# Resolving the Interference of Anti‐CD38 Antibodies on Blood Compatibility Assays Using CD38 “Baitbodies” Approach

## TL;DR

This paper introduces a new method to prevent false blood compatibility test results caused by anti-CD38 antibodies used in cancer treatment.

## Contribution

The novel CD38 'baitbody' Fc-fusion construct neutralizes anti-CD38 antibodies to avoid false positives in blood compatibility assays.

## Key findings

- CD38-mFc baitbody neutralized anti-CD38 monoclonal antibodies in spiked samples.
- The baitbody enabled detection of Rhesus, Kell, and Duffy alloantibodies without interference.
- CD38-mFc outperformed commercial reagents in mitigating anti-CD38 interference.

## Abstract

Blood transfusion safety depends on swift blood compatibility testing. Alloantibodies recognizing these blood group antigens determine blood compatibility, and the transfusion of incompatible blood can lead to life‐threatening hemolytic transfusion reactions. Recently, the landscape of blood compatibility testing has been complicated due to the interference caused by therapeutic antibodies targeting CD38, a key target in cancer immunotherapy that is also expressed on red blood cells. The presence of anti‐CD38 antibodies in blood samples has been found to bind to test or donor red blood cells, resulting in false positive tests. This interference poses a serious risk as it can potentially mask immunogenic alloantibodies and cause delays in supplying safe blood products. We present the development and application of fragment crystallizable (Fc)‐fusion constructs, referred to as “baitbodies”, designed to neutralize anti‐CD38 antibodies and mitigate false positive test outcomes. The extracellular domain of CD38 was fused to the Fc domain of a murine immunoglobulin G. These baitbody constructs were thoroughly characterized and applied in both serological microcolumn agglutination and automated solid‐phase red cell adherence assays. The CD38‐mFc baitbody successfully prevented agglutination reactions induced by three clinically relevant anti‐CD38 monoclonal antibodies—daratumumab, felzartamab and isatuximab—in spiked samples. This allowed the detection of alloantibodies of the Rhesus, Kell and Duffy blood groups without interference. The CD38‐mFc construct also demonstrated potential in a head‐to‐head comparison with commercial mitigation reagents, DaraEx and Grifols sCD38. Finally, the CD38‐mFc baitbody effectively neutralized daratumumab in patient samples, preventing false positive test outcomes.