The effects of cyclophosphamide on in vitro cytotoxic responses to a syngeneic tumour

Summary We have studied the effects of treating DBA/2 mice with high doses of cyclophosphamide upon their subsequent ability to generate cytotoxic cells in vitro against syngeneic tumour antigens or alloantigens. High doses of cyclophosphamide (100–200 mg/kg body weight) eliminated the response to both antigens. The addition of normal DBA/2 thymocytes into these cultures restored the response to allogeneic cells but not to tumour cells. The anti-tumour response could be restored by the addition of interleukin 2 to the cultures. Treatment with high doses of cyclophosphamide decreased the number of anti-tumour cytotoxic cell precursors in the spleen, but did not affect the capacity of bulk cultures of spleen cells to produce interleukin 2 when stimulated with the mitogen concanavalin A.Abbreviations CY Cyclophosphamide - CTL cytotoxic T cells - CTLp precursor cytotoxic T cells - IL2 interleukin 2 - Con A concanavalin A - FCS fetal calf serum     

A syngeneic splenic cell antigen induces a suppressor T cell in lymph nodes that controls cytotoxic T-cell and primary antibody responses

The nonspecific suppression of immunological responses that is generated within host popliteal lymph nodes upon exposure to syngeneic normal spleen cells has been examined. The suppression, which had previously been described as being capable of preventing initiation of cytotoxic T lymphocytes (CTLs) to hapten-altered self antigens, arises within 3 to 7 days after injecting the spleen cells. Suppression was shown to be attributable to an induced T cell that was functional when transferred intravenously. Although the cell surface marker(s) on both splenic B and T cells that stimulates appearance of Ts has not yet been identified, the cells possessing the marker were not required to be viable to cause the induction. We have shown here that the Ts is fully functional when it is put in the antigenic site used for CTL immunization. The induced Ts has been identified as bearing the Lyt 2.1 cell surface marker. Furthermore, it has been shown to be insensitive to cyclophosphamide (CY), thus differentiating it from the naturally occurring Ts cell (TS0) that is known to be CY sensitive. In addition to preventing induction of CTLs toward hapten-altered self antigens, exposing popliteal lymph nodes to syngeneic spleen cells induced Ts capable of suppressing the primary IgM antibody response to sheep red blood cells. The Ts cells that suppressed the primary antibody response possessed the same Lyt cell surface markers and CY insensitivity as the Ts that mediated suppression of the CTL response. Thus, evidence that two dissimilar immunological reactions may be down-regulated by the same suppressor mechanism has been provided. Results of a kinetic study showed that the Ts prevented development of both the humoral and the cell-mediated immune responses by affecting their inductive phases. Possible targets for suppression that more than likely would have to be common to the two widely different immune responses have been indicated.     

Human in vitro allogeneic responses. Demonstration of three pathways of T helper cell activation

In our study, we have measured in vitro proliferation and IL-2 production by human PBL to characterize the interactions between Th cells and accessory cells (AC) involved in responses to either conventional Ag or alloantigens. IL-2 production and proliferative responses to conventional Ag, such as influenza or tetanus, are exclusively dependent on the presence of CD4+ T cells and AC. In contrast, IL-2 and proliferative responses to alloantigen can be mediated by either CD4+ or CD8+ T cells. CD4+ T cells respond to alloantigen using either autologous AC (self-restricted), or allogeneic AC (allo-restricted), whereas CD8+ T cells respond to alloantigen using allogeneic AC only. The understanding of Th cell-AC interactions involved in in vitro allogeneic responses will be important for delineating the Th cell-AC interactions involved in transplantation immunity as well as in clinical disorders characterized by T cell dysfunction such as human immunodeficiency virus infection and systemic lupus erythematosus.     

The T cell repertoire to a multideterminant antigen. Clonal heterogeneity of the T cell response, variation between syngeneic individuals, and in vitro selection of T cell specificities.

The specificity of lysozyme-induced T cell proliferative responses by individual B10.A mice was compared by using a panel of three peptides. A surprising degree of variation in the focus of the responses was observed among individual animals, both in the newly isolated lymph node cell populations and in long term T cell lines. The responses to each determinant after hen egg-white lysozyme immunization were not equal and in examining the mice as a group some determinants tended to be dominant. However, despite each animal favoring a restricted number of determinants, the responding T cell populations were still highly heterogeneous. The data suggest that many determinants are involved in the response to the whole Ag. The role of one or more dominant determinants can be overestimated because the degree of heterogeneity in long term T cell lines appears to be less than in freshly obtained lymph node cells, indicating that a process of in vitro selection occurs. We observed that the T cells responsive to one peptide, 46-61, appeared to have a selective advantage in vitro culture.     

