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Early recruitment of neutrophils from the blood to sites of tissue infection is a hallmark of innate immune responses. However, little is known about the mechanisms by which apoptotic neutrophils are cleared in infected tissues during resolution and the immunological consequences of in situ efferocytosis. Using intravital multiphoton microscopy, we show previously unrecognized motility patterns of interactions between neutrophils and tissue-resident phagocytes within the influenza-infected mouse airway. Newly infiltrated inflammatory monocytes become a chief pool of phagocytes and play a key role in the clearance of highly motile apoptotic neutrophils during the resolution phase. Apoptotic neutrophils further release epidermal growth factor and promote the differentiation of monocytes into tissue-resident antigen-presenting cells for activation of antiviral T cell effector functions. Collectively, these results suggest that the presence of in situ neutrophil resolution at the infected tissue is critical for optimal CD8 + T cell–mediated immune protection. Kim and colleagues provide new insights into the function and fate of neutrophils during influenza infection and their roles in antiviral T cell responses.

Immune cell migration is required for the development of an effective and robust immune response. This elegant process is regulated by both cellular and environmental factors, with variables such as immune cell state, anatomical location, and disease state that govern differences in migration patterns. In all cases, a major factor is the expression of cell surface receptors and their cognate ligands. Rapid adaptation to environmental conditions partly depends on intrinsic cellular immune factors that affect a cell’s ability to adjust to new environment. In this review, we discuss both myeloid and lymphoid cells and outline key determinants that govern immune cell migration, including molecules required for immune cell adhesion, modes of migration, chemotaxis, and specific chemokine signaling. Furthermore, we summarize tumor-specific elements that contribute to immune cell trafficking to cancer, while also exploring microenvironment factors that can alter these cellular dynamics within the tumor in both a pro and antitumor fashion. Specifically, we highlight the importance of the secretome in these later aspects. This review considers a myriad of factors that impact immune cell trajectory in cancer. We aim to highlight the immunotherapeutic targets that can be harnessed to achieve controlled immune trafficking to and within tumors.

Although cancer immunotherapy is effective against hematological malignancies, it is less effective against solid tumors due in part to significant metabolic challenges present in the tumor microenvironment (TME), where infiltrated CD8 + T cells face fierce competition with cancer cells for limited nutrients. Strong metabolic suppression in the TME is often associated with impaired T cell recruitment to the tumor site and hyporesponsive effector function via T cell exhaustion. Increasing evidence suggests that mitochondria play a key role in CD8 + T cell activation, effector function, and persistence in tumors. In this study, we showed that there was an increase in overall mitochondrial function, including mitochondrial mass and membrane potential, during both mouse and human CD8 + T cell activation. CD8 + T cell mitochondrial membrane potential was closely correlated with granzyme B and IFN-γ production, demonstrating the significance of mitochondria in effector T cell function. Additionally, activated CD8 + T cells that migrate on ICAM-1 and CXCL12 consumed significantly more oxygen than stationary CD8 + T cells. Inhibition of mitochondrial respiration decreased the velocity of CD8 + T cell migration, indicating the importance of mitochondrial metabolism in CD8 + T cell migration. Remote optical stimulation of CD8 + T cells that express our newly developed “OptoMito-On” successfully enhanced mitochondrial ATP production and improved overall CD8 + T cell migration and effector function. Our study provides new insight into the effect of the mitochondrial membrane potential on CD8 + T cell effector function and demonstrates the development of a novel optogenetic technique to remotely control T cell metabolism and effector function at the target tumor site with outstanding specificity and temporospatial resolution.

Adoptive cell transfer of ex vivo-generated immune-promoting or tolerogenic T cells to either enhance immunity or promote tolerance in patients has been used with some success. However, effective trafficking of the transferred cells to the target tissue sites is the main barrier to achieving successful clinical outcomes. Here we developed a strategy for optically controlling T-cell trafficking using a photoactivatable (PA) chemokine receptor. Photoactivatable-chemokine C-X-C motif receptor 4 (PA-CXCR4) transmitted intracellular CXCR4 signals in response to 505-nm light. Localized activation of PA-CXCR4 induced T-cell polarization and directional migration (phototaxis) both in vitro and in vivo. Directing light onto the melanoma was sufficient to recruit PA-CXCR4–expressing tumor-targeting cytotoxic T cells and improved the efficacy of adoptive T-cell transfer immunotherapy, with a significant reduction in tumor growth in mice. These findings suggest that the use of photoactivatable chemokine receptors allows remotely controlled leukocyte trafficking with outstanding spatial resolution in tissues and may be feasible in other cell transfer therapies.

