Passive immunization against tumor necrosis factor partially abrogates interleukin 2 toxicity.

Passive immunization against TNF allowed non-tumor-bearing C3H/HEN mice and tumor-bearing C57BL/6 mice to tolerate significantly more doses of IL-2 before death (p less than 0.005 and p less than 0.001, respectively). The antitumor effect of IL-2 against both 3-d and 10-d pulmonary metastases was maintained in mice treated concurrently with neutralizing antibodies to TNF. In one experiment with 10-d pulmonary metastases, increased administration of IL-2 made possible by passive immunization against TNF significantly improved the antitumor response compared to equitoxic doses of IL-2 and control antibody. The results indicate that TNF is a mediator of IL-2 toxicity but contributes minimally to the antitumor effects of IL-2. Strategies to inhibit TNF may improve the therapeutic index of IL-2 as a neoplastic agent.

A recombinant human receptor antagonist to interleukin 1 improves survival after lethal endotoxemia in mice.

Interleukin 1 (IL-1) is an endogenously produced cytokine that mediates a variety of physiological effects that may be beneficial or deleterious to the host. C57Bl/6 mice treated intravenously with a recently characterized human recombinant receptor antagonist protein to IL-1 (IL-1ra) had improved survival when treated after a lethal Escherichia coli endotoxin (lipopolysaccharide [LPS]) challenge. IL-1ra was effective when treatment was initiated after LPS, and intravenous administration every 4 h for 24 h was required. Serum levels of tumor necrosis factor (TNF) activity after LPS and in vitro TNF cytotoxicity were not altered by treatment with IL-1ra. These experiments provide direct evidence that the lethal effects of LPS may be mediated through the action of IL-1 and that the IL-1ra can provide a new treatment strategy for disease processes mediated via this cytokine.

Tolerance to tumor necrosis factor in rats and the relationship to endotoxin tolerance and toxicity.

Treatment of rats with recombinant human TNF initially causes a marked decrease in food intake, a loss of body weight, and a negative nitrogen balance. These alterations normalize with continued twice daily intraperitoneal injections of the same dose. Rats tolerized to TNF in this manner are refractory to a lethal dose of TNF. Also, TNF-pretreated and -tolerized rats have prolonged survival and reversed histopathologic changes after injection of a lethal dose of endotoxin compared with control animals. The TNF-tolerant state is dependent on the dose of TNF used and the length of TNF pretreatment. TNF-induced tolerance is relatively short lived, being present 2-4 d after TNF pretreatment and dissipating by 2 wk. Rats made tolerant to endotoxin are also tolerant to a lethal dose of TNF. A bidirectional crossreacting tolerance exists between TNF and endotoxin. The mechanism of TNF tolerance is unclear, but it does not appear to be due to a humoral immune response or a perturbation of the uptake and clearance of injected TNF.

Passive immunization of mice against D factor blocks lethality and cytokine release during endotoxemia.

D factor, also known as leukemia inhibitory factor, is a pleiotropic cytokine whose role during acute injury and inflammation is not known. Intraperitoneal administration of Escherichia coli endotoxin induced D factor gene expression in mice, and passive immunization against D factor protected them from the lethal effects of endotoxin and blocked endotoxin-induced increases in serum levels of interleukin 1 and 6. Peak levels of tumor necrosis factor and interferon gamma were not affected. These results indicate that D factor is an essential early mediator of the inflammatory cytokine response and therefore may be important in the pathogenesis of the many inflammatory conditions, such as sepsis, arthritis, allograft rejection, and cancer immunotherapy.

Differentiation factor/leukemia inhibitory factor protection against lethal endotoxemia in mice: synergistic effect with interleukin 1 and tumor necrosis factor.

Differentiation factor (D factor), also called leukemia inhibitory factor (LIF), is a glycoprotein that has been increasingly recognized to possess a wide range of physiological activities. We examined the possibility that the administration of D factor may confer beneficial effects and enhance host resistance against lethal endotoxemia. A single intravenous dose of recombinant human D factor completely protected C57/Bl6 mice from the lethal effect of Escherichia coli endotoxin (lipopolysaccharide [LPS]). The protective effects were dose dependent and observed when administered 2-24 h before LPS. Previous work has shown that interleukin 1 (IL-1) and tumor necrosis factor (TNF) also protect against a subsequent LPS challenge in a dose-dependent manner. When human D factor was combined with sub-protective doses of IL-1 beta or TNF-alpha, there was dramatic synergistic protection against a subsequent lethal LPS challenge.

