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.