The failure of human leukocyte interferon to influence the growth of human glioma cell populations: in vitro and in vivo studies

Human SLFN5 is a transcriptional co-repressor of STAT1-mediated interferon responses and promotes the malignant phenotype in glioblastoma

We provide evidence that the IFN-regulated member of the Schlafen (SLFN) family of proteins, SLFN5, promotes the malignant phenotype in glioblastoma multiforme (GBM). Our studies indicate that SLFN5 expression promotes motility and invasiveness of GBM cells, and that high levels of SLFN5 expression correlate with high grade gliomas and shorter overall survival in patients suffering from GBM. In efforts to uncover the mechanism by which SLFN5 promotes GBM tumorigenesis, we found that this protein is a transcriptional co-repressor of STAT1. Type-I IFN treatment triggers the interaction of STAT1 with SLFN5, and the resulting complex negatively controls STAT1-mediated gene transcription via interferon stimulated response elements (ISRE). Thus, SLFN5 is both an IFN-stimulated response gene and a repressor of IFN-gene transcription, suggesting the existence of a negative-feedback regulatory loop that may account for suppression of antitumor immune responses in glioblastoma.

Growth inhibitory effects of IFN-beta on human liver cancer cells in vitro and in vivo

We investigated the effects of interferon-beta (IFN-beta) on the growth of human liver cancer cells. The effects of IFN-beta with or without 5-fluorouracil (5-FU) on the proliferation of 13 liver cancer cell lines were investigated in vitro. Chronologic change in IFN-alpha receptor 2 (IFNAR-2) expression was monitored in hepatocellular carcinoma (HCC) cells (HAK-1B) cultured with IFN-beta. After HAK-1B cells were transplanted into nude mice, various doses of IFN-beta were administered, and the tumor volume, weight, histology, tumor blood vessel, and angiogenesis factor expression were examined. IFN-beta inhibited the growth of 11 cell lines with apoptosis in a dose-dependent and time-dependent manner. With IFN-beta, IFNAR-2 expression in HAK-1B cells was significantly downregulated from 6 to 12 h. IFN-beta induced a dose-dependent decrease in tumor volume and weight and a significant increase of apoptosis in the tumor. Both basic fibroblast growth factor (bFGF) and blood vessel number in the tumor decreased only in mice receiving the lowest dose (1000 IU) of IFN-beta. IFN-beta with 10 muM of 5-FU frequently induced synergistic antiproliferative effects. IFN-beta with or without 5-FU induces strong antitumor effects in HCC cells, and we conclude that IFN-beta is useful for the prevention and treatment of HCC.

Second-generation interferons for cancer: clinical targets

IFNs were the first new therapeutic products resulting from recombinant DNA technology. IFNs were also the first human proteins effective in cancer treatment. There is however much to be discovered which will lead to new clinical applications. Areas which represent major research challenges for full understanding and application of the IFN system are: (i) the diversity of the IFN family; (ii) the role of induction; (iii) molecular mechanism of action; (iv) cellular modulatory effects; (v) advantages of combinations, and (vi) identification of new therapeutic indications. This review will emphasize the diversity of the IFN family and chemical modifications which will result in second-generation IFNs. Pre-clinical and clinical findings form the basis for new therapeutic directions in chronic myelogenous leukemia, lymphomas, myelomas, melanoma, urologic malignancies, primary brain tumors, and ovarian carcinoma.

Interferon-beta inhibits proliferation and progression through S phase of the cell cycle in five glioma cell lines

The growth inhibitory effect of IFN-beta was evaluated in 5 human glioma cell lines (AO2V4, GJC, GJR, NN and NNR) and in normal astrocyte cultures (SC and TM). All 5 glioma cell lines showed an anti-proliferative response to IFN-beta whereas normal glial cells were non-responsive. IFN-beta at 10, 100 and 500 U/ml lead to a 30%, 70% and 80% relative decrease in cell number after 12 days, respectively in AO2V4 cells. GJC and GJR cell lines also responded significantly to the lowest concentration of IFN-beta tested and at 500 U/ml the relative cell number decreased 55%. The NN and NNR cells were the least responsive to IFN-beta with maximum growth inhibition of 30% at 500 U IFN-beta/ml. Following treatment with IFN-beta, AO2V4, GJC, GJR and normal astrocytes all expressed mRNA encoding the anti-viral protein, 2-5A synthetase demonstrating that IFN-beta bound to receptors on all four cell lines and activated signal transduction pathways required for induction of an anti-viral protein. A determination of the relative number of viable cells showed that none of these cells exhibited a significant decrease in cell viability. Since the antiproliferative response to IFN-beta was not primarily due to cell death, the effect of IFN-beta on cell cycle progression was evaluated by flow cytometry. All treated glioma cell lines showed a relative increase in proportion of cells in S phase. AO2V4 cells had a 50%-80% increase in the percentage of cells in S phase, whereas GJC, GJR and NNR had percentage increases of 20%-40%. IFN-beta treatment of normal astrocytes did not significantly alter their cell cycle profile. These data suggest that IFN-beta exerts its antiproliferative effect on glioma cells by arresting the ordered progression through S phase or decreasing entry into G2/M phase of the cell cycle.

