Anticancer vaccination is a promising approach to increase the efficacy of cytotoxic T lymphocyte–associated protein 4 (CTLA-4) and programmed death ligand 1 (PD-L1) checkpoint blockade therapies. However, the landmark FDA registration trial for anti–CTLA-4 therapy (ipilimumab) revealed a complete lack of benefit of adding vaccination with gp100 peptide formulated in incomplete Freund’s adjuvant (IFA). Here, using a mouse model of melanoma, we found that gp100 vaccination induced gp100-specific effector T cells (Teffs), which dominantly forced trafficking of anti–CTLA-4–induced, non-gp100–specific Teffs away from the tumor, reducing tumor control. The inflamed vaccination site subsequently also sequestered and destroyed anti–CTLA-4–induced Teffs with specificities for tumor antigens other than gp100, reducing the antitumor efficacy of anti–CTLA-4 therapy. Mechanistically, Teffs at the vaccination site recruited inflammatory monocytes, which in turn attracted additional Teffs in a vicious cycle mediated by IFN-γ, CXCR3, ICAM-1, and CCL2, dependent on IFA formulation. In contrast, nonpersistent vaccine formulations based on dendritic cells, viral vectors, or water-soluble peptides potently synergized with checkpoint blockade of both CTLA-4 and PD-L1 and induced complete tumor regression, including in settings of primary resistance to dual checkpoint blockade. We conclude that cancer vaccine formulation can dominantly determine synergy, or lack thereof, with CTLA-4 and PD-L1 checkpoint blockade therapy for cancer.

Sepsis is a systemic infection that enhances host vulnerability to secondary infections normally controlled by T cells. Using CLP sepsis model, we observed that sepsis induces apoptosis of circulating memory CD8 T-cells (T_CIRCM) and diminishes their effector functions, leading to impaired CD8 T-cell mediated protection to systemic pathogen re-infection. In the context of localized re-infections, tissue resident memory CD8 T-cells (T_RM) provide robust protection in a variety of infectious models. T_RM rapidly ‘sense’ infection in non-lymphoid tissues and ‘alarm’ the host by enhancing immune cell recruitment to the site of the infection to accelerate pathogen clearance. Here, we show that compared to pathogen-specific T_CIRCM, sepsis does not invoke significant numerical decline of Vaccinia virus induced skin-T_RM keeping their effector functions (e.g., Ag-dependent IFN-γ production) intact. IFN-γ-mediated recruitment of immune cells to the site of localized infection was, however, reduced in CLP hosts despite T_RM maintaining their ‘sensing and alarming’ functions. The capacity of memory CD8 T-cells in the septic environment to respond to inflammatory cues and arrive to the site of secondary infection/antigen exposure remained normal suggesting T-cell-extrinsic factors contributed to the observed lesion. Mechanistically, we showed that IFN-γ produced rapidly during sepsis-induced cytokine storm leads to reduced IFN-γR1 expression on vascular endothelium. As a consequence, decreased expression of adhesion molecules and/or chemokines (VCAM1 and CXCL9) on skin endothelial cells in response to T_RM-derived IFN-γ was observed, leading to sub-optimal bystander-recruitment of effector cells and increased susceptibility to pathogen re-encounter. Importantly, as visualized by intravital 2-photon microscopy, exogenous administration of CXCL9/10 was sufficient to correct sepsis-induced impairments in recruitment of effector cells at the localized site of T_RM antigen recognition. Thus, sepsis has the capacity to alter skin T_RM anamnestic responses without directly impacting T_RM number and/or function, an observation that helps to further define the immunoparalysis phase in sepsis survivors. Infectious pathogens are generally relegated within barrier tissues; however, when infections enter the bloodstream the host enters a septic state that (when severe enough) can lead to widespread tissue damage and death. After resolution of acute stage of sepsis, patients often display enhanced susceptibility to secondary infections resulting from quantitative and qualitative alterations in the immune response. Previously, we and others have shown that sepsis dramatically reduces the number and function of memory CD8 T cells within the host, contributing to the state of immunoparalysis early after sepsis induction. The present study directly examines the impact of sepsis on tissue resident memory CD8 T cells (T_RM) that are restricted to barrier tissues and provide protection to localized infections. In contrast to circulating memory T cells found within lymphoid tissues, the number and function of T_RM within non-lymphoid peripheral tissue (such as the skin) was maintained during sepsis suggesting a protective niche for memory CD8 T cells within barrier tissues of septic hosts. However, the capacity of T_RM to provide protection upon re-infection was severely diminished in septic hosts, which was attributed to a sepsis-induced lesion in T_RM-extrinsic factors. Thus, this report supports the notion that sepsis has the capacity to influence host response to pathogen re-infection either by directly influencing memory CD8 T cell populations or by preventing other cell types to properly recognize localized pathogen-induced alarming signals delivered by resident memory CD8 T cells.