A high-resolution radiation hybrid map of the human genome draft sequence.

We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases.

Tissue effects after stereotactic body radiotherapy using cyberknife for patients with abdominal malignancies.

AIMS: To report the tissue effects of treatment with single fraction stereotactic body radiotherapy (SBRT) using Cyberknife on malignant tumours of the abdomen and adjacent normal organs. MATERIALS AND METHODS: The data from four autopsies with unresectable pancreatic carcinoma and one lymph node excision from a case of recurrent neuroblastoma were reviewed for radiation-related tissue effects within the primary cancer and the normal organs within the radiation field. RESULTS: Cases of unresectable pancreatic carcinoma consistently showed radiation-induced changes in both the primary tumour and the adjacent, non-malignant colorectal tissue. An additional case of lymph nodes exposed to stereotactic radiation showed typical radiation-related changes, including lymphocyte depletion and capsular fibrosis. CONCLUSIONS: A myriad of radiation-related tissue effects are seen after SBRT with Cyberknife. The changes parallel those reported after conventionally fractionated radiotherapy and suggest that the pathophysiological mechanisms of radiation-induced normal tissue damage are similar for biologically equivalent single and fractionated doses of radiotherapy.

Treatment with recombinant human tumor necrosis factor-alpha protects rats against the lethality, hypotension, and hypothermia of gram-negative sepsis.

Tumor necrosis factor (TNF) is a peptide secreted by macrophages in response to endotoxin that can produce many of the changes seen in septic shock. After cecal ligation and puncture (CLP) rats gradually develop tachycardia, hypotension, tachypnea, and hypothermia. At 5 h post-CLP, rats have a peak in serum levels of endotoxin and 60% of rats have blood cultures that grow Gram-negative rods (Escherichia coli and Klebsiella pneumonia). At 20 h post-CLP all rats develop positive blood cultures. Serum levels of TNF are not reproducibly measurable in rats following CLP. Rats undergoing CLP have a 50-80% mortality with deaths usually occurring 24-72 h postinjury. Repetitive (twice daily x 6 d) i.p. injection of sublethal doses of recombinant human TNF-alpha (100 micrograms/kg) to rats undergoing CLP 1 d after the treatment period resulted in a significant reduction in mortality compared to control rats previously unexposed to rTNF (P less than 0.03). Animals treated with rTNF had no hypotension or hypothermia after CLP and regained normal food intake faster than control rats. 12 h after CLP the gene expression for manganous superoxide dismutase (MnSOD), an inducible mitochondrial metalloenzyme responsible for cellular resistance to injury from toxic reactive oxygen species, was higher in livers of rats treated with rTNF suggesting that the TNF treatment augmented expression of this protective enzyme. Unlike MnSOD, expression of the gene for copper-zinc SOD was not affected by CLP or rTNF treatment. The results suggest that prior treatment with recombinant TNF can ameliorate the lethality, hypotension, hypothermia, and anorexia of Gram-negative sepsis in rats and that the mechanism may be related to enhanced hepatic expression of the gene for MnSOD. Repeated administration of recombinant TNF may be a strategy to minimize mortality and morbidity of Gram-negative sepsis.

Adaptation during surgical stress. A reevaluation of the role of glucocorticoids.

