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Annals of Surgical Oncology 10:455-462 (2003)
© 2003 Society of Surgical Oncology

ORIGINAL ARTICLES

Renal Cell Carcinoma Induces Prostaglandin E2 and T-Helper Type 2 Cytokine Production in Peripheral Blood Mononuclear Cells

Gordon P. Smyth, FRCSI, Philip P. Stapleton, PhD, Catherine B. Barden, MD, Juan R. Mestre, MD, Tracy A. Freeman, BA, Michael D. Duff, AFRCSI, Sirish Maddali, MD, Zhaoping Yan, MD and John M. Daly, MD, FACS

From the Department of Surgery, Weill Medical College of Cornell University/New York Presbyterian Hospital, New York, New York.

Correspondence: Address correspondence and reprint requests to: Philip P. Stapleton, PhD, Temple University School of Medicine, Departments of Surgery and Microbiology/Immunology, 3400 North Broad Street, Room 513 OMS, Philadelphia, PA 19140; Fax: 215-707-8820; E-mail: ppstap{at}temple.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Patients with renal cell carcinoma (RCC) do not develop an effective antitumor immune response, despite significant infiltration by lymphocytes. Tumor production of immunosuppressive factors may account for this failure. The object of this study was to investigate the production of immunosuppressive mediators, especially prostaglandin E2 (PGE2), by RCC.

Methods: Peripheral blood mononuclear cells (PBMC) were cocultured with conditioned medium (CM) from human RCC cell lines in the presence or absence of NS-398, a selective cyclooxygenase 2 (COX-2) inhibitor. Supernatants were analyzed for levels of PGE2, interleukin (IL)-10, IL-6, IL-2, interferon-{gamma}, and IL-12. The effects of RCC CM on PBMC proliferation were also examined. The expression of basal and stimulated COX-2 messenger RNA in the cell lines was assessed by reverse transcriptase-polymerase chain reaction.

Results: RCC CM significantly increased PGE2 production by PBMC. T-helper type 2 (Th2) cytokine production was also significantly increased. Th1 cytokines were unchanged or decreased. RCC CM increased proliferation of PBMC. Coculture with NS-398 reduced PBMC PGE2 production to below control levels and significantly decreased IL-6 production and PBMC proliferation. NS-398 had no effect on cellular production of IL-10 or Th1 cytokines.

Conclusions: Human RCC inhibits the host antitumor immune response by promoting PGE2 production and Th2 cytokines in PBMC. Selective inhibition of COX-2 may have a role in abrogating this effect.

Key Words: Renal cell carcinoma • Prostaglandin E2 • Th2 cytokines • Peripheral blood mononuclear cells • COX-2 inhibition


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Renal cell carcinoma (RCC) accounts for 2% to 3% of all malignancies in adults and causes 2.3% of all cancer deaths in the United States annually.1 One third to one half of the patient population with RCC has metastatic disease at presentation. The overall survival rate is approximately 50% at 5 years; however, patients with metastatic disease have a median survival duration of 7 to 11 months.2

RCC is relatively insensitive to cytotoxic agents and radiotherapy. The most promising agents used in the treatment of RCC are biological response modifiers such as interferon (IFN)-{alpha} or interleukin (IL)-2, but even these have shown tumor response rates only in the 10% to 20% range.

Resistance to antineoplastic therapy has been explained by multiple mechanisms, including the multidrug-resistance phenotype, defects in apoptotic pathways, and various modes of immune evasion. Immune evasion may result from the lack of tumor-specific antigens in most of these tumors, defective tumor-specific antigen presentation, the production of immunosuppressive factors by the tumor, or a combination of these. Tumors secrete products that can cause substantial changes in the normal host immune response, resulting in, for example, impaired tumor surveillance activities by the host.3,4 Moreover, through causing inappropriate secretion of cytokines and growth factors, host immune cells may assist in promoting tumor growth.3,4

