37. Which of the following statement about checkpoint blockade immunotherapy is NOT true? (A) Checkpoint blockade can augment immune responses to existing tumors. (B) Anti-PD-1 antibody immunotherapy acts to induce PD-1 signaling in T cells. (C) Anti-PD-I antibodies, pembrolizumab and nivolumab, are approved for treatment of several types of cancers. (D) Anti-CTLA-4 antibody, ipilimumab, is shown to be effective in treating metastatic melanoma.