Binding of NF-kB to the HIV-1 LTR is not sufficient to induce HIV-1 LTR activity

Galectin-3 is involved in HIV-1 expression through NF-κB activation and associated with Tat in latently infected cells

Galectin-3 (Gal-3) is involved in many biological processes and pathogenesis of diseases in part through nuclear factor (NF)-κB activation. We demonstrated that Gal-3 expression was significantly induced by tumor necrosis factor (TNF)-α or phorbol 12-myristate 13-acetate in OM-10.1 and ACH-2 cells, which are considered as a model of HIV-1 latently infected cells. The expression of Gal-3 was also associated with their viral production. However, the induction of Gal-3 by TNF-α was not observed in their uninfected parental cells. Knockdown of Gal-3 resulted in the suppression of NF-κB activation and HIV-1 replication in the latently infected cells. The expression level of Gal-3 was highly correlated with that of HIV-1 Tat in the latently infected cells stimulated with TNF-α. Furthermore, colocalization and possible interaction of Gal-3 and Tat were observed in the stimulated cells. These results suggent that Gal-3 expression is closely correlated with HIV-1 expression in latently infected cells through NF-κB activation and the interaction with Tat.

Trade-off between synergy and efficacy in combinations of HIV-1 latency-reversing agents

Eradicating HIV-1 infection is difficult because of the reservoir of latently infected cells that gets established soon after infection, remains hidden from antiretroviral drugs and host immune responses, and retains the capacity to reignite infection following the cessation of treatment. Drugs called latency-reversing agents (LRAs) are being developed to reactivate latently infected cells and render them susceptible to viral cytopathicity or immune killing. Whereas individual LRAs have failed to induce adequate reactivation, pairs of LRAs have been identified recently that act synergistically and hugely increase reactivation levels compared to individual LRAs. The maximum synergy achievable with LRA pairs is of clinical importance, as it would allow latency-reversal with minimal drug exposure. Here, we employed stochastic simulations of HIV-1 transcription and translation in latently infected cells to estimate this maximum synergy. We incorporated the predominant mechanisms of action of the two most promising classes of LRAs, namely, protein kinase C agonists and histone deacetylase inhibitors, and quantified the activity of individual LRAs in the two classes by mapping our simulations to corresponding in vitro experiments. Without any adjustable parameters, our simulations then quantitatively captured experimental observations of latency-reversal when the LRAs were used in pairs. Performing simulations representing a wide range of drug concentrations, we estimated the maximum synergy achievable with these LRA pairs. Importantly, we found with all the LRA pairs we considered that concentrations yielding the maximum synergy did not yield the maximum latency-reversal. Increasing concentrations to increase latency-reversal compromised synergy, unravelling a trade-off between synergy and efficacy in LRA combinations. The maximum synergy realizable with LRA pairs would thus be restricted by the desired level of latency-reversal, a constrained optimum we elucidated with our simulations. We expect this trade-off to be important in defining optimal LRA combinations that would maximize synergy while ensuring adequate latency-reversal.

HIV-1 infection typically requires lifelong treatment because a class of infected cells called latently infected cells remains hidden from drugs and host immune responses and can reignite infection when treatment is stopped. Massive efforts are ongoing to devise ways to eliminate latently infected cells. The most advanced of the strategies developed for this purpose involves using drugs called latency-reversing agents (LRAs), which reactivate latently infected cells, effectively bringing them out of their hiding. Multiple mechanisms are involved in the establishment of latency. Pairs of LRAs targeting distinct mechanisms have been found to synergize and induce significantly higher latency-reversal than individual LRAs. If this synergy can be maximized, latency-reversal can be achieved with minimal drug exposure. Using stochastic simulations of HIV-1 latency, we unraveled a trade-off between synergy and efficacy in LRA pairs. Drug concentrations that maximized synergy did not also maximize latency-reversal. Drug concentrations that yielded higher latency-reversal compromised synergy and vice versa. This trade-off would constrain the synergy realizable between LRAs and guide the identification of optimal LRA combinations that would maximize synergy while ensuring adequate latency-reversal.

