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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2024)

T lymphocytes are important key players that help mediate host protection from viruses by directly killing infected cells and eliminating the pathogen. However, in the setting of chronic viral infections and cancers the virus is never eliminated, and anti-viral T cells differentiate into a state of exhaustion. Exhausted T cells are characterized by their poor effector function, defective proliferation, and inability to kill infected cells. Importantly, high expression of immune checkpoints such as PD-1 during persistent antigen support T cell exhaustion by diminishing T cell receptor signaling. Adhesion molecule, P-selectin glycoprotein ligand-1 (PSGL-1) has recently been identified as a novel immune checkpoint. While studies have shown an improved immune response and elimination of viral particles and tumors with PSGL-1 deficiency or blockade in various disease models, the cell-intrinsic role of PSGL-1 in exhausted T cells remains unknown. In this dissertation, we used an adoptive co-transfer approach utilizing PSGL-1 deficient (Selplg-/-) TCR transgenic (Tg) virus specific T cells in a Lymphocytic choriomeningitis Virus (LCMV) Cl13 mouse model to investigate the function of PSGL-1 in its differentiation, maintenance, and reinvigoration of exhausted T cells. We found that Selplg-/- T cells initially expand to high frequencies in early stages of chronic viral infection, but eventually decrease to very low frequencies as infection progresses. Additionally, we found that while Selplg-/- T cells were initially more functional early during viral infection, they became phenotypically and functionally exhausted as the chronic infection progressed, albeit to a lesser extent than WT. Furthermore, we observed a decrease in progenitor exhausted T cells (Tpex) differentiation and an increase in Tex differentiation in Selplg-/- T cells at late stages of infection. Importantly, we show that Selplg-/- T cells became reinvigorated more effectively than WT after anti-PD-L1 antibody treatment. While we observed improved T cell response with PSGL-1 deficiency in T cells and PD-L1 blockade, the cell intrinsic role of both PSGL-1 and PD-1 combined within T cells has not been explored. In this dissertation, we also used an adoptive co-transfer approach utilizing PSGL-1 and PD-1 deficient (Selplg-/-Pdcd1-/-) TCR transgenic (Tg) virus specific T cells in a Lymphocytic choriomeningitis (LCMV) Cl13 mouse model to investigate any additive effect or synergistic effect that PSGL-1 might have in combination with PD-1, and its impact of differentiation, function, maintenance, and reinvigoration of exhausted T cells. We found that unlike Selplg-/- T cells, Selplg-/-Pdcd1-/- T cells are increased and remain increased throughout the course of chronic viral infection. Interestingly, while Selplg-/- T cells have increased functionality, Selplg-/-Pdcd1-/- T cells are less functional and less cytotoxic at both early and lates stages of infection. Furthermore, we saw that Selplg-/-Pdcd1-/- T cells had decreased and increased levels of TCF1 and TOX, respectively. Consistent with these results, we also observed that the differentiation of Tpex and Tex was more pronounced, with Tpex being further reduced and Tex being further increased in Selplg-/-Pdcd1-/- T cells compared to Selplg-/- T cells. T cells are also important during acute viral infections. They initially expand to kill virally infected cells and then contract and differentiate into different memory T cells as the pathogen is eliminated. Within the memory T cell population, there are subsets of memory T cells, each vital for its various functions. Memory T cells are crucial in that they are quick to respond to a pathogen upon secondary exposure. Prion proteins are glycoproteins expressed on all hematopoietic stem cells, and predominantly known for its role in transmissible spongiform encephalopathies (TSEs). While constitutively expressed on T cells, Prion proteins become highly upregulated after T cell activation. However, the role of Prion protein (Prnp) on effector and memory T cells during viral infection remains unknown. In this dissertation, we utilized acute Lymphocytic choriomeningitis Virus Armstrong (LCMV Arm) on mice deficient in Prnp to investigate the function of Prnp in virus specific T cell and its role in effector T cells and memory T cell differentiation. We found that Prnp deletion increased antigen specific memory T cells, with no differences in effector T cell frequencies. Correspondent with the increase in memory T cells, we also observed increased T cell function at the memory stage in Prnp deficient mice. Importantly, we show that Prnp deficiency changed the memory T cell subset differentiation of effector memory T cells and terminal effector memory T cells (Ttem). Lastly, we assessed the function of memory CD4 T cells and observed an increase in cytokine production in T cells deficient in Prnp. Altogether, this dissertation further contributes a better understanding of how combining multiple immune checkpoints, such as PSGL-1 and PD-1 or targeting novel molecules such as Prion protein impacts the function, differentiation and maintenance on effector, memory, and exhausted T cells. It also provides insight on the mechanisms by which these inhibitory pathways impact T cells and their potential therapeutic value in the settings of viral infections and cancer.

