Graft-versus-host disease is a major complication after allogeneic bone marrow transplantation. Dendritic cells play a critical role in the pathogenesis of graft-versus-host disease. The current article describes a novel bone marrow transplantation platform to investigate the role of dendritic cells in the development of graft-versus-host disease and the graft-versus-leukemia effect.
Allogeneic bone marrow transplantation (BMT) is an effective therapy for hematological malignancies due to the graft-versus-leukemia (GVL) effect to eradicate tumors. However, its application is limited by the development of graft-versus-host disease (GVHD), a major complication of BMT. GVHD is evoked when T-cells in the donor grafts recognizealloantigen expressed by recipient cells and mount unwanted immunological attacks against recipient healthy tissues. Thus, traditional therapies are designed to suppress donor T-cell alloreactivity. However, these approaches substantially impair the GVL effect so that the recipient's survival is not improved. Understanding the effects of therapeutic approaches on BMT, GVL, and GVHD, is thus essential. Due to the antigen-presenting and cytokine-secreting capacities to stimulate donor T-cells, recipient dendritic cells (DCs) play a significant role in the induction of GVHD. Therefore, targeting recipient DCs becomes a potential approach for controlling GVHD. This work provides a description of a novel BMT platform to investigate how host DCs regulate GVH and GVL responses after transplantation. Also presented is an effective BMT model to study the biology of GVHD and GVL after transplantation.
Allogeneic hematopoietic stem cell transplantation (BMT) is an effective therapy to treat hematological malignancies1,2 through the graft-versus-leukemia (GVL) effect3. However, donor lymphocytes always mount unwanted immunological attacks against recipient tissues, a process called graft-versus-host disease (GVHD)4.
Murine models of GVHD are an effective tool to study the biology of GVHD and the GVL response5. Mice are a cost-effective research animal model. They are small and efficiently dosed with molecules and biologics at early phases of development6. Mice are ideal research animals for genetic manipulation studies because they are genetically well defined, which is ideal for studying biological pathways and mechanisms6. Several mouse major histocompatibility complex (MHC) MHC-mismatched models of GVHD have been well established, such as C57BL/6 (H2b) to BALB/c (H2d) and FVB (H2q)→C57BL/6 (H2b)5,7. These are particularly valuable models to determine the role of individual cell types, genes, and factors that affect GVHD. Transplantation from C57/BL/6 (H2b) parental donors to recipients with mutations in MHC I (B6.C-H2bm1) and/or MHC II (B6.C-H2bm12) revealed that a mismatch in both MHC class I and class II is an important requirement for the development of acute GVHD. This suggests that both CD4+ and CD8+ T-cells are required for disease development7,8. GVHD is also involved in an inflammatory cascade known as the 'pro-inflammatory cytokine storm'9. The most common conditioning method in murine models is total body irradiation (TBI) by X-ray or 137Cs. This leads to the recipient's bone marrow ablation, thereby allowing donor stem cell engraftment and preventing rejection of the graft. This is done by limiting the proliferation of recipient T-cells in response to donor cells. Additionally, genetic disparities play an important role in disease induction, which also depends on minor MHC-mismatch10. Therefore, myeloablative irradiation dose varies in different mouse strains (e.g., BALB/c→C57BL/6).
Activation of donor T-cells by host antigen presenting cells (APCs) is essential for GVHD development. Among the APCs, dendritic cells (DCs) are the most potent. They are inheritably capable of inducing GVHD due to their superior antigen uptake, expression of T-cell co-stimulatory molecules, and production of pro-inflammatory cytokines that polarize T-cells into pathogenic subsets. Recipient DCs are critical for facilitating T-cell priming and GVHD induction after transplantation11,12. Accordingly, DCs have become interesting targets in the treatment of GVHD12.
TBI is required to enhance the donor cell engraftment. Due to the TBI effect, recipient DCs are activated and survive for a short time after the transplantation12. Despite major advancements in the usage of bioluminescence or fluorescence, establishing an effective model to study the role of recipient DCs in GVHD is still challenging.
