The mode of recognition of tumor antigens by noncytolytic-type antitumor T cells: role of antigen-presenting cells and their surface class I and class II H-2 molecules

β-Glucan: A dual regulator of apoptosis and cell proliferation

β-Glucans are polysaccharides generally obtained from the cell wall of bacteria, fungi, yeasts, and aleurone layer of cereals. β-Glucans are polymers, with β-1,3 glucose as core linear structure, but they differ in their main branch length, linkages and branching patterns, giving rise to high and low-molecular-weight β-glucans. They are well-known cell response modifiers with immune-modulating, nutraceutical and health beneficial effects, including anticancer and pro-apoptotic properties. β-Glucan extracts have shown positive responses in controlling tumor cell proliferation and activation of the immune system. The immunomodulatory action of β-glucans enhances the host's antitumor defense against cancer. In consonance with the above, many studies have shown that β-glucan treatment leads to the induction of apoptotic death of cancer cells. The ability of β-glucans to stimulate apoptotic pathways or the proteins involved in apoptosis prompting a new domain in cancer therapy. β-glucan can be a potential therapeutic agent for the treatment of cancer. However, there is a need to legitimize the β-glucan type, as most of the studies include β-glucan from different sources having different physicochemical properties. The body of literature presented here focuses on the effects of β-glucan on immunomodulation, proliferation, cell death and the possible mechanisms and pathways involved in these processes.

Infiltration of dendritic cells into regional lymph nodes in gastric cancer

BACKGROUND

Dendritic cells (DC), including epidermal Langerhans cells, are potent antigen-presenting cells that can carry and present tumor antigens to helper T-cells. An immunohistochemical study was performed to clarify the relationship between the extent of infiltration by DCs in primary gastric cancer and that in the regional lymph nodes.

METHODS

Paraffin blocks were prepared for staining with antibody against S-100 protein in 121 cases of gastric cancer. Infiltration of S-100 protein-positive DCs was evaluated in the primary tumor and in the peritumoral, primary, secondary, and tertiary nodes.

RESULTS

The extent of infiltration by DCs into the regional lymph nodes decreased significantly with an increasing distance of the nodes from the primary tumor. Correlation of the extent of such infiltration was observed among the peritumoral, primary, secondary, and tertiary nodes. However, the extent of infiltration into the primary tumor did not correlate with that into the primary, secondary, and tertiary nodes. Infiltration by DCs of the peritumoral nodes correlated with that of the tumor, particularly when lymph node metastasis was absent. There was no significant difference in the extent of infiltration into the peritumoral nodes even when lymph nodes were involved. However, infiltration of DCs increased in the primary and secondary nodes when the primary nodes were involved.

CONCLUSION

Infiltration of DCs may be regulated in the primary lesion of gastric cancer. The peritumoral lymph nodes serve as transmitters of DCs from the primary tumor to the regional lymph nodes. DCs in the regional lymph nodes are important for establishing immunologic defense mechanisms in cases of gastric cancer when metastasis is absent or limited to the primary nodes.

Transforming growth factor-beta (TGF-beta)-mediated immunosuppression in the tumor-bearing state: enhanced production of TGF-beta and a progressive increase in TGF-beta susceptibility of anti-tumor CD4+ T cell function

The present study deals with the effect of transforming growth factor-beta (TGF-beta) on anti-tumor immune responsiveness at various stages of the tumor-bearing state. Spleen cells from BALB/c mice bearing a syngeneic tumor (CSA1M) 1-3 wk after inoculation with CSA1M cells produced interleukin-2 (IL-2) and macrophage-activating factor (MAF)/interferon-gamma (IFN-gamma) upon in vitro culture without addition of exogenous tumor antigens. This lymphokine production was achieved through collaboration between anti-CSA1M CD4+ T cells and antigen-presenting cells that had been pulsed with CSA1M tumor antigens in vivo in the tumor-bearing state. The IL-2-producing capacity of CD4+ T cells reached the maximal level as early as one week after tumor implantation but decreased with the progress of tumor-bearing stages. In contrast, the capacity of CD4+ T cells to produce MAF/IFN-gamma was not affected but was maintained at high levels even late in the tumor-bearing state. The addition of recombinant TGF-beta (rTGF-beta) to cultures of spleen cells from various tumor-bearing stages resulted in the suppression of lymphokine production. However, the magnitude of the TGF-beta-induced suppression varied depending on which tumor-bearing stages of splenic cells were tested as a responding cell population; it was slight in cells from early (1-3 wk) tumor-bearing stages but increased in cells from donor mice at later tumor-bearing stages. Thus, spleen cells from late tumor-bearing stages with weak but significant IL-2-producing and considerable MAF/IFN-gamma producing capacities failed to produce these lymphokines when rTGF-beta was present in cultures. A progressive increase in the TGF-beta susceptibility was also observed for IL-4-producing Th2 as well as IL-2/MAF-producing Th1 cells. In addition, increased levels of TGF-beta were detected in plasma from tumor-bearing mice at late stages. Taken together, these results indicate that tumor-bearing mice exhibit enhanced production of TGF-beta as well as a progressive increase in the susceptibility of anti-tumor CD4+ T cells to TGF-beta-induced suppressive mechanisms.

