C1300 Neuroblastoma Cells Research Articles

Amyloid β-Peptide-induced Inhibition of MTT Reduction in PC12h and C1300 Neuroblastoma Cells: Effect of Nitroprusside

Takenouchi T. and E. Munekata. Amyloid β-peptide induced inhibition of MTT reduction in PC12h and C1300 neuroblastoma cells: effect of nitroprusside. Peptides 19(2) 365–372, 1998.—We have investigated the effect of amyloid β-peptide (Aβ) in rat pheochromocytoma PC12h and murine C1300 neuroblastoma cells by using MTT {3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide} reduction assay. Exposure of the cells to Aβ peptides, Aβ1–40 and its fragment Aβ25–35, induced a concentration-dependent inhibition of MTT reduction in both cell lines, and MTT-dependent LDH release due to cell lysis in PC12h cells. We also found that sodium nitroprusside (SNP), a spontaneous nitric oxide (NO) generator, significantly prevented the inhibition of MTT reduction and MTT-dependent LDH release caused by Aβ peptides at 10–100 μM, although a high concentration of SNP (≥333 μM) was remarkably toxic by itself. Since the inhibition of MTT reduction caused by Aβ is known as one of the first indicators of its toxicity, these findings suggest that Aβ peptides have a toxic effect in these cell lines, and SNP may attenuate the Aβ peptide-induced toxicity. In regard the mechanisms of the actions of SNP, hydroxylamine which also generates NO and 8-Br-cGMP, a membrane-permeable analogue of cyclic GMP (cGMP), failed to prevent the inhibition of MTT reduction caused by Aβ25–35 in PC12h cells, implying that the effect of SNP may be mediated by the NO-independent pathway. Since potassium ferrocyanide showed a significant prevention at 333 μM although it had toxic effect at this concentration, it is considered that the ferrocyanide portion of the SNP metabolite may be partially involved. The cell death induced by other oxidative insults, such as glutamate and hydrogen peroxide (H 2O 2), could not be attenuated by SNP in both cell lines. Thus, the observed effect of SNP might not be due to its direct antioxidative action.

Activin A andAll-Trans-Retinoic Acid Cooperatively Enhanced the Functional Activity of L-type Ca2+Channels in the Neuroblastoma C1300 Cell Line

Activin, a member of the transforming growth factor-β superfamily, regulates various physiological functions. In the present study, we investigated the effect of activin on neuronal differentiation, particularly the functional activity of voltage-dependent Ca2+channels, in murine neuroblastoma C1300 cells. A slight K+-induced increase in the intracellular free Ca2+([Ca2+]i) was observed in C1300 cells untreated and treated with either activin A orall-trans-retinoic acid, while treatment with both agents significantly enhanced the increase. The [Ca2+]iincreases potentiated by activin A andall-trans-retinoic acid were nearly abolished in the presence of 1.0 mM nickel or in the absence of extracellular Ca2+. Nifedipine (0.1 μM) and ω-conotoxin (1.0 μM), inhibitors of L- and N-type Ca2+channels, respectively, partially inhibited these responses, however the inhibitory effects of these compounds were not additive. In addition, Bay K 8644, an activator of L-type Ca2+channels, enhanced the K+-induced [Ca2+]iincrease. These findings indicated that depolarization evoked the Ca2+influx, at least in part, through L-type Ca2+channels in C1300 cells treated with both activin A andall-trans-retinoic acid.

Mature sensory neuron-derived hybrid cell line expressing NGF-dependent neurite extension

We established a hybrid cell line which extended neurites in the presence of nerve growth factor by fusion between adult mouse sensory neurons and neuroblastoma C1300 cells using emetine and actinomycin D. The serine-phosphorylated 200 and 160 kDa neurofilament proteins were detected in the hybrid cells. In comparison, C1300 cells expressed both subunit of non-phosphorylated neurofilaments at serine residues.

