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Background: Following the first investigational study on the use of extracorporeal photopheresis for the treatment of cutaneous T-cell lymphoma published in 1983, this technology has received continued use and further recognition for additional earlier as well as refractory forms. After the publication of the first guidelines for this technology in the JEADV in 2014, this technology has maintained additional promise in the treatment of other severe and refractory conditions in a multidisciplinary setting. It has confirmed recognition in well-known documented conditions such as graft-vs.-host disease after allogeneic bone marrow transplantation, systemic sclerosis, solid organ transplant rejection including lung, heart and liver and to a lesser extent inflammatory bowel disease., Materials and Methods: In order to further provide recognized expert practical guidelines for the use of this technology for all indications, the European Dermatology Forum (EDF) again proceeded to address these questions in the hands of the recognized experts within and outside the field of dermatology. This was done using the recognized and approved guidelines of EDF for this task. All authors had the opportunity to review each contribution as it was added., Results and Conclusion: These updated 2020 guidelines provide at present the most comprehensive available expert recommendations for the use of extracorporeal photopheresis based on the available published literature and expert consensus opinion. The guidelines were divided into two parts: PART I covers Cutaneous T-cell lymphoma, chronic graft-vs.-host disease and acute graft-vs.-host disease, while PART II will cover scleroderma, solid organ transplantation, Crohn's disease, use of ECP in paediatric patients, atopic dermatitis, type 1 diabetes, pemphigus, epidermolysis bullosa acquisita and erosive oral lichen planus., (© 2020 The Authors. Journal of the European Academy of Dermatology and Venereology published by John Wiley & Sons Ltd on behalf of European Academy of Dermatology and Venereology.)

Targeted therapy with the BRAF inhibitors vemurafenib and dabrafenib is an effective treatment regimen in patients with advanced melanoma carrying the BRAF V600E mutation. A common side effect is an enhanced rate of nonmelanoma skin cancer (NMSC). BRAF inhibition leads to a paradoxical enhanced MAPK signalling in BRAF wild-type cells, which might in part be responsible for the enhanced NMSC burden. It is known that disturbances of DNA repair result in an increased rate of NMSC. In the present study, it was investigated whether BRAF inhibitors might interfere with the repair of ultraviolet radiation-induced DNA damage in vitro. Epidermal keratinocytes of 11 Caucasian donors were treated with vemurafenib or dabrafenib and, 24 h later, exposed to ultraviolet A. DNA damage and repair capacity were analysed using south-western slot blot detecting cyclobutane pyrimidine dimers. Using PCR and DNA sequencing, RAS mutations and human papilloma virus genes were investigated. RNA expression was determined using a Gene Expression Chip and qRT-PCR. In 36% of keratinocytes, vemurafenib hampers the repair of ultraviolet A-induced DNA damage. No changes in DNA repair were observed with dabrafenib, indicating a possible substance-specific effect of vemurafenib. In none of the keratinocytes, pre-existing RAS mutations or human papilloma virus-associated DNA sequences were detected. The expression of the interferon-related damage resistance signature is decreased upon vemurafenib treatment in 36% of donors. The enhanced rate of NMSC in patients treated with vemurafenib might be partly related to a vemurafenib-driven impaired capacity for DNA repair.

Although infrared radiation (IR) represents more than 50% of the solar radiation reaching the Earth's surface, this waveband has been hardly investigated in terms of tumourigenesis. The objective of the present study was to investigate the influence of IR on ultraviolet B (UVB)-induced carcinogenesis in male and female wild type mice. For this purpose, male and female C57BL/6N mice were subjected to a long-term irradiation protocol. Mice were irradiated once neonatally and from the age of eight weeks for 36 weeks with a cumulative dose of 576 kJ m -2 UVB and/or 78 895 kJ m -2 IR. In order to resemble natural sun irradiation, exposure to physiological doses of UVB and IR was performed simultaneously. Mice were screened for arising lesions twice a week. Lesions were excised and histologically diagnosed. Kaplan-Meier analyses were carried out and lesion counts and cumulated hazard rates for the development of lesions in the UVB and IR + UVB-exposed groups in male and female mice were compared. We found that IR-exposure did not change the number of epithelial malignant tumours in UVB-exposed wild type mice. In combination with IR there was a tendency of more tumours with increased malignancy: 23 vs. seven spindle cell shaped sarcomas and seven vs. two MelanA+/S100+ tumours in groups of 35 C57BL/6 mice. IR did not influence UVB-induced carcinogenesis differently in male and female mice. However, comparing UVB and sham irradiated animals irrespective of IR exposure, UVB-induced non-epithelial tumours arose significantly earlier in male mice than in female mice.

