Biology subjects

Christian, D. A.

Publications and source records attributed to Christian, D. A..

15 recordsLinked to original sources

bioRxiv2026

The role of integrins in T cell-mediated resistance to Cryptosporidium parvum

Cryptosporidium is a protozoan that infects epithelial cells of the small intestine and is a cause of diarrhea and death in immunocompromised individuals and malnourished children. Immunity to this parasite is mediated by an intestinal T cell response, which is generated in gut-associated lymphoid tissues and dependent on type 1 conventional dendritic cells (cDC1s). The initial priming of T cells is accompanied by changes in integrin expression and subsequent trafficking to the site of infection. The role of specific integrins in trafficking to the ileum during cryptosporidiosis is largely unknown. The development of a transgenic Cryptosporidium strain that expresses MHCI and MHCII-restricted model antigens provides the ability to track T cell responses to this parasite. Our studies in this system revealed marked changes in the integrin profile of parasite-specific T cells as they are activated and traffic to the gut, and demonstrate that cDC1s contribute to the expression of the integrins 4, {beta}7, {beta}1, and L. Surprisingly, blockade of the canonical gut-homing integrin 4{beta}7 does not impact the ability of parasite-specific T cells to access the gut. However, blockade of integrin L decreases the parasite-specific T cell frequency at the site of infection and delays control of parasite burden. These datasets highlight an 4{beta}7-independent mechanism of T cell trafficking to the small intestine and indicate that L is an integrin required for T cell-mediated resistance to Cryptosporidium.

immunology↗

bioRxiv2025

The STORE.2 model of the T cell proliferative phase considering c-Myc

The generation of antigen-specific CD8+ T cell responses is dictated by the affinity of the cognate antigen, the stimulatory capacity of antigen presenting cells (APCs), and the metabolic pathways required for rapid cell proliferation. The complexity of these pathways is a significant challenge in designing vaccines against diseases that require a protective CD8+ T cell response. To understand the mechanisms underlying CD8+ T cell responses, the STORE.2 model was developed to simulate the early events of T cell priming and expansion at the site of priming. STORE.2 is a mathematical, stochastic, and agent-based model based on first-principles that tracks every individual CD8+ T cell and APC. It allows for the simulation of different antigen affinity (Signal 1) as well as levels of costimulation (Signal 2) and inflammatory cytokines (Signal 3) provided by APCs. The impact of Signals 1-3 is translated to T cell responses via the transcription factor c-Myc, which supports T cell proliferation. Enhanced glycolysis during T cell activation results in a change in the metabolic environment that includes an increase in extracellular lactate concentration. STORE.2 models the role of lactate in the inhibition of T cell metabolism and proliferation as a negative feedback mechanism on c-Myc production. STORE.2 accurately recapitulated the CD8+ T cell response during in vitro T cell priming assays that control for Signals 1-3 as well as lactate concentration. Finally, application of STORE.2 to an in vivo response to immunization demonstrated that the model accurately simulates CD8+ T cell activation at the site of priming.

immunology↗

bioRxiv2025

The type I IFN-IL-27 axis promotes mRNA vaccine-induced CD8+ T cell responses

The ability of lipid nanoparticle (LNP)-delivered mRNA vaccines to induce type I IFNs is critical to promote CD8+ T cell responses. The studies presented here indicate that immunization with nucleoside modified mRNA-LNP vaccines drives myeloid cell expression of the cytokine IL-27, which acts on antigen-specific CD8+ T cells to sustain T cell expansion. In vitro and in vivo studies revealed that type I IFN signaling is necessary for mRNA-LNP-induced IL-27 production, that immunization failed in IL-27 KO mice, and that immunization of IFNAR1-deficient mice with mRNA-LNP particles that also encode IL-27 mRNA restored antigen-specific CD8+ T cell responses. In addition, IL-27 mRNA-LNPs served as an adjuvant that improved cytolytic CD8+ T cell responses and the therapeutic efficacy of mRNA-LNPs to drive anti-pathogen and anti-tumor immunity. These studies highlight the central role of IL-27 in mRNA-LNP induced CD8+ T cell responses and the ability of this cytokine to augment the functionality of the CD8+ T cell response for prophylactic or therapeutic immunization.

immunology↗

bioRxiv2025

IL-27 limits HSPC differentiation during infection and protects from stem cell exhaustion

