TABLE 1.

Key molecules differentially expressed by T_RM compared to circulating T-cells.

Category	Marker	Observations1	Function	References (including reviews)
Transcription Factors	T-bet	Downregulated in TRM	Downregulation required for TGF-β responsiveness	[50, 64, 67]
	Eomes	Downregulated in TRM	Downregulation required for TGF-β responsiveness	[50, 64, 67]
	KLF2	Downregulated in TRM	Downregulation required for inhibition of S1PR1 and inhibition of tissue egress	[59, 64, 73]
	Hobit, Blimp1	Upregulated in mouse TRM	Loss prevents TRM development in mice; unclear if this holds true in humans	[64, 74]
Adhesion/Migration	CD69	Expressed by 50–90% of TRM; varies between tissues	Downregulates S1PR1, preventing tissue egress	[59, 64, 73, 74, 75]
	CD103	Expressed mainly by oral-GI tract TRM	Mucosal tethering integrin; expression varies between tissues	[59, 60, 64, 73, 74, 75]
	S1PR1	Downregulated in TRM	Required for tissue egress	[59, 64, 68, 73, 74, 75]
	CD49a	Upregulated in TRM	Adhesion marker	[64, 73]
	CCR7	Downregulated in TRM	Required for lymph node homing; expressed on central memory cells	[59, 64, 73, 74]
	CD62L	Downregulated in TRM	Required for lymph node homing; expressed on central memory cells	[59, 64, 73, 74]
Inhibitory Molecules	PD-1	Upregulated in TRM	Inhibits T-cell activation; potentially limits inflammation-induced tissue damage	[73, 74]
	IL-10	Upregulated in TRM		[73]
Activation-induced responses	IL-2	Expressed by higher proportions of stimulated TRM vs non-TRM	Stimulates NK cells and bystander memory CD8+ T-cells	[65, 71, 73]
	IFN-γ		Indirectly promotes recruitment of other immune cells (T, B); Induces broad innate antiviral responses	[65, 69, 71, 73, 74]
	Perforin	Expressed by higher proportions of TRM vs non- TRM, but also by higher proportions of blood vs tissue T-cells	Cytolytic capacity greater in TRM vs non-TRM from same tissues; greater in blood vs tissue T-cells	[50, 53, 74]

¹as compared to expression in circulating or non-resident T-cells.