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Method Article
Here, we present a tumor transplantation protocol for the characterization of tumor-inherent and periphery-derived tumor-infiltrated lymphocytes in a mouse tumor model. Specific tracing of the influx of recipient-derived immune cells with flow cytometry reveals the dynamics of the phenotypic and functional changes of these cells during antitumor immune responses.
T cell-mediated immunity plays a crucial role in immune responses against tumors, with cytotoxic T lymphocytes (CTLs) playing the leading role in eradicating cancerous cells. However, the origins and replenishment of tumor antigen-specific CD8+ T cells within the tumor microenvironment (TME) remain obscure. This protocol employs the B16F10-OVA melanoma cell line, which stably expresses the surrogate neoantigen, ovalbumin (OVA), and TCR transgenic OT-I mice, in which over 90% of CD8+ T cells specifically recognize the OVA-derived peptide OVA257-264 (SIINFEKL) bound to the class I major histocompatibility complex (MHC) molecule H2-Kb. These features enable the study of antigen-specific T cell responses during tumorigenesis.
Combining this model with tumor transplantation surgery, tumor tissues from donors were transplanted into tumor-matched syngeneic recipient mice to precisely trace the influx of recipient-derived immune cells into transplanted donor tissues, allowing the analysis of the immune responses of tumor-inherent and periphery-originated antigen-specific CD8+ T cells. A dynamic transition was found to occur between these two populations. Collectively, this experimental design has provided another approach to precisely investigate the immune responses of CD8+ T cells in TME, which will shed new light on tumor immunology.
CD8+ T cell-mediated immune response plays a pivotal role in controlling tumor growth. During tumorigenesis, naive CD8+ T cells get activated upon antigen recognition in an MHC class I-restricted manner and subsequently differentiate into effector cells and infiltrate into tumor mass1,2. However, within the tumor microenvironment (TME), prolonged antigen exposure, as well as immunosuppressive factors, drive infiltrated tumor-specific CD8+ T cells into a hyporesponsive state known as "exhaustion"3. Exhausted T cells (Tex) are distinct from effector or memory T cells generated in acute viral infection, both transcriptionally and epigenetically. These Tex cells are mainly characterized by the sustained and elevated expression of a series of inhibitory receptors as well as the hierarchical loss of effector functions. Further, the impaired proliferative capacity of exhausted CD8+ T cells results in decreasing numbers of tumor-specific T cells, such that the residual CD8+ T cells within the TME can barely provide sufficient protective immunity against tumor progression3. Thus, the maintenance or reinforcement of intratumoral antigen-specific CD8+ T cells is indispensable for tumor repression.
Moreover, immune checkpoint blockade (ICB) therapy is believed to reinvigorate Tex in tumors by increasing T cell infiltration and hence, T cell numbers and rejuvenating T cell functions to boost tumor repression. The widespread application of ICB treatment has changed the cancer therapy landscape, with a substantial subset of patients experiencing durable responses4,5,6. Nevertheless, the majority of patients and cancer types do not or only temporarily respond to ICB. Inadequate T cell infiltration in the TME has been postulated to be one of the underlying mechanisms accounting for ICB resistance7,8.
Several studies have demonstrated the heterogeneity of tumor-infiltrating CD8+ T cells (TILs) in both patients and mouse models9,10,11,12. It has been confirmed that a subset of CD8+ T cells expressing T cell factor-1 (TCF1) in a tumor mass exhibits stem cell-like properties, which could further give rise to terminally exhausted T cells and is responsible for the proliferation burst after ICB therapy12,13,14,15,16,17,18,19,20,21,22. However, it has been proved that only a small proportion of antigen-specific TCF1+CD8+ T cells exist in the TME and generate an expanded pool of differentiated progeny in response to ICB23,24,25,26. Whether the limited size of this population is enough to ensure the persistence of cytotoxic T lymphocytes (CTLs) to control tumor progression remains unknown, and whether there is replenishment from periphery tissues requires further investigation. Furthermore, recent research suggests the insufficient reinvigoration capacity of pre-existing tumor-specific T cells and the appearance of novel, previously non-existing clonotypes after anti-programmed cell death protein 1 treatment. This indicates that T cell response to checkpoint blockade may be due to the new influx of a distinct repertoire of T cell clones27. Together with the presence of bystander non-tumor-reactive cytotoxic T cell fraction in the TME, these findings prompted the establishment of a tumor allograft model to study the role of periphery-derived CD8+ T cells11.
