CD2-CD58 interactions stabilize contact between immune cells and target cells and participate in the organization of T-cell and NK-cell immune synapses, amplification of activation signals, and maintenance of effector functions. Loss of CD58 or insufficient CD2 signaling can weaken antitumor immunity and affect the efficacy of cell-based therapies.

Keywords: CD2; CD58; LFA-3; immune synapse; T cell; NK cell; tumor immune escape; CAR-T cell; costimulation; targeted therapy

1 Molecular Characteristics and Expression Distribution of CD2 and CD58

1.1 Structure and Expression of CD2

CD2 is a type I transmembrane glycoprotein with immunoglobulin-like domains in its extracellular region. Its cytoplasmic region is relatively long but lacks intrinsic kinase activity. CD2 is mainly expressed on thymocytes, mature T cells, and NK cells and participates in both cell adhesion and regulation of activation signals. Its extracellular domain is responsible for ligand recognition, whereas its cytoplasmic tail cooperates with membrane-proximal signaling complexes and cytoskeletal regulatory networks to convert cell contact into signal amplification.

1.2 Structure and Expression of CD58

CD58, also known as lymphocyte function-associated antigen 3 (LFA-3), is the principal ligand of human CD2. Human CD58 exists in both glycosylphosphatidylinositol (GPI)-anchored and transmembrane forms, which may localize to different membrane microdomains and participate in cell adhesion and signal regulation. CD58 can be expressed on antigen-presenting cells, hematopoietic cells, endothelial cells, epithelial cells, and various tumor cells, thereby providing an adhesive and costimulatory interface for CD2-positive T cells or NK cells.

1.3 Species Differences in CD2 Ligands

Human CD2 mainly binds CD58, whereas the principal ligand of CD2 in rodents is CD48. The human CD2-CD58 system is not completely equivalent to the murine CD2-CD48 system. Therefore, findings obtained in human CD2-CD58 systems should not be directly extrapolated to conventional mouse models. Animal studies should clearly specify whether they use a humanized CD58 system, a xenograft model, or the murine CD2-CD48 pathway as a substitute.

2 CD2-CD58 Interactions and Immune Synapse Formation

2.1 Regulation of Cell Contact and Intermembrane Distance

CD2-CD58 is a low-affinity adhesion receptor-ligand pair characterized by rapid association and dissociation. Although individual molecular interactions are relatively weak, accumulation of large numbers of CD2 and CD58 molecules at the cell-cell interface can create an adhesive region with high two-dimensional binding efficiency and maintain an intermembrane distance suitable for immune receptor recognition. This arrangement facilitates TCR recognition of peptide-MHC complexes and can also improve the stability of interactions between NK-cell activating receptors and ligands on target cells.

2.2 Spatial Distribution Within the Immune Synapse

(1) Early Stage of Synapse Formation

After a T cell or NK cell contacts a target cell, CD2-CD58 first contributes to cell binding and expansion of the contact area. Integrin-mediated adhesion pathways, such as LFA-1-ICAM-1, subsequently provide additional stabilization, allowing immune receptors to redistribute within the synaptic region.

(2) Mature Immune Synapse

In a mature T-cell immune synapse, CD2 can accumulate at the outer edge of the synapse and form a CD2-enriched structure distinct from the central TCR signaling region and the peripheral integrin region. This structure is commonly referred to as the CD2 corolla and can serve as a persistent adhesion and signaling platform associated with local cytoskeletal remodeling.

2.3 Coordination With the Cytoskeleton and Integrins

CD2-CD58 interactions can cooperate with the LFA-1-ICAM-1 axis to promote immune-cell spreading, polarization, and synapse stabilization. Actin polymerization drives receptor-cluster movement, synaptic reorganization, and directed transport of cytotoxic granules toward the contact interface. Disruption of actin polymerization may reduce CD2 spatial organization, cell contact, and effector function.

3 Activation of T Cells and NK Cells Mediated by the CD2-CD58 Signaling Axis

3.1 T-Cell Costimulation

CD2-CD58 binding cannot replace antigen-specific TCR recognition, but it can lower the stimulation threshold required for full T-cell activation. By stabilizing contact between T cells and antigen-presenting cells, this axis promotes enrichment of proximal signaling molecules within the synaptic region and enhances Ca²⁺ mobilization, ERK activation, IL-2 production, and cell proliferation. The supportive role of CD2 may be particularly evident under conditions of low antigen density, insufficient CD28 signaling, or chronic stimulation.

3.2 NK-Cell Activation

CD2 is widely expressed on the surface of human NK cells and can bind CD58 expressed by target cells or neighboring immune cells. CD2-CD58 generally acts together with LFA-1, 2B4, and other activating receptors to promote stable NK-cell binding to target cells and enhance degranulation, cytotoxicity, and cytokine secretion. Blocking CD2-CD58 interactions can reduce NK-cell killing and IFN-γ production, although the magnitude of the effect depends on the ligand composition of the target cell and the balance of other activating and inhibitory signals.

