Catherine Wölfel

A p16INK4a-insensitive CDK4 mutant targeted by cytolytic T lymphocytes in a human melanoma

A mutated cyclin-dependent kinase 4 (CDK4) was identified as a tumor-specific antigen recognized by HLA-A2. 1-restricted autologous cytolytic T lymphocytes (CTLs) in a human melanoma. The mutated CDK4 allele was present in autologous cultured melanoma cells and metastasis tissue, but not in the patients lymphocytes. The mutation, an arginine-to-cysteine exchange at residue 24, was part of the CDK4 peptide recognized by CTLs and prevented binding of the CDK4 inhibitor p16INK4a, but not of p21 or of p27KIP1. The same mutation was found in one additional melanoma among 28 melanomas analyzed. These results suggest that mutation of CDK4 can create a tumor-specific antigen and can disrupt the cell-cycle regulation exerted by the tumor suppressor p16INK4a.

TRANSPORTER (TAP)- AND PROTEASOME-INDEPENDENT PRESENTATION OF A MELANOMA-ASSOCIATED TYROSINASE EPITOPE

The melanosomal protein tyrosinase is considered as a target of specific immunotherapy against melanoma. Two tyrosinase‐derived peptides are presented in association with HLA‐A2.1 [Wölfel et al., Eur. J. Immunol., 24, 759–764 ( 1994 )]. Peptide 1‐9 (MLLAVLYCL) is generated from the putative signal sequence. The internal peptide 369‐377 is posttranslationally converted at residue 371, and its presentation is dependent on functional TAP transporters and proteasomes [Mosse et al., J. exp. Med.187, 37–48 ( 1998 )]. Herein, we report on the processing and transport requirements for the signal sequence‐derived peptide 1‐9 that were studied in parallel to those for peptide 369‐377. After infection of TAP‐deficient (T2) and TAP‐positive (T1) cells with a Modified Vaccinia Ankara construct carrying the human tyrosinase gene (MVA‐hTyr), we found that recognition by CTL against peptide 1‐9 did not require TAP function as opposed to recognition by CTL against peptide 369‐377. When target cells with intact processing and transport functions were infected with MVA‐hTyr, lysis by CTL against peptide 1‐9 was not impaired by lactacystin, a specific inhibitor for the proteasome, whereas lysis by CTL against peptide 369‐377 was completely abrogated. Taken together, peptide 1‐9 derived from the signal sequence of tyrosinase is presented in a TAP‐independent fashion and does not require proteasomes for processing. Cellular immune responses against this hydrophobic peptide can be monitored with lymphokine spot assays as documented in the case of a patient with metastatic melanoma, in whom we observed a preferential T‐cell response against tyrosinase peptide 1‐9 subsequent to chemoimmunotherapy. Independence of cytosolic processing and transport pathways and potentially enhanced expression levels make signal sequence‐derived peptides and their carrier proteins important candidates for specific immunotherapy.Int. J. Cancer 88:432–438, 2000.

Genetically engineered V79 Chinese hamster cells for stable expression of human cytochrome P450IA2.

V79 Chinese hamster cells were genetically engineered for stable expression of human P450IA2. Full length cDNA, encoding human P450IA2, was inserted into an SV40 early promoter containing eukaryotic expression vector and cointroduced with the selection marker neomycin phosphotransferase (conferring resistance to the neomycin derivative G418) into V79 Chinese hamster cells. The recombinant expression vector was introduced into two different V79 sublines, one expressing an endogenous acetyltransferase (V79-NH), the other not (V79-MZ). The presence of human cytochrome CYP1A2 cDNA in the G418 resistant V79 cell clones was confirmed by Southern blotting. The transcription of the cDNA into mRNA was detected by Northern blotting and the translation into an authentic cytochrome P450IA2 protein was shown by Western blotting. The enzymatic activity in these cells was determined by the cytochrome P450IA2-dependent methoxy-, ethoxy-, benzoxy-, and pentoxyresorufin dealkylation activity.

Acute myeloid leukemia (AML)-reactive cytotoxic T lymphocyte clones rapidly expanded from CD8+ CD62L(high)+ T cells of healthy donors prevent AML engraftment in NOD/SCID IL2Rγnull mice

