Additional Study Information: The purpose of this study is to assess the safety of the Investigational study drug called BNT351 and get information about how well it works for HIV. BNT351 is currently being tested in humans and is the first time the study drug will be given to people. It is not FDA approved yet. You will be invited to take part if you are 18 to 65 years of age in good health and you have been diagnosed with human immunodeficiency virus (HIV) infection and you have never taken any treatment for HIV infection, have stopped receiving standard combination treatment for HIV for at least 4 weeks, or have not received any long-acting antiviral therapy in the past 6 months. You would participate in Part B of the study which will be divided into 4 groups. The study will also assess how well the study drug can block HIV viruses in a laboratory. Blood samples collected from you will be used for these tests, but you will not be exposed to HIV viruses in any way in this study. Participation in a clinical study regularly involves some risk. These can be risks of the study drug or certain medical procedures that are performed to conduct the study doctor. This is the first time the study drug is being given to people, so the side effects it may cause are not fully known. For Part B, you will receive a minimum of approximately $1,200 in total for the completion of all required study visits. You will be reimbursed up to $100 at each in-person study visit for travel-related costs required to attend the visit. Receipts are required.