Pharmacologic doses of glucocorticoids are administered to patients with adrenal insufficiency during operative procedures to prevent hemodynamic instability, cardiovascular collapse, and death. Since these supraphysiologic doses might not be necessary and might have adverse effects, we examined the effects of different doses of glucocorticoids on hemodynamic adaptation during surgical stress in adrenalectomized primates. Sham-adrenalectomized placebo-treated animals served as controls. Adrenalectomized monkeys were maintained for 4 mo on physiologic glucocorticoid and mineralocorticoid replacement. The adrenalectomized monkeys were then stratified into three groups receiving, respectively, subphysiological (one-tenth the normal cortisol production rate), physiological, or supraphysiological (10 times the normal cortisol production rate) cortisol (hydrocortisone) treatment. 4 d later a cholecystectomy was performed. The intraoperative hemodynamic and metabolic parameters, perioperative survival rates, and postoperative wound healing were compared. The subphysiologically treated group was hemodynamically unstable before, during, and after surgery and had a significantly higher mortality rate than control. In this group, arterial blood pressure was low, and the cardiac index, systemic vascular resistance index, and left ventricular stroke work index were all reduced, suggesting decreased cardiac contractility and blood vessel tone. In contrast, the physiologically replaced group was indistinguishable from either supraphysiologically treated animals or sham-operated controls. All groups had similar metabolic profiles and normal wound healing. These findings suggest that the permissive actions of physiologic glucocorticoid replacement are both necessary and sufficient for primates to tolerate surgical stress. Supraphysiological glucocorticoid treatment has no apparent advantage during this form of stress in the primate.

Contribution of inert mass to experimental cancer cachexia in rats.

An inert artificial tumor (AFT) was inflated in male F344 rats to simulate, experimentally, the growth in mass of large transplantable tumors that produce cachexia. The AFT depressed host weight gain and skeletal muscle mass up to 30% and food intake up to 20% of the depression induced by tumors of comparable size. When the growth rate of the AFT was low, there was no depression of food intake. Work-induced hypertrophy of skeletal muscles, as assessed by a gastrocnemius tenotomy model, was approximately equal to that of normal, tumor-bearing, and AFT-bearing animals. The AFT elevated host total energy expenditure by 12.5% and compartment-of-energy expenditure attributable to motor activity by 10.5%. The elevation of energy expenditure accounted for most of the depression of weight gain of AFT-bearing animals below that of intact animals. The large mass of most transplantable tumors leads to an overestimate of the malignant tissue-depletive effects of tumor and an under-estimate of the asthenic effects.

Glucose turnover and gluconeogenesis during hypocaloric glucose infusion in tumor-bearing F344 male rats.

Glucose turnover ([3(3)H]glucose) and gluconeogenesis from alanine ([U-14C]alanine) were measured in non-tumor bearing (NTB) and tumor-bearing (TB) inbred F344 male rats during starvation and in response to graded levels of glucose infusion. All groups demonstrated a glucose turnover appropriate to the prevailing steady-state plasma glucose level. Whereas NTB animals exhibited maximal suppression of gluconeogenesis from alanine at infusion rates of 0.39 mg/100 g total body weight/minute, TB animals suppressed alanine-to-glucose conversion only at a glucose infusion rate of 0.71 mg/100 g total body weight/minute. Glucose clearance was consistently higher in TB groups but did not change in either NTB or TB groups during infusion. Blood lactate levels increased in response to glucose infusion only in TB animals. These results suggested that starved TB animals obligately utilized more glucose than did NTB controls but were able to adjust turnover appropriately to plasma glucose levels. However, gluconeogenesis was suppressed only at higher glucose infusion rates in TB rats compared to NTB animals.

Gluconeogenesis in the tumor-influenced rat hepatocyte: importance of tumor burden, lactate, insulin, and glucagon.

In an attempt to define the relationship between tumor burden (cachexia) and host hepatocyte gluconeogenesis, the following experiments were performed with the use of an F344 male rat bearing a transplantable sarcoma. Food intake of tumor-bearing (TB) rats was constant until day 24 following implant and a tumor burden of 18 +/- 5.2% (mean +/- SD), at which time food intake progressively declined daily. Tumor burden was arbitrarily divided at 12.8% to determine if any measured changes occurred prior to or following the approximate time when a significant decline in food intake occurred. Plasma glucose levels decreased with tumor burden. Whole-blood lactate levels increased with tumor burden. Fasting plasma alanine levels decreased with tumor burden. Plasma 3-methylhistidine levels increased with tumor burden. Plasma glucagon levels increased with tumor burden, whereas plasma insulin levels decreased. Hormone changes were noted at small tumor burdens prior to a decline in food intake. Viable hepatocytes were isolated from 4 groups: non-tumor-bearing (NTB), small tumor burden [(STB) 3.5% total body weight (TBW)], moderate tumor burden [(MTB) 14% TBW], and large tumor burden [(LTB) 23% TBW]. As expected in NTB rats, hepatocytes produced significantly more glucose with 20 mM lactate than 20 mM alanine or than Hanks' balanced salt solution (HBSS) alone. Hepatocytes from STB rats demonstrated the same basic relationship for lactate, alanine, and HBSS, but they produced significantly more glucose from lactate and HBSS alone than NTB hepatocytes. With alanine as substrate, the rates of glucose production by hepatocytes were not affected by the presence or size of tumor. However, with lactate as substrate, hepatocytes from MTB and LTB rats produced progressively less glucose as tumor burden increased (r = -0.85, p less than .001), which may partly explain the reduction in blood glucose and elevation in blood lactate levels observed. Elevated gluconeogenesis in TB rats occurred early prior to a decline in food intake. The key precursor appeared to be lactate. The balance between glucagon and insulin appeared to promote the abnormal host carbohydrate metabolism observed.

