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Development of safe and effective COVID-19 vaccines is a global priority and the best hope for ending the COVID-19 pandemic. Remarkably, in less than 1 year, vaccines have been developed and shown to be efficacious and are already being deployed worldwide. Yet, many challenges remain. Immune senescence and comorbidities in aging populations and immune dysregulation in populations living in low-resource settings may impede vaccine effectiveness. Distribution of vaccines among these populations where vaccine access is historically low remains challenging. In this Review, we address these challenges and provide strategies for ensuring that vaccines are developed and deployed for those most vulnerable.

Chagas disease, caused by Trypanosoma cruzi, is a major public health issue. Limitations in immune responses to natural T. cruzi infection usually result in parasite persistence with significant complications. A safe, effective, and reliable vaccine would reduce the threat of T. cruzi infections; however, no suitable vaccine is currently available due to a lack of understanding of the requirements for induction of fully protective immunity. We established a T. cruzi strain expressing green fluorescent protein (GFP) under the control of dihydrofolate reductase degradation domain (DDD) with a hemagglutinin (HA) tag, GFP-DDDHA, which was induced by trimethoprim-lactate (TMP-lactate), which results in the death of intracellular parasites. This attenuated strain induces very strong protection against reinfection. Using this GFP-DDDHA strain, we investigated the mechanisms underlying the protective immune response in mice. Immunization with this strain led to a response that included high levels of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α), as well as a rapid expansion of effector and memory T cells in the spleen. More CD8+ T cells differentiate to memory cells following GFP-DDDHA infection than after infection with a wild-type (WT) strain. The GFP-DDDHA strain also provides cross-protection against another T. cruzi isolate. IFN-γ is important in mediating the protection, as IFN-γ knockout (KO) mice failed to acquire protection when infected with the GFP-DDDHA strain. Immune cells demonstrated earlier and stronger protective responses in immunized mice after reinfection with T. cruzi than those in naive mice. Adoptive transfers with several types of immune cells or with serum revealed that several branches of the immune system mediated protection. A combination of serum and natural killer cells provided the most effective protection against infection in these transfer experiments.

A model of the cyst wall interactome was constructed using proteins identified through BioID. The proteins within this cyst wall interactome model encompass several proteins identified in a prior characterization of the cyst wall proteome. This model provides a more comprehensive understanding of the composition of the cyst wall and may lead to insights on how the cyst wall is formed., A characteristic of the latent cyst stage of Toxoplasma gondii is a thick cyst wall that forms underneath the membrane of the bradyzoite vacuole. Previously, our laboratory group published a proteomic analysis of purified in vitro cyst wall fragments that identified an inventory of cyst wall components. To further refine our understanding of the composition of the cyst wall, several cyst wall proteins were tagged with a promiscuous biotin ligase (BirA*), and their interacting partners were screened by streptavidin affinity purification. Within the cyst wall pulldowns, previously described cyst wall proteins, dense granule proteins, and uncharacterized hypothetical proteins were identified. Several of the newly identified hypothetical proteins were validated to be novel components of the cyst wall and tagged with BirA* to expand the model of the cyst wall interactome. Community detection of the cyst wall interactome model revealed three distinct clusters: a dense granule, a cyst matrix, and a cyst wall cluster. Characterization of several of the identified cyst wall proteins using genetic strategies revealed that MCP3 affects in vivo cyst sizes. This study provides a model of the potential protein interactions within the cyst wall and the groundwork to understand cyst wall formation.

Chagas disease is a major public health issue, affecting ∼10 million people worldwide. Transmitted by a protozoan named Trypanosoma cruzi, this infection triggers a chronic inflammatory process that can lead to cardiomyopathy (Chagas disease). Resolvin D1 (RvD1) is a novel proresolution lipid mediator whose effects on inflammatory diseases dampens pathological inflammatory responses and can restore tissue homeostasis. Current therapies are not effective in altering the outcome of T. cruzi infection, and as RvD1 has been evaluated as a therapeutic agent in various inflammatory diseases, we examined if exogenous RvD1 could modulate the pathogenesis of Chagas disease in a murine model. CD-1 mice infected with the T. cruzi Brazil strain were treated with RvD1. Mice were administered 3 μg/kg of body weight RvD1 intraperitoneally on days 5, 10, and 15 to examine the effect of RvD1 on acute disease or administered the same dose on days 60, 65, and 70 to examine its effects on chronic infection. RvD1 therapy increased the survival rate and controlled parasite replication in mice with acute infection and reduced the levels of interferon gamma and transforming growth factor β (TGF-β) in mice with chronic infection. In addition, there was an increase in interleukin-10 levels with RvD1 therapy in both mice with acute infection and mice with chronic infection and a decrease in TGF-β levels and collagen content in cardiac tissue. Together, these data indicate that RvD1 therapy can dampen the inflammatory response, promote the resolution of T. cruzi infection, and prevent cardiac fibrosis.

