Mononuclear Cells Of Cancer Patients Research Articles

THE EFFECT OF 1(10)Β-EPOXY-5,7Α,6Β(Н)-GUAI-3(4),11(13)-DIENE-6,12-OLIDE ON THE IMMUNE SYSTEM OF CANCER PATIENTS

The article discusses the effect of the plant immunomodulator 1(10)β-epoxy-5,7α,6β(Н)-guai-3(4),11(13)-diene-6,12-olide (hereinafter referred to as epoxyguaianolide) on the immune system of the cancer patients. According to the results of randomized clinical trials, the immunomodulatory effect of epoxyguaianolide was confirmed and its positive effect on the indicators of the LPO-AOD system and oxidative modification of proteins was determined. The paper shows the importance of immunophenotypic analysis of peripheral blood mononuclear cells of cancer patients. The immunomodulatory effect of epoxyguaianolide was determined, which manifests itself as a predominant effect on the T-cell link of immunity. Epoxyguaianolide has the ability to correct the immunosuppressive effect of cytostatics. Thus, the results of studies of epoxyguaianolide indicate the potential for the development of a new drug based on it with a pronounced cytostatic effect, thereby stimulating the immune system.

Identification and characterization of agonist epitopes of the MUC1-C oncoprotein

The MUC1 tumor-associated antigen is overexpressed in the majority of human carcinomas and several hematologic malignancies. Much attention has been paid to the hypoglycosylated variable number of tandem repeats (VNTR) region of the N-terminus of MUC1 as a vaccine target, and recombinant viral vector vaccines are also being evaluated that express the entire MUC1 transgene. While previous studies have described MUC1 as a tumor-associated tissue differentiation antigen, studies have now determined that the C-terminus of MUC1 (MUC1-C) is an oncoprotein, and its expression is an indication of poor prognosis in numerous tumor types. We report here the identification of nine potential CD8⁺ cytotoxic T lymphocyte epitopes of MUC1, seven in the C-terminus and two in the VNTR region, and have identified enhancer agonist peptides for each of these epitopes. These epitopes span HLA-A2, HLA-A3, and HLA-A24 major histocompatibility complex (MHC) class I alleles, which encompass the majority of the population. The agonist peptides, compared to the native peptides, more efficiently (a) generate T-cell lines from the peripheral blood mononuclear cells of cancer patients, (b) enhance the production of IFN-γ by peptide-activated human T cells, and (c) lyse human tumor cell targets in an MHC-restricted manner. The agonist epitopes described here can be incorporated into various vaccine platforms and for the ex vivo generation of human T cells. These studies provide the rationale for the T-cell-mediated targeting of the oncogenic MUC1-C, which has been shown to be an important factor in both drug resistance and poor prognosis for numerous tumor types.

LINE-1 methylation in the peripheral blood mononuclear cells of cancer patients

BackgroundRecently, we classified LINE-1 loci according to their methylation statuses and found that the percentage of hypomethylated LINE-1 loci (uCuC) can differentiate between the peripheral blood mononuclear cells (PBMCs) of oral cancer patients and normal controls with a higher specificity and sensitivity than overall methylation levels. Here, we evaluated the LINE-1 methylation levels and patterns in PBMCs from patients with cancers of the nasopharynx, lung, liver, bile duct, breast and colon. MethodsCombined Bisulfite Restriction Analysis (COBRA) of LINE-1 loci was performed to examine the LINE-1 methylation statuses of PBMCs from 216 cancer patients with 6 different types of cancer compared with 144 normal controls. ResultsOnly colorectal and nasopharyngeal cancer samples were found to have lower levels of overall LINE-1 methylation compared with normal controls (p<0.0001 and p=0.0022). However, %uCuC in cancers of the colon, liver, lung and nasopharynx was significantly higher compared with normal controls (p<0.0001, p<0.0001, p=0.01 and p=0.001, respectively). Furthermore, ROC curve analyses of these four cancer types also demonstrated the potential of %uCuC as a biomarker for cancer diagnosis. ConclusionChanges in the levels and patterns of genome-wide methylation of PBMCs are associated with cancer risk. For LINE-1, %uCuC is a more effective tumour marker for determining cancer risk than overall methylation levels.

