DB-2304, a Duality Immune Modulating Antibody‒Drug Conjugate (DIMAC) targeting BDCA2, displays strong potency in the suppression of pDC functions.

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Abstract Study Objective: BDCA2 is specifically expressed on plasmacytoid dendritic cells (pDCs), whose overproduction of type I IFN is crucial in SLE pathogenesis. Combining anti-BDCA2 mAB with glucocorticoids (GCs) has shown clinical efficacy. Previous studies revealed superior anti-inflammatory effects of anti-BDCA2 antibody‒drug conjugate (ADC), motivating the development of DB-2304, an anti-BDCA2 ADC using a novel glucocorticoid receptor agonist as a payload. This study assessed the preclinical efficacy and safety of DB-2304. Methods: A novel BDCA2 mAB, Hu033-03, was developed and conjugated with the DIMAC payload to generate DB-2304. The inhibitory potency of DB-2304 was evaluated in human PBMCs in vitro. The PK and safety profile and pDC function suppression were characterized in cynomolgus monkeys. Results: Hu033-03 exhibited high affinity for BDCA2, inducing rapid internalization upon binding. DB-2304 showed enhanced suppression of IFNa production and a broader spectrum of proinflammatory cytokines in human PBMCs without cytotoxicity. Reduction in pDC cytokine production capability and surface BDCA2 level occurred in an ADC serum concentration-dependent manner. DB-2304 exhibited a favorable safety profile, with an HNSTD of 125 mg/kg in cynomolgus monkeys. Conclusions: DB-2304 has demonstrated potent in vitro and in vivo anti-inflammatory effects on type I IFN genes and proinflammatory cytokines in pDC. These findings strongly support future clinical investigations of DB-2304.