Additional Study Information: The main purpose of this study is to: Learn about the safety of REGN4018 and to find out what dose of REGN4018 can be given alone or in combination with cemiplimab to research subjects with ovarian cancer without too many side effects. The study will also look at the levels of REGN4018 and/or cemiplimab in the body and measure how well your body can remove the study drug(s). This is called pharmacokinetics. The study will also look at any signs that REGN4018 alone or with cemiplimab can treat cancer.