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Molecular Oncology, Markers, Clinical Correlates |
1 Department of Surgery, College of Medicine, 2 Comprehensive Cancer Center, The Ohio State University, Columbus, Ohio, 3 Division of Medical Oncology, Department of Internal Medicine, College of Medicine, and the 4 Department of Psychology
| ABSTRACT |
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Experimental Design: Immune levels of 227 stage II/III breast cancer patients were measured immediately after surgery prior to chemotherapy and again 12 months later when all chemotherapies had been completed. T-cell blastogenesis and natural killer (NK) cell lysis levels of patients receiving taxanes (n = 55) were compared with levels of patients not receiving taxanes (n = 172).
Results: Regression analyses were conducted. The administration of taxane as part of combination chemotherapy predicted increased T-cell blastogenesis and NK cell cytotoxicity after the conclusion of all chemotherapies. For the Taxane group, average phytohemagglutinin-induced blastogenesis was 37% higher and NK cell cytotoxicity was 39% higher than the values for the No-Taxane group.
Conclusions: Data from group comparisons with appropriate controls in a sizable clinical sample contravene traditional wisdom that taxanes suppress patients immune cell functions. Problems in generalizing direct-contact laboratory models to the field of cancer treatment are highlighted.
| INTRODUCTION |
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In general, administration of cytotoxic chemotherapy is characterized by bone marrow suppression that manifests as reduced numbers of peripheral blood immune effectors. These effects are reversible and do not lead to permanent alterations in immune function. The taxanes appear to be no different in this regard. However, there are numerous reports that these drugs may exert unique immunomodulatory effects on immune cells, some of which may lead to activation of innate and specific immune effectors (4)
. Paclitaxel is able to bind to macrophages and stimulate responses that are similar to those induced by lipopolysaccharide, one of the major components of bacterial endotoxin. Stimulation of macrophages with paclitaxel leads to the induction of important pathways involved in the elimination of microbes (e.g., inducible nitric oxide synthesis) as well as the production of proinflammatory cytokines such as interleukin (IL)-1ß, tumor necrosis factor
, and IL-8 (5)
. Furthermore, paclitaxel-induced production of IL-12 by tumor-associated macrophages may be important in alleviating the T-cell suppression that is observed in the tumor-bearing host (6)
. In vitro studies of the direct effects of paclitaxel on the cytotoxic activity of T cells and natural killer (NK) cells have generally revealed an inhibitory effect, but some studies suggest a more complex effect of taxanes on the function of these lymphocyte populations in vivo. Mason et al. (7)
reported that 40% of murine mammary carcinomas responding to docetaxel showed heavy infiltration with T-helper lymphocytes and NK cells. Similarly, a clinical study indicated that the development of a lymphocytic infiltrate after chemotherapy correlated with a positive clinical response to neoadjuvant paclitaxel therapy (8)
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Few studies have systematically examined the overall immune effects of taxane administration in the setting of chemotherapy for breast carcinoma, and none to date have examined the long-term effects of these drugs in homogeneous populations. Tong et al. (9) studied lymphocyte subsets, levels of circulating cytokines, T-cell mitogenic function, and NK cell function in 10 patients with advanced cancer who received paclitaxel or docetaxel. They found that patients exhibiting a partial or complete response to therapy demonstrated higher than normal CD4:CD8 T-cell ratios and increased T-cell proliferation in response to phytohemagglutinin (PHA) at 4 weeks posttreatment. T-cell activation during the course of paclitaxel combination chemotherapy has also been described (10) . These findings suggest that taxanes may have complex and long-lasting effects on host immunity that could possibly impact the ability of a cancer patient to respond to infectious complications and the recurrence of malignant disease.
We have conducted a randomized Phase III clinical trial in patients with stage II and III breast cancer, investigating the effects of a stress reduction intervention on patient behavior and immune function. As a part of this study, patients underwent an extensive analysis of NK cell and T-cell function immediately after enrollment (i.e., shortly before the start of chemotherapy) and at regular intervals thereafter. During the accrual period, a taxane-containing adjuvant chemotherapy regimen came into widespread usage in patients with nodal disease. We used this change as an opportunity to identify two patient groups that differed in their exposure to taxane-based chemotherapy and to test for differential immune outcomes.
| PATIENTS AND METHODS |
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For the present study (see Fig. 1
), two groups (Taxane versus No-Taxane) were subsequently defined on the basis of whether or not patients had received any taxane (either paclitaxel or docetaxel) as part of their adjuvant treatment. The study design compares these two groups using two observations in time, with the initial assessment prior to the start of chemotherapy and a follow-up assessment at 12 months, after patients had completed adjuvant treatment.
