The safety of allogeneic innate lymphocyte therapy for glioma patients with prior cranial irradiation

The standard treatment of high-grade glioma presents a combination of radiotherapy, chemotherapy and surgery. Immunotherapy is proposed as a potential adjunct to standard cytotoxic regimens to target remaining microscopic disease following resection. We have shown ex vivo expanded/activated gamma delta T cells to be a promising innate lymphocyte therapy based on their recognition of stress antigens expressed on gliomas. However, successful integration of gamma delta T cell therapy protocols requires understanding the efficacy and safety of adoptively transferred immune cells in the post-treatment environment. The unique features of gamma delta T cell product and the environment (hypoxia, inflammation) can affect levels of expression of key cell receptors and secreted factors and either promote or hinder the feasibility of gamma delta T cell therapy. We investigated the potential for the gamma delta T cells to injure normal brain tissue that may have been stressed by treatment. We evaluated gamma delta T cell toxicity by assessing actual and correlative toxicity indicators in several available models including: (1) expression of stress markers on normal primary human astrocytes (as surrogate for brain parenchyma) after irradiation and temozolomide treatment, (2) cytotoxicity of gamma delta T cells on normal and irradiated primary astrocytes, (3) microglial activation and expression of stress-induced ligands in mouse brain after whole-brain irradiation and (4) expression of stress-induced markers on human brain tumors and on normal brain tissue. The lack of expression of stress-induced ligands in all tested models suggests that gamma delta T cell therapy is safe for brain tumor patients who undergo standard cytotoxic therapies.