Effects of nIFN beta and rIFN gamma on growth and morphology of two human melanoma cell lines: comparison between two- and three-dimensional culture

We compared the anti-proliferative effects of natural interferon beta (nIFN beta) and recombinant interferon gamma (rIFN gamma) on 2 human melanoma cell lines, IGRI and SK-Mel28, grown in 2-dimensional monolayer and in 3-dimensional spheroid culture. In monolayer culture, growth of both lines was inhibited in a dose-dependent manner by 5-day treatments with IFN in concentrations ranging between 1 and 5,000 IU/ml. Incubations with 120 IU/ml nIFN beta or 25 IU/ml rIFN gamma led to a 50% growth inhibition of IGRI cells. A 50% growth inhibition of SK-Me128 cells was obtained with 60 IU/ml nIFN beta, whereas even 5,000 IU/ml rIFN gamma inhibited the growth of this line by only 30%. Growing these melanoma cell lines in 3-dimensional spheroid culture for 5 days reduced their sensitivity to interferon. Growth inhibition values of 50% were achieved with 3,000 IU/ml rIFN gamma or 9,000 IU/ml nIFN beta for IGRI spheroids and 10,000 IU/ml nIFN beta for SK-Me128 spheroids, while 10,000 IU/ml rIFN gamma reduced the growth of SK-Me128 spheroids by only 25%. Outgrowth tests showed that the proliferative capacity after 5-day incubations with IFN was only reduced in IGRI spheroids treated with high doses of nIFN beta. The macroscopically observed increased density of interferon-treated spheroids could be confirmed by light microscopy as corresponding to reduced intercellular space in these spheroids. Scanning electron microscopy furthermore showed variations on the surface of IFN-treated spheroids as well as in cellular organization and structures between cells, hinting at a possible involvement of extracellular matrix substances in the reaction to interferons.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of interferons and other cytokines on tumors in animals: a review

The term cytokine describes a group of protein cell regulators involved in the control of cell growth and differentiation in embryogenesis, immunity and inflammation. They are of low molecular weight, are produced locally, and act in an autocrine or paracrine manner. In the past decade their use as cancer therapy has become a reality. Thirty years ago mice were treated with the antiviral protein interferon (IFN) which not only produced a reduction in the incidence of virus-induced tumors but also slowed the development of transplantable tumors. This was one of the first indications that cytokines can be negative regulators of cell growth. Here we outline current knowledge of the actions of IFNs and other cytokines in animal models, and draw parallels with clinical trials to illustrate the invaluable nature of this preclinical and mechanistic work.

Local immunotherapy (beta-IFN) and systemic chemotherapy in primary glial tumors

Dosage and schedules for the treatment of malignant glial tumors using IFN (interferon) are still uncertain and controversial. In this study we give the preliminary results of treatment in 28 patients with glioblastoma multiforme (GBM). 6 patients were treated with local injection of beta-IFN through an Ommaya reservoir; 4 patients with beta-IFN followed by systemic chemotherapy (Cisplatin + Etoposide), and 18 patients with chemotherapy only. Two end points were evaluated: 1) Whether or not the patients responded to treatment. 2) Length of Time to Tumor Progression (TTP) after surgery. We found that IFN alone was ineffective. Results were improved when local immunotherapy was associated with systemic chemotherapy. New drugs and investigation of possible pharmacological synergism are needed.

