Hyperacute GVHD occurs in ROS deficient mice after allogeneic transplantation.
ROS were crucial for human hematopoietic regulation and antioxidants were able to increase engraftment of HSCs in immune-deficient mice(6, 7). However, lower level of ROS could be more beneficial for allo-HSCT remains unknown, let alone ROS production deficiency.
To investigate the underlying mechanism of ROS in allo-HSCT, the NOX2-deficient mice (i.e., the CGD mice) were established on complete the major histocompatibility antigen (MHC)-mismatch GVHD model (Figure 1A). Surprisingly, the mice with ROS production deficiency – the CGD mice - died rapidly after receiving allo-HSCT, with a median survival time of 4 days (range, 3 to 5 days) versus 25 days (range, 22 to 28 days) for WT mice (Figure 1B). The CGD mice exhibited a complication similar to but somewhat distinct from typical aGVHD at day 3 including severe ruffling, lack of movement (unless stimulated), slight hunching and skin integration (Figure S1). Compared with WT mice receiving allo-HSCT, CGD mice exhibited continuous weight loss without a great rising tendency of GVHD scores (Figure 1C-D). The white blood cell count of CGD mice with allo-HSCT persisted at less than 1.0×109/L until the mice died and exhibited the lack of neutrophil repopulation, while that of WT mice recovered after day 8 (Figure 1E). Histological scoring analysis revealed different patterns of impairment in the liver, intestine and skin, which are classic target tissues of aGVHD (Figure 1F). The samples from WT mice showed clear symptoms of aGVHD on day 25, such as lymphocyte infiltration and hydropic degeneration. In contrast, CGD and WT mice at day 3 had nearly negative clear sign in target tissues (Figure1G-I).
In consideration of the lethally and rapidly progressive complications that CGD mice suffered from and depended only on allogeneic cells infusion, we turned our attention to the hyperacute GVHD phenotype. Based on hyperacute GVHD of humans characterized by unexplained fevers, diarrhea, skin rashes and hepatic toxicity that occur before engraftment (less than 14 days) in patients with allo-HSCT and its distinction from typical aGVHD (12), we defined hyperacute GVHD of mice using the following criteria. The symptoms occurred within 7 days after allogeneic transplantation before engraftment; the mice showed continuous weight loss with irradiation, poor grooming and impaired movement with or without hunching or skin integrated; and the animals died within 2 days after onset of symptoms and atypical histological changes of classical target organs.
The link between low ROS level and the development of hyperacute GVHD symptoms in patients after allo-HSCT.
To investigate the role of ROS in hyperacute GVHD of patients, we measured the level of ROS in the peripheral blood of 17 patients (Table 1) on the day of allo-HSCT, before the donor stem cells were infused (Figure 2A). These patients were followed up. Although none of the patients died of hyperacute GVHD at the early stage after allo-HSCT because the usage of prophylaxed immunosuppressants, 6 patients developed hyperacute GVHD symptoms, including 6 had unexplained fever, 3 developed diarrhea and 1 developed liver dysfunction seven days after transplantation. The level of ROS of these 6 patients was significantly lower than that of patients without hyperacute GVHD symptoms (Figure 2B). 5-year overall survival of patients with and without hyperacute GVHD symptoms was 50.0% and 90.9%, respectively (P= 0.052, Figure 2C). We further tested different cytokines of serum from each group. The level of IL-2R of patients with hyperacute GVHD symptoms were significantly higher than of patients without hyperacute GVHD symptoms on the day of allo-HSCT.
These findings, although being limited by the small number of patients, demonstrate that recipients with low ROS level before transplantation are more likely to have hyperacute GVHD symptoms after transplantation and suggest that a moderate level of ROS might be essential for patient receiving allo-HSCT.
Table 1 The relationship between the level of ROS and the development of hyperacute GVHD in patients receiving allo-HSCT.
