Immunomodulation by orally administered protein-bound polysaccharide PSK in patients with gastrointestinal cancer

Coriolus (Trametes) versicolor mushroom to reduce adverse effects from chemotherapy or radiotherapy in people with colorectal cancer

BACKGROUND

Radiotherapy and chemotherapy are used to improve survival in colorectal cancer but adverse effects can be a problem. Severe adverse effects may result in dose reduction or cessation of treatment, which have an impact on survival. Coriolus versicolor (Trametes versicolor or 'Turkey Tail') mushroom and its extracts have been used by cancer patients to help with adverse effects.

OBJECTIVES

To assess the effects of adjunctive Coriolus versicolor (Trametes versicolor) and its extracts on adverse effects and on survival during colorectal cancer treatment (chemotherapy and radiotherapy) compared with no adjunctive treatment.

SEARCH METHODS

We searched databases including CENTRAL, MEDLINE, Embase, AMED and CINAHL, Chinese and Japanese databases, and trials registers to 12th April 2022 without restriction of language or publication status. We screened reference lists and attempted to contact researchers in the field to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) investigating the efficacy and safety of Coriolus versicolor and its extracts in adult participants with a confirmed diagnosis of colorectal cancer, in addition to conventional treatment. Interventions included any preparation of Coriolus versicolor (raw, decoction, capsule, tablet, tincture, extract, injection), any part of the fungus (cap, stem, mycelium or whole), in any dose or regimen. Outcomes included adverse events rates, survival, disease progression and recurrence, response rates and quality of life.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened and selected studies, extracted outcome data, and assessed risk of bias. We evaluated the overall certainty of evidence using the GRADE approach.

MAIN RESULTS

We included seven parallel RCTs (1569 participants). Six studies (1516 participants) were conducted in Japan and one study (53 participants) in China. Studies included both male and female participants with colorectal cancer (five studies), colon cancer (one study) or rectal cancer (one study). Participants were diagnosed with cancer ranging from stage II to stage IV. Coriolus was used in the form of an extract in all seven studies and was generally used after curative resection, although in one study it was used preoperatively. Duration of treatment with the extract varied between four weeks and three years. Chemotherapeutic regimens in six studies consisted of an oral fluoropyrimidine which was preceded by weekly intravenous 5-Fluorouracil (5-FU) in one study, by mitomycin C in two studies, and which was combined with folinic acid (Leucovorin) in two studies and with radiotherapy preoperatively in one study. XELOX (oxaliplatin intravenous infusion and capecitabine) was used in the remaining study. We found very low-certainty evidence of little to no effect of adjunctive treatment with Coriolus (in the form of an extract, polysaccharide-Krestin, PSK) on withdrawal from treatment due to adverse events  (risk ratio (RR) 1.03, 95% confidence interval (CI) 0.45 to 2.34; 703 participants; 3 studies;). We are uncertain whether adjunctive Coriolus versicolor and its extracts compared to usual care alone resulted in a difference in adverse events including neutropenia (RR 0.41, 95% CI 0.24 to 0.71; 133 participants; 3 studies; very low certainty), oral cavity disorders such as oral dryness and mucositis (RR 0.37, 95% CI 0.13 to 1.03; 1022 participants; 5 studies; very low certainty), nausea (RR 0.73, 95% CI 0.44 to 1.22; 969 participants; 4 studies; very low certainty), diarrhoea (RR 0.77, 95% CI 0.32 to 1.86; 1022 participants; 5 studies; very low certainty), and fatigue (RR 0.76; 95% CI 0.33 to 1.78; 133 participants; 3 studies; very low certainty). We found low-certainty evidence of a small effect of adjunctive Coriolus on improved survival at five years compared with no adjunctive care (RR 1.08, 95% CI 1.01 to 1.15; 1094 participants; 3 studies; number needed to benefit (NNTB) = 16 (95% Cl 9 to 70). The effect at earlier time points was unclear.

AUTHORS' CONCLUSIONS

Due to the very low certainty of evidence, we were uncertain about the effect of adjunctive Coriolus (in the form of an extract PSK) on adverse events resulting from conventional chemotherapy for colorectal cancer. This includes effects on withdrawal of treatment due to adverse events and on specific adverse outcomes such as neutropenia and nausea. The uncertainty in the evidence also means that it was unclear whether any adverse events were due to the chemotherapy or to the extract itself. While there was low-certainty evidence of a small effect on overall survival at five years, the influence of reduced adverse effects on this could not be determined. In addition, chemotherapy regimens used in assessing this outcome do not reflect current preferred practice.

