Safety and Pharmacokinetic Assessment of the FIC CLDN18.2/4-1BB Bispecific Antibody in Rhesus Monkeys.

Gastric cancer is one of the most common cancers worldwide, particularly in China, with over half a million new cases and over 400 thousand deaths in 2022. Zolbetuximab, a first-in-class investigational monoclonal antibody (mAb) targeting tumor-associated antigen CLDN18.2 which is highly expressed on gastric cancer cells, was recently reported to meet the primary endpoint in Phase III trial as first-line treatment in CLDN18.2 positive and HER2-negative gastric cancers. In the present study, we developed a humanized bispecific antibody (bsAb) CLDN18.2/4-1BB named PM1032. PM1032 activates immune cells via CLDN18.2 mediated crosslinking of 4-1BB, a potent stimulator of T/NK cells. It induced strong immunological memory in multiple tumor-bearing animal models, indicating significant potential as an effective treatment for CLDN18.2 positive cancers such as gastric cancer. Since liver and gastrointestinal (GI) related toxicities were reported in 4-1BB and CLDN18.2 targeting programs during the clinical development, respectively, extensive pharmacokinetics (PK) and safety profile characterization of PM1032 was performed in rhesus monkeys. PM1032 had a half-life comparable to a conventional IgG1 mAb, and serum drug concentration increased in a dose-dependent pattern. Furthermore, PM1032 was generally well tolerated, with no significant abnormalities observed in toxicity studies, including the liver and stomach. In summary, PM1032 demonstrated good PK and an exceptional safety profile in rhesus monkeys supporting further investigation in clinical studies.

Development and Verification of an Immune-Based Gene Signature for Risk Stratification and Immunotherapeutic Efficacy Assessment in Gastric Cancer.

OBJECTIVE: Due to the molecular heterogeneity of gastric cancer, only minor patients respond to immunotherapeutic schemes. This study is aimed at developing an immune-based gene signature for risk stratification and immunotherapeutic efficacy assessment in gastric cancer. METHODS: An immune-based gene signature was developed in gastric cancer by LASSO method in the training set. The predictive performance was validated in the external datasets. KEGG pathways related to risk scores were assessed by GSEA. Based on multivariate Cox regression analysis, a nomogram was established. Sensitivity to chemotherapy drugs was evaluated between high- and low-risk samples. The relationships of risk scores with infiltration levels of immune cells, stromal scores, immune scores, immune cell subgroups, and overall response to anti-PD-L1 therapy were determined. RESULTS: Our results showed that high risk scores were indicative of undesirable survival outcomes both in the training set (p < 0.0001) and the validation set (p = 0.002). Moreover, this signature could independently predict patients' survival (HR: 2.656 (1.919-3.676) and p < 0.001). Subgroup analysis confirmed the sensitivity of this signature in predicting prognosis (all p < 0.05). Cancer-related pathways were primarily enriched in high-risk samples, such as MAPK and TGF-ß pathways (p < 0.05). By incorporating stage and the risk score, we established a nomogram for predicting one-, three-, and five-year survival probability. Patients with high-risk scores were more sensitive to chemotherapy drugs (p < 0.05). There was heterogeneity in immune cells between high- and low-risk samples (p < 0.05). Samples with progressive disease exhibited the highest risk score, and those with complete response had the lowest risk score (p < 0.05). CONCLUSION: This immune-based gene signature might be representative of a promising prognostic classifier for predicting risk stratification and immunotherapeutic efficacy in gastric cancer, assisting personalized therapy and follow-up plan.

Status of vaccine research and development for Helicobacter pylori.

Gastric adenocarcinoma is globally the third leading cause of death due to malignancy, with the bulk of this disease burden being suffered by low and middle income countries (LMIC), especially in Asia. The majority of these cancers develop as a result of a chronic gastritis that arises in response to infection with the stomach-dwelling bacterium, Helicobacter pylori. A vaccine against this pathogen would therefore be a powerful tool for preventing gastric adenocarcinoma. However, notwithstanding a proof-of-concept that vaccination can protect children from acquisition of H. pylori infection, there are currently no advanced vaccine candidates with only a single vaccine in Phase I clinical trial. Further, the development of a vaccine against H. pylori is not a current strategic priority of major pharmaceutical companies despite the large global disease burden. Given the involvement of such companies is likely to be critical for late stage development, there is therefore a need for an increased appreciation of the burden of this disease in LMIC and more investment to reinvigorate research in H. pylori vaccine Research and Development.

