Elevated expression of DNA polymerase kappa in human lung cancer is associated with p53 inactivation: Negative regulation of POLK promoter activity by p53.

DNA polymerase kappa (POLkappa) is a low fidelity translesional DNA polymerase implicated in spontaneous and DNA damage-induced mutagenesis. We have previously shown that POLkappa was frequently overexpressed in human lung cancer tissues as compared with their matched non-tumorous tissue counterpart. In the present study, we found a close correlation between elevated POLkappa expression and p53 inactivation in lung cancer tissues. To investigate whether POLK expression might be regulated by p53, we have determined the transcriptional initiation site of POLK gene and examined its promoter activity in A549, H358-129, and PC-3 human lung cancer cell lines. Wild-type p53, but not a mutant p53 (R273H) devoid of the DNA-binding activity, strongly inhibited POLK promoter activity in these cells. In addition, POLK promoter exhibited a significantly higher activity in p53-/- murine embryo fibroblasts (MEF) than in p53+/- and p53+/+ MEF. These results link p53 status with POLkappa expression and suggest that loss of p53 function may in part contribute to the observed POLkappa upregulation in human lung cancers.

Midkine promoter can mediate transcriptional activation of a fused suicide gene in a broader range of human breast cancer compared with c-erbB-2 promoter.

We examined the expression level of the midkine (MK) and c-erbB-2 genes in both tumorous and matched nontumorous specimens from 18 patients with breast cancer. Expression of the MK and c-erbB-2 genes in nontumorous regions was relatively low, and the expression levels of both genes were not markedly different among the nontumorous samples. In contrast, the expression of the MK and c-erbB-2 genes in tumorous specimens was upregulated in 18 and 6 specimens, respectively. Regulatory regions of the MK gene were able to activate a reporter gene to a similar degree as those of the c-erbB-2 gene in the human breast cancer cell lines tested. Transfection of breast cancer cells with either the MK promoter- or the c-erbB-2 promoter-linked herpes simplex virus thymidine kinase gene increased their sensitivity to the prodrug ganciclovir. These data showed that the MK promoter activated a therapeutic gene in a wider range of human breast cancer than the c-erbB-2 promoter and suggest that MK promoter-mediated gene therapy is potentially more favorable in clinical settings.

DNA polymerase theta is preferentially expressed in lymphoid tissues and upregulated in human cancers.

DNA polymerase theta (Pol theta) is a recently identified family A polymerase that contains an intrinsic helicase domain. Drosophila Pol theta mutants are hypersensitive to bifunctional DNA crosslinking agents and exhibit an elevated frequency of spontaneous chromosomal aberrations, suggesting a role for Pol theta in repair of DNA interstrand crosslinks and in the general maintenance of genome stability. To investigate a possible involvement of Pol theta in tumorigenesis, we have examined its expression in various normal and malignant tissues. Paired tumor and adjacent nontumorous tissues from patients with lung (n = 27), stomach (n = 28) and colon (n = 26) cancer, as well as 26 normal human tissues, were examined for Pol theta expression by RT-PCR, Northern or Western blot analysis. Pol theta was predominantly expressed in primary lymphoid organs including the fetal liver, thymus and bone marrow where lymphocyte progenitors undergo V(D)J rearrangements of their antigen receptor genes. In addition, Pol theta expression was upregulated in germinal center B cells, in which class switch recombination of the immunoglobulin genes occurs. Examination of Pol theta expression in matched cancer specimens revealed that Pol theta was barely detectable in the nontumorous tissues but was upregulated in 17 of 27 (63%) lung, 11 of 28 (39%) stomach and 20 of 26 (77%) colon cancers. Moreover, patients with high levels of Pol theta expression had a significantly poorer clinical outcome compared with those expressing low levels of Pol theta. These results implicate that Pol theta may have a specialized function in lymphocytes and that its overexpression may contribute to tumor progression.

Transduction of the IL-21 and IL-23 genes in human pancreatic carcinoma cells produces natural killer cell-dependent and -independent antitumor effects.

