Influence of bevacizumab, sunitinib and sorafenib as single agents or in combination on the inhibitory effects of VEGF on human dendritic cell differentiation from monocytes.

Vascular endothelial growth factor (VEGF) inhibits differentiation and maturation of dendritic cells (DC), suggesting a potential immunosuppressive role for this proangiogenic factor. Bevacizumab, sorafenib and sunitinib target VEGF-mediated angiogenesis and are active against several types of cancer, but their effects on the immune system are poorly understood. In this study, VEGF and supernatants of renal carcinoma cell lines cultured under hypoxia were found to alter the differentiation of human monocytes to DC. Resulting DC showed impaired activity, as assessed by the alloreactive mixed T-lymphocyte reaction. Bevacizumab and sorafenib, but not sunitinib, reversed the inhibitory effects of VEGF, but not of those mediated by tumour supernatants. Dendritic cells matured under the influence of VEGF expressed less human leukocyte antigen-DR (HLA-DR) and CD86, and this effect was restored by bevacizumab and sorafenib. Finally, tumour-cell supernatants decreased interleukin-12 (IL-12) production by mature DC, and such inhibition was not restored by any of the tested drugs, delivered either as single agents or in combination. The deleterious effects of tumour-cell supernatants were mainly mediated by thermostable molecules distinct from VEGF. These results indicate that inhibition of the differentiation of monocytes to DC is a multifactorial effect, and that they support the development of combinations of angiogenesis inhibitors with immunological modulators.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells.

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

Absence of surface expression of CD137 (4-1BB) on Myeloid-derived suppressor cells

Las células mieloides supresoras (Myeloid-derived suppressorcells, MDSC) pertenecen a un subtipo de leucocitos causantes deinmunosupresión en individuos portadores de tumor. En ratones,estas células han sido definidas como CD11b+GR1+IL-4Rá+y, debido a la presencia de tumores en modelos experimentales,se acumulan tanto en la lesión tumoral como en los órganos linfoides.CD137 (4-1BB) es un receptor de coestímulo de la familia dereceptores del factor de necrosis tumoral (TNF) principalmenteexpresado sobre la membrana de linfocitos T y de células NK(Natural Killer) activados, aunque también se encuentra en la superficiede otros leucocitos de estirpe mieloide como mastocitos, granulocitos,macrófagos, células dendríticas y endotelio. Anticuerposagonistas frente a CD137 incrementan la respuesta inmuneantitumoral potenciando los CTLs antitumorales. En este trabajo,células de carcinoma de colon C26 transfectadas para expresarGM-CSF se inocularon por vía subcutánea a ratones singénicosdebido a sus propiedades inductoras de un gran aumento enel número de las MDSCs. Mediante citometría de flujo multicolorhemos confirmado un notable aumento en el número de estascélulas CD11b+GR1+IL-4Rá+ tanto en el estroma tumoral comoen el bazo de los ratones portadores de tumor. La expresión deCD137 en este subtipo celular sin embargo, mostró resultadosnegativos. Por tanto, se pueden excluir los efectos directos de losmAbs sobre MDSCs como mecanismo de acción de la inmunoterapiacon anticuerpos anti-CD137. Según esto las terapias dirigidasa disminuir el número o función de MDSCs podrían sinergizarcon anticuerpos inmunoterapéuticos anti-CD137 ya queactúan sobre dianas diferentes

Myeloid-derived suppressor cells (MDSC) are a subset ofleukocytes associated with local and systemic T-cell immunosuppressionin tumor-bearing hosts. In mice these cells are bestdefined as CD11b+GR1+IL-4Rá+ and their numbers increase inresponse to the presence of an experimental malignancy both atthe tumor lesion and in lymphoid organs. CD137 is a co-stimulatoryreceptor that belongs to the tumor necrosis factor (TNF)receptor family characteristically expressed on activated T cellsand NK cells. Its expression has also been reported on myeloidcells such as mastocytes, granulocytes, macrophages, dendriticcells, and on endothelium. Agonist antibodies against CD137 areknown to increase the antitumor immune response through augmentingthe intensity of antitumor CTLs. In this study C26 coloncarcinoma cells transfected to express GM-CSF were subcutaneouslyimplanted in syngeneic mice because of its properties asthe most potent inducer of MDSCs. Indeed, multicolor flow cytometryconfirmed a dramatic numeric increase in CD11b+GR1+IL-4Rá+ cells both in the tumor stroma and in the spleen of tumorbearingmice. Analysis of CD137 expression on this cell subsetrendered completely negative results. Therefore direct effects ofimmunotherapeutic anti-CD137 monoclonal antibodies on MDSCscan be excluded as a mechanism of action, thus indicating thattherapies aimed at decreasing MDSCs might synergize withimmunotherapeutic anti-CD137 antibody as a result of dealing with different targets

The many faces of regulatory T cells

"Regulatory T cell" is a generic name that globally covers a number of T cell subsets that can mediate suppression of cellular immunity in some in vitro and in vivo experiments. One of these subsets becomes differentiated in the thymus and is chiefly characterized by the expression of the Foxp3 transcription factor. It is postulated that these natural T reg cells recognize self peptides complexed to self MHC with moderate affinity and are thought to contribute to the preservation of self tolerance beyond negative thymic selection against high affinity anti-self T cell receptors. This is illustrated by mice and human patients devoid of these cells, who develop aggressive and extended autoimmune lymphoid infiltrates in different organs. CD4+ T cells producing anti-inflammatory cytokines also down regulate cellular immunity although they might cooperate with certain humoral responses. The rapidly progressing knowledge on the surface phenotype, and the transcriptome/proteome of these cells is offering plenty of opportunities for immune intervention. Deactivation or depletion of Treg cells might lead to increased immunity against viral chronicity or malignant diseases, whereas adoptive transfer or agonist stimulations of their function might have a role in the treatment of organ specific autoimmunity. However, abundant experimental discrepancies and uncertainties challenge and complicate this promising field for translational research

El nombre de "células T reguladoras" define a una subpoblación de células T con capacidad supresora tanto in vitro como in vivo. Parte de esa subpoblación tiene origen tímico y se caracteriza por la expresión del factor de transcripción Foxp3; estas células son conocidas como “T reguladoras naturales” y contribuyen a preservar la tolerancia a lo propio. Se ha descrito que dichas células reconocen péptidos propios con afinidad intermedia tras un proceso de selección negativa en el timo donde previamente se habrían eliminado los clones de células T con alta afinidad por péptidos propios. Tanto en el hombre como en modelos animales, la ausencia de esta población de células T se traduce en fenómenos agresivos de autoinmunidad con un importante infiltrado linfocitario en diferentes órganos. Las células T CD4+ producen citocinas anti-inflamatorias que también colaboran en la supresión de la inmunidad celular. Los últimos hallazgos sobre el fenotipo de las células T reguladoras, así como en su genoma, están haciendo posible el desarrollo de múltiples estrategias para la inmunoterapia. La inactivación o depleción de las Treg podría aumentar la respuesta inmune frente a enfermedades virales crónicas, mientras que la transferencia adoptiva o la estimulación de estas células mediante agonistas sería de gran ayuda para el tratamiento de enfermedades autoinmunes. Sin embargo, la existencia de ciertas discrepancias en los modelos experimentales, hace que aún queden puntos por resolver antes de iniciar la inmunoterapia en clínica