A single-cell analysis of the NK-cell landscape reveals that dietary restriction boosts NK cell antitumor immunity via Eomesdermin.

Abnormal metabolism in tumor cells represents a potential target for tumor therapy. In this regard, dietary restriction (DR) or its combination with anticancer drugs is of interest as it can impede the growth of tumor cells. In addition to its effects on tumor cell, DR also plays an extrinsic role in restricting tumor growth by regulating immune cells. Natural killer (NK) cells are innate immune cells involved in tumor immunosurveillance. However, it remains uncertain whether DR can assist NK cells in controlling tumor growth. Herein, we demonstrate that DR effectively inhibits metastasis of melanoma cells to the lung. Consistent with this, the regression of tumors induced by DR was minimal in mice lacking NK cells. Single-cell RNA sequencing analysis revealed that DR enriched a rejuvenated subset of CD27+CD11b+ NK cells. Mechanistically, DR activated a regulatory network involving the transcription factor Eomesodermin (Eomes), which is essential for NK-cell development. Firstly, DR promoted the expression of Eomes by optimizing mTORC1 signaling. The upregulation of Eomes revived the subset of functional CD27+CD11b+ NK cells by counteracting the expression of T-bet and downstream Zeb2. Moreover, DR enhanced the function and chemotaxis of NK cells by increasing the accessibility of Eomes to chromatin, leading to elevated expression of adhesion molecules and chemokines. Consequently, we conclude that DR therapy enhances tumor immunity through non-tumor autonomous mechanisms, including promoting NK-cell tumor immunosurveillance and activation.

cGAS-activated endothelial cell-T cell cross-talk initiates tertiary lymphoid structure formation.

Aberrant activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway causes autoimmunity in humans and mice; however, the exact mechanism by which the cGAS-STING pathway initiates adaptive immunity and tissue pathology is still not fully understood. Here, we used a cGAS knockin (KI) mouse model that develops systemic autoimmunity. In the lungs of cGAS-KI mice, blood vessels were enclosed by organized lymphoid tissues that resemble tertiary lymphoid structures (TLSs). Cell-intrinsic cGAS induction promoted up-regulation of CCR5 in CD8+ T cells and led to CCL5 production in vascular endothelial cells. Peripheral CD8+ T cells were recruited to the lungs and produced CXCL13 and interferon-γ. The latter triggered endothelial cell death, potentiated CCL5 production, and was essential for TLS establishment. Blocking CCL5 or CCR5, or depleting CD8+ T cells, impaired TLS formation. cGAS-mediated TLS formation also enhanced humoral and antitumor responses. These data demonstrate that cGAS signaling drives a specialized lymphoid structure that underlies autoimmune tissue pathology.

Vps34 sustains Treg cell survival and function via regulating intracellular redox homeostasis.

The survival and suppressive function of regulatory T (Treg) cells rely on various intracellular metabolic and physiological processes. Our study demonstrates that Vps34 plays a critical role in maintaining Treg cell homeostasis and function by regulating cellular metabolic activities. Disruption of Vps34 in Treg cells leads to spontaneous fatal systemic autoimmune disorder and multi-tissue inflammatory damage, accompanied by a reduction in the number of Treg cells, particularly eTreg cells with highly immunosuppressive activity. Mechanistically, the poor survival of Vps34-deficient Treg cells is attributed to impaired endocytosis, intracellular vesicular trafficking and autophagosome formation, which further results in enhanced mitochondrial respiration and excessive ROS production. Removal of excessive ROS can effectively rescue the death of Vps34-deficient Treg cells. Functionally, acute deletion of Vps34 within established Treg cells enhances anti-tumor immunity in a malignant melanoma model by boosting T-cell-mediated anti-tumor activity. Overall, our results underscore the pivotal role played by Vps34 in orchestrating Treg cell homeostasis and function towards establishing immune homeostasis and tolerance.

SLAM-family receptors promote resolution of ILC2-mediated inflammation.

