The high-affinity receptor for IgG, FcgammaRI, shares its capacity to bind IgG2a immune complexes (IgG2a-IC) with the low-affinity receptor FcgammaRIII and complement factors, hampering the definition of its biological role. Moreover, in vivo, FcgammaRI is occupied by monomeric IgG2a, reducing its accessibility to newly formed IgG2a-IC. By using a variety of FcgammaR(-/-) mice, we demonstrate that in the absence of FcgammaRI, the IgG2a-IC-induced cellular processes of phagocytosis, cytokine release, cellular cytotoxicity, and antigen presentation are impaired. FcgammaRI(-/-) mice showed impaired hypersensitivity responses, strongly reduced cartilage destruction in an arthritis model, and impaired protection from a bacterial infection. We conclude that FcgammaRI contributes substantially to a variety of IgG2a-IC-dependent immune functions and immunopathological responses.

The ability of CD8 T lymphocytes to eliminate tumors is limited by their ability to engender an immunosuppressive microenvironment. Here we describe a subset of tumor-infiltrating CD8 T cells marked by high expression of the immunosuppressive ATP ecto-nucleotidase CD39. The frequency of CD39CD8 T cells increased with tumor growth but was absent in lymphoid organs. Tumor-infiltrating CD8 T cells with high CD39 expression exhibited features of exhaustion, such as reduced production of TNF and IL2 and expression of coinhibitory receptors. Exhausted CD39CD8 T cells from mice hydrolyzed extracellular ATP, confirming that CD39 is enzymatically active. Furthermore, exhausted CD39CD8 T cells inhibited IFNγ production by responder CD8 T cells. In specimens from breast cancer and melanoma patients, CD39CD8 T cells were present within tumors and invaded or metastatic lymph nodes, but were barely detectable within noninvaded lymph nodes and absent in peripheral blood. These cells exhibited an exhausted phenotype with impaired production of IFNγ, TNF, IL2, and high expression of coinhibitory receptors. Although T-cell receptor engagement was sufficient to induce CD39 on human CD8 T cells, exposure to IL6 and IL27 promoted CD39 expression on stimulated CD8 T cells from human or murine sources. Our findings show how the tumor microenvironment drives the acquisition of CD39 as an immune regulatory molecule on CD8 T cells, with implications for defining a biomarker of T-cell dysfunction and a target for immunotherapeutic intervention. The tumor microenvironment elicits a subset of functionally exhausted CD8 T cells by creating conditions that induce cell surface expression of CD39, an immunosuppressive molecule that can be therapeutically targeted to restore effector T-cell function. .

Dendritic cells (DCs) require a maturation signal to acquire efficient CTL-priming capacity. In vitro FcgammaR-mediated internalization of Ag-Ab immune complexes (ICs) can induce maturation of DCs. In this study, we show that IC-induced DC maturation in vitro enables DCs to prime peptide-specific CD8+ CTLs in vivo, independently of CD4+ Th cells. Importantly, OVA/anti-OVA IC-treated DCs not only primed CD8+ CTLs to an exogenously loaded peptide nonrelated to OVA, but also efficiently primed CTLs against the dominant CTL epitope derived from the OVA Ag present in the ICs. Our studies show that ICs fulfill a dual role in priming of CD8+ CTL responses to exogenous Ags: enhancement of Ag uptake by DCs and activation of DCs, resulting in "license to kill." These findings indicate that the presence of specific Abs can crucially affect the induction of cytotoxic cellular responses.

Personalized cancer vaccines (PCVs) targeting patient-specific neoantigens are a promising cancer treatment modality; however, neoantigen physicochemical variability can present challenges to manufacturing PCVs in an optimal format for inducing anticancer T cells. Here, we developed a vaccine platform ("SNP-7/8a") based on charge-modified peptide-TLR-7/8a conjugates that are chemically programmed to self-assemble into nanoparticles of uniform size (~20 nm) irrespective of the peptide antigen composition. This approach provided precise loading of diverse peptide neoantigens linked to TLR-7/8a (adjuvant) in nanoparticles that increased uptake by and activation of antigen-presenting cells that promote T cell immunity. Vaccination of mice with SNP-7/8a using predicted neoantigens (n=179) from three tumor models induced CD8 T cells against ~50% of neoantigens with high predicted MHC-I binding affinity and led to enhanced tumor clearance. SNP-7/8a delivering in silico-designed mock neoantigens also induced CD8 T cells in non-human primates. Altogether, SNP-7/8a is a generalizable approach for co-delivering peptide antigens and adjuvants in nanoparticles for inducing anticancer T cell immunity.

