Sunlight and skin cancer: inhibition of p53 mutations in UV-irradiated mouse skin by sunscreens.

UV-induced mutations in the p53 tumor suppressor gene play an essential role in skin cancer development. We report here that such mutations can be detected in UV-irradiated mouse skin months before the gross appearance of skin tumors. Application of SPF-15 sunscreens to mouse skin before each UV irradiation nearly abolished the frequency of p53 mutations. These results indicate that p53 mutation is an early event in UV skin carcinogenesis and that inhibition of this event may serve as an early end point for assessing protective measures against skin cancer development.

CD40-CD40 ligand interactions in vivo regulate migration of antigen-bearing dendritic cells from the skin to draining lymph nodes.

Whereas CD40-CD40 ligand interactions are important for various dendritic cell (DC) functions in vitro, their in vivo relevance is unknown. We analyzed the DC status of CD40 ligand -/- mice using a contact hypersensitivity (CHS) model system that enables multiple functions of DCs to be assessed in vivo. Immunohistochemistry of skin sections revealed no differences in terms of numbers and morphology of dendritic epidermal Langerhans cells (LCs) in unsensitized CD40 ligand -/- mice as compared with wild-type C57BL/6 mice. However, after contact sensitization of CD40 ligand -/- mice, LCs failed to migrate out of the skin and substantially fewer DCs accumulated in draining lymph nodes (DLNs). Furthermore, very few antigen-bearing DCs could be detected in the paracortical region of lymph nodes draining sensitized skin. This defect in DC migration after hapten sensitization was associated with defective CHS responses and decreased cutaneous tumor necrosis factor (TNF)-alpha production and was corrected by injecting recombinant TNF-alpha or an agonistic anti-CD40 monoclonal antibody. Thus, CD40-CD40 ligand interactions in vivo regulate the migration of antigen-bearing DCs from the skin to DLNs via TNF-alpha production and play a vital role in the initiation of acquired T cell-mediated immunity.

Assessing the potential role of photopheresis in hematopoietic stem cell transplant.

The First International Symposium on Photopheresis in Hematopoietic Stem Cell Transplantation was held in Vienna, Austria with an educational grant from Therakos Inc. from 25 May to 27 May 2005. Three general issues were addressed: (1) pathophysiology of graft-versus-host disease (GvHD), (2) induction of immune tolerance and the immunology of phototherapy and (3) current standard treatment and prevention strategies of acute and chronic GvHD and the use of extracorporeal photopheresis (ECP). The objectives of the meeting were to open a dialogue among leading researchers in photobiology, immunology, and hematopoietic stem cell transplantation; foster discussions and suggestions for future studies of the mechanism of action of ECP in acute and chronic GvHD; and promote collaboration between basic scientists and clinicians. As can be seen from the summaries of the individual presentations, important advances have been made in our understanding of GvHD, including the use of photoimmunology interventions and the development of robust model systems. It is our expectation that data from photoimmunology studies can be used to generate hypotheses in animal models that can further define the mechanism of action of ECP and help translate the findings to clinical trials of ECP for the prophylaxis and treatment of both chronic and acute GvHD.

p53 and Fas ligand are required for psoralen and UVA-induced apoptosis in mouse epidermal cells.

A combination of 8-methoxypsoralen (8-MOP) and ultraviolet-A (UVA) radiation (320-400 nm) (PUVA) is widely used in the treatment of psoriasis and other skin diseases. PUVA is highly effective in eliminating hyperproliferative cells in the epidermis, but its mechanism of action has not been fully elucidated. In this study, we used immortalized JB6 mouse epidermal cells, p53(-/-), and Fas ligand deficient (gld) mice to investigate the molecular mechanism by which PUVA induces cell death. The results indicate that PUVA treatment induces apoptosis in JB6 cells. In addition, PUVA treatment of JB6 cells results in p53 stabilization, phosphorylation, and nuclear localization as well as induction of p21(Waf/Cip1) and caspase-3 activity. In vivo studies reveal that PUVA treatment induces significantly less apoptosis in the epidermis of p53(-/-) mice compared to p53(+/+) mice. Furthermore, FasL-deficient (gld) mice are completely resistant to PUVA-induced apoptosis compared to wild-type mice. These results indicate that PUVA treatment induces apoptosis in mouse epidermal cells in vitro and in vivo and that p53 and Fas/Fas ligand interactions are required for this process, at least in vivo. This implies that similar mechanisms may be involved in the elimination of psoriatic keratinocytes from human skin following PUVA therapy.