Type 2 innate lymphoid cells (ILC2) initiate early allergic inflammation in the lung, but the factors that promote subsequent resolution of type 2 inflammation and prevent prolonged ILC2 activation are not fully known. Here we show that SLAM-family receptors (SFR) play essential roles in this process. We demonstrate dynamic expression of several SFRs on ILC2s during papain-induced type 2 immunity in mice. SFR deficiency exacerbates ILC2-driven eosinophil infiltration in the lung, and results in a significant increase in IL-13 production by ILC2s exclusively in mediastinal lymph nodes (MLN), leading to increased dendritic cell (DC) and TH2 cell numbers. In MLNs, we observe more frequent interaction between ILC2s and bystander T cells, with T cell-expressed SFRs (especially SLAMF3 and SLAMF5) acting as self-ligands to suppress IL-13 production by ILC2s. Mechanistically, homotypic engagement of SFRs at the interface between ILC2s and T cells delivers inhibitory signaling primarily mediated by SHIP-1. This prevents activation of NF-κB, driven by IL-7 and IL-33, two major drivers of ILC2-mediated type 2 immunity. Thus, our study shows that an ILC2-DC-TH2 regulatory axis may promote the resolution of pulmonary type 2 immune responses, and highlights SLAMF3/SLAMF5 as potential therapeutic targets for ameliorating type 2 immunity.

Hippo kinases Mst1 and Mst2 maintain NK cell homeostasis by orchestrating metabolic state and transcriptional activity.

Natural killer (NK) cells play a crucial role in immune response against viral infections and tumors. However, further investigation is needed to better understand the key molecules responsible for determining the fate and function of NK cells. In this study, we made an important discovery regarding the involvement of the Hippo kinases Mst1 and Mst2 as novel regulators in maintaining mouse NK cell homeostasis. The presence of high Mst1 and Mst2 (Mst1/2) activity in NK cells is essential for their proper development, survival and function in a canonical Hippo signaling independent mode. Mechanistically, Mst1/2 induce cellular quiescence by regulating the processes of proliferation and mitochondrial metabolism, thereby ensuring the development and survival of NK cells. Furthermore, Mst1/2 effectively sense IL-15 signaling and facilitate the activation of pSTAT3-TCF1, which contributes to NK cell homeostasis. Overall, our investigation highlights the crucial role of Mst1/2 as key regulators in metabolic reprogramming and transcriptional regulation for mouse NK cell survival and function, emphasizing the significance of cellular quiescence during NK cell development and functional maturation.

Eomesodermin spatiotemporally orchestrates the early and late stages of NK cell development by targeting KLF2 and T-bet, respectively.

Eomesodermin (Eomes) is a critical factor in the development of natural killer (NK) cells, but its precise role in temporal and spatial coordination during this process remains unclear. Our study revealed that Eomes plays distinct roles during the early and late stages of NK cell development. Specifically, the early deletion of Eomes via the CD122-Cre transgene resulted in significant blockade at the progenitor stage due to the downregulation of KLF2, another important transcription factor. ChIP-seq revealed direct binding of Eomes to the conserved noncoding sequence (CNS) of Klf2. Utilizing the CHimeric IMmune Editing (CHIME) technique, we found that deletion of the CNS region of Klf2 via CRISPRi led to a reduction in the NK cell population and developmental arrest. Moreover, constitutive activation of this specific CNS region through CRISPRa significantly reversed the severe defects in NK cell development caused by Eomes deficiency. Conversely, Ncr1-Cre-mediated terminal deletion of Eomes expedited the transition of NK cell subsets from the CD27+CD11b+ phenotype to the CD27-CD11b+ phenotype. Late-stage deficiency of Eomes led to a significant increase in T-bet expression, which subsequently increased the expression of the transcription factor Zeb2. Genetic deletion of one allele of Tbx21, encoding T-bet, effectively reversed the aberrant differentiation of Eomes-deficient NK cells. In summary, we utilized two innovative genetic models to elucidate the intricate mechanisms underlying Eomes-mediated NK cell commitment and differentiation.

Comparative single-cell RNA sequencing analysis of immune response to inactivated vaccine and natural SARS-CoV-2 infection.

