RIPK1 and lymphopenia: To further test whether RIPK1 kinase activity contributed to lymphopenia in Ripk3−/−Casp8ΔE385/ΔE385 mice, we generated Ripk1K45A/K45ARipk3−/−Casp8ΔE385/ΔE385 mice and observed that Ripk1K45A/K45ARipk3−/−Casp8ΔE385/ΔE385 mice showed lymphopenia and myeloid bias similar to Ripk3−/−Casp8ΔE385/ΔE385 mice (Figs. 6A–C and S5B–D).