Background: Ewing sarcoma (ES) is a rare tumor that affects children, adolescents, and young adults. ES is associated with high morbidity in all patients and high mortality for those who present with metastatic disease. A chromosomal translocation, either t(11;22)(q24;p12) or t(21;22)(q22;q12) leads to the fusion oncoproteins EWS::FLI1 or EWS::ERG in 95% of ES patients. We recognized a critical need for a stably sourced high-affinity antibody that recognizes EWS::FLI1 with maximal specificity. Understanding EWS::FLI1 protein complexes is a pivotal gap in ES knowledge that necessitates the development of antibodies capable of identifying native proteins in solution. Further, variable epitope sequencing of a monoclonal antibody enables the construction of degraders and nanobody identifiers. Methods: Monoclonal antibodies were produced following informed peptide synthesis, injection, and hybridoma creation. Hybridoma antibodies were validated for specificity and function. Results: Our results indicate that the FLI1 1.2 monoclonal antibody, which recognizes the EWS::FLI1 fusion oncoprotein, can be reliably applied to multiple molecular biology applications like immunoblot, immunoprecipitation, immunofluorescence, and immunohistochemistry. This FLI1 1.2 monoclonal antibody has a high affinity of 0.3 nM KD to EWS::FLI1. In terms of specificity, this antibody is highly specific to EWS::FLI1 and some cross reactivity with ERG. Conclusions: This reagent will provide the research community with valuable tools for further biochemical and genomic interrogation of the oncogenic activity of EWS::FLI1 in ES.

Background/Objectives: Three-dimensional (3D) in vitro cell culture models have recently stimulated great interest since they may have more pre-clinical value than conventional in vitro 2D models. In fact, 3D culture models may mimic the in vivo biophysical 3D structure of tumors and cell-to-cell interaction, thereby representing a more useful approach to testing drug responses. In this study we have developed a 3D culture model of an EBV+/CD30+cell line, D430B, previously characterized as an Anaplastic Large Cell Lymphoma of B phenotype (B-ALCL), to determine the cytotoxic activity of the antibody–drug conjugate Brentuximab Vedotin. Methods: By using of ultra-low attachment plates, we developed D430B spheroids that appeared particularly homogenous in terms of growth and size. Results: Brentuximab Vedotin treatment (1 to 20 μg/mL) turned out to be significantly cytotoxic to these cells, while the addition of the anti-CD20 chimeric antibody Rituximab (10 μg/mL) appeared almost ineffective, even though these cells express CD20. Moreover, when we co-cultured D430B cells with stromal cells (HS5), to re-create a microenvironment representative of neoplastic cell/mesenchymal cell interactions within the lymph node, we observed a significant, although faint, protective effect. Conclusions: This simple and reproducible method of generating D430B-ALCL spheroids to evaluate their response to Brentuximab Vedotin treatment, as here described, may provide a valuable preliminary tool for the future pre-clinical screening of patients’ primary lymphoma cells or the development of novel therapies for this type of pathology and related diseases.

Background/Objectives: T cell bispecific antibodies (TCBs) result in the activation of T cell receptor signaling upon binding to tumor antigens providing signal 1 to T cells. To enhance and sustain their activity, a co-stimulatory signal 2 is required. Here CEACAM5-targeted 4-1BBL antibody fusion proteins for combination with CEA-TCB (cibisatamab, RG7802) are described in an investigation of the relationship between the CEACAM5 epitope and T cell activity. Methods: CEACAM5-targeted bispecific 4-1BBL antibody fusion proteins (CEA-4-1BBLs) were generated based on different CEACAM5 antibodies and characterized in vitro in Jurkat-4-1BB reporter and PBMC cell assays. The impact of shed CEA on in vitro activity and cynomolgus cross-reactivity was studied. In vivo efficacy was assessed in human stem cell humanized NSG mice xenograft models bearing MKN-45 and HPAFII tumors. Results: MFE23-4-1BBL and Sm9b-4-1BBL showed superior functional activity in Jurkat-4-1BB reporter and primary T cell assays when combined with the CD3 antibody V9, whereas T84.66-LCHA-4-1BBL and A5B7-4-1BBL performed better when combined with CEA-TCB. In humanized NSG mice MKN-45 and HPAFII xenograft models, T84.66-LCHA-4-1BBL mediated the best anti-tumor efficacy. Conclusions: For the assessment of the combination of CEA-TCB with CEA-4-1BBL, co-stimulatory antibody fusion protein in vitro assays are not sufficient to fully capture the complex relationships affecting efficacy. Thus, screening with different cell assays and in vivo efficacy studies in combination with CEA-TCB are essential to select the best candidate. Based on the totality of data on the T84.66-LCHA-4-1BBL antibody fusion protein comprising the CEACAM5 antibody, T84.66-LCHA was selected as the optimal combination partner for CEA-TCB.

