Springing in Your "Cleanup" Journey.

Now, more than ever, nurses need to focus on self-care. This is especially true of school nurses returning to all regular responsibilities while managing multiple outbreaks of respiratory illnesses this past winter. In this brief article, the author discusses the various meanings of the word "clean-up" and how they can be applied to improved self-care.

A2A adenosine receptor protects tumors from antitumor T cells.

The A2A adenosine receptor (A2AR) has been shown to be a critical and nonredundant negative regulator of immune cells in protecting normal tissues from inflammatory damage. We hypothesized that A2AR also protects cancerous tissues by inhibiting incoming antitumor T lymphocytes. Here we confirm this hypothesis by showing that genetic deletion of A2AR in the host resulted in rejection of established immunogenic tumors in approximately 60% of A2AR-deficient mice with no rejection observed in control WT mice. The use of antagonists, including caffeine, or targeting the A2 receptors by siRNA pretreatment of T cells improved the inhibition of tumor growth, destruction of metastases, and prevention of neovascularization by antitumor T cells. The data suggest that effects of A2AR are T cell autonomous. The inhibition of antitumor T cells via their A2AR in the adenosine-rich tumor microenvironment may explain the paradoxical coexistence of tumors and antitumor immune cells in some cancer patients (the "Hellstrom paradox"). We propose to target the hypoxia-->adenosine-->A2AR pathway as a cancer immunotherapy strategy to prevent the inhibition of antitumor T cells in the tumor microenvironment. The same strategy may prevent the premature termination of immune response and improve the vaccine-induced development of antitumor and antiviral T cells. The observations of autoimmunity during melanoma rejection in A2AR-deficient mice suggest that A2AR in T cells is also important in preventing autoimmunity. Thus, although using the hypoxia-->adenosine-->A2AR pathway inhibitors may improve antitumor immunity, the recruitment of this pathway by selective drugs is expected to attenuate the autoimmune tissue damage.

CTL adoptive immunotherapy concurrently mediates tumor regression and tumor escape.

Tumor escape and recurrence are major impediments for successful immunotherapy. It is well-documented that the emergence of Ag-loss variants, as well as regulatory mechanisms suppressing T cell function, have been linked to inadequate antitumor activity. However, little is known regarding the role of Fas-mediated cytotoxicity by tumor-specific CD8(+) CTL in causing immune evasion of Fas resistant variants during adoptive immunotherapy. In this study, we made use of an adoptive transfer model of experimental lung metastasis using tumor-specific CTL as a relevant immune-based selective pressure, and wherein the Fas ligand pathway was involved in the antitumor response. Surviving tumor cells were recovered and examined for alterations in antigenic, functional, and biologic properties. We showed that diminished susceptibility to Fas-mediated cytotoxicity in vivo was an important determinant of tumor escape following CTL-based immunotherapy. Tumor escape variants (TEV) recovered from the lungs of CTL-treated mice exhibited more aggressive behavior in vivo. However, these TEV retained relevant MHC class I and tumor Ag expression and sensitivity to CTL via the perforin pathway but reduced susceptibility to Fas-mediated lysis. Moreover, TEV were significantly less responsive to eradication by CTL adoptive immunotherapy paradigms as a consequence of increased Fas resistance. Overall, we identified that Fas(low)-TEV emerged as a direct consequence of CTL-tumor interactions in vivo, and that such an altered neoplastic Fas phenotype compromised immunotherapy efficacy. Together, these findings may have important implications for both tumor progression and the design of immunotherapeutic interventions to confront these selective pressures or escape mechanisms.

Immune selection and emergence of aggressive tumor variants as negative consequences of Fas-mediated cytotoxicity and altered IFN-gamma-regulated gene expression.

Antitumor responses can be induced in patients via active or adoptive immunotherapy, yet complete tumor eradication occurs infrequently. This paradox in tumor immunology led us to address two questions: (a) Does an antitumor response, which is intended to destroy the aberrant target population, also at the same time select for aggressive tumor variants (ATV) in vivo? (b) If this process does occur, what is the contribution of the perforin- or Fas-mediated effector mechanism in the immune selection of such ATV? Here, in an experimental mouse lung metastasis model, we showed that ATV generated either naturally in vivo or in vitro by anti-Fas selection resembled each other biologically and genetically as judged by enhanced tumor growth and genome-scale gene expression profiling, respectively. Furthermore, ATV that survived CTL adoptive immunotherapy displayed an even more profound loss of Fas expression and function as well as enhanced malignant proficiency in vivo. ATV, however, retained sensitivity to perforin-mediated lysis in vitro. Lastly, such ATV displayed a diminished responsiveness in their expression of IFN-gamma-regulated genes, including those mechanistically linked to Fas-mediated death (i.e., Fas and caspase-1). Overall, we showed that (a) immune selection did occur in vivo and played an important role in the emergence of ATV, (b) ATV bearing a Fas-resistant phenotype was a chief consequence of immune selection, and (c) an overall diminished responsiveness of IFN-gamma-regulated gene expression was characteristic of ATV. Thus, in this model, Fas-mediated cytotoxicity, in concert with IFN-gamma-regulated gene expression, mechanistically constituted significant determinants of immune selection of ATV in vivo.

