A simple method of continuous passage of human tumors in immunocompetent mice]

A simple procedure is described for the continuous passage of a human tumor in immunocompetent mice. The BRO human melanoma was transplanted consecutively 25 times by implanting tumor tissue under the sub--renal capsule of mice which had been immunosuppressed by a single dose of whole--body irradiation or by cytosine arabinoside followed by irradiation. The tumor grew continuously for 14 days, and cytological examination showed that the growth consisted almost entirely of tumor cells.     

Quantitative evaluation of anticancer agents against human melanoma cells implanted in nude mice

BRO human melanoma cells, which are exceptionally tumorigenic and lethal for nude mice, were inoculated intraperitoneally or intracerebrally in varying numbers. An inverse linear correlation was observed between the logarithm of the number of cells inoculated and host survival. In mice bearing 10(7) cells intraperitoneally, 2.4-2.8 log10 units of cell kill were obtained after a single intraperitoneal injection of vincristine, and some mice inoculated with 10(5) cells were cured by this treatment. Fewer cells were killed by L-phenylalanine mustard. Vincristine did not prolong survival of nude mice with intracerebral BRO tumors. Cell kill after administration of anticancer agents can be quantitated for BRO cells inoculated intraperitoneally or intracerebrally.     

Antitumor effects of interleukin-2 and mismatched double-stranded RNA,individually and in combination,against a human malignant melanoma xenograft

Summary The antitumor effects of recombinant interleukin-2 (rIL-2) and mismatched double-stranded RNA (dsRNA) were assessed in tissue culture and in a nude mouse model. Mismatched dsRNA did not show a direct antiproliferative effect against the human malignant melanoma cell line, BRO, in tissue culture. However, treatment of the BRO cells with up to 1000 units/ml rIL-2 in culture showed a slight increase in growth rate. Combined rIL-2/mismatched dsRNA treatment also demonstrated a similar slight enhancement of growth. Nude mice bearing subcutaneous tumors were treated by intraperitoneal injection of low doses (5000–20 000 units) of rIL-2 and mismatched dsRNA (500 µg). The in vivo tumor growth was significantly inhibited by the combined treatments (P <0.05) and survival was significantly increased (P <0.05). Measurement of cytotoxicity using splenocytes from treated animals showed significant augmentation of lytic activity against natural killer(NK)-sensitive YAC-1 cells in all rIL-2/mismatched dsRNA treatment groups, compared to the individual treatments or controls (P <0.05). Cytotoxicity of the splenocytes against the NK-resistant BRO cells was also augmented in animals treated with mismatched dsRNA and the highest rIL-2 dose utilized here (P <0.01). Renal, liver, and hematological toxicity was evaluated by measurement of blood urea nitrogen, creatinine, serum asparrtate aminotransferase, and a complete blood count with differential. There were no significant differences in these parameters in any of the treatment groups. Similarly, no differences in weight of the animals was seen in any treatment group. These results indicate that the combination of low-dose rIL-2 and mismatched dsRNA can potentiate host-mediated antitumor effects, yielding increased survival, without significant toxicity.     

Growth factor production from fibrin-encapsulated human keratinocytes

Fibrin has been used extensively in cell encapsulation because it has important biological properties. Keratinocyte encapsulation in fibrin is a widely used technique in skin tissue engineering. The production of growth factors (EGF, TGF-β1 and PDGF-BB) was evaluated when keratinocytes are encapsulated in fibrin. Secretions of TGF-β1 and PDGF-BB increased more than five times compared to monolayer cultures. Encapsulated cells secreted about 80% active form of TGF-β1 (monolayer cells only secreted inactive form). An enhanced secretion of TGF-β1 and PDGF-BB was found in encapsulated cells, showing that fibrin capsules are favourable for the production of these growth factors.     