3.3 Effector Function Outputs

The effects of CD2-CD58 depend on antigen receptor signal strength, integrin activation, the cytokine environment, and the status of inhibitory receptors. Therefore, increased CD2 expression or the presence of CD58 does not necessarily indicate that a cell is fully activated. Phosphorylation signals and functional readouts should be analyzed together.

4 Abnormal CD2-CD58 Signaling and Tumor Immune Escape

4.1 Loss of CD58 in Tumor Cells

Some diffuse large B-cell lymphomas, classical Hodgkin lymphomas, and other tumors may exhibit CD58 mutations, deletions, or reduced surface expression. Decreased CD58 weakens adhesion between tumor cells and CD2-positive T cells or NK cells, thereby reducing immune synapse stability and the killing efficiency of effector cells. CD58 abnormalities may also coexist with defects in antigen presentation, creating multilayered immune escape.

4.2 Effects on Serial Killing by T Cells

CD2-CD58 interactions affect not only a single target-cell killing event but also directional migration of T cells and serial recognition of multiple target cells. When tumor cells express higher levels of CD58, T-cell migration, contact formation, and serial killing are generally more efficient. CD58 loss may prolong the time required to establish effective contact and reduce the ability of CAR-T cells to continuously eliminate target cells.

4.3 CD58 Loss and Immunosuppressive Pathways

The effects of CD58 loss are not limited to weakened adhesion. In some tumor models, CD58 loss can alter regulation involving LYN, CD22, SHP1, and JAK2-STAT1 and promote the expression of immunosuppressive molecules such as PD-L1 or indoleamine 2,3-dioxygenase. These changes suggest that CD58 loss may simultaneously affect immune synapses and immune-checkpoint pathways.

4.4 CD58 as a Treatment-Related Biomarker

CD58 expression may serve as a candidate indicator of the capacity of tumor cells to interact with effector lymphocytes. Higher pretreatment CD58 expression generally suggests that tumor cells can more readily establish effective contact with CD2-positive effector cells, whereas CD58 loss may impair CAR-T-cell function. However, CD58 alone cannot predict treatment outcome and should be analyzed together with target-antigen expression, MHC status, tumor burden, and T-cell quality.

5 Role of the CD2-CD58 Signaling Axis in Autoimmunity, Antiviral Responses, and Transplant Rejection

5.1 Regulation of Autoimmunity

Enhanced CD2-CD58 signaling can promote interactions between autoreactive T cells and antigen-presenting cells and may also alter the balance between effector T cells and regulatory T cells. CD58-associated genetic variants have been linked to susceptibility to diseases such as multiple sclerosis and rheumatoid arthritis, but the effects of different variants on CD58 expression and immune function are not identical. A genetic association does not directly mean that increased or decreased CD58 necessarily causes autoimmune disease.

5.2 Antiviral Responses

Virus-specific CD8⁺ T cells and NK cells must form effective immune synapses with infected cells, and CD2-CD58 can support this process and improve cytotoxic response efficiency. In some persistent viral infections, effector T cells with high CD2 expression can receive costimulation from CD58 on target cells or vascular cells and continue to release cytokines and cytotoxic granules even when CD28 signaling is weak. CD2-CD58 may therefore support infection control but may also amplify tissue inflammation during persistent infection.

5.3 Transplant Rejection

Alloantigen recognition requires recipient T cells to establish stable contact with donor antigen-presenting cells or graft cells. CD2-CD58 can participate in alloreactive T-cell activation and sustained effector responses after immune cells enter the graft. Anti-CD2 antibodies may reduce the number of CD2-positive T cells or inhibit their activation and may act synergistically with blockade of CD28-B7 costimulation. Such interventions require simultaneous evaluation of immunosuppressive intensity, infection risk, and the extent of lymphocyte depletion.

5.4 Immune Evasion of Regenerative Cells

In allogeneic cell therapy, B2M knockout can reduce T-cell recognition of transplanted cells but may trigger NK-cell "missing-self" responses. Further reduction of CD58 or other adhesion molecules on target cells can weaken NK-cell adhesion and killing. Such strategies may improve survival of allogeneic cells but may also reduce immune clearance of abnormal cells. Therefore, they should be combined with a controllable elimination system or safety switch.

6 Targeted Intervention of the CD2-CD58 Axis and Tumor Immunotherapy Research

6.1 Restoration of CD58 Expression in Tumor Cells

For tumors in which CD58 is epigenetically suppressed rather than completely deleted, restoration of CD58 expression through modulation of chromatin state may be investigated. Re-expression of CD58 may improve T-cell and NK-cell adhesion, immune synapse formation, and target-cell killing. Before intervention, it is necessary to distinguish among gene deletion, transcriptional repression, abnormal protein processing, and defective surface trafficking, because complete gene loss generally cannot be reversed by epigenetic drugs alone.

