PF-08046032: A Novel, Investigational CD25-Directed Antibody–Drug Conjugate Optimized for Selective Depletion of Regulatory T Cells in Advanced Malignant Tumors

Abstract Regulatory T cells (Treg) are known to suppress antitumor immune responses, and their presence in the tumor microenvironment is associated with cancer progression; therefore, Treg depletion is a promising strategy to enhance cancer immunotherapy. PF-08046032 is a novel antibody–drug conjugate (ADC) designed to target Tregs in the tumor microenvironment via CD25, the α-chain of the IL-2 receptor frequently upregulated by intratumoral Tregs. PF-08046032 is composed of an affinity-detuned anti-CD25 antibody linked to monomethyl auristatin E, a potent cytotoxic agent. Affinity detuning increases PF-08046032 selectivity for CD25high intratumoral Tregs while minimizing peripheral blood Treg depletion, thus reducing the risk of autoimmune toxicities. In preclinical experiments, PF-08046032 selectively depleted Tregs compared with CD8+ T cells and preferentially depleted Tregs with high CD25 expression. PF-08046032 showed dose-dependent antitumor activity in CD25-expressing human lymphoma xenograft models, whereas a similarly detuned anti-mouse CD25 surrogate ADC depleted intratumoral Tregs and drove CD8+ T-cell activation in murine tumor models. This effect resulted in robust antitumor activity as a single agent and in combination with anti-PD1 checkpoint inhibitor blockade. Lastly, PF-08046032 was well-tolerated in nonhuman primates and mitigated the persistent depletion of peripheral blood Treg that was observed with a high-affinity anti-CD25 ADC comparator, demonstrating the safety benefit of a detuned-affinity ADC format. PF-08046032 represents an innovative therapeutic approach for depletion of intratumoral Tregs that may offer an improved safety profile and efficacy over traditional Treg-depleting agents.