High level synthesis of recombinant soluble urokinase receptor (CD87) by ovarian cancer cells reduces intraperitoneal tumor growth and spread in nude mice

Focussing of the serine protease urokinase (uPA) to the tumor cell surface via interaction with its receptor (uPAR) is an important step in tumor invasion and metastasis. The human ovarian cancer cell line OV-MZ-6#8 was stably transfected with expression plasmids either encoding cell-associated uPAR (GPI-uPAR) or a soluble form of uPAR (suPAR) lacking its glycan lipid anchor. In vitro, high level synthesis of functionally active recombinant suPAR inhibited cell proliferation and led to reduced cell-associated fibrin matrix degradation, whereas fibrinolytic activity was increased in OV-MZ-6#8 cells overexpressing GPI-uPAR. Both OV-MZ-6#8-derived clones were inoculated into the peritoneum of nude mice and tested for tumor growth and spread. High level synthesis of recombinant suPAR (without altering the physiological expression levels of GPI-uPAR and uPA in these cells) resulted in a significant reduction of tumor burden (up to 86%) in the xenogeneic mouse model. In contrast, overexpression of GPI-uPAR in tumor cells did not affect tumor growth. Our results demonstrate that high levels of suPAR in the ovarian cancer cell vicinity can act as a potent scavenger for uPA, thereby significantly reducing tumor cell growth and cancer progression in vivo.     

Impairment of decidualization in SRC-deficient mice

Many signaling events induced by ovarian steroid hormones, cytokines, and growth factors are involved in the process of decidualization of human and rodent endometrium. We have reported previously that tyrosine kinase activation of SRC functionally participates in decidualization of human endometrial stromal cells. To address its essential role in decidualization, we examined, using wild-type and Src knockout mice, whether the process of decidualization was impaired in the absence of SRC. Immunohistochemistry using an antibody specific for the active form of SRC revealed that the active SRC was expressed prominently in the decidualizing stromal cells of the pregnant wild-type mouse. Moreover, the active SRC was upregulated in the uterine horn with artificially stimulated decidual reaction. In comparison with wild-type and Src heterozygous mice, the uterus of Src null mice showed no apparent decidual response following artificial stimulation. Ovarian steroid-induced decidualization in vitro, as determined by morphological changes and expression of decidual/trophoblast prolactin-related protein and prostaglandin-endoperoxide synthase 2 (also known as Cox2), both of which are decidualization markers, did not occur in a timely fashion in endometrial stromal cells isolated from the uteri of SRC-deficient mice compared to those from wild-type and Src heterozygous mice. Our results collectively suggest that SRC is an indispensable signaling component for maximal decidualization in mice.     

The kringle domain of tissue-type plasminogen activator inhibits in vivo tumor growth

The two-kringle domain of tissue-type plasminogen activator (t-PA) has previously been shown to contain anti-angiogenesis activity. In this study, we explored the potential in vivo anti-tumor effects of the recombinant kringle domain (TK1-2) of human t-PA. Anti-tumor effects of purified Pichia-driven TK1-2 were examined in nude mice models by subcutaneous implantation of human lung (A-549) and colon (DLD-1, HCT-116) cancer cell lines. Mice bearing the tumors were injected with PBS or purified TK1-2 (30 mg/kg) i.p. every day for 22 days. TK1-2 treatment suppressed the A-549, DLD-1, and HCT-116 tumor growth by 85.3%, 52.4%, and 62.5%, respectively. Immunohistological examination of the tumor tissues showed that TK1-2 treatment decreased the vessel density and also the expression of angiogenesis-related factors including angiogenin, VEGF, alpha-SMA, vWF, and TNF-alpha, and increased the apoptotic fraction of cells. TK1-2 neither inhibited in vitro growth of these cancer cells nor affected t-PA-mediated fibrin clot lysis. These results suggest that TK1-2 inhibits the tumor growth by suppression of angiogenesis without interfering with fibrinolysis.     

Human immunodeficiency virus (HIV)-infected tumor xenografts as an in vivo model for antiviral therapy: role of alpha/beta interferon in restriction of tumor growth in nude mice injected with HIV-infected U937 tumor cells.

