Mouse L cells expressing human prourokinase-type plasminogen activator: effects on extracellular matrix degradation and invasion

A cosmid (cos pUK0322) harboring the complete human urokinase-type plasminogen activator (u-PA) gene and Geneticin resistance as a selectable marker was isolated from a human genomic library and characterized. After transfection of cos pUK0322 into mouse L cells and selection, several plasminogen activator (PA)-expressing clones were obtained and one (LuPA) was chosen for additional study. The PA expressed was identical to human pro-u-PA in enzymatic, electrophoretic, and antigenic properties. The expression of PA was stable over 50 population doublings. The regulation of the transfected gene was studied by treatment of the cells with various hormones and other effectors. Expression of PA activity was inhibited fivefold by dexamethasone and stimulated two- to threefold by agonists of the adenylate cyclase dependent pathway of signal transduction, such as dibutyryl cyclic AMP and cholera and pertussis toxins. The modulation of PA activity was associated with corresponding changes in mRNA steady-state levels. The phenotypic changes associated with pro-u-PA expression were analyzed in vitro by degradation of 3H-labeled extracellular matrix (ECM), invasion of a matrigel basement membrane analogue, and by light and electron microscopy. LuPA cells and reference HT-1080 fibrosarcoma cells, in contrast to control Lneo cells transfected with the neomycin resistance gene, degraded the ECM and invaded the matrigel basement membrane. Matrix degradation correlated with the modulation of pro-u-PA gene expression as it was inhibited by dexamethasone and promoted by dibutyryl cyclic AMP. Inhibition of PA or plasmin using anti-u-PA IgG or aprotinin prevented ECM degradation and invasion. These results demonstrate that u-PA expression alone is sufficient to confer to a cell an experimental invasive phenotype.

Urokinase-type plasminogen activator biosynthesis is induced by the EJ-Ha-ras oncogene in CL26 mouse colon carcinoma cells

CL26 murine colon carcinoma cells express urokinase-type plasminogen activator (u-PA) mRNA and activity after transfection with the activated c-Ha-ras-I (EJ-ras) oncogene cloned from the EJ bladder carcinoma. PA activity and mRNA in control cells transfected with the non-mutated c-Ha-ras-I (CO-ras) gene remained negative. Ras mRNA was detected in EJ-ras- and CO-ras-transfected cells, but not in untransfected or pSV2-neo-transfected cells. These results indicate that u-PA biosynthesis can be modulated by EJ-Ha-ras-dependent pathways of signal transduction.

T cell antigen receptor expression in athymic (nu/nu) mice. Evidence for an oligoclonal beta chain repertoire

The expression of T cell antigen receptors (TCR) in congenitally athymic (nude) mice has been investigated. Lymph node T cells from 4-5-mo-old athymic mice expressed full-length transcripts for the TCR alpha and beta chains at a level two-to three-fold lower than normal littermate (nu/+) controls. Low levels of expression of TCR protein at the surface of a proportion of nude T cells was demonstrated by staining with monoclonal antibodies KJ16-133 and F23.1 (directed against protein products of a family of TCR beta chain variable region genes known as V beta 8). Immunoprecipitation studies confirmed that F23.1 reacted with a similar molecular species on nude and nu/+ T cells. Studies with individual nude mice revealed a striking heterogeneity in the proportion of T cells expressing KJ16/F23.1 that was not seen in normal animals. This heterogeneity correlated with the expression of mRNA specific for V beta 8 but not with total expression of full-length beta chain transcripts. Analysis of Lyt-2+ and L3T4+ T cell subsets in individual nude mice further demonstrated that F23.1 expression was frequently associated with only one subset, and several cases were seen in which all L3T4+ cells expressed F23.1. In contrast, a similar (and constant) proportion of Lyt-2+ or L3T4+ T cells expressed F23.1 in control mice. Southern blotting of Hind III-digested DNA from nude T cells with a C beta probe revealed a more restricted pattern of TCR beta chain rearrangements than was seen for normal T cells. Taken together, these data provide compelling evidence that TCR gene rearrangement and expression can occur extrathymically. Furthermore, they suggest a model according to which the restricted functional repertoire of T cells previously observed in individual nude mice results from an oligoclonal expansion of T cells that have randomly rearranged and expressed TCR beta chain genes.

