Bispecific antibodies targeting two receptors expressed on a cell of interest can have much higher specificity than mAbs targeting either receptor alone. Avidity drives this specificity, and multiple factors contribute to the observed synergy. Success requires finding the right epitopes, working within the final bispecific format, then tuning affinities to optimize selectivity. We discuss some of the physical parameters and strategies involved, then share real-world data on bispecific antibodies targeting cancer cells and tumor-localized Tregs.

Tumor stroma and immunosuppressive microenvironment are major obstacles for the clinical application of antibody-drug conjugates (ADCs) and bispecific antibodies (BsAbs) in refractory cancer. To overcome these drawbacks, we are developing analytical methods of pharmacokinetics/pharmacodynamics /mechanism of action. Moreover, we are also exploiting new technologies to improve antibody delivery and T cell migration. Here I will present our recent work of ADCs and BdAbs using DDS and molecular imaging.

The in vivo complexity of B cell differentiation, selection, and affinity maturation cannot be recapitulated in vitro. To facilitate therapeutic antibody discovery, several strains of humanized immunoglobulin mice were engineered, including a common human light chain model for bispecific/multispecific antibody discovery, drug target knockout mice to induce hyperimmunity, and an HLA-transgenic model for discovery of TCR-mimic antibodies. Together, these platforms serve to uncover best-in-class or first-in-class antibodies for novel targets

Multi-specific therapeutics have the potential to overcome PD-(L)1 checkpoint resistance in the treatment of cancer. CDX-527 is a clinical-stage bispecific antibody that is designed to simultaneously relieve PD-(L)1 suppression by inhibiting PD-L1 and stimulate CD27 to induce further T-cell activation. CDX-585 is a preclinical bispecific antibody candidate designed to inhibit myeloid suppression through ILT4/LILRB2 and overcome T cell suppression through PD-1 inhibition. Both bsAbs have demonstrated synergistic activity relative to the combination of individual parental mAbs in cultured immune assays and exhibited anti-tumor activity in animal models. The design, development and preclinical characterization of these bispecifics will be presented.

Our company has designed six CD47-based bispecific mAb-Trap molecules with enhanced Fc-Fc?R interaction and tested them in various mouse tumor models. Surprisingly, while four bispecific mAb-Traps (IMM0306: CD47/CD20, IMM2902: CD47/Her2, IMM2520: CD47/PD-L1, IMM5601: CD47/CD38) revealed potent synergistic anti-tumor activities, two (IMM0404: CD47/EGFR, IMM3202: CD47/VEGFR2), did not generate such effect. In those two mAb-Trap molecules, linkage of CD47 ligand trap (SIRPa decoy) onto EGFR antibody or VEGFR2 antibody actually reduced therapeutic effects. Thus the synergistic anti-tumor activities of CD47-based bi-specific molecules in experimental solid tumors are dependent on interaction of tumor targets; structural design and target selection deserve careful consideration.

Multipass membrane proteins remain valuable yet elusive targets for therapeutic antibodies. The MPS antibody discovery platform has a >95% success rate to reliably target these proteins. We describe recent advances including antigen engineering, mRNA immunization, use of divergent species, chicken antibody humanization, and bispecific screening to show how these approaches have yielded rare and functional antibodies against complex targets such as SARS-CoV-2, GPRC5d, Claudin 6, Claudin 18.2, P2X7 and SLC2A4. 

It is becoming clear that rules applied to standard use of RT need to be modified to best exploit the immunogenic effects of ionizing radiation. Dose and fractionation are both relevant and evidence of radiation immunogenicity at low dose of RT is also available,  encouraging clinical trials to further test this approach. The need to define the optimal sequencing of radiation with immunogenic systemic therapy is emerging, particularly when RT is combined with anti-PD1 immunotherapy.  

T cell-devoid “cold” tumors evade the immune response at one or more of three steps: 1) failure to express or present immunogenic antigens; 2) exclusion of effector T cells; and 3) production of immune-suppressive signals and/or recruitment of immune suppressive cells. Radiation therapy affects each of these three steps, and its ability to enhance responses to immunotherapy can be improved by countering radiation-enhanced immunosuppressive signals.

• Designing ARTEMIS Antibody TCR (AbTCR) T cells to address the major hurdles in treating solid tumor
  
• Infiltrating into solid tumor under immunosuppressive microenvironment
  
• Targeting Alpha-fetoprotein (AFP) and Glypican 3 (GPC3) in advanced hepatocellular carcinoma (HCC)
• Demonstrating superior safety and efficacy profile of ARTEMIS T cells​

Agonistic monoclonal antibodies targeting CD137 (4-1BB) have shown much preclinical promise, but their clinical development has been hampered due to a poor therapeutic index, in particular liver toxicity. CB307 is a novel trispecific Humabody therapeutic targeting CD137, prostate specific membrane antigen (PSMA) and human serum albumin (HSA). The molecular weight of CB307 is <50 kDa and it does not contain an Fc domain; half-life extension is achieved through a VH domain which binds HSA. The design of CB307 enables conditional agonism of CD137 only in the presence of PSMA positive tumour cells, enabling tumour-specific T cell activation whilst minimising systemic activation. Here we describe the generation of CB307 by formatting fully human VH domains matured in vivo by the Crescendo Mouse and we illustrate the expected mechanism of action. In an in vitro reporter assay, CB307 mediates CD137 signalling only in the presence of PSMA positive cells and not PSMA negative cells. In a transgenic syngeneic mouse model we show that CB307 can regress PSMA expressing tumours in vivo. Finally we describe design of the ongoing first in human clinical study (NCT04839991) and illustrate how the Humabody platform has been further leveraged to create a pipeline of novel, conditionally-active, T cell enhancing therapeutics.

AlivaMab Discovery Services’ (ADS) antibody discovery workflows are optimized for fast and efficient drug discovery and development for both standard and next generation antibody formats. To ensure success of every antibody discovery campaign, we implement custom immunization and screening strategies tailored to each set of antibody design goals. In this talk, examples of fit-for-purpose strategies will be presented.

Antibody and gene engineering technologies have been successfully translated to a first wave autologous CAR T cell products directed at B cell malignancies, with curative potential in a subset of patients. We discuss strengths and limitations of the current CAR T cell platform, major learnings to date, and next-generation immunotherapy applicable to a broader category of disease indications.

The first approved CAR T cell product was for a pediatric indication, pre-B ALL. The rapid responses seen reflect the biology of the disease, with non-transformed B cells and leukemia cells driving response.  In pediatric solid tumors, the physiological context suppresses CAR T activity, as in other solid tumor indications. By optimizing the CAR T cell product and by subverting myeloid cell-induced immunosuppression, avenues to develop new therapeutic advances were made apparent. By defining tumor-associated gene expression profiles associated with poor outcomes, and addressing tumor-associated macrophages and myeloid-derived suppressor cells, we are now able to treat rhabdomyosarcoma in model systems. 

Once infused into patients, there is little means of regulation of CAR T cell activity, proliferation, and specificity. To allow for quantitative control of CAR T cell activity, we first developed universal immune receptors (UnivIRs), a highly versatile platform that decouples the CAR antigen specificity domain from the intracellular signaling domains to permit on-demand, personalized redirection of UnivIRs-expressing T cells against a wide array of antigens using repurposed, tagged antigen-specific antibodies, with proof of concept established for an advanced theranostic UnivIR platform that utilizes clinically actionable agents that allow for tumor monitoring via imaging.