    Cover page: Investigating inhibitory pathways in the differentiation and function of virus-specific T cells during infection
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2022)
    Immune-checkpoint inhibitors have had impressive efficacy in some patients with cancer, reinvigorating long-term durable immune responses against tumors. Despite the clinical success of these therapies, most patients with cancer continue to be unresponsive to these treatments, highlighting the need for novel therapeutic options. Although P-selectin glycoprotein ligand-1 (PSGL-1) has been shown to inhibit immune responses in a variety of disease models, previous work has yet to address whether PSGL-1 can be targeted therapeutically to promote antitumor immunity. Using an aggressive melanoma tumor model, we targeted PSGL-1 in tumor-bearing mice and found increased effector CD4+ and CD8+ T-cell responses and decreased regulatory T cells (Treg) in tumors. T cells exhibited increased effector function, activation, and proliferation, which delayed tumor growth in mice after anti-PSGL-1 treatment. Targeting PD-1 in PSGL-1-deficient, tumor-bearing mice led to an increased frequency of mice with complete tumor eradication. Targeting both PSGL-1 and PD-1 in wild-type tumor-bearing mice also showed enhanced antitumor immunity and slowed melanoma tumor growth. Our findings showed that therapeutically targeting the PSGL-1 immune checkpoint can reinvigorate antitumor immunity and suggest that targeting PSGL-1 may represent a new therapeutic strategy for cancer treatment.
      Cover page: Targeting the PSGL-1 Immune Checkpoint Promotes Immunity to PD-1-Resistant Melanoma.
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2023)
      Acute and chronic viral infections result in the differentiation of effector and exhausted T cells with functional and phenotypic differences that dictate whether the infection is cleared or progresses to chronicity. High CD38 expression has been observed on CD8+ T cells across various viral infections and tumors in patients, suggesting an important regulatory function for CD38 on responding T cells. Here, we show that CD38 expression was increased and sustained on exhausted CD8+ T cells following chronic lymphocytic choriomeningitis virus (LCMV) infection, with lower levels observed on T cells from acute LCMV infection. We uncovered a cell-intrinsic role for CD38 expression in regulating the survival of effector and exhausted CD8+ T cells. We observed increased proliferation and function of Cd38-/- CD8+ progenitor exhausted T cells compared to those of wild-type (WT) cells. Furthermore, decreased oxidative phosphorylation and glycolytic potential were observed in Cd38-/- CD8+ T cells during chronic but not acute LCMV infection. Our studies reveal that CD38 has a dual cell-intrinsic function in CD8+ T cells, where it decreases proliferation and function yet supports their survival and metabolism. These findings show that CD38 is not only a marker of T cell activation but also has regulatory functions on effector and exhausted CD8+ T cells. IMPORTANCE Our study shows how CD38 expression is regulated on CD8+ T cells responding during acute and chronic viral infection. We observed higher CD38 levels on CD8+ T cells during chronic viral infection compared to levels during acute viral infection. Deleting CD38 had an important cell-intrinsic function in ensuring the survival of virus-specific CD8+ T cells throughout the course of viral infection. We found defective metabolism in Cd38-/- CD8+ T cells arising during chronic infection and changes in their progenitor T cell phenotype. Our studies revealed a dual cell-intrinsic role for CD38 in limiting proliferation and granzyme B production in virus-specific exhausted T cells while also promoting their survival. These data highlight new avenues for research into the mechanisms through which CD38 regulates the survival and metabolism of CD8+ T cell responses to viral infections.
        Cover page: Cell-Intrinsic CD38 Expression Sustains Exhausted CD8+ T Cells by Regulating Their Survival and Metabolism during Chronic Viral Infection
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2023)
        Chronic infections and cancers evade the host immune system through mechanisms that induce T cell exhaustion. The heterogeneity within the exhausted CD8+ T cell pool has revealed the importance of stem-like progenitor (Tpex) and terminal (Tex) exhausted T cells, although the mechanisms underlying their development are not fully known. Here we report High Mobility Group Box 2 (HMGB2) protein expression is upregulated and sustained in exhausted CD8+ T cells, and HMGB2 expression is critical for their differentiation. Through epigenetic and transcriptional programming, we identify HMGB2 as a cell-intrinsic regulator of the differentiation and maintenance of Tpex cells during chronic viral infection and in tumors. Despite Hmgb2-/- CD8+ T cells expressing TCF-1 and TOX, these master regulators were unable to sustain Tpex differentiation and long-term survival during persistent antigen. Furthermore, HMGB2 also had a cell-intrinsic function in the differentiation and function of memory CD8+ T cells after acute viral infection. Our findings show that HMGB2 is a key regulator of CD8+ T cells and may be an important molecular target for future T cell-based immunotherapies.
