Activated invariant natural killer T cells directly recognize leukemia cells in a CD1d‐independent manner

Invariant natural killer T (iNKT) cells are innate‐like CD1d‐restricted T cells that express the invariant T cell receptor (TCR) composed of Vα24 and Vβ11 in humans. iNKT cells specifically recognize glycolipid antigens such as α‐galactosylceramide (αGalCer) presented by CD1d. iNKT cells show direct cytotoxicity toward CD1d‐positive tumor cells, especially when CD1d presents glycolipid antigens. However, iNKT cell recognition of CD1d‐negative tumor cells is unknown, and direct cytotoxicity of iNKT cells toward CD1d‐negative tumor cells remains controversial. Here, we demonstrate that activated iNKT cells recognize leukemia cells in a CD1d‐independent manner, however still in a TCR‐mediated way. iNKT cells degranulated and released Th1 cytokines toward CD1d‐negative leukemia cells (K562, HL‐60, REH) as well as αGalCer‐loaded CD1d‐positive Jurkat cells. The CD1d‐independent cytotoxicity was enhanced by natural killer cell‐activating receptors such as NKG2D, 2B4, DNAM‐1, LFA‐1 and CD2, but iNKT cells did not depend on these receptors for the recognition of CD1d‐negative leukemia cells. In contrast, TCR was essential for CD1d‐independent recognition and cytotoxicity. iNKT cells degranulated toward patient‐derived leukemia cells independently of CD1d expression. iNKT cells targeted myeloid malignancies more than acute lymphoblastic leukemia. These findings reveal a novel anti–tumor mechanism of iNKT cells in targeting CD1d‐negative tumor cells and indicate the potential of iNKT cells for clinical application to treat leukemia independently of CD1d.     

CD155 mutation (Ala67Thr) increases the binding affinity for and the signaling via an inhibitory immunoreceptor TIGIT

CD155 is a shared ligand for activating and inhibitory immunoreceptors DNAX accessory molecule 1 (DNAM‐1), also called CD226, and T cell immunoglobulin and immunoreceptor tyrosine‐based inhibitory motif domain (TIGIT), which are expressed on natural killer (NK) cells and T cells, and positively and negatively regulates tumor immune responses, respectively. A recent study showed that the single nucleotide polymorphism rs1058402G>A causing a mutation to Thr from Ala at residue 67 of CD155 is associated with worse overall survival of patients with small cell lung cancer and suggested that this is caused by the decreased affinity of mutant CD155 for DNAM‐1 as a result of the 3D structural analysis. Unexpectedly, however, we found that the mutation increased the binding affinity for TIGIT rather than decreased the binding affinity for DNAM‐1 and induced a stronger signal than WT CD155. Our results suggest that the mutation suppresses tumor immune responses by generating a stronger inhibitory signal in immune cells in the tumor microenvironment.     

Infiltration of tumor‐associated macrophages is involved in CD44 expression in clear cell renal cell carcinoma

Cancer stem‐like cells (CSC) or cancer‐initiating cells are now considered to be an important cell population related to cancer recurrence and the resistance to anti‐cancer therapy. Tumor‐associated macrophages (TAM) are a main component of stromal cells and are related to cancer progression in clear cell renal cell carcinoma (ccRCC). Because the detailed mechanisms allowing the maintenance of CSC in cancer tissues remain unclear, we investigated the relationship between TAM and CD44‐expressing cancer cells in ccRCC. CD44 was used as a marker for CSC, and CD163 and CD204 were used as markers for TAM. CD44‐positive cancer cells were detected in 37 of the 103 cases. Although statistical analysis showed no relationship between CD44‐positive cancer cells and the clinical course, the distribution of CD44‐positive cancer cells was significantly associated with a high density of TAM. Our in vitro study using RCC cell lines and human macrophages demonstrated that CD44 expression was upregulated by direct co‐culture with macrophages. Silencing of TNF‐alpha on macrophages abrogated the upregulation of CD44 expression in cancer cells. Macrophage‐induced CD44 overexpression was also suppressed by NF‐κB inhibitors. These results suggest that TNF‐alpha derived from TAM is linked to CD44 overexpression via NF‐κB signaling in ccRCC.     

