Is arsenic trioxide effective in treating aGvHD? Results from an in vitro study

The severe consequences of acute graft-versus-host disease (aGvHD) following allogeneic hematopoietic stem cell transplantation are driving scientists to investigate new therapeutic options. The pathogenesis of aGvHD involves the activation of host antigen-presenting cells, donor T cells, and subsequent inflammation. Macrophages have two major polarization pathways, M1 and M2, and the imbalance of these has been found in many immune disorders. Macrophages have also been shown to be associated with aGvHD pathogenesis, but there is a lack of studies that demonstrate the involvement of macrophage polarization.

Arsenic trioxide (ATO) is an environmental toxic agent that is associated with cancer development. Recently, it has been identified as a potent treatment option for patients with promyelocytic leukemia. Xiao Liu and colleagues have conducted a preclinical study to investigate the role of macrophage polarization in aGvHD and ATO as an option for aGvHD management. Here, we summarize the results Liu presented during the Virtual Edition of the 25th European Hematology Association (EHA) Annual Congress.^1,2

Study design¹

Macrophage polarization was analyzed in the macrophages from the colon tissue of mice with or without GvHD.

• Immunofluorescence: F4/80, inducible nitric oxide synthase (iNOS), CD206
• Immunohistochemistry: tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-10, and transforming growth factor (TGF)-β

Peripheral blood from patients with aGvHD was used to isolate macrophages which were cultured in the presence or absence of ATO, and then analyzed for expression of CD86, CD80, CD163, and CD206.

To investigate the effect of ATO in GvHD mouse models:

• Mice with GvHD were injected with 1 µg/kg ATO, 2, 4, 6, 8, and 10 days after allogeneic transplantation, and the clinical signs of GvHD and overall survival were observed
• Skin, liver, intestine, and colon cells from mice were tested for pathological damage and macrophage polarization (expression of CD68, CD86, CD80, CD163, and CD206)

Results¹

The evaluation was carried out in three mice groups: (i) donor mice (bone marrow [BM] group), (ii) mice with GvHD but not treated with ATO (GvHD group), and (iii) mice with GvHD treated with ATO (ATO group).

• The ATO group demonstrated an increased survival and reduced organ damage with significantly lower GvHD scores in the skin and colon, compared to the GvHD group
• In colon samples, the GvHD group demonstrated higher numbers of M1 macrophages (F4/80⁺iNOS⁺ cells expressing TNF-α and IL-1β) compared with the BM group. In the ATO group, the imbalance was re-adjusted with an increased rate of M2 macrophages similar to the BM group
• In the murine macrophage cell line RAW264.7, ATO induced macrophage polarization towards the M2 phenotype with increased CD206 expression and reduced CD86 expression
• In peripheral blood cells from patients with aGvHD, ATO induced macrophage polarization towards the M2 phenotype (reduced CD86 and CD80 expression, increased CD163 and CD206 expression)

Conclusion

The in vitro data suggest that aGvHD is accompanied by M1-type macrophage polarization, which may indicate another mechanism for aGvHD development. In animal GvHD models and peripheral blood from patients with aGvHD, ATO is able to revert the M1/M2 imbalance and may therefore have potential in the treatment of aGvHD that needs further evaluation in future studies.