Morphology dependent field emission of acid-spun carbon nanotube fibers.

Acid spun carbon nanotube (CNT) fibers were investigated for their field emission properties and performance was determined to be dependent on fiber morphology. The fibers were fabricated by wet-spinning of pre-made CNTs. Fiber morphology was controlled by a fabrication method and processing conditions, as well as purity, size, and type of the CNT starting material. The internal fiber structure consisted of CNT fibrils held together by van der Waals forces. Alignment and packing density of the CNTs affects the fiber's electrical and thermal conductivity. Fibers with similar diameters and differing morphology were compared, and those composed of the most densely packed and well aligned CNTs were the best field emitters as exhibited by a lower turn-on voltage and a larger field enhancement factor. Fibers with higher electrical and thermal conductivity demonstrated higher maximum current before failure and longer lifetimes. A stable emission current at 3 mA was obtained for 10 h at a field strength of <1 V µm(-1). This stable high current operation makes these CNT fibers excellent candidates for use as low voltage electron sources for vacuum electronic devices.

Lack of FasL-mediated killing leads to in vivo tumor promotion in mouse Lewis lung cancer.

Lewis lung carcinoma (3LL) cells were constitutively resistant to Fas-mediated apoptosis, but overexpression of Fas on 3LL cells allowed Fas-mediated apoptosis after crosslinking with agonist anti-Fas antibody (Jo2) in vitro. Surprisingly, Fas-overexpressing 3LL cells showed enhanced in vivo tumor progression, whereas no promotion of in vivo tumor growth was observed for dominant negative (DN) Fas-overexpressing 3LL transfectants in which the cytoplasmic death domain was deleted. In addition, the promotion of in vivo tumor growth by Fas-overexpression was reduced in gld (FasL-mutation) mice compared to normal mice. These data indicate that intact Fas/FasL cell signaling is required for the promotion of in vivo tumor growth by Fas overexpression in 3LL cells. In contrast to the efficient Fas-mediated killing induced in vitro by crosslinking with anti-Fas antibody, Fas-overexpressing 3LL cells were resistant in vitro to Fas-mediated apoptosis by activated T cells or transient FasL transfection. These data suggest that agonist anti-Fas antibody and natural FasL can transmit qualitatively different signals, and crosslinking of Fas with natural FasL on 3LL cells does not deliver the expected death signal. Thus, our results demonstrate that in some cases overexpression of Fas can result in a survival advantage for tumor cells in vivo.

Hematopoietic switch from lymphoid to granulocytic development in 3LL tumor-bearing mice.

A significant splenomegaly and lymphadenopathy develops during the progressive growth of Lewis Lung (3LL) tumors in mice. Enlarged spleen and lymph nodes occur because of a pronounced increase in granulocytes in these organs. This granulocytosis in spleen and lymph node was not simply due to recruitment of granulocytes from peripheral blood to spleen and lymph nodes, but also a result of development and/or differentiation of granulocytes from the bone marrow. There was a marked increase in development of myeloid lineage cells, whereas lymphoid populations including T cells and B cells, were dramatically decreased in bone marrow and peripheral blood of 3LL tumor-bearing mice. These data demonstrate that host hematopoiesis shifts from lymphoid to granulocytic development in the 3LL tumor-bearing mice. Interestingly, a somatic mutation of N-Ras gene was found in 3LL tumor cells at codon 61, suggesting that mutated N-Ras may contribute to induction of granulocytosis in 3LL tumor-bearing mice.

Induction of transplantable mouse renal cell cancers by streptozotocin: in vivo growth, metastases, and angiogenic phenotype.

