Microrna-191 Regulates T-Cell Clonal Expansion during Graft-Versus-Host Disease

Allogeneic hematopoietic cell transplantation is a potentially curative treatment choice for a wide variety of hematological malignancies. However, graft-versus-host disease (GVHD), which is mediated by donor alloreactive T cells, limits the success of this procedure. Previous studies have demonstrated that several microRNAs (miRs) modulate graft-versus-host disease. miR-191 was previously reported to be able to support T cell survival after TCR stimulation. We hypothesize that miR191 regulates T cell response during GVHD.

To test this hypothesis, we first studied miR-191 expression in alloreactive T cells. The result demonstrated that miR-191 was up-regulated in donor T cells isolated from murine GVHD recipients, suggesting that miR-191 may play a role in GVHD induction. We further studied the role of miR-191in GVHD using miR-191 deficient T cells (KO). Lethally irradiated (8.5 Gy) BALB/c mice were injected intravenously with 1×10⁷ T cell-depleted bone marrow (TCDBM) cells along with 1×10⁶ purified T cells from wild-type (WT) or KO mice, which are in C57BL/6 background. Interestingly, all recipients in the WT group died within 35 days after transplantation, while only one out of ten animals died in the KO group during an observation period of 56 days. Body weights and clinical scores were also improved in KO T cell recipients when compared with the WT controls. Similar results were also observed in a second GVHD model (C57BL/6→C3H/HeJ).

To understand the mechanism by which miR-191 KO T cells have decreased ability to mediate GVHD, we first measured the ability of KO T cells to respond to alloantigens in vitro in a mixed lymphocytes reaction assay. Dramatically decreased alloresponse was observed with KO T cells as compared with WT T cells. Similarly, decreased clonal expansion was observed in KO T cells in vivo upon challenge with alloantigens as measured by bioluminescent imaging (Figure 1A). These results were further supported by data from a co-transfer experiment, in which equal numbers of WT and KO T cells were transplanted into the same GVHD recipient. At day7 after transplantation, KO T cells showed significantly reduced expansion in the spleen and liver compared with WT T cells. Reduced alloresponses mediated by KO T cells may not due to decreased proliferative capability directly as an in vivo carboxyfluorescein succinimidyl ester (CFSE) assay showed a comparable cell division between WT and KO T cells upon challenge with alloantigens. Rather, increased cell death is responsible for decreased alloresponse observed in KO T cells because dramatically increased number of dead cells was observed in KO group compared with WT group upon response to alloantigens in vitro and vivo.

To determine the genes that are regulated by miR-191, we did a screening based on the prediction. Humans and mice share more than 100 predicted targets for miR-191. We chose top 20 of these targets for RT-qPCR screening. The result demonstrated that Taf5 was a target gene of miR-191. Expression of TAF5 protein was down-regulated in activated KO T cells when compared with the WT T cells.

Finally, we investigated whether miR-191 KO T cells preserve graft-versus-leukemia effects. 1×10⁶ T cells from WT or KO mice were transplanted into lethally irradiated BALB/c mice along with 1×10⁷ TCDBM cells and 1×10⁵ host-type BCL-1 cells. While all recipients that received only TCDBM and tumor cells developed lethal leukemia/lymphoma, none of WT and KO T cells recipients developed tumor.

In conclusion, our findings reveal a critical role of miR-191 during GVHD process and demonstrate that miR-191 is a novel therapeutic target for GVHD.

Figure 1

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Figure 1

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