LAG3 Humanized Mouse Models

LAG3 Biology

LAG3 is an inhibitory receptor expressed on activated T cells:

• Expressed on activated CD4+ and CD8+ T cells
• Also expressed on regulatory T cells, NK cells, and plasmacytoid dendritic cells
• Binds MHC class II molecules with higher affinity than CD4
• Negatively regulates T cell proliferation and function
• Contributes to T cell exhaustion in chronic antigen exposure

LAG3 functions as an immune checkpoint, limiting T cell responses and contributing to tumor immune evasion.

Clinical Anti LAG3 Antibodies

Multiple anti LAG3 antibodies are in clinical development:

• Relatlimab (BMS 986016): FDA approved in combination with nivolumab for melanoma
• Ieramilimab (LAG525): Novartis anti LAG3 antibody in clinical trials
• MK 4280: Merck anti LAG3 antibody in development
• Multiple additional candidates in early to late stage trials

Clinical validation of LAG3 as an immunotherapy target drives demand for humanized preclinical models.

Species Specificity

Anti LAG3 therapeutic antibodies require humanized models:

• Clinical antibodies engineered for human LAG3 binding
• Limited cross reactivity with mouse Lag3
• Humanized LAG3 provides the appropriate target for antibody evaluation
• Essential for testing clinical candidates in mouse tumor models

Extracellular Domain Humanization

Replace mouse Lag3 extracellular domain with human LAG3 sequence:

• Human extracellular domain provides antibody binding epitopes
• Mouse transmembrane and intracellular domains preserved
• Maintains signaling compatibility with mouse immune cells
• Optimal for therapeutic antibody testing

ECD humanization is the preferred approach for most antibody evaluation applications.

Complete Gene Humanization

Full replacement of mouse Lag3 with human LAG3:

• Complete human LAG3 protein sequence
• Human specific signaling characteristics
• Study human LAG3 biology comprehensively
• Appropriate for mechanistic and signaling studies

Expression Pattern Preservation

LAG3 humanization design must maintain appropriate expression:

• Endogenous promoter preservation for physiological expression
• Expression on appropriate T cell subsets
• Inducible expression upon T cell activation
• Normal developmental regulation

Functional Validation

Humanized LAG3 must demonstrate functional activity:

• Surface expression on activated T cells
• Binding to MHC class II molecules
• Inhibitory function in T cell assays
• Therapeutic antibody binding confirmation

Anti LAG3 Monotherapy Testing

Primary application for LAG3 humanized mice:

• Test relatlimab and other clinical anti LAG3 antibodies
• Evaluate novel anti LAG3 candidates
• Compare antibody characteristics and potency
• Assess anti tumor efficacy in syngeneic models

Combination Immunotherapy

LAG3 inhibition is most effective in combination:

• LAG3 plus PD1 blockade (approved combination)
• LAG3 plus CTLA4 combinations
• LAG3 plus other emerging checkpoints
• Multi humanized models for clinical combinations

Mechanism of Action Studies

Understand LAG3 biology in tumor immunity:

• T cell exhaustion and reinvigoration
• Treg modulation
• Tumor microenvironment analysis
• Biomarker identification

Bispecific Antibody Testing

LAG3 is a target for bispecific antibodies:

• LAG3 x PD1 bispecific antibodies
• LAG3 x other target combinations
• Requires human LAG3 for binding evaluation

Strain Background

Choose strain background based on tumor model requirements:

• C57BL/6: MC38, B16, LLC, E0771
• BALB/c: CT26, 4T1, EMT6

Breeding Considerations

For multi checkpoint models:

• Single humanization: Standard breeding
• Double humanization: Intercross of single humanized lines
• Triple or higher: Sequential breeding or multi allele targeting

Phenotyping

Characterize LAG3 humanized mice:

• Flow cytometry for LAG3 surface expression
• T cell activation assays
• Therapeutic antibody binding confirmation
• Functional checkpoint activity assessment