A Phase 1 First-Time-in-Human, Open-Label Study of GSK4381562 Administered as Monotherapy and in Combination with Anticancer Agents in Participants with Selected Advanced Solid Tumors

• GSK4381562A is a PVRIG antibody to block this receptor thus preventing a signal that can inhibit the function of T cells in the immune system.

In this study, the sponsor and investigators want to learn:

• How much of the study agent, GSK4381562, can be given alone, or in combination with Dostarlimab, or in combination with Dostarlimab and Belrestotug with an acceptable level of side effects
• The effects of the study agent, GSK4381562, when given alone, or in combination with Dostarlimab, or in combination with Dostarlimab and Belrestotug (good and bad)
• How much of the study agent, GSK4381562, is absorbed into the blood and how fast it is removed
• How the study agent, GSK4381562, is acting on your body when given alone, or in combination with Dostarlimab, or in combination with Dostarlimab and Belrestotug
• If research tests can be used in the future to predict who will benefit from study agent, GSK4381562, when given alone, or in combination with Dostarlimab, or in combination with Dostarlimab and Belrestotug

This is a dose escalation/expansion study. Dose escalation means that the amount of the study agent given will be increased in each group of research participants, to find the most appropriate dose for further study. In the dose expansion part, a larger number of people receive a study agent dose determined to be appropriate in the dose escalation part of the study.

The study regimen will be given in cycles. Each cycle is 21 days (3 weeks).

For participants enrolled in Arm A, you will receive study agent, GSK4381562, once every 3 weeks as an infusion directly into a vein (IV) over about 30 minutes.

For participants enrolled in Arm B, you will receive study agent, GSK4381562, once every 3 weeks as an infusion directly into a vein (IV) over about 30 minutes. The infusion of Dostarlimab will be given 30 minutes after the infusion of the study agent, GSK4381562, over about 30 minutes.

For participants enrolled in Arm C, you will receive study agent, GSK4381562, once every 3 weeks as an infusion directly into a vein (IV) over about 30 minutes. The infusion of Dostarlimab will be given 30 minutes after the infusion of the study agent, GSK4381562, over about 30 minutes. The infusion of Belrestotug will be given 30 minutes after the infusion of Dostarlimab over about 30 minutes.