T cells play a major role in anti-tumour immunity, particularly in cutaneous squamous cell carcinoma (cSCC), however, the exact composition and functional attributes of memory T cell subtypes within cSCCs is currently unknown. In the current study, memory T cells from primary human cSCCs (n=42 tumours) were characterised and compared with memory T cells from non-lesional skin and blood from the same subjects. CD45RO+CD45RA- memory T cells comprised 64.9% of the cSCC T cell infiltrate, and included CCR7-CD45RA- effector memory (TEM) and CCR7+L-selectin+CD45RA- central memory T cells (81.0% and 13.6% of T cells respectively). cSCCs contained few CCR7+CD45RA+ naive and CCR7-CD45RA+ effector memory (TEMRA) T cells (0.7% and 5.0% of T cells respectively). Analysis of skin homing markers showed similar CLA+ T cell frequencies in cSCC (54.1%) and non-lesional skin (59.5%), whereas fewer T cells expressed CCR4 in cSCC (25.0%) compared with non-lesional skin (46.5%, p=0.0074). Although most TEMs from blood were CD27+CD28+, cSCC TEMs were heterogenous in CD27 and CD28 expression, suggesting greater differentiation of cSCC memory T cells. CD8+ T cells were the tumoral T cell subset with the highest frequency of CD69+CD103+ resident memory T (TRM) cells (22.3% of CD8+ T cells versus 1.1% of CD4+FOXP3+ Tregs and 7.9% of CD4+FOXP3- T cells, p<0.05). Following PMA/ionomycin stimulation, interferon-γ and TNF-α were produced by greater proportions of CD69+ TRMs than CD69- T cells (p<0.05). However, there were fewer IL-2+ T cells in cSCC than non-lesional skin (p=0.0048) and CD103+ TRMs were associated with reduced IL-2 expression compared with CD69+CD103- TRMs (p=0.0418). This data indicates that cSCCs contain a variety of memory T cell subtypes with distinct functional repertoires, with consequential effects of defective anti-tumour immunity.

Multiple functionally distinct memory T cell subtypes are present in cutaneous squamous cell carcinoma