Effect of combined anti-PD-1 and temozolomide therapy in a mouse glioblastoma model
Chang Gon Kim1, Junseong Park2, Seok-Gu Kang2, Eui-Cheol Shin1
1Department of Neurosurgery, Brain Tumor Center, Severance Hospital, Yonsei University College of Medicine, Seoul 03722, Republic of Korea; 2Graduate School of Medical Science and Engineering, KAIST, Daejeon 34141, Republic of Korea
Background: Although blocking antibodies against programmed death-1 (PD-1) are effective in treating several types of cancer, the efficacy of these agents in patients with glioblastoma (GBM) is largely unknown.
Materials and methods: Here, we evaluated therapeutic effects of anti-PD-1, temozolomide (TMZ), and their combination in an orthotopic murine GBM model. The composition, phenotype, and number of tumor-infiltrating lymphocytes (TILs) were evaluated using flow cytometry. Transcriptional profiles of tumor tissues were analyzed using microarrays. Generation of antitumor immune memory was investigated upon rechallenge.
Results: Whereas TMZ did not rescue GBM-implanted mice, anti-PD-1 completely eradicated GBM in 44.4% of treated mice, and combination of anti-PD-1 and TMZ in all mice. An analysis of TILs early after treatment revealed that anti-PD-1 significantly increased the number of tumor-infiltrating T cells and reduced the relative frequencies of PD-1+ or LAG-3+ exhausted CD8+ or CD4+ T cells, and CD4+CD25+FoxP3+ regulatory T cells and their functions. However, combining TMZ with anti-PD-1 significantly decreased the number of tumor-infiltrating T cells, which was also observed with TMZ treatment alone. A transcriptome analysis of tumor tissues also revealed that changes in the gene expression profile elicited by anti-PD-1 treatment were distinct from those caused by the combination or TMZ alone. To test immune memory, we re-implanted GBM into mice in which tumors had been completely eradicated, and evaluated tumor growth without further treatment. No tumor growth was observed in mice cured by anti-PD-1 monotherapy, whereas tumors regrew in mice cured by the combination treatment, indicating that anti-PD-1 monotherapy generated antitumor immune memory, whereas the combination with TMZ did not.
Conclusion: This study shows that PD-1 blockade induces long-term therapeutic response, and their combination with TMZ further enhances antitumor efficacy in a mouse GBM model. However, immunological memory is provoked by anti-PD-1 monotherapy, not by combined therapy.