Immunogenicity and cross-protection among b16 melanoma variants with differing proclivities to metastasize

We report here the lack of any relationship between immunogenicity and the potential to metastasize among four B16 melanoma variants. Groups of C57BL/6J mice were immunized with one of four B16 variant lines (maintained by serial IM passage) that were shown in separate experiments to produce the following incidences of pulmonary metastases four to six weeks after isograft excision: M1, 10%–15%; M2, 10%–20%; M3, 75%–80%; and M4, 75%–90%. After immunization, mice were challenged with one of the four variant lines in a crisscross fashion. Two challenge doses for each line were chosen on the basis of earlier experiments showing 100% and 50% challenge tumor take in nonimmunized animals. Despite earlier work published from this laboratory showing that splenocytes harvested from immunized mice could distinguish antigenic differences among the B16 variants, we could find no significant difference in immunogenicity or cross-protection among the lines regardless of their metastatic potential. We conclude that no correlation exists between the antigenic differences shown by in vitro splenocyte-mediated cytotoxicity assays among the B16 variants and in vivo immunogenicity or cross-protection experiments. Furthermore, the relationship (if any) between immunogenicity and the ability to metastasize among these B16 variants is not straightforward.     

99mTcOAADT]-(CH2)2-NEt2: a potential small-molecule single-photon emission computed tomography probe for imaging metastatic melanoma

Evaluation of [99mTc]oxotechnetium(V) complexes of the amine-amide-dithiol (AADT) chelates containing tertiary amine substituents as small-molecule probes for the diagnostic imaging of metastatic melanoma has shown that technetium-99m-labeled AADT-(CH2)2-NEt2 (99mTc-1) has the highest tumor uptake and other favorable biological properties. We have, therefore, assessed this agent in a more realistic metastatic melanoma model in which, after i.v. tail injection, a highly invasive melanoma cell line, B16F10, forms pulmonary tumor nodules in normal C57BL6 mice. Small melanotic lesions develop in the lungs and, on histologic examination, appear as small black melanoma colonies, increasing in size and number with time after tumor cell injection. Groups of mice received tumor cell inocula of 2 x 10(5), 4 x 10(5), or 8 x 10(5) B16F10 cells; 14 days later, 2 hours after 99mTc-1 administration, lung uptake of 2.83 +/- 0.21%, 3.63 +/- 1.07%, and 4.92 +/- 1.61% injected dose per gram of tissue (% ID/g), respectively, was observed, compared with normal lung uptake of 2.13 +/- 0.2% ID/g (P < 0.05). Additionally, a higher level of 99mTc-1 accumulation was seen 17 days after tumor cell inoculation as the lung lesions grew. These in vivo studies coupled with additional in vitro and ex vivo assessment show that 99mTc-1 has high and specific uptake in melanoma metastases in lungs and can potentially follow the temporal growth of these tumors.     

In vitro assay demonstrates similar invasion profiles for B16F1 and B16F10 murine melanoma cells

The variants of the B16 murine melanoma cell line were assayed for their invasive characteristics in the membrane invasion culture system (MICS) and concomitantly tested for their ability to form lung metastases in vivo. Specifically, the B16F1 (low metastatic variant) and the B16F10 (high metastatic variant) murine melanoma cell lines were examined for their ability to invade human amniotic basement membranes (BMs) in vitro and simultaneously examined for lung colony formation in vivo. The B16F1 and B16F10 cell lines both demonstrated similar invasion profiles over 72 h with the total percent invasion through the BMs for both cell lines not exceeding 5.0%. In vivo observations reconfirmed the significant difference in the metastatic capabilities of the 2 variants. These data suggest that tumor cells with differing metastatic propensities can invade an amniotic BM at similar rates, but their survival and metastatic lesion forming capabilities in vivo may vary considerably.     

