Abstract LB-096: Induction of systemic immunity through single-site intratumoral CD40 activation and checkpoint blockade eradicates melanoma in the brain
Authors: Singh Manisha , Vianden Christina , Diab Adi , Hwu Patrick , Overwijk Willem W. 
Published: July 2016

Background: Melanoma brain metastases (MBM) are a rapidly growing clinical problem with up to 60% of melanoma patients developing MBM over the course of their disease. Locoregional treatment with surgery, radiotherapy, radiosurgery, and newer drug classes such as checkpoint inhibitors and targeted agents against BRAF-mutation melanoma have shown limited effectiveness against MBM (Lancet 2015; 16: e486-97). MBM patients continue to have poor clinical outcomes and life expectancies of only 3-7 months. Thus, there is a significant unmet need for effective therapies for MBM patients. Direct intratumoral administration of a non-replicating adenovirus encoding a CD40-targeting chimeric immunostimulatory protein (ISF35) leads to generation of potent melanoma-specific T cells. When combined with checkpoint inhibitors, ISF35 generates synergistic systemic anti-melanoma immunity that eradicates both injected and uninjected distant melanoma with 40% of mice cured using a B16 model. Based on this evidence of systemic activity, we hypothesized that ISF35/checkpoint inhibitors combination treatment may have systemic activity against MBM.

Methods: A MBM mouse model was developed using luciferase-expressing B16 (B16-Luc). B16-Luc cells were subcutaneously (s.c.) implanted in the right flank of C57BL/6 mice 12 days prior to treatment. B16-Luc cells were then injected into the brain four days prior to treatment. Following tumor establishment at both sites, ISF35 was injected intratumorally in the right flank tumor on days 0, 4, 9, and 14. Simultaneously, anti-PD1 and anti-CTLA-4 antibodies were systemically administered.

Results: Intratumoral administration of ISF35 in combination with anti-PD-1 and anti-CTLA-4 significantly increased (p&lt;0.01) mouse survival compared to untreated mice. Median survival was not reached for the ISF35 plus checkpoint combination, was 10 days for untreated mice, 26 days for ISF35 monotherapy, and 17 days for anti-PD-1/anti-CTLA-4 combination therapy. ISF35/anti-PD-1/anti-CTLA-4 combination treatment of s.c. tumors resulted in complete and durable abscopal regression of brain tumors as assessed by bioluminescent imaging 30 days following initiation of treatment. In contrast, brain melanoma tumors continued to grow in the ISF35 monotherapy or anti-PD-1/anti-CTLA-4 treatment groups. The systemic anti-tumor activity of ISF35/anti-PD-1/anti-CTLA-4 was associated with greater production of melanoma-specific CD8 T cells with an activated phenotype, including upregulated PD-1 surface expression.

Conclusions: These results suggest ISF35 may improve the effectiveness of checkpoint inhibitors therapy for metastatic melanoma, including in the brain.

Citation Format: Manisha Singh, Christina Vianden, Adi Diab, Patrick Hwu, Willem W. Overwijk. Induction of systemic immunity through single-site intratumoral CD40 activation and checkpoint blockade eradicates melanoma in the brain. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-096.