Interleukin-2-based regimens of biological therapy have shown some clinical promise for the treatment of kidney cancer in humans, although the mechanisms responsible for tumor regression occurring in these patients remain unclear. Preclinical insight into these mechanisms is limited by a paucity of orthotopic animal models of kidney cancer. We have used streptozotocin, an antibiotic and diabetogenic nitrosamine compound derived from Streptomyces achromogenes to induce new kidney tumors in BALB/c mice. Single or multiple doses of streptozotocin induced kidney tumors in up to 25% of mice by 50-90 weeks of age, with up to 18% characterized as renal cell carcinomas (RCCs). Several transplantable lines were obtained from the RCCs, and one of these lines was subsequently cloned. The initial tumor isolates and sublines were histologically reconfirmed to be RCCs, and all grew progressively but slowly (mean survival times, 57 to >100 days) in vivo after intrarenal implant. None of the primary isolates or sublines revealed mutations in either the VHL or Ras genes, although karyotype analysis and chromosome painting revealed the consistent presence of a submetacentric chromosome resulting from the fusion of chromosomes 16 and 19. Biological characterization of these tumors revealed several features analogous to the growth of human kidney cancers, including a propensity for the formation of lung metastases and high vascularity. This hypervascularity is evident by both gross and microscopic analysis and correlates with the expression of several proangiogenic genes. Overall, the features of orthotopic transplantability, slower in vivo growth (relative to the rapid growth rates of other transplantable mouse kidney tumors), propensity for lung metastases, and hypervascularity may make these tumors valuable models for the study of new therapeutic strategies based on antineovascular agents and antitumor cytokines.

IFN-gamma and Fas/FasL are required for the antitumor and antiangiogenic effects of IL-12/pulse IL-2 therapy.

Systemic administration of IL-12 and intermittent doses of IL-2 induce complete regression of metastatic murine renal carcinoma. Here, we show that overt tumor regression induced by IL-12/pulse IL-2 is preceded by recruitment of CD8(+) T cells, vascular injury, disrupted tumor neovascularization, and apoptosis of both endothelial and tumor cells. The IL-12/IL-2 combination synergistically enhances cell surface FasL expression on CD8(+) T lymphocytes in vitro and induces Fas and FasL expression within tumors via an IFN-gamma-dependent mechanism in vivo. This therapy also inhibits tumor neovascularization and induces tumor regression by mechanisms that depend critically on endogenous IFN-gamma production and an intact Fas/FasL pathway. The ability of IL-12/pulse IL-2 to induce rapid destruction of tumor-associated endothelial cells and regression of established metastatic tumors is ablated in mice with a dysregulated Fas/FasL pathway. The common, critical role for endogenous IFN-gamma and the Fas/FasL pathway in early antiangiogenic effects and in antitumor responses suggests that early, cytokine-driven innate immune mechanisms and CD8(+) T cell-mediated responses are interdependent. Definition of critical early molecular events engaged by IL-12/IL-2 may provide new perspective into optimal therapeutic engagement of a productive host-antitumor immune response.

Complete regression of established spontaneous mammary carcinoma and the therapeutic prevention of genetically programmed neoplastic transition by IL-12/pulse IL-2: induction of local T cell infiltration, Fas/Fas ligand gene expression, and mammary epithelial apoptosis.

Using a novel transgenic mouse model of spontaneous mammary carcinoma, we show here that the IL-12/pulse IL-2 combination can induce rapid and complete regression of well-established autochthonous tumor in a setting where the host immune system has been conditioned by the full dynamic process of neoplastic progression and tumorigenesis. Further, this regimen inhibits neovascularization of established mammary tumors, and does so in conjunction with potent local induction of genes encoding the IFN-gamma- and TNF-alpha-inducible antiangiogenic chemokines IFN-inducible protein 10 and monokine induced by IFN-gamma. In contrast to untreated juvenile C3(1)TAg mice in which histologically normal mammary epithelium predictably undergoes progressive hyperplasia, atypical changes, and ultimately transition to overt carcinoma, the current studies also demonstrate a unique preventative therapeutic role for IL-12/pulse IL-2. In juvenile mice, early administration of IL-12/pulse IL-2 markedly limits the expected genetically programmed neoplastic transition within the mammary epithelium and does so in conjunction with enhancement of constitutive Fas and pronounced induction of local Fas ligand gene expression, T cell infiltration, and induction of apoptosis within the mammary epithelium. These events occur in the absence of a durable Ag-specific memory response. Thus, this novel model system demonstrates that the potent therapeutic activity of the IL-12/pulse IL-2 combination rapidly engages potent apoptotic and antiangiogenic mechanisms that remain active during the delivery of IL-12/pulse IL-2. The results also demonstrate that these mechanisms are active against established tumor as well as developing preneoplastic lesions.

IFN-gamma-dependent delay of in vivo tumor progression by Fas overexpression on murine renal cancer cells.