Transformation-associated 86 kDa Natural Killer Target Molecule Expressed on the Mouse, Rat and Human Cell Surface

We previously reported on the 86 kDa natural killer target molecule associated with transformation of the oncogene-transfected rat fibroblasts. This molecule may participate in the lethal hit phase of cytotoxicity by natural killer (NK) cells. Originally, this molecule was defined by mAb109, hut mAb109 could react only with rat tumor lines. In this report, to determine whether the 86 kDa molecule could be utilized as a natural killer target molecule in mammalian cells, we developed a polyclonal anti-86 kDa antibody (pAh109). Our data indicated that pAh109 preferentially reacted with NK-susceptible lines such as mouse YAC-1, rat W31 and human K562 cells, but reacted only weakly with NK-resistant mouse EL-4, rat fetal fibroblast WFB and human fetal fibroblast HEPM. In a cytotoxicity experiment, pAb109 F(ab')2 fragments could inhibit the cytolysis by NK cells of W31 and K562 cells. However, these fragments did not inhibit the cytotoxicity of non-NK cells such as CD3⁺, CD4⁻, CD8⁻ T cell receptor αβ⁻ -T cells (presumably γδ T cells) to W31 cells. Taken together, these data suggest that the cell transformation-associated 86 kDa molecule may be critical in NK cytotoxicity, and a candidate for the NK target structure in mammalian tumor cells.     

Indoleamine 2,3‐dioxygenase promotes peritoneal metastasis of ovarian cancer by inducing an immunosuppressive environment

Indoleamine 2,3‐dioxygenase (IDO) is a tryptophan‐catabolizing enzyme that has immunoregulatory functions. Our prior study showed that tumoral IDO overexpression is involved in disease progression and impaired patient survival in human ovarian cancer, although its mechanism remains unclear. The purpose of the present study is to clarify the role of IDO during the process of peritoneal dissemination of ovarian cancer. Indoleamine 2,3‐dioxygenase cDNA was transfected into the murine ovarian carcinoma cell line OV2944‐HM‐1, establishing stable clones of IDO‐overexpressing cells (HM‐1‐IDO). Then HM‐1‐IDO or control vector‐transfected cells (HM‐1‐mock) were i.p. transplanted into syngeneic immunocompetent mice. The HM‐1‐IDO‐transplanted mice showed significantly shortened survival compared with HM‐1‐mock‐transplanted (control) mice. On days 11 and 14 following transplantation, the tumor weight of peritoneal dissemination and ascites volume were significantly increased in HM‐1‐IDO‐transplanted mice compared with those of control mice. This tumor‐progressive effect was coincident with significantly reduced numbers of CD8⁺ T cells and natural killer cells within tumors as well as increased levels of transforming growth factor‐β and interleukin‐10 in ascites. Finally, treatment with the IDO inhibitor 1‐methyl‐tryptophan significantly suppressed tumor dissemination and ascites with reduced transforming growth factor‐β secretion. These findings showed that tumor‐derived IDO promotes the peritoneal dissemination of ovarian cancer through suppression of tumor‐infiltrating effector T cell and natural killer cell recruitment and reciprocal enhancement of immunosuppressive cytokines in ascites, creating an immunotolerogenic environment within the peritoneal cavity. Therefore, IDO may be a promising molecular target for the therapeutic strategy of ovarian cancer.     

CD276 suppresses CAR-T cell function by promoting tumor cell glycolysis in esophageal squamous cell carcinoma

BackgroundAs an immune checkpoint that suppresses antitumor immunity, CD276 is a potential therapeutic target for cancer immunotherapy. However, the role of CD276 in esophageal squamous cell carcinoma (ESCC) has not been thoroughly examined. A greater understanding of the regulatory mechanism of CD276 may improve the clinical response and efficacy of cancer immunotherapy.MethodsThe expression of CD276 was measured by qRT-PCR, IHC and flow cytometry analysis. T cell infiltration in ESCC was measured by qRT-PCR and immunofluorescence analysis. The regulation function of CD276 in glucose metabolism was examined by metabolism assays, western blotting and small molecule inhibitors. Transfection was used for gene editing. The oncogenic function of CD276 was examined in vivo by CAR-T cell therapy model.ResultsBased on our findings, CD276 regulated the expression of the PKM2 gene in ESCC. Overexpression of CD276 induced the phosphorylation of PKM2 by the STAT3 signalling pathway to promote glucose metabolism in tumors. The accumulation of lactic acid in the tumor microenvironment has been reported to regulate the immune cells, particularly CD8+ T cells. We further analyzed the effect of CD276 on the function of T cells. Chimeric antigen receptor T cells (CAR-T) targeting human epidermal growth factor receptor 2 (HER2) were used as effector cells to detect the effect of CD276 on immunotherapy. The therapeutic effects of CAR-T cells were markedly limited by CD276 overexpression.ConclusionsOur results are the first to show that tumor-derived CD276 supports disease progression. Overexpression of CD276 promoted glucose metabolism in tumor and inhibited the function of CD8+ T cells. Therefore, strategies targeting CD276 might improve the response to cancer immunotherapy of ESCC patients.     