          Cover page: HMGB2 regulates the differentiation and stemness of exhausted CD8+ T cells during chronic viral infection and cancerCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2018)
          Genome-wide investigations of host-pathogen interactions are often limited by analyses of mixed populations of infected and uninfected cells, which lower sensitivity and accuracy. To overcome these obstacles and identify key mechanisms by which Zika virus (ZIKV) manipulates host responses, we developed a system that enables simultaneous characterization of genome-wide transcriptional and epigenetic changes in ZIKV-infected and neighboring uninfected primary human macrophages. We demonstrate that transcriptional responses in ZIKV-infected macrophages differed radically from those in uninfected neighbors and that studying the cell population as a whole produces misleading results. Notably, the uninfected population of macrophages exhibits the most rapid and extensive changes in gene expression, related to type I IFN signaling. In contrast, infected macrophages exhibit a delayed and attenuated transcriptional response distinguished by preferential expression of IFNB1 at late time points. Biochemical and genomic studies of infected macrophages indicate that ZIKV infection causes both a targeted defect in the type I IFN response due to degradation of STAT2 and reduces RNA polymerase II protein levels and DNA occupancy, particularly at genes required for macrophage identity. Simultaneous evaluation of transcriptomic and epigenetic features of infected and uninfected macrophages thereby reveals the coincident evolution of dominant proviral or antiviral mechanisms, respectively, that determine the outcome of ZIKV exposure.
            Cover page: Deconvolution of pro- and antiviral genomic responses in Zika virus-infected and bystander macrophagesCreative Commons 'BY-NC-ND' version 4.0 license
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2025)
            Immune checkpoints are critical regulators of T-cell exhaustion, impairing their ability to eliminate antigens present during chronic viral infections. Current immune checkpoint inhibitors (ICIs) used in the clinic aim to reinvigorate exhausted T cells; yet, most patients fail to respond or develop resistance to these therapies, underscoring the need to better understand these immunosuppressive pathways. PSGL-1 (Selplg), a recently discovered immune checkpoint, negatively regulates T-cell function. We investigated the cell-intrinsic effects of PSGL-1, PD-1, and combined deletion on CD8+ T cells during chronic viral infection. We found that combined PSGL-1 and PD-1 (Selplg-/-Pdcd1-/-) deficiency in CD8+ T cells increased their frequencies and numbers throughout chronic infection compared to the wild type. This phenotype was primarily driven by PD-1 deficiency. Furthermore, while PD-1 deletion increased virus-specific T-cell frequencies, it was detrimental to their function. Conversely, PSGL-1 deletion improved T-cell function but resulted in lower frequencies and numbers. The primary mechanism behind these differences in cell maintenance was driven by proliferation rather than survival. Combined PSGL-1 and PD-1 deletion resulted in defective T-cell differentiation, driving cells from a progenitor self-renewal state to a more terminal dysfunctional state. These findings suggest that PD-1 and PSGL-1 have distinct, yet complementary, roles in regulating T-cell exhaustion and differentiation during chronic viral infection. Overall, this study provides novel insights into the individual and combined roles of PSGL-1 and PD-1 in CD8+ T-cell exhaustion. It underscores the potential of targeting these checkpoints in a more dynamic and sequential manner to optimize virus-specific T-cell responses, offering critical perspectives for improving therapeutic strategies aimed at reinvigorating exhausted CD8+ T cells.IMPORTANCEOur findings provide a comprehensive analysis of how the dual deletion of PD-1 and PSGL-1 impacts the response and function of virus-specific CD8+ T cells, revealing novel insights into their roles in chronic infection. Notably, our findings show that while PD-1 deletion enhances T-cell frequencies, it paradoxically reduces T-cell functionality. Conversely, PSGL-1 deletion improves T-cell function but reduces their survival. Whereas the combined deletion of PSGL-1 and PD-1 in CD8+ T cells improved their survival but decreased their function and progenitor-exhausted phenotypes during infection. We believe our study advances the understanding of immune checkpoint regulation in chronic infections and has significant implications for developing more effective immune checkpoint inhibitor (ICI) therapies.