The role of Fas in the regulation of solid tumor growth was investigated. Murine renal carcinoma (Renca) cells were constitutively resistant to Fas-mediated killing in vitro, but exhibited increased expression of Fas and sensitivity to Fas-mediated killing after exposure to IFN-gamma and TNF. Transfected Renca cells overexpressing Fas were efficiently killed in vitro upon exposure to anti-Fas Ab (Jo2). When Fas-overexpressing Renca cells were injected into syngenic BALB/c mice, there was a consistent and significant delay in tumor progression, reduced metastasis, and prolonged survival that was not observed for Renca cells that overexpressed a truncated nonfunctional Fas receptor. The delay of in vivo tumor growth induced by Fas overexpression was not observed in IFN-gamma-/- mice, indicating that IFN-gamma is required for the delay of in vivo tumor growth. However, there was a significant increase of infiltrated T cells and in vivo apoptosis in Fas-overexpressing Renca tumors, and Fas-overexpressing Renca cells were also efficiently killed in vitro by T cells. In addition, a strong therapeutic effect was observed on Fas-overexpressing tumor cells by in vivo administration of anti-Fas Ab, confirming that overexpressed Fas provides a functional target in vivo for Fas-specific ligands. Therefore, our findings demonstrate that Fas overexpression on solid tumor cells can delay tumor growth and provides a rationale for therapeutic manipulation of Fas expression as a means of inducing tumor regression in vivo.

Mice with a targeted mutation in lymphotoxin-alpha exhibit enhanced tumor growth and metastasis: impaired NK cell development and recruitment.

Mice deficient in lymphotoxin (LT)-alpha lack peripheral lymph nodes and Peyer's patches and have profound defects in development of follicular dendritic cell networks, germinal center formation, and T/B cell segregation in the spleen. Although LTalpha is known to be expressed by NK cells as well as T and B lymphocytes, the requirement of LTalpha for NK cell functions is largely unknown. To address this issue, we have assessed NK cell functions in LTalpha-deficient mice by evaluating tumor models with known requirements for NK cells to control their growth and metastasis. Syngeneic B16F10 melanoma cells inoculated s.c. grew more rapidly in LTalpha-/- mice than in the wild-type littermates, and the formation of experimental pulmonary metastases was significantly enhanced in LTalpha-/- mice. Although LTalpha-/- mice exhibited almost a normal total number of NK cells in spleen, they showed an impaired recruitment of NK cells to lung and liver. Additionally, lytic NK cells were not efficiently produced from LTalpha-/- bone marrow cells in vitro in the presence of IL-2 and IL-15. These data suggest that LTalpha signaling may be involved in the maturation and recruitment of NK cells and may play an important role in antitumor surveillance.

T cell- and NK cell-independent inhibition of hepatic metastases by systemic administration of an IL-12-expressing recombinant adenovirus.

IL-12 is a potent immunoregulatory cytokine that has been shown to mediate tumor regression in a variety of tumor models. We describe the construction of AdCMV-IL-12, a recombinant adenovirus that encodes both subunits of IL-12 under transcriptional control of the CMV promoter. This recombinant virus efficiently infects a wide variety of cell types leading to the production of high levels of biologically active IL-12. Because the liver is a primary site of infection after i.v.-administered adenovirus, we tested the therapeutic efficacy of this virus in a murine hepatic metastasis tumor model. Systemic administration of AdCMV-IL-12 dramatically inhibited the formation of 3-day Renca hepatic metastases (mean of 16 metastases per liver) compared with the control virus AdCMV-betagal (mean of 209) or vehicle alone (mean of 272). Histologic analysis indicated that metastatic growth inhibition was accompanied by a dramatic perivascular infiltrate consisting of T cells, macrophages, and neutrophils. Therapeutic efficacy was not diminished in animals depleted of CD4+ or CD8+ T cells, or in SCID mice, even after NK cell ablation. In the latter case, a hepatic perivascular infiltrate composed of macrophages and neutrophils was observed after AdCMV-IL-12-treatment, while numerous activated Kupffer cells were noted in the hepatic parenchyma. Analysis of therapy-induced changes in hepatic gene expression demonstrated increased levels of IP-10 and Mig RNAs, but no increase in iNOS, Fas, or FasL RNA levels was observed. Our data suggest a model of metastatic growth inhibition mediated by nonlymphocyte effector cells including macrophages and neutrophils and that may involve anti-angiogenic chemokines.