Microsporidia are important opportunistic human pathogens in immune-suppressed individuals, such as those with HIV/AIDS and recipients of organ transplants. The sporoplasm is critical for establishing microsporidian infection. Despite the biological importance of this structure for transmission, there is limited information about its structure and composition that could be targeted for therapeutic intervention. Here, we identified a novel E. hellem sporoplasm surface protein, EhSSP1, and demonstrated that it can bind to host cell mitochondria via host VDAC. Our data strongly suggest that the interaction between SSP1 and VDAC is important for the association of mitochondria with the parasitophorous vacuole during microsporidian infection. In addition, binding of SSP1 to the host cell is associated with the final steps of invasion in the invasion synapse., Microsporidia are opportunistic intracellular pathogens that can infect a wide variety of hosts ranging from invertebrates to vertebrates. During invasion, the microsporidian polar tube pushes into the host cell, creating a protective microenvironment, the invasion synapse, into which the sporoplasm extrudes. Within the synapse, the sporoplasm then invades the host cell, forming a parasitophorous vacuole (PV). Using a proteomic approach, we identified Encephalitozoon hellem sporoplasm surface protein 1 (EhSSP1), which localized to the surface of extruded sporoplasms. EhSSP1 was also found to interact with polar tube protein 4 (PTP4). Recombinant EhSSP1 (rEhSSP1) bound to human foreskin fibroblasts, and both anti-EhSSP1 and rEhSSP1 caused decreased levels of host cell invasion, suggesting that interaction of SSP1 with the host cell was involved in invasion. Coimmunoprecipitation (Co-IP) followed by proteomic analysis identified host cell voltage-dependent anion channels (VDACs) as EhSSP1 interacting proteins. Yeast two-hybrid assays demonstrated that EhSSP1 was able to interact with VDAC1, VDAC2, and VDAC3. rEhSSP1 colocalized with the host mitochondria which were associated with microsporidian PVs in infected cells. Transmission electron microscopy revealed that the outer mitochondrial membrane interacted with meronts and the PV membrane, mitochondria clustered around meronts, and the VDACs were concentrated at the interface of mitochondria and parasite. Knockdown of VDAC1, VDAC2, and VDAC3 in host cells resulted in significant decreases in the number and size of the PVs and a decrease in mitochondrial PV association. The interaction of EhSSP1 with VDAC probably plays an important part in energy acquisition by microsporidia via its role in the association of mitochondria with the PV.

Foxp3+CD4+ regulatory T (Treg) cells are essential for preventing fatal autoimmunity and safeguard immune homeostasis in vivo. While expression of the transcription factor Foxp3 and IL-2 signals are both required for the development and function of Treg cells, the commitment to the Treg cell lineage occurs during thymic selection upon T cell receptor (TCR) triggering, and precedes the expression of Foxp3. Whether signals beside TCR contribute to establish Treg cell epigenetic and functional identity is still unknown. Here, using a mouse model with reduced IL-2 signaling, we show that IL-2 regulates the positioning of the pioneer factor SATB1 in CD4+ thymocytes and controls genome wide chromatin accessibility of thymic-derived Treg cells. We also show that Treg cells receiving only low IL-2 signals can suppress endogenous but not WT autoreactive T cell responses in vitro and in vivo. Our findings have broad implications for potential therapeutic strategies to reprogram Treg cells in vivo., Regulatory T (Treg) cells are developed in the thymus, and are essential for suppressing detrimental autoimmunity. Here the authors show, using mice with dampened interleukin 2 (IL-2) signaling, that IL-2 helps position the pioneer factor SATB1 to control genome-wide chromatin accessibility to facilitate Treg cell lineage commitment in the thymus.

Recent findings have revealed roles for systemic and mucosa-resident memory CD8(+) T cells in the orchestration of innate immune responses critical to host defense upon microbial infection. Here we integrate these findings into the current understanding of the molecular and cellular signals controlling memory CD8(+) T cell reactivation and the mechanisms by which these cells mediate effective protection in vivo. The picture that emerges presents memory CD8(+) T cells as early sensors of danger signals, mediating protective immunity both through licensing of cellular effectors of the innate immune system and via the canonical functions associated with memory T cells. We discuss implications for the development of T cell vaccines and therapies and highlight important areas in need of further investigation.

NLR proteins are a diverse family of pattern recognition receptors that modulate immune system homeostasis in the gastrointestinal system. Recent studies have identified a sub-group of inflammasome forming NLRs that modulate the mucosal immune response during inflammatory bowel disease (IBD) and colitis associated tumorigenesis. To better elucidate the contribution of NLR family members in IBD and cancer, we conducted a retrospective analysis of gene expression metadata from human patients. These data revealed that NLRP1, an inflammasome forming NLR, was significantly dysregulated in IBD and colon cancer. To better characterize the function of NLRP1 in disease pathogenesis, we utilized Nlrp1b-/- mice in experimental colitis and colitis associated cancer models. Nlrp1b-/- mice demonstrated significant increases in inflammation and tumorigenesis compared to wild type mice. The increased inflammation and tumor burden was correlated with attenuated levels of IL-1β and IL-18. Further mechanistic studies revealed the increased disease pathogenesis in the Nlrp1b-/- mice was associated with non-hematopoietic derived cells and suggests that NLRP1 functions in the colon epithelial cells to attenuate tumorigenesis. Together, these data identify NLRP1 as an essential mediator of the host immune response during IBD and cancer. These findings are consistent with a model whereby multiple NLR inflammasomes attenuate disease pathobiology through modulating IL-1β and IL-18 levels in the colon.