Chemokines in cancer

Current view of the role of transforming growth factor beta 1 in skin carcinogenesis

Previously, we have shown that transforming growth factor beta 1 (TGFbeta1) overexpression in suprabasal epidermis suppresses skin carcinogenesis at early stages, but promotes tumor invasion at later stages. To elucidate the role of TGFbeta1 overexpression in naturally occurring human squamous cell carcinomas (SCC), we screened TGFbeta1 expression patterns in human skin SCC samples and found that TGFbeta1 was overexpressed with two distinct patterns: either predominantly in suprabasal layers or throughout tumor epithelia including basal proliferative cells. To determine the effect of TGFbeta1 overexpression in basal keratinocytes, we generated transgenic mice expressing wild-type TGFbeta1 in basal keratinocytes and hair follicles using the K5 promoter (K5.TGFbeta1(wt)). Surprisingly, these mice developed a severe inflammatory skin disorder. Inflammation was also observed in head and neck tissue when TGFbeta1 transgene expression was inducibly expressed in head and neck epithelia in our gene-switch-TGFbeta1 transgenic mice. Given the importance of inflammation in cancer development, our data suggest that TGFbeta1-induced inflammation may override its tumor-suppressive effect even at early stages of skin carcinogenesis. This notion is further suggested by our recent study that Smad3 knockout mice were resistant to skin chemical carcinogenesis at least in part via abrogation of endogenous TGFbeta1-induced inflammation.

Stromal cell-derived factor-1 (SDF-1) alleles and susceptibility to breast carcinoma

Stromal cell-Derived Factor-1 (SDF-1, CXCL12) is one the ELR- CXC angiogenic chemokines. It contributes to hematopoiesis and lymphocyte trafficking. SDF-1 and its exclusive receptor, CXCR4, are reported to play important roles in tumor growth, angiogenesis and metastasis of different types of tumors such as breast, lung, prostate and pancreatic cancers. SDF-1 gene polymorphism, known as SDF1-3'A, has been investigated in HIV-1 infection and the incidence of breast cancer. This investigation was aimed to study the frequency of SDF1-3'A mutation in Iranian women with breast cancer. Results showed that the frequency of AA and AG genotypes was higher among patients, while the frequency of GG genotype was lower compared to the controls. Thus AA and AG genotypes of SDF-1 may be considered as factors increasing the susceptibility of Iranian women to breast cancer.

Expression of chemokine receptor CXCR4 in nasopharyngeal carcinoma: pattern of expression and correlation with clinical outcome

Nasopharyngeal carcinoma (NPC) is a tumor derived from epithelial cells and Epstein-Barr virus infection has been reported to be a cause of this disease. Chemokine receptor CXCR4 was found to be involved in HIV infection and was highly expressed in human malignant breast tumors and the ligand for CXCR4, CXCL12 (SDF-1), exhibited high expression in organs in which breast cancer metastases are often found. The metastatic pattern of NPC is quite similar to that of malignant breast tumors. In this study, we investigated the expression of CXCR4 in nasopharyngeal carcinoma (NPC) tissues by immunohistostaining. We found different staining patterns, which included localization in the nucleus, membrane, cytoplasm or a combination of them. The staining intensity was also variable among samples. The metastatic rates in patients with high compared to low or absent expression was 38.6% versus 19.8%, respectively (P = 0.004). High expression of CXCR4 was associated with poor overall survival (OS = 67.05% versus 82.08%, P = 0.0225). These results suggest that CXCR4 may be involved in the progression of NPC and that a high level of CXCR4 expression could be used as a prognostic factor.

CXC chemokine ligand 12 (stromal cell-derived factor 1 alpha) and CXCR4-dependent migration of CTLs toward melanoma cells in organotypic culture