Method for production of neuronal hybridoma using emetine and actinomycin D

Neuronal hybrid cells established by somatic cell fusion are useful for studies of neuronal properties at the molecular level (Hammond, D.N., Lee, H.J., Tonsgard, J.H. and Wainer, B.H., Development and characterization of clonal cell lines derived from septal cholinergic neurons, Brain Res., 512 (1990) 190–200 [3]; Wainwright, M.S., Perry, B.D., Won, L.A., O'Malley, K.L., Wang, W.Y., Ehrlich, M.E. and Heller, A., Immortalized murine strial neuronal cell lines expressing dopamine receptors and cholinergic properties, J. Neurosci., 15 (1995) 676–688 [11]). The somatic cell fusion method requires a fusion partner which is unable to survive in the selection medium if it does not fuse with primary cells to isolate the hybrid cells. Hypoxanthine guanine phosphoribosyltransferase (HPRT)-deficient partner cells and hypoxanthine, aminopterin and thymidine (HAT) selection medium are commonly used for this procedure (Harlow, E. and Lane, D. (Eds.), Antibodies: a Laboratory Manual, Cold Spring Harbor Laboratory Publications, New York, 1988, pp. 139–243 [4]). The present method requires neither HPRT-deficient cells nor HAT medium. Primary neurons are fused with the C1300 neuroblastoma cells pretreated with emetine (Grollman, A.P., Inhibitors of protein biosynthesis, J. Biol. Chem., 243 (1968) 4089–4094 [1]), an inhibitor of ribosomes and actinomycin D (Perry, R.P., Selective effects of actinomycin D on the intracellular distribution of RNA synthesis in tissue culture cells, Exp. Cell Res., 29 (1963) 400–406 [8]), an inhibitor of ribosomal RNA (rRNA) synthesis, before fusion. By this treatment, we are able to isolate hybrid cells after fusion because non-fused C1300 cells die due to the loss of active ribosomes and protein synthesis, whereas C1300 cells fusing with primary cells survive due to the supply of intact ribosomes and rRNA from primary cells. This method produces neuronal hybrids at high efficiency.

Comparative analyses of the latency-associated transcript promoters from herpes simplex virus type 1 strains H129, +GC and KOS-63

We have analyzed the activity of a specific portion of the latency-associated transcript (LAT) promoter of three strains of herpes simplex virus type 1 (HSV-1) in neuronal and non-neuronal cell types. Restriction fragments containing the LAT promoter sequences and the 5′-end of the LATs were isolated from HSV-1 strains H129, +GC and KOS-63, sequenced and cloned into a chloramphenicol transferase (CAT) plasmid vector. These vectors were separately assayed for CAT production in human (SknSH) and mouse (C-1300) neuroblastoma cell lines and a human continuous cell line (HeLa). Strain KOS-63 contained a C to T base substitution within the LAT promoter binding factor element upstream of the cAMP response element binding sequence. In replicate experiments, in which the construct DNA was used for transfection, the CAT constructs from strains H129 and +GC functioned equally well in all three cell lines. In contrast, the strain KOS-63 CAT construct functioned significantly better in HeLa cells than in neuroblastoma cell lines and better than the identical CAT constructs from strains H129 and +GC. In addition, the construct from strain KOS-63 functioned less well in the human neuroblastoma cell line than in HeLa or C-1300 neuroblastoma cells. When LAT expression was examined directly in vivo by in situ hybridization, strain KOS-63 produced slightly less LAT RNA than strain H129 within trigeminal ganglionic neurons of latently infected rabbits. However, utilizing competitive gel-shift assays, DNA fragments containing the LAT promoter binding element from all three strains bound equivalent amounts of HeLa cell nuclear proteins. Together, these results suggest that the activity expressed by the strain KOS-63 LAT promoter in vivo and in vitro may relate to positive or negative effects of DNA binding proteins on LAT transcription, and that these effects are cell-type dependent.

The effects of measles virus persistent infection on AP-1 transcription factor binding in neuroblastoma cells

Measles virus (MV) persistence in brain cells has broad effects on different cellular functions. We have previously shown that NS20Y clone, originally derived from C1300 neuroblastoma cells, persistently infected with MV (NS20Y/MS), displays constitutively elevated levels of c- fos and PKC mRNAs, implying MV-mediated effects on transcriptional regulation. Nonetheless, the mode by which virus affects the transcriptional machinery still remains obscure. In order to define this phenomenon, we studied the binding properties of major transcription factors (AP-1 and NFκB) in NS20Y/MS cells. Using electrophoretic mobility shift approach (EMSA) with the appropriate oligonucleotide probes, we have found that the persistent MV infection does not affect NFκB binding, while the AP-1 binding was significantly decreased. Similar inhibition was not observed in NS20Y cells acutely infected with MV. Anti-measles antibody-mediated restriction of viral gene expression restored AP-1 binding, thus suggesting that measles virus proteins may affect the components of the host transcriptional machinery.

