Emerging clinical validation of costimulatory T cell engager strategies demonstrates the potential to improve the depth and durability of cancer patient responses. Therapeutic design considerations will be discussed for integrating TCR and costimulatory receptor activation, selecting alternative costimulatory pathways, and employing single versus multiple-tumor antigen targeting strategies, which together are crucial for maximizing selective tumor engagement and optimizing T cell effector activity to restore anti-tumor immunity in cancer patients.

A new wave of immuno-oncology therapeutics is harnessing T cell costimulatory pathways to achieve transformative outcomes in difficult-to-treat cancers. Rondo Therapeutics’ CD28 platform enables precise tuning of CD28 engagement, tailoring costimulation to each therapeutic context to maximize efficacy while preserving safety. Here, we highlight key platform design principles and provide an update on the clinical development of RNDO-564, the first CD28 × Nectin-4 bispecific antibody in development for advanced bladder cancer.

Solid tumor therapy with CD3-bispecifics remains a promising therapeutic approach; however, progress toward transformative clinical activity has been limited to date. Third Arc Bio has developed novel CD3 and CD28 based multispecific antibodies for the treatment of solid tumors.  Lead programs have been developed for ovarian cancer, and preclinical data on our novel CD28 bispecifics demonstrate robust costimulation and synergy with CD3-TCEs including ARC101, a CDLN6xCD3 currently in clinical development.

Blocking CD47 is an attractive therapeutic approach in oncology that has faced setbacks due to ubiquitous expression of this innate immune checkpoint. We have developed a bispecific approach, relying on unbalanced affinity arms to interfere with the SIRPa-CD47 “don’t eat me” signal in a tumor antigen dependent way. This approach has now achieved clinical proof-of-concept in heavily pretreated, platinum-resistant ovarian cancer patients.

This talk will explore early-phase clinical trials of lutikizumab, a dual-variable domain IgG targeting IL-1a and IL-1ß, in hidradenitis suppurativa, osteoarthritis, and inflammatory bowel disease. Key topics include the unique design considerations for multispecific antibodies, clinical results to date, strategies for translating across disease states, dosing challenges, and approaches to selecting optimal patient populations for these complex biologic therapies.

We developed a click-activatable IL12 cytokine prodrug by conjugating PEG masks to lysines via trans-cyclooctene linkers, which were designed to be tracelessly released upon click reaction with tetrazine. Intravenous administration of a targeted tetrazine conjugate to tumor-bearing mice, followed 24 hours later by the masked IL12 resulted in efficient unmasking of IL12 in the tumor, while avoiding IL12 activation in blood.

PRO-XTEN technology enables drug candidates to become active (or unmasked) only where they are needed—in the tumor microenvironment—mitigating off-tumor damage and reducing toxicity. Three T cell engagers based on PRO-XTEN are currently in clinical trials. T cell engagers against multiple additional targets are in preclinical discovery.

Monoclonal antibodies have advanced cancer therapy but remain limited by on-target, off-tumor toxicity. Conditional activation via antigen-binding site masking has emerged as a mitigation strategy, yet the determinants of optimal mask design are not fully defined. Using various binding assays and structural methods, we conducted mechanistic analyses of various masks with distinct properties and identified three key parameters governing performance: binding site, and association and dissociation rate constants. HDX-MS mapping and X-ray crystallography validated mask–antibody interactions. These results provide a framework for the rational design and discovery of next-generation affinity-based masks. 

Bispecific T cell redirecting antibodies are powerful therapeutics for cancer treatment. However, in a target space dominated by surface antigens, which are most frequently shared with normal cells, the amount of suitable antigens happen to be limited. Use of conditional bispecific formats rendering activation conditional to certain events has the potential to derisk bispecific antibodies and to extend the target space. I will discuss protease cleavable idiotypic masks as well as multitargeted logic gated antibody formats as potentially suitable means to overcome these limitations and deliver full benefit of bispecific antibody therapeutics to patients.

T cell engagers (TCEs) are potent cancer therapeutics but often cause toxicity due to antigen expression on healthy tissues. We structurally characterize a new anti-CD3 antibody, E10, and use it to engineer a pro-drug TCE activated by matrix metalloproteinase-2 (MMP-2), a tumor-overexpressed protease. MMP-2 cleavage restores T cell binding and tumor-selective killing. This masking strategy can be extended to other clinical anti-CD3 antibodies, offering a generalizable path to safer immunotherapies.