Plasminogen activators, plasminogen activator inhibitors and procoagulant analyzed in twenty human tumor cell lines

We have analyzed the CM of 20 human tumor cell lines for the presence of PA, PA-I and PC. Most of the cell lines expressed PA activity as measured by a radioiodinated fibrin plate assay. The urinary type and tissue-type PA activities were specifically quantified by means of purified inhibitory antibodies. U-PA and/or t-PA antigen, as measured by radioimmunoassays, were detected in all but 4 of the CM and were generally 10 times more concentrated than PA activity, indicating the presence of specific PA-Is. Analysis of CM by electrophoresis followed by fibrin-agarose zymography demonstrated the presence not only of free but also of inhibitor-complexed PA. Affinity purification demonstrated that 8/20 cell lines expressed detectable PA-I activity. The PA-I1 and PA-I2 inhibitors were most frequently observed, while PN was recovered only from CM of the HT1080 fibrosarcoma cell line. PC activity, as measured by the plasma recalcification time method, was found in 9/20 CM. It was of the thromboplastin tissue factor type since most of its activity was lost when assayed with a Factor VII-deficient plasma.

Human primary colon carcinomas xenografted into nude mice. II. Modulation of tumor plasminogen activator activity by the host tissue environment

The characterization and quantitation of plasminogen activators (PAs) expressed by human colon carcinoma cell lines and primary colon carcinomas inoculated into nude outbred (nu/nu) mice, either as subcutaneous or gut-implanted (GI) xenografts, were discussed. The two colon carcinoma cell lines used in this study, Col 112 (moderately differentiated) and Col 115 (poorly differentiated), differ in their PA expression, the former being a urinary-type PA and the latter being a tissue-type PA producer. Both cell lines demonstrate a positive correlation between tumor invasiveness and measured PA activity; subcutaneous xenografts growing as noninvasive pseudobenign tumor masses were associated with low levels of PA activity, whereas GI xenografts exhibiting invasive growth expressed higher PA activity. Furthermore, coinoculation of Col 115 tumor cells sc and GI in the same host induced high levels of PA activity in subcutaneous xenografts, suggesting a stimulatory effect of the GI xenograft on subcutaneous xenograft PA expression. Also, purified murine plasminogen was demonstrated to represent an efficient substrate for tumor-secreted human PA.

Developmental coordination of alpha-amylase and psp gene expression during mouse parotid gland differentiation is controlled posttranscriptionally

We have compared the developmental expression of psp and Amy-1a genes during postnatal differentiation of the mouse parotid gland. The mRNAs encoded by both genes accumulate with identical kinetics and accumulate in the same subset of acinar cells early in development. Transcriptional activation of the two genes is unexpectedly asynchronous. While the increase of alpha-amylase mRNA levels in development arise from increased Amy-1a transcription, psp is transcribed at almost adult levels at 12 days of age, but cellular psp mRNA accumulation is very low. Since nuclear processing of psp pre-mRNAs and transport of mature mRNA into the cytoplasm occur with similar efficiencies in young and adult mice, the rapid turnover of psp mRNA in young animals occurs in the cytoplasm.

Oxygenation and differentiation in multicellular spheroids of human colon carcinoma

Oxygenation and development of necrosis were evaluated in multicellular spheroids of poorly differentiated (HT29) and moderately well-differentiated (Co112) human adenocarcinoma of the colon. Spheroids were grown in vitro under well-controlled oxygen and nutrient conditions in spinner flasks up to sizes of 2800-micron diameter after 5 wk of culture. Morphological studies showed that the Co112 spheroids contained pseudoglandular structures with lumen, very similar to the characteristics of the original tumor specimen from the patient and to the cells when grown as xenograft tumors in nude mice. Microelectrodes were used to measure the oxygen tension (PO2) profile within individual spheroids at different stages of growth. Histological sections through the centers of spheroids were measured to determine the thickness of the viable rim of cells surrounding spheroid necrotic centers in order to estimate the size of the severely hypoxic zone of cells by comparison with the PO2 profiles of the same spheroids. The data demonstrate significant differences between these two human colon tumor spheroid systems. Both spheroid types exhibited steep PO2 gradients at relatively small sizes of less than 600-micron diameter, but for any given size in this range, the more differentiated Co112 spheroids were more hypoxic. Although severe hypoxia (PO2, less than 10 mm of Hg) was present in both spheroid types at larger sizes, there was a significant difference in the central PO2 values which were between 5 and 10 mm of Hg in large Co112 spheroids but remained at or close to 0 mm of Hg in large HT29 poorly differentiated human colon tumor spheroids. The presence of pseudoglandular structures and lumen in the Co112 spheroids was associated with changes in the shape of PO2 profiles. Such profiles have not previously been seen in other poorly differentiated human or rodent tumor spheroids. Furthermore, the PO2 profiles of both of these human tumor spheroid types were often continuously curving with a very shallow gradient in the inner edge of the viable rim of cells surrounding the necrotic center. Regulation of oxygen consumption and/or diffusion in these inner regions of human spheroids could produce these continuously curving PO2 gradients.