Organ-specific adhesion of neuroblastoma cells in vitro: Correlation with their hepatic metastasis potential

Neuroblastoma (NB) is the most common solid malignant tumor found in pediatric patients and the liver is one of the major sites of metastasis. To investigate the organ specificity of metastatic distribution, the adherence behavior of tumor cells was studied. The data presented are based on studies using a metastatic murine cell line C1300. In vivo, not only intrasplenic but also intravascular injection of C1300 NB cells consistently results in hepatic metastasis formation in syngeneic A J mice. An in vitro assay was used in which C1300 NB cell attachment to cryostat sections of liver, spleen, brain, kidney and lung obtained from normal A J mice was measured to compare organ-specific adhesion. A good correlation was found between their metastatic potential in the liver and the adhesion to the liver sections; C1300 NB cells adhered preferentially to liver cryostat sections. Enzyme assays indicated that cell surface glycoproteins were involved in cell adhesion. An adhesion assay with extracellular matrix proteins demonstrated that C1300 NB cells adhered preferentially to vitronectin and fibronectin, and the adherence was strongly inhibited by Arg-Gly-Asp (RGD)-containing peptides. Furthermore, adhesion of C1300 NB cells to liver cryostat sections could be blocked by the synthetic peptide GRGDS. This indicates that the interaction between RGD-containing matrix adhesion protein and cells has an important role for the specific adhesion of C1300 NB cells. The results suggested that tumor cell adhesion to liver cryostat sections could provide a useful tool in the study of host-tumor interactions in the metastasis of NB.

Improved method for producing neuronal hybrids using emetine and actinomycin D

We modified the method of somatic cell fusion for neurons to improve the efficiency of hybrid production. C1300 neuroblastoma cells were incubated with emetine and actinomycin D before fusion. After fusion between C1300 cells and adult mouse dorsal root ganglia neurons with polyethyleneglycol, we were able to select the hybrids from non-fused cells. We obtained hybrid clones at high efficiency (7.2 clones/ 10 4 neurons)

Improved method for producing neuronal hybrids using emetine and actinomycin D

We modified the method of somatic cell fusion for neurons to improve the efficiency of hybrid production. C1300 neuroblastoma cells were incubated with emetine and actinomycin D before fusion. After fusion between C1300 cells and adult mouse dorsal root ganglia neurons with polyethyleneglycol, we were able to select the hybrids from non-fused cells. We obtained hybrid clones at high efficiency (7.2 clones/ 104 neurons)

Further Identification of Neurokinin Receptor Types and Mechanisms of Calcium Signaling Evoked by Neurokinins in the Murine Neuroblastoma C1300 Cell Line

It has been suggested that murine neuroblastoma C1300 cells express endogenous neurokinin NK2 receptors with features that differ from those of NK2 receptors characterized in other systems. In this study, we have further characterized the neurokinin receptor types present in this cell line. RNA blots showed that mRNAs of NK2 and NK3 receptors, but not of NK1 receptors, were expressed in C1300 cells. The increase in the cytosolic calcium concentration ([Ca2+]i) induced by 0.33 microM neurokinin A was completely inhibited by SR 48968, an NK2 receptor antagonist, whereas the partial response to 0.33 microM neurokinin B was unaffected, and the response was completely inhibited by SR 142801, and NK3 receptor antagonist. In addition, the [Ca2+]i increase by 0.33 microM senktide, an NK3 receptor agonist, was inhibited by SR 142801 but not by SR 48968. These findings indicated that C1300 cells endogenously express functional NK2 and NK3 receptors. It was also demonstrated that NK2 and NK3 receptors can be activated independently by 3.3 microM neurokinin A in the presence of 1.0 microM SR 142801 or 1.0 microM senktide, respectively. Therefore, the mechanisms of Ca2+ signaling mediated by endogenous NK2 and NK3 receptors were investigated. The independent activation of NK2 or NK3 receptors induced not only the [Ca2+]i increase, but also stimulated the formation of inositol trisphosphates; both these responses were inhibited by U73122, a phospholipase C (PLC) inhibitor. In addition, NK2 and NK3 receptor-mediated [Ca2+]i increase was partially attenuated in the absence of extracellular Ca2+ or in the presence of nickel, an inorganic Ca2+ influx blocker, but was unaffected by nifedipine and omega-conotoxin, L- and N-type voltage-dependent Ca2+ channel blockers, respectively. Furthermore, the depolarization by 60 mM K+ did not affect the [Ca2+]i. These findings suggested that the NK2 and NK3 receptor-mediated [Ca2+]i increase was due to the activation of PLC and was dependent on the mobilization of internal Ca2+ and the entry of extracellular Ca2+ through voltage-independent channels. This study showed that the C1300 cell line is a useful system with which to investigate pharmacological functions and signaling pathways of endogenous NK2 and NK3 receptors.