6.2 Enhancement of CD2 Function in CAR-T Cells

CD58 loss is a potential mechanism of resistance to some CAR-T-cell therapies. Compensation may therefore be achieved by increasing CD2 expression in CAR-T cells or strengthening CD2-related signaling. Increased CD2 expression may improve CAR-T-cell immune synapse quality, serial killing, and persistence. The CD2 cytoplasmic domain may also be explored as an engineered signaling module. However, such designs still require evaluation of risks related to excessive activation, nonspecific adhesion, and cytokine release.

6.3 Combination Immunotherapy

CD58 loss may be accompanied by enhanced immunosuppressive mechanisms involving PD-L1 or IDO. Therefore, the relationship between CD2-CD58 status and immune-checkpoint inhibition, metabolic inhibition, or cell therapy can be investigated in combination strategies. In tumors retaining CD58, enhancement of CD2 costimulation may directly improve effector-cell function. In tumors with complete CD58 loss, bypass adhesion receptors, bispecific molecules, or CD58-independent cell-engineering strategies may be required.

6.4 Situations Suitable for CD2-CD58 Blockade

CD2-CD58 is not suitable only for enhancement. In autoimmunity, transplant rejection, or excessive T-cell activation, blocking antibodies, soluble receptors, or cell-depleting anti-CD2 antibodies may reduce immune-cell adhesion and activation. The therapeutic direction depends on the disease context: antitumor therapy generally aims to preserve or enhance this axis, whereas autoimmune and transplantation studies focus more on blockade or depletion of CD2-positive cells.

7 Experimental Evaluation and Research Methods for the CD2-CD58 Signaling Axis

7.1 Detection of Expression Levels

(1) Flow Cytometry

Flow cytometry can quantify CD2 on T cells, NK cells, or engineered cells and CD58 on tumor cells or antigen-presenting cells. Results should include both the percentage of positive cells and mean fluorescence intensity, together with single-color compensation controls, negative controls, and viability staining.

(2) Tissue-Based Detection

Immunohistochemistry or multiplex immunofluorescence can evaluate CD58 expression and the spatial distribution of CD2-positive lymphocytes in tumor tissues. Results should be analyzed together with tumor-cell markers to avoid misclassifying CD58 expressed by infiltrating immune cells as tumor-cell expression.

(3) Nucleic Acid and Protein Detection

qPCR and transcriptome sequencing can analyze CD2 and CD58 transcript levels, whereas Western blotting can detect total protein. When surface CD58 is reduced but total protein remains unchanged, abnormalities in membrane trafficking, shedding, internalization, or membrane localization should be further investigated.

7.2 Molecular Binding and Blocking Experiments

Recombinant extracellular domains of CD2 and CD58 can be used in enzyme-linked binding assays, surface plasmon resonance, or biolayer interferometry to evaluate binding strength and dissociation kinetics. In cell-based experiments, CD2- or CD58-blocking antibodies can be used to compare changes in cell adhesion, synapse formation, and function before and after blockade. Because CD2-CD58 is a low-affinity interaction with rapid kinetics, immobilization method, protein orientation, and the two-dimensional membrane environment may all affect the results.

7.3 Immune Synapse Imaging

Confocal microscopy, total internal reflection fluorescence microscopy, or imaging flow cytometry can be used to visualize the distribution of CD2, CD58, TCR, LFA-1, and F-actin at the contact interface. Supported lipid bilayers can control the density of CD58, ICAM-1, and antigen molecules and can be used to analyze CD2 corolla formation, receptor-cluster movement, and synapse stability. Common quantitative parameters include cell-binding rate, contact area, CD2 enrichment ratio, synapse duration, and the proportion of cells showing cytotoxic-granule polarization.

7.4 Evaluation of Cellular Functions

7.5 Genetic Intervention and Causal Validation

CRISPR-Cas9, siRNA, or overexpression vectors can be used to reduce or enhance CD2 in effector cells and CD58 in target cells. Experimental designs should include untreated controls, non-targeting controls, gene-knockout groups, and rescue groups to distinguish gene-specific effects from clonal-selection artifacts. Restoration of CD58 expression after CD58 knockout is an important approach for confirming that defects in immune synapse formation and killing are directly caused by this molecule.

7.6 Experimental Design Considerations

Human experimental systems should preferentially use CD2-positive effector cells and target cells with clearly defined CD58 expression status. When mouse cells are used, the CD2-CD48 system should be studied rather than directly applying the human CD2-CD58 mechanism. In studies using CAR-T cells or NK cells, target-antigen density, LFA-1-ICAM-1 status, and inhibitory receptors should also be measured to avoid attributing all functional differences to CD2-CD58.

8 Products Related to the CD2-CD58 Signaling Axis, Immune Synapses, and Effector Functions

The CD2-CD58 signaling axis links cell adhesion, immune synapse organization, and activation of effector lymphocytes. Enhancement of this axis can improve the antitumor functions of T cells and NK cells, whereas abnormal activation may also contribute to autoimmunity and transplant rejection.