Abstract 1345: Interleukin-4 promotes cancer cell proliferation through the activation of the p38-mitotic activated protein kinase (MAPK) signaling pathway

Abstract Introduction There is increasing data supporting the idea that tumor cells take advantage of the signaling molecules of the immune system to proliferate, survive, and invade other tissues. The cytokine, interleukin (IL)-4 plays a critical role in the regulation of immune responses and has been observed at high levels in the tumor microenvironment and in the peripheral blood mononuclear cells of cancer patients, correlating with the grade of malignancy. IL-4 has been associated with increased cell survival in tumor development; however, its effect on cancer cell proliferation has not been thoroughly explored. Here we investigated the signaling pathways activated by IL-4 that induce cancer cell proliferation. Experimental Procedures Prostate cancer PC3 cells, breast cancer MDA-MB-231 and salivary gland carcinoma A-253 cells were synchronized by serum starvation and plated in media containing 0.5% FBS alone or in combination with IL-4 (100 ng/ml). Proliferation was assessed using the WST-1 cell viability assay (Roche) and the activated pathways were analyzed with phosphospecific antibodies. Proliferation was also evaluated in PC3 cells treated with MAP kinase kinase (MEK1/2) inhibitor, U0126 (10 µM) or p38 MAPK-specific inhibitor, SB 220025 (0.5 µM) (Calbiochem), alone or in the presence of IL-4. Results A time course analysis of cancer cells (PC3, MDA-MB-231 and A-253) stimulated with IL-4 demonstrated an enhanced cell proliferation compared to the untreated cells. To analyze the signaling pathways induced by IL-4 that caused proliferation, PC3 and A253 cells were stimulated with IL-4 and subsequently evaluated by Western blot for the activation of common signaling molecules. It was found that IL-4 significantly enhanced the activation of MAPK/Erk1/2 and the p38 MAPK pathways in both cell types. In contrast, IL-4-dependent activation of Akt signaling was only induced in the PC3 cells. It was further demonstrated that the specific p38-MAPK inhibitor significantly affected the IL-4 induced cell proliferation in PC3 cells. Meanwhile, the MEK1/2 inhibitor (U0126) did not show a significant effect on the proliferation of IL-4 stimulated cells. Inhibition of phospho-p38 by using SB 220025 (0.5 µM) was confirmed by Western Blot. Conclusions Increased levels of IL-4 and phosphorylated p38 have been correlated with malignancy in several cancer types. Our results suggest that hyperactivation of p38-MAPK by IL-4 induces a potent proliferation response in various cancer cells from different origins. In addition to its important role in cancer cell survival, we propose that IL-4 enhances cell proliferation via potent activation of p38-MAPK, which is essential in the neoplastic progression. Currently, investigations are underway to further elucidate the interaction of the p38-MAPK signaling with other pathways that could play a critical role in this mechanism. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1345.

MUC4 as a diagnostic marker in cancer

Mucins are high molecular mass glycoproteins whose role in diagnosis, prognosis and therapy is being increasingly recognized owing to their altered expression in a variety of carcinomas. MUC4, a membrane-bound mucin encoded by a gene located on chromosome locus 3q29, is aberrantly expressed in several cancers including those of the bile duct, breast, colon, esophagus, ovary, lung, prostate, stomach and pancreas. This review considers the potential use of the MUC4 expression pattern in the diagnosis and prognosis of various cancers. MUC4 expression is a specific marker of epithelial tumors and its expression correlates positively with the degree of differentiation in several cancers. Importantly, MUC4 has emerged as a specific marker of dysplasia, being expressed in the earliest dysplastic lesions preceding several malignancies, including lethal pancreatic cancer. The presence of MUC4-specific antibodies in the serum and of the transcript in peripheral blood mononuclear cells of cancer patients raises the possibility of it emerging as a new diagnostic biomarker for bedside application in high-risk individuals and those with established cancer.

