The purpose of this study is to evaluate the efficacy and safety of SL-T10 and GX-I7 or SL-T10, GX-I7 and pembrolizumab in patients with metastatic castration-resistant prostate cancer (mCRPC).

The purpose of this study is to evaluate the safety, tolerability, and preliminary efficacy of SL-T10, GX-I7, and pembrolizumab in combination in patients with metastatic castration-resistant prostate cancer (mCRPC).

Inclusion Criteria:

1. Male patients 19 years of age or older at the date of written informed consent.
2. Patients with histopathologically or cytologically confirmed adenocarcinoma of the prostate, documented by bone or soft tissue lesions.
3. Patients with castration-resistant prostate cancer with a blood testosterone level of less than 50 ng/dL at the screening visit.
4. patients with metastatic castration-resistant prostate cancer (mCRPC) who meet the following criteria (based on PCWG3.0 modified RECIST 1.1)

1) Prior taxane therapy for metastatic prostate cancer or confirmed refusal or inadequacy of such therapy 2) Patients who have received prior docetaxel and at least one of the following agents: abiraterone acetate or enzalutamide before or after docetaxel treatment 3) Patients with progression of prostate cancer during/after prior therapy, in the investigator's judgment, with either of the following, in the internal or external castration state

1. PSA progression defined as at least 2 PSA level increases (≥1 week interval between each test) and a PSA level of ≥2 ng/mL at Screening
2. Advanced soft tissue disease as defined by RECIST 1.1
3. Progressive bone disease defined as ≥2 new lesions on bone scan (per PCWG3)

5. Patients who are on androgen deprivation therapy (ADT) of any kind (patients who have not undergone bilateral orchiectomy must begin internal castration therapy, such as luteinizing hormone-releasing hormone (LHRH) agonists, LHRH antagonists, or anti-androgenic agents, at least 4 weeks prior to Baseline and must continue for the entire duration of the study)

Exclusion Criteria:

1. patient has an active autoimmune disease or is receiving systemic steroid therapy or in immunosuppressive status.
2. Patient has history of chemotherapy, radiation chemotherapy, biological therapy, immunotherapy, or radiation therapy within 4 weeks prior to the screening visit (In case of nitrosoureas or mitomycin, 6 weeks prior to the screening visit)