Treatment Combining CD200 Immune Checkpoint Inhibitor and Tumor-Lysate Vaccination after Surgery for Pet Dogs with High-Grade Glioma

Abstract

Recent advances in immunotherapy have included inhibition of immune checkpoint proteins in the tumor microenvironment and tumor lysate-based vaccination strategies. We combined these approaches in pet dogs with high-grade glioma. Administration of a synthetic peptide targeting the immune checkpoint protein, CD200, enhanced the capacity of antigen-presenting cells to prime T-cells to mediate an anti-glioma response. We found that in canine spontaneous gliomas, local injection of a canine-specific, CD200-directed peptide before subcutaneous delivery of an autologous tumor lysate vaccine prolonged survival relative to a historical control treated with autologous tumor lysate alone (median survivals of 12.7 months and 6.36 months, respectively). Antigen-presenting cells and T-lymphocytes primed with this peptide suppressed their expression of the inhibitory CD200 receptor, thereby enhancing their ability to initiate immune reactions in a glioblastoma microenvironment replete with the immunosuppressive CD200 protein. These results support consideration of a CD200 ligand as a novel glioblastoma immunotherapeutic agent.

Keywords: dogs; glioma; immunotherapy; tumor lysate.

Figure 1

Experimental model. Full-length CD200 secreted from tumor cells binds to the CD200 inhibitory receptor (CD200R1) on antigen-presenting cells, shutting down an immune response. In addition to the inhibitory receptor, the CD200 checkpoint has CD200-like activation receptors (CD200R4) that have adjuvant-like properties when stimulated; ligation with the CD200 activation receptor peptide ligand (CD200AR-L) activates an as yet undetermined signaling cascade that surmounts the inhibitory signals and allows activation of and normal antigen presentation by the antigen presenting cell. Permission by Michael R. Olin, University of Minnesota, Minneapolis, MN. Unpublished work, 2018.

Figure 2

Treatment with the CD200 inhibitor extends progression free and overall survival in dogs. Following surgical resection of the tumors, serial vaccinations of autologous tumor lysate and canine-specific CD200AR-L were administered to each dog. Disease status was followed using magnetic resonance imaging (MRI) and calculated progression-free (black line) and overall survival (blue line) times were significantly longer than a cohort of dogs treated with tumor lysate alone after surgery (red line) (p = 0.0001). Ticks represent censored cases because the dog is still alive (n = 3) or had no evidence of disease on postmortem examination of the brain (n = 6).

Figure 3

Soluble CD200 (sCD200) predicts tumor recurrence prior to MRI evidence. (A) Serum levels of sCD200 decreased after surgery and vaccinations of autologous tumor lysate + CD200AR-L in one Boston terrier with a grade III glioma. (B) Serum sCD200 increased at 1 year although there was no evidence of tumor recurrence on the MRI at that time. (C) Six months later, an MRI was repeated when the dog developed severe breakthrough generalized seizure activity and tumor progression was seen (red circle).

Figure 4

CD200R1-related genes are associated with shorter overall survival in humans. (A) Transcriptome profile for glioblastoma showing clusters of genes associated with overall survival were analyzed in patient tumor samples available in The Cancer Genome Atlas database. Transcripts with increased levels are shown in yellow, while transcripts with decreased levels are shown in blue. Transcript level clusters with correlation >0.60 and containing ≥60 genes were systematically identified using Gene Cluster Expression Summary Scores. These clusters are visualized with a numbered black bar to the right of each of the heatmaps. Those with significant differences in survival based on Kaplan–Meier analyses are indicated with symbols and their associated p-values are shown. (B–D) Kaplan–Meier plots showing that patients expressing high levels of the gene cluster containing CD200 (red lines) had shorter overall survival times than those expressing lower levels (black lines). Comparisons are top quartile (Q1) versus three lowest quartiles (Q234), top two quartiles (Q12) versus the lowest two (Q34), and top three quartiles (Q123) versus the lowest (Q4).