Genetic variation and HIV-associated neurologic disease

HIV-associated neurologic disease continues to be a significant complication in the era of highly active antiretroviral therapy. A substantial subset of the HIV-infected population shows impaired neuropsychological performance as a result of HIV-mediated neuroinflammation and eventual central nervous system (CNS) injury. CNS compartmentalization of HIV, coupled with the evolution of genetically isolated populations in the CNS, is responsible for poor prognosis in patients with AIDS, warranting further investigation and possible additions to the current therapeutic strategy. This chapter reviews key advances in the field of neuropathogenesis and studies that have highlighted how molecular diversity within the HIV genome may impact HIV-associated neurologic disease. We also discuss the possible functional implications of genetic variation within the viral promoter and possibly other regions of the viral genome, especially in the cells of monocyte-macrophage lineage, which are arguably key cellular players in HIV-associated CNS disease.

Cellular protein TTRAP interacts with HIV-1 integrase to facilitate viral integration

TTRAP is a PML-NB protein that is involved in the NF-kappaB signaling pathway. TTRAP was recently identified by yeast two-hybrid analysis as a HIV-1 integrase (HIV-1 IN) interacting protein. This interaction was verified by co-immunoprecipitation, GST pull-down, and intracellular imaging, and deletion assays suggested that the N-terminal 180 residues of TTRAP are responsible for the interaction. In stable TTRAP knock-down cell lines, the integration of viral vectors decreased significantly compared with non-silenced cell lines. Conversely, overexpression of TTRAP by transient transfection increased the percentage of integration events. This is the first time that TTRAP has been shown to interact with HIV-1 IN and facilitate lentiviral vector integration. These findings reveal a new function of TTRAP and expand our understanding of the cellular response to HIV infection. The interaction between TTRAP and HIV-1 IN may be useful in designing new anti-viral strategies as well as for improving the efficiency of lentiviral-vector-mediated gene delivery.

Kaposi's sarcoma associated herpes virus-encoded viral FLICE inhibitory protein activates transcription from HIV-1 Long Terminal Repeat via the classical NF-kappaB pathway and functionally cooperates with Tat

BACKGROUND

The nuclear transcription factor NF-kappaB binds to the HIV-1 long terminal repeat (LTR) and is a key regulator of HIV-1 gene expression in cells latently infected with this virus. In this report, we have analyzed the ability of Kaposi's sarcoma associate herpes virus (KSHV, also known as Human Herpes virus 8)-encoded viral FLIP (Fas-associated death domain-like IL-1 beta-converting enzyme inhibitory protein) K13 to activate the HIV-1 LTR.

RESULTS

We present evidence that vFLIP K13 activates HIV-1 LTR via the activation of the classical NF-kappaB pathway involving c-Rel, p65 and p50 subunits. K13-induced HIV-1 LTR transcriptional activation requires the cooperative interaction of all three components of the IKK complex and can be effectively blocked by inhibitors of the classical NF-kappaB pathway. K13 mutants that lacked the ability to activate the NF-kappaB pathway also failed to activate the HIV-1 LTR. K13 could effectively activate a HIV-1 LTR reporter construct lacking the Tat binding site but failed to activate a construct lacking the NF-kappaB binding sites. However, coexpression of HIV-1 Tat with K13 led to synergistic activation of HIV-1 LTR. Finally, K13 differentially activated HIV-1 LTRs derived from different strains of HIV-1, which correlated with their responsiveness to NF-kappaB pathway.

CONCLUSIONS

Our results suggest that concomitant infection with KSHV/HHV8 may stimulate HIV-1 LTR via vFLIP K13-induced classical NF-kappaB pathway which cooperates with HIV-1 Tat protein.

Curcumin inhibits ultraviolet light induced human immunodeficiency virus gene expression

Recently, we reported that the herbal drug St. John's Wort is a potent inhibitor of UV-induced HIV-LTR activation in stably transfected HIVcat/HeLa cells. Our previous studies have demonstrated that the activation of p38 MAP kinase (stress-activated protein kinase-2) and NF-kappaB are both required for a full UV-induced HIV gene expression response. In this study we have investigated the mechanism by which curcumin inhibits UV-activated HIV-LTR gene expression. We found that treatment of HIVcat/HeLa cells with micromolar concentrations of curcumin completely abolished UV activation of HIV gene expression. Curcumin treatment at similar doses as those used to inhibit HIV gene expression also effectively blocked UV activation of NF-kappaB, as demonstrated by electrophoretic mobility shift assay. In contrast, curcumin did not inhibit UV-induced phosphorylation of p38 MAP kinase. This observation was also supported by findings that curcumin did not inhibit UV-induced phosphorylation of CREB/ATF-1 and ATF-2. Although curcumin was ineffective in preventing UV-induced p44/42 MAP kinase phosphorylation, the JNK (1 and 2) and AP-1 activation were efficiently blocked by curcumin in HeLa cells. We conclude that the mechanism by which curcumin modulates UV activation of HIV-LTR gene expression mainly involves the inhibition of NF-kappaB activation.