Extracorporeal photopheresis (ECP) has been in clinical use for over three decades after receiving FDA approval for the palliative treatment of the Sézary Syndrome variant of cutaneous T-cell lymphoma (CTCL) in 1988. After the first positive experiences with CTCL, additional indications have been successfully explored including areas such as graft-vs.-host disease (GVHD), scleroderma, and solid organ transplantation. The mechanism of action is still not fully resolved, but important steps in understanding ECP in recent years have been very informative. Originally, the primary hypothesis stated that psoralen and ultraviolet A (UVA) in combination induce apoptosis in the treated immune cells. This view shifted in favor of dendritic cell initiation, modification of the cytokine profile and stimulation of several T-cell lineages, in particular regulatory T-cells. A number of ECP guidelines have been produced to optimize treatment regimens in the clinical context. In CTCL, enough evidence is available for the use of ECP as a first line treatment for Sézary Syndrome (SS), but also as a second line or rescue treatment in therapy-refractory forms of mycosis fungoides (MF). ECP in the treatment of acute and chronic GVHD has shown promising results as second line therapy in steroid-refractory presentations. In solid organ transplantation, ECP has been used to increase tissue tolerance and decrease infections with opportunistic pathogens, attributed to the use of high doses of immunosuppressive medication. Infection with cytomegalovirus (CMV) remains a limiting factor affecting survival in solid organ transplantation and the role of ECP will be discussed in this review. A trend toward prophylactic use of ECP can be observed and may further contribute to improve the outcome in many patients. To further deepen our knowledge of ECP and thus facilitate its use in patients that potentially benefit most from it, future prospective randomized trials are urgently needed in this rapidly growing field. The aim of this review is to (1) introduce the method, (2) give an overview where ECP has shown promising effects and has become an essential part of treatment protocols, and (3) to give recommendations on how to proceed in numerous indications.

Adult wild-type mice are not supposed to be proper models for ultraviolet radiation (UVR)-induced melanoma since melanocytes are confined to hair follicles and cannot be sufficiently reached by UVR. On the other hand, in mutated mouse models used for melanoma research limitations, including an altered immune system and selection of affected pathways, lead to tumors phenotypically quite different from naturally occurring melanomas. We compared the distribution of epidermal melanocytes in UVR and not-UVR-exposed wild-type C57BL/6 mice. Starting at the age of 8 weeks, mice were exposed to physiologic doses of UVR three times weekly over 16 weeks. Back skin biopsies were taken 4, 8, 12 and 16 weeks after initiation of exposure, and stained for Melan-A, representing a highly selective marker for melanocytes. Surprisingly, after exposure to UVR, Melan-A positive cells were detected also in the interfollicular epidermis of C57BL/6 mice. We conclude that UVR is capable of inducing interfollicular epidermal melanocytes in wild-type mice.

