Myelin basic protein serum factor. An endogenous neuroantigen influencing development of experimental allergic encephalomyelitis in Lewis rats

Combining cytotoxic and immune-mediated gene therapy to treat brain tumors

Glioblastoma (GBM) is a type of intracranial brain tumor, for which there is no cure. In spite of advances in surgery, chemotherapy and radiotherapy, patients die within a year of diagnosis. Therefore, there is a critical need to develop novel therapeutic approaches for this disease. Gene therapy, which is the use of genes or other nucleic acids as drugs, is a powerful new treatment strategy which can be developed to treat GBM. Several treatment modalities are amenable for gene therapy implementation, e.g. conditional cytotoxic approaches, targeted delivery of toxins into the tumor mass, immune stimulatory strategies, and these will all be the focus of this review. Both conditional cytotoxicity and targeted toxin mediated tumor death, are aimed at eliminating an established tumor mass and preventing further growth. Tumors employ several defensive strategies that suppress and inhibit anti-tumor immune responses. A better understanding of the mechanisms involved in eliciting anti-tumor immune responses has identified promising targets for immunotherapy. Immunotherapy is designed to aid the immune system to recognize and destroy tumor cells in order to eliminate the tumor burden. Also, immune-therapeutic strategies have the added advantage that an activated immune system has the capability of recognizing tumor cells at distant sites from the primary tumor, therefore targeting metastasis distant from the primary tumor locale. Pre-clinical models and clinical trials have demonstrated that in spite of their location within the central nervous system (CNS), a tissue described as 'immune privileged', brain tumors can be effectively targeted by the activated immune system following various immunotherapeutic strategies. This review will highlight recent advances in brain tumor immunotherapy, with particular emphasis on advances made using gene therapy strategies, as well as reviewing other novel therapies that can be used in combination with immunotherapy. Another important aspect of implementing gene therapy in the clinical arena is to be able to image the targeting of the therapeutics to the tumors, treatment effectiveness and progression of disease. We have therefore reviewed the most exciting non-invasive, in vivo imaging techniques which can be used in combination with gene therapy to monitor therapeutic efficacy over time.

Nitric Oxide Plays a Critical Role in the Recovery of Lewis Rats from Experimental Autoimmune Encephalomyelitis and the Maintenance of Resistance to Reinduction

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease of the CNS and an animal model for the human demyelinating disease, multiple sclerosis. In the Lewis rat, myelin basic protein (MBP)-CFA-induced EAE is an acute monophasic disease from which animals recover fully, do not relapse, and develop a robust long-term resistance to further active reinduction of disease. In this paper, we report that rats recovering from MBP-CFA-induced EAE have significantly increased serum levels of reactive nitrogen intermediates indicative of increased NO production. These levels remain elevated after the recovery period and increase even further early after a rechallenge with MBP-CFA, and all animals are totally refractory to a second episode of disease. Oral treatment of rats with N-methyl-l-arginine acetate (l-NMA), beginning at peak disease on day 11 postimmunization, results in significant prolongation of disease and an alteration in the presentation of clinical symptoms from that of solely hind limb paresis/paralysis to severe fore limb involvement as well. Treatment of fully recovered rats with l-NMA 24 h before a rechallenge with MBP-CFA leads to decreased serum reactive nitrogen intermediate levels and results in a second episode of EAE in 100% of animals. Furthermore, l-NMA treatment of fully recovered rats in the absence of a rechallenge immunization leads to spontaneous relapse of disease.

Induction by cells of immune responses to intestinal epithelial cell-associated components (ECAC): transfer with cultured murine mesenteric and popliteal/axillary lymph node cells

Although systemic and mucosal immune responses to intestinal epithelial self-antigens occur in several human disorders, there is no model system with which to study the physiology and regulation of the underlying cellular events. Therefore, we undertook to induce an immune response to purified epithelial macromolecules in the Lewis rat; characterize in vitro the reactive cells; and then transfer with immunocytes this antiepithelial reactivity to naive syngeneic rats, identifying the fine specificity and site of humoral and cell-mediated immunity induced in the cell recipient. Donor animals sensitized systemically (via footpad) or locally in gut mucosa (via Peyer's patches) to syngeneic or xenogeneic epithelial antigens generated specific immunoglobulin and were found to have T lymphocytes in the draining nodal areas (including the mesenteric nodes) which were (a) antigen-specific, having a [3H]thymidine uptake in the presence of antigen 30-fold the control; (b) generally of the Thelper/inducer subclass (W3/25+) which, upon further culture, developed phenotype surface markers for activation (IL-2R+); (c) able to induce an antigen-specific humoral and cell-mediated responses upon intravenous injection into naive syngeneic hosts; and (d) demonstrable in gut-associated lymphoid tissue (mesenteric lymph nodes) and, to a lesser extent in spleen, of the cell recipient. Further, lymphocytes cloned from reactive mesenteric lymph node cells demonstrated specificity for a gel-purified subfraction of epithelial antigen, designated P1, containing highly conserved organ-specific macromolecules thought to be autoantigenic for gut.