Induction of lymphopenia has been exploited therapeutically to improve immune responses to cancer therapies and vaccinations. Whereas IL-15 has well-established roles in stimulating lymphocyte responses after lymphodepletion, the mechanisms regulating these IL-15 responses are unclear. We report that cell surface IL-15 expression is upregulated during lymphopenia induced by total body irradiation (TBI), cyclophosphamide, or Thy1 Ab-mediated T cell depletion, as well as in RAG^−/− mice; interestingly, the cellular profile of surface IL-15 expression is distinct in each model. In contrast, soluble IL-15 (sIL-15) complexes are upregulated only after TBI or αThy1 Ab. Analysis of cell-specific IL-15Rα conditional knockout mice revealed that macrophages and dendritic cells are important sources of sIL-15 complexes after TBI but provide minimal contribution in response to Thy1 Ab treatment. Unlike with TBI, induction of sIL-15 complexes by αThy1 Ab is sustained and only partially dependent on type I IFNs. The stimulator of IFN genes pathway was discovered to be a potent inducer of sIL-15 complexes and was required for optimal production of sIL-15 complexes in response to Ab-mediated T cell depletion and TBI, suggesting products of cell death drive production of sIL-15 complexes after lymphodepletion. Lastly, we provide evidence that IL-15 induced by inflammatory signals in response to lymphodepletion drives lymphocyte responses, as memory CD8 T cells proliferated in an IL-15–dependent manner. Overall, these studies demonstrate that the form in which IL-15 is expressed, its kinetics and cellular sources, and the inflammatory signals involved are differentially dictated by the manner in which lymphopenia is induced.

Protective lung tissue-resident memory CD8⁺T cells (Trm) form after influenza A virus (IAV) infection. We show that IAV infection of mice generates CD69⁺CD103⁺and other memory CD8⁺T cell populations in lung-draining mediastinal lymph nodes (mLNs) from circulating naive or memory CD8⁺T cells. Repeated antigen exposure, mimicking seasonal IAV infections, generates quaternary memory (4M) CD8⁺T cells that protect mLN from viral infection better than 1M CD8⁺T cells. Better protection by 4M CD8⁺T cells associates with enhanced granzyme A/B expression and stable maintenance of mLN CD69⁺CD103⁺4M CD8⁺T cells, vs the steady decline of CD69⁺CD103⁺1M CD8⁺T cells, paralleling the durability of protective CD69⁺CD103⁺4M vs 1M in the lung after IAV infection. Coordinated upregulation in canonical Trm-associated genes occurs in circulating 4M vs 1M populations without the enrichment of canonical downregulated Trm genes. Thus, repeated antigen exposure arms circulating memory CD8⁺T cells with enhanced capacity to form long-lived populations of Trm that enhance control of viral infections of the mLN.

Despite increasing evidence that uveitis is common and consequential in survivors of Ebola virus disease (EVD), the host-pathogen determinants of the clinical phenotype are undefined, including the pathogenetic role of persistent viral antigen, ocular tissue-specific immune responses, and histopathologic characterization. Absent sampling of human intraocular fluids and tissues, these questions might be investigated in animal models of disease; however, challenges intrinsic to the nonhuman primate model and the animal biosafety level 4 setting have historically limited inquiry. In a rhesus monkey survivor of experimental Ebola virus (EBOV) infection, we observed and documented the clinical, virologic, immunologic, and histopathologic features of severe uveitis. Here we show the clinical natural history, resultant ocular pathology, intraocular antigen-specific antibody detection, and persistent intraocular EBOV RNA detected long after clinical resolution. The association of persistent EBOV RNA as a potential driver of severe immunopathology has pathophysiologic implications for understanding, preventing, and mitigating vision-threatening uveitis in EVD survivors.

Lassa virus (LASV) is a rodent-borne mammarenavirus that causes tens to hundreds of thousands of human infections annually in Western Africa. Approximately 20% of these infections progress to Lassa fever (LF), an acute disease with case–fatality rates from ≈20–70%. Currently, there are no approved vaccines or specific therapeutics to prevent or treat LF. The LASV genome consists of a small (S) segment that has two genes, GP and NP, and a large (L) segment that has two genes, L and Z. In both segments, the two genes are separated by non-coding intergenic regions (IGRs). Recombinant LASVs (rLASVs), in which the L segment IGR was replaced with the S segment IGR or in which the GP gene was codon-deoptimized, lost fitness in vitro, were highly attenuated in vivo, and, when used as vaccines, protected domesticated guinea pigs from otherwise lethal LASV exposure. Here, we report the generation of rLASV/IGR-CD, which includes both determinants of attenuation and further enhances the safety of the vaccine compared with its predecessors. rLASV/IGR-CD grew to high titers in Vero cells, which are approved for human vaccine production, but did not cause signs of disease or pathology in guinea pigs. Importantly, guinea pigs vaccinated with rLASV/IGR-CD were completely protected from disease and death after a typically lethal exposure to wild-type LASV. Our data support the development of rLASV/IGR-CD as a live-attenuated LF vaccine with stringent safety features.