The chemokine CCL7 (MCP3) is known to promote the recruitment of many innate immune cell types including monocytes and neutrophils to sites of bacterial and viral infection and eosinophils and basophils to sites of allergic inflammation. CCL7 upregulation has been associated with many inflammatory settings including infection, cardiovascular disease, and the tumor microenvironment. CCL7's pleotropic effects are due in part to its ability to bind numerous chemokine receptors, namely CCR1, CCR2, CCR3, CCR5, and CCR10. CCL7-blockade or CCL7-deficiency is often marked by decreased inflammation and poor pathogen control. In the context of infection, CCL7 is specifically upregulated in the skin one-2 weeks after infection but its role in control is unclear. To determine CCL7's impact on the response to we infected WT and CCL7 C57BL/6 mice. infection of CCL7-deficient mice led to an unexpected in inflammation in the infected skin 2 weeks post-infection. A broad increase in immune cell subsets was observed but was dominated by enhanced neutrophilic infiltration. Increased neutrophil recruitment was associated with an enhanced IL-17 gene profile in the infected skin. CCL7 was shown to directly antagonize neutrophil migration and CCL7 add-back specifically reduced neutrophil influx into the infected skin revealing an unexpected role for CCL7 in limiting neutrophil recruitment during infection. Enhanced neutrophilic infiltration in CCL7-deficient mice changed the balance of infected host cells with an increase in the ratio of infected neutrophils over monocytes/macrophages. To determine the consequence of CCL7 deficiency on control we analyzed parasite load cutaneously at the site of infection and viscerally in the draining LN and spleen. The CCL7 mice supported robust cutaneous parasite control similar to their WT C57BL/6 counterparts. In contrast, CCL7-deficiency led to greater parasite dissemination and poor parasite control in the spleen. Our studies reveal a novel role for CCL7 in negatively regulating cutaneous inflammation, specifically neutrophils, early during infection. We propose that CCL7-mediated dampening of the early immune response in the skin may limit the ability of the parasite to disseminate without compromising cutaneous control.

Sepsis is a life-threatening systemic inflammatory condition causing approximately 11 million annual deaths worldwide. Although key hyperinflammation-based organ dysfunctions that drive disease pathology have been recognized, our understanding of the factors that predispose patients to septic mortality is limited. Due to the lack of reliable prognostic measures, the development of appropriate clinical management that improves patient survival remains challenging. Here, we discovered that a subpopulation of CD49c high neutrophils with dramatic upregulation of the complement component 1q (C1q) gene expression arises during severe sepsis. We further found that deceased septic patients failed to maintain C1q protein expression in their neutrophils, whereas septic survivors expressed higher levels of C1q. In mouse sepsis models, blocking C1q with neutralizing antibodies or conditionally knocking out C1q in neutrophils led to a significant increase in septic mortality. Apoptotic neutrophils release C1q to control their own clearance in critically injured organs during sepsis; thus, treatment of septic mice with C1q drastically increased survival. These results suggest that neutrophil C1q is a reliable prognostic biomarker of septic mortality and a potential novel therapeutic target for the treatment of sepsis.

T cells spend the majority of their time perusing lymphoid organs in search of cognate antigen presented by antigen presenting cells (APCs) and then quickly recirculate through the bloodstream to another lymph node. Therefore, regulation of a T-cell response is dependent upon the ability of cells to arrive in the correct location following chemokine gradients (“go” signal) as well as to receive appropriate T-cell receptor (TCR) activation signals upon cognate antigen recognition (“stop” signal). However, the mechanisms by which T cells regulate these go and stop signals remain unclear. We found that overexpression of the hematopoietic-specific RhoH protein in the presence of chemokine signals resulted in decreased Rap1–GTP and LFA-1 adhesiveness to ICAM-1, thus impairing T-cell chemotaxis; while in the presence of TCR signals, there were enhanced and sustained Rap1–GTP and LFA-1 activation as well as prolonged T:APC conjugates. RT-PCR analyses of activated CD4 ⁺ T cells and live images of T-cell migration and immunological synapse (IS) formation revealed that functions of RhoH took place primarily at the levels of transcription and intracellular distribution. Thus, we conclude that RhoH expression provides a key molecular determinant that allows T cells to switch between sensing chemokine-mediated go signals and TCR-dependent stop signals.