Studies in experimental animal models have demonstrated that chemokines produced by tumor cells attract chemokine receptor-positive T lymphocytes into the tumor area, which may lead to tumor growth inhibition in vitro and in vivo. However, in cancer patients, the role of chemokines in T lymphocyte trafficking toward human tumor cells is relatively unexplored. In the present study, the role of chemokines and their receptors in the migration of a melanoma patient's CTL toward autologous tumor cells has been studied in a novel organotypic melanoma culture, consisting of a bottom layer of collagen type I with embedded fibroblasts followed successively by a tumor cell layer, collagen/fibroblast separating layer, and, finally, a top layer of collagen with embedded fibroblasts and T cells. In this model, CTL migrated from the top layer through the separating layer toward tumor cells, resulting in tumor cell apoptosis. CTL migration was mediated by chemokine receptor CXCR4 expressed by the CTL and CXCL12 (stromal cell-derived factor 1alpha) secreted by tumor cells, as evidenced by blockage of CTL migration by Abs to CXCL12 or CXCR4, high concentrations of CXCL12 or small molecule CXCR4 antagonist. These studies, together with studies in mice indicating regression of CXCL12-transduced tumor cells, followed by regression of nontransduced challenge tumor cells, suggest that CXCL12 may be useful as an immunotherapeutic agent for cancer patients, when transduced into tumor cells, or fused to anti-tumor Ag Ab or tumor Ag.

Soluble mediators of inflammation during tumor development

Tissues maintain homeostasis by monitoring and responding to varied physical interactions between cells and their microenvironment. In situations where acute tissue damage occurs, such as wounding, pathogenic assault, or toxic exposure, regulatory circuits that monitor tissue homeostasis are rapidly engaged to initiate tissue repair by regulating cell polarity, proliferation and death, matrix metabolism, inflammation, and vascular and lymphatic function. The critical feature of regulating these acute responses is the innate ability to discriminate between homeostatic versus damaged tissue states and engage or disengage regulatory machinery as appropriate; thus, a major distinction between acute versus chronic disease is the altered ability to appropriately activate and?or inactivate reparative regulatory programs. Since cancer is a chronic disease characterized by altered cell polarity, enhanced cell survival, inflammation, increased matrix metabolism, and enhanced vascular and lymphatic function, considerable attention is now focused on understanding the cellular and molecular mechanisms regulating these responsive pathways. Since chemoattractant cytokines are important mediators of leukocyte recruitment following acute tissue stress, and demonstrate altered characteristics of expression and activation in chronically inflamed tissue, they have been implicated as key regulators of inflammation and angiogenesis during cancer development. This chapter focuses on the clinical and experimental data implicating proinflammatory cytokines and chemokines as important potentiators of carcinogenesis.

Chemokines in tumor progression and metastasis

Although chemokines have been thought of primarily as leukocyte attractants, a growing body of evidence indicates that they also contribute to a number of tumor-related processes, such as tumor cell growth, angiogenesis/angiostasis, local invasion, and metastasis. The current knowledge of the possible involvement of chemokines and their receptors in these cellular events are reviewed here. The operating mechanism of chemokines in relation to metastatic processes in vivo are also discussed.

The role of interleukin-8 and its receptors in gliomagenesis and tumoral angiogenesis

Interleukin-8 (IL-8, or CXCL8), which is a chemokine with a defining CXC amino acid motif that was initially characterized for its leukocyte chemotactic activity, is now known to possess tumorigenic and proangiogenic properties as well. In human gliomas, IL-8 is expressed and secreted at high levels both in vitro and in vivo, and recent experiments suggest it is critical to glial tumor neovascularity and progression. Levels of IL-8 correlate with histologic grade in glial neoplasms, and the most malignant form, glioblastoma, shows the highest expression in pseudopalisading cells around necrosis, suggesting that hypoxia/anoxia may stimulate expression. In addition to hypoxia/anoxia stimulation, increased IL-8 in gliomas occurs in response to Fas ligation, death receptor activation, cytosolic Ca(2+), TNF-alpha, IL-1, and other cytokines and various cellular stresses. The IL-8 promoter contains binding sites for the transcription factors NF-kappaB, AP-1, and C-EBP/NF-IL-6, among others. AP-1 has been shown to mediate IL-8 upregulation by anoxia in gliomas. The potential tumor suppressor ING4 was recently shown to be a critical regulator of NF-kappaB-mediated IL-8 transcription and subsequent angiogenesis in gliomas. The IL-8 receptors that could contribute to IL-8-mediated tumorigenic and angiogenic responses include CXCR1 and CXCR2, both of which are G-protein coupled, and the Duffy antigen receptor for cytokines, which has no defined intracellular signaling capabilities. The proangiogenic activity of IL-8 occurs predominantly following binding to CXCR2, but CXCR1 appears to contribute as well through independent, small-GTPase activity. A precise definition of the mechanisms by which IL-8 exerts its proangiogenic functions requires further study for the development of effective IL-8-targeted therapies.

