Agonistic CD40 antibodies activate dendritic cells and can expand and activate tumor-specific T cells. Our purpose was to assess the CD40 agonistic antibody ADC-1013 in the clinical setting including intratumoral administration since preclinical studies have indicated that intratumoral is better than intravenous administration. A Phase I, open label, multicenter study was conducted in patients with advanced solid tumors who had received established treatments. A modified 3 + 3 dose-escalation was applied (every other week dosing). Twenty-three patients were treated with ADC-1013 intratumorally (dosing from 22.5 μg/kg up to 400 μg/kg) or intravenously (dosing at 75 μg/kg). The pharmacodynamic effects observed in the patients were further verified in an hCD40tg mouse model. Adverse events were mostly Common Terminology Criteria for Adverse Events (CTCAE) Grades 1 or 2 and transient. The serum concentration ADC-1013 and cytokine release (MCP-1, TNFα and IL-6) were more pronounced in patients receiving injections in deep metastases compared to patients receiving injections in superficial metastases. Treatment with ADC-1013 resulted in a marked decrease in B cell levels in peripheral blood after 24 h while remaining B cells significantly increased their expression of the cell surface activation marker CD86. Activation of antigen-presenting cells and subsequent activation of T cells were demonstrated in hCD40tg mice. Moreover, ADC-1013 treatment in this mouse model acted synergistically with a PD-1 inhibitor. The results from the first-in-human study of ADC-1013 indicate that intratumoral administration of ADC-1013 into superficial lesions is well tolerated at clinically relevant doses and associated with pharmacodynamic responses.