Patient
|
ROS in PB
(unit)
|
Unexplained
fevers
|
Diarrhea
|
Skin
rashes
|
Hepatic
toxicity
|
Case 1
|
45.4
|
Yes
|
No
|
No
|
No
|
Case 2
|
51.2
|
Yes
|
Yes
|
No
|
Yes
|
Case 3
|
52.5
|
Yes
|
Yes
|
No
|
No
|
Case 4
|
53.3
|
Yes
|
Yes
|
No
|
No
|
Case 5
|
54.5
|
Yes
|
No
|
No
|
No
|
Case 6
|
85.2
|
No
|
No
|
No
|
No
|
Case 7
|
139.6
|
No
|
No
|
No
|
No
|
Case 8
|
148.6
|
No
|
No
|
No
|
No
|
Case 9
|
157.7
|
Yes
|
No
|
No
|
No
|
Case 10
|
174.1
|
No
|
No
|
No
|
No
|
Case 11
|
187.5
|
No
|
No
|
No
|
No
|
Case 12
|
232.2
|
No
|
No
|
No
|
No
|
Case 13
|
268.4
|
No
|
No
|
No
|
No
|
Case 15
|
300.8
|
No
|
No
|
No
|
No
|
Case 16
|
358.1
|
No
|
No
|
No
|
No
|
Case 17
|
399.2
|
No
|
Yes
|
No
|
No
|
Donor-derived splenic T cells account for hyperacute GVHD.
To further explored why ROS production deficiency mice suffered from hyperacute GVHD symptoms after allografting, we analyzed survival of WT and CGD mice by using different types of allogeneic cells sorted from BALB/c mice (Figure 3A). Neither of CGD and WT mice receiving donor BM cells displayed hyperacute GVHD at day 3-5. Nor did they develop aGVHD at day 20-30 after transplantation. Both WT and CGD mice survived at the end of observation (day 40). In contrast, all lethally irradiated mice (CGD or WT) receiving only PBS (PBS control) began to die at about 9 days after transplantation of bone marrow failure, much longer than that of CGD mice suffered from hyperacute GVHD (P<0.01). There was no statistical difference of survival between CGD and WT mice in PBS control group (Figure 3B). The survival time of CGD mice receiving T cells was significantly shorter than that of WT mice with the same treatment (Figure 3C, P<0.001), and the survival time was similar to that of CGD mice receiving allo-HSCT (Table S2, P>0.05). On the contrary, the survival time of CGD mice receiving T-cell-depleted cells sorted from donor spleens cell (TCD) transplantation was similar to that of WT mice with the same treatment (Figure 3D, P>0.05), but was significantly longer than that of CGD mice receiving allo-HSCT (Table S2, p=0.0092).
In order to evaluate the role of donor-derived HSCs and hematopoietic progenitor cells (HPCs) in hyperacute GVHD, we sacrificed CGD and WT mice at day 3 after they received allo-HSCT. As shown in Figure S2, the frequencies and absolute numbers of HSCs and HPCs failed to recover during hyperacute GVHD occurrence, indicating that the fatal complication only depended on the cells infused during transplantation.
Together, these results indicate that the donor spleen-derived T cells are crucial for the hyperacute GVHD phenotype of CGD mice after receiving allo-HSCT.
Elevated activity of allo-reactive T cells during hyperacute GVHD.
It is widely accepted that GVHD is related to reactivity of donor T cells against host antigens(2). In our study, the spleen of CGD mice sacrificed at day 3 after receiving allo-HSCT was statistically larger, heavier and contained more cells than the WT mice (Figure 4A), indicating that the allo-reactive T cells might be activated and proliferate in immune organs during hyperacute GVHD.
To test this hypothesis, we sacrificed recipient CGD mice suffering hyperacute GVHD at day 3 after allo-HSCT and used flow cytometry to analyze cell sizes (increased in activated T cells) and expression of T cell markers CD25, CD44, CD69 (highly expressed in activated T cells) and CD62L (lowly expressed in activated T cells)(18).
We found that during hyperacute GVHD, the proportion and absolute number of H-2Kd+CD3+CD8+ T cells in both the bone marrow and spleen of CGD mice were significantly higher than those of WT mice (Figure 4B). In addition, the number of activated CD8+ T cells (CD62-CD69+) was significantly higher than that of WT mice. In CGD mice, the change in H-2Kd+CD4+T was also consistent with that of H-2Kd+CD3+CD8+ T cells. Moreover, the proportion and absolute number of these cells increased in bone marrow and spleen, and the number of activated CD4+T cells also increased (Figure 4C). Moreover, the result of regular T cells (CD4+CD25+FOXP3+ T cells, T reg cells) in the spleen of WT mice and CGD mice indicated Treg cells were proliferated and activated during hyperacute GVHD (Figure 4D).
