In the version of this article initially published, the bars were not aligned with the data points or horizontal axis labels in Fig. 5d, and the labels along each horizontal axis of Fig. 5j-l indicating the presence (+) or absence (-) of doxycycline (Dox) were incorrectly included with the labels below that axis. Also, the right vertical bar above Fig. 7b linking 'P = 0.0001' to the key was incorrect; the correct comparison is αPD-1 versus Dox + αPD-1. Similarly, the right vertical bar above Fig. 7e linking 'P = 0.0002' to the key was incorrect; the correct comparison is αPD-1 versus Rosig + αPD-1. The errors have been corrected in the HTML and PDF versions of the article.