Noninvasive assessment of characteristics of novel anti-HER2 antibodies by molecular imaging in a human gastric cancer xenograft-bearing mouse model.

Human epidermal growth factor receptor 2 (HER2) overexpression occurs in various types of cancers. Regarding the anti-HER2 targeted therapies showed superior treatment outcomes in several (pre)clinical studies, we used multimodality image to rapidly select novel HER2-targeting antibodies for further therapeutics development. The four anti-HER2 antibodies (H32 IgG, 75 IgG, 61 IgG, and trastuzumab) labeled with either In-111 or a DyLight680 fluorescent dye were applied to perform cellular uptake, endocytosis, optical/microSPECT/CT imaging and biodistribution studies. In vitro and in vivo relative effectiveness of these antibodies were also compared in an N87 gastric cancer xenograft model. The internalized radioactivity of [111In]61 IgG in N87 cells increased from 33% at 12 hr to 56% at 48 hr after incubation, while the majority of other antibodies stayed on the cell membranes. Among these antibodies, 61 IgG showed the highest accumulation in tumors with the tumor-to-muscle ratio (T/M) of 131 ± 61.4 and 19.13 ± 3.42 conducted by IVIS and microSPECT/CT, respectively. We demonstrated that multimodality imaging is a reliable approach for selecting potential antibodies and found that 61 IgG manifested significant tumor accumulation with elevated internalization rate thus could be a suitable candidate for further development of new HER2-targeted therapies.

Multiplex serology of Helicobacter pylori antigens in detection of current infection and atrophic gastritis - A simple and cost-efficient method.

INTRODUCTION: Helicobacter pylori express a large array of antigens, each of which is duly responsible for successful colonization and pathogenesis. Here, we have studied host serum antibody responses to four of its immunodominant antigens in association with the infection status and the resulting clinical outcomes. METHODS: For this purpose, four individual H. pylori proteins (UreB, CagA, Tip-α and HP0175) were produced in recombinant forms. Serum antibody responses of 246 (75 GC and 171 NUD) patients, against the above antigens, were evaluated by multiplex immunoblotting. The associations between the resulting data and the infection status, as well as clinical outcomes were evaluated using logistic regression models. RESULTS: Serum antibodies to all four recombinant antigens increased the chances of detecting screening ELISA-positive subjects, in an escalating dose-dependent manner, ranging from 2.6 (1.5-4.7) for HP0175 to 14.3 for UreB (4.3-50.7), exhibiting the lowest and highest odds ratios, respectively (PAdj ≤ 0.001), such that 98.2% of the subjects with antibodies to all four antigens, were also positive by the screening ELISA (P < 0.0001). Among the screening ELISA-positive subjects, the three antigens of CagA, Tip-α, and HP0175 were able to segregate current from past H. pylori infection (P < 0.05). Accordingly, subjects with antibodies to one or more antigen(s) were at 5.4 (95% CI: 1.8-16.4) folds increased chances of having current infection, as compared to triple negatives (PAdj = 0.003). In reference to the clinical outcomes, those with serum antibodies to CagA were more prevalent among gastric cancer, as compared to NUD patients (ORAdj: 5.4, 95% CI: 2.4-12.2, PAdj < 0.0001). When NUD patients were categorized according to their histopathologic status, multiple antigen analysis revealed that subjects with serum antibodies to one or more of the 3 current infection-positive antigens (CagA, Tip-α, and HP0175) were at 9.7 (95% CI: 2.1-44.9, P = 0.004) folds increased risk of atrophic gastritis, in reference to triple negatives. CONCLUSION: The non-invasive multiplex serology assay, presented here, was able to not only detect subjects with current H. pylori infection, it could also screen dyspeptic patients for the presence of gastric atrophy. This simple and cost-efficient method can supplement routine screening ELISAs, to increase the chances of detecting current infections as well as atrophic gastritis.

KI-67 heterogeneity in well differentiated gastro-entero-pancreatic neuroendocrine tumors: when is biopsy reliable for grade assessment?

