Using a monoclonal antibody (MAb1.1ASML) raised against a surface glycoprotein of the metastasizing rat pancreatic carcinoma cell line BSp73ASML, cDNA clones have been isolated that encode glycoproteins with partial homology to CD44, a presumed adhesion molecule. In one of the clones, pMeta-1, the epitope marks an additional extracellular domain of 162 amino acids inserted into the rat CD44 protein between amino acid positions 223 and 247 (by analogy to human and murine CD44). The new variants are expressed only in the metastasizing cell lines of two rat tumors, the pancreatic carcinoma BSp73 and the mammary adenocarcinoma 13762NF; they are not expressed in the non-metastasizing tumor cell lines nor in most normal rat tissues. Overexpression of pMeta-1 in the nonmetastasizing BSp73AS cells suffices to establish full metastatic behavior.

Cytological screening for cervical cancer or its precursors using Papanicolaou's smear test (Pap test) has been highly efficient to reduce the morbidity and mortality of cervical cancer. However, evaluation of the Pap test relies on subjective diagnostic parameters and is affected by a high rate of false-positive and false-negative results. More objective diagnostic parameters to identify truly dysplastic or neoplastic cells in cervical smears as well as in cervical biopsy samples would therefore avoid insecurity for many patients and the high screening costs associated with repeated testing. Cervical dysplasia is induced by persistent infections through highrisk types of human papillomaviruses (HPVs). Outgrowth of dysplastic lesions is triggered by increasing expression of two viral oncogenes, E6 and E7, which both interact with various cell cycle-regulating proteins. Among these is the retinoblastoma gene product pRB, which is inactivated by E7. pRB inhibits transcription of the cyclin-dependent kinase inhibitor gene p16 INK4a . Increasing expression of the viral oncogenes in dysplastic cervical cells might thus be reflected by increased expression of p16 INK4a . In line with this hypothesis, we observed marked overexpression of p16 INK4a in all cervical intraepithelial neoplasm (CIN) I lesions (n ‫؍‬ 47) except those associated with low-risk HPV types (n ‫؍‬ 7), all CIN II lesions (n ‫؍‬ 32), all CIN III lesions (n ‫؍‬ 60) and 58 of 60 invasive cervical cancers. In contrast, no detectable expression of p16 INK4a was observed in normal cervical epithelium (n ‫؍‬ 42), inflammatory lesions (n ‫؍‬ 48) and low-grade cervical lesions (CIN I) associated with low-risk HPV types (n ‫؍‬ 7). Dysplastic cells could also be identified in cervical smears using a specific p16 INK4a monoclonal antibody. These data demonstrate that p16 INK4a is a specific biomarker to identify dysplastic cervical epithelia in sections of cervical biopsy samples or cervical smears.

Microsatellite instability (MSI) caused by defective DNA mismatch repair (MMR) is a hallmark of hereditary nonpolyposis colorectal cancers (HNPCC) but also occurs in about 15% of sporadic tumors. If instability affects microsatellites in coding regions, translational frameshifts lead to truncated proteins often marked by unique frameshift peptide sequences at their C-terminus. Since MSI tumors show enhanced lymphocytic infiltration and our previous analysis identified numerous coding mono-and dinucleotide repeatbearing candidate genes as targets of genetic instability, we examined the role of frameshift peptides in triggering cellular immune responses. Using peptide pulsed autologous CD40-activated B cells, we have generated cytotoxic T lymphocytes (CTL) that specifically recognize HLA-A2.1-restricted peptides derived from frameshift sequences. Among 16 frameshift peptides predicted from mutations in 8 different genes, 3 peptides conferred specific lysis of target cells exogenously loaded with cognate peptide. One peptide derived from a (؊1) frameshift mutation in the TGF␤IIR gene gave rise to a CTL bulk culture capable of lysing the MSI colorectal cancer cell line HCT116 carrying this frameshift mutation. Given the huge number of human coding microsatellites and assuming only a fraction being mutated and encoding immunologically relevant peptides in MSI tumors, frameshift protein sequences represent a novel subclass of tumor-specific antigens. It is tempting to speculate that a frameshift peptide-directed vaccination approach not only could offer new treatment modalities for existing MSI tumors but also might benefit asymptomatic at-risk individuals in HNPCC families by a prophylactic vaccination strategy. © 2001 Wiley-Liss, Inc. Key words: DNA mismatch repair; microsatellite instability; frameshift peptides; tumor antigens; T-cell epitopesThe accumulation of genetic alterations and resulting mutant proteins represents a major obstacle for tumor cells to escape immune surveillance. It has thus been hypothesized that mutant proteins or derived peptides must exist that are capable of eliciting specific cellular immune responses. In fact, CTL have been reported that recognize peptides of mutant or aberrantly expressed proteins such as p21/ras, MAGE-1, oncogenic fusion proteins, [1][2][3] products from alternative open reading frames 4 -6 and also frameshift mutated APC. 7 These tumor antigens originally have been identified in tumors showing chromosomal instability. 8 Much less is known about the immunogenicity of tumor cells that show more subtle genetic alterations such as small deletions and insertions in repetitive DNA sequences, termed microsatellites. 9,10 Microsatellite instability in these tumor cells is due to deficient DNA mismatch repair caused by germline and/or sporadic mutations in at least 5 different MMR genes, 11 leading to high spontaneous mutation rates. More than 90% of HNPCC and about 15% of sporadic cancers of different organs show MSI. 9,12 If instability affects microsatellites in coding re...

Abstract. Cell contact with the extracellular matrix component hyaluronic acid (HA) plays an important role in many developmental, physiological, and pathological processes, although the regulation of this contact is poorly understood. CD44 proteins carry an amino acid motif that mediates affinity to HA. Artificial clustering of the smallest 85-kD isoform of CD44 (CD44s) has previously been shown to promote binding of the protein to soluble HA (Lesley, J., R. Hyman, and P.W. Kincade. 1993. Adv. Immunol. 54:271-335; Persche, A., J. Lesley, N. English, I. Trowbridge, and R. Hyman. 1995. Eur. J. Immunol. 25:495-501). Here we show that in rat pancreatic carcinoma cells, splice variants of CD44 (CD44v), but not CD44s, form molecular aggregates in the plasma membrane. We demonstrate that reduction-sensitive dimerization of CD44v occurs, and also that larger aggregations of the protein can be stabilized by chemical cross-linking. Different CD44v proteins present on the same cell exclusively form homoaggregates. Molecular clustering does not require an intact cytoplasmic domain of the protein.The ability of cells to bind to soluble HA is upregulated more than one magnitude by the ectopic expression of CD44v4-v7, but only when the CD44v4-v7 protein forms intermolecular aggregates. Tunicamycin treatment inhibits HA binding by CD44v and at the same time destroys oligomerization. We propose that the regulation of clustering of CD44, mediated by factors including the presence of variant exons and glycosylation, allows cells in turn to regulate their HA binding properties.

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