Crosti Mariacristina, Longhi Renato, Consogno Giuseppe, Melloni Giulio, Zannini Piero, Protti Maria Pia
Laboratory of Tumor Immunology, Scientific Institute H. San Raffaele, Milan, Italy.
J Immunol. 2006 Apr 15;176(8):5093-9. doi: 10.4049/jimmunol.176.8.5093.
The carcinoembryonic Ag (CEA) is an attractive target for immunotherapy because of its expression profile and role in tumor progression. To verify the existence of spontaneous anti-CEA CD4+ T cells in lung cancer patients, we first identified CEA sequences forming naturally processed epitopes, and then used the identified epitopes to test their recognition by CD4+ T cells from the patients. We had previously identified CEA(177-189/355-367) as an immunodominant epitope recognized by CD4+ T cells in association with several HLA-DR alleles. In this study, we identified four additional subdominant CEA sequences (CEA(99-111), CEA(425-437), CEA(568-582), and CEA(666-678)), recognized in association with one or more HLA-DR alleles. Peptide-specific CD4+ T cells produced proinflammatory cytokines when challenged with the native protein and CEA-expressing tumor cells, thus demonstrating that the identified CEA sequences contain naturally processed epitopes. However, CEA is expressed in the thymus and belongs to the CD66 family that comprises highly homologous molecules expressed on hemopoietic cells, raising concerns about tolerance interfering with the in vivo development of anti-CEA immunity. We thus tested the spontaneous reactivity to the identified epitopes of peripheral blood CD4+ T lymphocytes from eight early-stage lung cancer patients bearing CEA-positive tumors. We found GM-CSF- and IFN-gamma-producing CD4+ T cells in two patients. Our data indicate that CD4+ immune responses against CEA develop in neoplastic patients, suggesting that tolerance toward CEA or cross-reactive CD66 homologous molecules might be either not absolute or be overcome in the neoplastic disease.
癌胚抗原（CEA）因其表达谱及在肿瘤进展中的作用，成为免疫治疗的一个有吸引力的靶点。为验证肺癌患者中是否存在自发的抗CEA CD4⁺ T细胞，我们首先鉴定了形成天然加工表位的CEA序列，然后用鉴定出的表位检测患者CD4⁺ T细胞对其的识别情况。我们之前已鉴定出CEA(177 - 189/355 - 367)是与多个HLA - DR等位基因相关的、被CD4⁺ T细胞识别的免疫显性表位。在本研究中，我们又鉴定出另外四个亚显性CEA序列（CEA(99 - 111)、CEA(425 - 437)、CEA(568 - 582)和CEA(666 - 678)），它们与一个或多个HLA - DR等位基因相关。肽特异性CD4⁺ T细胞在用天然蛋白和表达CEA的肿瘤细胞刺激时会产生促炎细胞因子，从而证明鉴定出的CEA序列包含天然加工表位。然而，CEA在胸腺中表达，且属于CD66家族，该家族包含在造血细胞上表达的高度同源分子，这引发了对耐受性干扰抗CEA免疫体内发育的担忧。因此，我们检测了8例患有CEA阳性肿瘤的早期肺癌患者外周血CD4⁺ T淋巴细胞对鉴定出的表位的自发反应性。我们在两名患者中发现了产生GM - CSF和IFN - γ的CD4⁺ T细胞。我们的数据表明，肿瘤患者中会产生针对CEA的CD4⁺免疫反应，提示对CEA或交叉反应性CD66同源分子的耐受性可能不是绝对的，或者在肿瘤疾病中可以被克服。