PURPOSE: Ki-67 heterogeneity can impact on gastroenteropancreatic neuroendocrine tumor grade assignment, especially when tissue is scarce. This work is aimed at devising adequacy criteria for grade assessment in biopsy specimens. METHOD: To analyze the impact of biopsy size on reliability, 360 virtual biopsies of different thickness and lengths were constructed. Furthermore, to estimate the mean amount of non-neoplastic tissue component present in biopsies, 28 real biopsies were collected, the non-neoplastic components (fibrosis and inflammation) quantified and the effective area of neoplastic tissue calculated for each biopsy. RESULTS: Heterogeneity of Ki-67 distribution, G2 tumors and biopsy size all play an important role in reducing the reliability of biopsy samples in Ki-67-based grade assignment. In particular in G2 cases, 59.9% of virtual biopsies downgraded the tumor and the smaller the biopsy, the more frequent downgrading occurs. In real biopsies the presence of non-neoplastic tissue reduced the available total area by a mean of 20%. CONCLUSIONS: By coupling the results from these two different approaches we show that both biopsy size and non-neoplastic component must be taken into account for biopsy adequacy. In particular, we can speculate that if the minimum biopsy area, necessary to confidently (80% concordance) grade gastro-entero-pancreatic neuroendocrine tumors on virtual biopsies ranges between 15 and 30 mm2, and if real biopsies are on average composed of only 80% of neoplastic tissue, then biopsies with a surface area not <12 mm2 should be performed; using 18G needles, this corresponds to a minimum total length of 15 mm.

Combination photoimmunotherapy with monoclonal antibodies recognizing different epitopes of human epidermal growth factor receptor 2: an assessment of phototherapeutic effect based on fluorescence molecular imaging.

Photoimmunotherapy is a new class of molecular targeted cancer therapy based on a monoclonal antibody (mAb) conjugated to a photosensitizer and irradiation with near-infrared (NIR) light for both imaging and therapy. Here, we sought to determine the feasibility of combining photoimmunotherapy using conjugates of human epidermal growth factor receptor 2 (HER2)-specific mAb-photosensitizer IR700, trastuzumab-IR700 and pertuzumab-IR700. HER2-expressing and non-expressing cells were treated with mAb-IR700 conjugates and irradiated with NIR light. Fluorescence imaging and cytotoxic effects were examined in cultured HER2-expressng cancer cell lines and in a mouse tumor xenograft model. Trastuzumab-IR700 and pertuzumab-IR700 could specifically bind to HER2 without competing, and the combination treatment of both agents yielded stronger HER2-specific IR700 fluorescence signals than with the treatment with either agent singly. A cytotoxicity assay showed that the combination treatment of both trastuzumab-IR700 and pertuzumab-IR700 followed by NIR light irradiation induced stronger cytotoxic effect than with treatment of either agent plus NIR light irradiation. Furthermore, the phototoxic and cytotoxic effects of mAb depended on HER2-specific IR700 signal intensities. Consistent with in vitro studies, in xenograft tumor models also, IR700 fluorescence imaging-guided NIR light irradiation after the combination treatment of trastuzumab-IR700 and pertuzumab-IR700 led to stronger antitumor effects than by treatment with either agent followed by NIR light irradiation. In conclusion, fluorescence molecular imaging can facilitate the assessment of treatment outcomes of molecular targeted photoimmunotherapy, which holds great potential in facilitating better outcomes in cancer patients.

Immune checkpoints aberrations and gastric cancer; assessment of prognostic value and evaluation of therapeutic potentials.

Till now, the prognosis of advanced gastric cancer looked dreadful; thus the search for newer better approaches for this lethal disease has been a strategic target for cancer researchers. In recent years, important immunobiological aspects of the tumor have been revealed with the subsequent proposal of immune check point inhibitors to target these pathways. Clinically, unselected use of immune checkpoint inhibitors in gastric cancer has been deemed with failure; in contrast to the clear success of more recent studies reporting on the use of pembrolizumab in molecularly selected patients. This may illustrate that any future use of immune checkpoint inhibitors in gastric cancer has to be molecularly supported. This review provides a delicate dissection of the clinical and immunobiological considerations underlying the use of these agents in addition to a thorough review of the published clinical data of immune checkpoint inhibitors in gastric cancer.

Impact of early postoperative enteral nutrition on clinical outcomes in patients with gastric cancer.