The host factors involved in the restriction of tumor growth were studied in nude mice transplanted with a cloned line of chronically human immunodeficiency virus (HIV)-infected U937 cells. HIV-infected and uninfected U937 cells exhibited the same growth patterns in culture. However, HIV-infected cells were not tumorigenic when injected subcutaneously in nude mice, whereas large solid tumors were observed in mice injected with uninfected U937 cells. Injection of nude mice with antibody to alpha/beta interferon (IFN-alpha/beta) enabled HIV-infected U937 cells to grow progressively in approximately 90 to 100% of mice. HIV-infected U937 cells formed solid tumors in the majority (60 to 90%) of either immunosuppressed (splenectomized, irradiated, and anti-asialo-GM1-treated) or genetically immunodeficient (bg/nu/xid) nude mice. In mice treated with antibodies to IFN-alpha/beta with established HIV-positive tumors, a direct correlation was found between p24 antigenemia and tumor size. Treatment of established HIV-positive U937 cell tumors with human IFN-alpha or mouse IFN-alpha/beta resulted in a clear-cut inhibition of both tumor growth and p24 HIV antigenemia. In contrast, treatment with tumor necrosis factor alpha markedly inhibited tumor growth but did not significantly decrease serum p24 levels. 3'-Azido-3'-deoxythymidine treatment did not affect either tumor growth or the levels of serum p24 antigen. These data indicate that endogenous IFN-alpha/beta is a crucial factor in the restriction of both tumor growth and p24 antigenemia in mice injected with HIV-infected tumor cells. Moreover, the results suggest that the development of HIV-1 p24 antigenemia in athymic immunosuppressed mice may represent an interesting in vivo model for anti-HIV therapy.     

The use of antifibrin antibodies for the destruction of tumor cells

Summary The transplantable methylcholanthrene-induced sarcoma (MC-D) in strain 13 guinea-pigs was used to test the hypothesis that tumor cells growing within a fibrin matrix could be destroyed by an immunologically specific strategy involving an indirect cell-mediated immune reaction. The experimental design consisted of two steps: (1) in vivo fixation of anti-guinea pig fibrin antibodies (AGFA) on the fibrin matrix enmeshing the tumor cells, and (2) the reaction between AGFA fixed to the fibrin matrix and lymphoid cells from syngeneic animals sensitized to xenogeneic immunoglobulins isotypic with AGFA. Indeed, tests with ⁵¹Cr-labelled lymphoid cells yielded evidence for the localization of these sensitized lymphoid cells within the fibrin lattice when the latter was coated with AGFA. Moreover, significant tumor growth suppression (P<0.01) was achieved in guinea-pigs that had received rabbit or goat AGFA intravenously and lymphoid cells from syngeneic guinea-pigs sensitized to a state of cell-mediated immunity to rabbit or goat IgG by the subcutaneous route. On the other hand, the administration of the antibodies or of the sensitized cells alone did not affect the growth of the tumor. Preliminary results suggest that peritoneal exudate cells may have an important role in the success of this strategy for tumor cell destruction.     

Tumor disposition of pegylated liposomal CKD-602 and the reticuloendothelial system in preclinical tumor models