Next, we sorted H-2Kd+CD3+ T cells from the spleen of CGD (CGD-T cells group) or WT mice (WT-T cells group) that received allo-HSCT 3 days to measure the killing ability and genome-wide RNA-seq. Then sorted CD3+ T cells were co-cultivated with H2Kb+eGFP+AF9 tumor cells for 18 hours and measured the killing ability of live cells by video-tracing of the cell-cell interactions over time. Rapid disappearance of green-labeled cells, which represented AF9 tumor cells, was seen for the CGD-T group (Video S1), but not for the WT-T group (Video S2). At the end of experimentation, the eGFP+ tumor cells in the CGD-T group were significantly fewer than those in the WT-T group (Figure 4 J). Then, we took advantages of the gene ontology (GO) analysis and found that the upregulated expressed genes of H-2Kd+CD3+CD8+ T and H-2Kd+CD3+CD4+ T cells from CGD and WT were principally associated T cell activation and acute inflammation response. Different from activation of B cells activation pathway in CD8+ and CD4+ T cells sorted from WT mine, positive regulation of T cells activation, myeloid leukocyte migration and acute inflammatory response were upregulated in T cells from CGD (Figure 4 F-G).
MDSCs with impaired ROS production cannot inhibit T cell proliferation and activation.
NADPH oxidase NOX2 is mainly expressed in myeloid cells, and the gp91 subunit of NADPH oxidase holoenzyme has been deleted in the CGD mice, leading to the defect in ROS production(13). While representing an escape mechanism for immune surveillance in cancer, MDSCs have a beneficial role in transplantation and function by suppressing alloreactive-T cell responses, reducing the occurrence of typical acute GVHD (aGVHD) (9, 19-32). Because allo-reactive T cells are massively activated and proliferate during hyperacute GVHD, we ask whether these changes can be linked to the level of ROS that is produced by MDSCs (CD11b+Gr1+).
First, we determined the level of ROS in CD11b+Gr1+ cells from the BM during hyperacute GVHD by using a chemiluminescence-based method. Not surprisingly, the ROS production in CD11b+Gr1+ cells of the CGD mice was defective and the ROS production in the BM of CGD mice receiving allo-HSCT after 3 days was significantly lower than that of WT mice (Figure S3A-B). Then, we found that during hyperacute GVHD, the proportion and absolute number of MDSCs in both the BM and spleen of CGD mice were significantly higher than those of WT mice and most all cells were coming from recipient mice (Figure 5A-C).
We subsequently tested whether the deficiency of ROS production could attenuate the suppressive function of MDSCs. CD3+ T cells sorted from spleen of normal BALB/c mice were cocultured at the ratio of 10:1 with MDSCs isolated from the BM of WT mice (WT-MDSCs group) or of the CGD mice (CGD-MDSCs group) at day 3 after allo-HSCT. The cell mixtures with or without stimulating factors were used as positive and negative controls. The WT-MDSCs showed strong suppressive ability toward proliferation of both CD8+ and CD4+ T cells based on CFSE labeling, decreased expression of activation CD69 and increased expression of CD62L. In contrast, CGD-MDSCs displayed impaired suppressive effect on the activation and proliferation of both CD8+ and CD4+ T cells, with more dividing cells, and marked up-regulation of the activity markers (Figure 5). Moreover, a larger number of CD3+ T cells could differentiate toward CD8+ T cells when cocultured with CGD-MDSCs (Figure 5C, G).
To explore the potential molecular mechanism of inability recipient-derived MDSCs during hyperacute GVHD, we further profiled the transcriptome sequencing of recipient-derived CGD-MDSCs and WT-MDSCs isolated from the BM of WT mice or of the CGD mice at day 3 after allo-HSCT. Pathway enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database and gene set enrichment analysis (GSEA) were performed. As shown in Figure 5 K-L, regulation of GVHD and allograft rejection were decreased in CGD-MDSC, consistent with the impaired function of CGD-MDSCs displayed on the activation and proliferation of T cells during hyperacute GVHD. These results indicated that ROS production might play a critical role in the suppressive effect of MDSCs on T cell proliferation and activation.
WT mice develop hyperacute GVHD with MDSC depletion.
