Introduction: Current therapies for multiple myeloma (MM), such as immunomodulatory agents, proteasome inhibitors, stem-cell transplantation, and monoclonal antibodies against tumor-associated antigens have greatly improved patient survival. However, MM remains an incurable disease as most patients will eventually relapse. Recent advances in targeted T-cell therapies have shown promise in clinical trials but the adaptive immune system may be insufficient to eradicate all MM clones. In contrast, treatments harnessing the innate immune system have been relatively underdeveloped in MM despite evidence suggesting a role of innate immunity in the efficacy of existing therapies. Innate or innate-like cells, such as NK and γδ T cells, have the potential to display strong anti-tumor activity, and strategies aimed to improve or re-direct their cytotoxicity represent a new opportunity for cancer immunotherapies and a complementary approach to existing therapies. Here we describe the preclinical characterization of CTX-8573, a novel multispecific antibody that targets B-cell maturation antigen (BCMA) on tumor cells and promotes potent cytotoxicity by NK and γδ T cells through engagement of the activating receptors NKp30 and CD16a. Method: Bispecific constructs were generated by appending two common-light chain compatible anti-NKp30 Fab fragments to the C-terminus of an anti-BCMA IgG1 antibody containing an afucosylated Fc for enhanced CD16a engagement. To test the effects of targeting NKp30 alone, variants were expressed with an aglycosylated Fc to eliminate CD16a binding. In-vitro assays were performed with primary NK or γδ T cells to determine innate-cell activation, cytokine production, proliferation, and target-cell cytotoxicity against tumor cell lines with a range of BCMA expression levels. In-vivo efficacy studies were performed in multiple humanized mouse models and pharmacokinetics and safety were evaluated in Cynomolgus monkeys. Results: CTX-8573 is highly expressed in CHO cells with minimal aggregation and displays stability, solubility, and binding to BCMA and NKp30 equivalent to the parental monoclonal antibodies. By engaging NKp30 and CD16a, CTX-8573 promotes potent cytotoxicity of BCMA expressing target cells by NK and γδ T cells with >100 fold reduced EC50 compared to the corresponding BCMA monoclonal antibody control. CTX-8573 also demonstrates robust killing of low BCMA expressing cell lines including RPMI-8226 where monoclonal BCMA antibodies lack activity. An aglycosylated variant of CTX-8573 lacking CD16a binding maintains cell killing activity, demonstrating that engagement of NKp30 alone is sufficient to promote innate cell activation and cytotoxicity, although activity is enhanced by CD16A engagement. Furthermore, CTX-8573 maintains its cytotoxic activity in presence of soluble BCMA or BCMA ligands APRIL and BAFF. CTX-8573 does not induce innate cell activation, cytokine production, or killing in the absence of BCMA expressing target cells, supporting a wide therapeutic window. Additionally, unlike daratumumab, CTX-8573 does not induce NK-cell fratricide. In-vivo, CTX-8573 demonstrates anti-tumor efficacy in multiple humanized mouse models including killing of low BCMA expressing cell lines. In Cynomolgus monkeys, CTX-8573 displays standard biphasic pharmacokinetics with a 16 day β-phase half-life and has no evidence of systemic immune activation as measured by C-reactive protein levels. Lastly, NKp30 expression is maintained on bone marrow NK cells from MM patients including the presence of a significant NKp30+CD16a- subpopulation. Conclusion: CTX-8573 represents a novel class of bispecific antibodies that promote potent tumor cell killing by NK and γδ T-cells through engagement of the activating receptors NKp30 and CD16a. CTX-8573 demonstrates strong anti-tumor efficacy in vitro and in vivo, a wide therapeutic window with no evidence of systemic toxicity, and monoclonal-like pharmacokinetics and manufacturability. Together, these data highlight the potential of CTX-8573 as a novel treatment for MM either alone or as a complement to existing therapies. Disclosures Watkins-Yoon: Compass therapeutics LLC: Employment, Equity Ownership. Guzman:Compass therapeutics LLC: Employment, Equity Ownership. Oliphant:Compass therapeutics LLC: Employment, Equity Ownership. Haserlat:Compass therapeutics LLC: Employment, Equity Ownership. Leung:Compass therapeutics LLC: Employment, Equity Ownership. Chottin:University of Louisiana at Lafayette: Employment. Ophir:Compass therapeutics LLC: Employment, Equity Ownership. Vekeria:Compass therapeutics LLC: Employment, Equity Ownership. Nanjappa:Compass therapeutics LLC: Employment, Equity Ownership. Markrush:Compass therapeutics LLC: Employment, Equity Ownership. McConaughy:Compass therapeutics LLC: Employment, Equity Ownership. Wang:Compass therapeutics LLC: Employment, Equity Ownership. Schilling:Compass therapeutics LLC: Employment, Equity Ownership. Kim:Compass therapeutics LLC: Employment, Equity Ownership. Wu:Compass Therapeutics LLC: Employment, Equity Ownership. Liu:Compass therapeutics LLC: Employment, Equity Ownership. Rogers:University of Louisiana at Lafayette: Employment. Villinger:University of Louisiana at Lafayette: Employment. Gong:Compass therapeutics LLC: Employment, Equity Ownership. Hamilton:Compass therapeutics LLC: Employment, Equity Ownership. Bobrowicz:Compass therapeutics LLC: Employment, Equity Ownership. Schuetz:Compass therapeutics LLC: Employment, Equity Ownership. Schmidt:Compass therapeutics LLC: Employment, Equity Ownership. Draghi:Compass therapeutics LLC: Employment, Equity Ownership.

