Profound Functional Suppression of Tumor-Infiltrating T-Cells in Ovarian Cancer Patients Can Be Reversed Using PD-1-Blocking Antibodies or DARPin® Proteins.

PD-1/PD-L1 blockade has revolutionized the field of immunooncology. Despite the relative success, the response rate to anti-PD-1 therapy requires further improvements. Our aim was to explore the enhancement of T-cell function by using novel PD-1-blocking proteins and compare with clinically approved monoclonal antibodies (mAbs). We isolated T-cells from the ascites and tumor of 17 patients with advanced epithelial ovarian cancer (EOC) and analyzed the effects using the mAbs nivolumab and pembrolizumab and two novel engineered ankyrin repeat proteins (DARPin® proteins). PD-1 blockade with either mAb or DARPin® molecule significantly increased the release of IFN-γ, granzyme B, IL-2, and TNF-α, demonstrating successful reinvigoration. The monovalent DARPin® protein was less effective compared to its bivalent equivalent, demonstrating that bivalency brings an additional benefit to PD-1 blockade. Overall, we found a higher fold increase of lymphokine secretion in response to the PD-1 blockade by tumor-derived T-cells; however, the absolute amounts were significantly lower compared to the release from ascites-derived T-cells. Our results demonstrate that PD-1 blockade can only partially reinvigorate functionally suppressed T-cells from EOC patients. This warrants further investigation preferably in combination with other therapeutics. The study provides an early pilot proof-of-concept for the potential use of DARPin® proteins as eligible alternative scaffold proteins to block PD-1.

Antibody-Drug Conjugates: Future Directions in Clinical and Translational Strategies to Improve the Therapeutic Index.

Since the first approval of gemtuzumab ozogamicin (Mylotarg; Pfizer; CD33 targeted), two additional antibody-drug conjugates (ADC), brentuximab vedotin (Adcetris; Seattle Genetics, Inc.; CD30 targeted) and inotuzumab ozogamicin (Besponsa; Pfizer; CD22 targeted), have been approved for hematologic cancers and 1 ADC, trastuzumab emtansine (Kadcyla; Genentech; HER2 targeted), has been approved to treat breast cancer. Despite a clear clinical benefit being demonstrated for all 4 approved ADCs, the toxicity profiles are comparable with those of standard-of-care chemotherapeutics, with dose-limiting toxicities associated with the mechanism of activity of the cytotoxic warhead. However, the enthusiasm to develop ADCs has not been dampened; approximately 80 ADCs are in clinical development in nearly 600 clinical trials, and 2 to 3 novel ADCs are likely to be approved within the next few years. While the promise of a more targeted chemotherapy with less toxicity has not yet been realized with ADCs, improvements in technology combined with a wealth of clinical data are helping to shape the future development of ADCs. In this review, we discuss the clinical and translational strategies associated with improving the therapeutic index for ADCs.