Can polysaccharide K improve therapeutic efficacy and safety in gastrointestinal cancer? a systematic review and network meta-analysis

Objective

To assess the comparative efficacy and safety of polysaccharide K (PSK), with or without chemotherapy, for patients with gastrointestinal cancer (GIC) through a systematic review and network meta-analysis.

Materials and Methods

We performed a network meta-analysis to identify evidence from randomized controlled trials. We searched PubMed, Embase and the Cochrane Library for publications up to May 2017. The prespecified primary efficacy outcomes were 1–7 year overall survival (OS), while the secondary efficacy outcomes were 1–7 year disease-free survival (DFS); we performed subgroup analyses and meta-regressions according to the cancer type (colorectal, esophagus and gastric cancer) and treatment arms (with or without chemotherapy). Safety outcomes were side effects of PSK. We conducted pairwise meta-analyses using a random-effects model and then performed random-effects network meta-analyses.

Results

A total of 23 trials were eligible, involving 10684 patients and 13 intervention arms. PSK treatment significantly increased 1–5 year OS and resulted in positive trends in 6–7 year OS; significant increases were also found in 1–7 year DFS, while no increase in side effects was observed. Significant efficacy outcomes obvious in colorectal and gastric cancer groups, as well as PSK combined with chemotherapy groups (iv, po, iv+po). Network meta-analysis revealed that PSK combined with chemotherapy was superior, with significantly increased 3-year and 5-year OS. The study is registered with PROSPERO (CRD42017065193)

Conclusions

The adjuvant immunochemotherapy agent PSK is effective and safe for patients with GIC. PSK combined with chemotherapy appears to be the preferred application of PSK.

Crude dietary polysaccharide fraction isolated from jackfruit enhances immune system activity in mice

Crude polysaccharides (PSs) were isolated from the fruit pulp of jackfruit, and their chemical composition determined and evaluated for an immune regulatory activity in mice. The PSs were isolated from water extracts of jackfruit pulp (JFP) using the ethanol precipitation method. The resulting precipitates were further purified by dialysis and protein depletion by the Sevage method. The phenol-sulfuric method was used to determine the content of the PSs. The composition of PSs was determined by the Sephadex-G200 column chromatography and high-performance liquid chromatography methods. The thymus index and macrophage phagocytic function methods in mice were used to evaluate the immune regulatory activity of JFP-PSs. The JFP-PSs content in jackfruit was about 21% (w/w) and the yield of crude PSs was 3.91%. The single molecular mass weight PS was the main constituent of JFP-PSs. The major monosaccharide residues were rhamnose, glucose, galactose, and arabinose. The JFP-PSs enhanced the thymus weight index and the phagocytic rate after 30 days of subchronic p.o. administration to mice at 4.5 mg/kg. The JFP contains single molecular PS and JFP-PS has immune-stimulating activities in mice. These data suggest that at least some of the traditional uses of JFP can be ascribed to its immunomodulatory effects.

Immunomodulatory dietary polysaccharides: a systematic review of the literature

BACKGROUND

A large body of literature suggests that certain polysaccharides affect immune system function. Much of this literature, however, consists of in vitro studies or studies in which polysaccharides were injected. Their immunologic effects following oral administration is less clear. The purpose of this systematic review was to consolidate and evaluate the available data regarding the specific immunologic effects of dietary polysaccharides.

METHODS

Studies were identified by conducting PubMed and Google Scholar electronic searches and through reviews of polysaccharide article bibliographies. Only articles published in English were included in this review. Two researchers reviewed data on study design, control, sample size, results, and nature of outcome measures. Subsequent searches were conducted to gather information about polysaccharide safety, structure and composition, and disposition.

RESULTS

We found 62 publications reporting statistically significant effects of orally ingested glucans, pectins, heteroglycans, glucomannans, fucoidans, galactomannans, arabinogalactans and mixed polysaccharide products in rodents. Fifteen controlled human studies reported that oral glucans, arabinogalactans, heteroglycans, and fucoidans exerted significant effects. Although some studies investigated anti-inflammatory effects, most studies investigated the ability of oral polysaccharides to stimulate the immune system. These studies, as well as safety and toxicity studies, suggest that these polysaccharide products appear to be largely well-tolerated.

