Relapse/progression of malignancy (RM) is an important cause of treatment failure and death following allogeneic hematopoietic stem cell transplantation (allo-HCT). CTLA-4 is an important negative regulator of effector T-cell activation. CTLA-4 inhibition has demonstrated potent anti-cancer effects in animal models, and in patients with some solid tumors. CTLA-4 blockade following allo-HCT may potentially augment graft-versus-malignancy but GVHD may also possibly be increased. We report the safety and preliminary efficacy of a dose-escalation study of a neutralizing human monoclonal antibody targeting CTLA-4 (ipilimumab) in patients with RM following allo-HCT. Eligibility criteria included allo-HCT ≥90 days previously, > 50% donor T-cell chimerism, no prior grade 3/4 GVHD, no prophylaxis/therapy for GVHD for ≥ 6 weeks. Patients received a single dose of ipilimumab over 90 min. DLI at a dose of 5 × 10e6 CD3 cells/kg was allowed 8 weeks following ipilimumab if no GVHD occurred and RM was present. A total of 29 patients were treated at four centers (23M, 6F; median age 43 (21–65); Hodgkins disease [HD] =14 Myeloma [MM]=6, CML=2, CLL=2, AML=2, NHL=1, Renal Ca =1, Breast Ca=1; 19 related donors, 10 unrelated; 6 myeloablative, 23 RICT).(4 at dose-level 1 [DL1] 0.1 mg/kg, 3 at 0.33 mg/kg [DL2], 4 at 0.66 mg/kg [DL3], 3 at 1.0 mg/kg [DL4] and 15 at 3.0 mg/kg [DL5]). Eight patients had failed prior DLI. Median time between BMT and ipilimumab was 366 d (125–2368). Dose-limiting toxicity was not encountered. No patient developed clinically significant GVHD within 90 days following ipilimumab alone. Three possible immune adverse events were documented: grade 3 polyarthropathy 14 weeks following ipilimumab, and 6 weeks post DLI, which resolved with corticosteroid therapy, (AML, DL1); grade 1 hyperthyroidism with thyroid-stimulating antibody 6 weeks post ipilimumab (CLL, DL3). Grade 2 pneumonitis responsive to corticosteroids (HD, DL5). Ten patients received DLI after ipilimumab. Three patients developed objective evidence of disease response after ipilimumab alone: PR in a patient with mantle cell NHL lasting 3m [DL4]; ongoing CR in a two patients with HD [DL5]. Two of these patients had failed prior DLI. Three additional patients demonstrated possible anti-cancer effects (MR in a HD patient, reduction of PB and BM blasts in AML, DL1; maintenance of molecular remission in a CML patient given ipilimumab alone for 3.5 yrs despite stopping imatinib, DL1). This study shows that doses of ipilimumab (up to 3.0 mg/kg) can safely be administered to patients with RM following allo-HCT without inducing/exacerbating GVHD while inducing regressions of malignancy including durable CR in some patients.

Author notes

Disclosure:Employment: Dr Lowy is an employee of Medarex Inc. Ownership Interests:; Dr Ball is a stockholder in Medarex Inc.