Glucose disposal and gluconeogenesis from alanine in tumor-bearing Fischer 344 rats.

For the study of glucose carbon recycling and incorporation of carbon atoms from plasma glucose, [3-3H]glucose and [U-14C]alanine were injected into inbred non-tumor-bearing (NTB) and tumor-bearing (TB) male F344 rats. The glucose and alanine kinetics were determined in relation to antecedent food intake and carcass weight loss. Whereas fed NTB and TB rats appropriately experienced reduced glucose disposal with decreased food intake (0.99 vs. 0.29 mg/min -100 g(-1) compared wtih observations in starved NTB rats), starved TB rats exhibited increased glucose utilization. Both fully fed and cachectic TB groups exhibited increased isotopic carbon recycling compared to the carbon recycling of NTB control groups, whereas starved TB rats did not demonstrate increased recycling compared to the carbon recycling (27% of C-atoms recycled). These findings suggest that alterations of glucose turnover, carbon recycling, and gluconeogenesis in the fed host parallel hypophagia and weight loss, regardless of TB status.

Doxorubicin-induced impairment of wound healing in rats.

The mortality rate induced by 3 doses of iv doxorubicin was evaluated in F344 rats, and a dose of 8 mg doxorubicin/kg body weight was the maximum dose tolerated with an acceptable mortality rate. Rats treated with 8 mg doxorubicin/kg prior to or on the day of wounding demonstrated decreased wound breaking strength in incisional wounds at all intervals after wounding. Decreased amounts of collagen and DNA and less cellularity were noted in wound chambers from rats treated in the same manner. In both the incisional wound and wound chamber models, rats treated with doxorubicin 7 days after wounding showed a less dramatic healing impairment. No difference in collagen types was noted between chambers from the doxorubicin-treated and untreated rats. Doxorubicin also produced a significant reduction in platelet and white blood cell counts 1 week after it was administered. The data indicate that doxorubicin impedes healing by decreasing wound cellularity and collagen synthesis.

Autoradiographic imaging of rat sarcoma in different anatomical sites using 2-[14C]deoxyglucose.

As sarcomas are known to have accelerated glycolysis, we used the radiolabeled glucose analogue 2-deoxy-d-[U-14C]glucose in autoradiographic imaging studies of a methylcholanthrene-induced rat fibrosarcoma placed in an i.m. site, and in models of pulmonary and hepatic metastases. Fifty muCi of 2-deoxy-d-[U-14C]glucose were injected i.p. into groups of rats bearing tumors in these three sites; sacrifice of animals for imaging was carried out 45 min later. Excellent imaging of sarcoma tissue in all three anatomical sites was obtained, with high visual contrast compared to the normal tissue background. Using densitometry of autoradiographs, tumor/tissue ratios were 7.1 for i.m. tumors, 3.8 for pulmonary metastases, and 2.8 for hepatic metastases. Autoradiographic imaging of sarcomas may be obtained based upon avidity of neoplastic tissue for the glucose analogue 2-deoxy-d-[U-14C] glucose. Such imaging is not dependent upon anatomical site and reproducibly images rat sarcomas in muscle, lung, and liver.

Insulin reversal of cancer cachexia in rats.