Growth inhibitory effects of interferon-beta but not interferon-alpha on human glioma cells: correlation of receptor binding, 2',5'-oligoadenylate synthetase and protein kinase activity

The antiproliferative effects of human recombinant interferon-alpha (rIFN-alpha A) and interferon-beta (rIFN-beta ser) were assessed in vitro against seven human glioma cell lines. Further analysis of one of these lines (EFC-2) in response to rIFN-alpha A demonstrated a minimum growth inhibition by day 6 of treatment, whereas a 50% inhibition of cell growth was observed with a dose of 50 U/ml of IFN-beta ser. No significant growth inhibition was seen by rIFN-alpha A at doses up to 500 U/ml. Addition of rIFN-alpha A to rIFN-beta ser-treated EFC-2 cells neither suppressed nor augmented the antiproliferative response to IFN-beta ser. The binding of 125I-labeled rIFN-alpha A or 125I-labeled rIFN-beta ser to EFC-2 cells was inhibited competitively by increasing concentrations of either unlabeled rIFN-alpha A or rIFN-beta ser. This suggests that the cellular receptors for both rIFN-alpha A and rIFN-beta ser appear to be intact and appear to bind both agents equally. Furthermore, incubation of EFC-2 cells for 72 h with either rIFN-alpha A or rIFN-beta ser resulted in an increase in 2',5'-oligoadenylate (2-5A) synthetase activity 5-fold with rIFN-alpha A and 50-fold with rIFN-beta ser. Similarly, the 68-kD IFN-induced protein kinase was induced substantially with rIFN-beta ser but only slightly induced with rIFN-alpha A treatment. These results suggest that EFC-2 human glioma cells demonstrate a differential sensitivity in terms of growth inhibition to rIFN-beta ser and to rIFN-alpha A which appears to correlate with a differential induction of both intracellular 2-5A synthetase and protein kinase activity. These results cannot be explained solely on the basis of surface receptor binding of rIFN-alpha A and rIFN-beta ser. These data do suggest that, for human glioma cells in culture, type I IFN receptors may display a subtle architectural variation that allows equivalent binding of both IFN-alpha and IFN-beta ser, but allows an enhanced signal transduction and biological effect only after binding a specific IFN subtype.

Intratumor administration of beta-interferon in recurrent malignant gliomas. A phase I clinical and laboratory study

We administered doses of 5 to 180 x 10(6) IU of beta-serine-interferon (IFN-beta ser17) twice weekly to 20 patients with recurrent malignant gliomas in a Phase I study. Interferon was given through an Ommaya reservoir connected by a catheter to the tumor cavity. Side effects of interferon therapy occurred in only one patient and consisted of nausea, vomiting, fever, and chills after each treatment, presumably due to rapid diffusion of interferon into ventricular cerebrospinal fluid (CSF). Problems with the Ommaya reservoir (obstruction in two patients and infection in four patients) led to six patients being terminated from the study, and represent the major difficulty with this form of therapy. Although this was primarily a study of interferon toxicity, of 12 evaluable patients, 3 had stable disease for 148, 192, and 539 days; 9 had progressive disease. In addition, we tested the effect of IFN-beta ser17 on the growth of early passage in vitro cultures of malignant gliomas established from patients. Growth inhibition varied from 0% to more than 50%. In all cultures evaluated, the combination of recombinant gamma-interferon plus IFN-beta ser17 enhanced growth inhibition. Further clinical and laboratory study is necessary to better define the therapeutic efficacy of IFN-beta ser17 and the role of combinations of interferons in the treatment of malignant gliomas.

The chemotherapeutic response of a murine (VM) model of human glioma

Using a cell line derived from the VM spontaneous murine astrocytoma, a reliable in vitro-in vivo model of human malignant glioma has been developed. In this paper we examine the effects of cytotoxic drugs with known activity against other animal brain tumour models and human disease on the in vivo VM model. The drugs BCNU, CCNU and vincristine produced significant volume reduction in tumours growing at a subcutaneous location in syngeneic animals. Procarbazine was ineffective. Similarly, BCNU, CCNU and vincristine produced small but statistically significant increases in survival of VM mice bearing the intracerebral tumour, but procarbazine was again ineffective. The modest, but significant, response of the VM model to the nitrosoureas mimics the human situation more closely than previously described animal models.