Uncovering the immune response to an inactivated SARS-CoV-2 vaccine (In-Vac) and natural infection is crucial for comprehending COVID-19 immunology. Here we conducted an integrated analysis of single-cell RNA sequencing (scRNA-seq) data from serial peripheral blood mononuclear cell (PBMC) samples derived from 12 individuals receiving In-Vac compared with those from COVID-19 patients. Our study reveals that In-Vac induces subtle immunological changes in PBMC, including cell proportions and transcriptomes, compared with profound changes for natural infection. In-Vac modestly upregulates IFN-α but downregulates NF-κB pathways, while natural infection triggers hyperactive IFN-α and NF-κB pathways. Both In-Vac and natural infection alter T/B cell receptor repertoires, but COVID-19 has more significant change in preferential VJ gene, indicating a vigorous immune response. Our study reveals distinct patterns of cellular communications, including a selective activation of IL-15RA/IL-15 receptor pathway after In-Vac boost, suggesting its potential role in enhancing In-Vac-induced immunity. Collectively, our study illuminates multifaceted immune responses to In-Vac and natural infection, providing insights for optimizing SARS-CoV-2 vaccine efficacy.

Unleashing a safe and potent pro-senescence anti-tumor strategy.

Inducing senescence in tumor cells can stimulate anti-tumor immune responses. In this issue of Cancer Cell, Colucci et al. demonstrate that the combination of the RAR agonist Adapalene with the chemotherapy drug Docetaxel enhances tumor-suppressing senescence and activates an anti-tumor immune response through natural killer cells.

Dual Activity of Type III PI3K Kinase Vps34 is Critical for NK Cell Development and Senescence.

Vps34 is the unique member of the class III phosphoinositide 3-kinase family that performs both vesicular transport and autophagy. Its role in natural killer (NK) cells remains uncertain. In this study, a model without Vps34 (Vps34fl/fl/CD122Cre/+) is generated, deleting Vps34 during and after NK-cell commitment. These mice exhibit a nearly 90% decrease in NK cell count and impaired differentiation. A mechanistic study reveals that the absence of Vps34 disrupts the transport of IL-15 receptor subunit alpha CD122 to the cell membrane, resulting in reduced responsiveness of NK cells to IL-15. In mice lacking Vps34 at the terminal stage of NK-cell development (Vps34fl/fl/Ncr1Cre/+), NK cells gradually diminish during aging. This phenotype is associated with autophagy deficiency and the stress induced by reactive oxygen species (ROS). Therefore, terminally differentiated NK cells lacking Vps34 display an accelerated senescence phenotype, while the application of antioxidants effectively reverses the senescence caused by Vps34 deletion by neutralizing ROS. In summary, this study unveils the dual and unique activity of Vps34 in NK cells. Vps34-mediated vesicular transport is crucial for CD122 membrane trafficking during NK cell commitment, whereas Vps34-mediated autophagy can delay NK cell senescence.

Requirements for human natural killer cells.

'Requirements for Human Natural Killer Cells' is the latest set of guidelines on human NK cells in China, jointly drafted and agreed upon by experts from the Standards Committee of Chinese Society for Cell Biology. This standard specifies requirements for the human natural killer (NK) cells, including the technical requirements, test methods, test regulations, instructions for use, labeling requirements, packaging requirements, storage and transportation requirements, and waste disposal requirements of NK cells. This standard is applicable for the quality control of NK cells, derived from human tissues, or differentiated/transdifferentiated from stem cells. It was originally released by the Chinese Society for Cell Biology on 30 August, 2022. We hope that the publication of these guidelines will promote institutional establishment, acceptance, and execution of proper protocols and accelerate the international standardization of human NK cells for applications.

Transcription factor TOX maintains the expression of Mst1 in controlling the early mouse NK cell development.

Rationale: TOX is a DNA-binding factor required for the development of multiple immune cells and the formation of lymph nodes. However, the temporal regulation mode of TOX on NK cell development and function needs to be further explored. Methods: To investigate the role of TOX in NK cells at distinct developmental phases, we deleted TOX at the hematopoietic stem cell stage (Vav-Cre), NK cell precursor (CD122-Cre) stage and late NK cell developmental stage (Ncr1-Cre), respectively. Flow cytometry was used to detect the development and functional changes of NK cell when deletion of TOX. RNA-seq was used to assess the differences in transcriptional expression profile of WT and TOX-deficient NK cells. Published Chip-seq data was exploited to search for the proteins directly interact with TOX in NK cells. Results: The deficiency of TOX at the hematopoietic stem cell stage severely retarded NK cell development. To a less extent, TOX also played an essential role in the physiological process of NKp cells differentiation into mature NK cells. Furthermore, the deletion of TOX at NKp stage severely impaired the immune surveillance function of NK cells, accompanied by down-regulation of IFN-γ and CD107a expression. However, TOX is dispensable for mature NK cell development and function. Mechanistically, by combining RNA-seq data with published TOX ChIP-seq data, we found that the inactivation of TOX at NKp stage directly repressed the expression of Mst1, an important intermediate kinase in Hippo signaling pathway. Mst1 deficient at NKp stage gained the similar phenotype with Toxfl/flCD122Cre mice. Conclusion: In our study, we conclude that TOX coordinates the early mouse NK cell development at NKp stage by maintaining the expression of Mst1. Moreover, we clarify the different dependence of the transcription factor TOX in NK cells biology.