Interleukin 10 suppresses tumor growth and metastasis of human melanoma cells: potential inhibition of angiogenesis.

Interleukin 10 (IL-10) inhibits the production of a wide range of cytokines in various cell types. The purpose of this study was to determine whether the expression of the IL-10 gene can influence tumor growth and metastatic properties of human melanoma cells. The human melanoma cell line, A375P, which does not produce endogenous IL-10, was transfected with a hygromycin expression vector (control) or a vector containing full-length murine IL-10 cDNA. A375P parental cells, A375P-Hygro, and A375P-IL-10-positive cells were injected s.c. and i.v. into nude mice. A375P-IL-10 cells produced significantly slower growing s.c. tumors and fewer lung metastases than control cells. The tumorigenicity of the human melanoma A375SM and the murine melanoma B16-BL6 cells was also significantly inhibited when they were admixed with A375P-IL-10 but not with A375P-Hygro before s. c. injection into nude mice. The suppression of tumor growth and metastasis was directly correlated with a decrease in neovascularity determined by immunostaining with anti-factor VIII. Because tumor-associated macrophages are the major source of angiogenic molecules in melanoma, we used reverse transcription-PCR to demonstrate that IL-10 down-regulates the production of vascular endothelial growth factor, the most potent angiogenic factor in activated macrophages. Other factors involved in angiogenesis such as IL-1beta, tumor necrosis factor-alpha, IL-6, and the proteinase matrix metalloproteinase-9 were also inhibited in activated macrophages by supernatants from A375P-IL-10 cells. Collectively, these data suggest that the production of IL-10 by tumor cells inhibits macrophages-derived angiogenic factors, and hence, tumor growth and metastasis.

Liposomes containing muramyl tripeptide phosphatidylethanolamine (MTP-PE) are excellent adjuvants for induction of an immune response to protein and tumor antigens.

Liposomes containing the synthetic lipophilic analog of muramyl dipeptide, muramyl tripeptide phosphatidylethanolamine (MTP-PE), were used as adjuvants for the induction of humoral and cellular immune responses following immunization with protein or tumor antigens. Cellular immune reactions, including delayed-type hypersensitivity and lymphoproliferation in vitro, were observed following immunization of mice with a mixture of antigen and liposome-MTP-PE. Immunization with murine melanoma K1735 cells, admixed with liposomal MTP-PE, induced a protective immune response as demonstrated by the rejection of transplanted tumor cells. Antibody production was also induced following immunization with protein antigens admixed with liposome-MTP-PE. The efficacy of adjuvant activity following immunization with antigens admixed with liposome-MTP-PE was equal to or better than that of complete Freund's adjuvant (CFA). Moreover, liposome-MTP-PE did not have the toxic side effects associated with CFA. These data suggest that phospholipid liposomes containing MTP-PE are superior adjuvants and should receive consideration for vaccine therapy.

The role of IL-4, IL-10, and TNF-alpha in the immune suppression induced by ultraviolet radiation.