CD155 expression and its clinical significance in non-small cell lung cancer

CD155 serves an important role in tumor progression by promoting cell proliferation and migration. CD155 is also involved in the immune evasion of tumor cells, which may cause the development and progression of tumors. Accordingly, CD155 has emerged as a novel target in cancer immunotherapy; however, its expression in lung cancer remains unclear. To assess CD155 expression and its prognostic significance, 96 patients with completely resected pathologic stage I adenocarcinoma of the lung were retrospectively reviewed. Immunohistochemical staining was performed to evaluate CD155 expression on tumor cells. Expression levels of programmed death-ligand 1 (PD-L1), another molecule participating in immune evasion, were also evaluated immunohistochemically. CD155 expression was positive in 37 patients (38.5%). CD155-positivity was associated with aggressive tumor behavior, such as pleural invasion and vascular invasion. In addition, CD155-positivity was a significant factor to predict a poor prognosis (5-year overall survival (OS) rate, 63.3% for CD155-positive patients vs. 93.1% for CD155-negative patients; P<0.001). Patients harboring tumors with positive CD155 and PD-L1 expression showed the poorest prognosis (5-year OS rate, 44.4% for both-positive patients vs. 85.4% for the other patients; P<0.001). The positive expression status of both CD155 and PD-L1 was a significant and independent unfavorable prognostic factor (hazard ratio, 3.86; 95% confidence interval, 1.51-9.89; P=0.004; in a multivariate analysis). In conclusion, CD155-positivity was associated with aggressive tumor behavior, and was a factor to predict a poor prognosis. Its prognostic impact was enhanced when combined with PD-L1 expression status. These results should be validated in a large-scale study.     

The CD155/poliovirus receptor enhances the proliferation of ras-mutated cells

Stimulation of the CD155/poliovirus receptor, which localizes in the cell-matrix and at cell-cell junctions, inhibits cell adhesion and enhances cell migration. Necl-5, a mouse homolog of CD155, is implicated in the formation of adherence junctions. Recently, Necl-5 has also been found to enhance cell proliferation via the stimulation of serum and platelet-derived growth factor through the Ras-Raf-MEK-ERK signaling pathway. In our present study, we find that CD155 significantly enhances the serum-induced cell proliferation of NIH3T3 cells which have been transformed by an oncogenic Ras (V12Ras-NIH3T3), but not the parental cells. CD155 expression in V12Ras-NIH3T3 cells is also found to upregulate cyclin D2, downregulate p27(Kip1) and shorten the G0/G1 phase of the cell cycle. An inhibitor of focal adhesion kinase does not reduce this CD155-mediated enhancement of V12Ras-NIH3T3 cell proliferation. The expression of CD155DeltaCP, which lacks the cytoplasmic region including the immunoreceptor tyrosine-based inhibitory motif (ITIM), has a reduced ability to enhance the serum responsiveness of V12Ras-NIH3T3 cells, suggesting that the ITIM might be required for this effect of CD155. In addition, the overexpression of exogenous CD155 enhances the serum responsiveness of HT1080 cells, which harbor a mutant N-ras gene. On the other hand, siRNA-induced knockdown of endogenous CD155 and/or CD155DeltaCP expression significantly repress the serum responsiveness of DLD-1 cells, which express endogenous CD155 and harbor a mutant K-ras gene, suggesting that this mutant may function in a dominant negative manner. Taken together, our present data suggest that CD155, at least in part, enhances the proliferation of ras-mutated cells.     