Identification of T cell-signaling pathways that stimulate latent HIV in primary cells

Eradication of HIV infection depends on the elimination of a small, but stable population of latently infected T cells. After the discontinuation of therapy, activation of latent virus can rekindle infection. To purge this reservoir, it is necessary to define cellular signaling pathways that lead to activation of latent HIV. We used the SCID-hu (Thy/Liv) mouse model of HIV latency to analyze a broad array of T cell-signaling pathways and show in primary, quiescent cells that viral induction depends on the activation of two primary intracellular signaling pathways, protein kinase C or nuclear factor of activated T cells (NF-AT). In contrast, inhibition or activation of other important T cell stimulatory pathways (such as mitogen-activated protein kinase, calcium flux, or histone deacetylation) do not significantly induce virus expression. We found that the activation of NF-kappaB is critical to viral reactivation; however, all pathways that stimulate NF-kappaBdonot reactivate latent virus. Our studies further show that inhibition of NF-kappaB does not prevent activation of HIV by NF-AT, indicating that these pathways can function independently to activate the HIV LTR. Thus, we define several molecular pathways that trigger HIV reactivation from latency and provide evidence that latent HIV infection is maintained by the functional lack of particular transcription factors in quiescent cells.

Calretinin and calbindin D-28k delay the onset of cell death after excitotoxic stimulation in transfected P19 cells

In some neurological diseases, injury to neurones reflects an over-stimulation of their receptors for excitatory amino acids. This response may disturb the Ca(2+)-homeostasis and lead to a pronounced and sustained increase in the intracellular concentration of this ion. On the basis of data derived from correlative studies, calcium-binding proteins have been postulated to play a protective role in these pathologies. We tested, directly, the capacity of the three calcium-binding proteins calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) to buffer [Ca(2+)], and to protect cells against excitotoxic death. We used P19 murine embryonic carcinoma cells, which can be specifically induced (by retinoic acid) to transform into nerve-like ones. The differentiated cells express functional glutamate-receptors and are susceptible to excitotoxic shock. Undifferentiated P19-cells were stably transfected with the cDNA for CR, CB or PV, induced to differentiate, and then exposed to NMDA, a glutamate-receptor agonist. The survival rates of clones expressing CR, CB or PV were compared with those of untransfected P19-cells using the lactate-dehydrogenase assay. CR- and CB-expressing cells were protected from death during the first 2 h of exposure to NMDA. This protection was, however, transient, and did not suffice to rescue P19-cells after prolonged stimulation. Two of the three PV-transfected clones raised were vulnerable to NMDA-induced excitotoxicity; the third, which expressed the lowest level of PV, was protected to a similar degree as that found for the CR- and CB-transfected clones. Our results indicate that in the P19-cell model, CR and CB can help to delay the onset of cell death after excitotoxic stimulation.

Therapeutic targeting of human immunodeficiency virus type-1 latency: current clinical realities and future scientific possibilities

Factors affecting HIV-1 latency present formidable obstacles for therapeutic intervention. As these obstacles have become a clinical reality, even with the use of potent anti-retroviral regimens, the need for novel therapeutic strategies specifically targeting HIV-1 latency is evident. However, therapeutic targeting of HIV-1 latency requires an understanding of the mechanisms regulating viral quiescence and activation. These mechanisms have been partially delineated using chronically infected cell models and, clearly, HIV-1 activation from latency involves several key viral and cellular components. Among these distinctive therapeutic targets, cellular factors involved in HIV-1 transcription especially warrant further consideration for rational drug design. Exploring the scientific possibilities of new therapies targeting HIV-1 latency may hold new promise of eventual HIV-1 eradication.