B cells have attracted increasing interest in the field of organ transplantation due to their newly discovered immunoregulatory properties in alloimmune responses. Traditionally, B cells have been primarily associated with adaptive immunity to foreign substances and alloreactive immune response to allografts, differentiating into antibody-producing plasma cells or memory cells upon antigen recognition and T cell collaboration. However, the existence of B cells with regulatory functions (Bregs) in humans has been widely confirmed, highlighting the presence of this subset, which has immunosuppressive properties and which might contribute to allograft tolerance, within the B cell compartment in humans and mice. In this mini review, we summarize all the information available in the published reports about the role of regulatory B cells in solid organ transplantation.

Background and Aims: C1q is an autoantigen in different autoimmune disorders, Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN) among them. The two functional domains of C1q, the collagen-like region (CLR) and the globular head region (gC1q), are frequently recognized by autoantibodies in SLE and LN when C1q is immobilized. We studied whether autoantibodies to C1q in SLE and LN patients recognized C1q as a soluble autoantigen and whether the act of immobilization was a prerequisite for the recognition of C1q autoepitopes localized on gC1q domains. Methods: The interaction of soluble C1q and its globular fragments ghA, ghB, and ghC with immobilized IgG autoantibodies (and vice versa) from sera of 48 patients with SLE and LN was studied with ELISA. Data were compared using Spearman correlation coefficient. Fluorescence spectroscopy was used to study the interaction between C1q and LN IgG autoantibodies both presented in solution. Results: We found that anti-C1q autoantibodies from SLE and LN patients specifically bound C1q and gC1q fragments, ghA, ghB, and ghC, both as immobilized and soluble antigens. Correlation analysis indicated a negative correlation between the levels of autoantibodies against immobilized and soluble C1q and immobilized and soluble gC1q fragments which indicates different epitopes when these proteins were recognized as autoantigens in soluble and immobilized conformations. Conclusions: Serum C1q in patients with SLE is a target molecule for binding from anti-C1q autoantibodies. The gC1q region undergoes a conformational change in an immobilized and a soluble form, thus exposing different epitope-binding sites.

Introduction: Simultaneous liver–kidney (SLK) transplant recipients are considered at lower immunologic risk than kidney-alone recipients, so steroid-only induction is often used. However, some centers continue to include basiliximab induction in their protocols. This study compared graft and infectious outcomes in SLK recipients receiving basiliximab (Bas) induction versus those without basiliximab (No Bas). Methods: Using TriNetX, we conducted a retrospective, propensity-score-matched study of SLK recipients comparing 3-, 6-, and 12-month graft and infectious outcomes. Patients receiving alemtuzumab or anti-thymocyte globulin were excluded; steroid induction was permitted but not required in either cohort. Maintenance immunosuppression included tacrolimus, mycophenolate, and prednisone. Cohorts were matched on 71 variables, including demographics, disease etiology, severity markers, and cPRA. Results: After matching, 292 patients were included per cohort (mean age 56.9 ± 10.1 years; 61% male). Kidney and liver rejection rates were similar. The No Bas cohort had more liver biopsies (25.5% vs. 18.2% at 1 year, p = 0.04). Kidney biopsy, graft failure, re-transplantation, delayed graft function, and mortality were comparable. Liver primary non-function was more frequent in Bas (2.8% vs. 0.4%, p = 0.04). The No Bas cohort had higher CMV at 3 months (13.4% vs. 6.7%, p = 0.008) and higher EBV at all time points (4.0% vs. 0.4% at 1 year, p = 0.004). Conclusions: SLK recipients without basiliximab induction had comparable rejection outcomes but more viral infections, potentially from greater steroid exposure, and more liver biopsies, which may reflect higher clinical suspicion for rejection or incomplete capture of rejection events in EMR data.

