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Human cytomegalovirus (HCMV) is the most common congenital infection and a leading cause of stillbirth, neurodevelopmental impairment, and pediatric hearing loss worldwide. Development of a maternal vaccine or therapeutic to prevent congenital HCMV has been hindered by limited knowledge of the immune responses that protect against HCMV transmission in utero. To identify protective antibody responses, we measured HCMV-specific IgG binding and antiviral functions in paired maternal and cord blood sera from HCMV-seropositive transmitting (n = 41) and non-transmitting (n = 40) mother-infant dyads identified via a large, US-based, public cord blood bank. We found that high-avidity IgG binding to HCMV and antibody-dependent cellular phagocytosis (ADCP) were associated with reduced risk of congenital HCMV infection. We also determined that HCMV-specific IgG activation of Fc[gamma]RI and Fc[gamma]RII was enhanced in non- transmitting dyads and that increased ADCP responses were mediated through both Fc[gamma]RI and Fc[gamma]RIIA expressed on human monocytes. These findings suggest that engagement of Fc[gamma]RI/Fc[gamma]RIIA and Fc effector functions including ADCP may protect against congenital HCMV infection. Taken together, these data can guide future prospective studies on immune correlates against congenital HCMV transmission and inform HCMV vaccine and immunotherapeutic development., Introduction Human cytomegalovirus (HCMV) is the most common congenital infection worldwide, affecting 1 of 200 births or nearly 1 million newborns annually (1, 2). Most congenital HCMV (cCMV) infections are [...]

Single antigen bead (SAB) assays are the most common and sensitive method used to detect and monitor post-transplant donor specific HLA antibodies (DSA). However, a direct comparison across traditional and modified SAB assays to improve routine DSA monitoring using pre-treated IgG sera to eliminate interference has not been performed. We performed a technical comparison of 251 post-transplant DSA from n = 91 serum samples tested neat (pre-treated, undiluted), at a single 1:16 dilution, in the C1q bead assay, and for IgG subclasses (IgG1, IgG2, IgG3, IgG4) with IgG-enriched sera. We found that DSAs that are detectable by 1:16 dilution and/or C1q are associated with higher IgG MFI values and results could be predicted by testing neat sera. DSA detected at 1:16 dilution correlated with >7000 IgG MFI in neat sera and identified DSA that exceeded the SAB linear range for semiquantitative measurements. C1q positive DSA correlated with >15,000 IgG MFI in neat sera. C1q binding correlated most strongly with total IgG MFI (Spearman r = 0.82, p = 0.002) and not specific subclasses, demonstrating that DSA C1q binding capacity in this cohort is driven by HLA-specific IgG concentration. Evaluation of engineered pan-HLA class I-specific human IgG1 and IgG2 subclass monoclonal antibodies by SAB C1q and C3d assays revealed that IgG2 antibodies can bind complement at higher concentrations. The strengths and limitations of modified SAB assays must be considered to optimize efficient testing and accurate clinical interpretation., Competing Interests: Declaration of competing interest The authors of this manuscript have conflicts of interest to disclose as described by Human Immunology. Annette Jackson, Nicole Valenzuela, Dongfeng Chen participate in the One Lambda Thermo Fisher Speaker Bureau. Annette Jackson receives grant support from CareDx and on the Scientific Advisory Board for Hansa BioPharma., (Copyright © 2024 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved.)