Human immunodeficiency virus type 1 genome activation induced by human T-cell leukemia virus type 1 Tax protein is through cooperation of NF-kappaB and Tat

For productive replication of human immunodeficiency virus type 1 (HIV-1) in host cells, the viral genome-encoded transactivator Tat and several cellular transcription factors are required for efficient viral gene transcription. However, it remains unclear how the viral genome initiates transcription before Tat is transcribed or when Tat is at suboptimal levels. Here, we utilized the human T-cell leukemia type 1 Tax protein as a molecular tool to investigate the mechanism of viral gene transcription that initiates the early phase of infection of HIV-1. Tax alone does not significantly increase the activity of HIV-1 long terminal repeat (LTR) in T lymphocytes, but it markedly enhanced the replication of an infectious HIV-1 provirus with a truncated nef gene. This enhancement is preferentially mediated by the cooperation of Tax and Tat which is dependent on TAR and duplicated kappaB cis elements of the HIV-1 LTR as well as the NF-kappaB activation domain of Tax. Furthermore, phorbol myristate acetate and membrane-targeted HIV-1 Nef also enhanced the LTR activity in the presence of Tat in the TAR- and kappaB cis element-dependent manner. These data suggest that activated NF-kappaB can functionally interact with a suboptimal amount of Tat and the HIV-1 LTR for efficient initiation of viral gene transcription.

Achieving transcriptional specificity with NF-kappa B

Nuclear Factor-Kappa B (NF-kappa B) was first identified by Sen and Baltimore (1986, Cell 46, 705-716) as a constitutively active transcription factor binding the kappa light chain immunoglobulin enhancer in B cells. Shortly afterwards, the same researchers found NF-kappa B to be present in other cell types in an inactive cytoplasmic form which upon cellular stimulation could be induced to translocate to the nucleus and bind DNA. Subsequently, it has been demonstrated that NF-kappa B performs a critical role as a regulator of the immune system, the response to stress, apoptosis, viral replication and is involved in many diseases, leading to it becoming one of the most intensively studied transcription factors of the last decade. The pivotal role played by NF-kappa B is illustrated not only by the great diversity of genes that it regulates, but also by the large variety of stimuli leading to its activation. This article will address how NF-kappa B, a ubiquitously expressed transcription factor composed of dimers formed from five subunits, differentially regulates the expression of such a diverse array of genes with different functions, in different cell types and at different times. Recent research indicates that this behavioral diversity arises from a delicately balanced network of protein: protein interactions: NF-kappa B activity is determined not only through its regulated nuclear localization but is also dependent on the cellular context in which it is found.

The Tat protein of human immunodeficiency virus type 1 is a substrate and inhibitor of the interferon-induced, virally activated protein kinase, PKR

We demonstrate that the interferon-induced, double-stranded (ds) RNA-activated kinase, PKR, is able to bind to and phosphorylate the human immunodeficiency virus type 1 (HIV-1) trans-activating protein, Tat. Furthermore, Tat can inhibit the activation and activity of the kinase. Phosphorylation of Tat by PKR is dependent on the prior activation of PKR by dsRNA and occurs on serine and threonine residues adjacent to the basic region important for TAR RNA binding and Tat function. Activated PKR efficiently phosphorylates both the two-exon form of Tat (Tat-86) and the single exon form (Tat-72). Mutagenesis indicates that the interaction between PKR and Tat requires the RNA-binding region of Tat. Tat competes with eukaryotic initiation factor 2, a well-characterized substrate of PKR, for phosphorylation by activated PKR. Tat also inhibits the autophosphorylation of PKR by dsRNA. This biochemical evidence of an intimate relationship between Tat, an important regulator of HIV transcription, and PKR, a pleiotropic cellular regulator, may provide insights into HIV-1 pathogenesis and, more generally, virus/host interactions.

Heat shock induces HIV-1 replication in chronically infected promyelocyte cell line OM10.1

