In recent years, with the emerging challenges of tumor heterogeneity, immune escape mechanisms and the complexity of the tumor microenvironment, regulation relying solely on two targets can no longer meet higher clinical therapeutic demands. Consequently, a variety of molecular formats with superior systematic regulatory capabilities have emerged, including TCR bispecific constructs, bispecific aptamers, and multispecific immunotherapies. These technologies not only feature multi-target synergistic effects but also reshape the logic of immune responses.
1. TCR Bispecific Constructs: From Intracellular Antigens to Therapeutic Targets
For a long time, antibody drugs have been limited to recognizing only cell surface antigens. However, tumor-specific targets are largely derived from intracellular components, such as mutated or abnormally expressed proteins. Such antigens can only be recognized by the immune system after being processed into antigenic peptides and presented on the cell surface via MHC molecules. The T-cell receptor (TCR) is the key molecule responsible for recognizing the peptide-MHC (pMHC) complex.
Leveraging this mechanism, TCR bispecific constructs have been engineered and applied: one end recognizes a specific pMHC complex, while the other binds to the CD3 molecule on the T-cell surface to trigger T-cell activation. Acting as a functional bridge between tumor cells and T cells, TCR bispecific constructs precisely direct immune cytotoxicity to specific targets, converting previously undruggable intracellular antigens into exploitable therapeutic targets.
TCR bispecific constructs hold great potential in solid tumors and immunotherapy. The value of this strategy lies not only in identifying novel targets but also in advancing next-generation immunotherapies toward more sophisticated engineered systems.
2. Bispecific Aptamers: Molecular Formats Beyond Antibodies
While TCR bispecific constructs expand the scope of targetable antigens, the development of aptamers brings innovation at the molecular level itself. Aptamers are functional molecules composed of DNA or RNA that bind to targets with high affinity through specific three-dimensional folded structures. Unlike antibodies that rely on mammalian cell expression systems, aptamers can be chemically synthesized, endowing them with unique advantages in production consistency and structural controllability.
A bispecific aptamer is formed by linking two aptamers with distinct targeting capabilities via a flexible linker. One end binds immune cells and the other targets diseased cells, thereby facilitating the formation of immune synapses.
Bispecific aptamers represent not merely functional alternatives to antibodies but fundamental molecular innovation. Their small molecular size enables enhanced tissue penetration; low immunogenicity offers potential benefits for long-term administration; and chemical synthesis allows greater flexibility for structural optimization, providing an entirely new drug format for next-generation immunotherapies.
Nevertheless, significant challenges remain. Aptamers are susceptible to degradation by nucleases in vivo, exhibit short half-lives, and are rapidly cleared from circulation, all of which limit their in vivo therapeutic efficacy. Accordingly, the development of aptamer therapeutics typically requires chemical modification and optimized delivery systems to improve overall stability.
3. Multispecific Immunotherapies: From Dual-Targeting to Systematic Regulation
Both TCR-based modalities and aptamers adopt a bispecific strategy, whereas the immune system itself functions as a highly sophisticated network. Hence, a core focus of future research is to integrate multiple functions into a single molecule for precise modulation of immune responses. Centered on this goal, multispecific immunotherapy has evolved a set of pivotal strategic approaches.
First is modular design. Distinct domains (e.g., targeting, activating, or inhibitory modules) can be assembled like building blocks. For instance, combining a tumor-targeting module with an immune effector activation module enables simultaneous action on tumor cells and immune cells. This design not only flexibly enhances targeting specificity but also adapts readily to diverse disease scenarios, boosting overall therapeutic efficiency.
Second, various delivery platforms can be deployed to optimize the in vivo distribution and stability of multispecific molecules, improving safety, amplifying therapeutic efficacy, and facilitating enrichment in target tissues. Therefore, the design of delivery systems and the systematic regulatory optimization of multispecific molecules act synergistically, collectively determining therapeutic outcomes.
Conclusion
Against the backdrop of evolving clinical needs, new challenges and research directions have arisen beyond conventional bispecific antibodies. The technological landscape continues to expand from TCR constructs and aptamers to multispecific immunotherapy platforms. Correspondingly, drug research and development is shifting from traditional molecular screening toward systematic engineering and rational design. Next-generation immunotherapies have entered an era of greater complexity and immense promise.
