Histologic study of autopsy specimens revealed malignant tumors with occasional pulmonary metastases. Human chorionic gonadotropin was found in the serum of mice that received choriocarcinoma cells.