Prostanoids have been of interest in cancer for many years after the demonstration of high levels in various tumors.5 There is considerable evidence that prostanoids possess immunosuppressive properties.6 Although epithelial cells may produce prostaglandins, there is evidence that significant amounts of tumor prostaglandins come from tumor-associated macrophages and that these prostaglandins may be crucial in allowing certain tumors to develop.7,8 In addition to having a paracrine effect on tumor cells, tumor-associated macrophages also seem to exert autocrine effects that induce tumor-infiltrating cells to promote tumor growth.9

Another target of such prostaglandin E2 (PGE2)-derived immune suppression may be the tumor-infiltrating T cells. There is now much evidence to suggest that the nature and value of the immune response are highly dependent on the type of cytokines produced by T cells.10 According to their cytokine profile, they have been classified into types 1 and 2, respectively regulated by T-helper type 1 (Th1) and type 2 (Th2) cell subsets of the CD4+ Th population.11,12 Th1 cytokines, such as IL-2 and IFN-{gamma}, function to generate or activate cytotoxic lymphocytes and natural killer cells, both of which play a central role in tumor defense. There is growing evidence to suggest that, in various cancers, patients have impaired cell-mediated immunity caused by a switch from a Th1 to a Th2 cytokine profile.12–14

PGE2, an arachidonic acid metabolite produced by various types of cells, regulates a broad range of physiological activities, but in the immune system, its effects are suppressive on Th-1 related immune responses. PGE2 suppresses IL-2 and IFN-{gamma} production by Th1 clones, but not IL-4 and IL-5 production by Th2 clones.15 In the differentiation phase of naïve T cells, PGE2 inhibits the differentiation of Th1 and IL-12 receptor expression via cyclic adenosine monophosphate accumulation.16,17 PGE2 also suppresses lipopolysaccharide-induced IL-12 production by antigen-presenting cells, but it enhances IL-10 production.18 IL-12 and PGE2 derived from antigen-presenting cells determine IFN-{gamma} production by T cells.19 PGE2 plays an important role toward polarizing a Th2-type response in BALB/c mice, and the administration of a selective inhibitor of cyclooxygenase (COX)-2, NS-398, induces the activation of a Th1-type response.20 These and other reports, then, demonstrate a tendency for PGE2 to favor a Th2 host immune response.

The object of this study was to examine mechanisms by which RCC might evade immune detection and destruction by altering the phenotype of the immune cells with which it comes into contact. We hypothesized that RCC causes an immune-suppressive phenotype in PBMC that is characterized by increased production of PGE2, leading to a Th2 response. We further hypothesized that the selective inhibition of the COX-2 isoform would reverse this immune suppression and thus might be considered a target for future therapeutic regimens to increase the efficacy of current immunotherapy.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Cell Lines and Culture Conditions
SK-RC-7 and SK-RC-9, two well-characterized human RCC cell lines, were used. Both were the generous gift of Dr. Neil Bander (Department of Urology, Weill Medical College of Cornell University). Cell lines were cultured in minimum essential medium (MEM) supplemented with 10% heat-inactivated fetal calf serum, 200 U/mL of penicillin, 200 µg/mL of streptomycin, and 2 mM of glutamine (Gibco BRL/Life Technologies, Grand Island, NY). Cell lines were maintained at 37°C in a humidified atmosphere containing 5% CO2. To make conditioned medium (CM) from the cell lines, cells were washed with phosphate-buffered saline, treated with .05% trypsin and .53 mM of EDTA-4Na, and re-plated at a density of 1 x 106/mL in serum-free MEM. After 24 hours of culture, the supernatants were harvested and centrifuged at 1100 x g. The cell-free supernatants were then passed through a .22-µm syringe filter and aliquoted. The RCC CM was stored at -70°C until used. RCC CM samples were assayed for endotoxin by using an E-Toxate (limulus amebocyte lysate) kit (Sigma Chemical Co. St. Louis, MO). All RCC CM samples tested negative.