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Numeration of Total T-lymphocyte Counts, T-Cell Subsets, and NK Cells.
PBLs were labeled with florescent-conjugated monoclonal antibodies specific for the following cell surface markers: total T lymphocytes (CD3, FITC), T4 subsets (CD4, rhodamine), T8 subset (CD8, FITC), and NK cells (CD56, rhodamine). Monoclonal antibodies were purchased from Beckman Coulter Corp. Briefly, an aliquot of PBLs (2.5 x 106 cells) was treated with Erythrocyte Lysis Buffer (154 mM NH4Cl, 10 mM KHCO3, 0.082 mM EDTA-Na), resuspended in Dulbeccos phosphate-buffered saline, and centrifuged for 5 min at 3300 rpm. Cells (0.5 x 106) were incubated with the appropriate monoclonal antibodies for 15 min in the dark on ice. After the incubation, the labeled cells were washed with Dulbeccos phosphate-buffered saline and were fixed with 2% formaldehyde (made using 10% ultrapure formaldehyde). Dual-labeled IgG was used to determine nonspecific immunofluorescence binding. Samples were analyzed with a Coulter EPICS XL-MCL flow cytometer.
NK Cell Cytotoxicity.
Briefly, PBLs were resuspended in complete medium at a density of 2.5 x 106 cells/ml and were seeded into 96-well V-bottomed microtiter plates in a volume sufficient to provide an E:T cell ratio of 100:1, 50:1, 25:1, 12.5:1, 6.25:1, or 3.13:1 (triplicate wells). Complete medium was added to each well to give a total volume of 200 µl. The NK-sensitive human myeloid K562 cell line was used as the target in a 51Cr assay (12
, 13)
. K562 cells were harvested from culture, labeled with 51Cr, and washed. Then, 5 x 103 K562 target cells were added to each well in a volume of 50 µl. Plates were centrifuged at 300 x g for 5 min and were incubated for 5 h in an atmosphere of 5% CO2 at 37°C. After this incubation, the plates were again centrifuged at 300 x g for 5 min, and 100 µl of supernatant were harvested and counted using a Beckman 5500 gamma counter. Minimum and maximum 51Cr release was determined using target cells that had been incubated in complete medium or 5% SDS detergent solution, respectively. Cytotoxicity was calculated using the following equation (12
, 13)
:
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Blastogenic Response to PHA.
Isolated PBLs, resuspended in supplemental RPMI without phenol red, were seeded in triplicate at 0.5 x 105 cells/well in the presence of PHA (2.5, 5.0, and 10.0 µg/ml) in sterile 96-well flat-bottomed plate and were incubated for 6872 h at 37°C, in an atmosphere of 5% CO2. Wells were pulsed for the final 4 h with MTS, i.e., 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4sulfophenyl)-2H-tetrazolium, inner salt (Promega Corp., Madison, WI) and phenazine methosulfate (PMS), an electron coupling reagent, to measure proliferative response. The MTS assay is a nonradioactive calorimetric procedure that labels metabolically active cells via reduction of a colored substrate. The amount of proliferation was determined via absorbance readings of the suspension in the well compared with cells and media alone, using an HTS7000 Bioassay microplate reader (Perkin-Elmer) at a determination wavelength of 492 nm and a reference wavelength of 690 nm, as has been noted previously (14
, 15)
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Statistics
Accrual and Retention.
The overall accrual rate was 52% and retention at 12 months, excluding subjects who had recurrent disease or died, was 85%. The accrual rate is comparable and retention is higher than that typically found in randomized clinical trials of behavioral interventions (16
, 17)
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Analysis Plan.