We examined whether novel cytokines, interleukin (IL)-21 and IL-23, that were expressed in tumors could produce antitumor effects in the inoculated mice. Human pancreatic cancer AsPC-1 cells were retrovirally transduced with murine IL-21 or IL-23 (p19-linked p40) gene (AsPC-1/IL-21, AsPC-1/IL-23) and were injected into nude or severe combined immunodeficiency (SCID) mice. Although the proliferation in vitro of the transduced cells remained the same as that of parent cells, growth of AsPC-1/IL-21 and AsPC-1/IL-23 tumors developed in nude mice was retarded compared with that of parent tumors. Treatment of nude mice with anti-asialo GM(1) antibody temporally abrogated the growth retardation of AsPC-1/IL-21, but not AsPC-1/IL-23 tumors; however, the growth of AsPC-1/IL-21 tumors came to be retarded thereafter with the regeneration of natural killer (NK) cells. The growth of AsPC-1/IL-21 tumors developed in SCID mice was also retarded compared with parent tumors and the growth retardation was abrogated by treatment with anti-asialo GM(1) antibody. The growth of AsPC-1/IL-23 tumors in SCID mice was not different from that of parent tumors. Cytotoxic activity and secretion of interferon-gamma in response to AsPC-1 cells were induced in spleen cells of the mice bearing AsPC-1/IL-21 or AsPC-1/IL-23 tumors. When nude mice were injected with a mixed population of AsPC-1/IL-21 and AsPC-1/IL-23 cells, no synergistic effects were observed. These data collectively suggest that expression of IL-21 and IL-23 in tumors can produce NK cell-dependent and -independent antitumor effects in an alpha beta T cell-defective condition, respectively.

Expression profiling and characterization of 4200 genes cloned from primary neuroblastomas: identification of 305 genes differentially expressed between favorable and unfavorable subsets.

Neuroblastoma (NBL), one of the most common childhood solid tumors, has a distinct nature in different prognostic subgroups: NBL in patients under 1 year of age usually regresses spontaneously, whereas that in patients over 1 year of age often grows aggressively and eventually kills the patient. To understand the molecular mechanism of biology and tumorigenesis of NBL, we decided to perform a comprehensive approach to unveil the gene expression profiles among the NBL subsets. We constructed the subset-specific oligo-capping cDNA libraries from the primary NBL tissues with favorable (F: stage 1, high expression of TrkA and a single copy of MYCN) and unfavorable (UF: stage 3 or 4, decreased expression of TrkA and MYCN amplification) characteristics and randomly cloned 4654 cDNAs. Among 4243 cDNAs sequenced successfully, 1799 (42.4%) were the genes with unknown function. Excluding the housekeeping genes, an expression profile of each subset was extremely different. To determine the genes expressed differentially between F and UF subsets, we performed semiquantitative reverse transcriptase (RT)-PCR for each of the 1842 independent genes using RNA obtained from 16 F and 16 UF NBLs as template. This revealed that 278 genes were highly expressed in the F subset as compared to the UF one, while, surprisingly, only 27 genes were expressed at higher levels in the UF rather than the F subset. These differentially expressed genes included 194 genes with unknown function. Many of the genes expressed at high levels in the F subset were related to catecholamine biosynthesis, small GTPases, synapse formation, synaptic vesicle transport, and transcription factors regulating differentiation of the neural crest-derived cells. On the other hand, the genes expressed at high levels in the UF subset included transcription factors and/or receptors that might regulate neuronal growth and differentiation. The chromosomal mapping of those genes showed some clusters. Thus, our mass-identification and characterization of the differentially expressed genes between the subsets may become a powerful tool for finding the important genes of NBL as well as developing new diagnostic and therapeutic strategies against aggressive NBL.

Cell growth- and P53-dependent transcriptional activity of the midkine promoter confers suicide gene expression in tumor cells.

Midkine (MK) is preferentially expressed in a number of human tumors, while the expression in adult normal tissues is restricted. Previous studies showed that a 2.3-kb regulatory region of the human MK gene could selectively activate a linked suicide gene in tumors. In this study, we explored the minimal promoter region using genomic fragments deleted from the 5'-upstream side and analyzed the mechanism of the preferential activation in tumor cells. Luciferase assays showed that the 0.3-kb fragment from the transcription start site contained a cis-acting element(s) for the promoter activity. Expression of the herpes simplex virus-thymidine kinase gene under the control of the MK promoter followed by ganciclovir administration produced antitumor effects in vivo. Transfection of the wild-type p53 gene into the immortalized fibroblasts bearing mutated p53 and tumor cell lines, which induced cell cycle arrest, decreased the MK promoter-mediated transcription more effectively than the SV40 or the cytomegalovirus promoter-mediated transcription. The P53-mediated downregulation of the MK promoter activity was stronger in p53-defective tumors than in wild-type p53-bearing tumors. Moreover, the MK promoter-mediated luciferase activity was greater in p53-deficient mouse embryonic fibroblasts than in those bearing wild-type p53 gene. The transcriptional activity of the MK promoter could be regulated by cell growth and in part P53-dependent pathways.