Alloreactive immune responses of transgenic mice expressing a foreign transplantation antigen in a soluble form

Transfection of cells with the H-2Kk gene lacking the transmembrane and cytoplasmic segments resulted in secretion of the H-2Kk protein, as determined by immunoprecipitation with monoclonal anti-H-2Kk antibodies. Transgenic (H-2b X H-2d)F1 mice were established carrying integrated copies of the modified H-2Kk gene. Expression of the soluble H-2Kk antigen in the transgenic mice was demonstrated in cell supernatants of biosynthetically labeled splenic and thymic Con A blasts as well as bone marrow-derived macrophages. Soluble H-2Kk molecules were also present in the sera of the transgenic animals. No cell-surface expression of the H-2Kk antigen could be observed. In spite of the presence of the soluble H-2Kk molecules in the transgenic mice, the animals were able to generate H-2Kk-specific cytolytic T cells as well as antibody responses when stimulated with cell-surface-bound H-2Kk antigens. These responses were indistinguishable from those of the nontransgenic littermates. Possible explanations for the observed lack of tolerance are discussed.

An immunochemical analysis of a myelin basic protein serum factor: cross reactivity with residues 69-71 of the rabbit encephalitogenic sequence 65-74 of myelin basic protein

A partially purified myelin basic protein serum factor (MBP-SF), cross-reactive with residues 65-74 (TTHYGSLPQK) of myelin basic protein, has been employed in an immunochemical study to identify the nature of the cross-reacting determinant more precisely. To probe the structural requirements of this determinant, Scatchard inhibition analyses and competitive peptide inhibition radioimmunoassays were employed with a series of peptide analogs of the 65-74 region and with three different reagent antisera: a rabbit anti-rat myelin antiserum (#My05) and two antisera, one rabbit (#162) and one chicken (#66), raised against synthetic peptide S24 (TTHYGSLPQKG). Scatchard inhibition analyses with MBP-SF revealed specific inhibition of binding of 125I-S24 to #162 and #My05, but not to #66. Further delineation of the structural requirements of the cross-reactive determinant, employing a liquid-phase radioimmunoassay, revealed a unique reactivity pattern for the chicken anti-S24 antiserum which, unlike #162 and #My05, did not cross-react under high-affinity conditions with synthetic peptide S20 (GSLPQK, representing the C-terminal half of S24). This, in concert with the Scatchard data, is suggestive of the presence of a cross-reactive determinant centered around residues 69-71 of MBP.

Suppressive effect of pregnancy on the development of experimental allergic encephalomyelitis in rabbits

In the present study we have investigated the influence of pregnancy on the induction and development of experimental autoimmune encephalomyelitis (EAE) in rabbits in relation to the time of gestation. Randomly bred rabbits were immunized with encephalitogenic bovine brain homogenate in complete Freund's adjuvant before or during pregnancy. The appearance of EAE was delayed and occurred only after delivery, abortion, or fetal resorption. The incidence of the disease was lower and the duration longer. The levels of antibodies to myelin basic protein, an autoantigen of EAE, as measured by solid phase radioimmunoassay, were lower in the pregnant rabbits as compared to the nonpregnant animals. The suppressive influence of pregnancy on the induction and the development of EAE confirms previous reports demonstrating amelioration of autoimmune diseases and other immunological reactions during the second half of human pregnancy. This effect might be partially attributed to the increased level of alpha-fetoprotein (AFP) and/or other pregnancy-associated factors in maternal serum.

Immunoglobulin-deficient rats fail to develop experimental allergic encephalomyelitis

Lewis rats were treated from day of birth with a rabbit anti-rat IgM antiserum. As adults these animals were found to have no detectable serum IgM and greatly reduced levels of IgG. They failed to respond to the B-cell mitogen LPS, or to make antibodies to sheep red blood cells (SRBC) or myelin basic protein (BP). These B-lymphocyte and immunoglobulin-deficient rats failed to develop clinical or histological evidence of EAE when sensitized with either whole spinal cord or purified BP. That some T-cell functions of these suppressed animals were not altered was seen by their ability to respond normally to PHA and to reject tissue allografts. The results would suggest that B-cell function (immunoglobulin-antibody production) is essential for the induction of EAE.

