Background Cancer immunotherapy exploiting T cell-activation approaches, such as CAR-T cells, T cell engaging CD3-bispecific antibodies (CD3 BsAbs), have demonstrated significant clinical benefit to patients with hematopoietic malignancies. However, use of T-cell activating therapies in patients with late-stage disease, refractory/relapsed disease, and patients with solid tumors remains challenging. Traditionally, T cell-activating approaches activate mature T cells, which are either CD4+ or CD8+. The currently approved CD3 BsAb, the CD3 binding domain derived from SP34 or OKT3 preferentially binds and activates CD4+ T cells. We hypothesize that a T cell engager that selectively binds and activates CD8+ T cells may lead to the reduced cytokine release and enhanced antitumor efficacy.
Methods CD19 was used as a target to test our hypothesis. A series of TCE recombinant proteins were generated including CD3 x CD19, CD8 x CD19, and CD3 x CD8 x CD19. In these TCEs, the CD19 binding domain was kept constant, while a variety of CD3 and CD8 Abs with different affinity and potency were tested. The biological properties of the above antibodies were evaluated in vitro and in vivo.
Results In vitro: The CD3 x CD19 engager showed preferential CD4+ T cell binding, CD4+ T cell activation and target killing. The CD8 x CD19 engager showed high affinity binding to CD8+ T cells, but no significant target killing. The CD3 x CD8 x CD19 tri-specific T cell engager (CD8 TCE) showed selective CD8+ T cell binding (80% to >99%). When comparing the bi-specific CD3 x CD19 TCE with the CD3 x CD8 x CD19 tri-specific TCE, a 2–4 log increase of CD8 binding affinity, a 1–3 log increase of CD8 T cell activation, a 6- to 100-fold enhanced target killing, and an increased IFNg and TNFa release in CD8+ T cells, was observed with the CD8 TCE. In vivo: In the mouse xenograft tumor model, the CD8 TCE showed dose-dependent antitumor activities. Furthermore, monkeys treated with CD8 TCE by single IV (2 hrs, 40 mg/kg, n=3) or by repeat SC (400 mg/kg, n=6) dosing, had significant peripheral B cell depletion, rapid CD8+ T cell redistribution, and low levels of cytokine release. We observed safe and tolerable SC dosing that also showed consistently low levels of cytokine release.
Conclusions These results demonstrate a novel tri-specific CD8 TCE that selectively activates CD8+ T cells. This novel biologic may have improved safety and enhanced efficacy for T-cell activating cancer treatment.
Ethics Approval The in vivo studies were approved by Institutional Animal Care and Use Committee of KYLIN lab Co., Ltd.; approval number KL02–009-2022.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See http://creativecommons.org/licenses/by-nc/4.0/.
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.