Cytotoxic CD8+ T lymphocytes (CTLs) undergo adaptive dysfunctional programming in the tumour microenvironment, which correlates with poor prognosis for patients. Persistent presentation of tumour-associated antigens (TAA) on major histocompatibility complex (MHC) molecules to cognate T cell receptor (TCR) is a defining factor for dysfunctional differentiation followed by abnormal synapse formation and poor cytotoxic activity. To study T cell dysfunction, we combined a low-level ovalbumin (OVA)-expressing-pre-B non-Hodgkin lymphoma model in mice with adoptive transfers of transgenic OT-I CD8+ T cells to interrogate the impacts of cancer progression in TCR signalling. Transgenic OT-I CTLs become tolerant to high lymphoma burden in a cognate fashion with poor cytotoxic responses in both in vivo and ex vivo assays. Relative to low tumour burden-experienced OT-I T cell controls, these dysfunctional OT-I cells had obvious defects in proximal signalling, with smaller immunological synapses and poor TCR phosphorylation on supported lipid bilayers (SLBL) functionalised with SIINFEKL:H-2Kb monomers and ICAM-1. Ex vivo restimulation also failed to upregulate the marker for immediate-early of TCR stimulation nuclear receptor subfamily 4 group A member 1 (Nr4a1). CTLs retrieved from animals with high lymphoma burden did not significantly downregulate surface TCR expression, or upregulate inhibitory receptor (PD-1, TIM-3, LAG3) expression but showed significantly lower expression of Lck than cells from low or no cancer burden animals. Our findings demonstrate that chronic stimulation with low antigen levels can lead to T cell dysfunction without the classically described TCR down-modulation or increased inhibitory receptor expression. Selective down-modulation of Lck indicates that the defect in these cells lies in the TCR proximal signalling cascade, leading to decreased sensitivity to TAA:MHC, highlighting a highly specific mechanism of dysfunction in the absence of other overt phenotypic changes.