Conditionally Activatable Antibody Platforms: Mechanisms, Modalities, and Clinical Translation Potential.

Conditionally activatable antibodies represent a promising strategy to improve the therapeutic index of antibody-based drugs by restricting their activity to disease sites, thereby minimizing systemic toxicity. These engineered platforms leverage disease-associated cues-such as protease activity, pH, redox gradients, or other microenvironmental factors-to modulate antigen binding or effector function in a spatially and temporally controlled manner. In this review, we categorize recent advances in activatable antibody technologies into three principal strategies: (1) masking domains or peptides that block target recognition until removed by disease-specific triggers, (2) structural rearrangement by fusing external domains to antibodies to regulate access to the paratope, and (3) payload activation approaches in antibody-drug conjugates. We summarize key design principles, representative examples, and their preclinical or clinical development status, highlighting strengths, limitations, and translational challenges. Special attention is given to linker chemistry, trigger specificity, and pharmacokinetic considerations that influence therapeutic performance. Finally, we discuss emerging trends, including multi-input activation systems and integration with next-generation modalities such as bispecific antibodies and immune cell engagers, which could further refine target selectivity and broaden therapeutic applications. This overview highlights representative advances to guide the rational design of future activatable antibody platforms and to accelerate their progression toward clinical use.