Hence, MDSCs intricately influence different CD8+ T-cell activation events in vitro, whereby some parameters are suppressed while others are stimulated. The discovery of

tumor-specific antigenic peptides recognized by CD8+ T cells has laid the foundation for immunotherapeutic approaches aimed at maximizing cytotoxic T lymphocyte (CTL) mediated eradication of cancer cells. The optimization of such therapies requires a thorough knowledge of the mechanisms regulating CTL induction and activity and of the countermeasures taken by tumors to avoid destruction. Naive CD8+ T cells constantly sample APCs in the secondary lymphoid organs. As a function of this activity, naive T cells express low levels of CD44 and high levels of the homing receptor CD62L, ensuring entry Sorafenib into LNs [1]. Upon activation at these sites, a series of events is initiated that dramatically alters the molecular repertoire of CD8+ T cells, enabling these cells to proliferate, migrate, and acquire effector functions [2]. Importantly, distinct features of CTL activation are obtained in different phases of the activation process and are not necessarily interdependent [3, 4]. Thus, a brief DC-T-cell encounter is sufficient to Temozolomide upregulate the early activation markers CD44 and CD69, but longer stable contacts are needed to initiate IL-2 and IFN-γ secretion and the abundant expression of activation markers (including CD25, generating

a high-affinity trimeric IL-2R). Finally, only upon dissociation from the DC, CD8+ T cells start to proliferate vigorously [3]. Cell-fate decisions in effector and memory CD8+ T-cell differentiation are regulated by the strength and duration of IL-2 signals during the primary activation [5, 6], and the expression of the transcription factor T-bet [5, 7]. Ultimately, cytotoxicity is the main function of effector CD8+ T cells, and is predominantly regulated at the level of the cytotoxic granule content rather than the process of degranulation itself [8]. However, immunoregulatory cell types may mafosfamide interfere with distinct aspects of CD8+ T-cell differentiation. For example,

CD4+CD25+ regulatory T cells inhibit granule exocytosis without interfering with normal effector differentiation [9]. Myeloid-derived suppressor cells (MDSCs), which consist of an immature monocytic CD11b+CD115+Ly6G−Ly6Chigh (monocytic (MO)-MDSC) and granulocytic CD11b+CD115−Ly6G+Ly6Cint (polymorphonuclear (PMN)-MDSC) population [10-13], also hamper T-cell functions during various pathologies, including cancer [14], infections [15], and transplantation [16]. These cells expand from bone marrow (BM) progenitors under the influence of hematopoietic growth factors and inflammatory cytokines [17] and can deploy a variety of mechanisms for T-cell suppression [18], whereby the spleen appears to be an important site of action in tumor-bearers [19].