Liposomes, such as pegylated-liposomal CKD-602 (S-CKD602), undergo catabolism by macrophages and dendritic cells (DCs) of the reticuloendothelial system (RES). The relationship between plasma and tumor disposition of S-CKD602 and RES was evaluated in mice bearing A375 melanoma or SKOV-3 ovarian xenografts. Area under the concentration-time curves (AUCs) of liposomal encapsulated, released, and sum total (encapsulated + released) CKD-602 in plasma, tumor, and tumor extracellular fluid (ECF) were estimated. A375 and SKOV-3 tumors were stained with cd11b and cd11c antibodies as measures of macrophages and DC. The plasma disposition of S-CKD602 was similar in both xenograft models. The ratio of tumor sum total AUC to plasma sum total AUC was 1.7-fold higher in mice bearing human SKOV-3 xenografts, compared with A375. The ratio of tumor ECF AUC to tumor sum total AUC was 2-fold higher in mice bearing human SKOV-3 xenografts, compared with A375. The staining of cd11c was 4.5-fold higher in SKOV-3, compared with A375 (P?<?0.0001). The increased tumor delivery and release of CKD-602 from S-CKD602 in the ovarian xenografts, compared with the melanoma xenografts, was consistent with increased cd11c staining, suggesting that variability in the RES may affect the tumor disposition of liposomal agents.     

人卵巢癌SCID小鼠移植瘤模型、细胞系建立及其生物学特性研究

目的建立人卵巢癌SCID小鼠移植瘤模型和相应体外细胞系.方法将病理证实的人卵巢浆液性乳头状腺癌手术切除标本移植于SCID小鼠皮下,成瘤后行鼠间传代,取移植瘤细胞体外分离培养、传代和建系,并应用细胞、分子生物学手段对移植瘤和建系细胞进行一系列生物学特性检测.结果历时14个月传至5代,皮下移植瘤存活率为90%,持续6个月,体外建系(OVA-319)细胞生长稳定.镜下观察组织形态学和超微结构符合原肿瘤组织基本特征;染色体分布在12～46条之间,多为异倍体,显示人类肿瘤异常染色体;流式细胞术和RT-PCR技术分析原代、体内移植瘤和OVA-319细胞结果一致,表现为瘤细胞生长活跃、细胞周期分布相仿,MAGE-2基因在mRNA水平异常表达.结论人卵巢癌SCID小鼠移植瘤模型和OVA-319细胞系为人类肿瘤的研究提供了良好的实验材料.     

Analysis of SRC Oncogenic Signaling in Colorectal Cancer by Stable Isotope Labeling with Heavy Amino Acids in Mouse Xenografts