Respiratory syncytial virus (RSV) is a public health concern that causes acute lower respiratory tract infection. So far, no vaccine candidate under development has reached the market and the only licensed product to prevent RSV infection in at-risk infants and young children is a monoclonal antibody (Synagis®). Polyclonal human anti-RSV hyper-immune immunoglobulins (Igs) have also been used but were superseded by Synagis® owing to their low titer and large infused volume. Here we report a new drug class of immunoglobulins, derived from human non hyper-immune plasma that was generated by an innovative bioprocess, called Ig cracking, combining expertises in plasma-derived products and affinity chromatography. By using the RSV fusion protein (F protein) as ligand, the Ig cracking process provided a purified and concentrated product, designated hyper-enriched anti-RSV IgG, composed of at least 15-20% target-specific-antibodies from normal plasma. These anti-RSV Ig displayed a strong in vitro neutralization effect on RSV replication. Moreover, we described a novel prophylactic strategy based on local nasal administration of this unique hyper-enriched anti-RSV IgG solution using a mouse model of infection with bioluminescent RSV. Our results demonstrated that very low doses of hyper-enriched anti-RSV IgG can be administered locally to ensure rapid and efficient inhibition of virus infection. Thus, the general hyper-enriched Ig concept appeared a promising approach and might provide solutions to prevent and treat other infectious diseases.ImportanceRespiratory Syncytial Virus (RSV) is the major cause of acute lower respiratory infections in children, and is also recognized as a cause of morbidity in the elderly. There are still no vaccines and no efficient antiviral therapy against this virus. Here, we described an approach of passive immunization with a new class of hyper-enriched anti-RSV immunoglobulins (Ig) manufactured from human normal plasma. This new class of immunoglobulin plasma derived product is generated by an innovative bioprocess, called Ig cracking, which requires a combination of expertise in both plasma derived products and affinity chromatography. The strong efficacy in a small volume of these hyper-enriched anti-RSV IgG to inhibit the viral infection was demonstrated using a mouse model. This new class of immunoglobulin plasma-derived products could be applied to other pathogens to address specific therapeutic needs in the field of infectious diseases or even pandemics, such as COVID-19.

Respiratory Syncytial Virus (RSV) is the major cause of lower respiratory tract infection in infants, in whom, the sensing of RSV by innate immune receptors and its regulation are still poorly described. However, the severe bronchiolitis following RSV infection in neonates has been associated with a defect in type I interferons (IFN-I) production, a cytokine produced mainly by alveolar macrophages (AMs) upon RSV infection in adults. In the present study, neonatal C57BL/6 AMs mobilized very weakly the IFN-I pathway upon RSV infection in vitro and failed to restrain virus replication. However, IFN-I productions by neonatal AMs were substantially increased by the deletion of Insulin-Responsive AminoPeptidase (IRAP), a protein previously involved in the regulation of IFN-I production by dendritic cells. Moreover, neonatal IRAPKO AMs showed a higher expression of IFN-stimulated genes than their wild-type C57BL/6 counterpart. Interestingly, depletion of IRAP did not affect adult AM responses. Finally, we demonstrated that newborn IRAPKO mice infected with RSV had more IFN-I in their lungs and eliminated the virus more efficiently than WT neonates. Taken together, early-life susceptibility to RSV infection may be related to an original age-dependent suppressive function of IRAP on the IFN-I driven-antiviral responses in neonatal AMs.