The anabolic effects of exogenous neutral protamine hagedorn insulin on tumor-bearing (TB) and non-tumor-bearing (NTB) rats were examined. Exogenous insulin (2 units/100 g/day) produced similar hypoglycemia in TB and NTB rats. Food intake and body weight gain were significantly increased by insulin in NTB rats. In TB rats in an early stage of cachexia, insulin increased food intake and host weight (total body weight minus tumor weight). In TB rats with severe cachexia, insulin increased food intake and stabilized host weight when untreated TB controls were not eating and were losing weight. When daily insulin administration was started at an early stage of tumor growth and continued until death, there was again significant enhancement of host weight and food intake. Heart and adrenal weights were significantly reduced in insulin-treated TB animals. Tumor growth was not stimulated by insulin treatment. Survival time was slightly reduced in TB rats treated with long-term insulin. Survival time in TB rats randomized to insulin during late cachectic decline was not different from untreated TB controls. Insulin did not have any measurable effect on energy expenditure or the motor activity compartment of energy expenditure in either TB or NTB rats. Insulin treatment can reverse experimental cancer cachexia. It is a nutritional therapy which preferentially feeds the host over the tumor. As yet, its beneficial effects have not prolonged survival of tumor-bearing animals.

Impact of insulin on doxorubicin-induced rat host toxicity and tumor regression.

To test whether the anorexia and host depletion following doxorubicin chemotherapy can be improved by concomitant insulin therapy, 70 F344 rats were divided equally between tumor-bearing (TB) and non-tumor-bearing (NTB) groups and studied for food intake, host weight, and tumor size changes. Sarcoma fragments were implanted s.c. in TB rats and 18 days later all rats received an i.v. dose of doxorubicin (8 mg/kg). The following day TB and NTB rats were randomized to receive neutral protaminehagedorn insulin (2 units/100 g/24 h) or normal saline until food intake returned to normal. Following doxorubicin administration food intake and host weight declined in an identical pattern in both NTB and TB rats treated with saline. However, beginning on day 6 insulin-treated TB and NTB rats ate significantly more than saline-treated controls. Insulin-treated animals returned to normal food intake levels in 50% less time than controls. This improved food intake resulted in an improved host mass beginning also on day 6 for both TB and NTB rats. In addition, it appeared that insulin treatment significantly improved the tumor shrinkage initiated by doxorubicin. Following doxorubicin, insulin-treated TB rats had a greater reduction of tumor size (10.6 +/- 1.2 cm3) compared to saline-treated rats (6.6 +/- 0.8 cm3, P less than 0.01). To further characterize the effect of insulin and/or doxorubicin on tumor growth, the experiment was repeated in the same manner except for two additional TB groups: saline- and insulin-treated tumor bearers with treatment beginning 19 days after tumor implant. Rats treated with doxorubicin had a significant reduction in tumor size compared to rats not treated with doxorubicin (P less than 0.001). Insulin alone did not affect tumor growth, but insulin plus doxorubicin significantly decreased tumor size compared to doxorubicin alone (P less than 0.01). In a second experiment using 80 rats insulin treatment had no apparent effect on reduction of peripheral blood counts including white blood cells, neutrophils, lymphocytes, platelets, and hematocrit induced by doxorubicin in either NTB or TB rats. Insulin given 24 h previously had minimal effect on plasma glucose. The marked improvement in food intake and host weight, as well as additional tumor reduction with exogenous insulin following doxorubicin, suggests that insulin may have a role in reversal of doxorubicin host nutritional toxicity and perhaps improvement of antitumor efficacy.

Impact of tolerance on antitumor efficacy of tumor necrosis factor in mice.