Regulatory T cell: a protection for tumour cells

Characterized by immunosuppression regulatory T cells (Tregs) play a key role in maintaining immune tolerance. A growing number of tumours have been found with Tregs accumulating in microenvironment and patients with high density of Tregs in tumour stroma get a worse prognosis, which suggests that Tregs may inhibit anti-tumour immunity in stroma, resulting in a poor prognosis. In this paper, we demonstrate the accumulation of Tregs in tumour stroma and the possible suppressive mechanisms. We also state the immunotherapy that has being used in animal and clinical trials.     

Hapten-specific T cell responses to 4-hydroxy-3-nitrophenyl acetyl. XIII. Characterization of a third T cell population involved in suppression of in vitro PFC responses

The involvement of a third-order suppressor T cell population (Ts3) in the suppression of in vitro PFC responses was analyzed. It was shown that Ts2 effector-phase suppressor cells, induced by the i.v. injection of NP-coupled syngeneic spleen cells, require a third suppressor T cell population to effect NPb idiotype-specific suppression of an in vitro B cell response. This Ts3 population was shown to be present in NP-primed but not unprimed donors. The Ts3 population specifically binds NP and is Lyt-1-, Lyt-2+, I-J+ and bears NPb idiotypic determinants. The involvement of the Ts3 population in a suppressor pathway that requires recognition of idiotypic determinants is discussed.     

Contrasting effects of T cell growth factors on T cell responses to melanoma in vitro

 Determinants of T cell responses to tumor cells remain largely unknown. In the present study we have used long-term cultures of human melanoma cells and autologous peripheral blood lymphocytes to examine the influence of cytokines with T cell growth activity on the phenotype and cytotoxic and proliferative response of T cells to melanoma. It was found that addition of interleukin-4 (IL-4) inhibited the response of CD8⁺ T cells and promoted the response of the CD4 subset. IL-2 or IL-7 was effective in increasing melanoma-specific cytotoxic T lymphocyte (CTL) activity in cultures where CD8 T cells were predominant, whereas IL-4 followed by IL-2 was most effective in cultures where CD4 T cells predominated. IL-10 or IL-12 inhibited proliferation and CTL activity against melanoma in long-term cultures. The effects of IL-12 were reproduced in long-term cultures of T cells stimulated with mAb against CD3 and were shown to depend on prior exposure of T cells to IL-12 before IL-2. As yet unidentified factors, such as co-factor expression on melanoma, appear to be as important as exogenous cytokines in determining the nature of T cell responses to melanoma. These results suggest that analysis of responses in long-term culture may assist in defining the role of key cytokines and other determinants of immune responses to melanoma. Received: 4 June 1996 / Accepted: 12 November 1996     

Participation of three lymphoid cell types in the in vitro activation of cell-mediated immunity to a syngeneic gross virus-induced lymphoma in rats.

W/Fu rats inoculated with the syngeneic Gross-virus induced lymphoma, (C58NT)D, had transient lymphocyte-mediated specific cytotoxicity against the tumor cells at 7–15 days after tumor injection. Spleen cells 40 days after immunization (spleen 40) were unreactive by a direct 4-hr ⁵¹Cr release assay, but activity appeared after in vitro culture of these spleen eclls by themselves for 18–24 hr. The nature of the cells involved in the activation of cytotoxicity and the characteristics of the effector cells themselves were studied. Significant differences were seen in the cell types involved in the activation phase and the effector phase. Activation appeared to require the cooperation of three cell types. Induction of activity was lost by treatment of cells with ATS plus complement, by passage over an EAC-column, or by treatment with carbonyl iron. Thus, T cells, CRL and macrophages were necessary for full activation of cytotoxicity in spleen 40. In contrast, after activation, only CRL seemed to be required for cytotoxicity, and treatment wih ATS or carbonyl iron had little effect. The effector cell detected after in vitro activation was quite distinct from that seen in the direct cytotoxicity assay with spleen cells at 10 days after tumor cell inoculation. The early, direct cytotoxic reactivity was dependent on T cells, being eliminated by treatment with ATS and complement but not by EAC columns or carbonyl iron. It appears therefore that the in vitro activation is a separate mechanism for cytotoxicity against tumor cells, rather than a simple recovery of T cells from in vivo inhibition.     

Cytotoxic and proliferative lymphocyte responses to allogeneic and xenogeneic antigens in vitro.