A long period of clinical latency before development of symptoms is characteristic of human immunodeficiency virus type 1 (HIV-1) infection. OM10.1, a promyelocyte cell line latently infected with HIV-1, has been developed as a model for studying the mechanism of viral latency and the activation of virus expression. We found that this latently infected cell line with heat shock at 42 degrees C for 2 h resulted in a high level of HIV-1 production without addition of any cytokines. The mechanism of activation was analyzed by using anti-TNF-alpha antibody and various inhibitors. Although the TNF-alpha level in culture supernatants was below the sensitivity of an ELISA assay system, addition of anti-TNF-alpha antibody in culture medium could partially suppress the heat shock induced HIV-1 production. Staurosporine (PKC inhibitor), pentoxifylline (NF-kappa B inhibitor), and Ro5-3335 (HIV-1 Tat inhibitor) also inhibited significantly the heat shock induced virus activation. In particular, staurosporine achieved approximately 90% inhibition of the HIV-1 antigen expression in heat shock-treated OM10.1 at a non-toxic concentration. Although the mechanism of HIV-1 activation with heat shock has not been fully elucidated yet, it is presumed PKC plays an important role in HIV-1 activation. Thus, the present observations will provide a further insight into the pathogenesis of HIV-1 infections.

HIV type 1 protease activation of NF-kappa B within T lymphoid cells

NF-kappa B is a nuclear protein of the rel oncogene family capable of enhancing transcription of several cellular genes, including IL-2 and the IL-2 receptor, and viral genes transcribed from the HIV-1 LTR. It has been reported that HIV-1 protease may cleave the NF-kappa B precursor to its active form in vitro. In this study the effects of HIV protease on NF-kappa B precursor activation were examined in Jurkat T cells by introducing a protease expression vector into the cells. Increased NF-kappa B activity was observed and this increased activity was blocked by a specific inhibitor of the viral protease. Viral transcription, as measured using LTR-CAT assays, was only slightly enhanced in the HIV-protease expressing cells, while secretion of IL-2 and expression of the IL-2 receptor were not affected. The limited activation of NF-kappa B by HIV protease appears unlikely to have a significant effect on virus expression or T cell function.

Stimulation of human immunodeficiency virus type 1 expression by ceramide

Ceramide, an intracellular lipid mediator of tumor necrosis factor alpha (TNF-alpha) action, was studied for its effects on the expression of the proviral human immunodeficiency virus type 1 genome in latently infected myelomonocytic cell lines U-1IIIB and OM-10.1. Ceramide treatment resulted in a 20- to 100-fold enhancement of HIV production in these cells. Ceramide also enhanced the expression of the chloramphenicol acetyltransferase gene directed by a human immunodeficiency virus type 1 long terminal repeat in transfected U-937 cells, indicating that ceramide acts at the level of viral transcription. These observations suggest that the TNF-ceramide signaling system may be involved in the regulation of HIV expression in certain myeloid cell types.

Cooperative inhibition of NF-kappa B and Tat-induced superactivation of human immunodeficiency virus type 1 long terminal repeat

Human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR)-regulated gene expression is stimulated independently by the cellular trans-activator NF-kappa B and the viral protein Tat. Noncytotoxic concentrations of the drug pentoxifylline (PTX) inhibited interaction of NF-kappa B with its motif and the stimulation of HIV-1 LTR-driven gene expression in Jurkat cells. Tat protein (from a cotransfected Tat-expression vector) also induced activation of HIV-1 LTR-driven gene expression. This activation was unaffected by PTX when NF-kappa B sites in the HIV-1 LTR were mutated, suggesting that this drug does not directly influence Tat function, which, however, was inhibited by the Tat-inhibitor Ro 24-7429. Transient reporter gene expression regulated by HIV-1 LTR with wild-type NF-kappa B motifs in the presence of Tat protein was 10- to 60-fold higher than in the presence of either of the trans-activators alone, demonstrating superactivation of HIV-1 LTR by the concerted action of both the trans-activators. Treatment of cells with either PTX or Ro 24-7429 inhibited this superactivation of the HIV-1 LTR. The inhibitory effect of these two drugs in combination, at concentrations that alone did not significantly influence viral promoter activity, was far more than additive. A cooperative action of PTX (NF-kappa B inhibitor) and Ro 24-7429 (Tat inhibitor) on HIV-1 LTR-regulated gene expression is suggested. Concentrations of the drugs that induced maximum inhibition of HIV-1 LTR through their cooperative action are far below cytotoxic levels. Thus, the combination of these two inhibitors could be very effective for anti-HIV therapy.