Volume-activated chloride channels in neuroblastoma cells are blocked by the antiestrogen toremifene.

The presence of volume-activated chloride channels has been examined in neuroblastoma C1300 cells using the whole-cell configuration of the patch-clamp technique. Chloride channels could not be detected under isotonic conditions. However, hypotonic challenge induced slowly developed inward and outward anionic currents that exhibited outward rectification and inactivation at the most depolarizing potentials, features that were similar to the currents described in other cell preparations where volume-activated Cl- channels have been associated with the expression of P-glycoprotein. This hypotonicity-activated Cl- currents could be reversibly blocked by extracellular exposure to toremifene, a novel synthetic antioestrogen. The fact that toremifene and its analog tamoxifen, have been shown to block P-glycoprotein-associated chloride channels and to reverse P-glycoprotein associated multidrug resistance in a number of cell lines suggest that P-glycoprotein could be involved in the generation of hypotonic-induced chloride conductance in neuroblastoma cells.

In vivo deletion analysis of the herpes simplex virus type 1 latency-associated transcript promoter.

During herpes simplex virus latency, transcripts accumulate from a single transcription unit of the viral genome. The promoter for these latency-associated transcripts (LAT) has been located, and a number of studies have documented the specific regions of this promoter which are important in transient assays of neuronal cells in culture. To examine the regulation of this promoter from the viral genome, both in vitro and in vivo, a series of seven promoter deletion viruses which drive the expression of the reporter gene beta-galactosidase was constructed. Rabbit skin cells were infected in cell culture with viruses bearing each promoter mutation, and the LAT promoter activity was compared with that obtained by infecting two neuronal cell lines, ND7 cells and C1300 neuroblastoma cells. Mouse dorsal root ganglia were also infected with these recombinant viruses by footpad inoculations, and beta-galactosidase activity was measured. Infected neuronal cells lines and dorsal root ganglia exhibit much more LAT promoter activity than infected rabbit skin cells, suggesting that the region upstream of -250 may contain one or several neuronal specific DNA-binding sites. However, a comparison of LAT promoter activities within the deletion series revealed many differences between neurons of the dorsal root ganglia infected in vivo and the two neuronal cell lines infected in vitro. These results suggest that neurons may vary extensively in the quantity or kind of transcription factors they contain.

Use of C1300 Neuroblastoma Cells to Evaluate the Protective Value of Hexamethonium, Trimethaphan, Hemicholinium, and Triethylcholine against Diisopropyl Phosphorofluoridate Toxicity

Our intent was to evaluate the C1300 neuroblastoma cell as anin vitrosystem for studying the mode of action and efficacy of drugs used to treat or prevent organophosphate intoxication. The anticholinergic drugs hexamethonium, trimethaphan, and hemocholinium and the triethylcholine and cholinesterase/reactivator 2‐pyridine aldoxime methochloride (2‐PAM) have been shown to be effective in preventing intoxication by diisopropyl phosphorofluoridate (also known as diisopropyl fluorophosphate, DFP)in vivo.We determined their efficacy in preventing cell death (as measured by trypan blue exclusion) of neuroblastoma cells alone or in combination. We also determined their efficacy in reversing the cytotoxic effects of DFP on cell DNA synthesis (as measured by [3H]‐thymidine incorporation), cell RNA synthesis (as measured by [3H]uridine incorporation), and on cell protein synthesis (as measured by [3H]leucine incorporation). The maximal nontoxic doses of the drugsin vitrowere determined. All anticholinergic agents studied reduced the cytotoxicity of DFP using one or more parameters. 2‐PAM, the cholinesterase reactivator, enhanced the cytotoxicity of DFP on cultured cells at a high concentration (1 mg/mL) and reduced it at a lower concentration (0.3 mg/mL). All four anticholinergic agents were capable of enhancing the uptake of [3H]thymidine. Only hexamethonium and hemicholinium reversed DFP inhibition of DNA synthesis. RNA synthesis was not affected by any anticholinergic agent and no agent reversed DFP inhibition of RNA synthesis. Protein synthesis was enhanced by every anticholinergic agent except hemicholinium; the inhibition of protein synthesis by DFP was reversed by trimethaphan and triethylcholine. The results indicated that the prophylactory effects of anticholinergics against organophosphate intoxication, observedin vivo, can be observed using anin vitrocell culture system. Our data suggest thatin vitrosystems can be used to evaluate the efficacy and toxicity of drugs used to protect against organophosphate intoxication.

