Table 4 Memory T cell subsets

T_CM (T central memory) cell

CD62L⁺, CCR7⁺

Other markers include CD27⁺, CX₃CR1⁻, CD45RO⁺ and CD45RA⁻

CD44^hi, CD62L⁺

Other markers include CD122^hi, TCF1⁺, CCR7⁺, CD103⁻, CX₃CR1⁻

Memory T cells that recirculate between lymph and blood, can cross resting HEVs

Often maintain the ability to proliferate and differentiate into, for example, T_EM and T_RM cells

T_EM (T effector memory) cell

CCR7⁻, CD45RA⁻

Other markers include CD62L⁻, but cell surface CD62L may get altered during processing

CD44^hi, CD62L⁻

Reliable CCR7 staining reagents are less readily available

Memory T cells that lack key homing receptors (CD62L, CCR7) that enable crossing of most resting HEVs in lymph nodes

Describes a wide range of differentiation states and biological properties

T_EMRA (CD45RA⁺ T effector memory) cell

CCR7⁻, CD45RA⁺

Other markers include CD27⁻, CX₃CR1^hi, CD57⁺

Often poised for rapid cytolytic activity and express granzyme B and perforin

ND

A subset of human T_EM cells that express CD45RA

Not applied to mice

T_RM (T resident memory) cell

KLF2^low, CD69⁺, CD62L⁻, CCR7⁻

Also CD103⁺ TCF1^low, CD49a⁺, CD101⁺ and CXCR6⁺

Assays include organ transplantation and comparing TCR sequences in different organs

KLF2^low, CD69⁺, CD62L⁻, CCR7⁻

Often P2RX7⁺

Also CD103⁺ TCF1^low, CD49a⁺, CD101⁺ and CXCR6⁺

Assays include organ transplantation, evaluating migration after transfer into blood, comparing TCR sequences in different organs, parabiosis surgery, and photoconversion

Memory T cells that reside within a single tissue or organ without recirculating through blood

ExT_RM cell

ND

Phenocopies T_EM or T_CM cells by most markers

May retain elevated CD43 (1B11 antibody clone)

A T_RM cell that differentiated and rejoined the circulation

May retain epigenetic imprint of tissue-specific residence programmes

T_PM (T peripheral memory) cell

CD45RA⁻, CCR7^int, CD27⁺

CX₃CR1^int, CCR7^int, CD27⁺

Used to describe memory T cells that recirculate between non-lymphoid tissues and blood

Currently, there are no definitive markers

T_SCM (T stem cell memory) cell

CD95⁺, CCR7⁺, CD27⁺, CD28⁺, CD45RA⁺, Eomes⁻

CD44^low, CD62L⁺, CD122⁺, CD27⁺, Sca-1⁺, CD127⁺

Relatively rare subset of less differentiated memory T cells

Retains the capacity to self-renew and differentiate into other T cell subsets

T_SCM share many markers with naive T cells