TOX deficiency facilitates the differentiation of IL-17A-producing γδ T cells to drive autoimmune hepatitis.

The specification of the αß/γδ lineage and the maturation of medullary thymic epithelial cells (mTECs) coordinate central tolerance to self-antigens. However, the mechanisms underlying this biological process remain poorly clarified. Here, we report that dual-stage loss of TOX in thymocytes hierarchically impaired mTEC maturation, promoted thymic IL-17A-producing γδ T-cell (Tγδ17) lineage commitment, and led to the development of fatal autoimmune hepatitis (AIH) via different mechanisms. Transfer of γδ T cells from TOX-deficient mice reproduced AIH. TOX interacted with and stabilized the TCF1 protein to maintain the balance of γδ T-cell development in thymic progenitors, and overexpression of TCF1 normalized αß/γδ lineage specification and activation. In addition, TOX expression was downregulated in γδ T cells from AIH patients and was inversely correlated with the AIH diagnostic score. Our findings suggest multifaceted roles of TOX in autoimmune control involving mTEC and Tγδ17 development and provide a potential diagnostic marker for AIH.

Manipulating Offense and Defense Signaling to Fight Cold Tumors with Carrier-Free Nanoassembly of Fluorinated Prodrug and siRNA.

Chemoimmunotherapy has shown great potential to activate an immune response, but the immunosuppressive microenvironment associated with T cell exhaustion remains a challenge in cancer therapy. The proper immune-modulatory strategy to provoke a robust immune response is to simultaneously regulate T-cell exhaustion and infiltration. Here, a new kind of carrier-free nanoparticle is developed to simultaneously deliver chemotherapeutic drug (doxorubicin, DOX), cytolytic peptide (melittin, MPI), and anti-TOX small interfering RNA (thymocyte selection-associated high mobility group box protein, TOX) using a fluorinated prodrug strategy. In this way, the enhanced immunogenic cell death (ICD) induced by the combination of DOX and MPI can act as "offense" signaling to increase CD8+ T-cell infiltration, while the decreased TOX expression interfered with siTOX can serve as "defense" signaling to mitigate CD8+ T-cell exhaustion. As a result, the integration of DOX, MPI, and siTOX in such a bifunctional system produced a potent antitumor immune response in liver cancer and metastasis, making it a promising delivery platform and effective strategy for converting "cold" tumors into "hot" ones.

SLAMF3 and SLAMF4 are immune checkpoints that constrain macrophage phagocytosis of hematopoietic tumors.

The interaction of SIRPα with CD47 represents a major mechanism for preventing macrophage phagocytosis. However, CD47-independent mechanisms are poorly defined. Here, we report a critical role of SLAM family receptors (SFRs), ubiquitously expressed on hematopoietic cells and forming homotypic interactions, in constraining macrophage phagocytosis. We found that SFR deficiency triggered macrophage phagocytosis of hematopoietic cells, leading to severe rejection of donor hematopoietic graft in recipient mice. Specific SFR members, mainly SLAMF3 and SLAMF4, were identified as "don't eat me" receptors on macrophages. These receptors inhibited "eat me" signals, such as LRP1-mediated activation of mTOR and Syk, through SH2 domain-containing phosphatases. SFRs combined with, but were independent of, CD47 to mitigate macrophage phagocytosis, and the combined deletion of SFRs and CD47 resulted in hematopoietic cytopenia in mice. This SFR-mediated tolerance was compromised in patients with hemophagocytic lymphohistiocytosis, a syndrome characterized by inappropriate phagocytosis toward hematopoietic cells. Loss of SFRs potently elicited macrophage rejection of hematopoietic tumors. Deletion of SFRs also significantly enhanced the phagocytosis of CD19-positive hematopoietic targets by the macrophages expressing the chimeric CD19 antigen receptor. Therefore, SFR-mediated inhibition of macrophage phagocytosis is critical to hematopoietic homeostasis, and SFRs may represent previously unknown targets for tumor immunotherapy.