Peripheral Blood Mononuclear Cell Preparation
Total peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood, obtained from healthy volunteers, by using density gradient centrifugation. Peripheral venous blood samples were collected into heparin-EDTA tubes, and then the whole blood was carefully layered onto an equal volume of Histopaque (Sigma Diagnostics, Inc., St. Louis, MO) in a 15-mL conical tube. The tubes were centrifuged at 400 x g for 30 minutes at room temperature. A sterile Pasteur pipette was used to collect the mononuclear cells at the interface, which were transferred to another 15-mL tube and washed three times in phosphate-buffered saline (Gibco BRL/Life Technologies) with centrifugation at 250 x g for 10 minutes each before immediate use. Cell viability was >95% confirmed via trypan blue exclusion. Cells were plated in 96-well plates at a density of 1 x 106/mL for 24 to 72 hours in a humidified incubator at 37°C with a 5% CO2 atmosphere for determination of cytokine concentrations. Cells were cocultured with RCC CM (10%) in the presence or absence of phytohemagglutinin (PHA; Sigma Diagnostics), plus or minus the selective COX-2 inhibitor NS-398 or its vehicle (.01% dimethyl sulfoxide [DMSO]). Cell supernatants were harvested and stored at -70°C for later determination of prostaglandin and cytokine production. In all cases, the storage times were no longer than 24 to 48 hours.

Determination of PGE2 and Cytokine Concentrations in PBMC Culture Supernatants
PGE2 concentration in the supernatants of PBMC culture was determined by enzyme-linked immunosorbent assay by using commercially available kits (Cayman Chemical Co., Ann Arbor, MI). The lower threshold of sensitivity of the assay was 7.8 pg/mL. IL-6, IL-10, IFN-{gamma}, IL-2, and IL-12 concentrations were determined by enzyme-linked immunosorbent assay kits (R&D Systems, Inc., Minneapolis, MN). The sensitivity threshold of the assay for IL-10 was 7.8 pg/mL, whereas for IL-6 it was 3.12 pg/mL. The lower threshold of detection of the assay for IFN-{gamma} was 15.6 pg/mL, and that for IL-2 was 31.2 pg/mL.

PBMC Proliferation Assay
The proliferative response of PBMC in response to PHA (Sigma Diagnostics) at two doses considered mitogenic (5 and 10 µg/mL) was determined by measuring [3H]thymidine (TdR) uptake. PHA was made freshly from stock for each set of experiments. One hundred microliters of PBMC was cultured in flat-bottomed 96-well plates at a density of 1 x 106/mL in the presence and absence of RCC CM, with or without NS-398. After 72 hours of incubation, the cells were pulsed for 6 hours with 1 µCi of [3H]TdR (6.7 mCi/mmol; NEN-DuPont, Boston, MA) and harvested on glass fiber filters. [3H]TdR uptake was measured with a ß-scintillation counter.

NS-398 Preparation
NS-398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide) was obtained from Cayman Chemical Co. and prepared in DMSO. Serial dilutions were made to coculture cells with a final concentration of 10 µM of NS-398 in .01% DMSO. Previously published work from our laboratory9 has shown that this dose of NS-398 is effective in inhibiting PGE2 production by human PBMC, cocultured with melanoma CM, by >90%. Control groups were cocultured with the .01% DMSO vehicle for comparisons with NS-398–treated groups.

RNA Preparation and Reverse Transcriptase-Polymerase Chain Reaction
The RCC cell lines were plated, as described previously, in complete MEM (Gibco BRL/Life Technologies) for 72 hours in a humidified incubator at 37°C with a 5% CO2 atmosphere. The medium was then replaced with serum-free medium (Gibco BRL/Life Technologies). Twenty-four hours later, cells were treated with vehicle or phorbol 12-myristate 13-acetate (PMA; 100 ng/mL) under serum-free conditions for various durations.

