The University of Texas MD Anderson Cancer Center Houston, Texas, United States
Background/Case Studies: Monoclonal antibody immunotherapy (mAb) is effective in treating various cancers but can interfere with pre-transfusion testing due to CD47 expression on most cells, including RBCs. The introduction of anti-CD47 mAbs into patient plasma can trigger pan-agglutination reaction, causing interference that may mask clinically significant alloantibodies. As a result, transfusion services (TS) are confronted with the task of supplying phenotypically matched RBC to transfusion-dependent patients, which are costly and can be difficult to acquire. While this option offers a high level of safety, it is important to note that the crossmatched (XM) reactions remain incompatible. An FDA approved murine monoclonal AHG (Gamma-clone) failed to recognize IgG4 subclass in indirect antiglobulin test (IAT). In contrast, an FDA approved rabbit polyclonal AHG recognized all IgG subclasses. Since IgG4 subclass is limited in its ability to activate antibody-depended immune responses, using an AHG reagent that does not bind to IgG4 would not substantially impact the detection of clinically significant antibodies. This could provide a practical solution for inference caused by anti-CD47 mAbs of the IgG4 subclass, such as Hu5F9-G4 and TTI-622. However, anti-CD47 mAbs of the IgG1 subclass, such as ALX148, will consistently interfere. By evaluating the use of clone specific reagents, TS can identify underlying clinically significant antibodies in patients on IgG4 subclass mAbs, reducing costs and improving turnaround time for XM compatible RBCs.
Study
Design/Methods: IAT in standard tube testing was performed on patients who received Hu5F9-G4, ALX-148, or TTI-622 using rabbit polyclonal and gamma-clone AHG reagents with LISS and PEG enhancement.Two IAT-negative and two anti-CD38, IgG1 subclass IAT-positive samples were used as control. Negative results were verified with Check Cells.
Results/Findings: Patients treated with anti-CD47 mAbs of IgG4 subclass Hu5F9-G4 or TTI-622 showed pan-agglutination with rabbit polyclonal AHG in IAT, but negative with gamma-clone AHG (See Table 1). ALX-148 (IgG1 subclass) consistently interferes, causing 2+ to 4+ pan-agglutination in IAT with both AHG reagents. The negative and positive controls exhibited the expected reactions. Conclusions: Gamma-clone AHG reagent, which does not detect IgG4, is shown to be effective in mitigating interference during pre-transfusion testing for Hu5F9-G4 or TTI-622 patients. Anti-CD47 mAbs of the IgG1 subclass, such as ALX-148, consistently cause interference regardless of the AHG reagent used. The implementation of clone specific AHG in pre-transfusion testing based on the patient treatment would support the patients’ transfusion needs.