OBJECTIVE Current in vitro techniques for isolating leukemia-reactive cytotoxic T lymphocytes (CTLs) from healthy donors are of relatively low efficiency and yield responder populations with unknown biological significance. This study aimed at the development of a more reliable approach, allowing generation and expansion of acute myeloid leukemia (AML)-reactive CTLs using primary in vitro stimulation. MATERIALS AND METHODS We established allogeneic mini-mixed lymphocyte-leukemia cultures (mini-MLLCs) by stimulating donor CD8(+) T cells with human leukocyte antigen (HLA) class I-matched AML blasts in microtiter plates. Before culture, CD8(+) T cells were separated into CD62L((high)+) and CD62L((low)+/neg) subsets enriched for naive/central memory and effector memory cells, respectively. RESULTS In eight different related and unrelated donor/AML pairs, numerous CTL populations were isolated that specifically lysed myeloid leukemias in association with various HLA-A, -B, or -C alleles. These CTLs expressed T-cell receptors of single Vbeta-chain families, indicating their clonal origin. The majority of CTL clones were obtained from mini-MLLCs initiated with CD62L((high)+) cells. Using antigen-specific stimulation, multiple CTL populations were amplified to 10(8)-10(10) cells within 6 to 8 weeks. Three of four representative CTL clones were capable of completely preventing engraftment of human primary AML blasts in nonobese diabetic/severe combined immune deficient IL2Rgamma(null) mice. CONCLUSION The mini-MLLC approach allows the efficient in vitro expansion of AML-reactive CTL clones from CD8(+)CD62L((high)+) precursors of healthy donors. These CTLs can inhibit leukemia engraftment in immunodeficient mice, suggesting their potential biological relevance.

Applications of stable V79-derived cell lines expressing rat cytochromes P4501A1, 1A2, and 2B1

1. Chinese hamster V79-derived cell lines, stably expressing cytochromes P4501A1, 1A2, and 2B1 activities, were constructed by genetic engineering in continuation of our work to establish a battery of V79 derived cell lines designed to study the metabolism of xenobiotics. 2. Cell lines XEM1 and XEM2, expressing cytochrome P4501A1, were capable of the O-dealkylation of 7-ethoxycoumarin and the hydroxylation of benzo[a]pyrene. 3. Cell lines XEMd.MZ and XEMd.NH, expressing P4501A2, were shown to hydroxylate 17 beta-estradiol and 2-aminofluorene. 4. Cell line SD1, expressing cytochrome P4502B1, was able to hydroxylate testosterone stereo- and regio-specifically at the 16 alpha and 16 beta positions. 5. Cell lines were validated in mutagenicity, cytotoxicity, and metabolism studies employing benzo[a]pyrene, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, cyclophosphamide, ifosfamide, and picene. 6. Construction of metabolically-competent V79-derived cell lines be recombinant DNA technology will be a fundamental improvement for the evaluation of the cytotoxic, genotoxic and pharmacological properties of a chemical.

Biotransformation of methylxanthines in mammalian cell lines genetically engineered for expression of single cytochrome P450 isoforms. Allocation of metabolic pathways to isoforms and inhibitory effects of quinolones.

V79 Chinese hamster cells genetically engineered for stable expression of single forms of rat cytochromes P450IA1, P450IA2, P450IIB1, human P450IA2, and rat liver epithelial cells expressing murine P450IA2 were used to allocate metabolic pathways of methylxanthines to specific isoforms and to test the suitability of such cell lines for investigations on drug interactions occurring at the cytochrome expressed. The cell lines were exposed to caffeine and/or theophylline and concentrations of metabolites formed in the medium were determined by HPLC. Caffeine was metabolized by human, rat and murine P450IA2, resulting in the formation of four primary demethylated and hydroxylated metabolites. However, there were differences in the relative amounts of the metabolites. The human and the mouse P450IA2 isoforms predominantly mediated 3-demethylation of caffeine. The rat cytochrome P450IA2 mediated both 3-demethylation and 1-demethylation of caffeine to a similar extent. The results support the hypothesis that caffeine plasma clearance is a specific in vivo probe for determining human P450IA2 activity. Addition of the quinolone antibiotic agents pipemidic acid or pefloxacin, both known to inhibit caffeine metabolism in vivo and in human liver microsomes, reduced formation rates of all metabolites of caffeine in cells expressing rat and human P450IA2. Theophylline was mainly metabolized via 8-hydroxylation. All cell lines tested were able to carry out this reaction, with highest activities in cell lines expressing rat or human P450IA2, or rat P450IA1.

Dissection and molecular analysis of alloreactive CD8+ T cell responses in allogeneic haematopoietic stem cell transplantation.

We applied a cDNA expression screening procedure with cryopreserved non-clonal CD8+ T cell populations (Lennerz et al., Proc. Natl. Acad. Sci. USA 102:16013-8, 2005) to the identification of candidate antigens for graft-versus-host disease (GvHD) and graft-versus-leukaemia (GvL) effects in allogeneic haematopoietic stem cell transplantation (allo-HSCT). In a patient–donor model system with HLA class I disparities, we identified an HLA-B*44 mismatch allele, HLA-B*4405, as the dominant target of alloreactive T cells expanded in vitro from donor peripheral blood mononuclear cells (PBMC). HLA-B*4405-reactive T cells were detectable after multiple in vitro stimulations in the patient’s post-HSCT PBMC. In a patient–donor model with full HLA compatibility, the major target antigen of donor lymphocytes stimulated in vitro with the respective patient’s pre-HSCT PBMC was restricted by HLA-A*0201 and was encoded by TRIM22-442C, a newly detected polymorphic allele of the tripartite motif family member TRIM22 (synonym: STAF50), preferentially expressed in cells of the haematopoietic system. An arginine(R)-to-cysteine(C) exchange at position 442 generated an immunogenic T cell epitope equivalent to a minor histocompatibility antigen (mHag). TRIM22-442C-specific T cells persisted long-term in the patient’s post-HSCT PBMC. Approximately, 1.3% of Caucasians carry TRIM22.442C in association with HLA-A*0201. In particular, the knowledge of a large and diverse panel of such mHags may be crucial for further improvement of donor selection and adoptive T cell transfer strategies. The procedure applied herein will help to accelerate and facilitate their identification.

