Background/Case Studies: Patients receiving monoclonal antibody therapy targeting CD47 were referred to the Immunohematology Reference Laboratory for antibody identification workup and compatibility testing. Anti-CD47 is largely an IgG4 antibody that interferes with the Indirect antiglobulin test (IAT) and sometimes at Immediate Spin. To avoid anti-CD47 reactivity at IAT and rule out underlying alloantibodies, anti-IgG reagent that does not detect IgG4 antibodies can be used for blood bank testing. However, some anti-CD47 drugs also include IgG2 and IgG3 subtypes which could be detected using the anti-IgG reagent. Platelets express CD47, therefore, platelet adsorption could theoretically remove ant-CD47 interference. This method may be useful if IgG2/IgG3 anti-CD47 therapies become more widely utilized. Another benefit of this method is that it avoids the risk of adsorbing commonly encountered clinically significant alloantibodies as well as many other specificities in patient samples.
Study
Design/Methods: A three cell antibody screen (ABS) of seven different patient samples containing anti-CD47 were performed at Gel-IAT. A titration of each sample was performed using 0.9% saline as the diluent. Each titration was tested against a CD47 positive cell at Gel-IAT. 0.5 mL of each plasma sample was adsorbed using 0.5 mL of pooled packed donor platelets. Donor platelet concentrates were pooled by combining the concentrates into 14 mL tubes and soft spun at 2000 g for 3 minutes to obtain platelet-rich-plasma (PRP). The PRP was then hard spun at 5000 g for 10 minutes to precipitate the platelets. This process was repeated until a 0.5 mL aliquot of pooled donor platelets was obtained. The adsorptions were incubated for 60 minutes at 37°C and mixed every 15 minutes. After incubation, the adsorptions were spun for 15 minutes to harvest adsorbed plasma, which were tested using the same three cell ABS. If reactivity was detected, the adsorbed plasma was titrated and tested at Gel-IAT.
Results/Findings: Table 1 shows the pre and post titer and antibody screen results for each sample.
Conclusions: Our results show anti-CD47 can be adsorbed using pooled platelets. This method was successful in completely adsorbing anti-CD47 from patient samples with titers of 8 or less. Three out of four samples with a titer greater than 8 showed a reduction in antibody titer after one adsorption. This method is more useful to adsorb samples with lower titers and opens the possibility to adsorb out high titer anti-CD47 interference with multiple adsorptions.