New Peptide Vaccine Candidates for Epithelial Cancer Patients With HLA-A3 Supertype Alleles

We previously identified 2 cancer-associated antigens, immediate early response gene X-1 (IEX) and small GTPase (Ran), and their 5 epitopes using human leukocyte antigen (HLA)-A33-restricted and tumor-infiltrating T cells from a colon cancer patient. In this study, we examined whether or not these peptides can induce cytotoxic T lymphocytes (CTLs) in HLA-A11+ or HLA-A31+ epithelial cancer patients because the HLA-A11, HLA-A31, and HLA-A33 alleles share binding motifs as an HLA-A3 supertype family, which is widely distributed in many ethnic populations. Among them, the 2 peptides, IEX 47-56 and IEX 61-69, induced peptide-specific CTLs from peripheral blood mononuclear cells of cancer patients with the HLA-A11 and HLA-A31 alleles more efficiently than the other 3 peptides. Antibody blocking and cold inhibition experiments revealed that the cytotoxicity of peptide-induced CTLs against cancer cells was attributable to peptide-specific and CD8+ T cells. Together with our previous findings, these results indicate that the 2 IEX peptides could be appropriate vaccine candidates for HLA-A11, HLA-A31, and HLA-A33 positive epithelial cancer patients. This information could expand the chance of a peptide-based cancer vaccine for epithelial cancer patients of many ethnic populations.

Altered expression profiles of clock genes hPer1 and hPer2 in peripheral blood mononuclear cells of cancer patients undergoing surgery

Patients undergoing surgery often develop symptoms of circadian rhythm disorders such as insomnia or delirium. However, the effect of surgery on the biological clock remains unknown. The present study examines the expression of clock genes in peripheral blood mononuclear cells (PBMCs) and measures plasma hormone concentrations in patients with esophageal cancer and early gastric cancer who underwent surgery. Six blood samples per day were collected from 9 patients with esophageal cancer before and after esophagectomy and from 9 patients with early gastric cancer before and after laparoscopy-assisted distal gastrectomy (LADG). The expression profiles of hPer1 and hPer2 mRNAs in PBMCs were determined by real-time RT-PCR. Plasma melatonin and cortisol concentrations were measured by radioimmunoassay. Plasma melatonin levels decreased in both groups throughout the day and plasma cortisol levels changed after surgery. The acrophase of clock gene expression was altered after surgery as follows: hPer1, from 6:19 ± 1:50 to 13:59 ± 0:59 ( p = 0.0003) and from 7:47 ± 1:27 to 12:33 ± 1:30 ( p = 0.0043) and hPer2, from 5:01 ± 2:59 to 19:30 ± 2:15 ( p < 0.0001) and from 6:49 ± 1:59 to 13:39 ± 3:06 ( p = 0.0171) in patients with esophageal and early gastric cancer, respectively. The post-operative phase change of hPer2 was more prominent after esophagectomy than after LADG. Our results suggest that surgical stress affects the peripheral clock as well as endogenous hormones in humans.

HER2/neu-derived peptides recognized by both cellular and humoral immune systems in HLA-A2+ cancer patients

HER2/neu is one of the most appropriate target antigens for anti-cancer therapy because of its expression in various types of epithelial cancer. HER2/neu can also be a target for both cellular and humoral immune responses. In this study, we attempted to identify HER2/neu-derived peptides, which are able to be recognized by both humoral and cellular immune systems in HLA-A2+ cancer patients. Among 12 HER2/neu-derived peptides having the HLA-A2 binding motifs, immunoglobulin G reactive to each of 7 HER2/neu peptides was detected in the plasma of >50% of cancer patients. Among these 7 peptides, 3 including HER2/neu 444-452, HER2/neu 466-474, and HER2/neu 484-492, effectively induced peptide-specific and HLA-A2-restricted cytotoxic T lymphocyte activity from peripheral blood mononuclear cells of cancer patients, regardless of different HLA-A2 subtypes. Experiments using blocking antibodies and cold inhibition targets revealed that the cytotoxicity against HER2/neu-expressing HLA-A2+ tumor cells was peptide-specific and CD8+ T cell-dependent. Overall, these results indicate that these 3 HER2/neu-derived peptides are efficiently recognized by both the humoral and cellular immune systems, and therefore could be useful for peptide-based immunotherapy for HLA-A2+ patients with various types of epithelial cancer.