HLA class I loss in metachronous metastases prevents continuous T cell recognition of mutated neoantigens in a human melanoma model

T lymphocytes against tumor-specific mutated neoantigens can induce tumor regression. Also, the size of the immunogenic cancer mutanome is supposed to correlate with the clinical efficacy of checkpoint inhibition. Herein, we studied the susceptibility of tumor cell lines from lymph node metastases occurring in a melanoma patient over several years towards blood-derived, neoantigen-specific CD8+ T cells. In contrast to a cell line established during early stage III disease, all cell lines generated at later time points from stage IV metastases exhibited partial or complete loss of HLA class I expression. Whole exome and transcriptome sequencing of the four tumor lines and a germline control were applied to identify expressed somatic single nucleotide substitutions (SNS), insertions and deletions (indels). Candidate peptides encoded by these variants and predicted to bind to the patients HLA class I alleles were synthesized and tested for recognition by autologous mixed lymphocyte-tumor cell cultures (MLTCs). Peptides from four mutated proteins, HERPUD1G161S, INSIG1S238F, MMS22LS437F and PRDM10S1050F, were recognized by MLTC responders and MLTC-derived T cell clones restricted by HLA-A*24:02 or HLA-B*15:01. Intracellular peptide processing was verified with transfectants. All four neoantigens could only be targeted on the cell line generated during early stage III disease. HLA loss variants of any kind were uniformly resistant. These findings corroborate that, although neoantigens represent attractive therapeutic targets, they also contribute to the process of cancer immunoediting as a serious limitation to specific T cell immunotherapy.

The cytotoxicity of mitomycin C and adriamycin in genetically engineered V79 cell lines and freshly isolated rat hepatocytes.

The objective of the present study was to investigate the cytotoxicity of Adriamycin (ADR) and mitomycin C (MMC) in tumor and non-tumor cells with respect to the role of cytochrome P450 (P450). Therefore, genetically engineered V79 Chinese hamster fibroblasts expressing only single enzymes of P450 were used. SD1 and XEM2 cells expressed rat P450IIB1 and P450IA1, respectively, whereas the V79 parental cells contained no detectable P450 levels. The cytotoxicity of ADR and MMC in the V79 cell system was compared with that in freshly isolated hepatocytes from phenobarbital (PB-hepatocytes)- and beta-naphthoflavone (beta NF-hepatocytes)-induced rats. Following 24 h of exposure to ADR equal cytotoxicity was observed in V79, SD1 and XEM2 cells. Addition of metyrapone (MP, an inhibitor of P450IIB1) and alpha-naphthoflavone (alpha NF, an inhibitor of P450IA1) had no effect on the ADR-induced cytotoxicity in SD1 and XEM2 cells, respectively. Likewise, MMC was equitoxic in V79 and SD1 cells. Co-incubation of SD1 cells with MP did not alter MMC-induced cytotoxicity. MMC, however, showed a decreased cytotoxicity in XEM2 cells when compared to the parental V79 cells. Unexpectedly, the cytotoxicity of MMC in XEM2 cells was increased by alpha NF to the same level as observed in the parental V79 cells. In contrast to V79- and V79-derived cells, in freshly isolated hepatocytes from PB or beta NF-induced rats, MMC was cytotoxic (measured as lactate dehydrogenase leakage) within 3 h of incubation. ADR, however, was only cytotoxic to the hepatocytes when intracellular glutathione was first depleted by diethylmaleate. The MMC- and ADR-induced cytotoxicity was found to be more pronounced in PB-hepatocytes than in beta NF-hepatocytes. Contrary to the findings in the V79-derived cells, MP afforded complete protection against both MMC- and ADR-induced cytotoxicity in PB-hepatocytes, whereas alpha NF only partially inhibited the cytotoxicity of MMC in beta NF-hepatocytes. In conclusion, we have demonstrated that PB-inducible P450s play a role in the cytotoxicity of both MMC and ADR in freshly isolated PB-hepatocytes but that P450IIB1 does not in genetically reconstituted SD1 cells. P450IA1, however, decreased the cytotoxicity of MMC in the XEM2 cells. The ADR-induced cytotoxicity, which was observed in XEM2 cells, was not mediated by P450IA1. The present study underscores the complexity in the comparison of ADR- and MMC-induced cytotoxicities in normal and tumor cells.