Characterization of a whole blood assay for quantifying myeloid-derived suppressor cells.

BACKGROUND: Myeloid-derived suppressor cells (MDSC) have been found to play an important role in limiting immune responses in cancer. Higher circulating MDSC levels have been associated with greater tumor burden, poorer response to immunotherapy, and poorer survival. Optimal measurement of MDSC levels could provide clinicians with a useful prognostic and/or management tool. METHODS: A whole blood (WB) nine color, 11 parameter flow cytometric assay was designed, utilizing fluorescently-labeled antibodies against CD45, CD3, CD19, CD20, CD56, CD16, HLA-DR, CD33, CD11b, CD14 and CD15, and BD Trucount beads for quantitation. Total MDSC were defined as CD45 + CD3-CD19-CD20-CD56-CD16-HLA-DR-CD33 + CD11b + cells, while the monocytic (M-MDSC) and polymorphonuclear subsets were defined as CD14+ or CD15+, respectively. RESULTS: A novel gating strategy was devised to eliminate granulocytes and improve consistency in gating. Several pre-analytical variables were found to significantly affect MDSC quantitation, including collection tube type and time elapsed between blood collection and testing. Total and M-MDSC levels were a mean of 63% and 73% greater, respectively, with K2EDTA compared to Na+heparin collection tubes (N = 5). In addition, time elapsed at room temperature prior to cell labeling affected MDSC quantitation; by 24 h after blood collection, total and M-MDSC levels were a mean of 26% and 57% lower compared to testing as soon as possible after collection (N = 6). Refrigeration of samples at 4 °C ameliorated time-dependent effects at both 4 and 8 h, but not 24 h after blood collection. To establish normal ranges for this assay, MDSC levels were quantified in 67 healthy subjects (30 male, 37 female) ages 20-93. No significant differences in total or M-MDSC levels were detected for ages ≤60 compared to > 60 (p = 0.5 and p = 0.8, respectively). Finally, assay results demonstrated significantly higher MDSC levels among patients with hepatocellular carcinoma (N = 55) compared to age-matched healthy controls (N = 27) for total and M-MDSC (p = 0.006 and 0.004, respectively). CONCLUSIONS: MDSC are a heterogenous group of cells, and their quantitation in WB can be affected by a number of pre-analytical variables. Consideration of these factors, and measurement using a material type that has not been manipulated, such as whole blood, is likely to yield the most accurate results.

Phase II trial of albumin-bound paclitaxel and granulocyte macrophage colony-stimulating factor as an immune modulator in recurrent platinum resistant ovarian cancer.

BACKGROUND: Granulocyte macrophage colony-stimulating factor (GM-CSF) stimulates immunity via recruitment of antigen presenting cells and tumor specific T-cell stimulation. Albumin-bound paclitaxel (nab-paclitaxel) followed by GM-CSF may enhance antitumor responses and prolong remissions in ovarian cancer. Immune phenotypes present before treatment may identify responders to chemo-immunotherapy. METHODS: Recurrent platinum-resistant ovarian, peritoneal, or fallopian tube cancer patients received nab-paclitaxel, 100mg/m2 days 1, 8, 15 followed by GM-CSF 250µg days 16-26 every 28days for 6 planned cycles. The primary endpoint was remission duration compared to immediate prior remission. Peripheral blood was evaluated by flow cytometry and interferon-γ ELISPOT. RESULTS: Twenty-one patients were enrolled. Six patients (29%) achieved a biochemical complete response and 9 (43%) a partial response for an overall response rate of 72%. Median time to progression was 4months and 10% of patients achieved longer remissions than the immediate prior regimen. Median overall survival (OS) was 16.8months. Fewer myeloid derived suppressor cells (MDSC) at enrollment significantly associated with complete response (p=0.05). T-cell responses to IGF1R-p1332-1346 (r=0.827, p=0.0003) and IGF1R-p1242-1256 (r=0.850, p=0.0001) during treatment correlated with time to progression. CONCLUSIONS: Nab-paclitaxel combined with GM-CSF demonstrated biochemical responses in a majority of patients, although responses were not sustained. This combination did not demonstrate an advantage in OS over prior studies of nab-paclitaxel monotherapy. Agents that modulate MDSC should be studied as potential adjuvants to therapy. Strategies to expand T cells recognizing tumor-associated antigens biologically significant in ovarian cancer should also continue to be investigated.