Identification of two novel tumor-associated antigens recognized by HLA-B46-restricted cytotoxic T lymphocytes

The objective of this study was to identify novel genes and peptides capable of inducing tumor-reactive cytotoxic T lymphocytes (CTLs) in cancer patients with an HLA-B46 allele, which is preferentially expressed in Asians. We show that two genes encoding splicing factor (SF) 2 and inosine triphosphate pyrophosphatase (ITPA) have epitopes recognized by HLA-B46-restricted and tumor cell-reactive CTL lines established from tumor-infiltrating lymphocytes of colon cancer. The SF2 is essential for constitutive pre-mRNA splicing, while the enzyme ITPA controls nucleotide levels. The mRNA expression levels of these genes were higher in tumor cells than those in normal tissues. Five peptides, three from SF2 and two from ITPA, had the ability to induce HLA-B46-restricted and peptide-specific CTLs reactive to tumor cells in peripheral blood mononuclear cells of cancer patients. These results may provide new information for better understanding of host-tumor interaction at the molecular level and the development of peptide-based immunotherapy for HLA-B46+ cancer patients.

Gross elevation of TT virus genome load in the peripheral blood mononuclear cells of cancer patients.

TT virus (TTV) is a recently described circular DNA virus of about 3.8 kb, which is related to the circoviridae viruses. It is commonly detected in healthy subjects and no association with any specific disease has been established. TTV was initially thought to be hepatotropic, but subsequent reports have shown that it is detectable in other tissues, including kidney, prostate, mammary gland, brain, bone marrow, and peripheral blood mononuclear cells. Plasma samples from cancer patients and healthy subjects were tested for the presence or absence of TTV by heminested polymerase chain reaction (PCR). We also developed a quantitative competitive PCR (QC-PCR) assay for TTV that permits accurate measurement of TTV DNA load. Using this assay, the TTV genome load in peripheral blood mononuclear cells (PBMCs) of healthy control subjects (n = 50) and patients with various types of cancer (n = 148), including breast cancer, non-Hodgkin's lymphoma, colon cancer, hepatocellular carcinoma, nasopharyngeal carcinoma, and other cancers, was measured. TTV DNA was detected in 69 of 100 plasma samples (69%) of cancer patients tested and in 39 of 100 plasma samples (39%) randomly selected from 1000 plasma samples of blood donors (p < 0.05). TTV DNA was detectable in the PBMCs of 99% of the cancer patients and 86% of the controls. However, the median virus load was more than 100-fold higher in the cancer patients (3599 copies/100,000 cells) than among the controls (30 copies/100,000 cells; p < 0.0001). There was no significant difference in TTV load among the different cancer types. Using a cutoff value of >250 copies per 100,000 PBMCs, 93.2% of cancer patients were "positive" compared to only 4% of healthy control subjects. Almost all the cancer patients have TTV infection and their TTV genome load in PBMCs is significantly higher than that in control subjects. It remains to be elucidated whether such findings are specific to cancer patients or occur in all seriously ill subjects.

Identification of SART3-derived peptides capable of inducing HLA-A2-restricted and tumor-specific CTLs in cancer patients with different HLA-A2 subtypes.

We recently identified the SART3 antigen encoding shared tumor epitopes recognized by HLA-A2402-restricted and tumor-specific CTLs. Our study investigated whether the SART3 antigen encodes peptides recognized by the HLA-A2-restricted CTLs. The HLA-A2-restricted and tumor-specific CTL line recognized COS-7 cells co-transfected with the SART3 gene and either HLA-A0201, -A0206 or -A0207 cDNA but not those co-transfected with the SART3 gene and HLA-A2402 or -A2601 cDNA. The 2 SART3 peptides at positions 302 to 310 and 309 to 317 possessed the ability to induce HLA-A2-restricted and tumor-specific CTLs from peripheral blood mononuclear cells of cancer patients with various histological types and different HLA-A2 subtypes. Therefore, these 2 peptides could be useful for specific immunotherapy of a relatively large number of HLA-A2(+) cancer patients.

Medroxyprogesterone acetate and megestrol acetate reduce cisplatin-induced serotonin release from human peripheral blood mononuclear cells of cancer patients.