Human primary colon carcinomas xenografted into nude mice. I. Characterization of plasminogen activators expressed by primary tumors and their xenografts

Analysis was made of plasminogen activator (PA) activities present in 0.125% Triton X-100 extracts of human primary colon carcinomas and of their respective serial subcutaneous xenografts in nude mice. A correlation between tumor invasiveness and PA expression was observed in that primary tumors exhibiting clearly invasive growth patterns demonstrated high concentrations of PAs while subcutaneous xenografts, exhibiting noninvasive pseudobenign growth, contained very low levels of PA activity. The decrease in fibrinolytic activity observed in subcutaneous xenografts was not due to an increase in inhibitors of fibrinolytic activity. Immunologic characterization of PAs in tumor extracts showed that over 90% of human PA activity was of the urokinase type. Furthermore, tumor-derived urokinase was shown to be present in a proenzyme form. It was resistant to diisopropyl fluorophosphate (DFP) and was not inhibited by purified PA inhibitor. However, after its activation into urokinase by plasmin, it was completely inhibited by DFP and PA inhibitor.

Establishment of two rabbit mammary epithelial cell lines with distinct oncogenic potential and differentiated phenotype after microinjection of transforming genes

The goal of this work was to establish an assay for transformation of epithelial cells. Two epithelial cell lines were obtained after microinjecting transforming genes into primary rabbit mammary secretory cells. The cell lines were analyzed for their oncogenic potential and for the maintenance of a differentiated phenotype. A fully transformed cell line, which retained epithelial cell organization, was obtained by coinjecting simian virus 40 DNA and the activated human c-Ha-ras gene. The proliferation rate of these cells was high, with a doubling time of 16 h. Their growth was anchorage independent, and they had lost contact inhibition. The cells were tumorigenic in nude mice, but had no metastatic potential. Both microinjected DNAs were efficiently transcribed and translated, in contrast to the casein genes, which were expressed in primary cells but not in the transformed cell line. An immortalized cell line established after injection with simian virus 40 DNA alone was characterized by a moderate rate of proliferation with a doubling time of approximately 30 h. The growth of these cells was contact inhibited and anchorage dependent. The cells were not tumorigenic in nude mice. The viral DNA was expressed during early passages, as shown by the presence of the large T antigen in cell nuclei, but not at later passages. A high number of lactogenic hormone receptors were found associated with the cell surface. Despite the presence of these receptors, no induction of genes coding for milk proteins was observed after addition of prolactin. These data demonstrate that this assay system can be used to assess the immortalizing and transforming potential of candidate oncogenes in epithelial cells.

Cellular growth and metabolic adaptations to nutrient stress environments in tumor microregions

Heterogeneity of cell subpopulation growth was significantly modulated by different oxygen and glucose environments and necrosis in multicellular tumor spheroids of rodent and human origin. PO2 profiles within spheroids measured with microelectrodes showed major differences associated with different oxygen and glucose supply conditions, indicating important interactions of these two substrates affecting oxygen consumption rates and cellular viability. Cellular interactions in association with the development of growth quiescence and differentiation changed oxygen consumption rates and slopes of PO2 profiles within spheroids. Protein synthesis in monolayer cells in culture was severely inhibited when exposed to extreme hypoxia, but certain proteins were synthesized at increased rates. Many of these oxygenated regulated proteins can also be induced by glucose deprivation. The data demonstrate cellular and subcellular changes in tumor models in vitro because of variations in oxygen and glucose supply. Many of these changes would be expected to occur in tumor microregions in vivo and could have important consequences for therapeutic responsiveness.

