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Macrophages (MΦs) are heterogeneous and metabolically flexible, with metabolism strongly affecting immune activation. A classic response to proinflammatory activation is increased flux through glycolysis with a downregulation of oxidative metabolism, whereas alternative activation is primarily oxidative, which begs the question of whether targeting glucose metabolism is a viable approach to control MΦ activation. We created a murine model of myeloid-specific glucose transporter GLUT1 (Slc2a1) deletion. Bone marrow–derived MΦs (BMDM) from Slc2a1M−/− mice failed to uptake glucose and demonstrated reduced glycolysis and pentose phosphate pathway activity. Activated BMDMs displayed elevated metabolism of oleate and glutamine, yet maximal respiratory capacity was blunted in MΦ lacking GLUT1, demonstrating an incomplete metabolic reprogramming. Slc2a1M−/− BMDMs displayed a mixed inflammatory phenotype with reductions of the classically activated pro- and anti-inflammatory markers, yet less oxidative stress. Slc2a1M−/− BMDMs had reduced proinflammatory metabolites, whereas metabolites indicative of alternative activation—such as ornithine and polyamines—were greatly elevated in the absence of GLUT1. Adipose tissue MΦs of lean Slc2a1M−/− mice had increased alternative M2-like activation marker mannose receptor CD206, yet lack of GLUT1 was not a critical mediator in the development of obesity-associated metabolic dysregulation. However, Ldlr−/− mice lacking myeloid GLUT1 developed unstable atherosclerotic lesions. Defective phagocytic capacity in Slc2a1M−/− BMDMs may have contributed to unstable atheroma formation. Together, our findings suggest that although lack of GLUT1 blunted glycolysis and the pentose phosphate pathway, MΦ were metabolically flexible enough that inflammatory cytokine release was not dramatically regulated, yet phagocytic defects hindered MΦ function in chronic diseases.

T cell dysfunction or ‘exhaustion’ is a hallmark of solid malignancies. Despite the critical importance of CD8 T lymphocytes in controlling tumor growth and immunotherapy efficacy, the mechanisms governing T cell exhaustion remain unclear. Here, we focused on resolving the heterogeneity and molecular programming of exhausted CD8 T cell states in the context of pancreatic cancer. Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with a discouraging 5-year survival rate of approximately 8%. PDAC tumors commonly present as immunologically ‘cold’, devoid of protective T cell populations, and are typically resistant to promising immunotherapies such as immune checkpoint blockade or adoptive cell therapy. Therefore, understanding the unique microenvironmental and CD8 T cell-intrinsic signals governing T cell exhaustion and accumulation in PDAC tumors may reveal crucial insight for engineering CD8 T cells for optimal immunotherapy efficacy. Here, we developed preclinical PDAC models for profiling tumor-specific murine CD8 T cell responses. Through application of spectral flow cytometry and multimodal single-cell sequencing approaches, we have uncovered impressively diverse antigen-specific CD8 T cell states in PDAC tumors. Select CD8 T cell populations identified within the PDAC tumor microenvironment included canonical populations of terminally-exhausted and progenitor-exhausted CD8 T cells as well as unexpected and uncharacterized CD8 T cell populations. Accordingly, we also have identified critical transcription factors controlling key features of CD8 T cell heterogeneity and persistence in PDAC tumors. These findings may ultimately provide insight for tailoring CD8 T cell fate and function in PDAC. Supported by 2022 AAI Intersect Fellowship for Computational Scientists and Immunologists

Obesity is associated with increased risk for infections and poor responses to vaccinations, which may be due to compromised B cell function. However, there is limited information about the influence of obesity on B cell function and underlying factors that modulate B cell responses. Therefore, we studied B cell cytokine secretion and/or Ab production across obesity models. In obese humans, B cell IL-6 secretion was lowered and IgM levels were elevated upon ex vivo anti-BCR/TLR9 stimulation. In murine obesity induced by a high fat diet, ex vivo IgM and IgG were elevated with unstimulated B cells. Furthermore, the high fat diet lowered bone marrow B cell frequency accompanied by diminished transcripts of early lymphoid commitment markers. Murine B cell responses were subsequently investigated upon influenza A/Puerto Rico/8/34 infection using a Western diet model in the absence or presence of docosahexaenoic acid (DHA). DHA, an essential fatty acid with immunomodulatory properties, was tested because its plasma levels are lowered in obesity. Relative to controls, mice consuming the Western diet had diminished Ab titers whereas the Western diet plus DHA improved titers. Mechanistically, DHA did not directly target B cells to elevate Ab levels. Instead, DHA increased the concentration of the downstream specialized proresolving lipid mediators (SPMs) 14-hydroxydocosahexaenoic acid, 17-hydroxydocosahexaenoic acid, and protectin DX. All three SPMs were found to be effective in elevating murine Ab levels upon influenza infection. Collectively, the results demonstrate that B cell responses are impaired across human and mouse obesity models and show that essential fatty acid status is a factor influencing humoral immunity, potentially through an SPM-mediated mechanism.