In the present study we evaluated the ability of either medroxyprogesterone acetate (MPA) or megestrol acetate (MA) to reduce cisplatin (CDDP)-induced serotonin (5-HT) release from peripheral blood mononuclear cells (PBMC) of cancer patients. Sixteen patients with cancer of different sites, all in advanced stage of disease, were studied (10 for MPA and 6 for MA). The levels of 5-HT in culture supernatants of PBMC stimulated with CDDP were higher than controls (100 nM vs 51 for MPA study and 123 vs 64 for MA study) and were in the same range of PHA-stimulated PBMC. The addition into cultures of MPA or MA was able to significantly reduce the CDDP-induced production of 5-HT (62 nM for MPA, and 46 for MA study). MPA as well as MA are able to inhibit 5-HT production and/or release by CDDP-stimulated PBMC of cancer patients: this finding to our knowledge has not been previously reported. The concentrations of MPA and MA used in cultures were in the same range as those raised in plasma following the clinical administration of daily doses of 1,000/2,000 mg of MPA and 320 to 960 mg of MA.

Cisplatin induces serotonin release from human peripheral blood mononuclear cells of cancer patients and methylprednisolone inhibits this effect

The aim of this study was to verify whether cisplatin (CDDP) can induce serotonin (5HT) release from peripheral blood mononuclear cells (PBMC) of cancer patients and determine whether methylprednisolone (MP) can inhibit such release. Ten patients (mean age 61.8 years) with cancer of different sites, all but one in advanced stage of disease were studied. Our study showed that unstimulated PBMC of cancer patients release a higher amount of 5HT than that of healthy subjects (57+/-5 nM vs 10+/-1 nM, p<0.001) and that similarly the stimulation with PHA or CDDP induces a higher amount of 5HT release by PBMC of cancer patients than that by PBMC of healthy subjects (74+/-6 vs 32+/-3 nM, p<0.001 and 91+/-8 vs 18+/-2 nM, p<0.001, respectively). The addition of MP to the culture in the presence of CDDP induced a significant decrease of 5HT levels: from 91+/-8 to 53+/-7 nM, p=0.002. This result obtained in cancer patients paralleled that previously obtained by us in healthy subjects. Our data confirm a new mechanism through which CDDP could induce emesis and provide a further possible explanation to the anti-emetic activity of corticosteroids, such as MP.

Medroxyprogesterone acetate reduces the production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients

Medroxyprogesterone acetate reduces the production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients

Medroxyprogesterone acetate reduces the production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients.

Medroxyprogesterone acetate (MEA) is widely used in oncology both in the treatment of hormonerelated cancers and as supportive therapy in anorexialcachexia syndrome (ACS), but conclusive data are not yet available to explain its anticachectic effect. ACS is characterised by weight loss, changes in metabolism, reduction of appetite, nausea and vomiting. Several cytokines, mainly interleukin (IL)-1, IL-2, IL-6 and tumour necrosis factor (r (TNFu), are involved in the pathogenesis of ACS. Additionally, nausea and vomiting can be mediated by factors inducing serotonin (S-HT) production and/or release by pleiotropic cells including activated T lymphocytes. In the present study, we report the effect of MPA on peripheral blood mononuclear cells (PBMC) from 10 cancer patients in advanced stage of disease (6 head and neck, 2 colon, 1 lung and 1 ovary). The proliferative response of PBMC to PHA, anti-CD3 monoclonal antibody (MAb) or recombinant IL-2 (rIL-2), the production of IL-lp, IL-2, IL-6, TNFa and 5-HT by PHA-stimulated PBMC and the expression of lymphocyte membrane-bound IL-2 receptor (IL-2R) subunities (CD25 and CD122) were studied. The addition of MPA significantly reduced the PBMC proliferative response to PHA and anti-CD3 MAb but not to rIL-2. MEA 0.2 pg/ml was also capable of reducing the levels of IL-lp, IL-6, TNFa and 5-HT produced in culture by PHA-stimulated PBMC, whereas it did not induce any change in the percentage of PBMC expressing either CD25 or CD122 or both molecules after stimulation with PHA or anti-CD3 mAb.

Medroxyprogesterone acetate reduces the production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients

Medroxyprogesterone acetate reduces the production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients

Medroxyprogesterone acetate reduces the in vitro production of cytokines and serotonin involved in anorexia/cachexia and emesis by peripheral blood mononuclear cells of cancer patients.