Interleukin 12 primes macrophages for nitric oxide production in vivo and restores depressed nitric oxide production by macrophages from tumor-bearing mice: implications for the antitumor activity of interleukin 12 and/or interleukin 2.

Interleukin-12 (IL-12) is a recently described immunoregulatory cytokine with potent therapeutic activity in various preclinical models of infectious or malignant disease. As part of our ongoing evaluation of potential mechanisms accounting for the potent antitumor activity of IL-12, we have investigated the influence of IL-12 administration on total serum nitrate/nitrite (NO(x)(-)) levels and the production of nitric oxide (NO) by peritoneal macrophages from normal and tumor-bearing mice. We report here that IL-12 administration to either normal or tumor-bearing mice for periods of time ranging from 7-19 days induced progressive increases in serum NO(x)(-) levels and primed peritoneal macrophages for NO production on subsequent exposure to lipopolysaccharide or IL-2 ex vivo. Treatment of resident peritoneal macrophages or the macrophage cell line ANA-1 with IL-12 alone or IL-12 in combination with various other stimuli failed to induce NO production, suggesting that the effects of IL-12 occurred via an indirect mechanism. Furthermore, we have shown that not only was the production of NO by macrophages from untreated long-term, tumor- bearing mice suppressed compared with control mice treated with vehicle or IL-12, but also that IL-12 administration overcame this suppression and delayed tumor growth. Lastly, we have shown that administration of weekly pulses of IL-2 in combination with IL-12 additively enhanced the priming of macrophages for NO production ex vivo and delayed tumor growth far more effectively than either agent alone. These observations and reports in the literature regarding the potential influence of NO on development of the immune response and on the regulation of tumor growth and vascularization suggest that NO may play a significant role in the antitumor activity of IL-12 and IL-2.

Administration of interleukin 12 with pulse interleukin 2 and the rapid and complete eradication of murine renal carcinoma.

BACKGROUND: Interleukin 2 (IL-2) and interleukin 12 (IL-12) are potent immunoregulatory cytokines that exhibit antitumor activity. Preliminary evidence suggests that combined administration of IL-2 and IL-12 may yield greater antitumor activity than that observed with either agent alone. PURPOSE: We evaluated the ability of combination regimens of IL-2 and IL-12 to induce regression of established primary and metastatic murine renal carcinoma (Renca) tumors. METHODS: BALB/c mice were given either subcutaneous or intrarenal injections of 10(5) Renca cells; tumor cell injections were given to 10-12 mice for each treatment group. Mice bearing subcutaneous primary tumors were treated with chronic IL-2 (300,000 IU given on a daily basis) or pulse IL-2 (300,000 IU given twice daily one day per week) alone, IL-12 alone (0.5 micrograms given on a daily basis), or IL-12 in combination with either chronic or pulse IL-2. Mice with metastatic tumors (arising from intrarenal implants; animals were nephrectomized to remove the primary tumors) were treated with IL-12 plus or minus pulse IL-2; in these experiments, IL-12 was given at doses of either 0.5 or 1.0 micrograms. In most experiments, treatment was continued for at least 3 weeks. Two-sided statistical tests were used to evaluate the data. RESULTS: Most mice with subcutaneous Renca tumors treated with the combination of IL-12 and chronic IL-2 died of treatment-related toxic effects within 7-14 days. In contrast, treatment with IL-12 plus pulse IL-2 was well tolerated, and six of 10 mice experienced complete tumor regression; none of the mice treated with either IL-12 alone or pulse Il-2 alone experienced a curative response. Seven of eight and nine of nine mice with metastatic tumors experienced complete tumor regression after treatment with 0.5 micrograms IL-12 plus pulse IL-2 or 1.0 microgram IL-12 plus pulse IL-2, respectively; two of 12 mice treated with pulse IL-2 alone and 10% or less of mice treated with IL-12 alone were cured of metastatic tumors (with 0.5 micrograms IL-12, none of 10 mice; with 1.0 micrograms IL-12, one of 10 mice). Five of 10 mice with metastatic tumors treated with a short-course regimen of IL-12 and pulse IL-2 (two pulses of IL-2 flanking 5 days of 0.5 micrograms IL-12) experienced complete tumor regression, while only one of the 12 mice treated with IL-2 alone and none of the mice treated with IL-12 alone experienced complete tumor regression. Virtually all curative response frequencies obtained with IL-12 and pulse IL-2 combination regimens differed significantly (P < .05) from those obtained with corresponding single-agent treatments. CONCLUSIONS: IL-12 administered in combination with pulse IL-2 induced rapid and complete regression of primary and metastatic Renca tumors and displayed greater antitumor activity than that observed with either IL-12 or IL-2 alone.