CONCLUSIONS

Taken as a whole, the oral polysaccharide literature is highly heterogenous and is not sufficient to support broad product structure/function generalizations. Numerous dietary polysaccharides, particularly glucans, appear to elicit diverse immunomodulatory effects in numerous animal tissues, including the blood, GI tract and spleen. Glucan extracts from the Trametes versicolor mushroom improved survival and immune function in human RCTs of cancer patients; glucans, arabinogalactans and fucoidans elicited immunomodulatory effects in controlled studies of healthy adults and patients with canker sores and seasonal allergies. This review provides a foundation that can serve to guide future research on immune modulation by well-characterized polysaccharide compounds.

Development and validation of a model that predicts early death among cancer patients participating in phase I clinical trials investigating cytotoxics

OBJECTIVE

Selecting patients for phase 1 studies remains challenging. Given the lack of clear and reliable guidance for the estimation of life expectancy, we retrospectively assessed predictive factors of early death (within 90 days following inclusion) among these patients.

METHODS

Two hundred fifty-seven consecutive cancer patients enrolled in phase I studies investigating cytotoxics at Oscar Lambret Cancer Center and Institut Claudius Regaud were included in the development database. Univariate and multivariate analyses (logistic regression model) were undertaken to determine the prognostic factors. A probability tree described the rate of early death in the different prognostic subgroups. This prognostic model was then evaluated on a second independent cohort of 128 patients treated at Léon Bérard Cancer Center.

RESULTS

The median overall survival was 8.4 months in the dataset population, and the rate of early death was 15%. In multivariate analysis, the two prognostic factors for early death were albumin <38 g/l (OR = 5.21) and lymphocytes <700/mm(3) (OR = 3.88). According to these two parameters, three prognostic subgroups were defined with early death rates of, respectively, 8/121 (6%), 19/119 (16%) and 13/17 (76%). In the validation dataset, the rates of early death according to three prognostic groups were 13/68 (19%), 20/57 (35%) and 3/3 (100%), respectively.

CONCLUSION

We do not recommend the enrolment of patients with albumin level below 38g/l and lymphocytes count below 700/mm(3), in phase 1 trial investigating cytotoxics. Our model is helpful to discriminate "patients with reasonable life expectancy" as defined in most phase 1 protocols.

Adjuvant therapy for completely resected stage II colon cancer

BACKGROUND

Colon cancer is potentially curable by surgery. Although adjuvant chemotherapy benefits patients with stage III disease, there is uncertainty of such benefit in stage II colon cancer. A systematic review of the literature was performed to better define the potential benefits of adjuvant therapy for patients with stage II colon cancer.

OBJECTIVES

To determine the effects of adjuvant therapy on overall survival and disease-free survival in patients with stage II colon cancer.

SEARCH STRATEGY

Ovid MEDLINE (1986-2007), EMBASE (1980-2007), and EBM Reviews - Cochrane Central Register of Controlled Trials ( to 2007) were searched using the medical headings "colonic neoplasms", "colorectal neoplasms", "adjuvant chemotherapy", "adjuvant radiotherapy" and "immunotherapy", and the text words "colon cancer" and "colonic neoplasms". In addition, proceedings from the annual meetings of the American Society of Clinical Oncology and the European Society of Medical Oncology (1996 to 2004) as well as personal files were searched for additional information.

SELECTION CRITERIA

Randomized trials or meta-analyses containing data on stage II colon cancer patients undergoing adjuvant therapy versus surgery alone.

DATA COLLECTION AND ANALYSIS

:Three reviewers summarized the results of selected studies. The main outcomes of interest were overall and disease-free survival, however, data on toxicity and treatment delivery were also recorded.

MAIN RESULTS

With regards to the effect of adjuvant therapy on stage II colon cancer, the pooled relative risk ratio for overall survival was 0.96 (95% confidence interval 0.88, 1.05). With regards to disease-free survival, the pooled relative risk ratio was 0.83 (95% confidence interval 0.75, 0.92).

AUTHORS' CONCLUSIONS

Although there was no improvement in overall survival in the pooled analysis, we did find that disease-free survival in patients with stage II colon cancer was significantly better with the use of adjuvant therapy. It seems reasonable to discuss the benefits of adjuvant systemic chemotherapy with those stage II patients who have high risk features, including obstruction, perforation, inadequate lymph node sampling or T4 disease. The co-morbidities and likelihood of tolerating adjuvant systemic chemotherapy should be considered as well. There exists a need to further define which high-risk features in stage II colon cancer patients should be used to select patients for adjuvant therapy. Also, researchers must continue to search for other therapies which might be more effective, shorter in duration and less toxic than those available today.

