Abstract 3192: Aptamers, antibodies and radiotherapy for the treatment of DIPG

Diffuse intrinsic pontine gliomas (DIPGs) is one of the most aggressive pediatric brain tumors. Radiotherapy (RT) constitute the standard of care of these tumors being its therapeutic effect just palliative. There is plenty of evidence that RT is able to activate immune responses through the induction of immunogenic cell death. However, it also elicits immunosuppressive effects and enforces immunological tolerance. The result is that in DIPGs the RT effect is just transitory. In this context, immune costimulatory or inhibitory molecules with the capability to boost the immune effect of RT could be amenable agents to use in combination to treat DIPGs. Agonist antibodies has been widely used in immunotherapy. Aptamers are high-affinity single-stranded nucleic acid ligands that exhibit remarkable affinity and specificity to their targets, comparable or exceeding that of antibodies. 4-1BB is a major costimulatory receptor promoting the survival and expansion of activated T cells. TIM-3 is a negative regulator of lymphocyte function that is involved in T-cell exhaustion. To this end, we examined the effect of RT in combination with either an agonist 4-1BB antibody or an aptamer against TIM-3. Importantly, both combined treatments showed a safe profile. Moreover, combination treatment of 4-1BB agonist antibody or TIM-3 aptamer with RT resulted in a significant improvement in the median survival of mice bearing DIPG orthotopic tumors when compared with single treatment in around 20 days (P=0.001 and P=0.04, for the combination of RT and 4-1BB or TIM-3,respectively). In addition, both combination led to long-term survivors (90 days). Rechallenge experiments in these animals showed the generation of memory against the tumors in both combined treatment. Mechanistic studies performed on day 16 showed an increase in CD8 effector cells, a decrease in T-regulators Foxp3+ cells and an increase in INF-gamma expression suggesting the triggering of an antitumor-immune response. Our data underscore that combination of RT with immune-boosting strategies for DIPGs are worth exploring. Citation Format: Naiara Martinez-Velez, Miguel Marigil, Javier Aristu, Luis Ramos, Fernando Pastor, Ana Patiño-García, Marc García-Moure, Juan Fueyo, Candelaria Gomez-Manzano, Ricardo Diez-Valle, Sonia Tejada, Marta M. Alonso. Aptamers, antibodies and radiotherapy for the treatment of DIPG [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14