Hypoxia, leukocytes, and the pulmonary circulation

Data are rapidly accumulating in support of the idea that circulating monocytes and/or mononuclear fibrocytes are recruited to the pulmonary circulation of chronically hypoxic animals and that these cells play an important role in the pulmonary hypertensive process. Hypoxic induction of monocyte chemoattractant protein-1, stromal cell-derived factor-1, vascular endothelial growth factor-A, endothelin-1, and tumor growth factor-beta(1) in pulmonary vessel wall cells, either directly or indirectly via signals from hypoxic lung epithelial cells, may be a critical first step in the recruitment of circulating leukocytes to the pulmonary circulation. In addition, hypoxic stress appears to induce release of increased numbers of monocytic progenitor cells from the bone marrow, and these cells may have upregulated expression of receptors for the chemokines produced by the lung circulation, which thus facilitates their specific recruitment to the pulmonary site. Once present, macrophages/fibrocytes may exert paracrine effects on resident pulmonary vessel wall cells stimulating proliferation, phenotypic modulation, and migration of resident fibroblasts and smooth muscle cells. They may also contribute directly to the remodeling process through increased production of collagen and/or differentiation into myofibroblasts. In addition, they could play a critical role in initiating and/or supporting neovascularization of the pulmonary artery vasa vasorum. The expanded vasa network may then act as a conduit for further delivery of circulating mononuclear cells to the pulmonary arterial wall, creating a feedforward loop of pathological remodeling. Future studies will need to determine the mechanisms that selectively induce leukocyte/fibrocyte recruitment to the lung circulation under hypoxic conditions, their direct role in the remodeling process via production of extracellular matrix and/or differentiation into myofibroblasts, their impact on the phenotype of resident smooth muscle cells and adventitial fibroblasts, and their role in the neovascularization observed in hypoxic pulmonary hypertension.

Chemokines bind to sulfatides as revealed by surface plasmon resonance

Chemokines bind to sulfated cell surface glycosaminoglycans and thereby modulate signaling mediated by G-protein-coupled seven-transmembrane domain chemokine receptors. Similar to glycosaminoglycans, sulfated oligosaccharides are also exposed on the cell surface by sulfatides, a class of glycosphingolipids. We have now identified sulfated glycosphingolipids (sulfatides) as novel binding partners for chemokines. Using surface plasmon resonance (SPR), the binding of proinflammatory and homeostatic chemokines to glycosphingolipids, in particular sulfatides, was investigated. Chemokines were immobilized while glycosphingolipids or additional phospholipids incorporated into liposomes were applied as soluble analytes. A specific affinity of the chemokines MCP-1/CCL2, IL-8/CXCL8, SDF-1alpha/CXCL12, MIP-1alpha/CCL3 and MIP-1beta/CCL4 to the sulfatides SM4s, SM3, SM2a and SB2, SB1a was detected. No significant interactions with the chemokines were observed for gangliosides, neutral glycosphingolipids or phospholipids. Chemokine receptors have been associated with the detergent-insoluble fraction supposed to contain 'rafts', i.e., glycosphingolipid enriched microdomains of the cell surface. Accordingly, the data suggest that early chemokine receptor signaling may take place in the vicinity of sulfated glycosphingolipids on the cell surface, whereby these sulfatides could modulate the chemokine receptor-mediated cell activation signal.

CXCR4 expression reflects tumor progression and regulates motility of bladder cancer cells

Transitional cell carcinoma of the urinary bladder remains life threatening due to the high occurrence of metastases. Emerging evidence suggests that chemokines and their receptors play a critical role in tumor metastases. In our study, we performed a systematic analysis of the mRNA and protein expression levels of all 18 chemokine receptors in normal urothelium and bladder cancer. CXCR4 was the only chemokine receptor whose mRNA expression level was upregulated in bladder cancer cell lines as well as in invasive and locally advanced bladder cancer tissue samples (pT2-pT4). In contrast, superficial bladder tumors (pTa and pT1) displayed low CXCR4 expression levels and normal urothelial cells were negative for CXCR4. Immunohistochemistry of a bladder cancer tissue microarray (TMA) confirmed that a subgroup of invasive bladder cancers revealed a high CXCR4 protein expression, while superficial bladder tumors showed low immunoreactivity. To investigate the functional significance of CXCR4 expression, we performed migration and invasion assays. Exposure of CXCR4-positive bladder cancer cells to CXCL12 in a Boyden chamber type assay provoked a significant increase in migration as well as invasion across a Matrigel barrier. Enhanced migration and invasion were inhibited by a CXCR4-specific blocking antibody. In contrast, normal urothelial cells did not respond to CXCL12 and lacked chemotactic migration. In conclusion, bladder cancer cells express CXCR4 progressively with advanced tumorigenesis and this receptor interacts with CXCL12 to mediate tumor chemotaxis and invasion through connective tissue. These properties identify CXCR4 as a potential target for the attenuation of bladder cancer metastases.