Immunobiology of brain tumors

In summary, many actual interactions between tumors in the CNS and the immune system have been demonstrated. The normal brain does not possess a lymphatic system and is partially hidden from the systemic immune system by the BBB, furthermore brain cells do not express MHC antigens which are necessary for the initiation of an immune response. In pathological conditions however, immunocompetent cells may find their way through transformed endothelial cells. Microglia and astrocytes may function as antigen presenting cells. Glioma cells when stimulated by cytokines such as IFN gamma can be induced to express MHC class I and class II antigens, thus making them more susceptible to an immune attack. In addition glioma cells are capable of secreting several cytokines including IL 1, IL 3 and IL 6 also involved in the generation of an immune response. Indeed, a functional analysis of lymphocytes infiltrating gliomas has revealed the accumulation at the tumor site of cytotoxic T lymphocytes as well as NK cells. However host-immune responses against gliomas seem to be weak in comparison to other cancers. Glioma cells are known to secrete TGF beta 2 and PGE 2 which may in part be responsible for this lack of immune response, thus shielding themselves from immune attack. In order to be recognized by the immune system the tumor cells must express TAA in addition to MHC antigens, and such TAA have been identified by MAbs. These MAbs can be used for "targeted" therapy when coupled to toxic agents or radionuclides. Preclinical studies have shown that, after intravenous or intracarotid injection, there is specific accumulation of the MAb in the tumor but in insufficient amounts for therapeutic use. The relatively small amount of MAb binding to the tumor in vivo can be due to several factors: not all the cells in a single tumor express a given tumor-associated antigens, the MAb may have a low affinity for the antigen, the BBB may hinder the passage of the MAb. Attempts have been made to overcome these drawbacks by opening the BBB for example. In addition MAbs can readily be used for the treatment of carcinomatous meningitis. There has been little success in the development of immunotherapy with IFN beta 1 and even less with adoptive immunotherapy using LAK cells plus IL 2. TIL as well as LAK cells can be expanded in vitro with IL2 and it is feasible to reinject these cells into the tumor site.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunology of central nervous system tumors

With progress in cellular immunology and the development of hybridoma technology, the idea of manipulating host-tumor immune interactions to improve the prognosis of brain tumors has aroused renewed interest. Although no brain tumor-specific antigens have been found, and in spite of the wide antigenic heterogeneity of brain tumor cells, some monoclonal antibodies possessing restricted specificity have been isolated and their potential clinical applications investigated. One of the most pronounced changes in the cellular immune responses of brain tumor patients is a profound depression of the T4-helper lymphocytes. Clinical and laboratory trials are under way to assess the ability of lymphokines, such as gamma-interferon or interleukin-2, to restore immunologic competence in these patients and potentiate a specific anti-tumor immunologic response. Recent work suggests that the endothelium-astrocyte complex may have a pivotal role in assisting the escape of brain tumors from the host's immunologic responses, since it is responsible for the intracerebral sequestration of antigens and local anti-tumor responses. In this review, the data on the antigenic properties of central nervous system tumors and the host's humoral and cellular immune responses to them are analyzed and potential immunologic therapies are discussed.

Systemic gamma-interferon therapy for recurrent gliomas

Recombinant gamma-interferon (2 mg/sq m) was administered intravenously twice weekly in 8-week courses to 14 patients with recurrent gliomas. Computerized tomography (CT) evidence of response was seen in only one patient, and stabilization for 12 to 86 weeks was recorded in three. This was a disappointing result, particularly in a series of patients with relatively small initial tumor volumes (less than 50 cu mm on enhanced CT) and Karnofsky functional ratings of 70 or higher. In addition, several instances of toxicity potentially attributable to gamma-interferon were observed.

An isotope agarose assay for rapid testing of the sensitivity of glioma biopsies to chemotherapeutic drugs and biological response modifiers. Effects of BCNU, vincristine, lymphokines and the recombinant agents interferon alpha 2c, interferon gamma and tumour necrosis factor