The two promoters of the mouse alpha-amylase gene Amy-1a are differentially activated during parotid gland differentiation

Mouse parotid acinar cells differentiate and proliferate mainly after birth. During the first 3 weeks of age, alpha-amylase mRNA, one of the major gene products of the adult tissue, increases from barely detectable to adult levels (10(4) copies/cell). Run-on transcription experiments show that this increase is transcriptionally regulated. Northern blot hybridization and in situ hybridization results indicate that the two promoters of the alpha-amylase gene Amy-1a are differentially switched on. First, the weaker downstream promoter is activated, and by 2 weeks of age, virtually all acinar cells have accumulated the transcript initiated at this promoter. At this age the strong Amy-1a promoter is utilized in only a minor proportion of acinar cells, while in the adult this promoter appears to be active in all acinar cells. Thus, the progressive accumulation of alpha-amylase mRNA during postnatal parotid differentiation is mainly the consequence of progressive acinar cell commitment to expression of the strong parotid-specific Amy-1a promoter. The pattern of committing cells during differentiation suggests that once an acinar cell has initiated expression of parotid-type alpha-amylase mRNA, this commitment is passed on to its daughter cells.

Immunohistological evidence, obtained with monoclonal antibodies, of small intestinal brush border hydrolases in human colon cancers and foetal colons

The expression of small intestinal hydrolases associated with the enterocyte brush border membrane was studied in human colon cancers and foetal colons, by means of monoclonal antibodies against human small intestinal sucrase-isomaltase (SI), maltase-glucoamylase (MGA), lactase (L), aminopeptidase N (APN), and dipeptidylpeptidase IV (DPP-IV). The enzymes were visualized by indirect immunofluorescence on cryostat sections of tumors developed in nude mice with 6 human colon carcinoma cell lines (HT-29, Caco-2, SW-480, HRT-18, HCT-8R, and Co-115), of 27 primary colorectal carcinomas from patients, and of human foetal (16 to 20 weeks of gestation) and normal adult small intestines and colons. All 5 monoclonals bound to the brush border of the adult small intestine, but not to that of the adult colon mucosa. Antibodies against SI, APN and DPP-IV also bound to the brush border of the foetal colons, to apical borders in HT-29 and Caco-2 tumors in nude mice, and to brush border-like structures in 7/27 tumors from patients. No binding was observed for MGA and L in either tumors or foetal colons. Binding of anti-SI antibodies to the brush border of the juxta-tumoral mucosal epithelium was observed in 9/11 samples tested. These data indicate that some colon tumors exhibit a typical pattern of enterocytic differentiation which is of foetal type and which involves at least 3 brush border membrane hydrolases. Monoclonal antibodies to small intestinal hydrolases may, therefore, be important tools for identification and characterization of some differentiated colonic tumors.

Human colorectal tumor xenografts in nude mice: expression of malignancy

Factors associated with the growth and progression of (human) tumor xenografts have been briefly reviewed. Intrinsic properties of tumor cells, most of them yet to be recognized, may interfere with multiple rejection processes and/or growth regulatory signals developed in various immunodeficient recipients. Using alternative hosts or new experimental conditions, it is hoped that the system can provide valuable information on the tumor invasive and metastasizing processes.

Interleukin 2 production by lymphoid cells from congenitally athymic (nu/nu) mice

The ability of lymphoid cells from congenitally athymic (nu/nu) mice to produce interleukin 2 (IL 2) was investigated. Spleen or lymph node cells (superficial or mesenteric) from nude mice on an N:NIH(S)II or BALB/c genetic background were stimulated with concanavalin A (Con A) or with irradiated allogeneic (DBA/2) spleen cells that had been depleted of T cells by treatment with monoclonal anti-Thy-1.2 antibody plus complement. After 24 hr, supernatants were harvested and assayed for their ability to support the proliferation of a cloned IL 2-dependent cytolytic T cell line. With this quantitative microassay, IL 2 production was not detectable in spleen and lymph nodes of 6-wk-old N:NIH(S)II nude mice; however, by 12 mo of age, IL 2 production increased more than 100-fold to reach levels comparable to control (nu/+) animals. Con A was more potent than alloantigen in the induction of IL 2 in either nude or control (nu/+) animals. Furthermore, differences in the genetic background of nude mice resulted in corresponding differences in both numbers of T cells (defined by monoclonal anti-Thy-1 antibody) and IL 2 production. By using negative selection with monoclonal antibodies plus complement, IL 2 production in aged nude mice was shown to depend upon a subpopulation of cells that expressed Thy-1 but not Lyt-2. These data thus demonstrate that a subpopulation of IL 2-producing cells with a Thy-1+ Lyt-2- surface phenotype can develop in the apparent absence of thymic influence.