苦参碱衍生物M19对于肿瘤细胞转移的抑制作用

目的:探讨苦参碱衍生物M19对于肝细胞癌和黑色素瘤细胞转移的抑制作用。方法:肝癌细胞Hep3B、MHCC-LM3和黑色素瘤细胞B16F10经M19处理后,检测肿瘤细胞体外迁移能力。建立C57BL/6小鼠黑色素瘤B16F10和裸鼠肝细胞癌MHCC-LM3转移模型,经M19体内给药后,观察肿瘤细胞肝、肺转移情况。结果:M19能浓度依赖性地抑制肝癌细胞和黑色素瘤细胞迁移。M19体内给药使B16F10细胞在小鼠肺的转移减少,且还能抑制MHCC-LM3细胞在裸鼠肺和肝的转移。结论:M19能在体内外抑制肝细胞癌和黑色素瘤细胞的转移。     

Immune RNA therapy as an effective adjuvant immunotherapy after surgery: an animal model

Transfer of tumor immunity as adjuvant cancer therapy has been a topic of intense interest. We have examined the efficacy of various combinations of surgery, xenogeneic immune RNA, xenogeneic normal RNA, tumor vaccine, and nonspecific splenocytes as adjuvant therapy for B16 melanoma in the C57BL/6J mouse system. B16 melanoma was transplanted by trocar into the right hind limb of 6-week-old mice. The tumors were readily palpable on the ninth day posttransplantation. The tumors were amputated at that time under mild anesthesia. Immune RNA was prepared by hot phenol extraction from immune sheep spleens. Various combinations of immune RNA, normal RNA, and tumor antigen, with or without normal mouse spleen cells, were administered every other day for a total of 10 injections. The survival and mode of death was followed up to 120 days. All mice without any treatment died within 30 days. Immunotherapy had no effect on the survival of mice that did not have surgical therapy. Individual group comparisons between mice that underwent surgery only and mice that had surgery plus immune RNA immunotherapy revealed a striking statistical improvement (P less than 0.01). Comparing all groups that received amputation plus various combinations of adjuvant immunotherapy showed no statistical difference in survival. However, immune RNA appears somewhat superior to normal RNA or antigen only. It appears that adjuvant immune RNA immunotherapy following surgical excision in the B16 melanoma model significantly improves survival and retards the spread of metastases.     

Genetically fluorescent melanoma bone and organ metastasis models.

We report here the establishment and metastatic properties of bright, highly stable, green fluorescent protein (GFP) expression transductants of the B16 mouse malignant melanoma cell line and the LOX human melanoma line. The highly fluorescent malignant melanoma cell lines allowed the visualization of skeletal and multiorgan metastases after i.v. injection of B16 cells in C57BL/6 mice and intradermal injection of LOX cells in nude mice. The melanoma cell lines were transduced with the pLEIN expression retroviral vector containing the GFP and neomycin resistance genes. Stable B16F0 and LOX clones expressing high levels of GFP were selected stepwise in vitro in levels of G418 of up to 800 microg/ml. Extensive bone and bone marrow metastases of B16F0 were visualized by GFP expression when the animals were sacrificed 3 weeks after cell implantation. Metastases for both cell lines were visualized in many organs, including the brain, lung, pleural membrane, liver, kidney, adrenal gland, lymph nodes, skeleton, muscle, and skin by GFP fluorescence. This is the first observation of experimental skeletal metastases of melanoma, which was made possible by GFP expression. These models should facilitate future studies of the mechanism and therapy of bone and multiorgan metastasis of melanoma.     

Antitumor properties of an anti-idiotypic monoclonal antibody in relation to N-glycolyl-containing gangliosides

We examined the antitumor effects of 1E10 monoclonal antibody, an anti-idiotypic IgG to an IgM monoclonal antibody, named P3, that reacts specifically with N-glycolyl-containing gangliosides and also recognizes antigens in human breast and melanoma tumors. Two murine tumor cell lines positive for the P3 antibody, F3II mammary carcinoma (BALB/c) and B16 melanoma (C57BL/6), were employed. In BALB/c mice, vaccination with several i.p. doses at 14-day intervals of 50 microgram of 1E10 coupled to keyhole limpet hemocyanin in Freund's adjuvant, significantly reduced s.c. tumor growth of F3II carcinoma cells and the number of spontaneous lung metastases. Also, the effect of 1E10 as a biological response modifier on tumor lung colonization was evaluated in C57BL/6 mice injected i.v. with B16 melanoma cells. Interestingly, i.v. administration of 10 microgram of uncoupled 1E10 antibody, 10-14 days after inoculation of B16 cells, dramatically reduced the number of experimental metastases in comparison with lungs from mice treated with an irrelevant IgG. The present data suggest that this 'non-internal image' anti-idiotypic monoclonal antibody may activate more than one mechanism of antitumor response against melanoma and mammary tumor cells.     

