Abstract

Summary Programmed cell death protein 1 (PD-1) checkpoint blockade therapy requires the CD28 co-stimulatory receptor for CD8 + T  cell expansion and cytotoxicity. However, CD28 expression is frequently lost in exhausted T cells and during immune senescence, limiting the clinical benefits of PD-1 immunotherapy in individuals with cancer. Here, using a cereblon knockin mouse model that regains in vivo T cell response to lenalidomide , an immunomodulatory imide drug, we show that lenalidomide reinstates the anti-tumor activity of CD28-deficient CD8 + T cells after PD-1 blockade. Lenalidomide redirects the CRL4 Crbn ubiquitin ligase to degrade Ikzf1 and Ikzf3 in T cells and unleashes paracrine interleukin-2 (IL-2) and intracellular Notch signaling , which collectively bypass the CD28 requirement for activation of intratumoral CD8 + T cells and inhibition of tumor growth by PD-1 blockade. Our results suggest that PD-1 immunotherapy can benefit from a lenalidomide combination when treating solid tumors infiltrated with abundant CD28 − T cells.