Interleukin 2 production by lymphoid cells from congenitally athymic (nu/nu) mice

The ability of lymphoid cells from congenitally athymic (nu/nu) mice to produce interleukin 2 (IL 2) was investigated. Spleen or lymph node cells (superficial or mesenteric) from nude mice on an N:NIH(S)II or BALB/c genetic background were stimulated with concanavalin A (Con A) or with irradiated allogeneic (DBA/2) spleen cells that had been depleted of T cells by treatment with monoclonal anti-Thy-1.2 antibody plus complement. After 24 hr, supernatants were harvested and assayed for their ability to support the proliferation of a cloned IL 2-dependent cytolytic T cell line. With this quantitative microassay, IL 2 production was not detectable in spleen and lymph nodes of 6-wk-old N:NIH(S)II nude mice; however, by 12 mo of age, IL 2 production increased more than 100-fold to reach levels comparable to control (nu/+) animals. Con A was more potent than alloantigen in the induction of IL 2 in either nude or control (nu/+) animals. Furthermore, differences in the genetic background of nude mice resulted in corresponding differences in both numbers of T cells (defined by monoclonal anti-Thy-1 antibody) and IL 2 production. By using negative selection with monoclonal antibodies plus complement, IL 2 production in aged nude mice was shown to depend upon a subpopulation of cells that expressed Thy-1 but not Lyt-2. These data thus demonstrate that a subpopulation of IL 2-producing cells with a Thy-1+ Lyt-2- surface phenotype can develop in the apparent absence of thymic influence.

Cell surface phenotype of cytolytic T lymphocyte precursors in aged nude mice

The cell surface phenotype of cytolytic T lymphocyte precursors (CTL-P) in congenitally athymic C57BL/6 nu/nu mice has been investigated. CTL-P were detected and quantitated in a limited dilution mixed leukocyte microculture assay system supplemented with interleukin 2. Minimal estimates of the frequency of CTL-P among nylon wool passed (NWP) nude spleen cells were obtained following elimination of Thy-1-bearing or Lyt-2-bearing cells with monoclonal antibodies plus complement. Alternatively, NWP spleen cells bearing Thy-1 or Lyt-2 were positively selected on a cell sorter and assayed for CTL-P frequency. Both positive and negative selection techniques demonstrated that essentially all (greater than 98%) CTL-P in NWP nude spleen expressed Thy-1 and that the majority (80-90%) expressed Lyt-2. In control NWP spleen cells from normal C57BL/6 mice, greater than 98% of CTL-P were positive for both Thy-1 and Lyt-2. These data demonstrate that most functional alloreactive CTL-P developing in the apparent absence of thymic influence already express both Thy-1 and Lyt-2 prior to exposure to antigen.

Age-associated increase in expression of the T cell surface markers Thy-1, Lyt-1, and Lyt-2 in congenitally athymic (nu/nu) mice: analysis by flow microfluorometry

The expression of T cell-associated surface markers by lymphoid cells from congenitally athymic (nude) mice has been quantitatively investigated using flow microfluorometry. Spleen and lymph nodes from old (greater than 6 mo) nude mice on either a C57BL/6 or BALB/c genetic background were found to contain significant numbers (5 to 13% in spleen and 15 to 24% in lymph nodes) of cells expressing Thy-1 antigen. The proportion of Thy-1 positive cells in nude spleen was dramatically increased (to 22 to 67%) after passage of the cells over nylon wool columns. In contrast to older animals, young (1- to 2-mo-old) nude mice had undetectable levels (less than 1%) of Thy-1 bearing cells in spleen and reduced levels (6%) in lymph nodes. After passage of their spleen cells over nylon wool, some Thy-1 positive cells (10%) were detectable in 2-mo-old nude mice but none were detectable at 1 mo. In addition to Thy-1, we were able to detect the T cell alloantigens Lyt-1 and Lyt-2 on nylon wool-passed spleen cells from older C57BL/6 or BALB/c nu/nu mice. In general, the proportion of Lyt-1 bearing cells in nude lymphoid populations was similar to the proportion of Thy-1 positive cells. A smaller fraction of nude cells (corresponding to 35 to 59% of the total Thy-1 positive cells) were found to express Lyt-2. Analysis of the forward light scatter distributions of nude lymphoid cells bearing either Thy-1, Lyt-1, or Lyt-2 antigens further demonstrated that an overlapping population of relatively large-size cells expressed these surface markers. These data strongly imply that at least 2 subsets of T cells (i.e., Lyt-1+2- and Lyt-1+2+) develop in older nude mice in the apparent absence of thymic influence.

