EVIDENCE meta-analysis: evaluating minimal residual disease as an intermediate clinical end point for multiple myeloma.

ABSTRACT: Estimating progression-free survival (PFS) and overall survival superiority during clinical trials of multiple myeloma (MM) has become increasingly challenging as novel therapeutics have improved patient outcomes. Thus, it is imperative to identify earlier end point surrogates that are predictive of long-term clinical benefit. Minimal residual disease (MRD)-negativity is a common intermediate end point that has shown prognostic value for clinical benefit in MM. This meta-analysis was based on the US Food and Drug Administration guidance for considerations for a meta-analysis of MRD as a clinical end point and evaluates MRD-negativity as an early end point reasonably likely to predict long-term clinical benefit. Eligible studies were phase 2 or 3 randomized controlled clinical trials measuring MRD-negativity as an end point in patients with MM, with follow-up of ≥6 months following an a priori-defined time point of 12 ± 3 months after randomization. Eight newly diagnosed MM studies evaluating 4907 patients were included. Trial-level associations between MRD-negativity and PFS were R2WLSiv, 0.67 (95% confidence interval [CI], 0.43-0.91) and R2copula 0.84 (0.64 to >0.99) at the 12-month time point. The individual-level association between 12-month MRD-negativity and PFS resulted in a global odds ratio (OR) of 4.02 (95% CI, 2.57-5.46). For relapse/refractory MM, there were 4 studies included, and the individual-level association between 12-month MRD-negativity and PFS resulted in a global OR of 7.67 (4.24-11.10). A clinical trial demonstrating a treatment effect on MRD is reasonably likely to eventually demonstrate a treatment effect on PFS, suggesting that MRD may be an early clinical end point reasonably likely to predict clinical benefit in MM, that may be used to support accelerated approval and thereby, expedite the availability of new drugs to patients with MM.

Standardization of flow cytometric detection of antigen expression.

Since response to antigen-based immunotherapy relies upon the level of tumor antigen expression we developed an antigen quantification assay using ABC values. Antigen quantification as a clinical assay requires methods for quality control and for interlaboratory and inter-cytometer platform standardization. A single lot of Cytotrol™ Lyophilized Control Cells (Beckman Coulter) used for all studies. The variability in antigen quantification across 4 different instrument platforms in 2 separate laboratories was evaluated. The effect of the antibody clone utilized, importance of custom 1:1 molar ratio (fluorophore to protein, F/P) verses off-the-shelf antibodies, and QuantiBrite PE calibration verses linearity calibration combined with a single point scale transformation with CD4 as reference were determined. Use of single lot control cells allowed validation of reproducibility between flow cytometer platforms and laboratories and allowed assessment of different antibody lots, cocktail preparation, and different antibody clones. Off the shelf antibody preparations provide reproducible estimates of antigen density, however custom 1:1 unimolar antibody preparations should be utilized for definitive measurement of antigen expression.Geometric Mean fluorescent Intensity (GeoMFI) was not comparable across instruments and inter-laboratory. The use of CD4 as the reference marker can minimize variability in ABC values. Comparable antigen quantification is vital in managing patients receiving antigen-based immunotherapy. If this assay is to be utilized in a clinical setting, quality control methods have to be instituted to assure reproducibility and allow validation across laboratories. We have demonstrated that use of a lyophilized cell control is highly valuable in achieveing these goals.