Because donor T-cells are the driving force for GVL activity, treatment strategies using immunosuppressive drugs such as steroids to suppress T-cell alloreactivity often cause tumor relapse or infection13. Therefore, targeting recipient DCs may provide an alternative approach to treat GVHD while preserving the GVL effect and avoiding infection.
In brief, the current study provides a platform to understand how different types of signaling in recipient DCs regulates GVHD development and the GVL effect after BMT.
The experimental procedures were approved by the Institutional Animal Care and Use Committee of University of Central Florida.
1. GVHD Induction
NOTE: Allogeneic bone marrow (BM) cell transplantation (step 1.2) is performed within 24 h after irradiation. All procedures described below are performed in a sterile environment. Perform the procedure in a tissue culture hood and use filtered reagents.
2. Cotransplantation Model
3. GVHD/GVL Models of BMT
The major MHC-mismatched B6 (H2kb)-BALB/C (H2kd) model closely corresponded to GVHD development after the transplantation (Figure 2). All six GVHD clinical signs established previously by Cooke et al.16 occurred in the recipients transplanted with WT-B6 T-cells but not in the recipients transplanted with BM alone (step 1.5), which represented the GVHD-negative group. There are two phases in GVHD development in this model. First, the peak of severity is approximately 11 days after the transplantation, followed by a reduction in the clinical scores and body weight recovery up to 16 days. In this phase, several mechanisms such as irradiation-induced inflammation and engraftment syndrome drives the disease pathogenicity and GVHD. The recipients uniformly succumb to GVHD about 30−40 days post-transplant.
At least 85% of the BM differentiated into DCs (Figure 3A). Interestingly, transplantation with fB-/- DCs improved the recipient survival and GVHD clinical score (Figure 3B,C). Given that fB-/- DCs have less antigen presenting capacity demonstrated by lower MHCII expression and reduced co-stimulatory receptor expression17, the co-transplantation protocol may be sufficient for examining various signaling or targets in recipient DCs in GVHD development after BMT.
The T-cell purity was 90% after enrichment (Figure 4A). Luciferase-transduced A20 B cell lymphoma allows monitoring tumor growth in live animals (Figure 4B). In this model, if the recipients died without any signal and a high GVHD clinical score, it was concluded that they died of GVHD. All the WT BALB/c recipients that received BM alone plus A20 died of tumor relapse (Figure 3B). By contrast, if the animal died of higher signal density, it was concluded that they died of tumor relapse. As demonstrated in Figure 3B, WT BALB/c recipients transplanted with BM and T-cells from ACC1fl/fl B6 donor (ACC1+/+ T-cells) died of GVHD. If animals died with signals of disease, it was concluded that they died of GVHD and tumor relapse. The animals that received BM and T-cells from the ACC1fl/fl x CD4 cre B6 donor (ACC1-/- T-cells) died of both GVHD and tumor relapse (Figure 3B). Animals can be placed back in the cage to be imaged at a later time point or euthanized for ex vivo imaging. Using the software, the tumor mass in the animal can also analyzed individually (Figure 3B).
Figure 1: Schematic representation of the BMT procedure. (A) Scheme for MHC-mismatched B6→BALB/c BMT model. (B) Scheme for DC co-transplanting FVB→B6 model. (C) Scheme for B6→BALB/c GVHD/GVL model. Please click here to view a larger version of this figure.
Figure 2: Major MHC-mismatched B6→BALB/c GVHD model. BALB/c mice were lethally irradiated and transplanted with 5 x 106 BM alone or with 0.75 x 106 T-cells. (A) Survival data, (B) body weight loss, and (C) clinical score data of the recipients of BM alone or with T-cells. Please click here to view a larger version of this figure.
Figure 3: DC co-transplanting HCT model. BM was isolated from WT and fB-/- B6 mice and differentiated into DCs by culturing with GM-CSF. (A) The purity of DCs was examined by flow cytometry by staining with CD11c and MHCII. Lethally irradiated B6 recipients were transplanted with BM (3 x 106/mouse) plus purified T-cells (1 x 106/mouse) from the FVB donors. The recipients also received 2 x 106 WT or fB-/- B6 BM-DCs cells on the day of transplantation. The survival (B) and clinical score (C) are shown. Please click here to view a larger version of this figure.
