mTOR activity and metabolic reprogramming of CD8+ T cells is impaired under hypoxia and within the multiple myeloma bone marrow.

Novel therapies for multiple myeloma aim to engage anti-tumour functions of T cells. However, evidence indicates these functions are limited within the bone marrow environment. This is relatively hypoxic in health and studies indicate widespread hypoxia in multiple myeloma. In this study, CD8+ T cell responses to stimulation were assessed under hypoxia, which identified that activation, proliferation and interferon-gamma (IFN-γ) secretion were profoundly suppressed, whilst cytotoxicity and tumour necrosis factor-alpha (TNF-α) expression were unaffected. These changes occurred alongside decreased mTOR activity and expression of c-Myc, which drives T cell metabolic reprogramming upon stimulation. Consistently, hypoxic CD8+ T cells demonstrated decreased activation-induced glycolysis and mitochondrial glutamine oxidation. Mechanistically, this was linked to elevated BNIP3 expression under hypoxia and reciprocally decreased abundance of its interaction partner, Rheb, an important mTOR activator. Assessment of BCMAxCD3 bispecific antibody activity confirmed impaired capacity to elicit CD8+ T cell activation, IFN-γ expression, proliferation and altered memory differentiation under hypoxia, although initial target cell killing was unaffected. Finally, assessment of bone marrow CD8+ T cells from multiple myeloma patients identified decreased proliferation, c-Myc and Rheb expression compared to peripheral blood cells, alongside elevated BNIP3, confirming mechanistic features of hypoxic exposure in this environment. Taken together, the findings indicate potential for bone marrow hypoxia to influence efficacy of T cell-directed therapies for multiple myeloma.