Background: Depletion of CD4+ immunosuppressive cells using an anti-CD4 monoclonal antibody (mAb) results in a strong antitumor effect by expanding a broad variety of tumor-reactive CD8+ T cells in mice. However, the impact of CD4+ cell depletion on the immune response in cancer patients is not known. Here, we analyzed changes in the T cell receptor (TCR) repertoire of blood and tumor biopsy samples following depletion of CD4+ cells by IT1208, a defucosylated humanized anti-CD4 mAb, in a first-in-human clinical trial.

Methods: Patients with advanced gastrointestinal tumors were treated with 0.1 or 1.0 mg/kg IT1208. The count and immunophenotype of peripheral blood T cells were analyzed by flow cytometry. Libraries for TCR sequencing were prepared from purified blood CD4+ and CD8+ T cells, and unfractionated tumor biopsies, collected before and after IT1208 treatment. TCR sequencing was performed using Ion Proton and Ion S5 sequencers, then changes in the repertoire, and temporal and inter-organ overlap after IT1208 treatment, were analyzed.

Results: Among 11 patients enrolled in the trial, one achieved a durable partial response and two achieved stable disease lasting at least 3 months. The blood CD4+ T cell count decreased rapidly after IT1208 treatment and remained low during the observation period. In contrast, the blood CD8+ T cell count increased from day 29 after treatment compared to baseline in most patients, resulting in a remarkably decreased CD4/8 ratio. Immunohistological analysis showed a decrease of CD4+ T cells in the tumor after IT1208 treatment. In the TCR repertoire analysis, a decrease in similarity and increase in clonality were observed in blood CD4+ and CD8+ T cells after IT1208 treatment, particularly in patients receiving 1.0 mg/kg IT1208. These changes persisted to at least day 60 after treatment in some cases. Temporal tracking of the blood TCR repertoire revealed that the number of expanded CD4+ T cell clones increased in a dose-dependent manner. In addition, the number of contracted CD8+ T cell clones showed a strong correlation with the increased CD8+ T cell count and CD45RAhi CCR7- effector population among CD8+ T cells in the blood. We also analyzed blood-tumor overlapping CD8+ T cell clones to investigate changes in potential tumor-associated clones. The frequency of overlapping CD8+ T cell clones in the blood tended to increase after treatment. Interestingly, an increased frequency of these overlapping clones in the blood was associated with maximum shrinkage in the tumor diameter.

Conclusion: IT1208 treatment depleted CD4+ T cells from the blood and tumor. This depletion promoted the replacement of CD4+ and CD8+ T cell repertoire systemically. The IT1208 treatment-induced increase of tumor-associated CD8+ T cell clones may be associated with its anti-tumor effect in cancer patients.

Citation Format: Hiroyasu Aoki, SATOSHI UEHA, Shigeyuki Shichino, Haru Ogiwara, Kohei Shitara, Tetsuya Nakatsura, Toshihiro Suzuki, Manami Shimomura, Toshiaki Yoshikawa, Kayoko Shoda, Shigehisa Kitano, Makiko Yamashita, Takayuki Nakayama, Akihiro Sato, Sakiko Kuroda, Masashi Wakabayashi, Shogo Nomura, Shoji Yokochi, Satoru Ito, Toshihiko Doi, Kouji Matsushima. Anti-CD4 monoclonal antibody immunotherapy exerts an antitumor effect by replacing the T cell receptor repertoire in patients with gastrointestinal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-019.