Molecular characterization of defective antigen processing in human prostate cancer.
BACKGROUND
Gene-modified tumor cell vaccines have shown efficacy in animal models of malignancy, including prostate cancer. Class I major histocompatibility complex (MHC) assembly and function in the cellular targets of such therapies is pivotal in determining the efficacy of specific cytokine-secreting tumor vaccines.


OBJECTIVE
To help guide development of genetically engineered vaccine therapy for human prostate cancer, potential immune resistance pathways were evaluated by analysis of class I MHC assembly in prostate cancer cells.


METHODS
Class I MHC assembly in metastasis-derived human prostate cancer cell lines (LNCaP, PPC-1, DU-145, PC-3, and TSU) and a normal prostate-derived cell line (TP-2) were characterized by phenotypic, molecular, and functional assays. Assembled class I MHC and antigen was measured by flow cytometry; mRNA levels of assembly components (class I MHC heavy chain, beta 2-microglobulin, and the antigen transporter gene product TAP-2) were determined; and antigen processing was measured with a chimeric reconstituted system using vaccinia vectors. Restoration of antigen processing was attempted by interferon gamma stimulation and by transfection with mouse class I MHC heavy-chain cDNA.


RESULTS
Assembled class I MHC was underexpressed in two (LNCaP and PPC-1) of five prostate cancer cell lines compared with normal prostate-derived controls. PPC-1 cells underexpressed TAP-2 mRNA despite abundant class I MHC and beta 2-microglobulin message. Induction of TAP-2 by interferon gamma indicated that coding sequences for TAP-2 message were present in PPC-1. Resistance to cytotoxic T lymphocytes (CTL) lysis showed a functional defect in antigen transport by PPC-1 cells; reversal of the molecular defect with interferon gamma led to restoration of functional antigen processing. In contrast, LNCaP cells had competent antigen transport but deficient class I MHC heavy-chain function despite abundant class I MHC RNA; though refractory to stimulation by interferon gamma, this defect responded to transfection of class I MHC heavy-chain cDNA.


CONCLUSIONS
Metastatic prostate cancer cells can escape T-cell recognition via divergent mechanisms of defective class I MHC assembly. The specific underexpression of TAP-2 gene product in PPC-1 cells contrasts with prior studies of TAP gene underexpression in lung cancer (which concurrently underexpressed class I MHC heavy chain) and provides evidence for a regulatory pathway controlling TAP-2 gene expression in human cancers that may not affect class I MHC heavy-chain expression.


CONCLUSIONS
In clinical application of gene therapy for prostate cancer, these findings provide a rationale for focusing on strategies that can circumvent sole reliance on class I MHC-mediated tumor cell recognition by CTL.
Sanda
M G
MG
Brady Urological Institute and Oncology Center, Johns Hopkins School of Medicine, Baltimore, MD, USA.
Restifo
N P
NP
Walsh
J C
JC
Kawakami
Y
Y
Nelson
W G
WG
Pardoll
D M
DM
Simons
J W
JW
D017951:Antigen Presentation / Q000235:genetics* / Q000276:immunology; D015152:Blotting, Northern; D015536:Down-Regulation; D005434:Flow Cytometry; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007167:Immunotherapy / Q000379:methods; D008297:Male; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000276:immunology* / Q000628:therapy; D014407:Tumor Cells, Cultured
D015395:Histocompatibility Antigens Class I