Pharmacological evidence for neurokinin receptors in murine neuroblastoma C1300 cells

We found that neurokinin A (NKA) and neurokinin B (NKB) induce an increase in the concentration of intracellular free Ca 2+ ([Ca 2+] i) in murine neuroblastoma C1300 cells (EC 50: NKA 87 ± 13 n M, NKB 97 ± 15 n M). Substance P (SP) also caused a transient Ca 2+ increase, although the potency of SP was much less than that of NKA and NKB. The increase in [Ca 2+] i induced by NKA and NKB was inhibited by SR 48,968, a selective antagonist for NK 2, and [βAla 8]NKA(4–10), a selective agonist for NK 2, did not stimulate the increase in [Ca 2+] i. NKA- and NKB-induced Ca 2+ mobilization was not inhibited by CP-96,345 and [Trp 7,βAla 8]NKA(4–10), selective antagonists for NK 1 and NK 3, respectively. These results suggested that C1300 cells express endogenous NK 2 neurokinin receptors that have different features from known NK 2 receptors.

A murine model for bone marrow metastasis established by an i.v. injection of C-1300 neuroblastoma in A/J mice.

A reproducible tumor model for bone marrow metastasis has been developed by an injection of murine C-1300 neuroblastoma (C-1300 NB) cells into the tail vein of syngeneic A/J mice. The animals died with liver metastases at 18-21 days after an injection of 10(5) tumor cells and often had bone marrow metastasis in the femur. N-methylformamide (NMF), a maturational agent, was administered to inhibit liver metastases and to extend survival in mice with advancing bone metastasis. Histological examination of bone marrow metastasis, demonstrated lesions varying from a few small colonies of C-1300 NB cells either in metaphysis or diaphysis to large foci replacing normal hematopoietic bone marrow, simultaneously invading epiphysis or cortex of bone as bone metastasis. This assay demonstrated the ability to detect neuroblastoma cells in the bone marrow histologically and could determine bone marrow TD50 by extraction of bone marrow cells after treatment with various doses of drug. Fifty per cent of mice injected with cyclophosphamide (CY) developed bone marrow metastasis without liver metastasis. Treatment with tamoxifen, an anti-calmodulin drug, suppressed tumor takes in the recipient mice with tamoxifen-dose-dependent fashion. This experimental system allows for investigations into the therapeutic response and biology of neuroblastoma metastases in the bone marrow.

Immune-mediated regression of ‘metastatic’ neuroblastoma in the liver

It is understood that neuroblastoma (NB) in the liver of patients with clinical stage IV-S disease may disappear, but the mechanism of such regression is unclear. A genetic hypothesis has previously been suggested, although heretofore an immunologic explanation had not been reported. Using C1300 NB in AJ mice, we developed a model of liver metastatic disease by directly injecting tumor cells into a subcutaneously translocated spleen. Intrasplenic inoculation of 2 × 10 6 C1300 NB cells produced liver subcapsular foci of NB in 100% of animals, whose mean survival period was 18 days. Three days after tumor inoculation, interleukin-2 (IL-2) (2,400 U/d) was continuously infused for 14 days via a miniosmotic pump, and daily survival was followed. Animals were sampled serially by histological and immunohistochemical staining. Animal survival was significantly prolonged ( P < .05) in the IL-2 group when compared with that of saline controls, but importantly, 50% of the mice were cured. Histological examination showed early infiltration of mononuclear cells, predominantly lymphocytes, around liver metastaic foci; and phenotypic analysis of these cells showed them to be Thy-1.2-positive and asialo GM1-positive, suggesting they are of natural killer (NK) and lymphokine-activated killer (LAK) origin. Most importantly, in cured animals the histological analysis of the liver demonstrated reversion to a scar-free anatomy, akin to that seen in stage IV-S NB survival. These data suggest that immune-mediated regression of NB in the liver is possible; whether the result of therapy or spontaneous, the liver histology reverts to normal. Furthermore, regional immunotherapy using IL-2 delivered via the splenoportal axis may be an efficacious therapy for NB in the liver.