Betulinic acid augments the inhibitory effects of vincristine on growth and lung metastasis of B16F10 melanoma cells in mice

We examined the antitumour effect of a combination of betulinic acid (BA) and vincristine (VCR) on murine melanoma B16F10 cells in vitro and in vivo. Betulinic acid, a pentacyclic triterpene, showed a synergistic cytotoxic effect on melanoma cells by combinational use of VCR. Betulinic acid and VCR induced cell cycle arrest at different points (BA at G1 phase and VCR at G2/M phase) and caused apoptosis in B16F10 melanoma cells. In the in vivo study, VCR inhibited metastasis of tumour cells to the lung. The addition of BA to VCR augmented suppression of the experimental lung metastasis of melanoma cells in C57BL/6 mice. The number of lung nodules of more than 1 mm in diameter in mice treated with BA and VCR was less than that in mice treated with VCR alone. These results suggest that BA is an effective supplement for enhancing the chemotherapeutic effect on malignant melanoma.     

B16 melanoma cell arrest in the mouse liver induces nitric oxide release and sinusoidal cytotoxicity: a natural hepatic defense against metastasis

The formation of liver metastases involves interactions between intravascular cancer cells and the hepatic microvasculature. Here we provide evidence that the arrest of intravascular B16F1 melanoma cells in the liver induces a rapid local release of nitric oxide (NO) that causes apoptosis of the melanoma cells and inhibits their subsequent development into hepatic metastases. B16F1 melanoma cells (5 x 10(5)) labeled with fluorescent microspheres were injected into the portal circulation of C57BL/6 mice. The production of NO in vivo was detected by electron paramagnetic resonance spectroscopy ex vivo using an exogenous NO-trapping agent. A burst of NO was observed in liver samples examined immediately after tumor cell injection. The relative electron paramagnetic resonance signal intensity was 667 +/- 143 units in mice injected with tumor cells versus 28 +/- 5 units after saline injection (P < 0.001). Two-thirds of cells arrested in the sinusoids compared with the terminal portal venules (TPVs). By double labeling of B16F1 cells with fluorescent microspheres and a TdT-mediated UTP end labeling assay, we determined that the melanoma cells underwent apoptosis from 4-24 h after arrest. The mean rate of apoptosis was 2-fold greater in the sinusoids than in the TPVs at 4, 8, and 24 h after injection (P < 0.05-0.01). Apoptotic cells accounted for 15.9 +/- 0.8% of tumor cells located in the sinusoids and 7.1 +/- 0.9% of tumor cells in the TPVs. The NO synthase inhibitor N(G)-nitro-L-arginine methyl ester completely blocked the NO burst (P < 0.001) and inhibited the apoptosis of B16F1 cells in the sinusoids by 77%. However, the rate of tumor cell apoptosis in the TPVs was not changed. There were 5-fold more metastatic nodules in the livers of N(G)-nitro-L-arginine methyl ester-treated mice (P < 0.05). The inactive enantiomer N(G)-nitro-D-arginine methyl ester had no effect on the initial NO burst or on apoptosis of tumor cells in vivo. Both annexin V phosphatidylserine plasma membrane labeling and DNA end labeling of apoptotic cells were demonstrated after a 5-min exposure (a time equivalent to the initial transient NO induction in vivo) of B16F1 cells to a NO donor in vitro. These results identify the existence of a natural defense mechanism against cancer metastasis whereby the arrest of tumor cells in the liver induces endogenous NO release, leading to sinusoidal tumor cell killing and reduced hepatic metastasis formation.     