Until now, several kinds of tumor implantation, as well as immune cell adoptive transfer, have been widely used in the field of tumor immunology28. TILs, peripheral blood mononuclear cells, and tumor-reactive immune cells originated from other tissues can be well-characterized using these methods. However, when studying the interactions between systemic and local antitumor immunity, these models appear inadequate to examine the interactions between immune cells derived from the periphery and the TME. Here, tumor tissues were transplanted from donors into tumor-matched recipient mice to precisely trace the influx of recipient-derived immune cells and observe the donor-derived cells in the TME concomitantly.
In this study, a murine syngeneic model of melanoma was established with the B16F10-OVA melanoma cell line, which stably expresses the surrogate neoantigen ovalbumin. TCR transgenic OT-I mice, in which over 90% of CD8+ T cells specifically recognize the OVA-derived peptide OVA257-264 (SIINFEKL) bound to the class I MHC molecule H2-Kb, enable the study of antigen-specific T cell responses developed in the B16F10-OVA tumor model. Combining this model with tumor transplantation, the immune responses of tumor-inherent and periphery-originated antigen-specific CD8+ T cells were compared to reveal a dynamic transition between these two populations. Collectively, this experimental design has provided another approach to precisely investigate the immune responses of CD8+ T cells in the TME, which sheds new light on the dynamics of tumor-specific T cell immune responses in the TME.
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All mouse experiments were performed in compliance with the guidelines of the Institutional Animal Care and Use Committees of the Third Military Medical University. Use 6-8-week-old C57BL/6 mice and naïve OT-I transgenic mice weighing 18-22 g. Use both male and female without randomization or "blinding."
1. Preparation of medium and reagents
2. Preparation of B16F10-OVA cell suspension
NOTE: Cell culture should be carried out in a biosafety hood under strict aseptic conditions.
3. Ectopic tumor implantation of B16F10-OVA cells in the inguinal region of mice
4. Adoptive transfer of congenically marked OT-I T cells into tumor-bearing mice
5. Dissect tumor mass from tumor-bearing donor mice
NOTE: Maintain sterile conditions during surgery in sections 5 and 6. Sterilize all surgical instruments by autoclaving before and after each use. Disinfect the operating area in the biosafety cabinet with 75% ethanol followed by ultraviolet irradiation. Wear a clean gown, cap, face mask, and sterile gloves.
6. Subcutaneous transplantation of donor-derived tumor onto the tumor-matched recipient mice
NOTE: The allograft is supposed to be implanted into the mouse's lower flank on the same side as the previously existing tumor to make two tumors drain to the identical lymph node. In the protocol presented here, as the B16F10-OVA tumor was implanted subcutaneously on the left inguinal region of the mouse (section 3), the donor-derived tumor tissue was transplanted onto the left flank of the recipient in this step. The transplantation site can be adapted to the first-implanted tumor site.
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The schematic of this protocol is shown in Figure 1. Eight days after tumor inoculation, CD45.1+ and CD45.1+CD45.2+ OT-I cells were injected into B16F10-OVA tumor-bearing C57BL/6 mice. The tumor was surgically dissected from CD45.1+ OT-I cell-implanted mice (donor) on day 8 post-transfer and transplanted into tumor-matched CD45.1+CD45.2+ OT-I cell-implanted mice (recipient) in the dorsal flank on the same side as the implanted...
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T cell-mediated immunity plays a crucial role in immune responses against tumors, with CTLs playing the leading role in eradicating cancerous cells. However, the origins of tumor antigen-specific CTLs within TME have not been elucidated30. The use of this tumor transplantation protocol has provided an important clue that intratumoral antigen-specific CD8+ T cells may not persist for a long time, despite the existence of stem-like TCF1+ progenitor CD8+ T cells. Nota...
