Few therapeutic options have been made available for treating
central nervous system tumors, especially upon recurrence. Recurrent
medulloblastoma is uniformly lethal with no approved
therapies. Recent preclinical studies have shown promising results for eradicating various solid
tumors by targeting the overexpressed
immune checkpoint molecule, B7-H3. However, due to several
therapy-related toxicities and reports of tumor escape, the full potential of targeting this pan-
cancer antigen has yet to be realized. Here, we designed and characterized bispecific chemically self-assembling nanorings (CSANs) that target the
T cell receptor, CD3ε, and
tumor associated
antigen, B7-H3, derived from the humanized 8H9
single chain variable fragment. We show that the αB7-H3-αCD3 CSANs increase T cell infiltration and facilitate selective cytotoxicity of B7-H3+
medulloblastoma spheroids and that activity is independent of target cell MHC class I expression. Importantly, nonspecific T cell activation against the ONS 2303
medulloblastoma cell line can be reduced by tuning the valency of the αCD3 targeted monomer in the oligomerized CSAN.
Intraperitoneal injections of αB7-H3-αCD3 bispecific CSANs were found to effectively cross the blood-
tumor barrier into the brain and elicit significant antitumor T cell activity intracranially as well as systemically in an orthotopic
medulloblastoma model. Moreover, following treatment with αB7-H3-αCD3 CSANs, intratumoral T cells were found to primarily have a central memory phenotype that displayed significant levels of characteristic activation markers. Collectively, these results demonstrate the ability of our multivalent, bispecific CSANs to direct potent antitumor T cell responses and indicate its potential utility as an alternative or complementary
therapy for immune cell targeting of B7-H3+
brain tumors.