Cytokines produced by keratinocytes play an essential role in the induction of immune suppression following ultraviolet (UV) exposure. Using antibodies specific for either interleukin-10 (IL-10) or tumor necrosis factor alpha (TNF-alpha), we present evidence indicating that IL-10 suppresses delayed-type hypersensitivity (DTH) but not contact hypersensitivity (CHS), whereas TNF-alpha suppresses CHS but not DTH following UV exposure. UV exposure also activates antigen-specific suppressor T cells. To determine whether the antigen-specific CD4+ T cells that transfer suppression in this system mediate their suppressive effect by releasing IL-4 or IL-10, we transferred UV Ts into normal mice that were then injected with either anti-IL-4 or anti-IL-10 antibody. Both anti-IL-4 and anti-IL-10 blocked the ability of UV Ts cells to suppress DTH in the recipient animals. When UV Ts that suppress CHS were transferred into normal recipients, however, neither antibody was able to block the UV Ts activity. These findings suggest that UV Ts suppress DTH by secreting IL-4 and IL-10 and appear to act like Th2 cells. Because anti-IL-4 and anti-IL-10 did not block the activity of the UV Ts that regulate contact hypersensitivity, their effects appear to be mediated by a different mechanism.

Supernatants from UVB radiation-exposed keratinocytes inhibit Langerhans cell presentation of tumor-associated antigens via IL-10 content.

Exposure of mice to midrange UV radiation (UVB) (280-320 mm) in vivo leads to suppression of the ability to induce delayed-type hypersensitivity (DTH). Systemic administration of supernatants from UVB-exposed keratinocytes (KC) similarly inhibits the ability to induce DTH and the presence of interleukin-10 (IL-10) in the supernatants has been shown to be responsible for this effect. It has been hypothesized that release of IL-10 by KC after exposure to UVB radiation in vivo may be responsible for UVB-induced inhibition of DTH and also for the inability of chronically UVB-irradiated mice to immunologically reject immunogenic UVB-induced skin tumors. To test directly whether supernatants from UVB-irradiated KC can inhibit presentation of tumor-associated antigens (TAA) by epidermal Langerhans cells (LC), cultures of the transformed murine KC line PAM 212 were exposed to 200 J/m2 of UVB radiation and 24 h supernatants obtained. CAF1 (H-2a/d) epidermal cells (EC) enriched for LC content were exposed to supernatants from irradiated (UV-SN) or mock-irradiated (MI-SN) PAM 212 cells for 3 h followed by culture for 16 h in granulocyte-macrophage colony-stimulating factor and then were pulsed with soluble TAA derived from the murine spindle cell tumor S1509a (H-2a). ECs were then washed and injected subcutaneously into naive CAF1 mice three times at weekly intervals for priming. One week after the final immunization these mice were challenged subcutaneously with live S1509a cells and tumor growth scored over time. Pretreatment of EC with UV-SN but not MI-SN inhibited the induction of effective immunity by this immunization scheme. ECs were also treated with UV-SN or MI-SN for 3 h then pulsed with TAA and injected into a hind footpad of previously immunized mice for elicitation of a DTH response. Pretreatment of EC with UV-SN but not MI-SN inhibited the ability of EC to elicit DTH. Neutralization studies with specific neutralizing antibodies to IL-10 demonstrated that the presence of IL-10 in UV-SN was responsible for the inhibition of antigen presentation both for induction and elicitation of immunity. UV-SN inhibits tumor antigen presentation by epidermal LC through the action of IL-10.

Presentation of endogenous tumor antigens to CD4+ T lymphocytes by murine melanoma cells transfected with major histocompatibility complex class II genes.

In a previous study, we demonstrated that K1735 transfectants expressing either Kk or Ak antigens alone produced tumors in syngeneic mice, whereas transfectants that expressed both antigens were rejected. In this study, we investigated whether K1735 transfectants expressing Ak molecules can present endogenous tumor antigens to CD4+ T lymphocytes in the absence of normal accessory cells. Our results indicate that K1735 transfectants expressing Kk and Ak molecules presented antigen to both CD4+ and CD8+ T lymphocytes, whereas K1735 transfectants expressing only the Ak or the Kk antigen preferentially stimulated either CD4+ or CD8+ T cells. Analogous to endogenous antigens, K1735 transfectants expressing Ak molecules also presented exogenous hen egg lysozyme (HEL) to HEL-specific 3A9 hybridomas in the absence of normal accessory cells. These results demonstrate that K1735 murine melanoma cells expressing Ak molecules can function as antigen-presenting cells and that the generation of an effective antitumor immune response by K1735 melanoma cells expressing Kk and Ak antigens is due to their ability to present endogenous tumor antigens to both helper and cytotoxic T cells.