Accumulation of p27 KIP1 is associated with BMP2-induced growth arrest and neuronal differentiation of human neuroblastoma-derived cell lines.

Bone morphogenetic proteins (BMPs) play an essential role in cell fate determination. In this study, we found that BMP2 treatment resulted in growth arrest and differentiation in human neuroblastoma-derived cell lines, SH-SY5Y and RTBM1. Within 30min of BMP2 exposure, phosphorylation of Smad1/5 was observed in these cell lines. In RTBM1 cells, BMP2-induced differentiation was accompanied by a significant decrease in the expression level of DAN, an antagonist of BMP in frog embryos. Immunoblot analysis revealed that BMP2 treatment caused a down-regulation of p53 family members and hence of cyclin-dependent kinase inhibitor p21(WAF1). We found a significant accumulation of p27(KIP1) in response to BMP2, whereas the expression level of Skp2, which is required for ubiquitin-dependent p27(KIP1) degradation, was decreased during this differentiation process. Our results suggest that p27(KIP1) contributes to the BMP-induced growth arrest and neuronal differentiation of neuroblastoma, and BMP treatment might provide a new therapeutic strategy.

Glioma-specific cytotoxic T cells can be effectively induced by subcutaneous vaccination of irradiated wild-type tumor cells without artificial cytokine production.

Effective induction of systemic antitumor immunity is a crucial step for success of immune gene therapy for intracerebral gliomas. We examined in this study the ability to induce glioma-specific cytotoxic T lymphocytes (CTL) by subcutaneous (s.c.) immunization of irradiated whole-tumor cell vaccine with or without artificial cytokine production, and also examined in vivo efficacy of the induced CTL against a rat brain tumor model with 9L gliosarcoma cells. Murine neuroblastoma C1300 cells transduced with the interleukin-2 (IL-2), IL-4 or granulocyte-macrophage colony-stimulating factor (GM-CSF) gene (C1300/IL-2, C1300/IL-4 or C1300/GM-CSF) were used as cytokine-producers. Glioma-specific CTL activity was equivalently induced in the rats vaccinated s.c. with irradiated 9L, irradiated IL-2-producing 9L cells or the mixed population of irradiated 9L and C1300/IL-2 cells, while the activity was relatively lower in the rats vaccinated with irradiated 9L cells mixed with either C1300/IL-4 or C1300/GM-CSF cells. In the rats immunized s.c. with irradiated 9L cells, intracerebral (i.c.) 9L tumors implanted together with either C1300/IL-2 or C1300/IL-4 were completely rejected. Pre-established brain tumor also could be eliminated by the s.c. immunization of irradiated 9L cells and i.c. transplantation of IL-2-producers. These results suggest that glioma-specific CTLs could be effectively induced by s.c. immunization of irradiated wild-type tumor cells without artificial cytokine production.

Inhibition of metastatic brain tumor growth by intramuscular administration of the endostatin gene.

The cancer patients suffering from brain metastases are basically incurable. The conventional tumoricidal strategies frequently cause severe side effects instead of life prolongation of such patients. On the other hand, antiangiogenic therapy seems to be a promising strategy to avoid such unfavorable effects. In the present study, we experimentally investigated tumor dormancy effect of the excessively produced endostatin, a potent angiostatic factor, by intramuscular administration of the endostatin gene against primary cancer and metastatic brain tumor. For this purpose, we established a model system in which FM3A P-15 cells, a high metastatic mouse breast cancer cell line, were inoculated simultaneously into the brain as an artificially metastatic brain tumor (herein referred as "metastatic brain tumor") and the mammary pad as a primary cancer (referred as "primary breast cancer"), and utilized a non-viral system to deliver an expression plasmid encoding a secretable form of mouse endostatin into muscle tissues. The plasmid vector formulated with the synthetic polymer, polyvinylpyrrolidone, was administrated at 3 and 10 days after the inoculation of FM3A P-15 cells. A significant increase in the serum level of endostatin was achieved at 7 days after second administration of the plasmid vector (p=0.0066). Consequently, the growth of metastatic brain tumor was significantly retarded (p=0.0455), while no significant change in the weight of primary breast cancer was observed (p=0.1531). Intratumoral microvessel density in metastatic brain tumor but not in primary cancer as revealed by Factor VIII immunohistochemistry was significantly decreased in the endostatin gene-administrated group (p=0.0027). In conclusion, the present study demonstrates the potential efficacy of intramuscular delivery of antiangiogenic gene for treatment of metastatic brain tumor.