Messenger RNA (mRNA) extraction was performed with an RNA extraction kit (Qiagen, Valencia, CA). Total mRNA (1 µg) was reverse-transcribed in a reverse transcriptase (RT) mastermix (50 mM of KCl, 10 mM of Tris-HCl, 5 mM of MgCl2, 1 mM of deoxynucleotide triphosphate, 2.5 mM of oligo d(T), 50 U of RT, 20 U of ribonuclease inhibitor, and nuclease-free water; all reagents were from PerkinElmer, Forster City, CA) with an initial 10-minute incubation at room temperature and then incubation at 42°C for an additional 10 minutes. The 1 µl of complementary DNA product was for COX-2 (sequence: 5'-GCCCACCCCAAACACAGTGCAC-3' as a sense primer, bases 259–280; and 5'-CTCGGAACCCCCAGTCCCTACTTG-3' as an antisense primer, bases 594–571; primer pair A) and glyceraldehyde phosphate dehydrogenase (sequence: 5'-CAGGAGCGACCCCACTAA-3' as a sense primer and 5'-GGCATCGAAGGTGGAAGAGT-3' as an antisense primer). The complementary DNA was run on a 1% agarose gel with 3 µl of ethidium bromide (10 mg/mL solution), and bands were visualized under UV illumination and recorded in an image-acquisition processing and analysis program (Eagle Eye 2; Stratagene, Cambridge, UK).

Statistical Analysis
Comparisons between groups were made with Student’s t-test. Each experimental condition was repeated at least three times, with n >= 3 per condition. A difference between groups of P < .05 was considered significant.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
COX-2 mRNA Expression After PMA Treatment
Although mRNA for COX-2 was either nondetectable (SK-RC-7) or was detected at low levels (SK-RC-9) in the nonstimulated RCC cell lines by RT-polymerase chain reaction, it was inducible by treatment with PMA (Fig. 1).



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  		FIG. 1. Induction of cyclooxygenase (COX-2) mRNA is shown in the human renal cell carcinoma (RCC) cell lines SK-RC-7 and SK-RC-9. Bands indicate levels of COX-2 expressed by the nonstimulated RCC cell lines (cultured either in serum-free media or with .01% dimethyl sulfoxide, the phorbol 12-myristate 13-acetate [PMA] vehicle), as well as the induction of COX-2 after PMA stimulation for 12 (P12) or 6 (P6) hours. GAPDH, glyceraldehyde phosphate dehydrogenase.

 
PGE2 Is Detected at Low Levels in the Supernatants of RCC Cell Lines
Low levels of PGE2, compared with those detected in nonstimulated PBMC or PBMC cocultured with RCC CM, were detectable in the supernatants of the untreated cell lines, i.e., <31.7 pg/mL. Table 1 shows the levels of PGE2 and cytokines detectable in RCC CM.


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  		TABLE 1. PGE2 and cytokine levels in renal cell carcinoma conditioned medium
 
RCC CM Induces Production of PGE2 by PBMC
Treatment of human control PBMC with 10% RCC CM induces an almost 10-fold increased production of PGE2 (Fig. 2). This was a dose-dependent effect that was seen at differing dilutions of the tumor-derived supernatants, down to as low as .2%. All subsequent experiments used a 10% concentration of RCC CM. Adding the selective COX-2 inhibitor NS-398 (10 µM) to the culture medium reversed this effect, returning mean PGE2 levels to below those of controls.



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  		FIG. 2. Mean production of prostaglandin E2 (PGE2) by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398 and CM + NS-398). *P < .0002, CM versus NM; **P < .0002, CM + NS-398 versus CM.

 
RCC CM Induces the Production of a Th2-Type Cytokine Profile in PBMC
Treatment of human control PBMC with 10% RCC CM induced a 20-fold increase in the PBMC mean production of IL-6 (Fig. 3). Mean IL-10 production was also increased from below the level of detection of the assay to in excess of 300 pg/mL (Fig. 4). These increases in production occur in the absence of any other stimulus. The addition of NS-398 to the culture medium caused a significant decrease in the measured mean levels of IL-6 while having no appreciable effect on mean levels of IL-10.



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  		FIG. 3. Mean production of interleukin (IL)-6 by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398 and CM + NS-398). *P < .003, CM versus NM; **P < .02, CM + NS-398 versus CM.