Platelet-activating factor induces cell cycle arrest and disrupts the DNA damage response in mast cells.

Platelet-activating factor (PAF) is a potent phospholipid modulator of inflammation that has diverse physiological and pathological functions. Previously, we demonstrated that PAF has an essential role in ultraviolet (UV)-induced immunosuppression and reduces the repair of damaged DNA, suggesting that UV-induced PAF is contributing to skin cancer initiation by inducing immune suppression and also affecting a proper DNA damage response. The exact role of PAF in modulating cell proliferation, differentiation or transformation is unclear. Here, we investigated the mechanism(s) by which PAF affects the cell cycle and impairs early DNA damage response. PAF arrests proliferation in transformed and nontransformed human mast cells by reducing the expression of cyclin-B1 and promoting the expression of p21. PAF-treated cells show a dose-dependent cell cycle arrest mainly at G2-M, and a decrease in the DNA damage response elements MCPH1/BRIT-1 and ataxia telangiectasia and rad related (ATR). In addition, PAF disrupts the localization of p-ataxia telangiectasia mutated (p-ATM), and phosphorylated-ataxia telangiectasia and rad related (p-ATR) at the site of DNA damage. Whereas the potent effect on cell cycle arrest may imply a tumor suppressor activity for PAF, the impairment of proper DNA damage response might implicate PAF as a tumor promoter. The outcome of these diverse effects may be dependent on specific cues in the microenvironment.

Cloning and mapping of a putative barley NADPH-dependent HC-toxin reductase.

The NADPH-dependent HC-toxin reductase (HCTR), encoded by Hm1 in maize, inactivates HC-toxin produced by the fungus Cochliobolus carbonum, and thus confers resistance to the pathogen. The fact that C. carbonum only infects maize (Zea mays) and is the only species known to produce HC-toxin raises the question: What are the biological functions of HCTR in other plant species? An HCTR-like enzyme may function to detoxify toxins produced by pathogens which infect other plant species (R. B. Meeley, G. S. Johal, S. E. Briggs, and J. D. Walton, Plant Cell, 4:71-77, 1992). Hm1 homolog in rice (Y. Hihara, M. Umeda, C. Hara, Q. Liu, S. Aotsuka, K. Toriyama, and H. Uchimiya, unpublished) and HCTR activity in barley, wheat, oats and sorghum have been reported (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080-1086, 1993). To investigate the sequence conservation of Hm1 and HCTR in barley and the possible relationship of barley Hm1 homolog to the known disease resistance genes, we cloned and mapped a barley (Hordeum vulgare) Hm1-like gene. A putative full-length cDNA clone, Bhm1-18, was isolated from a cDNA library consisting of mRNA from young leaves, inflorescences, and immature embryos. This 1,297-bp clone encodes 363 amino acids which show great similarity (81.6%) with the amino acid sequence of HM1 in maize. Two loci were mapped to barley molecular marker linkage maps with Bhm1-18 as the probe; locus A (Bhm1A) on the long arm of chromosome 1, and locus B (Bhm1B) on the short arm of chromosome 1 which is syntenic to maize chromosome 9 containing the Hm2 locus. The Bhm1-18 probe hybridized strongly to a Southern blot of a wide range of grass species, indicating high conservation of HCTR at the DNA sequence level among grasses. The HCTR mRNA was detected in barley roots, leaves, inflorescences, and immature embryos. The conservation of the HCTR sequence, together with its expression in other plant species (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080-1086, 1993), suggest HCTR plays an important functional role in other plant species.

Modulation of immunity by ultraviolet radiation: key effects on antigen presentation.

