Identification of tumor-associated, MHC class II-restricted phosphopeptides as targets for immunotherapy

Department of Surgery, The Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2009; 106(29):12073-8. DOI: 10.1073/pnas.0903852106
Source: PubMed


The activation and recruitment of CD4(+) T cells are critical for the development of efficient antitumor immunity and may allow for the optimization of current cancer immunotherapy strategies. Searching for more optimal and selective targets for CD4(+) T cells, we have investigated phosphopeptides, a new category of tumor-derived epitopes linked to proteins with vital cellular functions. Although MHC I-restricted phosphopeptides have been identified, it was previously unknown whether human MHC II molecules present phosphopeptides for specific CD4(+) T cell recognition. We first demonstrated the fine specificity of human CD4(+) T cells to discriminate a phosphoresidue by using cells raised against the candidate melanoma antigen mutant B-Raf or its phosphorylated counterpart. Then, we assessed the presence and complexity of human MHC II-associated phosphopeptides by analyzing 2 autologous pairs of melanoma and EBV-transformed B lymphoblastoid lines. By using sequential affinity isolation, biochemical enrichment, mass spectrometric sequencing, and comparative analysis, a total of 175 HLA-DR-associated phosphopeptides were characterized. Many were derived from source proteins that may have roles in cancer development, growth, and metastasis. Most were expressed exclusively by either melanomas or transformed B cells, suggesting the potential to define cell type-specific phosphatome "fingerprints." We then generated HLA-DRbeta1*0101-restricted CD4(+) T cells specific for a phospho-MART-1 peptide identified in both melanoma cell lines. These T cells showed specificity for phosphopeptide-pulsed antigen-presenting cells as well as for intact melanoma cells. This previously undescribed demonstration of MHC II-restricted phosphopeptides recognizable by human CD4(+) T cells provides potential new targets for cancer immunotherapy.

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Available from: Victor H Engelhard
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    • "CD4+ T cells contribute to the immunologic antitumor activity through their ability to mediate tumor cell destruction independent of CD8+ T cells as well as help activate CD8+ T cells classically [126–128]. Identification of MHC class II-restricted isotopes derived from several TAAs including melanoma differentiation antigens and several cancer-testis antigens becomes feasible to generate antigen-specific CD4+ T cells which can be used in ACT [129–131]. Several preclinical studies have described antitumor effect of ACT using CD4+ T cell population, and CD4+ T cells have cytolytic activity dependent on class II-restricted recognition of tumors [132–134]. In a recent early-phase dose escalation study of ACT for patient with metastatic melanoma using CD4+ T cell clones, the patients experienced partial responses including a case of a complete durable response [128, 135]. "
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    • "Because many phosphopeptides are differently expressed in normal and tumor tissues, they are potential targets for immunotherapy. Certain phosphoproteins, such as Mart-1 and tensin-3 expressed in melanomas, contain either MHC I-and MHC II-restricted epitopes, which raises the possibility of treatment approaches combining both MHC I-and MHC II-restricted phosphopeptides [18]. However, the capacity of the endogenous TCR to recognize the phosphopeptide varies, depending on the phosphoantigens encountered during thymic selection, a limitation that does not apply to CARs. "
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    • "Early proteomic studies were conducted with analyzers whose sensitivity (dynamic range) and accuracy were orders of magnitude inferior to that of MS analyzers that are now available (Depontieu et al, 2009; Yates et al, 2009; Nilsson et al, 2010). As a result, early studies on the immunopeptidome identified only the more abundant MIPs. "
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