Development of CDX-527: a bispecific antibody combining PD-1 blockade and CD27 costimulation for cancer immunotherapy

CD27 is a costimulatory molecule that provides a complementary target to the PD-1/PD-L1 checkpoint axis on T cells. Combining a CD27 agonist antibody with PD-1/PD-L1 blockade has shown synergistic antitumor activity in preclinical models, which led to clinical studies of the combination in cancer patients. We theorized that coupling CD27 costimulation with PD-1/PD-L1 blockade in a bispecific antibody (BsAb) may provide greater immune activating properties than combining the individual mAbs due to enhanced CD27 activation by cross-linking through PD-L1 and Fc receptors. To test this approach, we developed CDX-527, a tetravalent PD-L1xCD27 IgG1-scFv BsAb. CDX-527 potently inhibits PD-1 signaling and induces CD27-mediated T cell costimulation through PD-L1 cross-linking. In mixed lymphocyte reaction assays, CDX-527 is more potent than the combination of the parental antibodies, suggesting that cross-linking through both Fc receptors and PD-L1 results in enhanced CD27 agonist activity. CDX-527 was shown to mediate effector function against tumor cells overexpressing either CD27 or PD-L1. In human CD27 transgenic mice, we observed that antigen-specific T cell responses to a vaccine are greatly enhanced with a surrogate PD-L1xCD27 BsAb. Furthermore, the BsAb exhibits greater antitumor activity than the combination of the parental antibodies in a syngeneic lymphoma model. A pilot study of CDX-527 in cynomolgus macaques confirmed a mAb-like pharmacokinetic profile without noted toxicities. These studies demonstrate that CDX-527 effectively combines PD-1 blockade and CD27 costimulation into one molecule that is more potent than combination of the parental antibodies providing the rationale to advance this BsAb toward clinical studies in cancer patients.

CD27 costimulation augments the survival and antitumor activity of redirected human T cells in vivo

The costimulatory effects of CD27 on T lymphocyte effector function and memory formation has been confined to evaluations in mouse models, in vitro human cell culture systems, and clinical observations. Here, we tested whether CD27 costimulation actively enhances human T-cell function, expansion, and survival in vitro and in vivo. Human T cells transduced to express an antigen-specific chimeric antigen receptor (CAR-T) containing an intracellular CD3 zeta (CD3ζ) chain signaling module with the CD27 costimulatory motif in tandem exerted increased antigen-stimulated effector functions in vitro, including cytokine secretion and cytotoxicity, compared with CAR-T with CD3ζ alone. After antigen stimulation in vitro, CD27-bearing CAR-T cells also proliferated, up-regulated Bcl-XL protein expression, resisted apoptosis, and underwent increased numerical expansion. The greatest impact of CD27 was noted in vivo, where transferred CAR-T cells with CD27 demonstrated heightened persistence after infusion, facilitating improved regression of human cancer in a xenogeneic allograft model. This tumor regression was similar to that achieved with CD28- or 4-1BB–costimulated CARs, and heightened persistence was similar to 4-1BB but greater than CD28. Thus, CD27 costimulation enhances expansion, effector function, and survival of human CAR-T cells in vitro and augments human T-cell persistence and antitumor activity in vivo.

T cells redirected against CD70 for the immunotherapy of CD70-positive malignancies

T-cell therapy with genetically modified T cells targeting CD19 or CD20 holds promise for the immunotherapy of hematologic malignancies. These targets, however, are only present on B cell–derived malignancies, and because they are broadly expressed in the hematopoietic system, their targeting may have unwanted consequences. To expand T-cell therapies to hematologic malignancies that are not B cell–derived, we determined whether T cells can be redirected to CD70, an antigen expressed by limited subsets of normal lymphocytes and dendritic cells, but aberrantly expressed by a broad range of hematologic malignancies and some solid tumors. To generate CD70-specific T cells, we constructed a chimeric antigen receptor (CAR) consisting of the CD70 receptor (CD27) fused to the CD3-ζ chain. Stimulation of T cells expressing CD70-specific CARs resulted in CD27 costimulation and recognition of CD70-positive tumor cell lines and primary tumor cells, as shown by IFN-γ and IL-2 secretion and by tumor cell killing. Adoptively transferred CD70-specific T cells induced sustained regression of established murine xenografts. Therefore, CD70-specific T cells may be a promising immunotherapeutic approach for CD70-positive malignancies.