The impact of early enteral nutrition (EEN) on clinical outcomes of gastric cancer patients was investigated. Three hundred pa-tients undergoing gastric cancer surgery from July 2010 to May 2014 were randomly divided into experimental and control groups (n = 150/group). Experimental group patients received enteral nutrition in water during the early postoperative period. Control group patients received conventional perioperative treatment. Patients' clinical outcomes, post-operative immune function, and nutritional statuses were compared, which revealed that the postoperative fever duration (80.2 ± 6.0 vs 88.1 ± 8.1 h, P < 0.05), anal exhaust time (78.8 ± 9.3 vs 85.3 ± 8.4 h, P < 0.05), and length of hospitalization (7.73 ± 2.13 vs 9.77 ± 1.76 days, P < 0.01) differed significantly. Treatment costs in thousands of dol-lars were 31.24 ± 3.21 for the experimental group and 35.61 ± 2.32 for the control group; this difference was statistically significant (P < 0.01). The incidence of postoperative complications did not significantly differ between the experimental and control groups [14.0% (21/150) vs 17.3% (26/150), P > 0.05]. At postoperative days 3 and 7, the CD3(+), CD4(+), natural killer cell, albumin, and prealbumin levels and CD4(+)/CD8(+) ra-tio were significantly higher in the experimental group than the control group (all P < 0.05). CD8(+) cell counts were significantly lower in the experimental group than the control group (P < 0.05). Postsurgical oral EEN can improve nutritional status and immune function and promote early recovery of intestinal function in patients with gastric cancer.

[Serological assessment of Helicobacter pylori-specific antibodies and their association with gastric lesions in a high-risk population].

OBJECTIVE: To determine the distributions of six Helicobacter pylori (Hp)-specific antibodies in a high-risk population of gastric cancer (GC) and explore the relationship between Hp virulence factors and precancerous gastric lesions. METHODS: Based on the two intervention trials conducted in Linqu County, the seropositivities for CagA, VacA, GroEL, UreA, HcpC and GGT were assessed by recombinant immunoassay (recomLine) in 623 participants with H. pylori infection determined by (13)C-urea breath test ((13)C-UBT) and/or enzyme linked immunosorbent assay (ELISA). RESULTS: In a total of 623 participants were detected by recomLine analysis, of which 594 were Hp-positive. The seropositivities rates of CagA, VacA, GroEL, UreA, HcpC and GGT were 84.0%, 38.2%, 66.7%, 17.7%, 58.8% and 42.8%, respectively. A total of 523 participants were determined as type I infection of Hp, accounting for 88.1%. Compared with superficial gastritis (SG), the infection rate of Hp type I was higher in the chronic atrophic gastritis (CAG) (P = 0.001). CONCLUSIONS: The results of this population-based study suggest that the virulence factors of Hp may be related to the development of GC in a Chinese high-risk population. The recomLine analysis may serve as a tool for identification of Hp strains and prediction of high-risk population of GC.

[An assessment of peripheral blood lymphocytes populations and subpopulation in patients with stomach cancer]. / Ocena populacji i subpopulacji limfocytów krwi obwodowej u chorych na raka zoladka.

AIM: In the present study, we conducted the quantitative analysis of peripheral blood lymphocytes population and subpopulation in patients with stomach cancer, based on flow cytometry immunophenotyping. MATERIAL AND METHOD: The results were compared with the advancement of the disease (UICC/TNM), histological type (Lauren classification), and grade of differentiation of stomach cancer. Lymphocyte CD: (CD3/CD19, CD3/CD4, CD3/CD8, CD3/CD16, 56) were determined in 50 cancer patients and 30 healthy humans. RESULTS: The significant deficiency of total lymphocyte number, T and B lymphocytes, as well as CD4+ and CD8+ was found in stomach cancer patients. There was no depletion in NK cells number. In advanced stomach cancer, the number of NK cells decreased, along with further deterioration of lymphocytes T and B populations. In patients with diffuse-type of stomach cancer and III or IV stage, the more pronounced deficiency in T, CD4+ and CD8+ population was noted. The decrease grade of differentiation was correlated with the increase of NK cell population. There was no correlation between the number of B lymphocytes and the histologic type or grade of differentiation of stomach cancer. CONCLUSION: The obtained data demonstrated significant quantitative defect in defence of stomach cancer patients.

[Assessment of immunotoxicity of irinotecan determined by the novel method, by which productivity of TNF-alpha from whole blood is stimulated by lipopolysaccharide].