Figure 4: Major-MHC mismatched B6→BALB/c GVHD/GVL model. WT BALB/c recipients were transplanted with TCD-BM (5 x 106/mouse) alone or with ACC1+/+ T-cells or ACC1+/+ T-cells (1 x 106/mouse) isolated from B6 background donor mice. In addition, recipients received 2 x 103 A20-luc at the time of transplant. T-cell purity was examined by flow cytometry through staining with live/death yellow, CD3, CD4, and CD8 flow antibodies (A). The recipients were monitored for tumor growth determined by whole-body bioluminescence imaging (BLI) (B). Please click here to view a larger version of this figure.
The use of stem cells to suit a particular individual is an effective approach to treat advanced and resistant cancers18. Small molecule pharmaceuticals, however, have long remained a primary focus of personalized cancer therapy. On the other hand, in cellular therapy a multitude of interactions between donor and host can decisively influence the treatment outcomes, such as the development of GVHD after BMT1.
Major MHC-mismatched mouse models of BMT are a valuable tool in understanding the biology of GVHD and testing the efficacy of drugs in its treatment. Among of them, C57BL/6 (H2b) to BALB/c (H2d) and FVB (H2q)→C57BL/6 (H2b) are well-established models5,7. These models incorporate either myeloablative radiation conditioning as a single dose (BALB/c) or a fractionated dose (C57BL/6) in which 3–8 hour intervals are required to decrease gut toxicity5. Both models are dependent on both CD8+ and CD4+ T-cells. In these models, GVHD severity and survival are the main outcomes measured, and the transplanted recipient has consistent rapid kinetics and 100% penetrance. In order to monitor T-cell migration and expansion, T-cells from luciferase-transduced donor mice should be used for in vivobioluminescence imaging19. However, while 90% of the BMT performed are MHC-matched, the B6-BALB/c model does not perfectly resemble the clinical situation. The discovery of the MHC and minor histocompatibility antigens (miHAs) has significantly contributed to advancing the field of BMT10. Minor MHC-mismatched GVHD mouse models more closely mimic patient GVHD20. Conditioning intensity to induce donor cell engraftment causes tissue damage and can affect the GVHD outcome21. Conditioning regimens in murine models often involves TBI in contrast to chemotherapy in clinical settings22,23. Therefore, an immunosuppressive chemotherapy model has been used to mimic a reduced conditional intensity in clinics. The mouse model was C57BL/6 (H2b) to BALB/c (H2d) and transplanted recipients developed clinical and histological symptoms associated with GVHD24.
The potential advantage of the co-transplanted protocol is to test the role of recipient DCs without depending specifically on CD11c depleted mice. Because the BM-DC generation was performed ex vivo, this protocol can also be applied to test the role of other cell types such as macrophages or neutrophils in GVHD simply by modifying the culture conditions. Using CD45.1+ B6 mice as recipients allows researchers to distinguish BM-DCs (CD45.2+ CD11c+) from recipient DCs (CD45.1+ CD11c+) by flow analysis. The flexible number of cells generated ex vivo and adoptedinto the transplanted recipients is another benefit of the co-transplantation protocol. Furthermore, ex vivo culture allows us to screen the potential drugs to control GVHD.
The ability to track tumor patterns in vivo is a powerful tool that has the potential to test whether a drug can affect GVL activity. Using this GVHD/GVL model, tumor progression and metastasis can be monitored in live animals16. Moreover, this setting can be used for testing the GVL effect in multiple cancers.
The authors have nothing to disclose.
This study is supported by University of Central Florida College of Medicine start-up grant (to HN), the University of Pittsburgh Medical Center Hillman Cancer Center start-up grant (to HL), the United States NIH Grant #1P20CA210300-01 and Vietnamese Ministry of Health Grant #4694/QD-BYT (to PTH). We thank Dr. Xue-zhong Yu at Medical University of South Carolina for providing materials for the study.
