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Measuring Drug Concentrations and Anti-drug Antibodies

Several assays have been developed to measure anti-TNF drug levels and anti-drug
antibodies (Table 8.1). Importantly, earlier assays have had some shortcomings with
regard to measuring both drug levels and antibodies when each is present, often
making interpretation of the results of assays in initial clinical trials challenging
[ 30 ]. Given these differences, each assay will be reviewed, with particular focus on
each assay’s limitations.
Many initial studies employed a sandwich ELISA [ 15 ]. ELISAs involve add-
ing a patient’s serum to an infliximab-coated plate. After washing the plate,
labeled infliximab is then added, which cross-links to another binding site on
the anti-drug antibody. Importantly, the presence of serum anti-TNF levels can
induce a false- negative result for anti-drug antibodies with this assay, as the
drug can inhibit binding of the labeled drug after washing [ 21 , 41 , 42 ]. As such,

Table 8.1 Assays used to detect antibodies to infliximab

Assay type Advantages Disadvantages

Commercial

example in

United States

ELISA • Ease of

administration

• Generally low cost
  
  
  • False positives
  
  
  • Interference in
    measuring
    antibodies in the
    presence of drug
    
    
    • Early
      Prometheus
      and Esoterix
      assays
    
    
    
    
  
  
  
  

RIA • Can detect ATIs in

the presence of

infliximab

• More resistant to
  cross-reactivity with
  other antibodies
  
  
  • Requires the use
    of radioactive
    isotopes
  
  
  • Prolonged
    incubation time
    for equilibration
    of binding
    
    
    • None
    
    
    
    
  
  
  
  

HMSA • Not sensitive to

interference by other

antibodies

• Increased sensitivity
  compared to ELISA


• Able to measure all
  subtypes of
  immunoglobulins to
  anti-TNFs


• No radioactive
  component as in RIA
  
  
  • Requires further
    validation,
    relatively new
    assay
    
    
    • Prometheus
      (HMSA),
      Mayo
      (LC-MS/
      MS)
    
    
    
    
  
  
  
  

Electrochemiluminescence • Can measure ATIs in

the presence of drug

• Standardized lab
  equipment


• No radioactive
  components
  
  
  • ATIs interfere
    with drug level
    assessment
  
  
  • Not yet validated,
    relatively new
    assay
    
    
    • LabCorp
    
    
    
    
  
  
  
  

Adapted from Scott FI et al. [ 30 , 40 ]

F.I. Scott and M.T. Osterman