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Summary: There have been substantial strides forward in our understanding of the contribution of regulatory T (Treg) cells to cancer immunosuppression. In this issue, we present a series of papers highlighting emerging themes on this topic relevant not only to our understanding of the fundamental biology of tumour immunosuppression but also to the design of new immunotherapeutic approaches. The substantially shared biology of CD4+ conventional T (Tconv) and Treg cells necessitates a detailed understanding of the potentially opposing functional consequences that immunotherapies will have on Treg and Tconv cells, a prominent example being the potential for Treg‐mediated hyperprogressive disease following anti‐PD‐1 therapy. Such understanding will aid patient stratification and the rational design of combination therapies. It is also becoming clear, however, that Treg cells within tumours exhibit distinct biological features to both Tconv cells and Treg cells in other tissues. These distinct features provide the opportunity for development of targeted immunotherapies with greater efficacy and reduced potential for inducing systemic toxicity. [ABSTRACT FROM AUTHOR]

Altered metabolism is a hallmark of cancers, including shifting oxidative phosphorylation to glycolysis and up-regulating glutaminolysis to divert carbon sources into biosynthetic pathways that promote proliferation and survival. Therefore, metabolic inhibitors represent promising anti-cancer drugs. However, T cells must rapidly divide and survive in harsh microenvironments to mediate anti-cancer effects. Metabolic profiles of cancer cells and activated T lymphocytes are similar, raising the risk of metabolic inhibitors impairing the immune system. Immune checkpoint blockade provides an example of how metabolism can be differentially impacted to impair cancer cells but support T cells. Implications for research with metabolic inhibitors are discussed. [ABSTRACT FROM AUTHOR]

Cancer-germline genes in both humans and mice have been shown to encode antigens susceptible to targeting by cytotoxic CD8 T effector cells (CTL). We analysed the ability of CTL to kill different tumour cell lines expressing the same cancer-germline gene P1A ( Trap1a). We previously demonstrated that CTL expressing a T-cell receptor specific for the P1A35-43 peptide associated with H-2Ld, although able to induce regression of P1A-expressing P815 mastocytoma cells, were much less effective against P1A-expressing melanoma cells. Here, we analysed parameters of the in vitro interaction between P1A-specific CTL and mastocytoma or melanoma cells expressing similar levels of the P1A gene and of surface H-2Ld. The mastocytoma cells were more sensitive to cytolysis than the melanoma cells in vitro. Analysis by video-microscopy of early events required for target cell killing showed that similar patterns of increase in cytoplasmic Ca2+ concentration ([Ca2+]i) were induced by both types of P1A-expressing tumour cells. However, the use of CTL expressing a fluorescent granzyme B (GZMB-Tom) showed a delay in the migration of cytotoxic granules to the tumour interaction site, as well as a partially deficient GZMB-Tom exocytosis in response to the melanoma cells. Among surface molecules possibly affecting tumour-CTL interactions, the mastocytoma cells were found to express intercellular adhesion molecule-1, the ligand for LFA-1, which was not detected on the melanoma cells. [ABSTRACT FROM AUTHOR]

H60a is a minor histocompatibility antigen expressed in BALB and 129/Sv but not C57BL/6 mouse strains. The majority of CD8 T cells in C57BL/6 mice responding to BALB.B splenocytes are specific for H60a. Interestingly, H60a is expressed constitutively on tumour cells, but its nature as a tumour rejection antigen, as a parallel to its function as a transplant rejection antigen, has not been studied. In this report, we show that tumour cells that constitutively express H60a at the cell surface can be recognized by H60a-specific T cells. Furthermore, when H60a-expressing sarcoma cell lines are transplanted into C57BL/6 mice, H60a-specific T cells can be found at high percentages among the tumour-infiltrating CD8 T cells. These findings were seen in C57BL/6 but not F1 (C57BL/6 × 129) mice (which express H60a), suggesting that endogenous tolerance mechanisms suppress the antigenic properties of H60a. Our findings have implications for the generation of tumour vaccines against human natural killer group 2D ligands, such as MHC class I chain-like gene A, that are also transplantation antigens. [ABSTRACT FROM AUTHOR]