The non-receptor tyrosine kinase SRC is frequently deregulated in human colorectal cancer (CRC), and SRC increased activity has been associated with poor clinical outcomes. In nude mice engrafted with human CRC cells, SRC over-expression favors tumor growth and is accompanied by a robust increase in tyrosine phosphorylation in tumor cells. How SRC contributes to this tumorigenic process is largely unknown. We analyzed SRC oncogenic signaling in these tumors by means of a novel quantitative proteomic analysis. This method is based on stable isotope labeling with amino acids of xenograft tumors by the addition of [¹³C₆]-lysine into mouse food. An incorporation level greater than 88% was obtained in xenograft tumors after 30 days of the heavy lysine diet. Quantitative phosphoproteomic analysis of these tumors allowed the identification of 61 proteins that exhibited a significant increase in tyrosine phosphorylation and/or association with tyrosine phosphorylated proteins upon SRC expression. These mainly included molecules implicated in vesicular trafficking and signaling and RNA binding proteins. Most of these proteins were specific targets of SRC signaling in vivo, as they were not identified by analysis via stable isotope labeling by amino acids in cell culture (SILAC) of the same CRC cells in culture. This suggests that oncogenic signaling induced by SRC in tumors significantly differs from that induced by SRC in cell culture. We next confirmed this notion experimentally with the example of the vesicular trafficking protein and SRC substrate TOM1L1. We found that whereas TOM1L1 depletion only slightly affected SRC-induced proliferation of CRC cells in vitro, it drastically decreased tumor growth in xenografted nude mice. We thus concluded that this vesicular trafficking protein plays an important role in SRC-induced tumor growth. Overall, these data show that SILAC analysis in mouse xenografts is a valuable approach for deciphering tyrosine kinase oncogenic signaling in vivo.The non-receptor tyrosine kinase (TK)¹ SRC mediates cellular signaling induced by growth factors and integrins (1) leading to cell growth, survival, and migration. It also has oncogenic activity when deregulated, a role originally described for the constitutively active v-SRC (2) that has since been observed in a large variety of human cancers (3). Remarkably, elevated SRC kinase activity has been found in more than 80% of colorectal cancers (CRCs) to levels (5- to 10-fold) consistent with oncogenic properties (4). Moreover, SRC deregulation has been associated with poor clinical outcomes (3), suggesting an additional function of SRC during late tumorigenesis. SRC deregulation largely occurs in the absence of mutations in the SRC gene. Instead, it primarily involves protein over-expression (2) and inhibition of SRC negative regulators, such as the transmembrane protein Cbp/PAG (5, 6). A large body of evidence indicates that SRC deregulation is an important event in colon tumorigenesis (3, 6). Indeed, SRC controls growth, survival, and invasion of some CRC cell lines in vitro (4). Moreover, it contributes to tumor growth, angiogenesis, and metastasis formation in mouse colon tumor xenograft models (7–11). However, our knowledge of the SRC-dependent oncogenic signaling pathway in CRC is largely incomplete, mostly because the majority of data have been obtained in two-dimensional cell culture models. Moreover, the standard culture conditions of CRC cells do not allow the recapitulation of all the SRC-dependent signaling cascades that are activated during tumorigenesis to promote tumor growth, angiogenesis, and interactions with the microenvironment.MS-based quantitative phosphoproteomic technology has been a valuable tool for deciphering signaling pathways initiated by a given TK (12). Particularly, the method of stable isotope labeling with amino acids in cell culture (SILAC) has been employed for the characterization of oncogenic TK signaling pathways in cell culture, including HER2 (13) and BCR-ABL (14). We recently used this powerful approach to investigate SRC-dependent oncogenic signaling in CRC cells (15) and identified the first SRC-dependent tyrosine “phosphoproteome” in these cells. Additionally, we found that SRC phosphorylated a small cluster of TKs that mediate its oncogenic activity, thus uncovering a TK network that is important for the induction of CRC cell growth (15). Whether these signaling processes also operate in vivo is, however, currently unknown.SRC oncogenic signaling could be investigated in vivo using similar MS-based quantitative phosphoproteomic approaches in animal models or tumor biopsies. However, the application of the SILAC method in vivo has been challenging until recently because it requires efficient protein labeling in different tissues, which is conditioned by the rate of de novo protein synthesis. Recently, Mann et al. described the successful development of a SILAC approach for labeling mice that is based on the addition of [¹³C₆]-lysine to their food (16). They reported complete labeling from the F2 generation. Similar SILAC approaches were then described for additional multicellular organisms, such as worms (17), flies (18), and zebrafish (19). Here, we report a similar SILAC approach in which we labeled tumors in nude mice xenografted with human CRC cells. We reasoned that the high rate of de novo protein synthesis occurring in tumors should allow efficient tumor labeling in a short period of time. Indeed, we obtained consistent (>88%) labeling of the tumor proteome by feeding xenografted mice with the SILAC mouse diet for only 30 days. We then used this approach to compare the tyrosine phosphoproteome of SRC over-expressing tumors (labeled with heavy amino acids) and of control tumors (labeled with light amino acids) and report the first SRC-dependent tyrosine phosphoproteome of CRC in vivo. Finally, comparison of the in vivo and in vitro SRC-dependent tyrosine phosphoproteomes showed that some of the SRC substrates were specifically activated only in CRC xenograft tumors, and not in cultured CRC cells.     