Having shown that the level of ROS in mice after allogeneic transplantation is critical and that MDSCs with ROS production defect cannot inhibit T cells in vitro, we asked whether the MDSCs in the recipients are essential for preventing hyperacute GVHD. It has been reported that CD11b+Gr1+ MDSCs in BM, spleen and blood can be depleted by the use of an anti–Gr1 antibody(17). Accordingly, we injected anti-Gr1Ab (200ug/kg) into recipient WT mice 3 hours before and every 48 h after allo-HSCT, which reportedly induces severe granulopenia in mice for 3 to 4 days(16). Recipient WT mice injected with PBS were used as a control. As shown in Figure S1D, the responses of WT mice with anti-Gr1Ab injection at the early stage after allogenic transplantation (at day 5) were similar to those of the CGD mice suffering from hyperacute GVHD (Figure S1C). WT mice with anti-Gr1Ab died within 2 days after the onset of illness, and significant differences in survival rate between the anti-Gr1Ab and PBS control groups were observed from day 5 onwards (Figure 6B). In mice with anti-Gr1Ab injection, the size, weight and total cell number of spleen were significantly elevated (Figure 6C). The percentage and absolute number of donor-derived CD8+ T cells and CD4+ T cells from BM or spleen of the WT mice after anti-Gr1Ab injection were significantly higher than those of the WT mice with PBS treatment (Figure 6D, F). Moreover, the activity of the donor-derived CD8+ T cells and CD4+ T cells was elevated (Figure 6E,G). Together, these results further suggest that immunosuppressive ROS-producing MDSCs at the early stage of post-transplantation period serve as an important source to suppress the proliferation and activity of T cells to prevent hyperacute GVHD.
ROS agonist rescues the hyperacute GVHD phenotype of CGD mice
Because of the ROS production in the CGD mice was defective, we asked whether raising the level of ROS could rescue the CGD mice from obtaining the hyperacute GVHD phenotype. After daily intraperitoneal injection of BSO (a GSH biosynthesis inhibitor(13)) from day 0 to day 10, all of the CGD mice with BSO treatment did not show hyperacute GVHD symptoms at day 3-5 after transplantation, and the conditions of the mice were similar to those of the WT mice at the end of experimentation (Figure S1G). None of the CGD mice with BSO died from day 0 to day 10, and significant difference in survival was seen between BSO-treated CGD mice and those without the treatment (Figure7A-B). Furthermore, BSO treatment caused the size, weight and total cell number of the spleen to significantly reduce, while the number of donor-derived CD3+ T cells (both CD8+ T cells and CD4+ T cells) in the BM and spleen was significantly reduced (Figure 7C). Moreover, the percentage of activated T cells from both BM and spleen of mice after treated with BSO was significantly lower than that of the control group (Figure 7D-G).
Cytokine Release Syndrome and respiratory failure might play a role in the death of hyperacute GVHD.
To date, the cause of hyperacute GVHD symptoms remains unknown. It has been hypothesized that the inflammatory cytokine storm produced early on after the preparative regimen likely contributes to the manifestations(2). To identify the cytokine(s) that might induce the occurrence of hyperacute GVHD, we sacrificed WT and CGD mice with or without BSO treatment at day 3 after allo-HSCT and analyzed the production of multiple cytokines associated with T cells using a commercially available ProcartaPlex Immunoassay Kits. Three independent experiments were conducted. As showing in Table S3, we identified cytokines that were up-regulated by more than 3 fold in the serum of CGD mice with hyperacute GVHD when compared with the WT control; they include IL-1β, IL-2, IL-6, IL-13, IL-27, IFN-γ, IL-12p70, GM-CSF, TNF-α, IL-17A and IL-18. In contrast, daily injection of BSO into CGD mice caused a significant decrease in the level of the aforementioned cytokines (Figure 8A-B; statistical analyses are shown).
To determine the death of hyperacute GVHD, we delivered WT and CGD mice sacrificed at day 3 after receiving allo-HSCT to histological examinations. Nearly all tissues including heart, liver, intestine, kidney, etc. of CGD mice suffering hyperacute GVHD were generally normal (data did not shown). However, different from the lung of WT mice, the histological results of the tissue of CGD mice showed a large number of inflammatory cells infiltration, pulmonary hemorrhage and congestion, and an increased or retained inflammatory secretion in the bronchia (Figure 8C). Moreover, total nucleated cell number was increased in bronchoalveolar fluid of CGD mice (Figure 8D).