A method based on growth of cells from glioma biopsies in a triple layer agarose system has been used to test the sensitivity of the tumour cells to different chemotherapeutic and immunotherapeutic agents. A special agarose that could be melted at 65 degrees C, enabled registration of proliferation by an easy and precise thymidine incorporation technique. The well known concept that agarose permits proliferation of malignant cells and inhibits growth of benign cells was confirmed in this assay by using the malignant glioma cell lines T-MG 1 and U 251 MG, and the benign glia cells T-BG 2 and T-BG 3. All of the 15 glioma biopsies grew exponentially during the first 7 days. The correlation between thymidine incorporation on day 7 and colony number on day 14 was very good for the glioma cell line (r = 0.96) and also for the glioma biopsies (r = 0.89), indicating that the sensitivity evaluation can be done as early as 7 days after the operation. Lymphokines, made by BCG-stimulated lymphocytes, had a strong inhibitory effect on the growth of some glioma biopsies, while others were only slightly inhibited or even stimulated. There was also a huge variation in the sensitivity of the biopsies to BCNU, but the sensitivity pattern was completely different for BCNU and lymphokines. rIF-A had a moderate inhibitory effect on growth of the biopsies, while rTNF had a weak inhibitory effect. The response to rIF-G varied from stimulation of some biopsies to strong inhibition of others. There was no similarity in the sensitivity pattern of the biopsies to rIF-A and rIF-G.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitivities of human glioma cell lines to interferons and double-stranded RNAs individually and in synergistic combinations

The antiproliferative effects of human interferons (IFNs) and double-stranded RNAs (dsRNAs) were studied in five human glioma cell lines. Dose response curves were generated over a 72 hour treatment period. The concentration of interferon or double-stranded RNA necessary to produce a 50% antiproliferative response (GI50) was calculated by linear regression analysis. Two cell lines were more sensitive to IFN-beta than to IFN-alpha, one cell line was more sensitive to IFN-alpha than to IFN-beta and two cell lines had approximately equal sensitivities to both interferons. All cell lines showed some sensitivity to either IFN-alpha or IFN-beta. IFN-gamma had no antiproliferative effect on any of the cell lines. In addition, only one of the cell lines displayed sensitivity to dsRNA, in which the response to poly(I).poly(C) was greater than that to a mismatched analogue of poly(I).poly(C), r(I)n.r(C12,U)n (Ampligen). There was no correlation between the sensitivities to type I IFNs (alpha and beta), type II IFN (gamma) or the dsRNAs. The antiproliferative effect of combinations of IFNs, or IFNs and Ampligen, was studied in one of the cell lines. A significant synergistic antitumor effect was seen with all of the IFN/Ampligen combinations (p less than 0.02), including IFN-gamma/Ampligen, even though these cells were resistant to IFN-gamma alone. Synergy was also seen in the IFN-alpha/IFN-gamma (p less than 0.02) and IFN-beta/IFN-gamma (p less than 0.05) combinations. The IFN-alpha/IFN-beta combination gave an additive antitumor effect. These results indicate that IFN-alpha and IFN-beta alone or combinations of type I IFNs, type II IFNs and Ampligen can be effective in inhibiting the growth of glioma cells.

Growth inhibitory effect of recombinant alpha and beta interferon on human glioma cells

Growth inhibitory activity of recombinant alpha and beta interferon on two human glioma cell lines, EFC-2 and KE cells, was determined by two different growth assays. Recombinant beta interferon showed a slight growth inhibitory effect on EFC-2 cells at day 3, and maximum inhibition was seen on day 6 with an ID50 of 50 U/ml. Recombinant alpha interferon showed no significant growth inhibition at any concentration. KE cells were resistant to both recombinant alpha and beta interferon. The growth inhibitory activity of recombinant beta interferon on EFC-2 cells was not blocked by recombinant alpha interferon, although recombinant alpha and beta interferons shared same receptors on EFC-2 cells. Addition of DFMO (alpha-difluoromethylornithine) to interferon in the media showed additive effect rather than synergistic effect in growth inhibition of glioma cells. Out of 7 glioma cell lines tested, 4 showed heterogeneous sensitivity to recombinant beta interferon, and all were resistant to recombinant alpha interferon. These results suggest a differential sensitivity of EFC-2 cells to recombinant beta interferon, as well as a heterogeneous sensitivity to recombinant beta interferon among different glioma cell lines.

The effects of interferon on glial cells

The effects of a partially purified rat interferon (RIF) on cell lines cloned from a chemically induced rat glioma (A15A5) and normal rat brain (ARBOC9) were investigated. Interferon treatment reduced the rate of exponential growth and saturation density of both cell lines, but induced contrasting morphological changes. A15A5 cells became bipolar, developed longer processes and produced less extracellular fibronectin, whereas ARBOC9 cells became enlarged, showed increased multinuclearity, expressed more fibronectin and contained actin-like cytoplasmic filaments. These findings demonstrate that RIF has an antiproliferative activity in vitro on both neoplastic and non-neoplastic astrocytes, but that morphological and immunocytochemical responses differ.

