CD28 and neuroblastoma: Immunotherapy using a GD2-redirected 3rd generation CD28 OX40 CD3ζ CAR in a mouse xenograft neuroblastoma model was found to be augmented using all-trans retinoic acid (ATRA) which was able to eradicate monocytic MDSCs and diminish the suppressive capacity of G-MDSCs which otherwise limited CAR T-cell activity in the TME [168].