Fusion Protein Vaccine Based on Ag85B and STEAP1 Induces a Protective Immune Response against Prostate Cancer

Abstract

(1) Background: There are currently limited treatments for castration-resistant prostate cancer. Immunotherapy involving Sipuleucel-T has increasingly drawn attention for prostate cancer management. BCG plays a vital role in treating bladder cancer, mainly by inducing immune activation, but is rarely used for prostate cancer. (2) Methods: The TCGA database, PCR, and Western blotting were used to analyze the expression of STEAP1 in mouse and human tissues. Then, we constructed a fusion protein vaccine with Mycobacterium tuberculosis Ag85B and three repeated octapeptide epitopes of a six-transmembrane epithelial antigen of the prostate 1 (STEAP1186-193), Ag85B-3×STEAP1186-193. The uptake of the fusion protein vaccine by DCs was evaluated by confocal microscopy, and DC markers were detected using flow cytometry after incubation with the fusion protein. The immune response against prostate cancer was evaluated by the LDH assay and xenografts in vitro and in vivo. Then, the tumor microenvironment was determined using IHC and ELISA. In addition, the epitope was mutated using CRISPR-Cas9 to illustrate that the fusion protein elicited immunization against STEAP1. (3) Results: The TCGA database analysis, PCR, and Western blotting showed that STEAP1 was highly expressed in human and murine prostate cancer. After the uptake of the purified fusion protein vaccine by DCs, CD11c, CD80, CD86, and MHC II were upregulated and triggered a cytotoxic T lymphocyte (CTL) response against TRAMP-C1 and RM1 cells in vitro. Furthermore, the fusion protein vaccine inhibited tumor growth and improved the tumor microenvironment in vivo, with more CD3+ cells and fewer FOXP3+ cells in the tumor. Serum IFN-γ and IL-2 were significantly higher than in the control group, while IL-4 expression was lower, indicating that the fusion protein vaccine activated Th1 immunity. The immune response against prostate cancer was greatly suppressed when the antigen targets were knocked out using CRISPR-Cas9. (4) Conclusion: In summary, our results provide the first evidence that a vaccine based on a fusion protein consisting of Ag85B and a prostate cancer octapeptide epitope with complete Freund’s adjuvant (CFA), triggers a robust immune response and inhibits tumor growth in murine prostate cancer.

EFEMP1 binds to STEAP1 to promote osteosarcoma proliferation and invasion via the Wnt/β-catenin and TGF-β/Smad2/3 signal pathways

“…Research on the relationship between STEAP1 and tumor characteristics is still in its infancy; however, this relationship has been studied extensively in prostate cancer. As a promising candidate target, STEAP1 has been a recent focus of a number of studies targeting prostate cancer, such as antibody-drug conjugation therapy [15] , T cell immunotherapy [16] , fusion protein vaccines [17] , and the early detection of metastatic prostate cancer [11] . The expression pattern of STEAP1 varies among tumor types, and the role of STEAP1 in different aspects of malignant tumor phenotypes is controversial [5] , [18] .…”

Biomaterial engineering strategies for B cell immunity modulations

“…Wallis et al subsequently developed liposomal vaccine particles that displayed ErbB-2 and encapsulated OVA 323-339 peptides to improve antibodies against the cancer surface protein ErbB-2, also known as HER-2. 211 Leveraging pre-existing T cells can accelerate GC formation and amplify the magnitude of GC responses, [212][213][214][215] but the expansion on antigen-specific B cells appears to be minimal in other studies. 216 Additionally, while the enhancement effect is clearly T cell epitope dependent, the exact phenotype of the effector T cells involved in this process remains unclear.…”

STEAP1–4 (Six-Transmembrane Epithelial Antigen of the Prostate 1–4) and Their Clinical Implications for Prostate Cancer

“…Given its localization to surface cell–cell junctions, particularly that of the prostatic secretory epithelium, STEAP1 is a promising target for T-cell and antibody-based immunotherapy [ 61 , 62 ]. Because STEAP1 is overexpressed in malignant prostate tissue but expressed at low levels in normal prostate tissue, STEAP1 is an ideal therapeutic target ( Table 1 ) [ 59 , 60 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ].…”

“…In vitro cytotoxicity assays demonstrated that these epitopes induced strong CTL-mediated antitumor activity [ 80 ]. Other approaches for targeting STEAP in PCa include fusion protein vaccines, RNA–lipoplex vaccines, recombinant viral vaccines, DNA vaccines, and CAR-T cells [ 64 , 65 , 66 , 67 , 73 ]. These studies are promising, and there is much work to do before they can be translated into PCa therapeutics.…”