The K562 cell line derived from a CML patient in blast crisis was examined for properties of B and T lymphocytes and cell lines. K562 lacks the B markers of immunoglobulins, Epstein-Barr virus (EBV) genome and associated nuclear antigen, and receptors for EBV. A low proportion of cells from rosettes with sheep erythrocytes, the frequency of which is considerably increased after neuraminidase treatment. Unlike B lines but like T lines, K562 cells are lysed rapidly by C'/Fc receptor-positive human blood leukocytes and do not stimulate MLC reactions. On the other hand, K562 lacks T antigen, high radiosensitivity and sensitivity to growth inhibition by thymidine. The cells do not contain N-APase, an enzyme found in all lines derived from lymphoid cells and in lymphoproliferative diseases. By scanning electron microscopy, K562 cells were seen to be rounded and relatively smooth, with small numbers of short microvilli resembling undifferentiated leukemic cells. A few cells had narrow ridge-like profiles and small ruffles similar to granulocytic leukemic cells. K562 is strongly positive for immunoglobuln Fc receptors and pinocytosis, but does not phagocytose or mediate antibody-dependent phagocytosis or cytolysis. Among histochemical stains, K562 is positive for esterase, lipid, and acid phosphatase. There seems to be no doubt that K562 is not a B cell line. While it has some T cell properties, these are not exclusive. Some of its characteristics indicate that it is probably not lymphoid. Due to its low level of differentiation, its nature cannot be stated with certainty. On the basis of the possible presence of the cellular marker of chronic myeloid leukemia, the Ph chromosome, it may be regarded as belonging to the granulocytic series of cells.

The purpose of this study was to clarify whether HLA-DR expression of colorectal tumour cells or the CD4+/CD8+ ratio of the tumour infiltrating lymphocytes is significantly associated with the prognosis of colorectal cancer. Using flow cytometry, we studied the tumour cell expression of the HLA class II in 70 enzymatically dissociated colorectal cancers and the phenotype of tumour infiltrating lymphocytes (TILs) in 41 cases. There was no trend in 5-year survival between three levels (low, medium, high) of HLA-DR expression on the tumour cells. Patients with low CD4+/CD8+ ratios had a better clinical course, with significantly higher 5-year survival, p=0.046, independent of the Dukes stage and age. Our results have implications for tumour immunology; colorectal cancer cells might be a target for cytotoxic T-lymphocytes, however the tumour cells are not able to initiate an immune response. Stimulation of the immune system could possible be obtained using dendritic cells cultured in vitro and loaded with tumour antigens.

Incorporation of the serine protease active site reagent diisopropyl fluorophosphate (DFP) into a plasminogen activator with an Mr of approximately 52000 released from cultured human glioblastoma cells was strongly enhanced by incubation with plasmin. This observation led to the isolation of an inactive form of the enzyme from serum-free conditioned culture fluid by affinity chromatography on a column of a Sepharose-bound monoclonal antibody raised against urokinase. An 831-fold purification was obtained with a yield of 41%. The purified molecule was homogeneous as evaluated by polyacrylamide gel electrophoresis with sodium dodecyl sulfate (NaDodSO4), having one stainable band under nonreducing as well as reducing conditions with an Mr of approximately 52000. It was unable to activate plasminogen, but catalytic amounts of plasmin converted it into active enzyme. After NaDodSO4-polyacrylamide gel electrophoresis, the active enzyme showed one band under nonreducing conditions, but after reduction, two bands with Mr values of approximately 20000 and 32000 were observed. The active enzyme incorporated [3H]DFP into the approximately Mr 32000 band, while no incorporation was observed into the inactive form. These findings show that the Mr 52000 human plasminogen activator exists in a proenzyme form consisting of a single polypeptide chain that by proteolysis between half-cystine residues is converted into the active enzyme consisting of two chains with molecular weights of approximately 20000 and 32000, the active site being on the latter chain. The results are consistent with the active form of the enzyme being identical with the higher molecular weight form of urokinase, and together with recent observations that a murine plasminogen activator is released from sarcoma virus transformed cells as an inactive proenzyme, they suggest that zymogens to plasminogen activators are of more general occurrence.

The PTEN/MMAC1 gene on chromosome 10q23 encodes a lipid phosphatase with tumor-suppressive properties. Germline PTEN/MMAC1 mutations have been implicated as the predisposing factor in Cowden disease and other hamartoma syndromes, and somatic mutations and deletions have been identified in a wide range of human cancers, including 30-40% of metastatic melanoma cell lines. To study further the possible role of PTEN/MMAC1 in the pathogenesis and progression of malignant melanoma, we examined uncultured specimens from 16 primary and 61 metastatic tumors from 67 patients. Denaturing gradient gel electrophoresis was used to analyze systematically the coding region of PTEN/MMAC1 and revealed mutations in four of the metastatic samples (7%). Sequence analysis of the mutants identified a 1 bp frameshift insertion, a 2 bp frameshift deletion, an 11 bp frameshift deletion, and a single base substitution resulting in the generation of a premature stop codon. Analysis of two intragenic polymorphisms showed allelic loss in three of eight informative primary tumors (38%) and in 18 of 31 metastatic tumors (58%). One of the mutant cases showed allelic loss, suggesting that both PTEN/MMAC1 alleles were inactivated in this tumor. Altogether, these results suggest that mutation and deletion of PTEN/MMAC1 may contribute to the development and progression of malignant melanoma.

A cytotoxic T lymphocyte (CTL) clone generated in vitro from the peripheral blood of a healthy HLA-A2-positive individual against a synthetic p53 protein-derived wild-type peptide (L9V) was shown to kill squamous carcinoma cell lines derived from two head and neck carcinomas, which expressed mutant p53 genes, in a L9V͞HLA-A2 specific and restricted fashion. Thus, the normal tolerance against endogenously processed p53 protein-derived self-epitopes can be broken by peptide-specific in vitro priming. p53 proteinderived wild-type peptides might thus represent tumor associated target molecules for immunotherapeutical approaches.