G-CSF mobilized peripheral blood has emerged as the dominant source of stem cells for allogeneic stem cell transplantation. G-CSF modulates T cell function and Suppressor of Cytokine Signaling-3 (SOCS3) is the major regulator of signaling by this cytokine, although the downstream effects in vivo remain unclear. We have therefore examined the effect of SOCS3 in the well established B6 → B6D2F1 murine model of acute GVHD directed to major histocompatibility antigens. Using SOCS3−/Δvav mice in which SOCS3 deficiency is restricted to the haematopoietic compartment we transplanted splenocytes from G-CSF mobilized wild-type (WT) or SOCS3−/Δvav donors and demonstrated that the absence of SOCS3 within the graft accelerated GVHD (median survival 23 vs. 39 days, P=0.04). By using SOCS3−/ΔLysM and SOCS3−/Δlck donors in which SOCS3 deficiency was restricted to the myeloid or T cell lineage respectively we confirmed SOCS3 deficiency enhanced GVHD via effects only within the donor T cell (median survival 19 vs. 35 and 39 days in SOCS3−/Δlck vs. WT and SOCS3−/ΔLysM, P<0.0001). This protective effect of SOCS3 was also seen in the absence of G-CSF mobilization since bone marrow and purified donor T cells from SOCS3−/Δvav donor mice significantly accelerated GVHD mortality (median survival 29 vs. 44 days, P=0.04). In mixing experiments this acceleration of GVHD was again seen only when the donor T cell was SOCS-3 deficient.

SOCS3−/Δlck donor T cells underwent enhanced alloantigen dependent proliferation after transplantation as determined by CFSE dilution and demonstrated increased IL-10, IL-17 and IFNγ generation but reduced IL-4 secretion. In contrast no effects were seen in IL-6 and TNF secretion, or CD8 cytotoxicity against host-type targets. Consistent with the increased mortality, SOCS3−/Δlck donor T cells induced significantly more severe gastrointestinal GVHD as determined by semi-quantitative histopathology (GI tract scores 18 ± 1.7 vs. 10.2 ± 1.1, P=0.008). Blockade of the IL-10 receptor or IL-17 neutralization from the day of transplant or after the initiation of GVHD failed to attenuate the enhanced GVHD mortality induced by SOCS3−/Δlck donor T cells. The suppression of acute GVHD by SOCS3 is thus consistent with its ability to suppress IFNγ generation by the donor T cell, a cytokine which we have shown to be a key and direct mediator of GVHD within the GI tract (

Burman A et al,

These studies highlight the previously unrecognized role of the SOCS3 molecule in regulating alloreactive T cell responses and suggest that the delivery of small molecule SOCS3 agonists may prove to be useful for the inhibition of Th1 dependent acute GVHD.

Disclosures: No relevant conflicts of interest to declare.

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