Memory CD8+ T cells afford long-lived, durable protection against infection and malignancy. Despite the critical relevance of memory T cells to vaccination and immunotherapies, the transcriptional and epigenetic signals instructing memory T cell fate remain unclear. Here, we utilized a pooled RNA interference screen to evaluate the activity of transcription factors and chromatin modifiers governing memory T cell differentiation in vivo. The epigenetic ‘reader,’ Brd4 of the BET protein family, emerged as a top regulator of memory T cell differentiation. Through RNA interference, small molecule inhibition and inducible genetic deletion, we established a central role for Brd4 in mediating CD8+ T cell proliferation, differentiation and function during acute viral infection. Brd4 was required for optimal expression of fate-specifying transcription factors, and a deficiency of Brd4 activity resulted in diminished formation of effector memory and CD103+ tissue-resident memory CD8+ T cells. Given that BET inhibition has emerged as a powerful approach for suppressing tumor growth, we also evaluated how BET inhibition and Brd4-deficiency influence T cell activity during cancer. Brd4 was required for intratumoral accumulation and function of T cells in a mouse model of melanoma, and BET inhibition suppressed T cell-mediated control of tumor growth. However, epigenetic targeting of Brd4 constrained terminal differentiation of T cells within tumors, biasing tumor-resident T cells towards a reprogrammable TCF1-expressing phenotype. These studies establish a novel role for Brd4 in CD8+ T cell biology and provide insight for immunotherapy approaches designed to leverage the dynamic activity of CD8+ T cells in tumors.

The memory CD8+ T cell population consists of distinct subsets that collaborate to provide robust immunological protection. Within the circulation, two broad classes exist – the shorter-lived effector and effector memory (TEM) cells with heightened effector function for immediate protection and the longer-lived central memory (TCM) cells with stem-like qualities and increased proliferation potential. Tissue-resident memory (TRM) cells are the prominent cell type permanently residing in non-lymphoid tissues acting as sentinels against reinfection. Despite the critical importance of the TRM subset, the extent of their phenotypic and functional heterogeneity remains unknown. Using single-cell gene expression analyses, we assessed small intestine intraepithelial TRM cells over the course of acute infection. Distinct subsets were identified and distinguished by reciprocal expression of effector- and memory-associated transcriptional regulators, Blimp1 and Id3, respectively. While the Blimp1hi subset was prominent at early time points, the Id3hi population persisted and was more abundant over time. Importantly, examination of the subset-specific transcriptional profiles revealed considerable enrichment for the effector/effector-memory gene signature within the Blimp1hiTRM subset and the central-memory gene signature within the Id3hi TRM population. Furthermore, Id3hi TRM cells exhibited more stem-like characteristics including increased capacity to proliferate following rechallenge. Taken together, this study reveals that similar to circulating memory, the TRM population is heterogeneous, comprising cells with contrasting differentiation states and memory potential.

In response to an infection or vaccination, antigen-specific CD8+ T cells have the capacity to differentiate into long-lived memory T cells that ultimately confer critical protection against re-infection. The memory CD8+ T cell population is heterogeneous and comprised of circulating effector memory (Tem) and central memory (Tcm) cells as well as non-circulating memory cells or tissue-resident memory cells (Trm). Each memory T cell subset is characterized by distinct phenotypic and functional attributes as well as localization patterns. It has previously been demonstrated that circulating memory subsets can be further subdivided based on effector function or migration patterns. Here, we contribute to the clarification of this heterogeneity by characterizing the gene expression, functional activity and differentiation requirements of long-lived CD127loCD62Llo effector cells (LLE) that can persist at least one year after infection in mice. LLE were found to be phenotypically and functionally distinct from CD127hiCD62Llo Tem and CD127hiCD62LhiTcm subsets. LLE exhibited a unique transcriptional profile, with genes expressed in common with both CD127loKLRG1hi short-lived effector cells and Tem. Further, we refine roles for key fate-specifying transcription factors in controlling the differentiation of LLE versus Tem subsets. These studies further highlight the extent of memory T cell heterogeneity and may inform novel vaccination strategies.