Comparative levels of endogenous myelin basic protein-serum factors (MBP-SFs) in adult and suckling mice (B6CBAF1 and B6C3HF1, strains) and in neurologically mutant mice of the same genetic background

Normal adult B6C3HF1 and B6CBAF1 mice contained at least 10 times higher levels (1.17 microM) of endogenous myelin basic protein-serum factors (MBP-SFs) than previously found in adult Lewis rats. In rat MBP-SF levels in the adult (0.03 microM) were much less than in the suckling animals (0.74 microM). In mice, by contrast, the adult (1.17 microM) and suckling (0.75 microM) levels were similar. Suckling mice from 9 different neurologically mutant strains and their clinically normal littermates had MBP-SF levels (0.5 microM) slightly below that of normal suckling mice of the same genetic background (0.75 microM).

Cellular cytotoxicity and gastrointestinal inflammation in inbred rats: induction with gut organ-specific antigens

Although the ability to induce with organ-specific antigens autoimmune inflammatory lesions in the brain and thyroid is well-established, it has not been accomplished for the gastrointestinal system. Therefore, purified rat intestinal glycoproteins (RGCG and RCG) with defined biochemical and immunological properties and known to be organ-specific, were employed to study immune responses in four highly inbred strains of rats. Animals subcutaneously immunized with RGCG/RCG (or saline in controls) and Mycobacterium butyricum as the primary adjuvant were followed weekly for (a) weight loss and diarrhoea; (b) development of specific antibody; (c) cell-mediated cytotoxicity by a ⁵¹Cr release assay; (d) pathological changes (graded I—IV) in intestine at the time of serial killing; and (e) increase in lamina propria cell count in histological sections taken from both macroscopically normal and abnormal bowel wall.

Disease incidence was highest in LOU/Mn strain rats injected with RCG, where small bowel lesions began at the fifth week after immunization (one of three animals), their frequency progressively increasing through the seventh week (four of five animals) when weight loss was most marked. Lewis strain rats injected with RCG had similar small bowel lesions at the sixth and seventh week. Colonic lesions were found in LOU/Mn strain rats injected with RGCG. Antibody-dependent cellular cytotoxic responses to RCG were detectable at both 50:1 and 10:1 effector to target ratios, occurred principally in injected animals who progressed to disease, and were correlated in time with the onset of lesions (weeks 5–7). Pathologically, all small bowel lesions were grade III (dark red granular mucosa) or IV (granular with obvious haemorrhage). Involved segments were 4–16 cm long, confined to the ileum, and diffuse without punctate ulcers. Colonic lesions were 2 cm long and diffusely hyperemic (grade II). Histologically, sections from diseased animals showed three changes: distortion (blunting) of villus shape, a hypercellular lamina propria (grade, moderate) and disruption of columnar epithelial lining cells. Two (ACI and Wistar—Furth) of the four strains studied were non-responders with respect to disease induction. We conclude that purified organ-specific gut glycoproteins can induce bowel wall pathological changes and antibody-dependent cellular cytotoxic reactions in susceptible strains of immunized rats. This technique may be useful for studying both the origin of, and the mediators for, autoimmune disease of the intestine.

Endogenous myelin basic protein-serum factors (MBP-SFs) and anti-MBP antibodies in humans. Occurrence in sera of clinically well subjects and patients with multiple sclerosis

Sera of normal subjects and patients wtih multiple sclerosis (MS) have been frequently found to contain picomolar quantities of endogenous myelin basic protein-serum factors (MBP-SFs). These serum factors, collectively representing a heterogeneous spectrum, were detected and measured by means of a competitive inhibition radioimmunoassay (RIA) designed to distinguish their respective binding affinities with anti-MBP reagent antiserum. Anti-MBP antibodies in these same normal and patient sera were also detected and their differing binding affinities determined. In general, when sera of normal subjects were found to contain free MBP-SFs, the reagent anti-MBP antibodies in the reagent antiserum used to detect them were of relatively high binding affinity (8 X 10(8) M-1). When normal sera were found to contain free anti-MBP antibodies, the affinities of such antibodies were invariably lower (0.06-0.7 X 10(8) M-1). In contrast, sera of patients with active MS and exhibiting clinical fluctuations in their disease, infrequently contained high or medium high affinity MBP-SFs, whereas higher affinity anti-MBP antibodies were commonly detected. These patterns of MBP-SFs and anti-MBP antibodies in normal and MS human sera resemble those previously observed in studies of normal Lewis rats and rats developing experimental allergic encephalomyelitis (EAE). The findings here reported provide additional support for the view that circulating endogenous MBP-SFs may function as neuroautotolerogens that restrict expansion of MBP-reactive lymphoid cell clones having potentially injurious effector activity for central nervous system (CNS) tissue.

