Competing interests M.R., S.G. hold patents related to CART22. C.H.J. has received grant support from Novartis, and has patents related to CAR therapy with royalties paid from Novartis to the University of Pennsylvania. C.H.J. is also a scientific founder and holds equity in Tmunity Therapeutics. S.A.G. has received support from Novartis, Servier and Kite, and serves as a consultant, member of the scientific advisory board or study steering committee for Novartis,

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Therapeutic efficacy of adoptive immunotherapy of malignancies is proportional to the number of effector T cells transferred. Traditionally, exogenous IL-2 treatment has been used to promote the survival and function of transferred cells. Recently, we described the therapeutic effects of in vivo ligation of the costimulatory receptor, OX-40R, on activated T cells during early tumor growth. In this study, we examined the effects of IL-2 and OX-40R mAb on adoptive immunotherapy of advanced tumors. For treatment of 10-day 3-methylcholanthrene 205 pulmonary metastases, systemic transfer of 50 × 106 activated tumor-draining lymph node T cells resulted in >99% reduction of metastatic nodules. With either IL-2 or OX-40R mAb conjunctional treatment, only 20 × 106 cells were required. Advanced 10-day 3-methylcholanthrene 205 intracranial tumors could be cured by the transfer of 15 × 106 L-selectinlow T cells derived from draining lymph nodes. In this situation, IL-2 administration inhibited therapeutic effects of the transferred cells. By contrast, 5 × 106 T cells were sufficient to cure all mice if OX-40R mAb was administrated. Studies on trafficking of systemically transferred T cells revealed that IL-2, but not OX-40R mAb, impeded tumor infiltration by T cells. Tumor regression required participation of both CD4 and CD8 T cells. Because only CD4 T cells expressed OX-40R at cell transfer, direct CD4 T cell activation is possible. Alternatively, OX-40R might be up-regulated on transferred T cells at the tumor site, rendering them reactive to the mAb. Our study suggests OX-40R mAb to be a reagent of choice to augment T cell adoptive immunotherapy in clinical trials.

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