We thank D. Rudner, R. Mazitschek, and R. Moellering for helpful insights; J. Horn and J. Marchionna for custom screening plate manufacture and technical advice; D. Flood and S. Rudnicki for technical support in the primary screen; and J. Wang and J. Moore for technical support in the flow cytometry assay. All primary screening was performed at Harvard Medical School ICCB-L Screening Facility. This work was supported in part by National Institute of Allergy and Infectious Diseases grant U54 AI057159, US National Institutes of Health grants R01 GM081617 (to R.K.) and GM086258 (to J.C.), European Research Council FP7 ERC grant 281891 (to R.K.) and a National Science Foundation Graduate Fellowship (to L.K.S.).