Cooperative disengagement of Fas and intercellular adhesion molecule-1 function in neoplastic cells confers enhanced colonization efficiency.

Understanding the mechanisms of tumor progression is crucial toward the development of therapeutic interventions. Although the loss of sensitivity to cell death is a hallmark of neoplastic progression, it is likely one of several essential features that underlie a malignantly proficient or aggressive tumorigenic phenotype. Here, we identified intercellular adhesion molecule-1 (ICAM-1) as a molecule with expression coordinately regulated with Fas and inversely correlated with malignant phenotype between matched pairs of differentially aggressive malignant subpopulations in three mouse models. To determine whether coordinate expression of Fas and ICAM-1 regulated malignant behavior, tumor sublines were produced that expressed either lower levels of both Fas and ICAM-1, lower levels of Fas, or lower levels of ICAM-1 and then assessed for metastatic lung tumor growth. Tumor sublines rendered both Fas incompetent and ICAM-1 incompetent displayed significantly higher numbers of tumor nodules compared with tumor sublines separately expressing low levels of Fas or ICAM-1. However, all tumor sublines regardless of their Fas and ICAM-1 levels comparably infiltrated the lung, suggesting that Fas- and ICAM-1-based interactions ultimately influenced lung colonization efficiency. Overall, these data suggested that both Fas and ICAM-1 pathways cooperated to regulate tumor progression and that the coordinate down-regulation of Fas and ICAM-1 intensified malignant progression at the level of colonization. Thus, a Fas(lo)ICAM-1(lo) phenotype may be characteristic of at least certain advancing, immune-resistant neoplastic subpopulations.

The Fas/Fas ligand pathway is important for optimal tumor regression in a mouse model of CTL adoptive immunotherapy of experimental CMS4 lung metastases.

The mechanisms of CTL-mediated tumor regression in vivo remain to be fully understood. If CTL do mediate tumor regression in vivo by direct cytotoxicity, this may occur via two major effector mechanisms involving the secretion of perforin/granzymes and/or engagement of Fas by Fas ligand (FasL) expressed by the activated CTL. Although the perforin pathway has been considered the dominant player, it is unclear whether Fas-mediated cytotoxicity is additionally required for optimal tumor rejection. Previously, we produced H-2L(d)-restricted CTL reactive against the CMS4 sarcoma, which expresses a naturally occurring rejection Ag recognized by these CTL and harbors a cytokine (IFN-gamma plus TNF)-inducible, Fas-responsive phenotype. The adoptive transfer of these CTL to syngeneic BALB/c mice with minimal (day 3 established) or extensive (day 10 established) experimental pulmonary metastases resulted in strong antitumor responses. Here we investigated whether a FasL-dependent CTL effector mechanism was important for optimal tumor regression in this adoptive immunotherapy model. The approach taken was to compare the therapeutic efficacy of wild-type to FasL-deficient (gld) CTL clones by adoptive transfer. In comparison with wild-type CTL, gld-CTL efficiently mediated tumor cytolysis and produced comparable amounts of IFN-gamma, after tumor-specific stimulation, as in vitro assessments of Ag recognition. Moreover, gld-CTL mediated comparably potent antitumor effects in a minimal disease setting, but were significantly less effective under conditions of an extensive tumor burden. Overall, under conditions of extensive lung metastases, these data revealed for the first time an important role for a FasL-dependent CTL effector mechanism in optimal tumor regression.

Mechanisms of ganglioside inhibition of APC function.

Gangliosides shed by tumor cells exert potent inhibitory effects on cellular immune responses. Here we have studied ganglioside inhibition of APC function. When human monocytes were preincubated in 50 micro M highly purified ganglioside G(D1a), pulsed with tetanus toxoid (TT), and washed, the expected Ag-induced proliferative response of autologous normal T cells added to these monocytes was inhibited by 81%. Strikingly, there was also almost complete (92%) and selective inhibition of the up-regulation of the monocyte costimulatory molecule CD80, while I-CAM-1, LFA-3, HLA-DR, and CD86 expression were unaffected. Purified LPS-stimulated monocytes that had been preincubated in G(D1a) likewise showed inhibition of CD80 up-regulation (59%) as well as down-regulation of CD40 (54%) and impaired release of IL-12 and TNF-alpha (reduced by 59 and 51%). G(D1a)-preincubated human dendritic cells (DC) were also affected. They had reduced constitutive expression of CD40 (33%) and CD80 (61%), but not CD86, and marked inhibition of release of IL-6 (72%), IL-12 (70%), and TNF-alpha (46%). Even when pulsed with TT, these ganglioside-preincubated DC remained deficient in costimulatory molecule expression and cytokine secretion and were unable to induce a normal T cell proliferative response to TT. Finally, significant inhibition of nuclear localization of NF-kappaB proteins in activated DC suggests that disruption of NF-kappaB activation may be one mechanism contributing to ganglioside interference with APC expression of costimulatory molecules and cytokine secretion, which, in turn, may diminish antitumor immune responses.