CD200 immune checkpoint reversal at the site of tumor vaccine inoculation: A novel approach to glioblastoma immunotherapy
Authors: Xiong Zhengming , Ampudia-Mesias Elisabet , Pluhar G. Elizabeth , Rathe Susan K. , Largaespada David A. , Sham Yuk Y. , Moertel Christopher L. , Olin Michael R. 
Published: August 2019

AbstractPurposeAdvances in immunotherapy have revolutionized care for some cancer patients. However, current checkpoint inhibitors are associated with significant toxicity and yield poor responses for patients with central nervous system tumors, calling into question whether cancer immunotherapy can be applied to glioblastoma multiforme. We determined that targeting the CD200 activation receptors (CD200AR) of the CD200 checkpoint with a peptide inhibitor overcomes tumor-induced immunosuppression. We have shown the clinical efficacy of the peptide inhibitor in a trial in companion dogs with spontaneous high-grade glioma; adding the peptide to autologous tumor lysate vaccines significantly increased overall survival relative to tumor lysate alone (median survival of 12.7 and 6.36 months, respectively).Experimental design: This study was developed to elucidate the mechanism of the CD200ARs and develop a humanized peptide inhibitorWe developed macrophage cell lines with each of four CD200ARs knocked out to determine their binding specificity and functional responses. Using proteomics, we developed humanized peptide inhibitors to explore their effects on cytokine/chemokine response, dendritic cell maturation and CMV pp65 antigen response in CD14+ cells. GMP-grade peptide was further validated for activity.ResultsWe demonstrated that the peptide specifically targets the CD200AR complex to induce an immune response. Moreover, we developed and validated our humanized peptides for inducing chemokine response, stimulating immature dendritic cell differentiation and significantly enhancing an antigen-specific response. We also determined that the use of the peptide downregulated the expression of CD200 inhibitory and PD-1 receptors.ConclusionThese results support consideration of a CD200 peptide ligand as a novel platform for immunotherapy against multiple cancers including glioblastoma multiforme.Translational relevanceThis report evaluates the ability to modulate the CD200 immune checkpoint by employing synthetic peptides directed as ligands to its paired immune activation receptor. We previously reported the presence of CD200 in the sera and tumor vasculature of patients with glioblastoma multiforme (GBM). We have also shown that a canine CD200 activation receptor ligand extends the lives of companion dogs with high grade glioma. The data we present here show that the human peptide ligand (hCD200ARL) directed to the CD200 activation receptor on CD14+ cells activates immune upregulation through induction of a cytokine response and dendritic cell differentiation. In addition, hCD200ARL downregulates the inhibitory CD200 and PD-1 receptors. These findings provide a basis to evaluate hCD200ARL as a novel immune therapy for patients with GBM. Downregulation of PD-1 suggests that hCD200ARL may also obviate the need for PD1 and PD-L1 directed therapies for GBM and other malignancies.