T cells constantly circulate throughout the body until an invading pathogen calls them into action. Microbes often cause localized infections, so how do T cells know where to go? Lim et al. explore this question in a mouse model of influenza infection and find that immune cells called neutrophils help guide the way (see the Perspective by Kiermaier and Sixt). Upon infection, neutrophils quickly traffic to the trachea. There, they lay down “tracks” enriched in proteins called chemokines, especially the chemokine CXCL12, which guide CD8 + T cells to the infected organ. Mice whose neutrophils could not lay down such tracks exhibited defects in CD8 + T cell recruitment and viral clearance. Science , this issue 10.1126/science.aaa4352 ; see also p. 1055 Trails of chemokines left behind by neutrophils guide T cells to sites of viral infection. [Also see Perspective by Kiermaier and Sixt ] During viral infections, chemokines guide activated effector T cells to infection sites. However, the cells responsible for producing these chemokines and how such chemokines recruit T cells are unknown. Here, we show that the early recruitment of neutrophils into influenza-infected trachea is essential for CD8 + T cell–mediated immune protection in mice. We observed that migrating neutrophils leave behind long-lasting trails that are enriched in the chemokine CXCL12. Experiments with granulocyte-specific CXCL12 conditionally depleted mice and a CXCR4 antagonist revealed that CXCL12 derived from neutrophil trails is critical for virus-specific CD8 + T cell recruitment and effector functions. Collectively, these results suggest that neutrophils deposit long-lasting, chemokine-containing trails, which may provide both chemotactic and haptotactic cues for efficient CD8 + T cell migration and localization in influenza-infected tissues.

OBJECTIVES/GOALS: #NAME? METHODS/STUDY POPULATION: Cell culture & protein identification: human T cells were purified from healthy blood, then activated & cultured for 5d. CAR-T cells were collected from infusion bags of cancer patients undergoing CAR-T. Silver staining of naive & activated healthy T-cell lysates was compared; B-II spectrin was upregulated and confirmed by Western blot. Migration assays: naive & activated T-cells were imaged during migration on ICAM-1 and ICAM-1 + CXCL12 coated plates. T-cells were transfected with BII-spectrin cDNA & the chemokine dependence of migration was compared with controls. In-vivo studies: in a melanoma mouse model, BII-spectrin transfected or control T-cells were injected; tumors were followed with serial imaging. Human patient records were examined to correlate endogenous BII-spectrin levels and CAR-T response. RESULTS/ANTICIPATED RESULTS: Activated T-cells downregulate the cytoskeletal protein B-II spectrin compared to naive cells, leading to chemokine-independent migration in in vitro assays and off-target trafficking when CAR-T cells are given in vivo. Restoration of B-II spectrin levels via transfection restores chemokine-dependence of activated T-cells. In a mouse melanoma model, control mice injected with standard activated T-cells showed fewer cells in the tumor site and more cells in the off-target organs (spleen, lungs) when compared to mice injected with B-II spectrin transfected cells. Furthermore, among 3 human patients undergoing CAR-T therapy, those with higher endogenous B-II spectrin levels experienced fewer side-effects, measured by the neurotoxicity and cytokine release syndrome grades. DISCUSSION/SIGNIFICANCE: A major hurdle to widespread CAR-T therapy for cancer is significant, often fatal side-effects. Our work shows that the protein B-II spectrin is downregulated during CAR-T production, and that restoring B-II spectrin levels decreases side-effects while increasing tumor clearance--hopefully translating to better CAR-T regimens for the future.

Adoptive transfer of genetically engineered chimeric antigen receptor (CAR) T cells is becoming a promising treatment option for hematological malignancies. However, T cell immunotherapies have mostly failed in individuals with solid tumors. Here, with a CRISPR–Cas9 pooled library, we performed an in vivo targeted loss-of-function screen and identified ST3 β-galactoside α-2,3-sialyltransferase 1 (ST3GAL1) as a negative regulator of the cancer-specific migration of CAR T cells. Analysis of glycosylated proteins revealed that CD18 is a major effector of ST3GAL1 in activated CD8 + T cells. ST3GAL1-mediated glycosylation induces the spontaneous nonspecific tissue sequestration of T cells by altering lymphocyte function-associated antigen-1 (LFA-1) endocytic recycling. Engineered CAR T cells with enhanced expression of βII-spectrin, a central LFA-1-associated cytoskeleton molecule, reversed ST3GAL1-mediated nonspecific T cell migration and reduced tumor growth in mice by improving tumor-specific homing of CAR T cells. These findings identify the ST3GAL1–βII-spectrin axis as a major cell-intrinsic program for cancer-targeting CAR T cell migration and as a promising strategy for effective T cell immunotherapy. CAR T cell success requires targeting tumors, but these cells can get trapped in other tissues, such as in the lungs, where they can cause pathology. Here, the authors use a loss-of-function CRISPR screen to identify regulators of CAR T cell tumor trafficking and engineer CAR T cells accordingly to overcome this limitation.