The Effectiveness of Rapamycin Combined with Eltrombopag in Murine Models of Immune-Mediated Bone Marrow Failure

Recent research has found that Rapamycin (Rapa) was an effective therapy in mouse models of immune-mediated bone marrow failure. However, it has not achieved satisfactory effect in clinical application. At present, many studies have confirmed that Eltrombopag (ELT) combined with IST can improve the curative effect of AA patients. Then whether Rapa combined with Elt in the treatment of AA will be better than single drug application. In this study, we tested efficacy of Rapa combined with Elt as a new treatment in mouse models of immune-mediated bone marrow failure.

1. Compared with AA group, the whole blood cell count of Rapa+Elt group increased significantly (Figure 1A) (P<0.05). Survival of mice of Rapa+Elt group was significantly higher than that in the Rapa group (p <0.01)(Figure 1B).
2. There was no obvious difference in the numbers of NK cells and their subsets were noted in Rapa group,CsA group and Rapa+Elt group.The expression of NKG2D on peripheral functional NK cells was up-regulated in CsA group, Rapa group and Rapa+Elt group compared with AA group (P<0.05). But there was no significant difference between effect of Rapa and CsA on the function of NK cells (Figure 1C).
3. When Rapa combined with Elt, the expression of CD80 and CD86 are down-regulated more compared to Rapa group, but there is no statistical significance. Although these results suggested that Rapa+Elt had no statistical significance effect on numbers of mDC and expression of its functional molecule CD80 and CD86, the combined therapy still indicated that there is a potential synergy with immunosuppressant on AA mice to improve its outcome (Figure 1D).
4. The results showed that CD4+/CD8+ ratio in CsA group, Rapa group, Rapa + Elt group had an obvious elevation than AA group (all P<0.05). But there were no significant difference among the three groups on the CD4+/CD8+ ratio (Figure 1E,1F). As for INF-gamma, Rapa can reduce the secretion of IFN-γ from CD8+T cells with efficacy similar to that of the standard dose of CsA, and had a better outcome when combined with Elt in bone marrow failure mice (Figure 1E,1G).
5. CsA group, Elt group, Rapa group, Rapa + Elt group showed notable increased ratio of Tregs compared with AA group, among which there were only Rapa group, Rapa + Elt group showed statistical significance(P<0.05). for IL-10/Tregs ratio, Rapa group and Rapa +Elt group were superior to than CsA group(P<0.05) (Figure 1H,1I).
6. Rapa+Elt group and Rapa showed more lower level of IFN-γ compared with CsA group, and there was significant difference in Rapa+Elt group(P<0.05). As for IL-10, IL-12p70, IL-2, IL-6, KC/GRO and TNF-α, the Rapa+Elt group showed more significant effect than Rapa or Elt alone(Figure1J). Thus, Rapa+Elt significantly down-regulated cytokines related to Th1 immune responses, such as IFN-γ, and upregulated cytokines related to Th2 immune responses, such as IL-10. To some extent, Rapa combined with Elt has a synergistic effect with CsA and Rapa alone in AA treatment.

Conclusions

1. In this study, Although Rapa combined with Elt had no significant improvement effect on the number and function of NK cells and their subsets, mDCs, and CD4+/CD8+ ratio in AA mice compared with Rapa alone, the Rapa+Elt can increase the secretion of IL-10 of Tregs and the number of Tregs, but has no significant effect on the number of Treg cells compared to with Rapa alone.
2. Compared with AA group, the level of plasma IFN-γ, IL-2 and TNF-α decreased significantly (P<0.05), but IL-10, IL-4, IL-5 and IL-1β increased significantly in Rapa group(P<0.05). As for IL-10, IL-12p70, IL-2, IL-6, KC/GRO and TNF-α, the Rapa+Elt group showed more significant effect than Rapa alone.
3. intervention treatment with Rapa in combination Elt in the AA mouse model more obviously ameliorated pancytopenia, improved bone marrow cellularity, and extended animal survival in a manner comparable to the standard dose of CsA and Rapa alone. Combination therapy support potential clinical utility in aplastic anemia treatment, which may further improve the efficacy of AA patients.

Keywords：Rapamycin, Eltrombopag, murine models, bone marrow failure