HHLA2 and neoplasm: Given its emerging role of suppressing tumor immune responses with possible different immune evasion mechanisms from PD-1/PD-L1 pathways (Zang et al., 2010; Janakiram et al., 2012), there has been a great interest for exploration of HHLA2 as a therapeutic immune target (Jeon et al., 2014; Janakiram et al., 2015b).