PB0491 - Influence of emicizumab administration on humoral and cellular components of the immune system and results of assays for transfusion-transmitted viral infections

Background: Emicizumab is a modified bispecific IgG4 monoclonal antibody that bridges activated factor IX and factor X to restore the function of missing FVIIIa. It is administered subcutaneously for prophylaxis of bleeding in patients with hemophilia A with and without inhibitor. Literature data about the possible effect of long-lasting emicizumab administration on immune system components are sparse.

Aims: To investigate the influence of long-lasting administration of emicizumab on cellular and humoral components of the immune system as well as to examine the effect of emicizumab treatment on the results of serological assays for anti-HIV, anti-HCV, and HBsAg.

Methods: In 8 patients with severe hemophilia A (5 with and 3 without inhibitors), median age 37 (range 29-61) years, enumeration of peripheral blood lymphocyte (Ly) subpopulations (B-Ly, CD4+T-Ly, CD8+T-Ly, NK-Ly) was performed by multiparametric flow cytometry and dual-platform assay before and at least 6 months after the start of regular emicizumab administration. Also, the concentration of immunoglobulins was measured, and qualitative assays for anti-HIV, anti-HCV, and HBsAg were determined simultaneously.

Results: Before and at least 6 months after the start of emicizumab prophylaxis, the mean values ± SD were as follows: WBC count (x109/L) ( 6.0±2.4 vs. 5.65±1.0), B-Ly (cell/µL) (164.62±73.2 vs. 174.9±74.8), total T-Ly (cell/µL) (1185.5±227.9 vs. 1251.4±140.0), CD4+T-Ly (cell/µL) (658.5±115.0 vs. 682.75±99.3), CD8+T-Ly (cell/µL) (473.25±182.0 vs 513.9±130.6), NK-Ly (cell/µL) (258±96.5 vs. 275.9±108.4), (P>0.05 for all parameters). The blood concentration of IgG, IgA, and IgM immunoglobulins did not change significantly in 6 months of emicizumab prophylaxis. Interestingly, in 2 out of 3 anti-HCV negative patients, seroconversion to anti-HCV positive occurred during treatment, but repeated HCV-RNA assay remained negative.

Conclusion(s): Administration of emicizumab for 6 months did not significantly affect the main humoral and cellular immune components. It seems that emicizumab treatment may cause false positivity for anti-HCV assay in some patients.