In addition to being the major cause of non-melanoma skin cancer, the ultraviolet radiation (UVR) present in sunlight is a potent immunosuppressive agent. Indeed, studies with mice and humans have indicated that the immune suppression induced by UVR is a risk factor for skin cancer development. These observations gave rise to the discipline of photoimmunology, which studies the interaction of electromagnetic radiation, primarily UVB (280-320 nm) light, with the immune system. The focus of this paper will be to review recent studies designed to unravel the mechanisms through which UVR suppresses immune reactivity. Particular emphasis is placed on the effects of UVR on antigen presentation.

Photoinactivation of T-cell function with psoralen and UVA radiation suppresses the induction of experimental murine graft-versus-host disease across major histocompatibility barriers.

Bone marrow transplantation is employed in the treatment of a number of hematologic and malignant diseases. A major complication is the induction of graft-versus-host disease. Whereas removal of T lymphocytes from the donor marrow effectively reduces the incidence of graft-versus-host disease, the incidence of graft failure often increases when T cells are depleted from the transplanted marrow. In the current study, photoinactivation of the donor cells with 8-methoxypsoralen coupled with exposure to long-wavelength ultraviolet radiation (PUVA therapy) was used to inactivate the response of the donor T cells against the host. PUVA therapy suppressed the ability of spleen cells to respond to alloantigen in the in vitro mixed lymphocyte reaction. The induction of acute graft-versus-host disease across complete major histocompatibility barriers in lethally X-irradiated mice was significantly suppressed after bone marrow transplantation with photoinactivated bone marrow cells. Long-term survivors demonstrated allogeneic reconstitution and partial restoration of T-cell function. Because PUVA therapy had no inhibitory effect on hematopoiesis, these data suggest that using phototherapy to inactivate the alloreactivity of T cells may provide an alternative to purging T cells from the donor marrow, thus suppressing both the incidence of graft-versus-host disease and the incidence of graft failure.

Activation of keratinocytes with psoralen plus UVA radiation induces the release of soluble factors that suppress delayed and contact hypersensitivity.

Exposure of mice to psoralen plus ultraviolet A (320-400 nm) radiation or midrange ultraviolet B (280-320 nm) radiation causes a systemic suppression of the immune response. Although the mechanisms involved in the induction of suppression are not entirely clear, recent studies have demonstrated that ultraviolet B--irradiated keratinocytes release soluble factors that depress delayed-type hypersensitivity to alloantigens and activate the suppressor cell pathway. The purpose of this study was to determine whether PUVA-treated keratinocytes could also cause the release of such immunosuppressive factors. Treatment of keratinocytes with psoralen and UVA radiation induced the release of a factor that depressed the delayed-type hypersensitivity reaction to alloantigen. The suppressive factor was released regardless of whether the psoralen formed monofunctional or bifunctional adducts with DNA and regardless of its phototoxicity. In addition, keratinocytes treated with psoralen and lower doses of UVA radiation released a factor that inhibited contact but not delayed-type hypersensitivity, suggesting that more than one immunosuppressive factor is released following treatment of keratinocytes with appropriate doses of psoralen and UVA radiation. Our findings provide evidence that immunosuppressive factors released from keratinocytes may play a role in the induction of systemic immune suppression following PUVA treatment. Moreover, they demonstrate that PUVA treatment, unlike UVB treatment, can cause the release of more than one immunosuppressive factor from keratinocytes.

Immunosuppression by factors released from UV-irradiated epidermal cells: selective effects on the generation of contact and delayed hypersensitivity after exposure to UVA or UVB radiation.

