An invariant VLR-like receptor refines the T-like cell framework in lamprey

Jawless vertebrates employ variable lymphocyte receptors (VLRs) to mount adaptive immunity. Although six VLRs (VLRA–F) and T/B-like lymphocytes are identified in lampreys, it remains unclear how VLR diversity is organized at the cellular level and whether individual lymphocytes may integrate multiple VLRs. Using single-cell transcriptomics, we identify a germline-encoded, mature, non-diversified VLR-like receptor (VLR-like) in lamprey Lethenteron reissneri. VLR-like retains structural features of canonical VLRs, and is a GPI-anchored receptor expressed by T-like cells. We generate a VLR-like monoclonal antibody, enabling the identification of VLR-like+ lymphocytes across multiple tissues. Upon PHA stimulation, VLR-like+ lymphocytes exhibit robust ERK and JNK phosphorylation and proliferation, consistent with T-like cell features. In parallel, VLR-like+ cells fail to phagocytose, present antigen, or secrete soluble VLR-like, indicating the absence of B-like characteristics. Notably, VLR-like+ cells are distinct from VLRA+ lymphocytes but comprise both VLR-like+VLRC+ and VLR-like+VLRC- populations. Consistently, VLR-like interacts with VLRC but not VLRA. Together, we demonstrate that VLR-like defines a distinct T-like population with heterogeneous VLRC co-expression, and suggest a mode of receptor organization in which an invariant VLR-like coordinates a diversified VLR within an individual T-like cell, potentially contributing to adaptive immunity in lamprey. Lampreys use variable lymphocyte receptors (VLRs) for adaptive immunity, but the cellular organization of VLR diversity is unknown. This study reveals an invariant VLR-like receptor in lamprey T-like cells that coordinates with diversified VLRC, defining a distinct T-like sub-population in lamprey.