Many inflammatory stimuli can induce progenitor cells in the bone marrow to produce increased numbers of myeloid cells as part of the process of emergency myelopoiesis. These events are associated with trained immunity and have long-term impacts on hematopoietic stem and progenitor cell (HSPC) development but can also compromise their function. While many cytokines support emergency myelopoiesis, less is known about the mechanisms that temper these events. When mice that lack the cytokine IL-27 were infected with Toxoplasma gondii, there was enhanced generation of monocyte progenitors and increased numbers of inflammatory monocytes. In the bone marrow of infected mice there was increased production of IL-27 that localized with HSPCs and a survey of cytokine receptor expression highlighted that HSPCs were uniquely poised to respond to IL-27. Furthermore, the use of in vitro differentiation assays and mixed bone marrow chimeras revealed that HSPCs from IL-27 deficient mice are pre-disposed towards the monocyte lineage. Additional studies highlighted that after infection loss of the IL-27R resulted in reduced HSPC fitness that manifested as reduced proliferative responses and a decreased ability to reconstitute the hematopoietic system. Thus, the ability of IL-27 to act on HSPC provides a regulatory brake on differentiation to limit monocyte induction and preserve HSPC stemness.

immunology↗

bioRxiv2024

IL-27 Stablizes Myc-Mediated Transcription In Memory-Fated, Vaccine-Elicited CD8+ T Cells

Protection from pathogens relies on both humoral (antibody-mediated) and cellular (T cell-mediated) responses. While infections robustly elicit both types of immunity, currently approved vaccine adjuvants largely fail to induce T cell responses on par with that instigated by infections. Our goal was to investigate the transcriptional programming that supports the formation of CD8+ T cells elicited by subunit vaccines compared to those elicited by infections. Our data show that vaccine-elicited T cells represent a transcriptionally unique subset of activated T cells with high proliferative capacity and a memory cell fate. This relies on IL-27 signaling, which stabilizes c-Myc and thereby supports the biomass acquisition necessary for clonal expansion. Collectively, our findings reveal that subunit vaccine-elicited T cells uniquely combine aspects of both memory and effector T cell subsets, and selectively utilize IL-27 signaling to sustain the clonal expansion of cells dedicated to a memory fate. One Sentence SummaryIn contrast to infection, subunit vaccines induce a distinct population of CD8+ T cells with memory fate characteristics which maintain their proliferative capacity during the expansion phase through IL-27 receptor signaling.

immunology↗

bioRxiv2024

An IL-12 mRNA-LNP adjuvant enhances mRNA-LNP vaccine induced CD8+ T cell responses

The design of vaccines that induce CD8+ T cell responses has historically been a challenge, but the development of viral vectors or lipid nanoparticles (LNPs) to deliver mRNA that encode for target antigens provide more effective strategies to generate protective CD8+ T cell memory. Because interleukin-12 (IL-12) supports CD8+ T cell expansion and acquisition of effector functions, studies were performed to assess its contribution to the ability of an mRNA vaccine to promote CD8+ T cell responses. In vitro and in vivo, mRNA-LNPs did not stimulate myeloid cell production of IL-12, and the CD8+ T cell response to vaccination with the model antigen ovalbumin (OVA) was IL-12 independent. However, co-administration of IL-12 mRNA-LNPs with OVA mRNA-LNPs enhanced OVA-specific CD8+ T cell expansion, improved acquisition of effector function and resulted in an expanded memory CD8+ T cell pool. These heightened responses were associated with improved protective responses against Listeria monocytogenes-OVA and B16 FO-OVA melanoma. Thus, modification of mRNA vaccine formulations by inclusion of a cytokine mRNA provides a strategy to enhance CD8+ T cell mediated protection.

immunology↗

bioRxiv2024

The latent stage of Toxoplasma gondii is targeted by the immune response and host protective

Latency is a microbial strategy for persistence. For Toxoplasma gondii the ability of the bradyzoite stage to form long-lived cysts is critical for transmission, while their presence in neurons is considered important for immune evasion. Development of a mathematical model highlighted that immune pressure on bradyzoites should contribute to dynamics of cyst formation and reactivation. Experimental data demonstrated that a cyst-derived antigen was recognized by CD8+ T cells and that IFN-{gamma} signaling in neurons contributes to cyst control. In addition, modeling and the use of a parasite strain unable to form bradyzoites revealed that this stage was not required for long-term persistence, but the absence of cyst formation resulted in increased tachyzoite replication in the CNS with associated tissue damage and mortality. Thus, the latent form of T. gondii is under immune pressure, mitigates infection-induced damage, and promotes survival of host and parasite.

microbiology↗

bioRxiv2023

Intestinal cDC1s provide IL-12 dependent and independent functions required for CD4+ T cell mediated resistance to Cryptosporidium