 


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  		FIG. 4. Mean production of interleukin (IL)-10 by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398 and CM + NS-398). *P < .0002, CM versus NM.

 
RCC CM Changes the Relative Balance of Th1- Versus Th2-Type Cytokine Production in PBMC
In the absence of any other stimulus, RCC CM does not induce production of IFN-{gamma}, IL-2, and IL-12 (data not shown). When PHA (10 µg/mL) was added to the culture media, RCC CM caused a significant reduction in the production of IL-12 (Fig. 5). The production of both IFN-{gamma} and IL-2 remained unchanged after treatment of the PHA-stimulated PBMC with RCC CM (Figs. 6 and 7). Treatment of the culture conditions with NS-398 did not alter the Th1-type cytokine profile (Figs. 5–7).



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  		FIG. 5. Mean production of interleukin (IL)-12 by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM 1) and SK-RC-9 (CM 2). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398, CM 1 + NS-398, and CM 2+NS-398). *P < .003, CM 1 versus NM.

 


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  		FIG. 6. Mean production of interferon (IFN)-{gamma} by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM 1) and SK-RC-9 (CM 2). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398, CM 1 + NS-398, and CM 2+NS-398).

 


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  		FIG. 7. Mean production of interleukin (IL)-2 by peripheral blood mononuclear cells (PBMC) with or without NS-398 is shown. Data represent PBMC cultured in normal media (NM) and cultured in normal media supplemented with 10% renal cell carcinoma conditioned medium from SK-RC-7 (CM). The effect of the addition of NS-398 (10 µM) to each group is represented (NM + NS-398 and CM + NS-398).

 
RCC CM Increases Proliferation of PBMC
To determine the functional significance of coculturing PBMC with RCC CM, proliferation studies were performed. The addition of 10% RCC CM to culture media resulted in significantly increased uptake of [3H]TdR by PBMC treated with PHA at doses of both 5 and 10 µg/mL. To determine the contribution of PGE2 to this phenomenon, NS-398 was added to the culture conditions. The addition of NS-398 significantly reduced cellular proliferation back toward control levels when PHA was used at a concentration of 5 µg/mL. When the higher PHA dose (10 µg/mL) was used, this reduction was not significant (Fig. 8).



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  		FIG. 8. The effects are shown of renal cell carcinoma conditioned medium (SK-RC-9) on the proliferation of peripheral blood mononuclear cells after stimulation with phytohemagglutinin (PHA) at concentrations of 5 and 10 µg/mL. Data are expressed as uptake of [3H]thymidine in counts per minute (cpm). The effect of the addition of NS-398 is shown. NM, normal medium; CM, conditioned medium. *P < .03, CM versus NM; **P < .03, CM + NS-398 versus CM for 5 µg/mL of PHA; #P < .03, CM versus NM for 10 µg/mL of PHA.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
For many years, metastatic RCC was considered an occasionally immunoresponsive malignancy. This view has been supported by observations of spontaneous remissions21 and responses to tumor-specific vaccines.22 However, in most patients with RCC, tumor progression continues to occur despite the presence of a substantial lymphoid infiltrate and clones capable of preferentially recognizing tumor antigen.23,24 Functional T cells, capable of normal activation and clonal expansion, represent a central component of an effective antitumor immune response. Studies have documented a diminished capacity of tumor-infiltrating T cells to proliferate25 or mediate cytotoxic activity.26 At least one study has demonstrated an increased expression of IL-10 mRNA in RCC infiltrating lymphocytes.27