Molecular identification of GD3 as a suppressor of the innate immune response in ovarian cancer

Tumors often display mechanisms to avoid or suppress immune recognition. One such mechanism is the shedding of gangliosides into the local tumor microenvironment, and a high concentration of circulating gangliosides is associated with poor prognosis. In this study, we identify ganglioside GD3, which was isolated from the polar lipid fraction of ovarian cancer-associated ascites, as an inhibitory factor that prevents innate immune activation of natural killer T (NKT) cells. Purified GD3 displayed a high affinity for both human and mouse CD1d, a molecule involved in the presentation of lipid antigens to T cells. Purified GD3, as well as substances within the ascites, bound to the CD1d antigenic-binding site and did not require additional processing for its inhibitory effect on NKT cells. Importantly, in vivo administration of GD3 inhibited α-galactosylceramide (α-GalCer)-induced NKT cell activation in a dose-dependent manner. These data therefore indicate that ovarian cancer tumors may use GD3 to inhibit the antitumor NKT cell response as an early mechanism of tumor immune evasion.     

CD155 contributes to the mesenchymal phenotype of triple‐negative breast cancer

Patients with triple‐negative breast cancer (TNBC) lack molecular targets and have an unfavorable outcome. CD155 is overexpressed in human cancers, but whether it plays a role in TNBC is unexplored. Here we found that CD155 was enriched in both TNBC cell lines and tumor tissues. High CD155 expression was related to poor prognosis of breast cancer patients. CD155 was associated with a mesenchymal phenotype. CD155 knockdown induced a mesenchymal‐epithelial transition in TNBC cells, and suppressed TNBC cell migration, invasion and metastasis in vitro and in vivo. Mechanistically, CD155 cross‐talked with oncogenic IL‐6/Stat3 and TGF‐β/Smad3 pathways. Moreover, CD155 knockdown inhibited TNBC cell growth and survival. Taken together, these data indicate that CD155 contributes to the aggressive behavior of TNBC; targeting CD155 may be beneficial to these patients.     

HLA-E/β2 microglobulin overexpression in colorectal cancer is associated with recruitment of inhibitory immune cells and tumor progression

The host immune response plays a major role in colorectal carcinoma (CRC) progression. A mechanism of tumor immune escape might involve expression of the human leucocyte antigen (HLA)-E/β2m on tumor cells. The inhibitory effect of HLA-E/β2m on CD8+ cytotoxic T lymphocytes and natural killer (NK) cells is mediated by the main HLA-E receptor CD94/NKG2A. As the pathophysiological relevance of this mechanism in CRC remains unknown, this prompted us to examine, in situ, in a series of 80 CRC (i) the HLA-E and β2m coexpression by tumor cells, (ii) the density of CD8+, cytotoxic, CD244+ and NKP46+ intraepithelial tumor-infiltrating lymphocyte (IEL-TIL) and (iii) the expression of CD94/NKG2 receptor on IEL-TIL. These data were then correlated to patient survival. We provided (i) the in situ demonstration of HLA-E/β2m overexpression by tumor cells in 21% of CRC characterized by an overrepresentation of signet ring cell carcinomas, mucinous carcinomas and medullary carcinomas, (ii) the significant association between HLA-E/β2m overexpression by tumor cells and increased density of CD8+ cytotoxic, CD244+ and CD94+ IEL-TIL and (iii) finally, the unfavorable prognosis associated with HLA-E/β2m overexpression by tumor cells. Our findings show that HLA-E/β2m overexpression is a surrogate marker of poor prognosis and point to a novel mechanism of tumor immune escape in CRC in restraining inhibitory IEL-TIL.     

High density of CD204‐positive macrophages predicts worse clinical prognosis in patients with breast cancer

Recent studies have indicated the clinical significance of tumor‐associated macrophages (TAM) in several malignant tumors including breast cancer. Although recent studies have focused on CD68‐positive or CD163‐positive TAM in breast cancer, no study has investigated the significance of CD204‐positive TAM in breast cancer. We found that CD204 expression on macrophages was evaluated following stimulation with the conditioned medium (CM) of breast cancer cell lines. Paraffin sections of 149 breast cancer samples which were diagnosed as invasive ductal carcinoma were immunohistochemically analyzed for CD68, CD163 and CD204 expression. The results of analyses indicated that a high number of CD204‐positive TAM was associated with worse clinical prognoses, including relapse‐free survival, distant relapse‐free survival and breast cancer‐specific survival; however, neither the numbers of CD68‐positive or CD163‐positive TAM were associated with clinical courses. Of the clinicopathological factors investigated, estrogen receptor, Ki‐67 index, hormone subtype, and histological grade were significantly related to the increased number of CD163‐positive and CD204‐positive TAM. These data indicate the clinical significance of CD204‐positive TAM in breast cancer progression and CD204 is a marker for predicting clinical prognosis in breast cancer.     