In vivo and in vitro reactivity of rat spleen cells against regressor and progressor colon-cancer cell variants

Previous reports demonstrated that progressor and regressor tumor-cell variants isolated from the same colon carcinoma chemically induced in a BD-IX rat differed in their capacity to induce an immune response. The present study was aimed at analyzing the characteristics of the responses to the regressor REGb and progressor PROb clones. Spleen cells from rats bearing early REGb tumors neutralized PROb cell tumorigenicity in a Winn-type local transfer assay, but responded occasionally to REGb and PROb cells in vitro. However, spleen cells from rats immunized by several injections of REGb and PROb cells strongly proliferated when cultured with PROb or REGb cells. This response was selective for the cell lines generated from the individual tumor at the origin of PROb and REGb lines, was dependent on CD4+ spleen cells, and was partially inhibited by an antibody against major histocompatibility complex class-II molecules. Although PROb cells shared tumor-rejection antigen(s) with REGb cells, splenocytes from PROb tumor-bearing rats did not neutralize PROb-cell tumorigenicity in vivo, nor did they proliferate when cultured with PROb or REGb cells in vitro. The unresponsiveness of spleen cells from PROb tumor-bearing rats was not due to the presence of immune suppressive cells, and a defect of antigen-presenting cells was shown to be unlikely. This unresponsiveness was limited to a lymphocyte subpopulation, since spleen cells from tumor-bearing rats responded normally to stimulation by PHA or allogeneic lymphocytes. These results strongly suggest that unresponsiveness of spleen cells from tumor-bearing rats is due to a tumor-specific anergy of the lymphocyte clones able to respond to tumor-associated antigens.

Tumor-specific T cell lines: capacity to proliferate and produce interleukin 2 in response to various forms of tumor antigens

Anti-tumor proliferative T cell lines were established from cultures of lymph node cells from BALB/c mice immunized to syngeneic CSA1M fibrosarcoma with the CSA1M tumor cell membrane. The cultures were maintained throughout in the absence of exogenous interleukin 2 (IL2). Cell surface phenotypes of all T cell lines established were Thy-1+, Ig-, L3T4+ and Lyt-2-. Their proliferation was induced in a tumor antigen dose-dependent fashion and a tumor antigen-specific way. Such proliferative responses were inhibited by the addition to cultures of anti-class II H-2d (anti-I-Ad) or anti-L3T4 but not of anti-class I H-2d or anti-Lyt-2 monoclonal antibody. None of the T cell lines exhibited any cytotoxic T lymphocyte activity but they all produced IL2 upon stimulation with CSA1M tumor antigens, indicating that they represent helper-type T cell (Th) lines. The activation of these tumor-specific Th lines was induced with either CSA1M tumor cells themselves, or their membrane or detergent-solubilized fraction depending on the presence of antigen-presenting cells (APC). Most importantly, activation was also inducible by membranous tumor antigen-pulsed APC, which were capable of producing potent anti-tumor protective immunity when administered in vivo into syngeneic BALB/c mice. These results indicate that the tumor-specific Th lines established here can be activated with various forms of tumor antigens for their expression of helper function. Since Th lines of this type have not been described previously, our Th lines provide an intriguing tool for investigating the cellular and molecular mechanisms by which tumor-specific Th recognize tumor antigens.

Tumor-immunotherapy with the use of tumor-antigen-pulsed antigen-presenting cells

Our previous study demonstrated that the administration of antigen-presenting cells (APC) pulsed with tumor cell membrane fraction to naive syngeneic mice results in effective induction of tumor-specific protective immunity in vivo. The present study examined whether tumor-antigen-pulsed APC can produce the inhibitory effect on the growth of tumor cells when administered to tumor-bearing hosts. Naive BALB/c mice were inoculated with viable tumor cells. Five days later, these mice started to receive the relevant tumor-antigen-pulsed APC at 3- to 4-day intervals. The administration of tumor-antigen-pulsed APC induced the rejection or growth inhibition of a growing tumor in approximately half of the recipient mice. Moreover, it was demonstrated that tumor-specific immunity was induced in such tumor-regressed mice. These results indicate that tumor-antigen-pulsed APC are effectively applicable to the tumor-specific immunotherapy.

T-cell subsets, IFN-gamma production and efferent specificity in anti-parental tumor immunity induced by mouse sensitization with xenogenized variant cells

In addition to previous evidence for a role of L3T4+ T cells in the protective anti-parental tumor immunity induced by xenogenized variant cells of a murine lymphoma (L5178Y/DTIC), we have investigated the possible participation in this effect of L5178Y tumor-specific lymphocytes of the Lyt-2+ T cell subset. Spleen cells from L5178Y/DTIC tumor-immunized mice produced high levels of IFN-gamma in vitro in response to parental antigens, and this activity was only abolished by treating the responder population with anti-Thy-1.2 antibody or a combination of anti-L3T4 and anti-Lyt-2.2 monoclonal antibodies (MAbs) plus complement. Positively selected L3T4+ and Lyt-2+ cells also produced IFN-gamma in vitro, provided accessory cells (plastic-adherent and Thy-1- Ia- splenocytes, respectively) were added to the lymphocyte-tumor cell cocultures. The production of IFN-gamma by purified L3T4+ and Lyt-2+ cells was inhibited by addition of the respective anti-class-II and anti-class-I H-2 antibody to the cultures. Administration of anti-IFN-gamma MAb in vivo significantly impaired the resistance of L5178Y/DTIC-immune mice to challenge with parental cells, as manifested by survival criteria and increased tumor-cell proliferation in the spleens of antibody-treated mice. Although anti-parental tumor protection in vivo and T-cell activation in vitro for IFN-gamma production were strictly antigen-specific, bystander tumor inhibition was observed when antigenically irrelevant cells were inoculated with the L5178Y lymphoma. These results suggest that both L3T4+ and Lyt-2+ T cells play a role in the protective anti-parental tumor immunity induced by xenogenized cells, and that their activity may involve IFN-gamma-mediated stimulation of non-specific tumoricidal mechanisms.