Exposure of murine epidermal cells to UV radiation in vitro causes the release of immunoregulatory factors that mimic some of the immunosuppressive effects of in vivo UV irradiation. The purpose of this study was to investigate the spectrum of immune responses affected following i.v. injection of supernatants obtained from cultures of epidermal cells exposed in vitro to UV radiation. Treatment of primary epidermal cell cultures or transformed keratinocytes (Pam 212 cells) with UVB (280-320 nm) radiation caused the release of factors that suppressed the induction of delayed hypersensitivity to alloantigen and trinitrophenyl-modified self-antigens in syngeneic and allogeneic mice. Contrary to expectations, however, the injection of supernatants from UVB-irradiated epidermal cells had no effect on the induction of contact hypersensitivity to trinitrochlorobenzene. On the other hand, treatment of the keratinocytes with UVA radiation (320-400 nm, filtered to remove wavelengths in the UVB region) resulted in the release of a factor that suppressed contact but not delayed hypersensitivity. Neither the UVA-induced nor the UVB-induced suppressive factor inhibited the generation of an antibody response to sheep erythrocytes, indicating that, like the suppression that occurs after in vivo exposure to UV radiation, the suppression induced by factors from UV-irradiated keratinocytes is selective in nature. These data support the hypothesis that soluble keratinocyte-derived suppressive factors are involved in the induction of systemic immune suppression by UV radiation. In addition, they suggest that multiple suppressive factors, having different immunosuppressive properties, are produced by different wavelengths of UV radiation.

Ultraviolet a radiation suppresses an established immune response: implications for sunscreen design.

The ultraviolet radiation present in sunlight is the primary cause of nonmelanoma skin cancer and has been implicated in the development of cutaneous malignant melanoma. In addition, ultraviolet is immune suppressive and the suppression induced by ultraviolet radiation has been identified as a risk factor for skin cancer induction. Ultraviolet also suppresses the immune response to infectious agents. In most experimental models, ultraviolet is applied to immunologically naive animals prior to immunization. Of equal concern, however, is the ability of sunlight to suppress established immune reactions, such as the recall reaction in humans, which protects against microbial infections. Here we demonstrate that solar-simulated ultraviolet radiation, applied after immunization, suppresses immunologic memory and the elicitation of delayed-type hypersensitivity. Further, we found that wavelengths in the ultraviolet A region of the solar spectrum were critical for inducing immune suppression. Ultraviolet A (320-400 nm) radiation was as effective as solar-simulated ultraviolet A + B (290-400 nm) in suppressing the elicitation of an established immune response. Irradiation with ultraviolet AI (340-400 nm) had no effect. Supporting a critical role for ultraviolet A in ultraviolet-induced immune suppression was the observation that applying a sunscreen that contained an ultraviolet B only filter had no protective effect, whereas, a sunscreen containing both ultraviolet A and ultraviolet B filters totally blocked ultraviolet-induced immune suppression. These data suggest that sunlight may depress the protective effect of prior vaccination. In addition, the observation that ultraviolet A is immunosuppressive indicates the need for ultraviolet A protection when designing sun protection strategies.

Aloe barbadensis extracts reduce the production of interleukin-10 after exposure to ultraviolet radiation.

Cutaneous exposure to ultraviolet radiation suppresses the induction of T cell mediated responses such as contact and delayed type hypersensitivity (DTH) by altering the function of immune cells in the skin and causing the release of immunoregulatory cytokines. Extracts of crude Aloe barbadensis gel prevent this photosuppression. Because the regulation of contact hypersensitivity and DTH responses differ, we investigated whether protection was afforded by a single or multiple agents in Aloe and the mechanism by which this material prevents suppression of DTH immunity. The ability of Aloe gel to prevent suppression of contact hypersensitivity responses to hapten decayed rapidly after manufacture. In contrast, agents that protected against systemic suppression of DTH responses to Candida albicans were stable over time. Oligosaccharides prepared from purified Aloe polysaccharide prevented suppression of DTH responses in vivo and reduced the amount of IL-10 observed in ultraviolet irradiated murine epidermis. To assess the effect of Aloe extracts on keratinocytes, Pam 212 cells were exposed in vitro to ultraviolet radiation and treated for 1 h with Aloe oligosaccharides. Culture supernatants were collected 24 h later and injected into mice. Supernatants from ultraviolet irradiated keratinocytes suppressed the induction of DTH responses, whereas Aloe oligosaccharide treatment reduced IL-10 and blocked the suppressive activity of the supernatants. These results indicate that Aloe contains multiple immunoprotective factors and that Aloe oligosaccharides may prevent ultraviolet induced suppression of DTH by reducing keratinocyte derived immunosuppressive cytokines.