To develop a strategy that promotes efficient antiviral immunity, hybrid virus-like particles (VLP) were prepared by self-assembly of the modified porcine parvovirus VP2 capsid protein carrying a CD8 ؉ T cell epitope from the lymphocytic choriomeningitis virus nucleoprotein. Immunization of mice with these hybrid pseudoparticles, without adjuvant, induced strong cytotoxic T lymphocyte (CTL) responses against both peptide-coated-or virus-infected-target cells. This CD8 ؉ class I-restricted cytotoxic activity persisted in vivo for at least 9 months. Furthermore, the hybrid parvovirus-like particles were able to induce a complete protection of mice against a lethal lymphocytic choriomeningitis virus infection. To our knowledge, this study represents the first demonstration that hybrid nonreplicative VLP carrying a single viral CTL epitope can induce protection against a viral lethal challenge, in the absence of any adjuvant. These recombinant particles containing a single type of protein are easily produced by the baculovirus expression system and, therefore, represent a promising and safe strategy to induce strong CTL responses for the elimination of virus-infected cells. CD8ϩ cytotoxic T lymphocytes (CTLs) play an important role in the elimination of cells infected by pathogens and in the regression of tumors. CTLs recognize antigen-derived peptides presented by major histocompatibility complex (MHC) class I molecules on the cell surface and are usually activated by peptides resulting from the processing of endogenous intracellular proteins (1). Because antigens have to gain access to the cytosol to enter the class I-restricted presentation pathway, exogenous soluble proteins are usually unable to stimulate CTL responses. Therefore, several strategies have been developed to deliver exogenous antigens into the cytosol. Protein or peptide antigens delivered in association with appropriate adjuvants [complete Freund's adjuvant (2), incomplete Freund's adjuvant (3), or saponin (4)], liposomes (5), ISCOMs (6), or in particulate form linked to latex microspheres (7) efficiently stimulate CTL responses. However, alum (aluminum salts) is still the only adjuvant currently licensed for use in human vaccines. Recombinant live vectors [such as attenuated virus, vaccinia virus (8), mengo virus (9)] or bacteria [bacillus Calmette-Guérin (10), Salmonella (11), or Listeria (12)] have also been shown to sensitize CTLs in vivo but are risk-prone. Recombinant canarypox virus expressing gp160 from HIV-1, which cannot replicate in mammalian species, was recently shown to induce CTL responses in humans but only in less than 40% of the volunteers (13). DNA vaccination may also represent a powerful strategy to activate CTL responses (14), but the safety of this method remains to be determined. Therefore, the development of a safe strategy to induce CTL responses with nonreplicating antigens is still an important prerequisite for the design of new efficient vaccines.Recently, we have developed an antigen delivery system based on ...

Dendritic cells (DCs) are the only APCs capable of initiating adaptive immune responses. The initiation of immune responses requires that DCs 1) internalize and present Ags; and 2) undergo a differentiation process, called “maturation”, which transforms DCs into efficient APCs. DC maturation may be initiated by the engagement of different surface receptors, including certain cytokine receptors (such as TNFR), Toll-like receptors, CD40, and FcRs. The early activation events that link receptor engagement and DC maturation are not well characterized. We found that FcR engagement by immune complexes induced the phosphorylation of Syk, a protein tyrosine kinase acting immediately downstream of FcRs. Syk was dispensable for DC differentiation in vitro and in vivo, but was strictly required for immune complexes internalization and subsequent Ag presentation to T lymphocytes. Importantly, Syk was also required for the induction of DC maturation and IL-12 production after FcR engagement, but not after engagement of other surface receptors, such as TNFR or Toll-like receptors. Therefore, protein tyrosine phosphorylation by Syk represents a novel pathway for the induction of DC maturation.

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Highlights d Genomically simple RTs are infiltrated by T cell and myeloid populations d Clonally expanded T cell phenotypes suggest a tumorspecific response d Checkpoint blockade induces tumor regression and immune memory in vivo d Endogenous retrovirus expression is linked to the immunogenicity of RTs