Comparative in vivo and in vitro proliferation of murine tumor cells in the bone microenvironment

To examine the effect of bone microenvironmental factors on the growth of metastatic cells, the in vivo proliferative features of three murine cell lines were determined at skeletal metastatic sites and correlated with their ability to grow in vitro in the presence of bone-derived factors. Bones, ovaries, adrenals and the brain were most affected by metastasis, following an intraarterial injection of B16/F1 and B16/F10 melanoma and FS/L10 fibrosarcoma cells into C57BL/6 mice. Melanoma cells showed a marked metastatic preference for bone, while fibrosarcoma cells developed brain metastasis in all animals. Tumor burden in bones was highest (19+/-2%) for B16/F10 cells, compared to B16/F1 (10+/-2%) or FS/L10 (3+/-1%) cells. Autoradiographic studies demonstrated organ- and cell type-specific differences in tumor cell proliferation, with B16/F10 cells displaying the lowest labelling indexes in bone (12+/-2% for B16/F10 vs 28+/-2% and 27+/-4% for B16/F1 and FS/L10 cells, respectively). To test if bone-derived factors differentially affected tumor cell growth in these three cell lines H-3-thymidine uptake by these tumor cells was assessed after in vitro incubation with bone-derived conditioned medium. Under these conditions, we observed stimulation of B16/F10 cell proliferation, but inhibition of uptake in the other two cell lines. Thus, these results demonstrate that, in this in vivo experimental model, growth properties of metastatic cells are organ- and cell type-specific. Additionally, we show that the in vitro proliferative behavior of tumor cells in the presence of bone-derived factors correlates and may predict skeletal tumor growth properties in vivo.     

抑制整合素α9基因的表达对黑色素瘤细胞B16F1的生长和肺转移的影响

目的 观察shRNA干扰整合素α9（ITGA9）的表达对黑色素瘤细胞B16F1的生长和肺转移的影响。方法 用RNA干扰技术下调B16F1中ITGA9的表达,建立小鼠皮下成瘤和肺转移模型,观察肿瘤生长情况,计数肺转移灶数量。结果 ITGA9-shRNA转染组的肿瘤生长速度减慢（P＜0.05）,实验终点,该组肿瘤平均体积与scramble-shRNA组相比下降36%;肺转移灶数量显著减少（P＜0.05）。结论 下调ITGA9的表达可抑制黑色素瘤细胞B16F1在小鼠体内的生长和肺转移。ITGA9可能成为黑色素瘤的治疗靶点。     

Lung colonization and metastasis by disseminated B16 melanoma cells: H-2 associated control at the level of the host and the tumor cell

We have studied the experimental metastasis of H-2+ and H-2- melanoma sublines in H-2b/b and H-2a/b hosts by enumerating pulmonary colonies 20-50 days after i.v. inoculation of tumor cells. In H-2b/b hosts, the H-2+ "B16-S" cells gave rise to a moderate number of metastatic colonies (mean: 6.3 +/- 6). The "BL16-L" sublines that had lost the expression of MHC class-I antigens, according to FACS-analysis and quantitative absorption tests, gave no metastases under the same conditions. Pretreatment of the H-2+ met+ B16-S with interferons (beta or alpha + beta) increased their H-2 antigen expression and the number of metastatic colonies (mean: 25 +/- 16). Interferon pretreatment of B16-L cells partially restored their H-2b expression and induced them to form a small number of metastatic colonies. The reduction in pulmonary colonization by the H-2 negative B16-L cells could be attributed to their rapid elimination by natural killer cells, already observed within 24 hr of inoculation of radiolabelled cells. H-2- B16-L cells were more susceptible than H-2+ B16-S cells to in vitro lysis by poly I:C-treated splenocytes, and they acquired full metastatic abilities if the hosts were treated with anti-asialo GM-I serum. In H-2a/b heterozygous hosts, the H-2+ B16-S cells also failed to metastasize. Reduced pulmonary colonization was evident by 24 hr after injection in comparison with H-2b/b hosts, and could be reversed by anti-asialo GM-I treatment of the hosts. In vitro, H-2a/b splenocytes were more cytotoxic to the B16 cells than syngeneic effectors. The results are discussed in relation to a recent hypothesis on a surveillance mechanism for elimination of cells on the basis of their lack (or insufficient expression) of host MHC genes.     

