Definition of an immunologic response using the major histocompatibility complex tetramer and enzyme-linked...

Area of Science:

• Immunology
• Cancer Research
• Clinical Trials

Background:

• Monitoring T-cell responses is crucial for evaluating immunotherapy efficacy.
• Standardized assays are needed to accurately define immunologic responses.
• Assay variability can obscure true treatment-related T-cell expansion.

Purpose of the Study:

• To define an immunologic response using tetramer and enzyme-linked immunospot (ELISPOT) assays.
• To establish criteria for detecting T-cell expansion in response to immunotherapy.
• To assess assay performance metrics including lower limit of detection (LLD) and coefficient of variation (CV).

Main Methods:

• Evaluated tetramer and ELISPOT assays in healthy subjects and melanoma patients (n=31).
• Determined LLD, analytic CV (aCV), and physiologic CV (pCV) for both assays.
• Calculated reference change value (RCV) to define significant changes beyond assay imprecision.
• Monitored T-cell expansion after CTLA4 blockade with ticilimumab.

Main Results:

• Tetramer assay LLD was 0.038% CD8+ cells; ELISPOT LLD was 7 spots/10^5 PBMCs.
• Tetramer assay aCV was <10%, while ELISPOT aCV ranged from 24.69-36.32%.
• Marked between-subject variability in baseline T-cell levels was observed, correlated with prior antigen exposure.
• Defined immunologic response based on change from negative to positive or exceeding assay RCV.
• Observed T-cell expansions for EBV and MART1 antigens in four patients receiving ticilimumab.

Conclusions:

• A combined approach using LLD and RCV can define meaningful changes in circulating antigen-specific T cells.
• This methodology provides a robust framework for assessing responses to immunotherapy.
• Accurate definition of immunologic response is key for interpreting T-cell dynamics during cancer treatment.