The kinase PDK1 regulates regulatory T cell survival via controlling redox homeostasis.

Rationale: Regulatory T cells (Treg cells) play an important role in maintaining peripheral tolerance by suppressing over-activation of effector T cells. The kinase PDK1 plays a pivotal role in conventional T cell development. However, whether PDK1 signaling affects the homeostasis and function of Treg cells remains elusive. Methods: In order to evaluate the role of PDK1 in Treg cells from a genetic perspective, mice carrying the floxed PDK1 allele were crossbred with Foxp3Cre mice to efficiently deleted PDK1 in Foxp3+ Treg cells. Flow cytometry was used to detect the immune cell homeostasis of WT and PDK1fl/flFoxp3Cre mice. RNA-seq was used to assess the differences in transcriptional expression profile of WT and PDK1-deficient Treg cells. The metabolic profiles of WT and PDK1-deficient Treg cells were tested using the Glycolysis Stress Test and Mito Stress Test Kits by the Seahorse XFe96 Analyser. Results: PDK1 was essential for the establishment and maintenance of Treg cell homeostasis and function. Disruption of PDK1 in Treg cells led to a spontaneous fatal systemic autoimmune disorder and multi-tissue inflammatory damage, accompanied by a reduction in the number and function of Treg cells. The deletion of PDK1 in Treg cells destroyed the iron ion balance through regulating MEK-ERK signaling and CD71 expression, resulting in excessive production of intracellular ROS, which did not depend on the down-regulation of mTORC1 signaling. Inhibition of excessive ROS, activated MEK-Erk signaling or overload Fe2+ could partially rescue the survival of PDK1-deficient Treg cells. Conclusion: Our results defined a key finding on the mechanism by which PDK1 regulates Treg cell survival via controlling redox homeostasis.

Declined miR-181a-5p expression is associated with impaired natural killer cell development and function with aging.

MicroRNAs (miRNAs) regulate gene expression and thereby influence cell development and function. Numerous studies have shown the significant roles of miRNAs in regulating immune cells including natural killer (NK) cells. However, little is known about the role of miRNAs in NK cells with aging. We previously demonstrated that the aged C57BL/6 mice have significantly decreased proportion of mature (CD27- CD11b+ ) NK cells compared with young mice, indicating impaired maturation of NK cells with aging. Here, we performed deep sequencing of CD27+ NK cells from young and aged mice. Profiling of the miRNome (global miRNA expression levels) revealed that 49 miRNAs displayed a twofold or greater difference in expression between young and aged NK cells. Among these, 30 miRNAs were upregulated and 19 miRNAs were downregulated in the aged NK cells. We found that the expression level of miR-l8la-5p was increased with the maturation of NK cells, and significantly decreased in NK cells from the aged mice. Knockdown of miR-181a-5p inhibited NK cell development in vitro and in vivo. Furthermore, miR-181a-5p is highly conserved in mice and human. MiR-181a-5p promoted the production of IFN-γ and cytotoxicity in stimulated NK cells from both mice and human. Importantly, miR-181a-5p level markedly decreased in NK cells from PBMC of elderly people. Thus, our results demonstrated that the miRNAs profiles in NK cells change with aging, the decreased level of miR-181a-5p contributes to the defective NK cell development and function with aging. This opens new strategies to preserve or restore NK cell function in the elderly.

Evaluation of the Safety and Immune Efficacy of Recombinant Human Respiratory Syncytial Virus Strain Long Live Attenuated Vaccine Candidates.