In vitro drug sensitivity testing in human gliomas

In vitro drug sensitivity assays have been developed with the goal of predicting the clinical response to chemotherapy. The colony-forming assay, radiolabeled precursor inhibition assay, and microcytotoxicity assay are most commonly used. In retrospective studies, the assays correctly predict clinical response to a chemotherapeutic agent in 50% to 70% of patients and predict clinical resistance in nearly 100% of patients. All of the assays suffer from technical and theoretical problems. In vitro assays depend on cell culture and therefore do not entirely simulate in vivo conditions. Heterogeneity in chemosensitivity is commonly found and can complicate the interpretation of results. Further investigation is needed to determine if these assays will be able to select prospective chemotherapy for patients. The malignant origin of the cells in culture must be verified if meaningful conclusions are to be made.

Human non-malignant and malignant brain tumor derived cell cultures: proliferation and sensitivity to natural human fibroblast (beta) interferon

Twenty-one human brain tumor biopsies were processed by mechanical and enzymatic methods to produce mixed cell suspensions. Cultures were prepared in small plastic flasks, and primary outgrowth occurred in 16/21 cultures. The period required for primary outgrowth ranged from 3 days to 14 days. We established serial propagation with 15/16 of the primary cultures. Sensitivity to HuIFN-beta was determined between passages 3 to 12, using a microassay based on cell viability (uptake of a supravital stain, neutral red). Extracted dye was quantified in acidic-methanol using the MR580 Microelisa Autoreader (Dynatech). We observed a broad range of responsiveness to the drug among the 12 cell-strains tested. Thus, 4 cell strains were relatively sensitive; 4 were resistant to 10(4) IRU/ml of purified HuIFN-beta. Four cell strains exhibited a level of responsiveness that was intermediate to that of these two groups. During propagation of these biopsies, cytopathology suggestive of paramyxovirus-infection appeared in 4 of the cell-strains. This characteristic was not uniformly associated with high sensitivity to human beta interferon which is a very potent, naturally occurring antiviral substance. Our results support the concept that information concerning sensitivity to HuIFN-beta and other cytostatic agents may be rapidly obtained using microcultures of brain tumor cultures in conjunction with supravital stain uptake studies. Additionally, these results suggest that further clinical studies with beta interferon should be undertaken to define the parameters which determine successful in vivo application.

Immunobiology of primary intracranial tumors. Part 10: Therapeutic efficacy of interferon in the treatment of recurrent gliomas

Human lymphoblastoid alpha-interferon was administered intravenously or intramuscularly to 19 patients with recurrent gliomas. Each patient had previously undergone surgery and radiation therapy. The treatment course consisted of 8 weeks of therapy with an escalating daily dosage and number of days of treatment per week to a total dose of 900 X 10(6) U/sq m. Response to treatment was determined by serial computerized tomography (CT) scans. Seven of the 17 evaluable patients were determined to be treatment responders at 12 weeks (1 month after completion of treatment), and the other 10 patients exhibited tumor progression during this period. Median survival time was 511 days for the responders versus 147 days for the non-responding patients. Interferon appears to be efficacious in the treatment of recurrent anaplastic gliomas as defined by CT brain scan responses following therapy.

Interferon-beta in patients with low-grade astrocytomas--a phase I study

In 3 patients with low-grade astrocytomas clinical pharmacology of interferon-beta (10(7) U/mg protein) was investigated. Interferon-beta with escalating dosage (2.3, 6.9, 23, 69 X 10(6) U/patient) was given to each patient in 4 infusions at weekly time intervals. In these patients dose-dependent plasma-levels of interferon-beta of up to 5800 IU/ml were achieved. Plasma concentrations showed a biphasic decline (T1 1/2:0.095-0.49 hrs and T2 1/2: 5-14.5 hrs). Side effects were: mild fatigue, myalgia, tachycardia, hypertension, and fever; the latter was well controlled by pretreatment application of paracetamol. Hematological changes included lymphopenia (2-6 hrs after infusion) and granulocytosis (3-6 hrs after infusion). Natural Killer cell activity was also monitored: 6 hours after infusion a drop of activity - not clearly dose dependent - was observed to a minimum of 1% pretreatment activity; 24 hrs after infusion activity increased up to a maximum of 400%. In this phase I study high biological activity of interferon-beta could be detected in plasma of astrocytoma patients - clinical tolerance was good and only mild toxicity was observed.