Dendritic cell ICAM-1 strengthens immune synapses but is dispensable for effector and memory responses

Lymphocyte priming in lymph nodes (LNs) depends on the formation of functional TCR specific immune synapses (ISs) with antigen (Ag) presenting dendritic cells. The high affinity LFA-1 ligand ICAM-1 has been implicated in different ISs studied in vitro . The in vivo roles of DC ICAM-1 in Ag stimulated T cell differentiation have been unclear. In newly generated DC conditional ICAM-1 knockout mice, we report that under Th1 polarizing conditions, ICAM-1 deficient DCs could not engage in stable conjugates with newly generated CD8 blasts. Nevertheless, these DCs triggered normal lymphocyte priming, proliferation and differentiation into functional cytotoxic T cells (CTLs) and central memory lymphocytes (Tcm) in both vaccinated and virus infected skin. Single cell RNAseq analysis confirmed that Tcm were normally generated in these mice and gave rise to normal T effectors during a recall skin response. Our results suggest that although CD8 T cell blasts tightly bind DC-ICAM-1, strongly adhesive DC-T ISs are not necessary for functional TCR dependent DC mediated CD8 T cell proliferation and differentiation into productive effector and memory lymphocytes. Summary Sapoznikov et al generated a new genetic murine model deficient in dendritic cell expression of the key adhesion molecule ICAM-1 and found that CD8 lymphocytes do not require strong adhesion to dendritic cells for antigen-dependent differentiation into effector and memory T cells.