Cytokine Gene Expression in Peripheral Blood Mononuclear Cells Points to Interleukin-10 as an Inhibitor of Alloreactivity Following Hematopoietic Cell Transplantation with Nonmyeloablative Conditioning.

Cytokines are thought to play an important role in the pathophysiology of Graft-versus-Host disease (GVHD). To study the relationship between cytokines and GVHD, we obtained peripheral blood mononuclear cells (MNC) from 21 patients with hematologic malignancies and their human leukocyte antigen identical sibling donors before and sequentially after hematopoietic cell transplantation (HCT) with nonmyeloablative conditioning. The MNC were cultured for 72 hours either alone or in mixed lymphocyte cultures with irradiated MNC of recipient, donor or HLA-mismatched third-party origin. The gene expression of interleukin (IL)-2, IL-4, IL-10, IL-18, tumor necrosis factor-α and transforming growth factor-β in each culture was then measured by real-time quantitative RT-PCR. The composition of the responder MNC differed between patients and donors and changed following HCT with a possible influence on the results. Early after transplant (day +14) the IL-10 mRNA level in response to recipient or donor antigens was higher in patients who did not develop clinical significant acute GVHD when compared to the level in patients who subsequently developed acute GVHD grades II–IV (p=0.005 and p=0.004, respectively). The IL-10 mRNA level on day +14 was highly correlated to the pre-transplant mRNA level of the recipient MNC but not to the level of the donor MNC, suggesting that the IL-10 mRNA detected on day +14 originated from responder cells of recipient origin. A higher IL-10 mRNA level was found in MNC obtained pre-transplant from recipients who progressed or relapsed after the transplant when compared to the level in patients who did not, p=0.03. In conclusion we find that detection of cytokine gene expression in MNC by real-time quantitative RT-PCR is an interesting tool in the study of the immune responses following HCT. A number of factors are likely to influence the results obtained and in this study we have identified the composition of the MNC as such a factor. Our results suggest a role for IL-10 as an inhibitor of alloreactivity following nonmyeloablative HCT. This inhibition may have dual effects by limiting the degree of acute GVHD and at the same time increase the probability of relapse.