The exact correlation between melanoma and sun-light is still a controversially debated issue. Although natural sunlight contains various ratios of UVA and UVB, most investigators so far focused on the effects of single solar wavebands and neglected possible interactions. Therefore, in this study primary human melanocytes of three donors were simultaneously exposed to physiologic doses of UVA1 and UVB. Effects on apoptosis were analysed using annexin V assays and cell death ELISAs, and effects on DNA damage were investigated using southwestern slot blots. While UVA1 did not influence UVB-induced apoptosis, UVA1 impaired the repair of UVB-induced cyclobutane pyrimidine dimers (CPD) as the amount of CPD was 1.8 times higher in UVA1 + UVB than in UVB only exposed melanocytes six hours after irradiation. We conclude that UVA1 might contribute to melanomagenesis as it partially inhibits the repair of UVB-induced CPD in human melanocytes while it does not affect UVB-mediated apoptosis., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The link between solar radiation and melanoma is still elusive. Although infrared radiation (IR) accounts for over 50% of terrestrial solar energy, its influence on human skin is not well explored. There is increasing evidence that IR influences the expression patterns of several molecules independently of heat. A previous in vivo study revealed that pretreatment with IR might promote the development of UVR-induced non-epithelial skin cancer and possibly of melanoma in mice. To expand on this, the aim of the present study was to evaluate the impact of IR on UVR-induced apoptosis and DNA repair in normal human epidermal melanocytes. The balance between these two effects is a key factor of malignant transformation. Human melanocytes were exposed to physiologic doses of IR and UVR. Compared to cells irradiated with UVR only, simultaneous exposure to IR significantly reduced the apoptotic rate. However, IR did not influence the repair of UVR-induced DNA damage. IR partly reversed the pro-apoptotic effects of UVR via modification of the expression and activity of proteins mainly of the extrinsic apoptotic pathway. In conclusion, IR enhances the survival of melanocytes carrying UVR-induced DNA damage and thereby might contribute to melanomagenesis., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Extracorporeal photopheresis (ECP) improves skin sclerosis in systemic sclerosis (SSc) patients. SSc is associated with an increased risk of lung cancer. As ECP is supposed to exert immunomodulatory effects, a possible impact of ECP on the incidence of lung cancer in SSc patients was evaluated., Methods: Seventy-one SSc patients treated with ECP at the Photopheresis Unit of the Department of Dermatology at the Medical University of Vienna between 1991 and 2013 were analyzed retrospectively., Results: We calculated a standardized incidence ratio (SIR) for lung cancer in ECP-treated SSc patients of 2.34 [95% confidence interval (CI) 1.63-2.49]. This is in accordance with recent meta-analyses demonstrating a significantly enhanced risk of lung carcinoma in SSc patients. Comparison of the lung cancer risks of these patients with our ECP-treated patients revealed that ECP has no influence. Each patient with lung carcinoma had previously been diagnosed with lung involvement of the non-specific interstitial pneumonitis (NSIP) type., Conclusion: We confirm that SSc patients are at significantly increased risk for lung cancer. However, ECP does not influence this risk. NSIP may be a risk factor for lung cancer in SSc patients., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Induction of DNA damage by UVR is the key event in photocarcinogenesis. IL-12 and IL-23 are related heterodimeric cytokines consisting of a common p40 unit and a p35/IL-12 and a p19/IL-23 chain, respectively. Both exert immunomodulatory activities but are also found to reduce UVR-induced DNA damage presumably via induction of DNA repair. As both cytokines are also produced in the skin, they may mitigate the risk to develop UVR-induced skin cancer. This appears to be the case as mice lacking p40 were previously shown to be at higher risk for skin tumors upon chronic UVR exposure. As these mice express neither IL-12 nor IL-23, the individual effects of IL-12 or IL-23 could not be evaluated. Thus, mice lacking p35 (IL-12p35-/-) or p19 (IL-23p19-/-) were subjected to chronic UVR exposure. The Kaplan-Meier analysis indicated a significantly increased probability of tumor development in IL-23p19-/- but not in IL-12p35-/- mice. Taken together, in our model, loss of IL-23, but not of IL-12, enhances development of UVR-induced skin tumors, indicating that IL-23 but not IL-12 may counteract photocarcinogenesis. This may have impact on the development of future strategies utilizing antibodies against IL-12 and IL-23, respectively, for the treatment of inflammatory dermatoses.

Several lines of evidence suggest that besides antioxidant also prooxidant properties are crucially involved in cytotoxic and protective activities of the major green tea catechin epigallocatechin-3-gallate (EGCG) in vitro (Elbling et al., 2011). Furthermore recent data suggest that EGCG induces oxidative stress also in vivo (Li et al., 2010). Here we set out to identify factors modulating cellular effects of EGCG in vitro. Using the HaCat keratinocytes model, we demonstrate that the cytotoxic, genotoxic and signal-activating effects of EGCG are significantly dependent on the ratio of cell number to working volume. Treatment with identical EGCG concentrations at altered experimental settings resulted in IC(50) values differing up to orders of magnitude and could even exert contradictory effects. This effect was based on cell-mediated clearance of autooxidation-derived H(2)O(2) from the supernatant. In order to estimate EGCG/H(2)O(2) concentrations equally effective under different settings, we have rationally derived and experimentally verified a simple algorithm relating concentration, working volume, cell number and - indirectly - exposure time. Algorithm application resulted in similar H(2)O(2) clearance curves from cell supernatants as well as comparable EGCG/H(2)O(2) effects at different settings. Our results demonstrate the importance of standardized experimental settings when investigating cytotoxic and/or beneficial effects of autooxidizing compounds., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

