Background: Immunotherapies with checkpoint inhibitors have revolutionized the treatment of advanced melanomas. Nonetheless, a subset of patients fail to benefit clinically from these immunotherapeutics, and thus strategies aimed at inducing a favorable inflammatory tumor microenvironment prior to immunotherapy are currently being investigated by means of combination therapies. Bacillus Calmette-Guerin (BCG) is a living attenuated strain of Mycobacterium bovis that stimulates cell-mediated immunity by producing a localized and self-limiting infection. This immunostimulatory agent has shown evidence of anti-tumor activity in several clinical studies with suggested induction of non-specific immune responses, thereby warranting further investigation in a combination therapy setting.

Methods: This phase I study aimed to determine the safety, clinical efficacy and immunogenicity of the administration of intralesional BCG followed by up to four intravenous infusions of ipilimumab (anti-CTLA4) (NCT01838200). Patients with histologically confirmed stage III/IV metastatic melanoma with at least one injectable lesion, and no prior immunotherapy or autoimmune disease were recruited for this study. Patients received up to four 3 mg/kg ipilimumab infusions every 3 weeks from 36 days after intralesion BCG injection containing 0.16 - 0.64 x 106 colony-forming units. Serum samples were collected prior to each therapeutic intervention as a means of investigating immunogenicity. Humoral immune responses were investigated using the Immunome protein array, a high-content array with 1627 full-length, correctly folded, and fully functional immobilized proteins that enables the interrogation of the depth and breadth of the immune response.

Results: 5 patients were enrolled in this study, with 2 displaying high grade immune-related adverse events (irAEs) (grade 3 hepatitis and grade 4 colitis), which led to the early discontinuation of this trial. These irAEs were in accordance with ipilimumab-related reported toxicities. Furthermore, all patients displayed evidence of clinically progressive disease, with no evident therapeutic benefit. Patients displaying irAEs were characterized by drastic increases in their antibody repertoire towards tumor and self-antigens, when compared to those with no reported irAEs (42% vs. 3% of array content, respectively). This high order of de novo and induced antibodies was detected in time points preceding clinical detection of these high-grade toxicities. However, these antibody profiles did not overlap between patients, with unique antigen targets detected in each patient, suggesting evidence of a systemic B-cell deregulation, rather than an induced specific anti-tumor response.

Conclusions: Intralesional BCG followed by ipilimumab therapy was not well tolerated in advanced melanoma patients, and showed no evidence of clinical benefit. Investigating humoral immunity may offer a means to detect the early onset of irAEs in an immunotherapeutic clinical trial setting.

Citation Format: Jessica Duarte, Katherine Woods, Andreas Behren, Jonathan Cebon. A phase I study of intralesional Bacillus Calmette-Guerin (BCG) followed by ipilimumab therapy in patients with advanced metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT099. doi:10.1158/1538-7445.AM2017-CT099