0.5 M EDTA pH 8.0 100ML | Fisher Scientific | BP2482100 | MACS buffer |
10X PBS | Fisher Scientific | BP3994 | MACS buffer |
A20 B-cell lymphoma | University of Central Florida | In house | GVL experiment |
ACC1 fl/fl | Jackson Lab | 30954 | GVL experiment |
ACC1 fl/fl CD4cre | University of Central Florida | GVL experiment | |
Anti-Biotin MicroBeads | Miltenyi Biotec | 130-090-485 | T-cell enrichment |
Anti-Human/Mouse CD45R (B220) | Thermo Fisher Scientific | 13-0452-85 | T-cell enrichment |
Anti-mouse B220 FITC | Thermo Fisher Scientific | 10452-85 | Flow cytometry analysis |
Anti-mouse CD11c- AF700 | Thermo Fisher Scientific | 117319 | Flow cytometry analysis |
Anti-Mouse CD25 PE | Thermo Fisher Scientific | 12-0251-82 | Flow staining |
Anti-Mouse CD4 Biotin | Thermo Fisher Scientific | 13-0041-86 | T-cell enrichment |
Anti-Mouse CD4 eFluor® 450 (Pacific Blue® replacement) | Thermo Fisher Scientific | 48-0042-82 | Flow staining |
Anti-mouse CD45.1 PE | Thermo Fisher Scientific | 12-0900-83 | Flow cytometry analysis |
Anti-Mouse CD8a APC | Thermo Fisher Scientific | 17-0081-83 | Flow cytometry analysis |
Anti-mouse H-2Kb PerCP-Fluor 710 | Thermo Fisher Scientific | 46-5958-82 | Flow cytometry analysis |
Anti-mouse MHC Class II-antibody APC | Thermo Fisher Scientific | 17-5320-82 | Flow cytometry analysis |
Anti-Mouse TER-119 Biotin | Thermo Fisher Scientific | 13-5921-85 | T-cell enrichment |
Anti-Thy1.2 | Bio Excel | BE0066 | BM generation |
B6 fB-/- mice | University of Central Florida | In house | Recipients |
B6.Ly5.1 (CD45.1+) mice | Charles River | 564 | Donors |
BALB/c mice | Charles River | 028 | Transplant recipients |
C57BL/6 mice | Charles River | 027 | Donors/Recipients |
CD11b | Thermo Fisher Scientific | 13-0112-85 | T-cell enrichment |
CD25-biotin | Thermo Fisher Scientific | 13-0251-82 | T-cell enrichment |
CD45R | Thermo Fisher Scientific | 13-0452-82 | T-cell enrichment |
CD49b Monoclonal Antibody (DX5)-biotin | Thermo Fisher Scientific | 13-5971-82 | T-cell enrichment |
Cell strainer 40 uM | Thermo Fisher Scientific | 22363547 | Cell preparation |
Cell strainer 70 uM | Thermo Fisher Scientific | 22363548 | Cell preparation |
D-Luciferin | Goldbio | LUCK-1G | Live animal imaging |
Fetal Bovine Serum (FBS) | Atlanta Bilogicals R&D system | D17051 | Cell Culture |
Flow cytometry tubes | Fisher Scientific | 352008 | Flow cytometry analysis |
FVB/NCrl | Charles River | 207 | Donors |
Lipopolysacharide (LPS) | Millipore Sigma | L4391-1MG | DC mature |
LS column | Mitenyi Biotec | 130-042-401 | Cell preparation |
MidiMACS | Miltenyi Biotec | 130-042-302 | T-cell enrichment |
New Brunswick Galaxy 170R incubator | Eppendorf | Galaxy 170 R | Cell Culture |
Penicilin+streptomycinPenicillin/Streptomycin (10,000 units penicillin / 10,000 mg/ml strep) | GIBCO | 15140 | Media |
RPMI 1640 | Thermo Fisher Scienctific | 11875-093 | Media |
TER119 | Thermo Fisher Scientific | 13-5921-82 | T-cell enrichment |
Xenogen IVIS-200 | Perkin Elmer | Xenogen IVIS-200 | Live animal imaging |
X-RAD 320 Biological Irradiator | Precision X-RAY | X-RAD 320 | Total Body Irradiation |