There is increasing concern about the interaction between infrared radiation (IR) and ultraviolet radiation (UVR) with regard to carcinogenesis because prolonged solar exposure is associated with an increased cumulative load not only of UVR but also of IR. We recently demonstrated that IR-pretreatment reduces UVR-induced apoptosis. As this might support the survival of UVR-damaged cells and thus carcinogenesis, we performed an in vivo photocarcinogenesis study. One group of mice were treated with IR prior to each UVR exposure; additional groups were treated with IR or UVR alone. IR alone did not induce skin cancer. UVR-induced tumor formation was not enhanced in IR-pretreated mice, but, in contrast, seemed to occur with delay. This correlated with a reduction of p53 mutated clones in the skin. However, once developed, tumors in IR-pretreated mice grew faster which was confirmed by their enhanced Ki-67 expression. The enhanced aggressiveness of tumors derived from IR-pretreated mice was associated with a higher prevalence of sarcomas than epithelial tumors. Hence, the impact of IR on UVR-induced carcinogenesis has to be interpreted with caution. Although IR may delay the onset of UVR-induced tumors, it might contribute to a worse outcome by shifting these tumors into a more aggressive phenotype., (© 2011 John Wiley & Sons A/S.)

The beneficial health effects of (-)-epigallocatechin-3-gallate (EGCG), the main catechin of green tea, have been attributed to complex interactions with a focus on antioxidative properties. Susceptibility to autoxidation and production of cytotoxic reactive oxygen species (ROS), mostly H(2)O(2), have been suggested to occur in vitro but also in vivo. In this study, we address whether autoxidation-derived H(2)O(2) may be involved in the cytoprotective effects of EGCG. To that end we investigated keratinocyte-derived HaCat and HL-60 promyelocytic leukemia cells with significantly different sensitivities to H(2)O(2) (IC(50) 117.3 versus 58.3 μM, respectively) and EGCG (134.1 versus 84.1 μM). HaCat cells significantly resisted cytotoxicity and DNA damage based on enhanced H(2)O(2) clearance, improved DNA repair, and reduced intracellular ROS generation. Cumulative versus bolus EGCG and H(2)O(2) treatment and H(2)O(2) pretreatment before subsequent high-dose EGCG and vice versa significantly reduced DNA damage and cytotoxicity in HaCat cells only. Addition of catalase abolished the protective activities of low-dose H(2)O(2) and EGCG. In summary, our data suggest that autoxidative generation of low-dose H(2)O(2) is a significant player in the cell-type-specific cytoprotection mediated by EGCG and support the hypothesis that regular green tea consumption can contribute as a pro-oxidant to increased resistance against high-dose oxidative stressors., (Copyright © 2010 Elsevier Inc. All rights reserved.)

UVR-induced DNA damage is the major molecular trigger for photoimmunosuppression. The cytokines IL-12 and IL-18, which reduce DNA damage through induction of DNA repair, prevent UVR-induced immunosuppression. IL-12 but not IL-18 can break established UVR-induced immunotolerance through modulation of regulatory T cells (Treg). IL-23 is related to IL-12 by sharing the p40 subunit. Hence, we studied whether (i) IL-23 can reduce UVR-induced DNA damage and thereby prevent UVR-induced immunosuppression and (ii) can suppress the activity of Treg. IL-23 reduced UVR-induced apoptosis of keratinocytes. Injection of IL-23 into UVR-exposed mice diminished the number of apoptotic keratinocytes and the amounts of DNA damage. This was not observed in DNA repair-deficient xeroderma pigmentosum A knock-out mice (Xpa-KO mice), implying that IL-23 reduces DNA damage through induction of DNA repair. Similarly, UVR-mediated suppression of the induction of contact hypersensitivity was prevented on injection of IL-23 in wild-type but not in Xpa-KO mice. However, in contrast to IL-18, IL-23 inhibited the activity of UVR-induced Treg as demonstrated by adoptive transfer experiments. Our data indicate that IL-23, similar to IL-12 and IL-18, can reduce UVR-induced DNA damage and thereby prevent immunosuppression. IL-23 shares with IL-12 the still unique capacity to restore suppressed immune responses because of its effect on Treg.

