Press Release Details

– First patient enrolled in dose escalation portion of Phase 1/2 study of EOS-448, an antagonist anti-TIGIT antibody that enables antibody dependent cellular cytotoxicity (ADCC) –

– ADCC-enabled TIGIT programs are progressing into pivotal trials –

– Initial clinical data expected in 1H 2021 –

Cambridge, MA and Gosselies, Belgium – February 27, 2020 – iTeos Therapeutics Inc., a privately-held clinical-stage biotechnology company developing innovative cancer immunotherapies, announced today that it has enrolled the first patient in its Phase 1/2 study with EOS884448 (EOS-448), the company’s investigational ADCC-enabled antagonist anti-TIGIT antibody drug candidate.

Michel Detheux, PhD, President and Chief Executive Officer of iTeos, commented: “EOS-448 is an ADCC-enabled antagonist anti-TIGIT antibody that has been designed to maximize the therapeutic benefit of blocking TIGIT checkpoint inhibitors while engaging Fcγ receptors. The importance of TIGIT as a target for next-generation immunotherapy is becoming increasingly apparent in our field and, alongside our best-in-class adenosine A_2A receptor antagonist EOS-850, iTeos now has two highly innovative immunotherapy programs in clinical development for patients suffering with advanced cancers.”

Joanne Lager, M.D., Chief Medical Officer of iTeos, added, “ADCC-enabled antagonist anti-TIGIT programs are emerging as promising new immuno-oncology therapies. In preclinical studies, EOS-448 promotes anti-tumor immunity both alone and in combination with other oncology therapies. We believe it is well-positioned to provide important new therapeutic options for cancer patients. We look forward to evaluating EOS-448 in our now initiated Phase 1/2 trial and to reporting initial safety and efficacy results in the first half of 2021.”

About the EOS-448 Phase 1/2 Trial

This Phase 1/2 study of EOS-448 is an open-label, dose-escalation study to assess the safety, pharmacokinetic, pharmacodynamic and preliminary clinical activity of EOS-448 in participants with advanced cancers. Participants’ tumors will be sampled before treatment and during treatment, to identify and confirm biomarkers to be used in further clinical development. Following dose escalation and determination of the recommended Phase 2 dose, the study design allows for the seamless expansion of patient cohorts to evaluate the anti-tumor activity of EOS-448 in specific tumor types. The trial will be conducted at multiple clinical sites in Europe and is expected to enroll approximately 30 patients with advanced cancer in the dose escalation portion.

About TIGIT and EOS-448

TIGIT is an immune checkpoint inhibitor, which interacts with CD155 expressed on antigen-presenting cells or tumor cells to down-regulate T cell and Natural Killer (NK) cell functions. EOS-448 is a novel fully human IgG1 mAb against the TIGIT receptor to treat a wide range of tumor types expressing ligands of TIGIT and/or being infiltrated by TIGIT expressing immune cells. EOS-448 was designed to encompass multiple mechanisms to activate anti-tumor immunity, not only by restoring T cell effector functions, but also by depleting immunosuppressive Tregs or inducing direct cytotoxicity of TIGIT-expressing tumor cells and creating local inflammation by engaging Fcγ receptors on effector cells. During preclinical development, EOS-448 demonstrated potent competition with TIGIT-ligand binding as well as in vitro and ex-vivo ability to restore T cell function in human samples. EOS-448 has also confirmed preferred direct cytotoxicity on regulatory T cells when tested in human cancer samples and demonstrated a clean toxicity profile. EOS-448 has also demonstrated potent anti-tumor efficacy in a humanized mouse tumor model.

For further information, please contact:

Michel Detheux, CEO

iTeos Therapeutics SA

info@iteostherapeutics.com

Amber Fennell, Paul Kidwell, Matthew Neal and Sukaina Virji

Consilium Strategic Communications

+44 203 709 5700

iteos@consilium-comms.com

Sarah McCabe and Zofia Mita

Stern Investor Relations, Inc.

+ 1 212 362 1200

iTeos@sternir.com