Rabbit antithymocyte globulin is one of the most commonly used agents for induction immunosuppression in renal transplantation. It has contributed significantly to improved allograft survival and has a favorable safety profile. Despite its advantages, rabbit antithymocyte globulin carries a rare but potentially life-threatening risk of anaphylaxis, which can lead to severe morbidity and mortality. Anaphylaxis is an acute and dramatic complication that requires prompt recognition and immediate management. In this review, we discuss the pathophysiology, clinical features, and management of rabbit antithymocyte globulin-associated anaphylaxis. We have also included practical insights from our clinical experience to guide early recognition and management, aiming to help clinicians safely manage this critical adverse event.

Antibodies are produced by cells of the adaptive immune response and recognize epitopes of microbial structures with high affinity and specificity. Antibodies are recognized by Fc fragment receptors (FcRs) found on the surface of phagocytic cells (neutrophils, monocytes, macrophages) and NK cells, among others. Hence, antibodies link the adaptive immune response with the innate immune response. The functions of antibodies are related to the N-glycosylation profile of these proteins. In this review, we describe how N-glycosylation of the Fc fragment of the different antibody classes is carried out, and which oligosaccharides are most commonly found in these antibodies. Subsequently, we summarize the biological effects of N-glycosylation of antibodies: on the binding of antibodies to FcRs (which affects various functions, such as antibody-dependent cellular cytotoxicity, antibody-dependent phagocytosis, and the production of pro- or anti-inflammatory chemokines and cytokines), on the ability of antibodies to activate complement and on the ability of some antibodies to directly neutralize the adhesion of bacteria and viruses to host cells (independently of Fab recognition). We describe how the N-glycosylation profile of antibodies is modified during certain infections (such as tuberculosis, COVID-19, influenza and dengue) and in response to vaccination, and the potential use of this profile to identify the stage and severity of an infection. Finally, we review the importance of N-glycosylation for the pharmacokinetic, pharmacodynamic and safety profiles of therapeutic monoclonal antibodies.

Background: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by joint inflammation that leads to tissue damage and disability. RA affects approximately 0.5–1% of the global population and is driven by a complex interplay of genetic susceptibility, environmental factors, and immune dysregulation. While biologic and targeted synthetic DMARDs improved RA treatment, they have limitations in efficacy, safety, and accessibility. B-cell-targeting therapies, such as anti-CD20, have shown effectiveness, but only with broad immunosuppression, which can increase infection risk and compromise humoral immunity. Therefore, there is an unmet need for more selective therapeutic strategies that modulate pathogenic immune pathways while preserving protective immune functions. It has been suggested that targeting the BAFF pathway may offer a more favorable therapeutic approach compared to targeting CD20. Objectives: In this study, we evaluated the therapeutic potential of V3-46s mIgG2a, an anti-BAFF-R (BR3) antibody in a mouse RA model, hypothesizing that it would offer a more selective and effective strategy. Methods: We expressed and purified four antibody variants and assessed their binding and neutralizing activity in vitro. V3-46s mIgG2a was selected for in vivo evaluation in a collagen-induced arthritis (CIA) model. Results: Treatment with this antibody delayed disease onset and reduced arthritis severity, spleen index, and B-cell populations. Conclusions: These findings highlight the potential of BAFF-R-targeting antibodies as a therapeutic approach for RA treatment. This preclinical work lays the groundwork for future development of BAFF-R blockade as a complementary or alternative strategy to current biologic treatments.

Background: Antibody-dependent cellular cytotoxicity (ADCC) is an immune response where antibodies bind to target cells and activate effector cells through Fcγ receptors, ultimately leading to the destruction of the target cells. Methods: This study examined the ADCC activities of charge variants of a therapeutic IgG1, MAB1, using an internally developed reporter gene assay. In this assay, the proprietary target was expressed on DiFi cells, while FcγRIIIa was expressed on Jurkat effector cells. Results: The results revealed that different charge variants had varying levels of ADCC activity, with variants containing C-terminal lysine residues showing enhanced activity. The charge variants arose from modifications such as the presence of sialic acid at the glycan moiety, deamidation, and C-terminal lysine truncation, including K2 (two C-terminal lysine residues), K1 (one C-terminal lysine residue), and K0 (no C-terminal lysine residues) variants. Notably, the K1 and K2 variants demonstrated higher ADCC activity compared to the K0 and acidic variants. However, the observed increase was attributed not to the lysine residue itself, but rather to the MAN5 glycan associated with the lysine-containing variants. Conclusion: These findings challenge previous assumptions about the role of C-terminal lysine in ADCC, suggesting a shift in understanding the functional significance of charge variants and emphasizing the critical influence of glycan composition in therapeutic antibody efficacy.