Irinotecan hydrochloride shows much different responses in each patient, and it has severe adverse effects. Therefore, a sensitive marker for the side effect of irinotecan on immunotoxicity may be able to prevent the severe complications by the early detection. We have recently developed a method to assess the immunotoxicity by measuring the productivity of TNF-alpha from whole blood containing monocytes when stimulated by lipopolysaccharide. By using this method, the effects of continuous low-dose irinotecan therapy on immunotoxicity were assessed in 10 patients with advanced gastric or colon cancer. When compared this method with the others such as white blood cell count, lymphocyte blastoid transformation by phytohem agglutinin (PHA), and natural killer cell activity in terms of the sensitivity, immunotoxicity by this method was found earlier than the other methods. Because our original method is easy to perform and sensitive as compared to the conventional methods, it can be widely used as one of the laboratory tests useful for patients treated with immunosuppressive agents.

Preoperative assessment of gastric cancer vascularity by flash echo imaging.

BACKGROUND: Tumor vascularity as indicated by immunohistochemical staining is a significant prognostic factor in gastric and other cancers. Non-invasive preoperative assessment of the vascularity of gastric cancers has not been possible. We aim to determine the reliability of harmonic flash echo imaging (FEI) for assessment of vascularity of gastric cancers by comparison with CD34 staining of resected specimens. METHODS: Twelve patients undergoing surgical resection of advanced gastric cancer were studied. An ultrasound system transmitting ultrasound pulses at 2.3 MHz and receiving them at 4.6 MHz (second harmonic image) was used for harmonic FEI. Approximately 30 s after intravenous injection of ultrasonic contrast medium (SHU 508A, Levovist), second harmonics (4.6 MHz) emitted from microbubbles were obtained to enhance the B-mode images. Using the tumor image showing strongest enhancement in each FEI series, regions of interest were determined to measure mean echo intensity in the tumor. Immunohistochemistry using antibodies against CD34 was carried out in resected specimens. Tumor vascularity was determined by counting stained microvessels. RESULTS: A significant positive correlation was noted between sonographic amplitude determined preoperatively by FEI analysis and number of CD34-stained microvessels in tumor specimens (r = 0.869, P = 0.004). CONCLUSION: Vascularity of gastric cancers now can be evaluated non-invasively by harmonic FEI.

[Effectiveness of quarterly assessment of CEA, TPA and GICA serum levels in gastric and colorectal carcinomas: Prospective study of 174 patients undergoing radical surgery]. / Efficacia della valutazione trimestrale dei livelli sierici del CEA TPA e GICA nei carcinomi gastrici e colorettali. Studio prospettico su 174 pazienti operati radicalmente.

One-hundred seventy four consecutive patients who underwent curative resection for gastric and colorectal cancer between 1983 and 1985, were studied prospectively to evaluate the roles of sequential CEA, TPA and GICA determinations and independent clinical examinations, in the early diagnosis of resectable recurrences. Sixty-six recurrences (33 from gastric and 33 from colorectal cancer) were detected between 6 and 42 months after primary surgery. In gastric cancer CEA, TPA and GICA showed a sensitivity of 64%, 73%, and 60%, and a specificity of 67%, 65% and 54% respectively. Nine patients (27%) underwent surgical treatment for the recurrent disease, and 4 of them (44.4%) had resectable recurrence, for a total resectability rate of 12%. Out of these four patients, three patients are still living after 12, 36 and 44 months respectively from re-operation without evidence of neoplastic disease. In one of these patients re-operation was performed on the basis of the elevation of the three markers, without any other clinical sign of disease, this patient had a resectable solitary hepatic recurrence. In colorectal cancer CEA, TPA and GICA showed a sensitivity of 73%, 73%, and 49%, and a specificity of 77%, 87%, and 97% respectively. Fourteen patients (42.4%) underwent surgical treatment for the recurrent disease, and 8 of them (57%) showed a resectable recurrence, for a total resectability rate of 24.2%. Six patients are still living after 9, 16, 21, 31, 41 and 53 months respectively from reoperation without evidence of neoplastic disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of proliferating cell nuclear antigen expression in precursor stages of gastric carcinoma using the PC10 antibody to PCNA.