Reversal of C1300 Murine Neuroblastoma Multidrug Resistance by CremophorEL, A Solvent for Cyclosporin A

We previously developed a homoharringtonine resistant C-1300 neuroblastoma cell line with cross-resistance to adriamycin and increased levels of p-glycoprotein, and showed that drug resistance could be reversed in this cell line by cyclosporin A. The present study shows that cremophor EL, a parenteral vehicle for cyclosporin A, can also completely reverse this multidrug resistance in a clonogenic assay system. Cremophor EL incubated with resistant cells for up to six days did not reduce levels of p-glycoprotein. Intracellular homoharringtonine analysis using HPLC revealed increased drug accumulation in resistant cells treated with cremophor EL. The increased drug level was not due to blocking of drug efflux commonly seen in other multidrug resistant models. The data suggest that resistance modulation with cyclosporin A should be interpreted with caution when cremophor EL is a solvent. Our work suggests cremophor EL, a relatively nontoxic lipophylic solvent, may have a direct effect on membrane permeability, although other mechanisms cannot be ruled out.

C1300 neuroblastoma cells possess quisqualate sensitive glutamate binding sites.

C1300 neuroblastoma cells possess quisqualate sensitive glutamate binding sites.

Enhancement of interleukin-2 immunotherapy with L-arginine.

Nutrient substrates have been shown to enhance cell-mediated immunity, but their role as adjuvants to immunotherapy has not been previously determined. This study evaluated L-arginine as an essential substrate for optimal generation of lymphokine-activated killer (LAK) cells. This experiment also assessed supplemental dietary L-arginine as a means to potentiate the host antitumor response to interleukin-2 (IL-2) in a murine neuroblastoma (NRB) model. A/J mice received 1% arginine or isonitrogenous 1.7% glycine in addition to a regular diet 14 days before subcutaneous inoculation with C1300 NRB cells. Twenty-four hours later, animals received low (1 x 10(6) U/kg three times a day) or high (3 x 10(6) U/kg three times a day) doses of IL-2 or saline intraperitoneally for 4 days. On days 4 and 10 post-C1300 NRB inoculation, mice were killed for assessment of natural killer cell and tumor specific cytotoxicity. Remaining animals were followed for tumor incidence, tumor growth, and duration of host survival. Interleukin-2 therapy in mice receiving dietary arginine compared with those receiving glycine resulted in significantly augmented natural killer cell cytotoxicity (day 4) and generation of specific tumoricidal mechanisms (day 10). The addition of dietary arginine to low-dose IL-2 therapy significantly diminished C1300 NRB engraftment (p less than 0.05) and growth (p less than 0.001) and prolonged the duration of host survival (p less than 0.05) compared with the glycine treatment group. In vitro studies demonstrated that L-arginine is an essential substrate for optimal generation of LAK cells. Thus, supplemental dietary L-arginine enhances lymphocyte cytotoxic mechanisms and potentiates IL-2 immunotherapy.

Influence of primary tumor site on host anti-tumor immunity.

Stage IV-S neuroblastoma, characterized by a primary tumor plus disseminated tumors in liver, skin and bone marrow, has a favorable clinical prognosis when compared to metastatic Stage IV neuroblastoma. This favorable outcome also characterized mice receiving tumor transplants to these "IV-S" sites. We report the testing of the hypothesis that enhanced anti-tumor immunity in "IV-S" site neuroblastoma recipients explains this improved survival. A million murine C1300 neuroblastoma cells were inoculated into 256 A/J mice to either "IV-S" sites of skin, liver, peritoneal cavity, or to the disseminated stage "IV" sites of subcutaneous tissue, muscle, kidney and lung. After 21 and 28 days of tumor growth, spleen cells from tumor bearing mice were harvested and analyzed by a 51 Cr release lymphocytotoxicity assay. Cytotoxic T cell activity was consistently higher at day 28 than day 21. In the liver and in the peritoneal cavity, cytotoxic T cell activity was higher than in other organs, and at day 28 these values were significantly higher than Stage "IV" sites. On the other hand, skin is not a immunologically privileged site in vivo study.