t-mAbs ,SPE, IFE: Problems and Solutions

Therapeutic Monoclonal Antibodies (t-mAbs) and Interference with Serum Protein Electrophoresis (SPE) and Immunofixation Electrophoresis (IFE): Problems and Solutions

Introduction

Therapeutic monoclonal antibodies (t-mAbs) have transformed the treatment of hematologic malignancies including multiple myeloma, Waldenström macroglobulinemia, and systemic amyloidosis. Among them, agents such as daratumumab, isatuximab, and elotuzumab have taken center stage.

But t-mAb use has added a new degree of complexity to laboratory testing. Diagnostics like serum protein electrophoresis (SPE) and immunofixation electrophoresis (IFE), which play an important role in the identification and follow-up of monoclonal proteins (M-proteins), may be misleading by the presence of these therapeutic antibodies.

The exogenous immunoglobulin components of t-mAbs behave similar to endogenous monoclonal proteins while migrating. They can thus appear as false bands or peaks, possibly causing misinterpretation including:

• A false diagnosis of biclonal gammopathy
• Overestimation of the disease burden
• Difficulty in distinguishing between disease progression and treatment effect
  This article gives a detailed overview of how t-mAbs disrupt electrophoretic methods, diagnostic challenges for clinicians, and what laboratory and healthcare teams can implement to guarantee accuracy.

Understanding Therapeutic Monoclonal Antibodies (t-mAbs)

What are t-mAbs?

Monoclonal antibodies are laboratory-produced immunoglobulins engineered to bind to precise antigens on cancerous plasma cells. In hematology, anti-CD38 (e.g., daratumumab, isatuximab) and anti-SLAMF7 (e.g., elotuzumab) antibodies are common.

Role in Therapy

• Daratumumab (anti-CD38): Highly efficacious in multiple myeloma and systemic AL amyloidosis.
• Isatuximab (anti-CD38): Alternative anti-CD38 mAb with differing pharmacokinetics.
• Elotuzumab (anti-SLAMF7): Engages natural killer (NK) cells in multiple myeloma.
  These antibodies enhance survival and outcomes, but their immunoglobulin conformation (typically IgG kappa) creates overlap with the laboratory identification of patient-derived monoclonal proteins.

The Role of SPE and IFE in Plasma Cell Disorders

Serum Protein Electrophoresis (SPE)

• Splits proteins in serum according to their charge and size.
• Detects the M-protein spike (paraprotein) in the gamma region.
• Applied for diagnosis and monitoring of plasma cell disorders (PCDs).

Immunofixation Electrophoresis (IFE)

• Performs specific immunoglobulin typing (IgG, IgA, IgM, kappa, lambda).
• Picks up low-level M-proteins that SPE may not detect.
• Important in monitoring for minimal residual disease (MRD).
  Both tests are pillars in diagnosing and monitoring conditions like multiple myeloma, AL amyloidosis, and MGUS (monoclonal gammopathy of undetermined significance).

How t-mAbs Cause Interference

Migration Pattern Overlap

• t-mAbs are IgG kappa in structure in most cases.
• They yield a small but distinct band in the gamma region on SPE.
• On IFE, they are seen as extra IgG kappa bands, which can simulate a biclonal gammopathy.

Example: Daratumumab

• Reported to present as a false monoclonal spike.
• Imitates endogenous M-protein, resulting in misdiagnosis or overestimation of disease.
• Can disrupt during response assessment, complicating confirmation of complete remission.

Broader Impact

• Elotuzumab and isatuximab can also interfere, although less predominantly than daratumumab.
• Misunderstanding may result in unnecessary treatment escalation or inappropriate prognosis.

Diagnostic Challenges

1. False Biclonal Gammopathy

• Patients on daratumumab can demonstrate two different IgG kappa bands.
• Danger of reporting a false second clone.

1. Failure to Confirm Complete Remission

• Despite the disappearance of endogenous M-protein, daratumumab can be seen in IFE.
• Results in false-negative remission status.

1. Difficulty in Distinguishing Residual Disease from Drug Presence

• Distinguishing if the band is therapeutic antibody or persistent disease clone.

1. Overinterpretation in Low M-protein Burden Patients

• Especially challenging in amyloidosis where M-protein is frequently subtle.

Strategies to Overcome Interference

1. Daratumumab-Specific Assay (DIRA)

• Daratumumab-specific immunofixation reflex assay (DIRA) alters the migration of daratumumab such that clear differentiation from endogenous proteins can be made.
• Universally taken up in specialized centers.

2. Mass Spectrometry (MS)-Based Methods

• MALDI-TOF and LC-MS identify specific peptide signatures of t-mAbs.
• Can differentiate therapeutic antibodies from patient-derived M-proteins.

3. Clinical Communication

• Laboratories should be alerted when a patient is being treated with t-mAb.
• Reports should explicitly label: “Patient is receiving daratumumab, results may reflect therapeutic antibody interference.”

4. Alternative Monitoring Techniques

• Employ serum free light chain (FLC) assays for monitoring in cases of SPE/IFE uncertainty.
• MRD testing using next-generation flow cytometry (NGF) or NGS could circumvent these problems.

Clinical Implications for Patients

• Evaluation of response to treatment can be delayed or incorrectly classified.
• Unnecessary anxiety for patients if false bands are mistaken for relapse.
• Incorrect interpretation can affect continuation, intensification, or discontinuation of therapy.
• Emphasizes the role of multidisciplinary team working between hematologists, pathologists, and laboratory scientists.

Future Directions

• Standardization of reporting protocols between laboratories.
• Increased utilization of DIRA and MS techniques in regular clinical practice.
• Investigation of non-immunoglobulin-based therapy to minimize diagnostic overlap.
• Creation of AI-assisted interpretation tools for electrophoresis patterns.

FAQs

Q1: Why does daratumumab interfere with IFE?

Since it is an IgG kappa antibody, its band gets overlapped with endogenous IgG kappa M-proteins.
Q2: Can labs differentiate therapeutic antibodies from disease clones?

Yes, through specific tests such as DIRA or mass spectrometry.
Q3: Does interference impact all patients?

Primarily those on t-mAbs like daratumumab or isatuximab; variable by disease burden.
Q4: Is treatment response still reliable to monitor?

Yes—integrating clinical examination, serum free light chain testing, and sophisticated methods such as MRD testing.
Q5: Are there other methods to monitor beyond electrophoresis?

Yes, flow cytometry and next-generation sequencing are able to identify minimal residual disease without interference.

Conclusion

Therapeutic monoclonal antibodies (t-mAbs) such as daratumumab have revolutionized outcomes for patients with plasma cell disorders. However, their structural homology with endogenous immunoglobulins poses substantial diagnostic challenges in SPE and IFE.

The risk of false biclonal results, misinterpretation of remission, and patient anxiety highlights the need for accurate laboratory techniques and clear clinical communication.

Through technology innovations like DIRA, mass spectrometry, and next-generation MRD testing, clinicians and laboratories are well-positioned to overcome these hurdles. In the end, awareness and accommodation are the secrets to providing both optimal treatment and accurate monitoring in the age of immunotherapy.