Descriptive analyses compared the Taxane and No-Taxane groups using
2 or ANOVA as appropriate. Patients baseline characteristics and other variables that might affect 12-month immune outcomes were also examined. These included immune level at initial assessment, age, study arm (intervention versus assessment), menopausal status, disease characteristics (hormone receptor status, number of nodes), treatment (surgery type, receipt of radiation, hormonal therapy recommended, receipt of hormonal therapy at 12 months, days elapsed at 12 months because of completion of chemotherapy/radiation), and cell counts (e.g., NK cell counts for NK cell cytotoxicity, T-cell counts for T-cell blastogenesis). Variables that were significantly correlated with an immune outcome were identified as control variables for the multiple regression analyses described below.
Nested ordinary least squares linear regression models were used for each of the two functional immune outcomes, NK cell cytotoxicity and the PBL blastogenic response to PHA, at 12 months. NK cell cytotoxicity was expressed as the mean of standardized scores (i.e., Z-scores, differences in SD units from the overall mean) from three E:T ratios (12.5:1, 6.25:1, and 3.13:1). These ratios were selected based on previous observations in the investigators laboratory that they were the most sensitive to chemotherapy effects. PHA blastogenesis was expressed as the mean of standardized scores from the three dilutions (2.5, 5.0, and 10.0 µg/ml). The first step in each nested linear regression procedure entered the control variables as predictors. The second step added a binary variable representing the administration of taxane (0 = no, 1 = yes) as a predictor. This second step tests whether taxane explains significant variance (P < 0.05) in an immune outcome beyond that explained by control variables.
Before conducting the ordinary least squares regression analyses, we checked major assumptions of this model: error variance normality and constancy (homoscedasticity) and the appropriateness of the linear model. Residual plots and formal tests indicated that the above assumptions were not violated. Analyses detected outliers, but follow-up analyses indicated that the outliers did not significantly influence the fit of the regression function. In sum, linear ordinary least squares regression was an appropriate model for the present analyses.
| RESULTS |
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Table 2
provides mean and SD values of the immune measures at initial (baseline) and at 12 months. Across all of the immune variables, there were no significant differences between the groups at the initial assessment (all Ps > 0.06). However, the groups differed significantly at 12 months. As shown in Fig. 2
, patients in the Taxane group exhibited greater 12-month PHA-induced blastogenesis and NK cell cytotoxicity than patients in the No-Taxane group across the dilutions and E:T ratios. These differences were generally significant for the NK cytotoxicity assays (P = 0.004, 0.0003, and 0.0003, for the 12.5:1, 6.25:1, and 3.125:1 E:T ratios, respectively) as well as for the PHA blastogenesis assays (P = 0.071, 0.004, and 0.001 for the 10, 5, and 2.5 µg/ml dilutions, respectively). Specifically, average PHA blastogenesis levels at the 10, 5, and 2.5 µg/ml dilutions were 25, 41, and 45% (mean, 37%) higher in the Taxane group than in the No-Taxane group. Similarly, NK cell cytotoxicity levels were 27, 39, and 50% (mean, 39%) higher in the Taxane group for the 12.5:1, 6.25:1, and 3.125:1 E:T ratios, respectively.
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As shown in Table 3
, the Controls-Only model explained 13% of the variance in PHA blastogenesis at 12 months. Consideration of the Taxane group in the second step significantly improved the model (P = 0.007). Taxane administration predicted PHA blastogenesis even after controlling for baseline PHA blastogenesis values and other variables such as extent of surgery and study arm. Although study arm was a significant predictor of greater PHA blastogenesis, follow-up analyses indicated that the impact was equivalent in the Taxane and No-Taxane groups. Graphs A through C in Fig. 2
provide a pictorial representation of changes in blastogenesis over time per dilution.