Cryptosporidium is an enteric pathogen that is a prominent cause of diarrheal disease. Control of this infection requires CD4+ T cells, though the processes that lead to T cell-mediated resistance have been difficult to assess. Here, Cryptosporidium parasites that express MHCII-restricted model antigens were generated to dissect the early events that influence CD4+ T cell priming and effector function. These studies highlight that parasite-specific CD4+ T cells are primed in the draining mesenteric lymph node (mesLN) and differentiate into Th1 cells in the gut, where they mediate IFN-{gamma}-dependent control of the infection. Although type 1 conventional dendritic cells (cDC1s) were not required for initial priming of CD4+ T cells, cDC1s were required for CD4+ T cell expansion and gut homing. cDC1s were also a major source of IL-12 that was not required for priming but promoted full differentiation of CD4+ T cells and local production of IFN-{gamma}. Together, these studies reveal distinct roles for cDC1s in shaping CD4+ T cell responses to enteric infection: first to drive early expansion in the mesLN and second to drive effector responses in the gut. SummaryCryptosporidium parasites that express model antigens were generated to dissect how parasite-specific CD4+ T cells are primed and mediate effector functions required to control this enteric pathogen. cDC1s produced IL-12p40 and were required for early expansion and gut homing of CD4+ T cells. However, IL-12p40 was only required for the development of Th1 CD4+ T cell effector function in the gut.

immunology↗

bioRxiv2023

Dendritic cell-mediated responses to secreted Cryptosporidium effectors are required for parasite-specific CD8+ T cell responses

Cryptosporidium causes debilitating diarrheal disease in patients with primary and acquired defects in T cell function. However, it has been a challenge to understand how this infection generates T cell responses and how they mediate parasite control. Here, Cryptosporidium was engineered to express a parasite effector protein (MEDLE-2) that contains the MHC-I restricted SIINFEKL epitope which is recognized by TCR transgenic OT-I CD8+ T cells. These modified parasites induced expansion of endogenous SIINFEKL-specific and OT-I CD8+ T cells that were a source of IFN-{gamma} that could restrict growth of Cryptosporidium. This T cell response was dependent on the translocation of the effector and similar results were observed with another secreted parasite effector (ROP1). Although infection and these translocated effector proteins are restricted to intestinal epithelial cells (IEC), type I dendritic cells (cDC1) were required to generate CD8+ T cell responses to these model antigens. These data sets highlight Cryptosporidium effectors as targets of the immune system and suggest that crosstalk between enterocytes and cDC1s is crucial for CD8+ T cell responses to Cryptosporidium.

immunology↗

bioRxiv2022

PD-1 and CTLA-4 exert additive control of effector regulatory T cells

At homeostasis, a substantial proportion of Foxp3+ T regulatory cells (Tregs) have an activated phenotype associated with enhanced TCR signals and these effector Treg cells (eTregs) co-express elevated levels of PD-1 and CTLA-4. Short term in vivo blockade of the PD-1 or CTLA-4 pathways results in increased eTreg populations, while combination blockade of both pathways had an additive effect. Mechanistically, combination blockade resulted in a reduction of suppressive phospho-SHP2 Y580 in Treg cells which was associated with increased eTreg proliferation, enhanced production of IL-10, and altered dendritic cell expression of CD80 and MHC-II. Thus, at homeostasis, PD-1 and CTLA-4 function additively to regulate eTreg function and the ability to target these pathways in Treg cells may be useful to modulate inflammation.

immunology↗

bioRxiv2022

Impact of secondary TCR engagement on the heterogeneity of pathogen-specific CD8+ T cell response during acute and chronic toxoplasmosis

Initial TCR engagement of CD8+ T cells results in T cell expansion, and these early events influence the generation of diverse effector and memory populations. During infection, some activated T cells re-encounter cognate antigen, but how these events influence local effector responses or formation of memory populations is unclear. To address this issue, OT-I T cells which express the Nur77-GFP reporter of TCR activation were paired with T. gondii that express OVA to assess the impact of TCR activation on CD8+ T cell responses. During acute infection, TCR stimulation in affected tissues correlated with parasite burden and was associated with markers of effector cells while Nur77-GFP- OT-I showed signs of effector memory potential. However, adoptive transfer of Nur77-GFP negative or positive OT-I from infected mice into naive recipients resulted in formation of similar memory populations. During the chronic stage of infection in the CNS, TCR activation was associated with large scale transcriptional changes and the acquisition of an effector T cell phenotype as well as the generation of a population of CD103+ CD69+ Trm like cells. However, while inhibition of parasite replication resulted in reduced effector responses it did not alter the Trm population. These data sets highlight the contribution of recent TCR activation on the phenotypic heterogeneity of the CD8+ T cell response but suggest that this process has a limited impact on memory populations at acute and chronic stages of infection. Author SummaryCD8+ T cells are important to control many acute and chronic infections, however the role that recent T cell receptor stimulation plays in the formation of ongoing T cell responses is unclear. Here, we utilize a genetic reporter of TCR stimulation and high parameter flow cytometry to characterize TCR-driven phenotypes of pathogen specific T cell responses to the parasite Toxoplasma gondii during acute and chronic infection in the periphery and central nervous system. This work demonstrates the importance of recent TCR stimulation in driving local effector CD8+ T cell responses in peripheral tissues during infection, as well as the plasticity of the formation of memory T cells. Additionally, we utilize static and live imaging to investigate how Toxoplasma gondii life cycle impacts the ability to present antigen to CD8+ T cells. These studies aid in our understanding of how effector and memory CD8+ T cell responses are generated and maintained during an infection.