Liposomal glucocorticoids as tumor-targeted anti-angiogenic nanomedicine in B16 melanoma-bearing mice

This study evaluates whether the inhibitory effects of prednisolone phosphate (PLP) encapsulated in long-circulating liposomes (LCL-PLP) on tumor growth and tumor angiogenesis described previously can be generalized to other types of glucocorticoids (GC) encapsulated in LCL (LCL-GC). Four types of synthetic GC, i.e. budesonide disodium phosphate (BUP), dexamethasone disodium phosphate (DXP), methylprednisolone disodium phosphate (MPLP), and PLP, were selected based on the difference in their potency to activate the human glucocorticoid receptor. The effects of all LCL-GC on the production of angiogenic/inflammatory factors in vivo in the B16.F10 murine melanoma model as well as on the viability and proliferation of tumor cells and endothelial cells in vitro were investigated. Our results show that all four selected LCL-GC formulations inhibit tumor growth, albeit to different degrees. The differences in antitumor activity of LCL-GC correlate with their efficacy to suppress tumor angiogenesis and inflammation. The strongest antitumor effect is achieved by LCL-encapsulated BUP (LCL-BUP), due to the highest potency of BUP versus the other three GC types. The in vitro results presented herein suggest that LCL-BUP has strong cytotoxic effects on B16.F10 melanoma cells and the anti-proliferative effects of all LCL-GC towards angiogenic endothelial cells play a role in their antitumor activity.     

Anti-tumor vaccine adjuvant effects of IL-2 liposomes in mice immunized against MCA-102 sarcoma.

MCA-102, a murine sarcoma previously reported to be non-immunogenic in C57/BL6 murine tumor models was used in a tumor vaccine preparation which included liposome encapsulated IL-2 as an adjuvant. C57/BL6 mice were immunized in the right hind footpad with irradiated MCA-102 murine sarcoma cells on days 0, 7, and 21 with or without IL-2 liposome adjuvant at 25,000 IL-2 units/injection. Mice were challenged with live tumor in the right flank on day 35. Survival of mice given IL-2 liposomes with irradiated MCA-102 cells was significantly prolonged over mice given tumor antigen with saline, and non-immunized mice. In addition, mice which received the IL-2 liposome adjuvant also had prolonged survival over those mice immunized with the additional control adjuvants of free IL-2 or dimyristoyl phosphatidyl choline (DMPC) lipid in the form of empty liposomes. IL-2 liposome plus tumor antigen also yielded a significant local protective response against live MCA-102 tumor challenge. When live tumor was injected into the site of previous immunizations on day 21 after two immunizations, the IL-2 liposome adjuvant group showed significantly delayed local growth of tumor compared to animals immunized without adjuvant, or with the adjuvants of empty liposomes or free IL-2. Finally, immunized mice were challenged with irradiated tumor cells and saline intradermally in the ears and delayed type hypersensitivity (DTH), an indicator of helper T cell response, was measured.(ABSTRACT TRUNCATED AT 250 WORDS)     

Encapsulated human primary myoblasts deliver functional hFIX in hemophilic mice

BACKGROUND: Hemophilia B is a bleeding disorder caused by defective factor IX (FIX), currently treated by regular infusions of plasma-derived or recombinant FIX. We propose a gene therapy strategy based on the implantation of cells secreting FIX enclosed in alginate microcapsules as a highly desirable alternative treatment. We have reported sustained delivery of human factor IX (hFIX) in immunocompetent mice implanted with encapsulated primary mouse myoblasts engineered to secrete hFIX. As a step towards the treatment of human patients, in this study we report the implantation of encapsulated human primary myoblasts secreting hFIX in hemophilia B mice. METHODS: Human primary myoblasts were transfected with plasmids pKL4M-hFIX, pLNM-betaIXL, pMFG-hFIX, and transduced with retrovirus MFG-hFIX. Two human primary myoblast clones secreting approximately 1 microg hFIX/10(6) cells/day were enclosed in biocompatible alginate microcapsules and implanted intraperitoneally into SCID and hemophilic mice. RESULTS: Circulating hFIX (peak of approximately 120 ng/ml) was detected in hemophilia B mice on day 1 after implantation. Human FIX delivery was transient, however, becoming undetectable on day 14. Concurrently, anti-hFIX antibodies were detected. At the same time, activated partial thromboplastin time (APTT) was reduced from 94 s before treatment to 78-80 s. Tail bleeding time decreased from 15 min to 1.5-7 min after treatment, some mice being normalised. These findings indicate that the delivered hFIX is biologically active. Similarly treated NOD/SCID mice had circulating hFIX levels of 170 ng/ml on day 1 that remained detectable for 1 month, albeit at low levels. Cell viability of microcapsules retrieved on day 60 was below 5%. CONCLUSIONS: Our findings indicate that encapsulated human primary myoblasts secrete functional hFIX. Furthermore, implantation of encapsulated human primary myoblasts can partially correct the phenotype of hemophilia B mice, supporting the feasibility of this gene therapy approach for hemophilia B. However, the long-term viability of the encapsulated human myoblasts must first be improved.     