Effect of cell wall skeleton and monophosphoryl lipid A adjuvant on the immunogenicity of a murine B16 melanoma vaccine

We examined the effect of a new adjuvant consisting of purified mycobacterial cell wall skeleton (CWS) and monophosphoryl lipid A (MPL) on the immunogenicity of a murine melanoma vaccine. C57BL/6 mice were immunized to partially purified B16 melanoma vaccine given alone or together with different dose levels of adjuvant, or with saline or adjuvant alone. Humoral response, delayed-type hypersensitivity (DTH), in vitro cytotoxicity, and tumor-protective immunity to melanoma were measured following three biweekly immunizations. The adjuvant potentiated the antibody response to some, but not all, melanoma antigens in a dose-dependent fashion. The adjuvant also potentiated cellular immunity as measured by in vitro cytotoxicity assays. No potentiation of tumor-protective immunity was detected. In comparison to Freund's complete adjuvant, cell wall skeleton plus monophosphoryl lipid A (CWS:MPL) induced fewer cutaneous toxic effects and stronger antibody and DTH responses but resulted in no greater in vitro cytotoxicity or tumor-protective immunity. Thus, the adjuvant had a selective and dose-dependent effect on humoral responses to vaccine immunization but did not potentiate a tumor-protective immunity to B16 melanoma.     

Biological and antitumor effects of recombinant human macrophage colony-stimulating factor in mice

The administration of recombinant human macrophage colony-stimulating factor (M-CSF) i.p. in doses of 25 or 100 micrograms twice daily for 5 consecutive days to non-tumor-bearing C57BL/6 mice resulted in a dose-dependent infiltration of mononuclear cells in the livers but not the lungs of these treated animals. Immunohistochemical examination of fixed liver tissue with the murine macrophage-specific monoclonal antibody, F4/80, revealed a greater than 5-fold increase in the number of hepatic macrophages. Quantification of F4/80-positive cells in a mononuclear single cell suspension derived from liver revealed a greater than 25-fold expansion in the number of hepatic macrophages compared to control mice. These cells were then tested in 18-h 51Cr release assays for tumoricidal activity, after an 18-h incubation with or without gamma-interferon, against cultured P815 targets. Significant tumor cell lysis by these liver-associated mononuclear cells occurred, which was enhanced by gamma-interferon preincubation. The systemic administration of M-CSF alone at high dose had no antitumor impact in vivo against 3-day pulmonary metastases from the MCA-203 sarcoma and B16 melanoma or hepatic metastases from the B16 melanoma or MCA-105, -203, or -207 sarcomas. Although the systemic administration of M-CSF in combination with tumor-specific monoclonal antibody had no effect on 3-day pulmonary metastases from the B16 melanoma, significant reductions in liver metastases were seen. These murine studies demonstrate the biological activity of recombinant human M-CSF in vivo and suggest that the administration of this cytokine in combination with specific monoclonal antibody may be useful in the treatment of patients with metastatic disease at sites of monocyte/macrophage accumulation.     