Immunohistochemistry using the PC10 antibody to proliferating cell nuclear antigen (PCNA) was applied to archival material from mucosa adjacent to gastric carcinoma ('normal', hyperplasia, complete and incomplete intestinal metaplasia and dysplasia) and non-cancer controls (normal and complete intestinal metaplasia). Overall, increased PCNA indices, with expansion and altered location of the proliferative zones, were observed in carcinoma fields and compared with controls (P < 0.001). These differences were particularly significant in 'normal' mucosa far from carcinoma as compared with normal in controls (P < 0.001). In carcinoma 'fields' distinct patterns of PCNA expression were noted in complete and incomplete intestinal metaplasia. Similarly, in dysplastic lesions high PCNA indices were present either throughout the gland or found predominantly in the upper compartment. We conclude that these differences in PCNA index and staining patterns might prove useful in monitoring the evolution of the disease in the follow-up of patients at risk of developing gastric cancer.

Generation of somatic cell hybrids capable of proliferating and secreting human monoclonal antibody without any growth factor supplements.

A novel cell line called Trioma, which can proliferate and secrete a human monoclonal antibody in the basal medium, was established. Trioma was generated by somatic cell hybridization with human x human hybridoma and A431c, which is a cell line able to grow autonomously in the basal medium. A Trioma called TriH8 has been kept growing in the DMEM/F-12 medium for over 1 year and stably producing stomach cancer-reactive human IgM into culture medium at 10 micrograms/ml. TriH8 has a characteristic cytological phenotype, that is, to diminish cell growth in the presence of epidermal growth factor.

Assessment of proliferative activity in carcinomas of the human alimentary tract by Ki-67 immunostaining.

The monoclonal antibody (MAb) Ki-67, which is directed against a proliferation-associated nuclear antigen, was used to measure tumor proliferation in 165 carcinomas of the esophagus, stomach, colon and rectum with an indirect immunoperoxidase technique. The percentage of Ki-67-positive tumor cells (Ki-67 index) was evaluated with the point-counting method. The Ki-67 index in gastric cancers (mean, 24.8%; standard deviation, 11.1%) was significantly lower than in tumors of the esophagus (35.7 +/- 12.6%), colon (37.6 +/- 15.2%), and rectum (34.3 +/- 16.4%). A wide range of the Ki-67 index (5.9-75.3%) could be observed within the various tumor types. In recurrent colorectal carcinomas, the Ki-67 index significantly increased to 51.9%. The Ki-67 index was independent of pathologic (e.g., TNM-stage, grading, tumor volume, tumor site) and clinical variables (age and gender of the patients). A marked heterogeneity of Ki-67 expression within different tumor stages was noted. Statistically significant regional variations in tumor proliferation existed between different areas within the same tumor.

Assessment of tumor cell kinetics by monoclonal antibody Ki-67.

The expression of Ki-67 antigen in 71 patients with advanced gastric cancer was studied by immunohistochemical technique. Immunohistochemical staining with Ki-67 produced clear labeling of a portion of tumor cell nuclei, and the nucleoli stained intensely. The Ki-67 labeling rates of the 71 specimens ranged from 7.7 to 70.5% (mean: 29.2%; standard deviation: 12.9%). There was no significant association between Ki-67 labeling rates and macroscopic type, peritoneal metastasis, or serosal invasion. The tumors showing high Ki-67 labeling rates (greater than 25%) are more likely to have liver metastasis and lymph node involvement. Larger tumors, with a diameter greater than 6 cm, more frequently showed high Ki-67 labelling rate than those with a diameter less than 6 cm. When the Ki-67 labeling rate and 9 clinicopathologic parameters, as conventional prognostic factors, were entered simultaneously into the regression model, nodal status and Ki-67 labeling rate emerged as independent prognostic factors. These results indicate that the in situ determination of the growth fraction by Ki-67 antibody may be a reliable prognostic marker of advanced gastric cancer.

Immunohistochemical assessment of splenic lymphocyte and macrophage subpopulations in patients with gastric cancer.

In order to assess the effects of malignant tumors on the immune system, 25 spleens from patients with gastric carcinoma were studied by in situ immunohistochemical methods for lymphocyte subsets and cells of the mononuclear phagocyte system. Highly significant reductions of CD4+ T cells (P less than 0.001), Ki M2+ and Ki M-3+ MPS cells (P less than 0.02 and P less than 0.05), and a stage-dependent reduction of Ki 67+ B cell proliferation activity (P less than 0.05) were seen in spleens of patients with gastric cancer. These results, which were obtained by morphologic methods in a noninvolved lymphatic organ, reflect the systemic immunosuppressive and immunodepleting effects of malignant tumors that are probably mediated by tumor-associated cytokines.