Administration of recombinant human IL-7 to mice alters the composition of B-lineage cells and T cell subsets, enhances T cell function, and induces regression of established metastases.

These studies investigate the effects of exogenously administered recombinant human IL-7 (rhIL-7) on mouse leukocyte subsets in vivo in normal and tumor-bearing mice. The administration of rhIL-7 to normal mice caused a pronounced leukocytosis (three- to fivefold increase over background) in the spleen and lymph nodes, with B-lineage and T cells, NK cells, and macrophages all being increased. CD8+ T cells increased disproportionately, such that the CD4 to CD8 ratio decreased dramatically. The rhIL-7-induced effects were dose-dependent, increased with duration of treatment, and were reversible after cessation of rhIL-7 administration. T cell number increases after rhIL-7 treatment were primarily a result of an expansion of the peripheral T cell population. Importantly, splenocytes from rhIL-7-treated mice have enhanced proliferative responses to various T cell stimuli in vitro and were able to potentiate an allogeneic CTL response in vivo. The rhIL-7-induced changes in T cell number and the CD4 to CD8 ratio also were observed in mice bearing early Renca renal adenocarcinoma pulmonary metastases, and these changes coincided with up to a 75% reduction in pulmonary metastases. Overall, these results demonstrate that the administration of rhIL-7 to mice profoundly increases the number of B and T cells, and reduces the number of pulmonary metastases. The results also suggest that IL-7 may be useful for restoring lymphoid subsets in immunosuppressed hosts and in enhancing T cell-mediated immune responses. Such effects may be useful in the treatment of microbial diseases and cancer.

Antitumor effects of interleukin-7 and adoptive immunotherapy on human colon carcinoma xenografts.

The antitumor properties of recombinant human IL-7 (rhIL-7) on a human tumor was evaluated by engrafting a human colon carcinoma into immunodeficient mice and then treating the mice with rhIL-7 and adoptively transferred human peripheral blood T cells. It was found that rhIL-7 alone had no effect on the survival of the tumor-bearing recipients. However, the combination of rhIL-7 and human T cells significantly promoted the survival of the recipients compared with mice receiving either treatment by itself. When the surviving mice were analyzed 6 mo later for the degree of human cell engraftment, the recipients receiving both rhIL-7 and human T cells had greater numbers of human CD8+ T cells in the spleens. However, the human T cells recovered from the surviving mice showed low lytic activity against the tumor in vitro. Supernatants from human T cells cultured with the tumor and rhIL-7 in vitro were found to inhibit tumor growth and were demonstrated to contain high levels of IFN-gamma. Antibodies to IFN-gamma neutralized the growth inhibition of the tumor both in vitro and in vivo demonstrating that the in vivo mechanism underlying the antitumor effects of this regimen was partly dependent on the production of IFN-gamma by the T cells and not their cytolytic capability. Interestingly, systemic administration of rhIFN-gamma to tumor-bearing mice yielded little antitumor effect suggesting that adoptive immunotherapy with rhIL-7 was superior possibly because of the continuous local release of the cytokines. Therefore, rhIL-7 may be of clinical use as an antineoplastic agent and the human/mouse model is a potentially important preclinical model for in vivo evaluation of the efficacy of this and other immunotherapies.

Engraftment and activity of anti-CD3-activated human peripheral blood lymphocytes transferred into mice with severe combined immune deficiency.