Role for CD40L in the Therapy of Human Cancer

CD40L-CD40 interaction is central to the control of thymusdependent humoral immunity and cell mediated immune responses. CD40, a member of the tumor necrosis factor receptor （TNF- R） family, has been found on the surface of B lymphocytes, monocytes, hematopoietic progenitors, dendritic cells （DCs）, endothelial cells, epithelial cells and so on. Its natural ligand （CD40 ligand, CD40L）, CD154, a member of the tumor necrosis factor （TNF） family, is mainly expressed on activated CD4^＋ T lymphocytes. A direct growth-inhibitory effect can be found when ligated CD40 is on human breast, ovarian, cervical, bladder, non-small cell lung, and squamous epithelial carcinoma cells. This effect is related to the induction of cell cycle blockage and/or apoptosis. CD40L induces phenotypic and functional maturation of DCs, and can increase tumor immunogenicity through up-regulation of costimulatory molecular expression and cytokine production by epithelial cancer cells. As a result, CD40L can enhance tumor rejection immune responses. Furthermore, by means of a “bystander effect”, even CD40-negative tumor subsets can be eliminated by activated tumor-reactive cytotoxic T lymphocytes（CTL）. This review summarizes recent findings on CD40L recombinant protein and gene therapy-based tumor treatment approaches.     

CD47 agonist peptide PKHB1 induces immunogenic cell death in T‐cell acute lymphoblastic leukemia cells

T‐cell acute lymphoblastic leukemia (T‐ALL) has a poor prognosis derived from its genetic heterogeneity, which translates to a high chemoresistance. Recently, our workgroup designed thrombospondin‐1‐derived CD47 agonist peptides and demonstrated their ability to induce cell death in chronic lymphocytic leukemia. Encouraged by these promising results, we evaluated cell death induced by PKHB1 (the first‐described serum‐stable CD47‐agonist peptide) on CEM and MOLT‐4 human cell lines (T‐ALL) and on one T‐murine tumor lymphoblast cell‐line (L5178Y‐R), also assessing caspase and calcium dependency and mitochondrial membrane potential. Additionally, we evaluated selectivity for cancer cell lines by analyzing cell death and viability of human and murine non‐tumor cells after CD47 activation. In vivo, we determined that PKHB1‐treatment in mice bearing the L5178Y‐R cell line increased leukocyte cell count in peripheral blood and lymphoid organs while recruiting leukocytes to the tumor site. To analyze whether CD47 activation induced immunogenic cell death (ICD), we evaluated damage‐associated molecular patterns (DAMP) exposure (calreticulin, CRT) and release (ATP, heat shock proteins 70 and 90, high‐mobility group box 1, CRT). Furthermore, we gave prophylactic antitumor vaccination, determining immunological memory. Our data indicate that PKHB1 induces caspase‐independent and calcium‐dependent cell death in leukemic cells while sparing non‐tumor murine and human cells. Moreover, our results show that PKHB1 can induce ICD in leukemic cells as it induces CRT exposure and DAMP release in vitro, and prophylactic vaccinations inhibit tumor establishment in vivo. Together, our results improve the knowledge of CD47 agonist peptides potential as therapeutic tools to treat leukemia.     

A mesenchymal‐like phenotype and expression of CD44 predict lack of apoptotic response to sorafenib in liver tumor cells