Background: Suppression of the adaptive immune system by UV radiation plays an important role in photocarcinogenesis. Exacerbation of skin infections has been proposed as a further consequence of UV-induced immunosuppression. Clinically bacterial infections are not a problem. For defense against bacteria, the innate immune response including the release of antimicrobial peptides is much more relevant than the adaptive immune response. Keratinocytes have the capacity to release antimicrobial peptides., Objective: We asked whether UV radiation induces antimicrobial peptides in vitro and in vivo., Methods: Antimicrobial peptide expression by normal human keratinocytes was measured by real-time PCR and fluorescence-activated cell sorting analysis. Biopsies taken from human volunteers and skin explants were studied with immunohistochemistry., Results: Real-time PCR of normal human keratinocytes revealed a dose-dependent increase of human beta-defensin-2, -3, ribonuclease 7, and psoriasin (S100A7) after UV radiation. This was confirmed at the protein level by intracellular fluorescence-activated cell sorting and in vitro immunofluorescence analysis. Immunohistochemistry of biopsies taken from healthy volunteers exposed to different UV radiation doses revealed enhanced epidermal expression of antimicrobial peptides after UV exposure. This was also confirmed by exposing human skin explants to UV radiation., Conclusion: UV radiation exerts diverse effects on the immune system, suppressing the adaptive but inducing the innate immune response. This may explain why T-cell-mediated immune reactions are suppressed on UV exposure but not host defense reactions against bacterial attacks.

Infrared radiation (IR) is increasingly used for wellness purposes. In this setting, it is frequently combined with UV radiation, primarily for tanning purposes. The impact of IR on UV-induced carcinogenesis is still unclear. Hence, we investigated the interplay between IR and UV with regard to UV-induced apoptosis. Pretreatment of murine keratinocytes with IR before UV reduced the apoptotic rate. Likewise, the number of sunburn cells was reduced in mice preexposed to IR before UV. The amounts of UV-induced DNA damage were reduced by IR both in vitro and in vivo. This was not observed in DNA repair-deficient mice. UV-induced downregulation of the antiapoptotic proteins FLIP(L) and BCL-X(L) was prevented by IR, whereas the proapoptotic protein BAX was downregulated. These data indicate that IR reduces UV-induced apoptosis that may be mediated by several pathways, including reduction of DNA damage and induction of antiapoptotic proteins. The antiapoptotic effects of IR may support the survival of UV-damaged cells and thus carcinogenesis. As, however, IR reduces UV-induced DNA damage, the balance between these two effects may be important. Thus, in vivo carcinogenesis studies are required to define the role of IR and its interaction with UV in photocarcinogenesis.

Background: Since 2003, an ongoing outbreak of lymphogranuloma venereum (LGV), caused by Chlamydia trachomatis biovar L2b, has been reported among men who have sex with men., Methods: Twenty-four samples positive for C. trachomatis were analyzed for specific biovars and genovariants by genotyping of the variable segment (VS) 4, VS2 and VS1 regions of the outer membrane protein (omp) A. In addition we assessed the patients' sociodemographic background and clinical signs and symptoms., Results: Twenty-four men who have sex with men presented with either anorectal or inguinal symptoms and tested positive for C. trachomatis DNA. Of these, the L2 genotype accounted for 15 patients, with a high coinfection rate with HIV (73.3%) and other sexually transmitted infections (53.4%). Analysis of the VS1, VS2, and VS4 regions of the ompA gene revealed the variant L2b in 8 patients. In 4 patients, 3 new L2 sequences were identified with nucleotide changes in the VS1, VS2, and VS4 region, respectively, defining new strains designated L2c, d, e., Conclusions: This outbreak of LGV represents the further spread of C. trachomatis L2 infection. Sequence analysis of ompA regions shows heterogeneity of L2 variants, suggesting more than 1 source of the LGV infections diagnosed in Vienna.

