Few epitopes are available for vaccination therapy of patients with squamous cell carcinoma of the head and neck (SCCHN). Using a tumor-specific CTL, aldehyde dehydrogenase 1 family member A1 (ALDH1A1) was identified as a novel tumor antigen in SCCHN. Mass spectral analysis of peptides in tumor-derived lysates was used to determine that the CTL line recognized the HLA-A*0201 (HLA-A2) binding ALDH1A1 [88][89][90][91][92][93][94][95][96] peptide. Expression of ALDH1A1 in established SCCHN cell lines, normal mucosa, and primary keratinocytes was studied by quantitative reverse transcription-PCR and immunostaining. Protein expression was further defined by immunoblot analysis, whereas ALDH1A1 activity was measured using ALDEFLUOR. ALDH1A1 88-96 peptide was identified as an HLA-A2-restricted, naturally presented, CD8 + T-cell-defined tumor peptide. ALDH1A1 88-96 peptide-specific CD8 + T cells recognized only HLA-A2 + SCCHN cell lines, which overexpressed ALDH1A1, as well as targets transfected with ALDH1A1 cDNA. Target recognition was blocked by anti-HLA class I and anti-HLA-A2 antibodies. SCCHN cell lines overexpressing ALDH1 had high enzymatic activity. ALDH1A1 protein was expressed in 12 of 17 SCCHN, and 30 of 40 dysplastic mucosa samples, but not in normal mucosa. ALDH1A1 expression levels in target cells correlated with their recognition by ALDH1A1 88-96 peptide-specific CD8 + T cells. Our findings identify ALDH1A1, a metabolic antigen, as a potential target for vaccination therapy in the cohort of SCCHN subjects with tumors overexpressing this protein.A smaller cohort of subjects with SCCHN, whose tumors express little to no ALDH1A1, and thus are deficient in conversion of retinal to retinoic acid, could benefit from chemoprevention therapy. [Cancer Res 2007;67(21):10538-45]

Hydroxysteroid (17β) dehydrogenase type 12 (HSD17B12) is a multifunctional isoenzyme functional in the conversion of estrone to estradiol (E2), and elongation of long-chain fatty acids, in particular the conversion of palmitic to archadonic (AA) acid, the precursor of sterols and the inflammatory mediator, prostaglandin E2. Its overexpression together with that of COX-2 in breast carcinoma is associated with a poor prognosis. We have identified the HSD17B12114–122 peptide (IYDKIKTGL) as a naturally presented HLA-A*0201 (HLA-A2)-restricted CD8+ T-cell-defined epitope. The HSD17B12114–122 peptide, however, is poorly immunogenic in its in vitro ability to induce peptide-specific CD8+ T cells. Acting as an “optimized peptide”, a peptide (TYDKIKTGL), which is identical to the HSD17B12114–122 peptide except for threonine at residue 1, was required for inducing in vitro the expansion of CD8+ T-cell effectors cross-reactive against the HSD17B12114–122 peptide. In IFN-γ ELISPOT assays, these effector cells recognize HSD17B12114–122 peptide-pulsed target cells, as well as HLA-A2+ squamous cell carcinoma of the head and neck (SCCHN) and breast carcinoma cell lines overexpressing HSD17B12 and naturally presenting the epitope. Whereas growth inhibition of a breast carcinoma cell line induced by HSD17B12 knockdown was only reversed by AA, in a similar manner, the growth inhibition of the SCCHN PCI-13 cell line by HSD17B12 knockdown was reversed by E2 and AA. Our findings provide the basis for future studies aimed at developing cancer vaccines for targeting HSD17B12, which apparently can be functional in critical metabolic pathways involved in inflammation and cancer.