Prognostic factors among cancer patients with good performance status screened for phase I trials

BACKGROUND

Selecting patients for phase I trials in order to investigate cytotoxic agents is challenging, since there is no clear and reliable guidance to estimate life expectancy among these patients. We retrospectively assessed prognostic factors in cancer patients screened for Phase1 trials between October 1997 and October 2002.

METHODS

148 consecutive patients, screened for inclusion in phase I trials investigating cytotoxic agents, were included in the present study. 70 out of them actually received phase I trial regimens. Univariate and multivariate analysis were undertaken to determine the prognostic factors for overall survival (OS) from the date of screening.

RESULTS

The median OS of the 148 patients was 5.7 months. Ninety-two percent of them had PS<or=1. The Cox model identified serum albumin<38 g/l [HR 2.51 (1.51-4.18), p=0.0001] and lymphocyte count<700/mm3 [HR 2.27 (1.13-4.62), p=0.024] as independent prognostic for overall survival. All patients presenting both prognostic factors died within 90 days.

CONCLUSIONS

We propose a simple model, easily obtained at the bedside, which can discriminate patients who are likely to be alive at 3 months and thus could be included in a phase 1 anti-cancer trial. This model now needs to be validated on an independent cohort.

Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curative resections of gastric cancer

Non-specific immunopotentiators, such as polysaccharide K (PSK), also known as OK-432, induce anti-tumor effects via immunological responses. The efficacy of combination immunochemotherapy using these immunopotentiators has been examined by multiple previous studies. The survival benefits of immunochemotherapy for patients with curative resections of gastric cancers are not widely accepted. To clarify this issue, we performed a meta-analysis to evaluate the effect of immunochemotherapy on survival in patients with curative resections of gastric cancer. For this study, we compared the results of chemotherapy and immunotherapy using the biological response modifier PSK as an immunopotentiator. The meta-analysis included 8,009 patients from eight randomized controlled trials after central randomization. The overall hazard ratio for eligible patients was 0.88 (95% confidence interval, 0.79-0.98; P = 0.018) with no significant heterogeneity [chi (2)(8) for heterogeneity = 11.7; P = 0.16]. The results of this meta-analysis suggest that adjuvant immunochemotherapy with PSK improves the survival of patients after curative gastric cancer resection.

Immunostimulatory principles from Chlorella pyrenoidosa--part 1: isolation and biological assessment in vitro

Our proprietary preparation obtained by extraction of Chlorella pyrenoidosa cells, ONC-107 (Respondin), was recently found to selectively boost antibody response to the influenza vaccine in a human clinical trial. Respondin is a potent stimulator of mouse B cell proliferation and an activator of macrophages. Bioactivity-guided resolution concluded that Respondin is composed of a mixture of immunostimulatory principles of different chemical nature. A combination of size exclusion, anion exchange and hydrophobic interaction chromatography revealed that the bulk of the immunostimulatory activity resides in polysaccharide/protein complexes with molecular masses larger than 100 kDa that are composed primarily of galactose, rhamnose and arabinose.

Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curatively resected colorectal cancer: a meta-analysis of centrally randomized controlled clinical trials

The benefits of immunochemotherapy employing the biological response modifier polysaccharide K (PSK) for patients with curatively resected colorectal cancer was reassessed by means of a meta-analysis of data with center randomization from 1,094 patients enrolled in three clinical trials. In all three trials, patients were followed up for at least 5 years after surgery and enrollment of the last patient and outcomes for standard chemotherapy were compared with those for chemotherapy plus PSK. The endpoints were overall survival and disease-free survival; and intent-to-treat analysis was performed without patient exclusion. Data were analyzed using the weighted average of the individual log hazard ratios. The overall survival risk ratio for all eligible patients was 0.71 (95% confidence interval (CI) : 0.55-0.90; P=0.006), and the disease-free survival risk ratio was 0.72 (95% CI: 0.58-0.90; P=0.003). The results of this meta-analysis suggest that adjuvant immunochemotherapy with PSK can improve both survival and disease-free survival of patients with curatively resected colorectal cancer.