Human respiratory syncytial virus (RSV) infection is the leading cause of lower respiratory tract illness (LRTI), and no vaccine against LRTI has proven to be safe and effective in infants. Our study assessed attenuated recombinant RSVs as vaccine candidates to prevent RSV infection in mice. The constructed recombinant plasmids harbored (5' to 3') a T7 promoter, hammerhead ribozyme, RSV Long strain antigenomic cDNA with cold-passaged (cp) mutations or cp combined with temperature-sensitive attenuated mutations from the A2 strain (A2cpts) or further combined with SH gene deletion (A2cptsΔSH), HDV ribozyme (δ), and a T7 terminator. These vectors were subsequently co-transfected with four helper plasmids encoding N, P, L, and M2-1 viral proteins into BHK/T7-9 cells, and the recovered viruses were then passaged in Vero cells. The rescued recombinant RSVs (rRSVs) were named rRSV-Long/A2cp, rRSV-Long/A2cpts, and rRSV-Long/A2cptsΔSH, respectively, and stably passaged in vitro, without reversion to wild type (wt) at sites containing introduced mutations or deletion. Although rRSV-Long/A2cpts and rRSV-Long/A2cptsΔSH displayed  temperature-sensitive (ts) phenotype in vitro and in vivo, all rRSVs were significantly attenuated in vivo. Furthermore, BALB/c mice immunized with rRSVs produced Th1-biased immune response, resisted wtRSV infection, and were free from enhanced respiratory disease. We showed that the combination of ΔSH with attenuation (att) mutations of cpts contributed to improving att phenotype, efficacy, and gene stability of rRSV. By successfully introducing att mutations and SH gene deletion into the RSV Long parent and producing three rRSV strains, we have laid an important foundation for the development of RSV live attenuated vaccines.

mTORC1 and mTORC2 coordinate early NK cell development by differentially inducing E4BP4 and T-bet.

Natural killer (NK) cell development is a multistep process that requires a variety of signals and transcription factors. The lack of mammalian target of rapamycin (mTOR) kinase severely impairs NK cell development in mice. mTOR binds to Raptor and Rictor to form two complexes, mTORC1 and mTORC2, respectively. How mTOR and its two complexes regulate NK cell development is not fully understood. Here, we developed two methods to inactivate mTOR, Raptor, or Rictor in early stage NK cells (using CD122-Cre) or in late-stage NK cells (using Ncr1-CreTg). First, we found that when mTOR was deleted by CD122-Cre during and after NK cell commitment, NK cell development was severely impaired, while Ncr1-CreTg mediated mTOR deletion slightly affected NK cell terminal differentiation, suggesting that mTOR is essential for early NK cell differentiation. Second, we found that CD122-mediated deletion of Raptor significantly limited the differentiation of CD27+CD11b- immature NK (iNK) cell into mature NK cells. In contrast, the absence of Rictor significantly interfered with the differentiation of CD27-CD11b- early iNK cells. Third, Ncr1-mediated deletion of Raptor, rather than Rictor, moderately affected NK cell terminal differentiation. In terms of mechanism, mTORC1 mainly promotes the expression of NK cell-specific transcription factor E4 promoter-binding protein 4 (E4BP4), while both mTORC1 and mTORC2 can enhance the expression of T-bet. Therefore, mTORC1 and mTORC2 subtly coordinate NK cell development by differentially inducing E4BP4 and T-bet.

Asparagine enhances LCK signalling to potentiate CD8+ T-cell activation and anti-tumour responses.

Nutrient availability is central for T-cell functions and immune responses. Here we report that CD8+ T-cell activation and anti-tumour responses are strongly potentiated by the non-essential amino acid Asn. Increased Asn levels enhance CD8+ T-cell activation and effector functions against tumour cells in vitro and in vivo. Conversely, restriction of dietary Asn, ASNase administration or inhibition of the Asn transporter SLC1A5 impairs the activity and responses of CD8+ T cells. Mechanistically, Asn does not directly alter cellular metabolic fluxes; it instead binds the SRC-family protein tyrosine kinase LCK and orchestrates LCK phosphorylation at Tyr 394 and 505, thereby leading to enhanced LCK activity and T-cell-receptor signalling. Thus, our findings reveal a critical and metabolism-independent role for Asn in the direct modulation of the adaptive immune response by controlling T-cell activation and efficacy, and further uncover that LCK is a natural Asn sensor signalling Asn sufficiency to T-cell functions.

Detection of CD8+ T cell-mediated immune responses to bacterial infection in mice.

Efficient activation of CD8+ T cells is critical for bacterial resistance and eradicating malignancy in the body. Here, we present a step-by-step protocol to use Listeria monocytogenes expressing OVA (LmOVA) to stimulate endogenous CD8+ T cells. We describe the steps for adoptive transfer of OT-I CD8+ T cells to CD45.1 mice and then detail the steps for detection of the antigen-specific CD8+ T cells in response to LmOVA. For complete details on the use and execution of this protocol, please refer to Wu et al. (2021).