Low CD8 T Cell Counts Predict Benefit from Hypoxia-Modifying Therapy in Muscle-Invasive Bladder Cancer

BACKGROUND: As hypoxia can drive an immunosuppressive tumour microenvironment and inhibit CD8+ T cells, we investigated if patients with low tumour CD8+ T cells benefitted from hypoxia-modifying therapy.

METHODS: BCON was a phase III trial that randomised patients with muscle-invasive bladder cancer (MIBC) to radiotherapy alone or with hypoxia-modifying carbogen plus nicotinamide (CON). Tissue microarrays of diagnostic biopsies from 116 BCON patients were stained using multiplex immunohistochemistry (IHC) with the markers CD8, CD4, FOXP3, CD68 and PD-L1, plus DAPI. Hypoxia was assessed using CA9 IHC ( n = 111). Linked transcriptomic data ( n = 80) identified molecular subtype. Relationships with overall survival (OS) were investigated using Cox proportional hazard models.

RESULTS: High (upper quartile) vs. low CD8 T cell counts associated with a better OS across the whole cohort at 16 years (n = 116; HR 0.47, 95% CI 0.28-0.78, p = 0.003) and also in the radiotherapy alone group ( n = 61; HR 0.39, 95% CI 0.19-0.76, p = 0.005). Patients with low CD8+ T cells benefited from CON ( n = 87; HR 0.63, 95% CI 0.4-1.0, p = 0.05), but those with high CD8 T cells did not ( n = 27; p = 0.95). CA9 positive tumours had fewer CD8+ T cells ( p = 0.03). Prognostic significance of low CD8+ T cells in the whole cohort remained after adjusting for clinicopathologic variables. Basal vs. luminal subtype had more CD8+ cells ( p = 0.02) but was not prognostic ( n = 80; p = 0.26). Exploratory analyses with other immune markers did not improve on findings obtained with CD8 counts.

CONCLUSIONS: MIBC with low CD8+ T cell counts may benefit from hypoxia-modifying treatment.