Repetitive sublethal doses of tumor necrosis factor (TNF) can induce tolerance or tachyphylaxis to the toxic effects of TNF. Because tumor-bearing (TB) mice are more sensitive to the toxic effects of TNF, this study investigates whether similar tolerance occurs in TB mice and whether it affects the antitumor response of TNF. Nontumor-bearing C3H/Hen mice were treated with twice daily i.p. sublethal escalating doses of human recombinant TNF (2, 2, 3, 3, 4, and 4 micrograms i.p. every 12 h for 6 days) and were challenged 2 days later with a lethal i.v. dose (40 micrograms) of TNF. TNF-pretreated mice had 100% survival as compared to 0% survival in control mice previously treated with saline (P less than 0.01). Tumor-bearing C57BL/6 mice bearing an MCA-106 or MCA-102 sarcoma were treated with an identical TNF-tolerizing regimen (2, 2, 3, 3, 4, and 4 micrograms i.p. every 12 h for 6 days) beginning 3 days following tumor inoculation and were similarly more resistant to a subsequent 100% lethal i.v. treatment dose of TNF than control TB mice. A significantly greater percentage of TNF-pretreated mice bearing the MCA-106 sarcoma survived treatment doses of 8, 12, and 16 micrograms of TNF i.v. than control TB mice. Similarly, a significantly greater percentage of TNF-pretreated mice bearing the MCA-102 sarcoma survived treatment doses of 6 and 9 micrograms of TNF i.v. than control TB mice. However, the ability to administer higher doses of TNF i.v. to TNF-pretreated TB mice did not improve therapeutic efficacy. In mice bearing the MCA-106 tumor the most efficacious treatment responses were seen in animals that were previously naive to TNF, and treatment toxicity (lethality) correlated directly with antitumor efficacy such that larger treatment doses of TNF in tolerant mice resulted in similar antitumor effects as smaller treatment doses in control TB mice. In mice bearing the MCA-102 tumor, equitoxic treatment doses of TNF produced similar antitumor effects in both control and tolerant TB mice. There were no differences in cure rate for TNF-tolerant or control TB mice bearing either tumor. The results suggest that TNF tolerance occurs in TB mice and reduces the toxicity as well as the therapeutic efficacy of TNF.

High cytokine production and effective antitumor activity of a recombinant vaccinia virus encoding murine interleukin 12.

We have constructed a recombinant vaccinia virus (recVV), vKT0334 mIL-12, containing the genes encoding the p35 and p40 subunits of murine interleukin-12 (mIL-12). In vitro experiments demonstrated that vKT0334 mIL-12 efficiently infected a variety of murine and human tumor cell lines and produced very high amounts (1.5 micrograms/10(6) cells/24 h) of biologically active mIL-12. Mice injected s.c. with 10(6) MCA 105 sarcoma cells, followed by injection at the same site with saline or a control recVV, vKT033, containing no mIL-12 genes, all developed progressively growing tumor, whereas 60% of animals injected with vKT0334 mIL-12 remained tumor free (P < 0.0005). Furthermore, tumor growth was significantly reduced in the remaining mice treated with vKT0334 mIL-12 that did develop tumor compared with mice treated with vKT033 (P < 0.03) or saline (P < 0.0001). We conclude that recVV expressing high levels of mIL-12 offers an effective in vivo method of cytokine gene delivery and expression in tumors with subsequent antitumor effect.

Cachectin/tumor necrosis factor: a possible mediator of cancer anorexia in the rat.

Cachectin/tumor necrosis factor (TNF) is a macrophage product which may have a role in cancer cachexia. Recombinant human cachectin/TNF (Cetus Corporation) was administered i.p. twice daily to male F344 rats at varying, nonlethal dosages for either 5 or 10 days, and daily rat food intake and body weight were measured. There was a dose-dependent cachectin/TNF-induced decline in food intake and body weight gain over the treatment period. However, after 1 day rats became tolerant to these effects and increased food intake and gained body weight despite receiving cachectin/TNF. Rats were subsequently inoculated with a transplantable methylcholanthrene-induced sarcoma, and survival was measured. Rats previously treated with high-dose (either 100 or 200 micrograms/kg/day) cachectin/TNF survived significantly longer following tumor inoculation than did control rats given saline or rats given 10 micrograms/kg/day of cachectin/TNF. Analysis of tumor growth curves and tumor weight indicated that high-dose cachectin pretreatment did not retard tumor growth. Analysis of food intake and tumor burden following tumor inoculation indicated that high-dose cachectin pretreatment decreased the reduction in food intake associated with progressive tumor growth and allowed rats to withstand a greater tumor burden at death. Rats immunized with low-dose human cachectin/TNF developed high IgG titers against human TNF, but failed to demonstrate the same protection against a methylcholanthrene-induced tumor challenge as rats made tolerant with repetitive twice daily high-dose cachectin/TNF. The observation of reduced cancer-associated anorexia and increased survival of tumor-bearing rats associated with previous tolerance to exogenous cachectin/TNF strengthens the contention that endogenously produced cachectin may be a factor in the pathogenesis of cancer anorexia in the tumor-bearing rat. The mechanism of this tolerance is unclear but does not appear to be a humoral immune response.