Inhibition of solar simulator-induced p53 mutations and protection against skin cancer development in mice by sunscreens.

We demonstrated previously that p53 mutations can be detected in ultraviolet B-irradiated mouse skin months before the gross appearance of skin tumors and that applying sun protection factor 15 sunscreens to mouse skin before each Kodacel-filtered FS40 sunlamp irradiation resulted in the reduction of such mutations. To determine whether there is an association between reduction of ultraviolet-induced p53 mutations by sunscreens and protection against skin cancer using an environmentally relevant light source, we applied sunscreens (sun protection factors 15-22) on to the shaved dorsal skin of C3H mice 30 min before each exposure to 4.54 kJ ultraviolet B (290-400 nm) radiation per m2 from a solar simulator. Control mice were treated 5 d per wk with ultraviolet only or vehicle plus ultraviolet. p53 mutation analysis indicated that mice exposed to ultraviolet only or vehicle plus ultraviolet for 16 wk (cumulative exposure to 359 kJ ultraviolet B per m2) developed p53 mutations at a frequency of 56%-69%, respectively, but less than 5% of mice treated with sunscreens plus ultraviolet showed evidence of p53 mutations. More importantly, 100% of mice that received a cumulative dose of 1000 kJ ultraviolet B per m2 only, or vehicle plus ultraviolet B developed skin tumors, whereas, the probability of tumor development in all the mice treated with the sunscreens plus 1000 kJ ultraviolet B per m2 was 2% and mice treated with sunscreens plus 1500 kJ ultraviolet B per m2 was 15%. These results demonstrate that the sunscreens used in this study not only protect mice against ultraviolet-induced p53 mutations, but also against skin cancers induced with solar-simulated ultraviolet. Because of this association, we conclude that inhibition of p53 mutations is a useful early biologic endpoint of photoprotection against an important initiating event in ultraviolet carcinogenesis.

Regulation of tumor growth and metastasis by interleukin-10: the melanoma experience.

Because interleukin-10 (IL-10) has potent immunosuppressive and anti-inflammatory properties and is produced by some cancers, including melanoma, we hypothesized that its production by tumor cells may contribute to the escape from immune surveillance. To test this hypothesis, we transfected human A375P melanoma cells that do not express IL-10 with the murine IL-10 gene and subsequently analyzed for changes in tumor growth and metastasis in nude mice. Surprisingly, IL-10 gene transfer resulted in a loss of metastasis and significant inhibition of tumor growth. In addition, the growth of other murine or human melanoma cells was also inhibited when they were admixed with IL-10-transfected cells before injection into nude mice. We provide evidence that IL-10 exerts its antitumor and antimetastatic activity by inhibiting angiogenesis in vivo. The in vivo decrease in neovascularization found in IL-10-secreting tumors is most likely due to the ability of IL-10 to downregulate the synthesis of vascular endothelial growth factor (VEGF), interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-6, and matrix metalloproteinase-9 (MMP-9) in tumor-associated macrophages. Other studies have shown that IL-10 inhibits tumor metastasis through a natural killer (NK) cell-dependent mechanism. The inhibitory effects of IL-10 on tumor growth and metastasis were also demonstrated in other tumor models, including breast cancers. Furthermore, administration of rIL-10 into mice resulted in inhibition of tumor metastasis. Because IL-10 has little toxicity when given systemically to human volunteers, its efficacy as an antimetastatic agent should be further explored, both as an independent and in combination with other inhibitors of neovascularization.

A disposable diffusion chamber system used to study immunoregulation by soluble factors.

A disposable two-chamber culture system is described which is useful for studying various soluble factors which regulate the immune response. This method requires small numbers of cells and less than 2 ml of medium per culture. The vessel is compact, relatively inexpensive and all component parts are readily available from commercial suppliers. This culture system circumvents the major problems associated with dual chamber methods previously developed for the study of immunoregulatory molecules affecting antibody production.