Human PBL (huPBL) were activated with anti-CD3 mAb in vitro and then were transferred into mice with severe combined immune deficiency (SCID) to determine the effect of activation on engraftment and to determine if the engrafted human cells could provide antitumor effects in mice. Some mice were also treated with human rIL-2 after huPBL transfer. Mice were analyzed 6 to 8 wk after cell transfer and the number of human cells in the peripheral lymphoid organs was determined. Mice receiving anti-CD3-activated huPBL demonstrated a significant increase in the incidence of human T cell engraftment in the periphery as assessed by flow cytometry. Human cells were also detected in the murine thymus after anti-CD3 stimulation indicating that human T cells can migrate to the murine thymus provided that they are activated before the transfer. The transfer of anti-CD3-activated huPBL also resulted in an xenogeneic graft-vs-host reaction manifested primarily by proliferation of murine splenic hemopoietic cells. When SCID mice received the human colon carcinoma HT29, the concurrent transfer of anti-CD3-activated human cells resulted in a significant increase in survival. However, the human cells displayed low cytolytic activity toward human tumor targets when they were recovered from the lymphoid organs of the SCID recipients. Supernatants from the anti-CD3-activated cells were able to inhibit the growth of HT29 in vitro, partly because of the presence of IFN-gamma, suggesting that the human T cells are producing cytokines in vivo that have antitumor effects. Thus, the use of anti-CD3-activated huPBL in SCID mice may be of value for optimizing human cell engraftment in the human/mouse lymphoid chimeras and may be used to evaluate potential anti-neoplastic therapies that employ human effector cells.

In vivo distribution and cytokine gene expression by enriched mouse LAK effector cells.

Lymphokine activated killer (LAK) cells administered in combination with interleukin 2 (IL2) can mediate antitumor activity in tumor-bearing mice and advanced cancer patients. Relatively little is known about the mechanism by which adoptively transferred LAK cells plus IL2 mediate these antitumor effects in vivo, and it remains unclear to what extent the actual LAK effector cells can accumulate in tumors. In the present study, enriched cytolytic LAK effector cells were obtained by fractionation of bulk LAK cell cultures on Percoll density gradients. About 95% of the total lytic activity was recovered from the 55% of cells isolated in fraction 2 (Fr2). The cells recovered in Fr2 are mostly large, proliferating lymphoblasts that express either the NK-associated surface markers NK1.1 (38%) or LGL-1 (31%), or the cytotoxic T cell phenotype, Lyt2 (39%). The cytolytic lymphoblasts obtained from Fr2 were radiolabelled with either 111Indium-Oxine (111InOx) which labels all cells in the population, or with 125Iododeoxyuridine (125IUdR) which labels only proliferating cells, and injected iv into mice bearing murine renal cancer (Renca). 111InOx-labeled Fr2 cells migrated mostly to spleen (28%) and liver (35%), with approximately 5% of the injected label detectable in the Renca-bearing kidney by 24 hrs. In contrast, Fr2 cells labeled with 125IUdR, which labels only the proliferating blasts thought to include the actual effector cells, exhibited a very different localization pattern. 125IUdR-Fr2 cells were retained in the lungs at higher levels than were 111InOx-Fr2 cells and very little label was detectable in liver (6%), spleen (3%), or tumor bearing kidney (2%) at 24 hrs. These results suggest that most of the large, proliferating lymphoblasts are cleared from the body by 24 hrs and very few localize into even large tumors. Subsequently, Northern blot analyses performed on bulk LAK cells revealed a potent induction of mRNA for TNF alpha by 6 hrs and for IFN gamma by 48 hrs. The intensity of gene expression for both cytokines was increased in Fr2 as compared to the unfractionated bulk LAK cells or to non-cytolytic cells obtained from Fr3. Overall, these results suggest that at least some of the antitumor effects mediated by LAK cells occur by the release of cytokines that synergize with exogenous IL2 for the activation of host effector cells.

Augmentation of natural killer activity, induction of IFN and development tumor immunity during the successful treatment of established murine renal cancer using flavone acetic acid and IL-2.

