Antibody-drug conjugates have demonstrated enhanced efficacy and reduced toxicity by targeted delivery of toxic payloads, yet they can also be used to deliver non-toxic payloads (peptides and oligonucleotides) tailored for disease-specific needs. We have previously developed an adaptable drug conjugate strategy using a high-affinity single-chain variable fragment specific for a short unstructured synthetic peptide tag (pTag). When this fragment is fused to an antibody structure, payload loading can be performed by a simple mixing step provided that the pTag is part of the payload. To assess the impact on conjugate stability and biological responses, we evaluated variants of the pTag by introducing amino acid changes at a central position for affinity binding. In a competition ELISA, a 2.4-fold reduction in IC50 was noted for a non-conservative amino acid alteration (pTag K8L ), whereas a conservative amino acid substitution (pTag K8H ) resulted in a 1.3-fold decrease compared to the pTag. The non-conservative amino acid change (pTag K8L ) negatively influenced the stability of the conjugate, illustrated in a hydrogel model. Additionally, the pTag K8L alteration led to increased CD8 + T cell proliferation and a slight decrease in CD4 + T cell proliferation in vitro . This was irrespective of whether formulated with the bispecific antibody or not. In vivo , the data displayed that the pTag led to significantly higher T cell expansion than the pTag K8L , suggesting that lower affinity may impair immune activation and that conjugation stability is key to achieving the desired targeted delivery capacity.
Laurén et al. (Sun,) studied this question.