A novel expression of macrophage derived chemokine in human bladder cancer

PURPOSE

Successful bacillus Calmette-Guerin (BCG) immunotherapy for bladder cancer is associated with proper induction of T helper (Th)1 immunity. Unfortunately, 30% to 40% of bladder tumors never respond to BCG. We sought evidence of antagonistic Th2 chemokine production by bladder tumors as a potential cause of BCG nonresponsiveness.

MATERIALS AND METHODS

Expression of interferon-gamma inducible protein-10 (IP-10), a Th1 chemokine, and macrophage derived chemokine (MDC), a Th2 chemokine, was examined in 9 clinical bladder tumor specimens and 7 human bladder cancer lines by sandwich enzyme-linked immunosorbent assay, immunohistochemistry and immunofluorescence. Regulation of these chemokine expressions in the human RT4 bladder cancer line was also explored by reverse transcription-polymerase chain reaction and electrophoretic mobility shift assay.

RESULTS

Eight of 9 clinical specimens expressed IP-10 and 5 expressed MDC. However, of 7 cancer lines only 1 low grade line (RT4) expressed IP-10 and MDC, and 1 high grade line (T24) expressed IP-10. Histological staining demonstrated MDC and IP-10 expression in human bladder tumors. Interestingly interferon-gamma and tumor necrosis factor-alpha up-regulated and synergized the expression of these 2 chemokines in RT4 cells. Such positive effects appeared to be mediated by nuclear factor-kappaB but not by the AP-1 signaling pathway.

CONCLUSIONS

These results indicate that certain bladder tumors produce the Th2 chemokine MDC, which may antagonize the local Th1 environment induced by BCG. MDC production by bladder tumors appears to be mediated by signals distinct from those identified in macrophages.

GCP-2/CXCL6 synergizes with other endothelial cell-derived chemokines in neutrophil mobilization and is associated with angiogenesis in gastrointestinal tumors

The precise role of chemokines in neovascularization during inflammation or tumor growth is not yet fully understood. We show here that the chemokines granulocyte chemotactic protein-2 (GCP-2/CXCL6), interleukin-8 (IL-8/CXCL8), and monocyte chemotactic protein-1 (MCP-1/CCL2) are co-induced in microvascular endothelial cells after stimulation with pro-inflammatory stimuli. In contrast with its weak proliferative effect on endothelial cells, GCP-2 synergized with MCP-1 in neutrophil chemotaxis. This synergy may represent a mechanism for tumor development and metastasis by providing efficient leukocyte infiltration in the absence of exogenous immune modulators. To mimic endothelial cell-derived GCP-2 in vivo, GCP-2 was intravenously injected and shown to provoke a dose-dependent systemic response, composed of an immediate granulopenia, followed by a profound granulocytosis. By immunohistochemistry, GCP-2 was further shown to be expressed by endothelial cells from human patients with gastrointestinal (GI) malignancies. GCP-2 staining correlated with leukocyte infiltration into the tumor and with the expression of the matrix metalloproteinase-9 (MMP-9/gelatinase B). Together with previous findings, these data suggest that the production of GCP-2 by endothelial cells within the tumor can contribute to tumor development through neovascularization due to endothelial cell chemotaxis and to tumor cell invasion and metastasis by attracting and activating neutrophils loaded with proteases that promote matrix degradation.

The Δ32 allele distribution of the CCR5 gene and its relationship with certain cancers in a Turkish population

OBJECTIVE

In the present study, we determined the frequency of delta32 allele distribution and its relationship with various carcinomas in a Turkish population.

