Additional Study Information: You are being invited to take part in a research study that includes studying JNJ-78278343 in subjects with prostate cancer. This is an investigational drug which means that this is a new approach for the treatment of people who have prostate cancer. The main purpose of this study is to find a safe dose of JNJ-78278343 that can be used in the treatment of prostate cancer. To do this, we must find out if JNJ-78278343 can cause side-effects. Also, we need to find out how long JNJ-78278343 stays in and acts on your body and how your body responds to it. Prostate cancer is known to have high levels of a protein called KLK2 or hK2. KLK2 is a protein responsible for activating prostate-specific antigen (PSA) which in higher levels can indicate the presence of prostate cancer. hK2 is a protein responsible for the production of glucose-6-phosphate which is used in the metabolism of glucose. JNJ-78278343 is an antibody-like drug that is designed to attach to your T cells (a type of white blood cells in your immune system) and also to KLK2 on your cancer cells. JNJ-78278343 attaches to both of these in order to bring them closer together, starting the killing of the cancer cells by your body's own T cells. JNJ-78278343 has been studied in test tubes and in animals only. This is the first time that JNJ-78278343 is tested in humans.