The importance of the inducible isoform of the COX enzyme, COX-2, in cancer development and progression has been documented now in many studies. Prostaglandins seem to promote tumor proliferation by regulating cell growth,28 inhibiting apoptosis,27 promoting angiogenesis,28 and suppressing host immune surveillance of cancer cells.29 Moreover, the observation that cancers form more prostaglandins than the normal tissue from which they arise has been documented for several tumors.30–33 Increased levels of COX-2 have been detected in several tumors in humans and in experimental animal models of cancer.34–37 Messenger RNA for COX-2 was detectable at low levels in one human RCC cell line, was undetectable in the second, and was inducible by treatment with a tumor-promoting phorbol ester in both. PGE2 was detectable in the RCC CM at very low levels, compared with those produced by nonstimulated PBMC, for example. Other cancers, such as colon, breast, hypopharynx, and squamous cell carcinoma of the head and neck, produce PGE2, at least in supernatants of cell lines derived from these tumors.38 However, coculture of control PBMC with a 1/10 dilution of the RCC CM, in the absence of any other stimulus, caused a 10-fold increase in PBMC production of this important immunosuppressive mediator, compared with PBMC cocultured with normal complete medium.

Because of the cellular functional abnormalities in tumor-infiltrating lymphocytes in RCC, we sought to examine the Th cytokine profile. In the absence of other stimuli, RCC CM induced highly significant increases in production of the Th2-type cytokines IL-10 and IL-6. Levels of the Th1-type cytokines IFN-{gamma}, IL-2, and IL-12 were undetectable after coculture with RCC CM. RCC CM did not alter the production of either IFN-{gamma} or IL-2 after coculture with PBMC stimulated with PHA. However, levels of IL-12 in stimulated PBMC were significantly decreased after treatment with RCC CM.

IL-12 is known to induce CD4+ Th differentiation along the Th1 pathway39 and to enhance CD8+ T-cell maturation and activation.40,41 The antitumor effect of IL-12 has, thus, been attributed to augmentation of antigen-specific antitumor responses.42

There is an association between COX-2–derived PGE2 and PBMC cellular function, especially in relation to its regulation of Th1- and Th2-type responses.20 Our hypothesis was that the tumor secreted some soluble mediator(s) that caused the PBMC to produce PGE2, which encouraged a shift toward a Th2-type cytokine response in the PBMC in an autocrine manner. This hypothesis is all the more intriguing because of the widespread commercial availability of pharmacological agents that selectively inhibit COX-2, without many of the side effects that attend the use of traditional nonsteroidal anti-inflammatory drugs.

The addition of a selective COX-2 inhibitor, NS-398, at a dose known to completely block the enzyme restored PGE2 levels to below those of controls. Mean production of IL-6 was also significantly reduced. Mean production of IL-10 was unchanged by the addition of NS-398, as was the mean production of Th1-type cytokines.

We performed proliferation studies to determine what, if any, was the functional significance of this increased production of PGE2. RCC CM significantly increased the proliferation of PBMC after stimulation with 5 µg/mL of PHA. In addition to its effects on cells of the immune system, IFN-{gamma} is known to slow proliferation of most somatic cells, including tumor cells.42 Although the addition of RCC CM did not decrease absolute levels of IFN-{gamma}, the balance of cytokine production was skewed to favor a Th-2 type response, perhaps leading to decreased efficacy of IFN-{gamma} function and leading to increased proliferation. This effect was abrogated by selective blockade of COX-2.

These results demonstrate that RCC induces PBMC to produce significant quantities of the immunosuppressive mediator PGE2. RCC causes the cytokine profile of PBMC to be shifted in favor of a Th2 response. In contrast to other studies,25,43 we show that RCC CM increases proliferation of PBMC.

In conclusion, RCC may inhibit host cell–mediated immunity by promoting PGE2 production and a Th2-type cytokine profile. Selective COX-2 inhibition seems to have a role to play, singly or in combination, in abrogating this effect, thus perhaps making RCC more amenable to various forms of immunotherapy.


   Footnotes
 
The object of this study was to investigate the induction, by renal cell carcinoma (RCC), of an immune-suppressive phenotype in peripheral blood mononuclear cells. Conditioned media from RCC cell lines induced the production of prostaglandin E2 and a T-helper type 2 cytokine profile in peripheral blood mononuclear cells and increased their proliferation. Selective blockade of cyclooxygenase 2 abrogated some of these effects, indicating a possible therapeutic role.

Received for publication June 27, 2001. Accepted for publication November 21, 2002.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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