DESIGN AND METHODS

We determined the allelic frequency of CCR5-delta32 in 267 healthy individuals as well as 39 breast, 34 laryngeal, 30 thyroid and 20 brain carcinomas in a Turkish population using polymerase chain reaction (PCR).

RESULTS

The frequency of mutant delta32 alleles in the Turkish population was 2.18%. The population was in the Hardy-Weinberg equilibrium. The frequency of the mutant allele was the highest in patients with breast carcinoma (3.85%) among all the carcinomas studied, but there was no statistically significant relationship (P = 0.334).

CONCLUSION

The frequency of the delta32 allele detected in the Turkish population was slightly lower in comparison with the previous reports. The frequency of heterozygote genotypes remained an independent risk factor for the development of breast cancer (odd ratio = 1.628; confidence intervals = 0.442-5.992) as well as other cancers examined in this study.

Up-regulation of the interferon gamma (IFN-gamma)-inducible chemokines IFN-inducible T-cell alpha chemoattractant and monokine induced by IFN-gamma and of their receptor CXC receptor 3 in human renal cell carcinoma

BACKGROUND

The antiangiogenic CXC chemokines interferon gamma (IFN-gamma)-inducible T-cell alpha chemoattractant (I-TAC) and monokine induced by IFN-gamma (Mig) are known as members of IFN-gamma-inducible antiangiogenic CXC chemokines. However, the expression of these chemokines in highly angiogenic tumors remains poorly understood. The authors examined expression of I-TAC, Mig, and their receptor, CXCR3, in tissue samples from patients with renal cell carcinoma (RCC).

METHODS

Twenty-one samples of untreated RCC and corresponding normal renal tissues were obtained from surgical specimens. The expression levels of I-TAC, Mig, and CXCR3 were investigated using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, real-time RT-PCR analysis, and Western blot analysis. Immunohistochemistry was carried out to clarify the localization of both chemokines and of CXCR3.

RESULTS

RT-PCR analysis showed strong expression levels of I-TAC, Mig, and CXCR3 in RCC tissues and very weak or undetectable expression in normal kidney tissues. Real-time RT-PCR analysis showed that expression levels of I-TAC, Mig, and CXCR3 in RCC tissues were 14.9 times greater, 30.3 times greater, and 9.9 times greater compared with the levels in the corresponding normal kidney tissues, respectively (P < 0.01). Western blot analysis showed up-regulation of I-TAC, Mig, and CXCR3 at the protein level. Immunofluorescence double stainings revealed that I-TAC coincided with pericytes and vascular smooth muscle cells (VSMCs) in tumor angiogenic vessels. Mig was detected in tumor endothelial cells (TECs) and in infiltrating leukocytes. In the corresponding normal kidney tissues, neither VSMCs nor endothelial cells showed positive stainings for these chemokines. CXCR3 was expressed in both tumor cells and infiltrating leukocytes.

CONCLUSIONS

The results revealed special feature of vascular mural cells and TECs in RCC. The up-regulated I-TAC and Mig, produced by tumor vessels, may interact with CXCR3 expressed in tumor cells, with possible pathophysiologic significance in RCC progression.

Molecular investigation of the stromal cell-derived factor-1 chemokine in lymphoid leukemia and lymphoma patients from Brazil

The stromal cell-derived factor-1 (SDF-1) gene contains a common polymorphism, termed SDF1-3'A, in an evolutionarily conserved segment of the 3'-untranslated region (3'-UTR). We compared SDF-1 genotypes in patients diagnosed with lymphoid leukemias and lymphomas. Since the SDF1-3'A variant deletes the MspI restriction site, PCR-restriction fragment length polymorphism (RFLP) analysis was used for identification of genotypes. We identified the heterozygous genotype (3'A/wt) in 38.8% (24/62) of lymphoma patients and in 26.2% (11/42) of lymphoid leukemias. The percentage of 3'A carriers was significantly higher in lymphomas (43.5%) than in lymphoid leukemias (26.2%; P < 0.05). Our study indicates that lymphoma patients from Brazil are more likely to carry the 3'A gene than patients with lymphoid leukemias, suggesting that this polymorphism may be a differential determinant of lymphomas and lymphoid leukemia.