Immunogenicity of synthetic peptide sequences S81 and S82 (residues 68-83 and 65-83) of bovine myelin basic protein. Time-course of antibody responses in rats and rabbits

The timing and intensity of the antibody responses to the marker determinants of synthetic peptide S81 and S82 sequences of bovine myelin basic protein (MBP) (residues 68-83 and 65-83, respectively) were studied in 20 Lewis rats and 6 rabbits. All rats immunized with either peptide in CFA responded with antibody development. All rabbits immunized with S82 and CFA developed both antibodies and experimental allergic encephalomyelitis. In contrast only one rabbit developed antibodies against S81 and none of the S81-challenged rabbits developed disease. On the basis of extrapolation of linear time-response curves to zero activity, the time of appearance of anti-peptide antibody activity in the Lewis rats was 15.1 +/- 1.7 days after a single immunization, a week longer than the normal latent period before appearance of anti-MBP antibodies. The time of appearance of anti-S82 antibody activity in rabbits exhibiting linear response curves was 18 days, 4 days after a booster immunization with S82 in incomplete Freund's adjuvant. The development of clinical signs of experimental allergic encephalomyelitis occurred within 4 weeks after initial challenge (a few days after boosting) and continued for 8--13 days in all S82-immunized rabbits.

Studies of rat antibodies specific for myelin basic protein (MBP). Antibody-dependent cell-mediated lysis of MBP-sensitized targets in vitro

Rats immunized with rat myelin basic protein (MBP) in an encephalitogenic regimen produce antibodies which cooperate with spleen cells from unimmunized rats in the specific lysis of MBP-sensitized chicken erythrocytes (MBP-CRBC) in vitro. Antibodies against MBP capable of participating in antibody-dependent cell-mediated cytotoxicity (ADCC) were detected in serum 9 days post immunization, and prior to the onset of experimental allergic encephalomyelitis (EAE). Measurements based on a sensitive radioimmunoassay technique had previously established that anti-MBP activity emerges by day 9, early enough to participate in events leading up to EAE. The ADCC assay was designed to further characterize functions of immunoglobulins associated with the humoral response to MBP, with emphasis on the cytophilic properties of early antibodies. The assay described was found to be nearly as sensitive as the RIA and could detect specific syngeneic rat anti-MBP at concentrations of about 0.03 pmoles/ml serum. Whether ADCC-type reactions take place in the central nervous system during acute EAE is not known; however, the presence of early cytophilic antibody in serum suggests that humoral immunity may play an ancillary role to that demonstrated for T-cell immunity in EAE.

Endogenous myelin basic protein-serum factors (MBP-SFs) in Lewis rats. Evidence for their heterogeneity and reactivity with anti-MBP antibodies of different affinities

MBP-SF, previously described as an endogenous myelin basic protein-serum factor in Lewis rats with a suggested function as a neuroautotolerogen, appears not to be a single factor but a heterogeneous collection of serum factors (MBP-SFs), most probably small fragments of MBP, each cross-reactive with a different region of the multideterminant parent molecule. The heterogeneity of the MBP-SFs in any serum sample is defined and limited by the spectrum of binding affinities of the antibody populations represented in a given reagent anti-MBP antiserum. Some samples of normal Lewis rat serum have been found to contain high affinity MBP-SFs which coexist with low affinity anti-MBP antibodies whereas other sera have shown the reversed pattern, viz. low affinity MBP-SFs and high affinity antibodies. Additional sera have been found to contain MBP-SFs of several different affinities. In time-course studies of rats sensitized to neuroantigen-adjuvant a variety of MBP-SFs and anti-MBP antibodies of different affinities may be observed in sequentially collected sera from a given animal. In no animal has any serum sample been found to contain the full spectrum of MBP-SFs. Although some MBP-SFs have been found to increase temporarily during the 2nd week after neuroantigen/CFA sensitization, all MBP-SFs tend to disappear in the 2nd week and to be replaced by anti-MBP antibodies of differing affinities 3-4 weeks following sensitization.