In vitro lymphoproliferative responses to foreign histocompatibility antigens are phylogenetically restricted. Responses occur most readily to allogeneic or closely related xenogeneic leucocytes, but not to unrelated xenogeneic cells. Specific cytotoxic T cell responses to foreign histocompatibility antigens show the same phylogenetic restriction. This lack of xenoreactivity is not due to a lack of precursor cells for the xenoantigens; guinea-pig lymphocytes, although normally unresponsive to mouse antigens, have a similar precursor frequency for these antigens as do lymphocytes of allogeneic mouse strains. Specific cytotoxic responses of guinea-pig lymphocytes to mouse antigens can be generated if a factor released from con A stimulated guinea-pig spleen cells is added to the culture medium. The factor produced by con A-activated spleen cells (CS) is also phylogenetically restricted in its action; CS must be obtained from animals homologous with the donor of the responding lymphocytes.     

Reciprocal T cell responses in the liver and thymus of mice injected with syngeneic tumor cells.

We investigated the T cell responses in various tissues, especially in the liver and thymus, of mice injected with syngeneic tumors. This study was undertaken since recent evidence indicated that the liver is one of the important immune organs for T cell proliferation. When C3H/He mice were intraperitoneally injected with mitomycin-treated syngeneic MH134 tumors (1 x 10(7)/mouse), a transient increase of liver mononuclear cells (MNC) was induced, showing a peak at Day 4 after injection. Histological study of such liver showed a sinusoidal dilatation and an accumulation of MNC in the sinusoids. The most predominant MNC induced were double negative (CD4-8-) alpha beta T cells and gamma delta T cells. These gamma delta T cells varied, showing unique time-kinetics. Despite a continuous increase of whole liver MNC and alpha beta T cells, the proportion of gamma delta T cells in the liver decreased beginning 4 days after injection. In contrast with the response in the liver, a striking decrease in the cell number of thymocytes was induced after tumor injection, showing a basal level at Day 6. This hypocellularity in the thymus appears to be an inverted response of the lymphocytosis in the liver. At this time, a corresponding decrease in the proportion of double positive (CD4+8+) T cells was always seen in the thymus. Analysis of cell proliferative response showed that the increase of liver MNC after tumor injection was accompanied by augmented proliferation, whereas the decrease of thymocytes was accompanied by depressed proliferation. The present results indicate that there exists a unique, reciprocal response of T lymphocytes between the liver and thymus, and that the presence of tumor appears to stimulate T cell response in the liver but alternatively inactivates such response in the thymus.     

Hydrogen peroxide and tumour necrosis factor-alpha induce NF-kappaB-DNA binding in primary human T lymphocytes in addition to T cell lines.

Reactive oxygen intermediates (ROIs), such as hydrogen peroxide (H2O2), have been implicated as second messengers in the activation of NF-kappaB by a variety of stimuli, including tumour necrosis factor-alpha (TNF-alpha). The aim of the present study was to examine the effects of ROIs on NF-kappaB activation in primary human CD3+ T lymphocytes and human peripheral blood mononuclear cells (PBMCs). For comparison purposes, Jurkat T cells (subclones JR and JE6.1) were also investigated. Cells were incubated in the presence of either H2O2 or TNF-alpha and nuclear proteins were extracted. NF-kappaB binding was assessed by electrophoretic mobility shift assays (EMSAs). The concentration of H2O2 required to activate NF-kappaB in human primary CD3+ T lymphocytes was as low as 1 microM. In contrast, much higher concentrations of H2O2 were required to activate NF-kappaB in PBMCs and in the JR subclone of Jurkat T cells. H2O2-induced NF-kappaB activation was not observed in the JE6.1 subclone of Jurkat T cells. NF-kappaB was activated by TNF-alpha in all four cell types tested. In PBMCs and Jurkat T cells (subclones JR and JE6.1), this activation could be inhibited by pre-treatment with the antioxidants, pyrrolidine dithiocarbamate (PDTC) and N-acetyl-L-cysteine (NAC). Our results support a role for ROIs in NF-kappaB-DNA binding in human primary T lymphocytes.     

Inhibition of in vitro T cell activation by corneal endothelial cells.