The 25-kDa heat shock protein (Hsp25) is associated with various malignancies and is expressed at high levels in biopsies as well as circulating in the serum of breast cancer patients. In this study, we used RNA interference technology to silence the hsp25 gene in 4T1 breast adenocarcinoma cells, known as a poorly immunogenic, highly metastatic cell line. We demonstrate that transfection of 4T1 cells with short interference RNA-Hsp25 dramatically inhibits proliferation as compared with control transfected cells. In addition, we show that 4T1 cells transfected with short interference RNA-Hsp25 abrogates tumor migration potential by a mechanism that is in part due to the repression of matrix metalloproteinase 9 expression and a concomitant upregulation of its antagonist, tissue inhibitor metalloproteinase 1. Taken together, these findings provide a model system for the study of metastatic potential of tumors and are suggestive of an earlier unrecognized role for Hsp25 in tumor migration., (Copyright 2006 S. Karger AG, Basel.)

There is evidence that heat pre-treatment protects cultured human keratinocytes and normal murine and human skin from ultraviolet (UV) radiation-induced cell death. It has been suggested that heat-shock proteins (hsps), particularly hsp72, are involved in this effect. Hsps are expressed in response to various types of stress, such as UV radiation. Whether heat shock interferes with the repair of UV-induced DNA damage and whether this can be regarded as a protective mechanism is poorly understood and needs further experimental investigation. This review gives an overview of the current state of research in the area.

We describe a patient with therapy-resistant cutaneous T-cell lymphoma, Sézary syndrome variant, in association with concurrent polyarthritis and vitiligo, who was successfully treated with extracorporeal photochemotherapy (ECP). The combination of Sézary syndrome with seronegative rheumatoid arthritis is rare. In our patient the T-cell lymphoma was refractory to standard treatments that included psoralen-UVA, lymph node irradiation, and polychemotherapy. ECP has been shown to be effective in the treatment of selected cases of Sézary syndrome. There is a strong suggestion that ECP as a monotherapy can provide a significant benefit for other T-cell-mediated diseases including rheumatoid arthritis. In spite of a disease duration of 10 years, a very low CD8 cell count (2% of lymphocytes), a very high CD4 cell count (94%), and multiple unsuccessful chemotherapeutic trials before initiation of ECP, our patient achieved a long-lasting complete remission of both diseases with normalization of the CD4+ and CD8+ T-lymphocyte subsets. Concurrent developing vitiligo was unaffected by ECP.

In the present study we used a murine melanoma model to investigate the effect of the 25-kDa heat shock protein (Hsp25) on natural killer (NK) cytotoxicity. The melanoma lines K1735-C123 (low metastatic potential) and K1735-M2 (high metastatic potential) were transfected with hsp25 and a control plasmid. Highly purified interleukin (IL)-2-stimulated DX-5+ NK cells showed enhanced lysis of Hsp25-overexpressing K1735-C123 targets in comparison with controls. In contrast, there was no difference in susceptibility to lysis by purified IL-2-stimulated DX-5+ NK cells between Hsp25-overexpressing and control-transfected K1735-M2 targets. Fluorescence-activated cell sorter analysis revealed that Hsp25 is displayed on the cell surface independently of Hsp25 overexpression and metastatic phenotype. Thus, surface localization of Hsp25 does not correlate with the target cell susceptibility to killing. To sum up, a cytoplasmic overexpression of Hsp25 is associated with an increased susceptibility to lysis by DX-5+ NK cells in the low-metastatic murine melanoma model investigated.

In the present communication, the role of the M(r) 27,000 human small heat shock protein (hsp27) in tumorigenicity was examined. Stable transfectants of a melanoma cell line (A375) and an epidermal squamous carcinoma cell line (A431), isolated by cotransfection of a hsp27 expression vector (pSG-2711) and a neomycin-resistant plasmid, were obtained. Clones expressing high levels of hsp27 were analyzed using immunohistochemistry and immunoblotting. Cells transfected with only the plasmid for neomycin were used as control cells. Growth analysis of transfectants in A375 and A431 tumor cells showed in vitro a lower proliferation rate than control clones derived from both lines. To investigate the correlation of hsp27 expression and tumorigenicity, transfectants of each cell type and control cells were injected into nude mice. A delay in tumor development was detected in animals inoculated with cells overexpressing hsp27. However, after this initial delay, tumors appeared in some of these animals and no difference could be observed in their growth dynamics compared to control tumors. When tumors transfected with the hsp27 construct were analyzed using immunohistochemistry and PCR, no evidence for hsp27 expression was obtained which implicates instability of the transduced foreign DNA when maintained under nonselective conditions. The present study shows that genetic manipulation of tumor cells may provide valuable information on the role of hsp27 in tumor growth.