The investigational drug flavone acetic acid (FAA) has been previously shown to systemically augment NK activity in vivo in normal mice within 24 h of i.p. or i.v. administration. The current study investigates the ability of FAA, and/or rIL-2, to augment NK activity and antitumor responses in mice bearing murine renal cancer (Renca). The results demonstrate that FAA potently augments NK activity in the blood, spleen, and liver of Renca-bearing mice and that the administration of rIL-2 in addition to FAA results in a further augmentation of NK activity over that observed with FAA alone. Renca-bearing mice treated with FAA (200 to 250 mg/kg) plus rIL-2 exhibited a significantly increased incidence of long term survivors (59%) over that observed following treatment with FAA (0%) or rIL-2 (5%) alone. Therapeutic synergy between FAA and rIL-2 was observed against primary tumors, minimal residual disease, and experimental-induced pulmonary metastases. Mice cured of Renca by FAA plus rIL-2 treatment were largely resistant to rechallenge with Renca suggesting a role for T lymphocytes. The augmentation of NK activity and the therapeutic effects of FAA coincided with the rapid induction of high titers of serum IFN of the alpha/beta type within 4 h of FAA administration. Subsequent studies demonstrated that the contribution of FAA could be partially replaced by the administration of several doses of human rIFN-alpha A/D Bg1 before the initiation of rIL-2 administration. The observed synergistic antitumor effects of FAA plus rIL-2 coincided with the augmentation of NK activity, induction of IFN-alpha/beta, and induction of long lasting tumor immunity. Overall, these results suggest that this approach may obviate the need for adoptive immunotherapy in association with rIL-2 administration for at least some tumor types.

Flavone-8-acetic acid augments systemic natural killer cell activity and synergizes with IL-2 for treatment of murine renal cancer.

The investigational drug flavone-8-acetic acid (FAA) potently augments NK activity in the spleen, liver, lungs, and peritoneum in a dose-dependent manner after i.v. or i.p. administration. Augmented NK activity peaks by 24 h after FAA injection and returns to normal after 6 days. Combined treatment of established murine renal cancer with FAA and rIL-2 results in up to 80% long term survival whereas FAA or rIL-2 alone were unable to induce any long term survivors. The optimal dose of rIL-2 required for use with FAA was in the range of 10,000 to 30,000 U/day. Further studies demonstrated that the regimen of FAA plus rIL-2 administration that was effective in treating established murine renal cancer also induced a more potent augmentation of NK activity than did either FAA or rIL-2 alone. Subsequent studies revealed that the therapeutic effectiveness of FAA plus rIL-2 was significantly reduced when tumor-bearing mice were treated with anti-asialo GM1 serum. These results are consistent with a role for augmented NK activity in the therapeutic effects of FAA plus rIL-2 murine renal cancer. In addition, these studies demonstrate that FAA and rIL-2 is a useful approach for cancer treatment in that subtoxic doses of rIL-2 can be used and significant anti-tumor efficacy occurs even without accompanying adoptive immunotherapy.

Regulation of bone marrow cell survival in short-term cultures: a new macrophage function.

The involvement of macrophages (M phi) in the regulation of bone marrow (BM) cell survival in short-term cultures was studied. We developed a system to measure the survival of fresh BM cells in vitro, by evaluating 111indium (111In) release from prelabeled BM cells. 111In release was proportional to cell death and inversely related to the number of trypan blue excluding cells. Upon 24 hr of culture in conventional medium, more than 50% of BM cells died. In order to investigate whether BM cell death could be reduced by coculture with other cell types, 111In-labeled BM cells were incubated for 24 hr with peritoneal M phi, thymocytes (THY), or polymorphonuclear cells (PMN) and then assayed for their survival. We found that coculture of BM cells with M phi dramatically increased BM survival, whereas THY or PMN consistently failed to enhance BM survival. The ability to promote BM cell survival, here designated nurse activity, represented a novel function of M phi and was further characterized. The stage of activation of M phi did not influence their nurse activity, since M phi elicited in vivo by proteose-peptone, thioglycollate, or Bacillus Calmette-Guérin, as well as resident M phi unstimulated or activated in vitro with lipopolysaccharide, equally sustained survival of BM cells. BM-derived M phi (adherent cells from BM cultures maintained in 20% L-cell-conditioned medium for 14 days) were equally effective in exerting nurse activity. Moreover, nurse activity was also exerted across the histocompatibility barriers. Supernatants from M phi cultures or killed M phi were ineffective. We propose that the nurse effect of M phi on BM is a primitive function that may play an important role in the development of the hemopoietic system.