Cells and tissues of the anterior uvea and aqueous humor express activities which inhibit immune responses. These activities include soluble factors such as TGF-beta and uncharacterized cell surface interactions. Relatively little is known regarding the immunologic activities of corneal endothelium, despite its potentially important role in contributing to the immune privilege of the anterior chamber and the high success rate of corneal transplantation. In this report, in vitro studies of cultured rat corneal endothelial (CE) cells were done using S-antigen-specific LEW rat T cell lines, or S-antigen-specific T cell hybridomas, to examine the immunologic capabilities of CE cells. Monolayers of LEW rat CE cells were unable to present antigen or a mitogen, Con A, to T cell lines or hybridomas as assessed by the lack of a proliferative response or IL-2 secretion. Furthermore, the CE cells exerted a potent inhibitory effect when added to in vitro proliferation assays of T cell lines stimulated with antigen or Con A. When T cells were preactivated on conventional antigen presenting cells and then transferred to wells containing CE cells, their proliferation was not inhibited. Although CE cells inhibited activation of T cell lines and hybridomas, they did not inhibit the growth of T cell hybridomas or CTLL cells, nor did the CE cells adversely affect the viability of resting T cells cultured on CE monolayers. The inhibitory effect was reversible as preincubation of T cells on CE cells for up to 6 days followed by washes restored T cell responsiveness when assayed on splenocytes. The inability to stimulate proliferative responses was not affected by preincubation of the CE cells with lymphokines which increase MHC antigen expression. The inhibition observed in these assays was not MHC-restricted as CE cells from both LEW and BN rats were equally inhibitory. CE cells from rabbits and cats were also potent inhibitors of T cell activation, suggesting that the mechanism is evolutionarily conserved. The mechanism of inhibition of CE cells is unknown at this time.     

T cell activation responses are differentially regulated during clinorotation and in spaceflight.

Studies of T lymphocyte activation with mitogenic lectins during spaceflight have shown a dramatic inhibition of activation as measured by DNA synthesis at 72 h, but the mechanism of this inhibition is unknown. We have investigated the progression of cellular events during the first 24 h of activation using both spaceflight microgravity culture and a ground-based model system that relies on the low shear culture environment of a rotating clinostat (clinorotation). Stimulation of human peripheral blood mononuclear cells (PBMCs) with soluble anti-CD3 (Leu4) in clinorotation and in microgravity culture shows a dramatic reduction in surface expression of the receptor for IL-2 (CD25) and CD69. An absence of bulk RNA synthesis in clinorotation indicates that stimulation with soluble Leu4 does not induce transition of T cells from G0 to the G1 stage of the cell cycle. However, internalization of the TCR by T cells and normal levels of IL-1 synthesis by monocytes indicate that intercellular interactions that are required for activation occur during clinorotation. Complementation of TCR-mediated signaling by phorbol ester restores the ability of PBMCs to express CD25 in clinorotation, indicating that a PKC-associated pathway may be compromised under these conditions. Bypassing the TCR by direct activation of intracellular pathways with a combination of phorbol ester and calcium ionophore in clinorotation resulted in full expression of CD25; however, only partial expression of CD25 occurred in microgravity culture. Though stimulation of purified T cells with Bead-Leu4 in microgravity culture resulted in the engagement and internalization of the TCR, the cells still failed to express CD25. When T cells were stimulated with Bead-Leu4 in microgravity culture, they were able to partially express CD69, a receptor that is constitutively stored in intracellular pools and can be expressed in the absence of new gene expression. Our results suggest that the inhibition of T cell proliferative response in microgravity culture is a result of alterations in signaling events within the first few hours of activation, which are required for the expression of important regulatory molecules.     

Isolated soluble fractions from the murine B16 melanoma induce primary in vitro syngeneic antitumor responses

Summary This paper extends our previous studies, which documented our ability to isolate immunogenic entities from nonimmunogenic or weakly immunogenic tumors.B16 melanoma cells failed, in our in vitro experimental system, to induce anti-B16 cytotoxic responses in spleen cells derived from normal syngeneic C57BL/6 mice. The B16 melanoma cellular homogenate was fractionated on an Ultrogel AcA 34 column, and the various fractions were tested for their ability to induce anti-B16 cytotoxic responses under the same conditions as those used for intact B16, the nonimmungenic tumor cells. Certain fractions, some of them with relatively low protein concentrations, induced anti-B16 cytotoxic responses in spleen cells of normal C57BL/6 mice, whereas others, some of them with relatively high protein concentrations, failed to induce such responses. One fraction (Fr.), designated Fr. 5/6, was examined in detail. It was found that in normal syngeneic spleen cells this fraction induced effector cells that efficiently killed (at various E : T ratios) the relevant B16 target cells and RBL5 syngeneic tumor cells, but not the YAC allogeneic tumor cells or C57BL/6 lymphoblasts. Furthermore, an excess of unlabeled B16 cells most efficiently blocked the ability of these anti-B16 effector cells to kill radiolabeled B16 target cells. RBL5 tumor cells, YAC tumor cells, or C57BL/6 lymphoblasts failed to block these effector cells efficiently. A significant fraction of the effector cells induced with Fr. 5/6 was characterized as thymus-derived cells (Thy-1⁺, Thy-2⁺3⁺ cells). It was suggested that another fraction of the cellular population was natural killer cells, which cytolyzed the RBL5 target cells. Various theoretical and practical aspects of these findings are discussed.     