Investigations of the cytotoxic activity of T cells induced following one or two intraperitoneal doses of live Salmonella revealed that cytotoxicity was restricted to the Lyt-2+ T-cell subset and was enhanced following secondary infection with Salmonella. Initial studies using the lectin-dependent cellular cytotoxicity (LDCC) assay detected Lyt-2+ cytotoxic T cells in peritoneal cell suspensions of S. enteritidis 11RX (11RX)-infected mice, with the peak of activity occurring 5 days after infection. This did not correlate with the proliferative activity of these cells, which peaked 10-12 days after infection. Secondary challenge with 11RX or S. typhimurium C5 (C5) induced a rapid increase in the cytotoxic activity of Lyt-2+ peritoneal T cells and was detected even 21 days later. The antigen specificity of some of these cells was confirmed in cytotoxicity assays using P815 tumour cells infected with 11RX organisms as targets. No cytotoxic activity was detected in the spleen cell suspensions of infected (and normal) mice unless the cells were first activated by in vitro culture with concanavalin A (Con A). Both types of activated spleen cells showed LDCC but Salmonella-specific cytotoxic Lyt-2+ T cells were detected only in spleen cell (SC) cultures prepared from mice challenged with a second dose of Salmonella. [ABSTRACT FROM AUTHOR]

A CTL line (CTLL-D4) mediating specific cytolytic activity against radiation-induced leukaemia RL♂1 has been established and maintained on a long-term basis without the addition of exogeneous TCGF. This line was originally selected by the limiting dilution of MLTC cells from RL♂1-immune (BALB/c × C57BL/6) F1-nu/+(CB6F1-nu/+) spleen cells (500 cells/well) in the presence of 5% rat TCOF, 2000 rads-irradiated normal C86F1-nu/ + spleen cells as the feeder cells, and 10,000 rads-irradiated RL♂ 1 tumour cells as the stimulator. After expansion only with the feeder and tumour cells, CTLL-D4 shows highly specific cytotoxic activity against RL♂1 by in vitro CMC assay, since cells such as RL♂6. RL♀8, RL♀9, P815, MOPC-315 (H-2d), EL-4 (H-2b) and YAC (H-2a) are not killed. Microcytoxicity assay of this line has revealed that CTLL-D4 comprises three subsets of T lymphocytes (100% Thy-1.2+): 15-25% Lyt-l+23 , 60-75% Lyt-1 +23+ and 10-15% Lyt-l- 23+. The proliferation of this line seems to depend largely upon the syngeneic MLR-like responsiveness of the Lyt- 1+23- subsets of CTLL-D4 to the Ia-positive cells in CB6F1-nu/+ splenic feeder cells, and has been restricted to the H-2d-haplotype of the feeder cells, in spite of the vigorous cell proliferation by coculturing with the feeder cells alone, the cytolytic activity of this line begins to decrease after some 7 days of culture in the absence of the stimulator RL♂1 cells which have no capacity to stimulate by themselves. Thus, by long-term culture of CTLL-D4 with the syngeneic feeder cells alone, a new non-cytolytic line (D4f) was established. Mechanisms enabling the long-term maintenance of CTL activity and subset composition have been discussed in terms of cellular cooperation between the subsets of this line. [ABSTRACT FROM AUTHOR]

To distinguish between direct and indirect involvement of oxygen metabolites in CTL cytotoxicity a comparison was made of cloned CTLs and mixed cells from mouse spleen. Tumour cells could be protected from cloned CTLs and from spleen CTLs by the thiol protecting reducing agents DTT and DETC. Cytotoxic activity was inhibited by diversion of reducing power from NAD(P)H to artificial electron acceptors and by the inhibitor of NAD(P) linked enzymes cibacron blue. Although H2O2 formation could be detected during the lysis of P815 by spleen CTLs it did not prove to be a necessary requirement for cytolysis since it was not formed when glutaraldehyde-treated P815 cells were lysed. Of the scavengers of toxic oxygen metabolites tested only the hydroxyl radical scavenger sodium benzoate inhibited cytotoxicity. [ABSTRACT FROM AUTHOR]

We have examined the development of specific cytotoxic T-cell activity in the lungs and the epithelium and lamina propria of the small intestine following tumour cell inoculation by subcutaneous or intraperitoneal routes. After an intraperitoneal injection of tumour cells, large amounts of cytotoxic activity are detectable in the lungs and lamina propria. In comparison, the epithelial lymphocytes of the small intestine display low cytotoxio activity. After a subcutaneous injection, little cytotoxicity is detectable except in the lungs and the development of such cytotoxicity has a much shorter time course compared with that induced by an intraperitoneal inoculation of tumour cells. The data indicate a marked difference in the functional capacity of lymphocytes from the epithelium and lamina propria of the small intestine. [ABSTRACT FROM AUTHOR]