The multikinase inhibitor sorafenib is the only effective drug in advanced cases of hepatocellular carcinoma (HCC). However, response differs among patients and effectiveness only implies a delay. We have recently described that sorafenib sensitizes HCC cells to apoptosis. In this work, we have explored the response to this drug of six different liver tumor cell lines to define a phenotypic signature that may predict lack of response in HCC patients. Results have indicated that liver tumor cells that show a mesenchymal‐like phenotype, resistance to the suppressor effects of transforming growth factor beta (TGF‐β) and high expression of the stem cell marker CD44 were refractory to sorafenib‐induced cell death in in vitro studies, which correlated with lack of response to sorafenib in nude mice xenograft models of human HCC. In contrast, epithelial‐like cells expressing the stem‐related proteins EpCAM or CD133 were sensitive to sorafenib‐induced apoptosis both in vitro and in vivo. A cross‐talk between the TGF‐β pathway and the acquisition of a mesenchymal‐like phenotype with up‐regulation of CD44 expression was found in the HCC cell lines. Targeted CD44 knock‐down in the mesenchymal‐like cells indicated that CD44 plays an active role in protecting HCC cells from sorafenib‐induced apoptosis. However, CD44 effect requires a TGF‐β‐induced mesenchymal background, since the only overexpression of CD44 in epithelial‐like HCC cells is not sufficient to impair sorafenib‐induced cell death. In conclusion, a mesenchymal profile and expression of CD44, linked to activation of the TGF‐β pathway, may predict lack of response to sorafenib in HCC patients.     

Inhibition of T cell and natural killer cell function by adenosine and its contribution to immune evasion by tumor cells (Review)

The resistance of many human cancers to immune-based therapies, including adoptive immunotherapy and the administration of therapeutic cancer vaccines, has been attributed to tumor-associated immune suppression, due in part to immunosuppressive molecules located within the tumor microenvironment. Adenosine is a purine nucleoside found within the interstitial fluid of solid tumors at concentrations that are able to inhibit cell-mediated immune responses to tumor cells. It is well established that extracellular adenosine inhibits T lymphocyte activation and effector function, including T cell adhesion to tumor cells and cytotoxic activity, by signaling primarily through A2a and A3 adenosine receptors on the surface of T cells. Importantly, A2a adenosine receptor-deficient mice exhibit enhanced anti-tumor immune responses by CD8+ T cells, as well as a dramatic reduction in the growth of experimental tumors in comparison to wild-type controls. A2a adenosine receptor signaling has also been implicated in adenosine-mediated inhibition of cytokine production and cytotoxic activity by activated natural killer (NK) cells, although the process of NK cell granule exocytosis is apparently suppressed via a distinct and as yet uncharacterized adenosine receptor. In this report, we review the evidence that adenosine is a potent inhibitor of cellular immune responses and may therefore be a major barrier to the successful immunotherapy of human carcinomas. The signaling pathways through which adenosine exerts its inhibitory effects on cell-mediated immune responses are also discussed. The accumulated evidence suggests that the effectiveness of immune-based therapies for solid tumors may be enhanced by selective antagonism of the adenosine receptor subtypes through which adenosine inhibits the anti-tumor activity of T lymphocytes and NK cells.     

Reconstitution of Anti-tumor Effects of Lentinan in Nude Mice: Roles of Delayed-type Hypersensitivity Reaction Triggered by CD4-positive T Cell Clone in the Infiltration of Effector Cells into Tumor

Lentinan, an antitumor polysaccharide used clinically in Japan, requires the intact T cell compartment to manifest its antitumor effects. The aim of the current study was to clarify the mechanisms playing crucial roles in the T cell requirement in the expression of antitumor effects of lentinan. Lentinan treatment of BDF1 mice transplanted intradermally with FBL-3 induced complete tumor regression and a marked increase in survival time. The antitumor action of lentinan was abolished in mice treated simultaneously with antibodies to CD4 and CD8 antigens, whereas antibody to CD4, CD8 or NK1.1 alone was ineffective. The natural killer, cytotoxic T lymphocyte, and helper T cell activities were already augmented in this FBL-3/BDF1 system and thus further augmentation of these activities by lentinan was not observed. These activities did not correlate with the antitumor activity of lentinan, as was confirmed in lymphocyte subset depletion experiments. On the contrary, the delayed-type hypersensitivity (DTH) response against tumor-associated antigens was triggered by lentinan and was abrogated only in mice treated simultaneously with antibodies to CD4 and CD8 antigens. Furthermore, a non-cytolytic tumor-associated antigen-specific CD4⁺ T cell clone able to induce the DTH response in concert with lentinan reconstituted the antitumor effects in B6 nude mice when administered with lentinan. These results suggest that, in addition to the augmentation of immune effector cell activity against tumors, infiltration of these cells into the tumor burden initiated by the DTH responses at tumor sites may be involved in eradication of tumors by lentinan.