Unconventional anticancer agents: a systematic review of clinical trials

PURPOSE

A substantial number of cancer patients turn to treatments other than those recommended by mainstream oncologists in an effort to sustain tumor remission or halt the spread of cancer. These unconventional approaches include botanicals, high-dose nutritional supplementation, off-label pharmaceuticals, and animal products. The objective of this study was to review systematically the methodologies applied in clinical trials of unconventional treatments specifically for cancer.

METHODS

MEDLINE 1966 to 2005 was searched using approximately 200 different medical subject heading terms (eg, alternative medicine) and free text words (eg, laetrile). We sought prospective clinical trials of unconventional treatments in cancer patients, excluding studies with only symptom control or nonclinical (eg, immune) end points. Trial data were extracted by two reviewers using a standardized protocol.

RESULTS

We identified 14,735 articles, of which 214, describing 198 different clinical trials, were included. Twenty trials were phase I, three were phase I and II, 70 were phase II, and 105 were phase III. Approximately half of the trials investigated fungal products, 20% investigated other botanicals, 10% investigated vitamins and supplements, and 10% investigated off-label pharmaceuticals. Only eight of the phase I trials were dose-finding trials, and a mere 20% of phase II trials reported a statistical design. Of the 27 different agents tested in phase III, only one agent had a prior dose-finding trial, and only for three agents was the definitive study initiated after the publication of phase II data.

CONCLUSION

Unconventional cancer treatments have not been subject to appropriate early-phase trial development. Future research on unconventional therapies should involve dose-finding and phase II studies to determine the suitability of definitive trials.

Protein-bound polysaccharide K induced apoptosis of the human Burkitt lymphoma cell line, Namalwa

Protein-bound polysaccharide K (PSK), which is derived from mushrooms belonging to the Basidiomycetes genus, has been clinically used as a biological response modifier (BRM) for the treatment of epithelial cancer patients in Japan and other Asian countries. There are a large number of studies on the biological activities of PSK as regards the activation of immunocompetent cells and the potential cytotoxic effects on epithelial cancer cells. However, only a few studies have been conducted to see the direct cytotoxic effects of PSK on hematological malignant cells. In this study, we investigated whether or not PSK was able to induce cellular apoptosis in hematological malignant cells. PSK was found to inhibit cell growth, and induced subsequent cellular apoptosis in the Burkkit lymphoma cell line (Namalwa), out of 33 hematological malignant cell lines tested. This PSK-induced apoptosis was neutralized by the addition of galactose to the culture medium, whereas apoptosis was augmented by treatment with beta-galactosidase, indicating the inhibitory involvement of galactose in the mechanism of action. These results provide initial evidence of the direct cytotoxic activity of PSK in a hematological malignant cell line, thus encouraging further molecular-level study of PSK-mediated apoptosis in malignant hematological cells.

Herbs or natural products that decrease cancer growth part one of a four-part series

PURPOSE/OBJECTIVES

To provide evidence-based research information about 31 herbs and natural products that have shown potential in early research to decrease cancer growth or as adjuncts with cancer treatment.

DATA SOURCES

Names of herbs and natural products with potential to decrease cancer growth have been selected from listings in the Natural Medicines Comprehensive Database and Lawrence Review of Natural Products-Monograph System. Information about these herbs has been found in evidence-based studies cited in references.

DATA SYNTHESIS

In preliminary studies, 31 herbs and natural products appear to have potential for cancer treatment.

CONCLUSIONS

This preliminary evidence may be useful to healthcare professionals and patients with cancer.

IMPLICATIONS FOR NURSING

The information in this article is designed to provide quick access for healthcare professionals working in clinical oncology. Oncology nurses who have this information can become resources for patients and other healthcare professionals.

Individualized Patient Dosing in Phase I Clinical Trials: The Role of Escalation With Overdose Control in PNU-214936

Purpose

A patient-specific dose-escalation scheme using a Bayesian model of Escalation with Overdose Control (EWOC) was conducted to establish the maximum tolerated dose (MTD) of PNU-214936 in advanced non–small-cell lung cancer (NSCLC). PNU-214936 is a murine Fab fragment of the monoclonal antibody 5T4 fused to a mutated superantigen staphylococcal enterotoxin A (SEA).

Patients and Methods

Seventy-eight patients with NSCLC were treated with an individualized dose of PNU-214936 calculated using EWOC, based on their anti-SEA antibody level, and given as a 3-hour infusion on 4 consecutive days.

