An Affinity Threshold for Maximum Efficacy in Anti-PD-1 Cancer Immunotherapy
Name
cowles-scowles-phd-chemicalengineering-2022-thesis.pdf
Description
Thesis PDF
Size
6.14 MB
Format
Adobe PDF
Checksum (MD5)
ac285882212db5d7c9be03579579ec7c
Author(s)
Cowles, Sarah Clare
Advisor(s)
Wittrup, K. Dane
Date Issued
May 2022
Publisher
Massachusetts Institute of Technology
Abstract
Monoclonal antibodies (mAbs) targeted to the programmed cell death protein 1 (PD-1) remain the most prevalent cancer immunotherapy both as a monotherapy and in combination with additional therapies. Despite the extensive success of anti-PD-1 mAbs in the clinic, the experimental relationship between binding affinity and functional potency for anti-PD-1 antibodies in vivo has not been reported. Two widely-used FDA-approved anti-PD-1 antibodies, nivolumab and pembrolizumab have similar single digit nanomolar equilibrium binding constants (KD). Anti-PD-1 antibodies with higher and lower affinity than nivolumab or pembrolizumab are entering the clinic and show varied pre-clinical efficacy. Here, we explore the role of broad-ranging affinity variation on efficacy within a single lineage in a syngeneic immunocompetent mouse model.
Using yeast surface display and affinity maturation, we engineered a panel of murine anti-PD-1 antibodies with varying affinity (ranging from KD = 20 pM - 15 nM). A combination of equilibrium and kinetic sorting strategies was used to both improve and reduce the affinity of a parental anti-PD-1 clone, 29F.1A12. We characterized the affinity of the antibodies using a number of methods, including ELISA, off-rate bead assays, and bio-layer interferometry, to confirm the wide range of affinity. We also characterized the internalization rate and pharmacokinetic clearance rate of our antibodies to confirm a consistent drug profile aside from mPD-1 affinity. Using these experimentally-determined rates and literature values, we developed a physiologically-based pharmacokinetic (PBPK) model to complement the in vivo results and highlight the direct relationship between dose, affinity, and PD-1 target saturation in the tumor.
Through in vivo efficacy studies using the MC38 murine adenocarcinoma model, we found that there is an affinity threshold required for maximum efficacy at a given dose of anti-PD-1 immunotherapy. We demonstrate that efficacy can be rescued by increasing the dose of a low affinity clone. Thus alternatively, we show that for a given affinity, there is a dose threshold required to achieve maximum efficacy. Ultimately, we conclude that the anti-PD-1 affinity/dose relationship supports a clear receptor-occupancy mechanism of action.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
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