Chemokines in the recruitment and shaping of the leukocyte infiltrate of tumors

Leukocytes, and macrophages in particular, are an important component of the stroma of neoplastic tissues. Tumor-associated macrophages (TAM) have the properties of a polarized M2 population and are a key component of inflammatory circuits which promote tumor growth and progression. Chemokines play a key role in the recruitment and positioning of TAM and dendritic cells in tumors and contribute to shaping their functional properties. Chemokine-recruited and positioned tumor infiltrating leukocytes are a key component of inflammatory circuits which promote tumor progression.

Susceptibility to neoplastic and non-neoplastic pulmonary diseases in mice: genetic similarities

Chronic inflammation predisposes toward many types of cancer. Chronic bronchitis and asthma, for example, heighten the risk of lung cancer. Exactly which inflammatory mediators (e.g., oxidant species and growth factors) and lung wound repair processes (e.g., proangiogenic factors) enhance pulmonary neoplastic development is not clear. One approach to uncover the most relevant biochemical and physiological pathways is to identify genes underlying susceptibilities to inflammation and to cancer development at the same anatomic site. Mice develop lung adenocarcinomas similar in histology, molecular characteristics, and histogenesis to this most common human lung cancer subtype. Over two dozen loci, called Pas or pulmonary adenoma susceptibility, Par or pulmonary adenoma resistance, and Sluc or susceptibility to lung cancer genes, regulate differential lung tumor susceptibility among inbred mouse strains as assigned by QTL (quantitative trait locus) mapping. Chromosomal sites that determine responsiveness to proinflammatory pneumotoxicants such as ozone (O3), particulates, and hyperoxia have also been mapped in mice. For example, susceptibility QTLs have been identified on chromosomes 17 and 11 for O3-induced inflammation (Inf1, Inf2), O3-induced acute lung injury (Aliq3, Aliq1), and sulfate-associated particulates. Sites within the human and mouse genomes for asthma and COPD phenotypes have also been delineated. It is of great interest that several susceptibility loci for mouse lung neoplasia also contain susceptibility genes for toxicant-induced lung injury and inflammation and are homologous to several human asthma loci. These QTLs are described herein, candidate genes are suggested within these sites, and experimental evidence that inflammation enhances lung tumor development is provided.

Serum concentration modifies amplitude and kinetics of voltage-gated Na+ current in the Mat-LyLu cell line of rat prostate cancer

Voltage-gated Na+ channel (VGSC) expression has previously been shown to be upregulated in strongly metastatic prostate cancer cells (rat and human) and its activity shown to potentiate a variety of cellular behaviours integral to the metastatic cascade. However, the mechanism(s) responsible for the Na+ channel upregulation is not known. As a step towards evaluating the role of the extracellular biochemical environment in this regard, we have determined the effects of serum concentration on characteristics of Na+ channel expressed in the strongly metastatic Mat-LyLu rat prostate cancer cell line. Whole-cell patch-clamp recording techniques were used to study the effects of serum concentrations, above and below the normal 1%. Both the amplitude and the kinetics of the currents were analysed. The following results were obtained: (1) Adding 1% foetal calf serum to cells starved of serum for 24h increased Na+ current density; however, increasing serum concentration further (to 5%) caused a reduction. (2) Serum-free medium produced Na+ currents with slower kinetics of activation (time to peak) and inactivation (exponential decay). (3) Increased serum concentration (a) shifted steady-state inactivation to more positive potentials without affecting conductance and (b) increased tetrodotoxin sensitivity. It is concluded that serum concentration is an important determinant of the Na+ channel characteristics leading to possible transcriptional and post-translational modifications of channel expression and/or activity. Experiments are now needed to determine which constituents (protein hormones, growth factors, etc.) are responsible for these effects.

Local delivery of recombinant vaccinia virus expressing secondary lymphoid chemokine (SLC) results in a CD4 T-cell dependent antitumor response