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The authors have no conflicts of interest to disclose.
This study was supported by grants from the National Natural Science Fund for Distinguished Young Scholars (No. 31825011 to LY) and the National Natural Science Foundation of China (No. 31900643 to QH, No. 31900656 to ZW).
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Name | Company | Catalog Number | Comments |
0.22 μm filter | Millipore | SLGPR33RB | |
1 mL tuberculin syringe | KDL | BB000925 | |
1.5 mL centrifuge tube | KIRGEN | KG2211 | |
100 U insulin syringe | BD Biosciences | 320310 | |
15 mL conical tube | BEAVER | 43008 | |
2,2,2-Tribromoethanol (Avertin) | Sigma | T48402-25G | |
2-Methyl-2-butanol | Sigma | 240486-100ML | |
70 μm nylon cell strainer | BD Falcon | 352350 | |
APC anti-mouse CD45.1 | BioLegend | 110714 | Clone:A20 |
B16F10-OVA cell line | bluefbio | BFN607200447 | |
BSA-V (bovine serum albumin) | Bioss | bs-0292P | |
BV421 Mouse Anti-Mouse CD45.2 | BD Horizon | 562895 | Clone:104 |
cell culture dish | BEAVER | 43701/43702/43703 | |
centrifuge | Eppendorf | 5810R-A462/5424R | |
cyclophosphamide | Sigma | C0768-25G | |
Dulbecco's Modified Eagle Medium | Gibco | C11995500BT | |
EasySep Mouse CD8+ T Cell Isolation Kit | Stemcell Technologies | 19853 | |
EDTA | Sigma | EDS-500g | |
FACS tubes | BD Falcon | 352052 | |
fetal bovine serum | Gibco | 10270-106 | |
flow cytometer | BD | FACSCanto II | |
hemocytometer | PorLab Scientific | HM330 | |
isoflurane | RWD life science | R510-22-16 | |
KHCO3 | Sangon Biotech | A501195-0500 | |
LIVE/DEAD Fixable Near-IR Dead Cell Stain Kit, for 633 or 635 nm excitation | Life Technologies | L10199 | |
needle carrier | RWD Life Science | F31034-14 | |
NH4Cl | Sangon Biotech | A501569-0500 | |
paraformaldehyde | Beyotime | P0099-500ml | |
PE anti-mouse TCR Vα2 | BioLegend | 127808 | Clone:B20.1 |
Pen Strep Glutamine (100x) | Gibco | 10378-016 | |
PerCP/Cy5.5 anti-mouse CD8a | BioLegend | 100734 | Clone:53-6.7 |
RPMI-1640 | Sigma | R8758-500ML | |
sodium azide | Sigma | S2002 | |
surgical forceps | RWD Life Science | F12005-10 | |
surgical scissors | RWD Life Science | S12003-09 | |
suture thread | RWD Life Science | F34004-30 | |
trypsin-EDTA | Sigma | T4049-100ml |
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An erratum was issued for: Tumor Transplantation for Assessing the Dynamics of Tumor-Infiltrating CD8+ T Cells in Mice. The Protocol was updated.
Step 6.10 of the Protocol was updated from:
Administer penicillin every 8-12 h after the surgery for 3 days. Monitor the mouse's eating, drinking, moving, and the area operated on. Return the transplant recipient to the company of other animals only after it has fully recovered.
NOTE: The administration of buprenorphine is suggested to prevent post-surgical pain [delete sentence]. The mouse typically recovers from the trauma of the surgery within 3 days. If the mouse is not back to normal feeding and mobility and shows any manifestations of infection, consult a veterinarian for interventions or euthanize it.
to:
Administer buprenorphine subcutaneously at a dose of 0.1 mg/kg body weight every 8 h three times after surgery to alleviate the pain. Monitor the mouse's eating, drinking, moving, and the area operated on. Return the transplant recipient to the company of other animals only after it has fully recovered.
NOTE: The mouse typically recovers from the trauma of the surgery within 3 days. If the mouse is not back to normal feeding and mobility and shows any manifestations of infection, consult a veterinarian for interventions or euthanize it.
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