MHC class I antigen cross-presentation mediated by PapMV nanoparticles in human antigen-presenting cells is dependent on autophagy.

Nanoparticles made of the coat protein of papaya mosaic virus (PapMV) and a single-strand RNA were previously shown to be an efficient antigen presentation system for the trigger of cellular immunity. Engineering of PapMV nano with a cytotoxic T lymphocyte epitope was previously shown activating specific T lymphocytes through a proteasome-independent major histocompatibility complex class I (MHC-I) cross-presentation. In this study, we provide new insights into the mechanism of the MHC-I cross-presentation mediated by PapMV nanoparticles. We demonstrate that PapMV nanoparticles do not require the transporter associated with antigen presentation (TAP), but rather depend on lysosome acidification and cathepsin S protease activity for presentation of the T cell epitope. We have also linked the induction of autophagy with this vacuolar MHC-I cross-presentation process. Interestingly, autophagy is induced in antigen-presenting cells after PapMV nanoparticles exposure and inhibition of autophagy reduce MHC-I cross-presentation. This study demonstrates that autophagy is associated with TAP- and proteasome-independent MHC-I cross-presentation. A deeper understanding of the autophagy-dependent MHC-I cross-presentation will be useful in designing vaccination platforms that aim to trigger an efficient cytotoxic T lymphocyte response.

CD40L-Stimulated B Lymphocytes Are Polarized toward APC Functions after Exposure to IL-4 and IL-21.

B lymphocytes have multiple functions central to humoral immunity, including Ag presentation to T cells, cytokine secretion, and differentiation into Ab-secreting plasma cells. In vitro expansion of human B cells by continuous IL-4 stimulation and engagement of their CD40 receptor by CD40L has allowed the use of these IL-4-CD40-B cells in research for the induction of Ag-specific T cell immune responses. However, in vivo, follicular helper T cells also influence B cell activity through the secretion of IL-21. The impact of both cytokines on multiple B cell functions is not clearly defined. To further understand these cytokines in CD40-B cell biology, we stimulated CD40-B cells with IL-4 or IL-21 or both (Combo) and characterized the proliferation, subsets, and functions of these cells. We demonstrate that IL-21- and Combo-CD40-B cells are highly proliferative cells that can be rapidly expanded to high numbers. We show that IL-21-CD40-B cells polarize to Ab-secreting plasma cells, whereas IL-4- and Combo-CD40-B cells are mostly activated mature B cells that express molecules associated with favorable APC functions. We further demonstrate that both IL-4- and Combo-CD40-B cells are efficient in promoting T cell activation and proliferation compared with IL-21-CD40-B cells. Thus, our study provides a better appreciation of CD40-B cell plasticity and biology. In addition, the stimulation of B cells with CD40L, IL-4, and IL-21 allows for the fast generation of high numbers of efficient APC, therefore providing a prospective tool for research and clinical applications such as cancer immunotherapy.

Fludarabine downregulates indoleamine 2,3-dioxygenase in tumors via a proteasome-mediated degradation mechanism.

Indoleamine 2,3-dioxygenase (IDO) is found in multiple malignancies and exerts immunosuppressive effects that are central in protecting tumors from host T lymphocyte rejection. IDO is an enzyme involved in the catabolism of tryptophan resulting in inhibition of T lymphocyte function. While inhibition of IDO enzymatic activity results in tumor rejection, it is still unknown how we can directly target IDO expression within tumors using drugs. We have chosen to interfere with IDO expression by targeting the key-signaling event signal transducer and activator of transcription 1 (STAT1). We evaluated the efficacy of fludarabine, previously described to inhibit STAT1 phosphorylation. Interestingly, fludarabine was efficient in suppressing protein expression and consequently IDO activity in two different cell lines derived from breast cancer and melanoma when IDO was activated with interferon-gamma (IFN-γ) or supernatants prepared from activated T lymphocytes. However, fludarabine had no inhibitory effect on STAT1 phosphorylation. Other IFN-γ-responsive genes were only marginally inhibited by fludarabine. The level of IDO transcript was unaffected by this inhibitor, suggesting the involvement of post-transcriptional control. Strikingly, we have found that the inhibition of proteasome partially protected IDO from fludarabine-induced degradation, indicating that fludarabine induces IDO degradation through a proteasome-dependent pathway. Currently used in the clinic to treat some malignancies, fludarabine has the potential for use in the treatment of human tumors through induction of IDO degradation and consequently, for the promotion of T cell-mediated anti-tumor response.