T-cell-dependent antitumor effects produced by CD40 ligand expressed on mouse lung carcinoma cells are linked with the maturation of dendritic cells and secretion of a variety of cytokines.

CD40/CD40 ligand (CD40L) interaction plays an essential role in cell-mediated immune responses. We examined whether expression of CD40L in murine lung carcinoma (A11) cells could produce antitumor effects. The proliferation rate in vitro of A11 cells transfected with the murine CD40L gene (A11/CD40L) was not different from that of parent cells; however, half of the immunocompetent mice inoculated with A11/CD40L cells did not form tumors and the growth of A11/CD40L tumors developed in the rest of mice was significantly retarded compared with that of parent tumors. Protective immunity was also induced in the mice that had rejected A11/CD40L cells. In T-cell-defective nude mice, these antitumor effects were not observed. Bone-marrow-derived dendritic cells (DCs), when cultured with A11/CD40L cells, formed clusters with the tumors and showed upregulated CD86 expression. Expression of the interleukin-23 (IL-23) p19, IL-12p35, IL-18, interferon-gamma (IFN-gamma) and Mig (monokine induced by IFN-gamma) genes was induced in the DCs that were cultured with A11/CD40L but not with A11 cells, and P40, the subunit of both IL-12 and IL-23, was secreted from the cocultured DCs. These data directly showed that the expression of CD40L in tumors facilitated the interaction between DCs and the tumors, enhanced the maturation of DCs, induced secretion of cytokines, and consequently produced T-cell-dependent systemic immunity.

Expression of the interleukin-21 gene in murine colon carcinoma cells generates systemic immunity in the inoculated hosts.

Interleukin-21 (IL-21) is a novel cytokine that can induce proliferation of activated T cells and maturation of natural killer (NK) cells. We therefore examined whether expression of the IL-21 gene in tumor cells could generate antitumor responses. Murine colon carcinoma Colon 26 cells that were transduced with the mouse IL-21 gene (Colon 26/IL-21) were rejected in syngeneic mice and the mice subsequently acquired protective immunity. The growth of Colon 26/IL-21 tumors developed in nude mice was retarded compared with that of parent tumors, and this growth suppression was not observed in nude mice that were treated with anti-asialo GM(1) antibody. Spleen cells from the mice that had rejected Colon 26/IL-21 cells showed cytotoxic activity to Colon 26 but not to irrelevant tumor cells, and produced larger amounts of interferon-gamma upon stimulation with irradiated Colon 26 cells. Spleen cells from Colon 26/IL-21-tumor- but not parent-tumor-bearing mice had lytic activity to YAC-1 cells. These data suggest that expression of IL-21 in tumors induces T- and NK-cell-dependent antitumor effects.

Fas ligand-expressing tumors induce tumor-specific protective immunity in the inoculated hosts but vaccination with the apoptotic tumors suppresses antitumor immunity.

The interaction between Fas and Fas ligand (FasL) is involved in the apoptotic death of a number of cells including lymphocytes. Forced expression of FasL in tumors can induce apoptosis of infiltrating Fas-positive T cells; accordingly, tumors can survive in the milieu of systemic immune responses. However, FasL-expressing murine lung carcinoma (A11) and melanoma (B16) cells did not develop subcutaneous tumors and FasL-expressing A11 (A11/FasL) cells produced few spontaneous lung metastatic foci in syngeneic mice. The mice that rejected A11/FasL cells were resistant to subsequent challenge of parent A11 but not irrelevant B16 cells. Vaccination of mice with UV-treated A11/FasL, but not UV-treated A11 cells, however, augmented the growth rate of A11 but not B16 tumors, both of which were subsequently inoculated. The number of lung metastatic foci of A11 cells was also increased in the mice that received UV-treated A11/FasL but not UV-treated A11 cells. Intraperitoneal injection of UV-treated A11/FasL cells resulted in the production of larger amounts of immunosuppressive TGF-beta in peritoneal exudate than that of UV-treated A11 cells. Expression of the CD80 costimulatory molecule in tissues where UV-treated A11/FasL cells were inoculated was lower than the expression at an untreated A11/FasL-injected site. Our results indicated that apoptotic FasL-expressing tumor cells could impair host immune responses against the tumors, in contrast to potent antitumor immunity generated by viable FasL-expressing tumors.