Cytolytic T lymphocyte precursor cells in congenitally athymic C57BL/6 nu/nu mice: quantitation, enrichment, and specificity

A sensitive limiting dilution microculture system was used to obtain minimal estimates of the frequency of CTL precursor cells (CTL-P) in spleens from 5- to 14-mo-old C57BL/6 nu/nu mice. Frequency determinations of CTL-P directed against H-2d alloantigens ranged from 1/159,000 to 1/12,400. The relatively low frequency of CTL-P was enriched nearly 10-fold (to 1/2300) by passage of nude spleen cells over a column of nylon wool. After priming nude spleen cells for 7 days in conventional MLC, 1 to 3% of the MLC cells could be operationally identified as CTL-P. Furthermore, the progeny of MLC-primed nude CTL-P were specifically cytolytic for target cells of the strain used for priming. Such a system may be useful for analyzing the specificity repertoires of cells of the T cell lineage that have not undergone thymic influence.

Cytolytic T lymphocyte precursor cells in congenitally athymic C57BL/6 nu/nu mice: quantitation, enrichment, and specificity

A sensitive limiting dilution microculture system was used to obtain minimal estimates of the frequency of CTL precursor cells (CTL-P) in spleens from 5- to 14-mo-old C57BL/6 nu/nu mice. Frequency determinations of CTL-P directed against H-2d alloantigens ranged from 1/159,000 to 1/12,400. The relatively low frequency of CTL-P was enriched nearly 10-fold (to 1/2300) by passage of nude spleen cells over a column of nylon wool. After priming nude spleen cells for 7 days in conventional MLC, 1 to 3% of the MLC cells could be operationally identified as CTL-P. Furthermore, the progeny of MLC-primed nude CTL-P were specifically cytolytic for target cells of the strain used for priming. Such a system may be useful for analyzing the specificity repertoires of cells of the T cell lineage that have not undergone thymic influence.

Age-associated increase in expression of the T cell surface markers Thy-1, Lyt-1, and Lyt-2 in congenitally athymic (nu/nu) mice: analysis by flow microfluorometry

The expression of T cell-associated surface markers by lymphoid cells from congenitally athymic (nude) mice has been quantitatively investigated using flow microfluorometry. Spleen and lymph nodes from old (greater than 6 mo) nude mice on either a C57BL/6 or BALB/c genetic background were found to contain significant numbers (5 to 13% in spleen and 15 to 24% in lymph nodes) of cells expressing Thy-1 antigen. The proportion of Thy-1 positive cells in nude spleen was dramatically increased (to 22 to 67%) after passage of the cells over nylon wool columns. In contrast to older animals, young (1- to 2-mo-old) nude mice had undetectable levels (less than 1%) of Thy-1 bearing cells in spleen and reduced levels (6%) in lymph nodes. After passage of their spleen cells over nylon wool, some Thy-1 positive cells (10%) were detectable in 2-mo-old nude mice but none were detectable at 1 mo. In addition to Thy-1, we were able to detect the T cell alloantigens Lyt-1 and Lyt-2 on nylon wool-passed spleen cells from older C57BL/6 or BALB/c nu/nu mice. In general, the proportion of Lyt-1 bearing cells in nude lymphoid populations was similar to the proportion of Thy-1 positive cells. A smaller fraction of nude cells (corresponding to 35 to 59% of the total Thy-1 positive cells) were found to express Lyt-2. Analysis of the forward light scatter distributions of nude lymphoid cells bearing either Thy-1, Lyt-1, or Lyt-2 antigens further demonstrated that an overlapping population of relatively large-size cells expressed these surface markers. These data strongly imply that at least 2 subsets of T cells (i.e., Lyt-1+2- and Lyt-1+2+) develop in older nude mice in the apparent absence of thymic influence.

Lymphocytes which differentiate in an allogeneic thymus. II. Evidence for both central and peripheral mechanisms in tolerance to donor strain tissues

Nude mice which have been grafted with an allogeneic H-2-incompatible thymus are frequently specifically tolerant to skin grafts from the thymus donor strain. The evidence presented here indicates that both clonal deletion and peripheral suppressor cells play a part in maintaining this tolerance.