immunology↗

bioRxiv2021

Crosstalk between enterocytes and innate lymphoid cells drives early IFN-g-mediated control of Cryptosporidium

The intestinal parasite, Cryptosporidium, is a major contributor to global child mortality and causes opportunistic infection in immune deficient individuals. Innate resistance to Cryptosporidium, which specifically invades enterocytes, is dependent on the production of IFN-{gamma}, yet whether enterocytes contribute to parasite control is poorly understood. In this study, utilizing the natural mouse pathogen, Cryptosporidium tyzzeri, we show that epithelial-derived IL-18 synergized with IL-12 to stimulate innate lymphoid cell (ILC) production of IFN-{gamma}. This innate IFN-{gamma} was required for early parasite control. Loss of STAT1 in enterocytes, but not dendritic cells or macrophages, antagonized early parasite control. Transcriptional profiling of enterocytes from infected mice identified an IFN-{gamma} signature and enrichment of anti-microbial effectors like IDO, GBP and IRG. Deletion experiments identified a role for Irgm1/m3 in parasite control. Thus, enterocytes promote ILC production of IFN-{gamma} that acts on enterocytes to restrict the growth of C. tyzzeri.

immunology↗

bioRxiv2021

IL-33 promotes innate lymphoid cell-dependent IFN-γ production required for innate immunity to Toxoplasma gondii

IL-33 is an alarmin required for resistance to the parasite Toxoplasma gondii, but its role in innate resistance to this infection is unclear. T. gondii infection promotes increased stromal cell expression of IL-33 and levels of parasite replication correlate with IL-33 release. In response to infection, a subset of innate lymphoid cells (ILC) emerges composed of IL-33R+ NK cells and ILC1s. In Rag-/- mice, where NK cells and ILC1 provide an innate mechanism of resistance to T. gondii, the loss of IL-33R reduced ILC responses and increased parasite replication. Furthermore, administration of IL-33 to Rag-/- mice resulted in a marked decrease in parasite burden, increased production of IFN-{gamma} and the recruitment and expansion of inflammatory monocytes associated with parasite control. These protective effects of exogenous IL-33 were dependent on endogenous IL-12p40 and the ability of IL-33 to enhance ILC production of IFN-{gamma}. These results highlight that IL-33 synergizes with IL-12 to promote ILC-mediated resistance to T. gondii.

immunology↗

bioRxiv2020

PD-L1 - PD-1 interactions limit effector Treg cell populations at homeostasis and during infection

While much is known about the factors that promote the development of diverse Treg cell responses, less is known about the pathways that constrain Treg cell activities. The studies presented here reveal that at homeostasis there is a population of effector Treg cells that express PD-1, and that blockade of PD-L1 or loss of PD-1 results in increased Treg cell activity. In response to infection with the parasite T. gondii, the early production of IFN-{gamma} results in widespread upregulation of PD-L1. Moreover, blockade of PD-L1, whole body deletion of PD-1, or lineage-specific deletion of PD-1 in Foxp3+ cells prevented the loss of the effector Treg cells but resulted in reduced pathogen specific CD4+ T cell responses during infection. Thus, at homeostasis basal PD-L1 expression constrains and tunes the pool of Treg cells, but during infection the upregulation of PD-L1 provides a mechanism to contract the Treg cell population required to maximize the development of pathogen specific CD4+ T cell responses.

immunology↗

bioRxiv2020

cDC1 Coordinate Innate and Adaptive Responses in the Omentum required for T cell Priming and Memory

The omentum in the peritoneal cavity contains fat associated lymphoid clusters (FALCs) whose role in the response to microbial challenge are poorly understood. After intraperitoneal immunization with Toxoplasma gondii, type I dendritic cells (cDC1) were critical to induce innate sources of IFN-{gamma} required to recruit monocytes to the FALCs. The migration of infected peritoneal macrophages into T and B cell rich areas of the FALCs allowed the TCR-induced activation of parasite-specific T cells. Unexpectedly, cDC1 were not required for T cell priming but rather supported the expansion of parasite-specific CD8+ T cells. An agent-based mathematical model predicted that the lack of cDC1 would impact the early proliferative burst, and we confirmed that cDC1 were required for optimal T cell expression of nutrient uptake receptors and cell survival. These studies highlight that cDC1 in the FALCs have distinct roles in the co-ordination of the innate and adaptive responses to microbial challenge.

immunology↗