Silymarin inhibits in vitro T-cell proliferation and cytokine production in hepatitis C virus infection.

BACKGROUND & AIMS: Silymarin, an extract from the seeds of the milk thistle plant Silybum marianum, has been used for centuries for the treatment of chronic liver diseases. Despite common use by patients with hepatitis C in the United States, its clinical efficacy remains uncertain. The goal of this study was to determine whether silymarin has in vitro effects on immune function that might have implications for its potential effect on hepatitis C virus (HCV)-induced liver disease. METHODS: Freshly isolated peripheral blood mononuclear cells (PBMC) and T cells from HCV-infected and uninfected subjects were tested in vitro for responses to nonspecific and antigenic stimulation in the presence and absence of a standardized preparation of silymarin (MK001). RESULTS: Minimal MK001 toxicity on PBMC was found at concentrations between 5 and 40 microg/mL. MK001 dose dependently inhibited the proliferation and secretion of tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-2 by PBMC stimulated with anti-CD3. In addition, MK001 inhibited proliferation by CD4(+) T cells to HCV, Candida, and tetanus protein antigens and by HLA-A2/HCV 1406-1415-specific CD8(+) T cells to allogeneic stimulation. MK001 inhibited T-cell TNF-alpha and IFN-gamma cytokine secretion to tetanus and Candida protein antigens. Finally, MK001 inhibited nuclear factor-kappaB transcriptional activation after T-cell receptor-mediated stimulation of Jurkat T cells, consistent with its ability to inhibit Jurkat T-cell proliferation and secretion of IL-2. CONCLUSIONS: Silymarin's ability to inhibit the proliferation and proinflammatory cytokine secretion of T cells, combined with its previously described antiviral effect, suggests a possible mechanism of action that could lead to clinical benefit during HCV infection.

Interpretation of positive transcription-mediated amplification test results from polymerase chain reaction-negative samples obtained after treatment of chronic hepatitis C.

UNLABELLED: The Siemens VERSANT transcription-mediated amplification (TMA) assay is extremely sensitive for the detection of hepatitis C virus (HCV) RNA in serum. Eleven of 180 subjects in the Hepatitis C Antiviral Long-term Treatment against Cirrhosis (HALT-C) Trial who achieved polymerase chain reaction (PCR)-defined sustained virological response (SVR) at week 72 also had TMA-positive results from the same blood draw; six were positive on repeat testing. We report the follow-up on these 11 patients, and the reproducibility of TMA test results from PCR-negative samples in relationship to antiviral treatment outcome. Peginterferon and ribavirin treatment was initiated in 1145 prior interferon nonresponders with advanced hepatic fibrosis. Treatment was continued for 48 weeks if patients had undetectable HCV RNA by PCR at treatment week 20. Frozen serum samples from weeks 12, 20, 24, 48, and 72 were subsequently tested by TMA. Nine of the 11 patients returned for testing (median, 30 months after the week 72 visit), and all had undetectable HCV RNA by TMA and PCR. Among 759 PCR-negative samples obtained during treatment that were tested twice by TMA, 17% overall exhibited consistently positive results, and 21% exhibited inconsistently positive results. SVR was more likely if TMA was consistently negative than if consistently or inconsistently positive. With continued treatment, patients with inconsistently positive TMA results were more likely to become TMA-negative than TMA-positive (P < 0.0001). CONCLUSION: In PCR-negative samples, positive TMA results may indicate the presence of low levels of HCV RNA. However, because patients with positive TMA results may achieve SVR, management decisions during therapy should not be based on a single positive TMA test result.