Murine sarcoma virus (MSV)-induced tumors in mice. I. Distribution of MSV-immune cytolytic T lymphocytes in vivo

Quantitative studies using a 51Cr release assay were performed to analyse the time-course of appearance and specificity of cytolytic cells in C57Bl/6 mice inoculated with Moloney murine sarcoma virus (MSV). Various lymphoid organs were studied including spleen, mesenteric lymph nodes (MLN), lymph nodes regional to the MSV-induced tumor (RLN), and peripheral blood. Furthermore, the kinetics of appearance of cytolytic cells within the MSV-induced tumor was determined. In agreement with previous studied, it was found that cytolytic T lymphocytes (CTL) specific for MSV-associated antigens were present among the cells extracted from the tumor and from the lymphoid organs. However, differences in the kinetics of CTL activity could be documented: lymphoid cells from spleen, RLN and peripheral blood showed peak activity at the time of maximum tumor diameter, while intratumoral cells showed peak activity at the onset of tumor regression. MLN cells showed cytolytic activity only when tumor regression had begun. Naturally cytotoxic cell populations of thymus-independent origin, present in normal control mice, were also detected in MSV-infected mice.

Mechanism of target cell lysis of cytolytic T lymphocytes. I. Characterization of specific lymphocyte-target cell conjugates separated by velocity sedimentation

Differential velocity sedimentation was applied for separating alloimmune T lymphocytes bound to target cells (TC) from free lymphocytes. Maximal size differences between lymphocytes and TC were achieved a) by isolating the fraction of small peritoneal lymphocytes (SPL) from an alloimmune peritoneal cell population, and b) by selecting large tumor cells as TC. Under the conditions used, most of the conjugates formed at room temperature consisted of one SPL bound to one TC, and adequate separation of bound from free SPL could be achieved within less than 5 min. Functional studies of the conjugate-enriched fractions showed that a minimum of 60% of TC-bound SPL were indeed cytolytic. Conjugate-depleted fractions, however, were still lytic, suggesting that not all effector cells formed stable conjugates at room temperature. Transmission and scanning electron microscopy studies revealed that binding between SPL and TC was achieved through interpenetrating membrane projections and was characterized by point and broad zone contacts. When lysis was allowed to proceed, prominent changes of the TC membrane morphology, including loss of microvillous projections, appearance of localized blebs, pseudopod-like projections, and membrane defects were documented.

Establishment of a cell line (Co-115) from a human colon carcinoma transplanted into nude mice

A human colon carcinoma cell line, Co-115, has been established in vitro from solid xenografts maintained in nude mice and subcultured for 95 passages. Co-115 cells grow in vitro as tightly packed, epithelial-like colonies, have a doubling time of about 36 hr, have a relatively low plating efficiency in agar, and release significant amounts of carcinoembryonic antigen to the culture medium. Their epithelial nature has been confirmed by ultrastructural examination. The injection of Co-115 cells into nude mice reinduced the formation of solid tumor masses that could be retransplanted and showed a morphology comparable of that of the original xenograft.

[Characterization of megakaryocyte colonies in vitro]

Agar cultures of mouse bone marrow cells can be stimulated by medium conditioned by activated mouse lymphoid cells to produce pure or mixed colonies containing up to 80 megakaryocytes. These have been characterized on the basis of their morphology, polyploid mitoses and DNA content and high cytoplasmic content of acetylcholinesterase.

Human endometrial carcinomas serially transplanted in nude mice and established in continuous cell lines

Three out of five human endometrial carcinomas were successfully grafted into nude mice (BALB/c/nu/nu). Two of these tumors could be maintained by serial transplantation. The morphological characteristics displayed by the grafted tumors were comparable to those of the original carcinomas. Permanent cell lines were established from these two tumors. Reinjection of cells grown in vitro into nude mice produced nodules of identical histology as compared to original solid transplants. The influence of medroxyprogesterone acetate on tumor growth in vivo and cell proliferation in vitro was studied. This hormonal treatment did not produce any significant effect on tumor cells, either in vitro or in vivo, for the two endometrial carcinomas. After medroxyprogesterone administration, a slight but non-significant growth inhibition of the tumor cells in vitro was observed and the tumor transplants in vivo did not appear to be influenced. The experiments illustrate the possible use of this model for testing potential anti-cancer agents.