Medroxyprogesterone acetate (MPA) is widely used in oncology both in the treatment of hormone-related cancers and as supportive therapy in anorexia/cachexia syndrome (ACS), but conclusive data are not yet available to explain its anticachectic effect. ACS is characterised by weight loss, changes in metabolism, reduction of appetite, nausea and vomiting. Several cytokines, mainly interleukin (IL)-1, IL-2, IL-6 and tumour necrosis factor alpha (TNF alpha), are involved in the pathogenesis of ACS. Additionally, nausea and vomiting can be mediated by factors inducing serotonin (5-HT) production and/or release by pleiotropic cells including activated T lymphocytes. In the present study, we report the effect of MPA on peripheral blood mononuclear cells (PBMC) from 10 cancer patients in advanced stage of disease (6 head and neck, 2 colon, 1 lung and 1 ovary). The proliferative response of PBMC to PHA, anti-CD3 monoclonal antibody (MAb) or recombinant IL-2 (rIL-2), the production of IL-1 beta, IL-2, IL-6, TNF alpha and 5-HT by PHA-stimulated PBMC and the expression of lymphocyte membrane-bound IL-2 receptor (IL-2R) subunities (CD25 and CD122) were studied. The addition of MPA significantly reduced the PBMC proliferative response to PHA and anti-CD3 MAb but not to rIL-2. MPA 0.2 microgram/ml was also capable of reducing the levels of IL-1 beta, IL-6, TNF alpha and 5-HT produced in culture by PHA-stimulated PBMC, whereas it did not induce any change in the percentage of PBMC expressing either CD25 or CD122 or both molecules after stimulation with PHA or anti-CD3 mAb.

Immunological characterization and clinical significance of low mobility cells appearing in the peripheral blood mononuclear cells of cancer patients

The characteristics of low mobility cells (LMC) in the peripheral blood mononuclear cells (PBMC) of cancer patients were studied using a Parmoquant-L, a fully automated electrophoresis instrument, and a fluorescence-activated cell sorter (FACS). The L/H ratio (%) of LMC ( <0.95 μm/s/V/cm) to high mobility cells (HMC) ( ⩾0.95) was used to analyze the electrophoretic mobility (EPM) histogram of PBMC. In the cancer patient, the L/H ratio increased as a result of the appearance of LMC. As the ratio closely correlated with clinical stage of cancer, recurrence of cancer, and performance status in the patients, the method is a useful parameter for prognosis of cancer, practically, for early detection of recurrence in the follow-up study of cancer patients. The EPM of monocytes and subsets of lymphocytes was determined to characterize LMC. Monocytes were in LMC. T-Cells such as helper/inducer (Leu- 3 + ), suppressor (Leu-2 + Leu- 15 + ) and cytotoxic (Leu- 2 + Leu- 15 − ) cells and natural killer (NK) cells (Leu-7 + or Leu- 11 + ) were in HMC. The percentage of monocytes correlated significantly with the mean EPM of PBMC. In cancer patients, the percentage of monocytes increased significantly. On the other hand, suppressor T-cells did not increase enough to account for LMC. The appearance of suppressor T-cells correlated with that of monocytes. These results suggest that LMC in cancer patients consisted of mainly monocytes rather than suppressor T-cells.

Cyclic AMP and prostaglandin levels in circulating mononuclear cells of cancer patients

Cyclic AMP and prostaglandin levels in circulating mononuclear cells of cancer patients

Clinical studies on cell-mediated immunity in patients with malignant disease

In vitro mitogenic responses of lymphocytes of patients with advanced cancer of the stomach or lung were determined and the cells involved in the depressed responses of patients characterized. Proliferative responses to phytohemagglutinin and concanavalin A of lymphocyte rich mononuclear cells of the patients were impaired, but increased after in vitro unstimulated culture for seven days. Mitogenic responses were enhanced by depletion of monocytes using a Sephadex G-10 column, and further enhanced by removal of nylon wool nonadherent cells. Nylon wool nonadherent cells of the patients suppressed the mitogenic responses of autologous and allogeneic lymphocytes, but lost the suppressive activity during seven days' in vitro culture. Nonadherent cells of normal donors did not inhibit mitogenic responses. The results suggest that peripheral blood mononuclear cells of cancer patients may contain at least two populations of suppressor cells for mitogenic responses, monocytes and nylon wool nonadherent cells, which could be one of the causes of impaired mitogenic responses in these cancer patients.