Splicing DNA-damage responses to tumour cell death

The ability of a tumour cell to evade programmed cell death (apoptosis) is crucial in the development of cancer. The process of apoptosis is complex and involves the careful interplay of a host of signalling molecules. Cellular stresses, such as DNA-damage, can initiate apoptosis through multiple pathways, all of which eventually lead to eradication of damaged cells that may otherwise go on to form a tumour. Moreover, the relevance of this to combating cancer is very strong since several therapeutic agents used to treat malignant disease utilize the cells' apoptotic machinery. The purpose of this review is to provide an insight into what we know about how apoptosis is initiated by DNA-damaging agents, how pro- and anti-apoptotic signals converge in the execution of cell death, and how such mechanisms can be perturbed in cancer.     

In vitro endothelial cell activation and inflammatory responses in end-stage heart failure.

BACKGROUND: vascular endothelial cell activation and dysfunction are observed in patients with severe heart failure and may contribute to systemic manifestations of this syndrome. It remains unknown whether inflammatory activation of these cells occurs in these patients because of increased circulating proinflammatory mediators. Aim: to determine whether the serum from patients with heart failure possesses a net proinflammatory bioactivity to active proinflammatory pathways in cultured endothelial cells. METHODS: serum was obtained from stable patients with end-stage heart failure undergoing elective cardiac transplantation (Tx) and severely decompensated patients with heart failure requiring emergency left ventricular assist device (LVAD) implantation. Net proinflammatory bioactivity of serum was investigated by monitoring IkappaBalpha degradation and E-selectin expression in cultured human pulmonary artery endothelial cells (HPAEC) following incubation with serum samples. Serum cytokine concentrations were measured by ELISA and neutralizing antibodies were used to determine the role of specific factors in the observed bioactivity. RESULT: serum from both patient groups induced HPAEC IkappaBalpha degradation. Low basal HPAEC E-selectin expression significantly increased following treatment with Tx but not LVAD serum. Serum tumor necrosis factor-alpha (TNF-alpha) and IL-10 concentrations were higher in patients with LVAD than those with Tx, and soluble TNF-alpha receptor expression was high in both groups. Neither TNF-alpha nor IL-10 blocking experiments altered either bioassay result. CONCLUSION: activation of a specific profile of pro- and anti-inflammatory mediators is associated with heart failure resulting in HPAEC nuclear factor (NF)-kappaB activation. However, E-selectin expression is further regulated by unidentified factors. TNF-alpha is upregulated but appears to play no part in NFkappaB activation in these patients. These findings could have important therapeutic implications.     

Cytotoxic T cell responses to Streptococcus are associated with improved prognosis of oral squamous cell carcinoma

Several species of Streptococcus, such as S. salivarius, S. mitis, and S. anginosus, are found to extensively colonize the oral cavity and the upper respiratory tract, and have been shown to increase in patients with oral squamous cell carcinoma (OSCC). Accumulating evidence have revealed that commensal bacteria are involved in antitumor immunity via T cell-mediated mechanisms, but the role of Streptococcus enrichment in OSCC is yet unclear. In this study, we stimulated peripheral blood mononuclear cells from non-cancer controls (NCs) and OSCC patients with S. salivarius, S. mitis, and S. anginosus. We observed that compared to NC subjects, OSCC patients at earlier stages had higher frequencies of granzyme B-expressing CD8 T cells for all Streptococcus species tested, while OSCC patients at more advanced stages had higher frequencies of granzyme B-expressing CD8 T cells for S. anginosus but not other Streptococcus species. In OSCC patients, the Streptococcus-reactive CD8 T cells presented significantly lower levels of PD-1 and TIM-3 expression than Streptococcus-nonreactive CD8 T cells. The clinical outcomes of OSCC patients in our cohort were tracked for 24 months after the resection of the primary tumor. In patients that did not present tumor recurrence, the frequencies of S. salivarius-reactive and S. mitis-reactive CD8 T cells were significantly higher than that in patients that developed recurrent tumor. Furthermore, in patients with tumor recurrence, the duration between primary tumor resection and tumor recurrence was positively associated with the frequencies of S. salivarius-reactive and S. anginosus-reactive CD8 T cells. Together, we demonstrated that Streptococcus-reactive CD8 T cell responses might contribute to antitumor immunity in OSCC patients.