PDCD1 and neoplasm: Interestingly, upon T-cell activation, the costimulatory molecule CD226 was reported to be one of the most enriched VAV1 interactors.40 Significantly less CD96+CD8+ T cell infiltration was observed in Bcl9–/– mice bearing CT26 tumor cells suggesting that Bcl9 deficiency may promote T cell activation and potentially enhance responsiveness to PD-1 checkpoint blockade (Fig. 6a).