Interleukin-12-mediated induction of systemic immunity in the periphery and recruitment of activated T cells into the brain produce limited antitumor effects compared with interleukin-2.

Interleukin-12 (IL-12) stimulates the type 1 helper T (Th1) cell responses and augments antitumor immunity. We examined possible antitumor effects of IL-12 secreted intracerebrally (i.c.) and/or subcutaneously (s.c.) in an experimental glioblastoma model and compared the effects with those of IL-2. Rat 9L gliosarcoma cells retrovirally transduced with the IL-12 or IL-2 gene (9L/IL-12 and 9L/IL-2, respectively) were completely rejected when they were s.c. inoculated. The transduced cells, implanted i.c., developed progressive brain tumors at reduced rates compared with 9L brain tumors and the growth retardation of 9L/IL-2 tumors was greater than that of 9L/IL-12 tumors. When rats were s.c. immunized with either 9L/IL-12 or 9L/IL-2 cells, the growth of 9L brain tumors developed in the rats was suppressed compared with that of 9L tumors in naive rats. Among various combinations of simultaneous inoculations of cytokine producers s.c. and i.c., 9L/IL-2 but not 9L/IL-12 cells inoculated i.c. were rejected when the rats were s.c. immunized with either 9L/IL-12 or 9L/IL-2 cells. The synergistic antitumor effects induced were correlated with the infiltration levels of CD8+ and CD4+ T cells into brain tumors. Tumor-specific cytotoxic activity was induced in the rats immunized s.c. with 9L/IL-2 but not fully in the rats with 9L/IL-12 cells. These results collectively suggest that the antitumor activity with IL-2 was superior to IL-12 both in the induction of cytotoxic T cells and in the recruitment of activated T cells into brain tumors.

Identification of the small interstitial deletion at chromosome band 1p34-p35 and its association with poor outcome in oligodendroglial tumors.

To narrow down the putative tumor-suppressor gene locus and to assess the predictability of clinical courses by genomic alterations, we analyzed 46 oligodendroglial tumors for loss of heterozygosity (LOH) in the distal region of the short arm of chromosome 1. LOH at 1p was found in 43 tumors (93.5%), including all 28 oligodendrogliomas, all eight oligo-astrocytomas, six of eight anaplastic oligodendrogliomas, and in one of two anaplastic oligo-astrocytomas. Thirty-seven tumors showed LOH patterns consistent with a large terminal deletion, whereas six tumors showed LOH suggesting interstitial deletions. Our data also showed two small regions of overlap at 1p34-p35 (approximately 5.7 Mb) and at 1p36.1-p36.2 ( approximately 12 Mb). Among the six tumors with interstitial deletion, the proximal region was deleted in five tumors, whereas the distal region was deleted in only half of them. Overall, 91% of tumors showed deletion including this proximal region. To examine the clinical significance of the LOH pattern, the samples were classified into three groups: tumors without 1p LOH (Group 1, n = 3), tumors with an interstitial deletion (Group 2, n = 6), and tumors with a large terminal deletion (Group 3, n = 37). Both overall and progression-free survival of patients in Group 2 was extremely poor compared with those included in Group 3 (P = 0.0006 and P = 0.003, respectively). As to the clinical response to chemotherapy, nimustine prevented tumor recurrence in Group 3 (P = 0.034) but not in Group 2. Our results demonstrate that a putative tumor-suppressor gene(s) in oligodendroglial tumors is localized at 1p34-p35 and that small interstitial deletions, in contrast to large terminal deletions, are strongly predictive of both chemoresistance and aggressive characteristics of these tumors.

Cutting edge: a novel role for Fas ligand in facilitating antigen acquisition by dendritic cells.

