An emerging checkpoint axis with recent FDA approval–measuring engagement could optimize patient selection.
LAG-3 is structurally related to CD4 and binds MHC class IILoading... with higher affinity than CD4. On exhausted T cells in tumors, LAG-3 is co-expressed with PD-1 and other inhibitory receptors, contributing to the exhaustion phenotype.
LAG-3 also has additional ligands including LSECtin, Galectin-3, and FGL1–suggesting complex regulation beyond MHC II binding. The relative contribution of each ligand in different tumor contexts remains under investigation.
Another Brake Pedal: LAG-3 on T cells binds MHC class II on other cells and delivers an inhibitory signal. It often works alongside PD-1 to dampen immune responses.
Exhaustion Marker: LAG-3 is upregulated on exhausted T cells and is often increased when PD-1 is blocked—a potential resistance mechanism.
Relatlimab became the first anti-LAG-3 antibody to receive FDA approval (March 2022), in combination with nivolumab for metastatic melanoma. The RELATIVITY-047 trial showed improved progression-free survival compared to nivolumab alone.
The approval of a third checkpoint target validates the strategy of targeting multiple non-redundant pathways. However, patient selection remains empirical–no companion diagnosticLoading... exists for LAG-3/MHC II engagement.
Clinical Status: Relatlimab (anti-LAG-3) combined with nivolumab is FDA-approved for melanoma. Multiple other anti-LAG-3 drugs are in development.
Combination Logic: Blocking LAG-3 along with PD-1 may overcome resistance from LAG-3 upregulation.
As with PD-1/PD-L1Loading..., LAG-3 expression alone may not predict which patients benefit from blockade. The relevant biology is whether LAG-3 is functionally engaged with MHC II at tumor-immune interfaces.
iFRETLoading...'s ability to measure receptor-ligand interactions at 1–10 nm makes it applicable to LAG-3/MHC II quantification. Developing engagement-based biomarkers for emerging checkpoints could avoid repeating the limitations of PD-L1 IHCLoading....
The Gap: There's no routine test for LAG-3/MHC-II engagement. Patients receive anti-LAG-3 therapy without knowing if LAG-3 is actively suppressing immunity in their tumor.
Opportunity: The same iFRET approach validated for PD-1/PD-L1 could potentially measure LAG-3/MHC-II engagement for patient selection.
Theoretical Application: LAG-3/MHC-II interaction represents an emerging checkpoint target suitable for QF-Pro development. With FDA approval of relatlimab, there is clinical need for biomarkers predicting response to LAG-3 blockade.
QF-Pro's iFRET methodology–already validated for intercellular checkpoint interactions–could potentially quantify LAG-3/MHC-II engagement state, providing mechanism-direct patient selection for LAG-3-targeted therapies.
Status: Theoretical application pending assay development.
Future potential: With relatlimab (anti-LAG-3) now FDA-approved, there's clinical need for LAG-3 biomarkers. QF-Pro's validated iFRET approach could measure LAG-3/MHC-II engagement to select patients for LAG-3 therapy.