              Cover page: Contrasting roles of PSGL-1 and PD-1 in regulating T-cell exhaustion and function during chronic viral infectionCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2025)
              The differentiation and functionality of virus-specific T cells during acute viral infections are crucial for establishing long-term protective immunity. While numerous molecular regulators impacting T cell responses have been uncovered, the role of cellular prion proteins (PrPc) remains underexplored. Here, we investigated the impact of PrPc deficiency on the differentiation and function of virus-specific T cells using the lymphocytic choriomeningitis virus (LCMV) Armstrong acute infection model. Our findings reveal that Prnp-/- mice exhibit a robust expansion of virus-specific CD8+ T cells, with similar activation profiles as wild-type mice during the early stages of infection. However, Prnp-/- mice had higher frequencies and numbers of virus-specific memory CD8+ T cells, along with altered differentiation profiles characterized by increased central and effector memory subsets. Despite similar proliferation rates early during infection, Prnp-/- memory CD8+ T cells had decreased proliferation compared with their wild-type counterparts. Additionally, Prnp-/- mice had higher numbers of cytokine-producing memory CD8+ T cells, indicating a more robust functional response. Furthermore, Prnp-/- mice had increased virus-specific CD4+ T cell responses, suggesting a broader impact of PrPc deficiency on T cell immunity. These results unveil a previously unrecognized role for PrPc in regulating the differentiation, proliferation, and functionality of virus-specific T cells, providing valuable insights into immune system regulation by prion proteins during viral infections.
                Cover page: Prion protein modulation of virus-specific T cell differentiation and function during acute viral infectionCreative Commons 'BY-NC' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2025)
                Understanding flavivirus immunity is critical for the development of pan-flavivirus vaccines. Dendritic cells (DC) coordinate antiviral innate and adaptive immune responses, and they can be targeted by flaviviruses as a mechanism of immune evasion. Using an unbiased genome-wide approach designed to specifically identify flavivirus-modulated pathways, we found that, while dengue virus (DENV) robustly activates DCs, Zika virus (ZIKV) causes minimal activation of genes involved in DC activation, maturation, and antigen presentation, reducing cytokine secretion and the stimulation of allogeneic and peptide-specific T cell responses. Mechanistically, ZIKV inhibits DC maturation by suppressing NF-κB p65 recruitment and the subsequent transcription of proinflammatory and DC maturation-related genes. Thus, we identify a divergence in the effects of ZIKV and DENV on the host T cell response, highlighting the need to factor such differences into the design of anti-flavivirus vaccines.
                  Cover page: Zika but not Dengue virus infection limits NF-κB activity in human monocyte-derived dendritic cells and suppresses their ability to activate T cells.Creative Commons 'BY-NC-ND' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2022)
                  The emergence of Zika virus (ZIKV) as a global health threat has highlighted the unmet need for ZIKV-specific vaccines and antiviral treatments. ZIKV infects dendritic cells (DC), which have pivotal functions in activating innate and adaptive antiviral responses; however, the mechanisms by which DC function is subverted to establish ZIKV infection are unclear. Here we develop a genomics profiling method that enables discrete analysis of ZIKV-infected versus neighboring, uninfected primary human DCs to increase the sensitivity and specificity with which ZIKV-modulated pathways can be identified. The results show that ZIKV infection specifically increases the expression of genes enriched for lipid metabolism-related functions. ZIKV infection also increases the recruitment of sterol regulatory element-binding protein (SREBP) transcription factors to lipid gene promoters, while pharmacologic inhibition or genetic silencing of SREBP2 suppresses ZIKV infection of DCs. Our data thus identify SREBP2-activated transcription as a mechanism for promoting ZIKV infection amenable to therapeutic targeting.
                    Cover page: SREBP2-dependent lipid gene transcription enhances the infection of human dendritic cells by Zika virusCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2022)
                    Zika virus (ZIKV) and dengue virus (DENV) are arthropod-borne pathogenic flaviviruses that co-circulate in many countries. To understand some of the pressures that influence ZIKV evolution, we mimic the natural transmission cycle by repeating serial passaging of ZIKV through cultured mosquito cells and either DENV-naive or DENV-immune mice. Compared with wild-type ZIKV, the strains passaged under both conditions exhibit increased pathogenesis in DENV-immune mice. Application of reverse genetics identifies an isoleucine-to-valine mutation (I39V) in the NS2B proteins of both passaged strains that confers enhanced fitness and escape from pre-existing DENV immunity. Introduction of I39V or I39T, a naturally occurring homologous mutation detected in recent ZIKV isolates, increases the replication of wild-type ZIKV in human neuronal precursor cells and laboratory-raised mosquitoes. Our data indicate that ZIKV strains with enhanced transmissibility and pathogenicity can emerge in DENV-naive or -immune settings, and that NS2B-I39 mutants may represent ZIKV variants of interest.
                      Cover page: A Zika virus mutation enhances transmission potential and confers escape from protective dengue virus immunityCreative Commons 'BY-NC-ND' version 4.0 license
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