Background Sensitization to HLA antigens poses significant obstacles for successful transplantation and increase risk for antibody-mediated rejection (ABMR). IL-6/IL-6R interactions are known to have a significant stimulatory effect on Th17 cells and IL-6 also is an important terminal growth factor for B-cells and plasma cells. Using a mouse model of HLA-A2 sensitization, we found that targeting the IL-6R using a mousenized rat-anti-mouse IL-6R mAb (mMR16-1) is effective in suppressing de novo donor-specific antibody (DSA) responses.

Methods C57BL/6 mice were pre-sensitized with skin allograft (SG) from a HLA.A2 transgenic mouse. At Day 70 the pre-sensitized mice were re-stimulated with a second HLA.A2+ skin graft and divided into 4 different treatment groups, including (1) mMR16-1, (2) control antibody, (3) anti-CD20 and (4) IVIG. Recall alloantibody responses were monitored weekly for 4 weeks by measurement of serum anti-HLA.A2 antibodies. T, B and plasma cells and their expression of membrane-bound IL-6R alpha and co-receptor pg130 (CD130) were analyzed in FACS. Soluble IL-6R and IL-6 were measured in ELISA.

Results All the pre-sensitized mice had moderate levels (143.9+-47 MFI) of anti- HLA-A2 (DSA) IgG prior to 2nd skin grafting. Re-sensitization in the control group (n=6) resulted in a recall responses featured by a surge of anti-HLA.A2 IgG at day 14 (633+-52 MFI) and a peak at day 28 (827+-110 MFI). mMR16-1 significantly reduced DSA IgG levels (336+-116 MFI at day 14 and 530+-136 MFI at day 28, P=0.003, P=0.015, respectively, as compared to the control). In contrast, anti-CD20 treatment resulted in no significant reduction in DSA IgG levels (472+-274 MFI at day 14, P=0.05 as compared to control) despite >90% B220+ cell depletion in the spleens. Human IVIG had no effect on DSA IgG levels in the re-sensitized mice (826+-368 MFI, P>0.05). FACS analysis showed that anti-CD20 significantly depleted B220+ B cells in the spleens and BM, but had no effect on CD138+/CD38+ plasmablasts. On the other hand, mMR16-1 has no depleting effect on splenic T-cells, B-cells and CD11b+ monocyte/macrophages in the spleens. However, there was a reduction in CD138+ plasma cells in the BM.

Conclusion Antibody therapy targeting the IL-6/IL-6R pathway reduces recall alloantibody responses in a robust model of allosensitization. Although unclear, reduction in BM plasma cell populations may be important mechanistically.

« Back to 2013 American Transplant Congress