Results

Fever (82%; grade 3 to 4, 2.6%) and hypotension (57%; grade 3 to 4, 9%) were the most common toxicities. Eight dose-limiting toxicities occurred, as defined as any grade 4 toxicity occurring within the first 5 days. The MTD was defined as a function of pretreatment anti-SEA antibody level. MTD ranged from 103 ng/kg for patients with anti-SEA concentrations ≤ 10 pmol/mL, to 601 ng/kg for patients with anti-SEA concentrations of 91 to 150 pmol/mL. A minor tumor response was demonstrated in five of 66 assessable patients.

Conclusion

EWOC determined phase I doses of PNU-214936 that were adjusted for patient anti-SEA antibody level, while safeguarding against overdose. Furthermore, the method permitted the construction of a dosing algorithm that would allow patients in subsequent clinical investigations to be treated with a dose of PNU-214936 that is tailored to their specific tolerance for the agent, as reflected by their pretreatment anti-SEA.

Patient specific dosing in a cancer phase I clinical trial

Recent improvements in our understanding of drug metabolism have led to the development of anticancer therapies that accommodate patient differences in drug tolerance. Such methods adjust the dose level according to measurable patient characteristics in order to obtain a target drug exposure. This paper describes the utilization of a patient specific dosing scheme in the statistical design of a phase I clinical trial involving patients with advanced adenocarcinomas of gastrointestinal origin. During the trial, dose levels were adjusted according to each patient's pretreatment concentration of an antibody that was shown in preclinical testing to moderate the effect of the agent under investigation. The design of the trial permitted a continual adjustment of the model used to tailor the dose to each patient's individual needs.

Polysaccharide (ANK-102) from Polianthes tuberosa cells deteriorates the resistance of mice to Listeria monocytogenes infection

Modulatory effect on the murine self defense system by a newly discovered acidic polysaccharide (ANK-102) produced by P. tuberosa cells in liquid culture was examined. Pretreatment with ANK-102 deteriorated the murine survival against lethal infection of Listeria monocytogenes, an intracellular gram-positive bacterium eliminated mainly by macrophages through T-cell mediated immune response. Pretreatment with ANK-102 resulted in the accumulation of Mac 1 and Mac 2 positive cells in the peritoneal cavity of the infected animals and the reduction of Thy1.2 expression on the surface of the thymocytes. A new type of immunosuppressive polysaccharide ANK-102 was introduced.

Effect of PSK and its subfractions on peripheral blood lymphocytes mediated cytotoxicity against urinary bladder tumor cells

Our previous studies have indicated that the protein-bound polysaccharide Kreha (PSK) enhances the cytotoxic activity of peripheral blood lymphocytes (PBL) against the T24 human urinary bladder tumor cell line in patients with bladder tumor. Since PSK consists of a mixture of various kinds of protein-bound polysaccharides, the present study was designed to examine which subfractions of PSK mediated the enhancement of cytotoxicity. When PSK was separated according to size, treatment of PBL with the 50 kilodalton (kd) or less fraction killed T24 cells more efficiently than unfractionated PSK-treated PBL. The higher molecular weight fractions did not enhance killing above the control level. PSK was fractionated on a diethylaminoethyl (DEAE)-cellulose column to obtain a protein rich fraction that absorbed onto the column and a polysaccharide rich fraction that did not. PBL treated with the polysaccharide rich fraction were able to kill T24 cells more effectively than unfractionated PSK-treated PBL. The protein rich fraction had no effect on the killing. Further fractionation of the polysaccharide rich fraction was performed by differential precipitation with ammonium sulfate. PBL treated with the precipitated fraction at 70-80% saturation (PSK Fraction D) enhanced cytotoxicity equal to that of the polysaccharide rich fraction. Treatment of PBL with the other fractions did not augment the cytotoxicity. These enhancement by PSK fractions were observed in healthy donors and also in patients with bladder tumor. An increase of the proliferative response of PBL to PSK Fraction D as well as unfractionated PSK was observed. Treatment of PBL with PSK Fraction D had no effect on the proportion of PBL binding to T24 cells, thus suggesting a post-binding effect. The structure of PSK Fraction D as inferred from the results of methylation analysis was mainly an alpha-glucan. These results demonstrate that PSK mediated enhancement of cytotoxicity and proliferation of PBL may be largely due to an alpha-glucan of less than 50 kd.