Metastatic dissemination of B16 melanoma: pattern and sequence of metastasis

The progressive metastatic spread from subcutaneous transplants of two subpopulations of the mouse B16 melanoma, slow-growing clone G3.5 and fast-growing clone G3.12, was examined during tumor growth in C57BL/6 mice and after surgical excision of tumors of various sizes. In addition to enumeration of visible and lethal or potentially lethal ("clinically relevant") metastases, the occurrence of visibly undetectable proliferating (occult) or nonproliferating (dormant) micrometastases was assessed by implanting lymph nodes and organs subcutaneously into normal mice and monitoring for resulting tumor growth. Occult or dormant metastases were disseminated initially to the lungs from G3.5 tumors of 3-4 mm in mean geometric diameter (MGD) and G3.12 tumors of 6-7 mm in MGD. The ipsilateral axillary lymph node (IALN), the regional draining lymph node for these tumors, received metastases after the lungs, initially from 10 to 12-mm tumors. Subsequently, occult or dormant and visible metastases first appeared in systemic organs and lymph nodes (kidneys, adrenal glands, ovaries, and contralateral axillary lymph node) at tumor sizes of about 26 mm in MGD. Systemic metastases occurred only in mice with large and numerous lung metastases and did not depend on the continuing presence of the subcutaneous tumor or on the presence of IALN metastases, which indicated that established lung metastases were a generalizing site from which systemic metastatic spread initiated. After tumor excision, death generally resulted from extensive lung metastasis. Occasional lethal or clinically relevant metastases were also observed in the IALN, kidneys, adrenal glands, ovaries, brain, eyes, and urinary bladder; liver involvement was evident exclusively as occult or dormant micrometastases. Terminal metastatic patterns of these B16 melanoma transplants were as widespread and indiscriminate as those of malignant melanoma in humans.     

Anti-angiogenic effects of the thienopyridine SR 25989 in vitro and in vivo in a murine pulmonary metastasis model

Neovascularisation is a key step in tumour growth and establishment of distant metastases. We have recently demonstrated that the thienopyridine SR 25989 an enantiomer of the anti-aggregant clopidogrel (Plavix) lacking anti-aggregant activity, inhibits endothelial cell proliferation in vitro by increasing the expression of endogenous thrombospondin-1, a natural potent inhibitor of angiogenesis. The anti-angiogenic effect of SR 25989 was further assessed in vitro in a quantitative assay of angiogenesis comprising a fragment of rat aorta embedded in a fibrin gel and in vivo in a pulmonary metastatic model using C57BL/6 mice inoculated in the foot pad with the highly metastatic melanoma cell line B16 F10. SR 25989 induced a dose dependent inhibition of spontaneous microvessel development in vitro reaching half maximal inhibition at around less than 50 microM and caused platelet derived growth factor induced angiogenesis to regress as a function of thienopyridine concentration. In vivo, SR 25989 did not alter significantly the growth rate of the primary tumour in the foot pad and did not inhibit development of inguinal nodes which appeared after amputation. However, the number and size of lung metastases were reduced in treated animals when examined at the time of sacrifice. In addition, the few metastases over 1 mm3 did not show any neovascularisation, as confirmed by negative von Willebrand immunostaining and in contrast to intense vascularisation seen in metastases developed by control mice. These results confirm that SR 25989 possesses potent anti-angiogenic properties and is able to inhibit metastatic dissemination and growth. The lack of effect on the primary tumour and inguinal nodes illustrates the complexity of the mechanisms involved in tumoural neo-angiogenesis and points out the possibility for distinct processes leading to neovascularisation in primary tumour as opposed to metastases.     

Pivotal role of CXCR3 in melanoma cell metastasis to lymph nodes

Chemokines and their receptors play key roles in leukocyte trafficking and are also implicated in cancer metastasis to specific organs. Here we show that mouse B16F10 melanoma cells constitutively express chemokine receptor CXCR3, and that its ligands CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC induce cellular responses in vitro, such as actin polymerization, migration, invasion, and cell survival. To determine whether CXCR3 could play a role in metastasis to lymph nodes (LNs), we constructed B16F10 cells with reduced CXCR3 expression by antisense RNA and investigated their metastatic activities after s.c. inoculations to syngeneic hosts, C57BL/6 mice. The metastatic frequency of these cells to LNs was markedly reduced to approximately 15% (P < 0.05) compared with the parental or empty vector-transduced cells. On the other hand, pretreatment of mice with complete Freund's adjuvant increased the levels of CXCL9 and CXCL10 in the draining LNs, which caused 2.5-3.0-fold increase (P < 0.05) in the metastatic frequency of B16F10 cells to the nodes with much larger foci. Importantly, such a stimulation of metastasis was largely suppressed when CXCR3 expression in B16F10 cells was reduced by antisense RNA or when mice were treated with specific antibodies against CXCL9 and CXCL10. We also demonstrate that CXCR3 is expressed on several human melanoma cell lines as well as primary human melanoma tissues (5 of 9 samples tested). These results suggest that CXCR3 inhibitors may be promising therapeutic agents for treatment of LN metastasis, including that of melanoma.     