Fas ligand (FasL)-expressing tumor cells are found to effectively mediate rejection of the coinoculated FasL negative parental cells while having no effect on the growth of histologically distinct tumor cells. These observations indicate that FasL induces a specific immune response against Ag derived from FasL-bearing tumors and suggest a possible role for FasL in tumor Ag presentation. Indeed, tumor cells expressing FasL can efficiently interact with dendritic cells (DCs) and this interaction requires the expression of membrane-bound FasL on tumors and Fas on DCs. Moreover, DCs cocultured with FasL-expressing tumors are able to elicit a tumor-specific immune response in vivo, suggesting that DCs acquire tumor Ag during the Fas/FasL-mediated DC-tumor contact. These results identify a novel role for FasL in augmenting tumor-DC interactions and subsequent tumor Ag acquisition by DCs, and suggest that FasL-expressing tumor cells could be used to generate tumor-specific DC vaccines.

p73-dependent expression of DAN during cisplatin-induced cell death and osteoblast differentiation.

We previously reported that DAN, a founding member of the DAN family of secreted proteins, acts as an inhibitor of cell cycle progression and is closely involved in retinoic acid-induced neuroblastoma differentiation. In this study, we found that DAN as well as p73, the recently identified p53 family member, was up-regulated during osteoblast differentiation. Additionally, the expression of DAN was increased in response to cisplatin-induced cell death of neuroblastoma SH-SY5Y cells. Consistent with the previous reports, p73 was accumulated after the treatment with cisplatin. Intriguingly, we found a putative p53/p73-binding site in the 5'-upstream region of the human DAN gene. A luciferase reporter assay and an in vitro DNA-binding experiment revealed that this canonical p53/p73-binding site was a functional responsive element and was specific for p73. Our results suggest that there exists a functional association between DAN and p73 during osteoblast differentiation as well as cisplatin-induced cell death.

A promoter region of midkine gene can activate transcription of an exogenous suicide gene in human pancreatic cancer.

We examined a possible application of regulatory regions of the midkine (MK) gene for suicide gene therapy of pancreatic cancer. The expression of MK has been demonstrated in human pancreatic cancer tissues but scarcely in normal adult tissues. Northern blot analysis confirmed that human pancreatic cancer cell lines expressed the MK gene. A 609-bp genomic fragment in the 5'-regulatory region of the MK gene, when transfected into human pancreatic cancer cells, activated the transcription of a fused reporter gene to an extent greater than the SV40 promoter. In contrast, the 609-bp fragment-mediated promoter activity tested in fibroblast cells was significantly weak. Human pancreatic cancer cells (AsPC-1) that were transduced with the herpes simplex virus-thymidine kinase gene linked with the 609-bp promoter markedly increased their sensitivity to a prodrug, ganciclovir, compared with untransduced cells. The present study suggests that preferential cytotoxic effects for pancreatic tumors can be achieved by using the MK promoter.

Secretion of interleukin-10 from murine colon carcinoma cells suppresses systemic antitumor immunity and impairs protective immunity induced against the tumors.

Interleukin-10 (IL-10) is a T helper type 2 (Th2) cytokine that suppresses Th1-mediated, cell-mediated immune responses and reciprocally enhances antibody-mediated responses. Previous studies, however, demonstrated that forced expression of the IL-10 gene in tumor cells could unexpectedly produce antitumor effects. We then examined whether tumor-derived IL-10 could modulate systemic immune responses. Murine colon carcinoma (Colon 26) cells that were retrovirally transduced with the murine IL-10 gene (Colon 26/IL-10) were inoculated in syngeneic immunocompetent or T cell-defective nude mice. Growth of Colon 26/IL-10 tumors was augmented in immunocompetent and, to less extent, in nude mice compared with that of wild-type tumors developed in respective mice. Growth of wild-type tumors was accelerated to the same level as that of Colon 26/IL-10 tumors when wild type and Colon 26/IL-10 cells were respectively inoculated in different flanks of the same immunocompetent mice. This enhanced growth of wild-type tumors was not observed in nude mice. Immunocompetent mice that had rejected IL-2- or IL-12-secreting Colon 26 cells developed protective immunity and became completely resistant to wild-type Colon 26 cells subsequently challenged. However, some of the mice that had rejected IL-2 or IL-12 producers developed Colon 26/IL-10 tumors inoculated thereafter. The present study showed that production of IL-10 from tumor cells impaired T cell- and non-T cell-mediated systemic antitumor immunity in hosts.