Immunotherapies targeting Programmed death 1 (PD-1) co-inhibitory receptor have shown great promise for a subset of cancer patients. However, robust and safe combination therapies are still needed to bring the benefit of cancer immunotherapy to broader patient populations. In our effort to search for an optimal strategy of combinatorial immunotherapy, we have compared the anti-tumor activity of anti-4-1BB/anti-PD-1 combination with that of anti-PD-1/anti-LAG-3 combination in the poorly immunogenic B16F10 melanoma model. Pronounced tumor inhibition occurred only in animals receiving anti-PD-1 and anti-4-1BB concomitantly, while combining anti-PD-1 with anti-LAG-3 led to a modest degree of tumor suppression. The activity of anti-4-1BB/anti-PD-1 combination was dependent on IFN-γ and CD8+ T cells. Both 4-1BB and PD-1 proteins were elevated on the surface of CD8+ T cells by anti-4-1BB/anti-PD-1 co-treatment. In the tumor microenvironment, an effective anti-tumor immune response was induced as indicated by increased CD8+/Treg ratio and the enrichment of genes such as CD3ε, CD8α, IFN-γ and Eomesodermin. In the spleen, the combination treatment shaped the immune system to an effector/memory phenotype and increased the overall activity of tumor-specific CD8+ CTLs, reflecting a long-lasting systemic anti-tumor response. Furthermore, combination treatment in C57BL/6 animals showed no additional safety signals, and only minimally increased severity of the known toxicity relative to 4-1BB agonist alone. Therefore, in the absence of any cancer vaccine, anti-4-1BB/anti-PD-1 combination therapy is sufficient to elicit a robust anti-tumor effector/memory T cell response in an aggressive tumor model and is therefore a candidate for combination trials in patients.
- Received June 18, 2014.
- Revision received October 13, 2014.
- Accepted October 27, 2014.
- Copyright © 2014, American Association for Cancer Research.