Correction to: Nature Medicine https://doi.org/10.1038/s41591-018-0135-2, published online 13 August 2018.

In the version of this article originally published, the figure callout in this sentence was incorrect: “Furthermore, in S1P1-KI mice themselves, whereas PD-1 blockade was ineffectual as monotherapy, the effects of 4-1BB agonism and checkpoint blockade proved additive, with the combination prolonging median survival and producing a 50% long-term survival rate (Fig. 6f).” The callout should have been to Supplementary Fig. 6b. The error has been corrected in the PDF and HTML versions of the article.