Generation of cytotoxic T lymphocytes in vitro. IV. Functional activation of memory cells in the absence of DNA synthesis

Re-exposure of day 14 mixed leukocyte culture (MLC) cells to the original stimulating alloantigens (secondary response) has previously been shown to result in significant proliferation and in rapid reappearance of high levels of cytolytic T-lymphocyte (CTL) activity within the next 4 days. Moreover, evidence has been presented that CTL precursor cells in day 14 MLC populations, while they derived from cells were large at peak of the primary response (day 4) were themselves small lymphocytes which developed into large CTL after restimulation. In this study, inhibition of DNA synthesis by cytosine arabinoside (ARA-C) was used to investigate whether CTL formation could be dissociated from proliferation during the secondary response. It was found that within the first 24 h after restimulation (a) CTL activity increased 6-to-20-fold, (b) 60-70% of the small T lymphocytes became medium- to large-sized cells, and (c) both events were independent of DNA synthesis. By using two successive cell separations by velocity sedimentation at unit gravity, before and after stimulation of day 14 MLC cells for 24 h in the presence or absence of ARA-C, direct evidence was obtained that small CTL precursor cells developed into large CTL, irrespective of DNA synthesis. The presence of ARA-C for periods longer than 24 h inhibited any further increase in CTL activity, in contrast to a parallel increase in lytic activity and cell number from day 1 to day 4 in control restimulated cultures. Taken together with the finding that 90% of the medium- and large-sized lymphoid cells in control restimulated cultures underwent DNA synthesis within 24 h, these results thus suggest that during a secondary MLC response there is initially a differentiation step leading to the formation of CTL which, although it can be clearly dissociated from DNA synthesis, is under normal conditions followed by proliferation of these effector cells.

Antibody-dependent cell-mediated cytotoxicity: heterogeneity of effector cells in human peripheral blood

We have compared antibody-dependent cell-mediated cytotoxicity (ADCMC) of human peripheral blood leukocytes (PBL) in three model systems. target cells were 51Cr-labeled mouse mastocytoma cells, chicken erythrocytes (CRBC), and human erythrocytes (HRBC) coated with appropriate heterologous or isologous antisera. Effector cells were characterized on the basis of their adherence, phagocytosis, radiosensitivity, and sedimentation velocity(s) at 1 g. In predominantly mononuclear (Ficoll-Isopaque-purified) PBL preparations (MPBL) HRBC were lysed by an adherent, phagocytic population of cells that was markedly radio-resistant. Sedimentation velocity analysis further established that these effector cells were restricted to rapidly sedimenting fractions (s greater than 4.5 mm/hr). On the other hand, mastocytoma cells were lysed by a population of MPBL that was nonadherent, nonphagocytic, and relatively radiosensitive. These cells mainly restricted to slowly sedimenting fractions (s greater than 4.5 mm/hr) following 1 g velocity sedimentation. CRBC appeared to be susceptible to lysis by both types of mononuclear effector cell. In some experiments, enriched populations of polymorphonuclear leukocytes (PMN) were isolated. These cells were found to lyse both HRBC and CRBC very efficiently, whereas mastocytoma cells were lysed very little if at all by the same effector populations. Taken together, these results suggest that antibody-coated mastocytoma cells are lysed uniquely by effector cells in human peripheral blood with the physical properties of lymphocytes, whereas antibody-coated HRBC are lysed by both monocytes and PMN, but not by lymphocytes. Antibody-coated CRBC would appear to be lysed by all of the three effector cell types tested.

Growth of mouse megakaryocyte colonies in vitro

Mouse bone marrow and spleen cells formed pure or mixed colonies of up to 80 megakaryocytes in agar cultures after stimulation by medium conditioned by activated mouse lymphoid cells. Megakaryocytes were identified on the basis of their morphology, polyploid mitoses and DNA content, and high cytoplasmic content of acetylcholinesterase. Megakaryocyte colony-forming cells were relatively small with a peak sedimentation velocity of 4.2 mm/hr. Spleen, lymph node, and thymus cells produced the factor stimulating megakaryocyte proliferation after culture in medium containing 2-mercaptoethanol, with or without added mitogens or allogeneic spleen cells. Peak activity in conditioning medium was associated with the small lymphocyte fractions in mouse spleen.