This clinical trial is focused on studying a type of lung cancer known as Non-small Cell Lung Cancer (NSCLC), specifically in stages II, IIIA, and IIIB. The study is investigating the effects of a treatment combination involving two medications: V940 (mRNA-4157) and Pembrolizumab, which is also known by the brand name KEYTRUDA. Pembrolizumab is a medication that helps the immune system fight cancer cells, while mRNA-4157 is a new type of treatment that uses a small piece of genetic material to help the body recognize and attack cancer cells.

The purpose of the study is to compare the effectiveness of the combination of V940 and Pembrolizumab against a combination of a placebo and Pembrolizumab. Participants in the study will have already undergone surgery to remove their lung cancer and will receive additional treatment to help prevent the cancer from returning. The study will involve regular visits to the clinic for treatment and monitoring over a period of time. Participants will receive either the active treatment or a placebo, which is a substance with no active medication, along with Pembrolizumab.

The study aims to understand how well the treatment works in preventing the return of cancer and improving survival rates. It will also monitor the overall health and quality of life of participants during the study. The trial will help determine if the new treatment combination is more effective than the current standard treatment in keeping the cancer from coming back and improving the lives of those affected by this type of lung cancer.