Effect of human lymphoblastoid interferon on human yolk sac tumors in nude mice

The effect of human lymphoblastoid interferon on the growth of human tumors heterotransplanted into nude mice was examined. The human tumor lines examined, named YST-1, YST-2 and YST-3, were derived from yolk sac tumors of the ovary. Daily intraperioneal injection of 3 X 10(4) U interferon per mouse for 14 days did not inhibit the growth of any of these three human tumor lines. A close correlation was observed between the tumor volume and the level of alpha-fetoprotein in sera of mice bearing the YST-1 tumor (r = 0.55) or YST-2 tumor (r = 0.70). No histological differences were detected between tumor cells of interferon-treated and control mice. Tumor-bearing mice treated with interferon showed no marked weight loss.     

Human T cells targeted with anti-T3 cross-linked to antitumor antibody prevent tumor growth in nude mice

Human peripheral blood T cells were tested for the ability to prevent tumor growth in nude mice when targeted with anti-T3 cross-linked to antitumor antibodies. LS174T human colon adenocarcinoma cells were mixed with human PBL coated either with anti-T3 (Fab) cross-linked to 315F6 (Fab) (an antitumor monoclonal antibody) or with no antibody, and were injected subcutaneously into nude mice. Tumor growth was totally inhibited at effector to target (E:T) ratios of 7.0:1 and 2.1:1, and was partially inhibited at 0.7:1 with antibody-coated PBL, but was not inhibited by uncoated PBL. T cell-mediated protection against tumor growth occurred when an antitumor was physically cross-linked to anti-T3. Neither a mixture of unlinked anti-T3 and antitumor antibodies nor anti-human MHC class I cross-linked to antitumor antibody prevented tumor growth. Whereas in vitro cytotoxicity was mediated exclusively by T8+ cells and was augmented by brief exposure of effector cells to IL 2, tumor neutralization in vivo was mediated by both T4+ and T8+ cells and was not significantly stimulated by prior exposure of the cells to IL 2. We conclude that human T cells, when targeted with appropriate antibody heteroaggregates, can specifically inhibit tumor growth at low E:T ratios, and that cells mediating tumor neutralization in vivo may differ from those mediating cytotoxicity in vitro.     

Growth of tumor cells with different sensitivities for murine natural killer cells in young and adult athymic nude mice

Of four tumor cell lines, the murine YAC lymphoma, the human K562 lymphoma, and the human prostatic carcinomas PC3 and PC93, the susceptibility to murine natural killer (NK) cells as well as the tumorigenicity in young (3.5-4 weeks old) and in adult (8-10 weeks old) nude mice were studied. In young nude mice, which exhibited a lower level of NK cell activity than adult nude mice, the formation of solid tumors after inoculation of tumor cell suspensions occurred more frequently and with a shorter time lag than in adult animals. These effects were observed not only with the NK-sensitive YAC cells, but also with the relatively NK-insensitive PC3 and PC93 cells, indicating that also factors other than NK cell susceptibility may influence the growth of tumor cells in nude mice. Therefore, the use of young nude mice may enhance the rate of success of heterotransplantation of human tumors, regardless of the NK cell susceptibility of the tumor cells.