Figure 1. Hallmarks of anti-tumor efficacy in adoptively transferred T cells. This figure delineates six interrelated hallmarks that underpin the anti-tumor efficacy of adoptively transferred T cells. Collectively, these characteristics empower T cells with stem-like functions, allowing for the replenishment of cellular populations within the target tissues to combat tumor growth effectively. These features include (i) proliferative capacity, the ability of T cells to undergo multiple rounds of division, expanding their numbers within the tumor microenvironment; (ii) stemness, the capacity of transferred cells to undergo self-renewal, ensuring longevity and sustained presence in the host to maintain anti-tumor activity over time as well as the capacity to differentiate into effector cells; (iii) tumor recognition, which for solid tumors implies polyclonal attack to address tumor heterogeneity; (iv) polyfunctionality, the capacity of cells to produce the diverse cytokines and chemokines to trigger upregulation of antigen presentation on targets and to attract other immune cells to the site; (v) metabolic fitness whereby transferred T cells are utilizing oxidative phosphorylation and fatty acid oxidation but can acquire glycolytic metabolism upon activation in vivo. This integrative portrayal of T cell attributes emphasizes the multifaceted approach required to achieve a robust and lasting anti-tumor response. The hallmarks serve as a framework for the design and evaluation of adoptive T cell therapies, with the potential to guide future advancements in cancer immunotherapy.