Immunization with tumor-derived ER chaperone grp170 elicits tumor-specific CD8+ T-cell responses and reduces pulmonary metastatic disease

Glucose-regulated protein (grp) 170 is a molecular chaperone localized in endoplasmic reticulum (ER), which has been demonstrated to interact with the peptides translocated by transporter associated with antigen presentation (TAP). In our study, we have evaluated the therapeutic efficacy of tumor-derived grp170 against the highly metastatic and poorly immunogenic murine melanoma B16F10. Immunization of mice with grp170 preparations from autologous tumor significantly delayed progression of the primary cancer and reduced established pulmonary metastases, which was associated with the prolonged survival of metastases-bearing mice. However, grp170 from normal liver or antigenically distinct tumor failed to exhibit therapeutic effect. In addition, tumor-derived grp170 elicited a potent cytotoxic T-lymphocyte response specific for B16F10 tumor, which correlates with in vivo protective effects. Adoptive transfer of splenocytes obtained from B16F10-grp170-primed animals remarkably suppressed pulmonary metastases. Depletion of either CD4(+) or CD8(+) T cells in priming phase significantly abrogated the tumor immunity induced by the B16F10-grp170. However, the vaccine activity was intact when CD4(+), not CD8(+), T cells were depleted in effector phase. It suggests that CD4(+) T helper cells play an important role in the generation of effective antitumor response, whereas CD8(+) T cells are predominantly involved in direct killing of tumor cells. These observations have strong clinical implications for using tumor-derived grp170 as a therapeutic vaccine against metastatic diseases.     

Retinoic acid stimulation of the induction of mouse killer T-cells in allogeneic and syngeneic systems.

The ability of retinoic acid (RA), a potent antitumor agent, to stimulate cell-mediated cytotoxicity (CMC) in mice was investigated. Low doses of RA (5-300 micrograms/mouse/day) administered ip into C57BL/6 mice for 5 days daily or for 1--3 months three times a week before immunization in vivo or in vitro with allogeneic BALB/c S194 myeloma cells led to an enhanced cytotoxic activity of their spleen effector cells. Similarly, in a syngeneic situation injection of RA into C57BL/6 or BALB/c mice before in vitro challenge with EL 4 (C57BL/6) or S194 (BALB/c) tumor cells strongly stimulated CMC. The enhanced cytotoxic activity was effected by thymus-derived lymphocytes (T-cells) and specific for the H-2 histocompatibility antigens in the case of the allogeneic sensitization or specific for tumor antigens in the case of the syngeneic sensitization. Because RA had no effect on the effector step of CMC, RA likely enhanced the induction step of T-CMC. The action of RA was antigen-dependent, and it is therefore a true adjuvant rather than a nonspecific stimulator or polyclonal activator of cytotoxic T-cells.     

3,4-Dihydroxybenzylamine: a dopamine analog with enhanced antitumor activity against B16 melanoma.

3,4-Dihydroxybenzylamine (DHBA), a dopamine analog, was much less toxic than dopamine when tested against the B16 melanoma in vivo and in vitro. Daily doses of 1,000 mg DHBA/kg were better tolerated than doses of 400 mg dopamine/kg. When tested against the B16 melanoma in (C57BL/6 x DBA/2)F1 mice, DHBA had a significantly improved therapeutic effect as shown by a life-span increased 70% as compared to 48% with dopamine. DHBA shared the catecholamine property of selectively inhibiting thymidine incorporation as compared to leucine or uridine incorporation. Because the inhibitory effects of DHBA on the B16 melanoma cells in vitro were similar to those of dopamine, much of the improved efficacy in vivo might be attributed to decreased toxicity.