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| DISCUSSION |
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Previous work suggests that the taxanes exert primarily inhibitory effects on immune effectors of the lymphocyte compartment. Indeed, short-term exposure of lymphocytes to Taxol leads to significant inhibition of the T-cell proliferative response. In one set of experiments, splenic CD4+ T cells from tumor-bearing mice were exposed to Taxol for 4 h and then were tested for their proliferative response to Concanavalin A. Importantly, there was a significant reduction in the T-cell response to this mitogen (18)
. This effect was not due to a direct toxic effect, because the lymphocytes remained viable for the duration of the assay. Similarly, both paclitaxel and docetaxel cause a significant suppression of lymphocyte activation and growth in response to stimulatory concentrations of IL-2 [e.g., 10 and 50 µg/ml (19)
]. In vitro studies of T-cell and NK cell cytotoxic activity after taxane exposure reveal an overall inhibitory effect for this class of agents (20)
. The most commonly documented immune response in patients receiving paclitaxel is the development of myelosuppression in the weeks after the administration of this cytotoxic agent (21)
. However, an analysis of leukocyte subsets in patients receiving taxane therapy revealed no alterations in T-cell or B-cell frequency or CD4:CD8 ratio (9)
. Other reports purporting a stimulatory effect of paclitaxel have focused on its ability to activate immune effectors such as monocytes/macrophages that have receptors for lipopolysaccharides and other foreign compounds that can cross-react with the paclitaxel molecule (22)
. These effects are limited primarily to monocyte production of pro-inflammatory cytokines such as tumor necrosis factor
, IL-1ß, and inducible nitric oxide synthesis (5)
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There appears to be precedence for our observations. Krainer et al. (23) examined 15 patients who had received BEP chemotherapy (bleomycin, etoposide, and cisplatin) for testicular cancer for evidence of immune modulation over a 1-year period. They examined the prevalence of CD3+, CD4+, and CD8+ T cells in these patients as well as the blastogenic response to a standard panel of mitogens. Interestingly, this group found that polychemotherapy led to a significant increase in the T-cell mitogenic response at 1 year, but not at the 5-year time point, despite no change in the prevalence of CD3+ lymphocytes. Thus, the positive effects of chemotherapy on immune functioning may not be limited to Taxol-based regimens.
As of this writing, there is no clear mechanism for the long-term-immunostimulatory effects of taxane that were observed in the present study. A careful analysis of T-cell subpopulations in our study patients revealed no changes in the overall prevalence of CD4+ helper T cells or CD8+ cytotoxic T cells. Neither did NK cell numbers appear to be affected in the long term by taxane administration. Therefore, the positive effects of taxane on T-cell proliferation and NK cytolysis did not appear to be simply the result of increased numbers of effector cells. It is possible that the effects of taxane on T cells and NK cells in this study reflect an alteration in the makeup of these populations (24) . It is also possible that the changes induced in the T-cell and NK cell populations are quite subtle and not easily detected with the immune assays used in this study. Indeed, we have determined that stress and anxiety after the breast cancer diagnosis can lead to altered expression of NK cell adhesion molecules and killer-inhibitory receptors that are not normally measured in clinical studies of immune function (25) . Alternatively, taxane chemotherapy might have caused changes in the peripheral and/or bone marrow microenvironment that led to alterations in the maturation rate or activation state of T cells and NK cells. Importantly, these two cell populations exhibit a number of similarities at the level of cell surface adhesion molecules and signaling intermediates (26) . Hence, one might expect any type of chemotherapeutic effect to have similar influences on both cell compartments.
The functional significance of the observed immune changes is not yet known, and clarification of this issue will require further follow-up in the two patient subsets. Of prime concern is the potential for cancer recurrence in patients who have experienced alterations in the functional capacity of their T-cell and NK cell compartments. Whether patients receiving taxane will exhibit fewer tumor recurrences depends on the contribution of the measured parameters to the elimination of malignant cells. These issues have not yet been resolved in large prospective clinical trials, and it is not clear whether we currently possess effective measures of antitumor immunity as they relate to the postoperative patient. Certainly, one would predict that robust T-cell blastogenesis would favor the development of an antitumor immune response, and it is even possible that patients might respond more favorably to micrometastatic autologous tumor cells after taxane chemotherapy. Of note, one study has shown a correlation between the development of tumor-infiltrating lymphocytes in breast cancer metastases after neoadjuvant paclitaxel chemotherapy and complete clinical response (27) .
In summary, group comparisons with appropriate controls in a sizable cancer sample contravene conventional wisdom that taxane chemotherapy leads to a suppression of patients immune cell function. Follow-up will be required to determine any effect of the immune alterations on immune surveillance and disease recurrence. Additional immune analyses are under way to determine the scope and nature of the changes that have occurred in the T-cell and NK cell populations.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: William E. Carson III, Department of Surgery, College of Medicine, The Ohio State University, N708 Doan Hall, 410 W. 10th Avenue, Columbus, OH 43210-1222. Phone: (614) 293-6306; Fax: (614) 688-4366; E-mail: Carson-1{at}medctr.osu.edu
Received 7/10/03; revised 2/ 6/04; accepted 2/ 6/04.
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