Identification of c-fos-responsive elements downstream of TAR in the long terminal repeat of human immunodeficiency virus type-1

Activation of HIV-1 requires the binding of host cell transcription factors to cis elements in the proviral long terminal repeat (LTR). This study identifies c-fos-responsive sequence motifs in the U5 transcribed noncoding leader sequences downstream of the viral transactivator responsive (TAR) element. These DNA sequence motifs are the most downstream regulatory elements described thus far in the HIV-1 LTR. Functional studies, using human colon epithelial cell lines, demonstrate that the downstream elements are transactivated by expression of the c-fos protooncogene and can transmit PMA and TNF alpha activation signals to the viral LTR. Moreover, the c-fos-responsive elements mediate HIV-1 LTR transcription independent of Tat and the NF kappa B-binding enhancer element. Nuclear extracts of colon epithelial cells form distinct gel mobility shift complexes with the c-fos-responsive elements. These complexes comigrate with a gel shift complex formed on a classical CRE oligonucleotide and are competed by CRE oligonucleotides. These data indicate that the HIV-1 LTR contains previously unrecognized functional DNA cis-regulatory elements downstream of TAR in the transcribed noncoding 5' leader sequence and suggest that early response genes such as c-fos play a role in the activation of HIV-1 gene expression.

Hexadecylphosphocholine differs from conventional cytostatic agents

Alkylphosphocholines, and especially their main representative hexadecylphosphocholine (HPC), show high anticancer activity in methylnitrosourea (MNU)-induced autochthonous rat mammary carcinoma. The regression of MNU-induced rat mammary carcinoma during HPC treatment can be evaluated by computed tomography and sonography. This allows a noninvasive monitoring of therapy in vivo (tumor size, morphology, and blood supply). Both diagnostic modalities can show a rapid concentric decrease in tumor volume as well as the appearance of cystic, scarry, and necrotic areas in the tumor tissue as a result of HPC treatment. In addition, prior to, during and after therapy tumor perfusion can be assessed by color Doppler sonography in vivo. A more than 4-fold difference in HPC efficacy was observed when the colony growth of explanted MNU-induced mammary carcinoma cells was measured in the methylcellulose colony assay (IC50 = 180 mumol HPC/l) and the Hamburger Salmon colony assay (IC50 = 740 mumol HPC/l). In the latter assay, growth of concomitantly seeded untransformed cells, especially of fibroblasts, is much lower than in the methyl-cellulose colony assay. We therefore assume that the antitumor efficacy of HPC against MNU-induced mammary carcinoma is enhanced by neighboring cells such as fibroblasts. Cell culture experiments with the three MNU-induced rat mammary carcinoma cell clones 1-C-2, 1-C-30, and 1-C-32 revealed IC50 values in the range of 50-70 mumol HPC/l. The volume of 1-C-2 cells increased up to 4-fold after 72 h of permanent exposure to 100 mumol HPC/l, a concentration that completely inhibited proliferation of tumor cell numbers without being cytotoxic. Nucleotide triphosphate levels dropped significantly after 24 h and were slowly restored in spite of continued exposure. After 72 h, they nearly reached those levels observed in plateau-phase cells. This suggests that HPC-induced growth inhibition has similarities with physiologically occurring growth arrest. Finally, replication of RNA viruses and DNA viruses was suppressed 30-fold and 7-fold, respectively, at low concentrations of HPC (12 mumol/l), which caused no or negligible growth inhibition in the virus-harboring cells, thus demonstrating specific antiviral activity of HPC. From these observations we conclude that HPC differs in many important aspects from conventional cytostatic agents and is certainly worth following-up in further investigations.

Glucose depletion enhances the anti-tumor effect of TNF

Treatment of human carcinoma xenotransplants in athymic mice with recombinant human tumor necrosis factor (rh TNF) causes necrosis mainly in the central parts of the tumors, while peripheral sections remain mitotically active. As tumors are known to be supplied with adequate glucose exclusively in their periphery, the influence of the lack of glucose on the cytotoxic activity of rh TNF was studied. The absence of glucose enhanced the killing of tumor cell lines by rh TNF in tissue culture. Meth-A, a cell line known to be resistant to TNF in vitro but highly sensitive to it in vivo, was readily killed in tissue-culture medium lacking glucose. All non-transformed cell lines tested were found to be resistant to rh TNF, regardless of the presence or absence of glucose. In tumor-bearing mice a reduction of the blood glucose content augmented by insulin led to increased anti-tumor efficiency of rh TNF. The enhanced anti-tumor activity was reflected both in histological sections of the tumor xenotransplants, by extensive central necroses, and by reduction of the tumor volumes.