The Addition Of Interleukin-6 Inhibition To Standard Gvhd Prophylaxis Prevents Acute Gvhd: Interim Results Of a Phase I/II Clinical Study

We and others have demonstrated the dysregulation of interleukin-6 (IL-6) early after experimental bone marrow transplantation (BMT) and protection from acute GVHD following the administration of an anti-IL-6 receptor (IL-6R) antibody. In these models, where GVHD prophylaxis is not administered, systemic IL-6, IFNγ and TNF levels peak 7 days after BMT before returning to baseline by the third week. We have determined cytokine dysregulation in a large clinical cohort of allogeneic stem cell transplant (SCT) recipients conditioned with myeloablative Cy/TBI (12 Gy, n = 25) or reduced intensity Flu/Mel (120mg/m², n = 25) receiving standard GVHD prophylaxis with cyclosporine and MTX (d 1 at 15mg/m², d 3, 6, 11 at 10mg/m²). IL-6 levels rose from pre-transplant levels of 6.4 ± 0.7 pg/ml to a peak of 58.8 ± 8.8 pg/ml at day 7 (P < 0.0001) with a fall at day 14 to 39.0 ± 12.5 pg/ml (P < 0.0001) and return to baseline by day 30 (6.2 ± 0.9 pg/ml), consistent with the preclinical data. IL-6 dysregulation was not different in recipients of matched sibling or unrelated donor grafts but was proportional to the intensity of conditioning (day 7 levels after Cy/TBI vs. Flu/Mel: 83.3 ± 12.2 pg/ml vs. 31.0 ± 10.1 pg/ml, P< 0.0001). In contrast to preclinical mouse data, no systemic increases were seen in any other cytokine including IFNγ, TNF, IL-17, IL-4, IL-13 and IL-10.

We thus initiated a phase I/II study whereby a human neutralizing monoclonal antibody (mAb) against the IL-6R was administered on day -1 to patients receiving Cy/TBI or Flu/Mel conditioned allogeneic SCT from HLA (10/10)–matched sibling or unrelated donors with standard cyclosporine/MTX GVHD prophylaxis. There was no T cell depletion. The primary endpoint was the incidence of grade II-IV acute GVHD and the study has achieved its planned enrollment (n = 48). There was no toxicity attributable to IL-6R antibody administration. Pharmacokinetic analysis confirmed high levels of IL-6R Ab at day 3 (mean 64.7 ug/ml) which persisted in all patients 3 weeks after BMT (mean = 9.8 ug/ml) and remained above the level of detection (0.1ug/ml) in 75% of patients at day 30 (mean = 1.9 ug/ml). IL-6 levels were dramatically increased (relative to baseline) in patients receiving antibody due to the inability to excrete the inactive IL-6 – soluble IL-6R antibody complex (peak IL-6 levels at day 7 = 773.6 ± 207.9 pg/ml; P < 0.0001) and remained increased at day 30 (60.9 ± 24.4 pg/ml; P < 0.0001), returning to baseline by day 60 (9.5 ± 1.7 pg/ml), consistent with antibody clearance. Soluble IL-6R levels also rose over the first month of SCT and levels at day 30 correlated with residual antibody levels (r² = 0.72, P = 0.02). Neutrophil (> 0.5x10⁹/L) and platelet (> 20x10⁹/L) recovery was normal relative to a matched untreated control cohort at a median of 16 and 18 days respectively. Donor chimerism and immune reconstitution (conventional T, regulatory T and B cells) was equivalent at day 30 in recipients of IL-6R inhibition versus the control cohort. In contrast, changes in innate immunity were seen in patients receiving IL-6R inhibition with increases in plasmacytoid DC (P = 0.002), CD1c⁺ conventional DC (P = 0.04) NKT cells (P =0.03) and marked reductions in inflammatory (CD14⁺CD16⁺) monocytes (P < 0.0001). Transcriptional profiling of T cell subsets is underway. With 36 patients evaluable (beyond day 100, median follow up of 297 days), the incidence of grade II-IV GVHD is 11.1% in recipients of IL-6R inhibition versus 39.6% in the matched (n = 53) control cohort (P = 0.004). The incidence of grade III/IV acute GVHD is 5.6% in recipients of IL-6R inhibition versus 20.8% in the control cohort (P = 0.045). Protection from grade II-IV acute GVHD was noted in patients receiving both Cy/TBI (7.7% vs. 40.7%, P=0.045) and Flu/Mel conditioning (13.0% vs. 38.5%, P = 0.044). Rates of CMV reactivation were very low in the IL-6R neutralized patients (16.7% vs. 35.8% in controls, P = 0.04), likely due to the prevention of acute GVHD and its’ consequent therapy. At one year, the relapse incidence and disease free survival in patients receiving IL-6R inhibition versus the control cohort is 21.2% vs. 30.0% (P = 0.28) and 73.1% vs. 62.4% (P = 0.14) respectively. IL-6 is thus the principal inflammatory cytokine dysregulated after clinical allogeneic SCT and its inhibition appears to offer profound protection from acute GVHD despite robust immune reconstitution, without compromise of the GVL effect.