Secondary lymphoid chemokine (SLC) attracts mature dendritic cells (DCs) and naïve T cells. Co-localization of these cells within local tumor environments may enhance the induction of tumor-specific T cells. However, the presence of danger signals or other DC maturation signals are required to optimize T-cell priming. We hypothesized that expression of SLC in vaccinia virus would provide local chemokine delivery and adjuvant factors. A recombinant vaccinia virus expressing murine SLC (rVmSLC) was constructed and characterized. SLC expression was confirmed by Western blot analysis and functional activity was determined by in vitro chemotaxis assay. Supernatants from rVmSLC-infected cells attracted CD4 T cells, and also induced the migration of CD8 T cells and DCs. Although poxviruses are known to express several chemokine-binding proteins, systemic injection of rVmSLC was well tolerated in mice up to a dose of 1 x 10(7) pfu and did not significantly alter vaccinia-specific T-cell immunity. Local injection of rVmSLC into established tumors derived from the murine colon cancer line, CT26, resulted in enhanced infiltration of CD4 T cells, which correlated with inhibition of tumor growth. The central role of CD4 T cells was further demonstrated by loss of anti-tumor activity in CD4 T-cell depleted mice. Intratumoral delivery of SLC using a poxviral vaccine extends the use of SLC in anti-tumor therapies and may present an effective alternative for improving the immunotherapy of cancer alone or in combination with other anti-tumor agents for clinical therapy.

Chemokine gene modification of human dendritic cell-based tumor vaccines using a recombinant adenoviral vector

Previous animal studies conducted in our laboratory have shown that tumor antigen-pulsed dendritic cells (TP-DC) can mediate antitumor effects in vivo. However, durable and complete regression of established tumors has been difficult to achieve through the administration of TP-DC alone. To better augment immune priming to tumors in vivo, we have hypothesized that it is necessary to achieve an increased number of host-derived, naïve T cells at the site of TP-DC vaccine injections. To accomplish this goal, we have embarked on a series of studies that utilize defined chemokines. One of these molecules, secondary lymphoid tissue chemokine (SLC), has been shown to be uniquely chemoattractant for naïve T cells and dendritic cells. We propose that gene modification of DC-based tumor vaccines to produce human SLC will enhance T-cell recruitment and immune priming to tumor-associated antigens, and thereby translate into improved antitumor vaccine efficacy in vivo. Utilizing an E1-, E3-deleted adenoviral vector containing the gene for human SLC, we have been able to transduce human DC to produce biologically active human SLC that chemoattracts human T cells in vitro. SLC production by transduced DC was markedly enhanced upon DC maturation. Additionally, these SLC-secreting DC were found to be viable to a large extent despite the cytopathic effect inherent in adenoviral gene transfer and, most importantly, functional as determined by their ability to prime autologous T cells to a known melanoma-associated antigen, MART-1. Based on these encouraging results, we plan to initiate Phase I clinical studies utilizing DC-SLC to treat patients with advanced solid tumors.

Intratumoral CC Chemokine Ligand 5 Overexpression Delays Tumor Growth and Increases Tumor Cell Infiltration

Chemokines participate in the antitumor immune response by regulating the movement and positioning of lymphocytes as well as effector functions and may thus be candidates for use in antitumor therapy. To test whether CCL5, a chemokine involved in the recruitment of a wide spectrum of immunocompetent cells, can control tumor growth, we forced its expression at mouse tumor sites. Tumor growth was reduced in mice with s.c. syngeneic CCL5-EL-4 compared with EL-4-injected mice, whereas both reduced tumor growth and incidence were observed in mice with OVA-expressing EG-7 transfected with CCL5 compared with EG-7-injected mice. Significant antitumor effects were observed soon after intratumoral injection of DNA plasmid coding for chimeric CCL5-Ig. Importantly, quantitative RT-PCR assays showed that the amount of CCL5 expression at the tumor site determined the effectiveness of the antitumor response, which was associated with infiltration of increased numbers of NK, CD4, and CD8 cells at the tumor site. This effect was lost in mice deficient for T/B lymphocytes (RAG-2 knockout) or for CCR5 (CCR5 knockout). Together, these data demonstrate the antitumor activity of intratumoral CCL5 overexpression, due to its recruitment of immunocompetent cells, and the potential usefulness of chimeric CCL5-Ig DNA as an agent in cancer therapy.

The three Es of cancer immunoediting

After a century of controversy, the notion that the immune system regulates cancer development is experiencing a new resurgence. An overwhelming amount of data from animal models--together with compelling data from human patients--indicate that a functional cancer immunosurveillance process indeed exists that acts as an extrinsic tumor suppressor. However, it has also become clear that the immune system can facilitate tumor progression, at least in part, by sculpting the immunogenic phenotype of tumors as they develop. The recognition that immunity plays a dual role in the complex interactions between tumors and the host prompted a refinement of the cancer immunosurveillance hypothesis into one termed "cancer immunoediting." In this review, we summarize the history of the cancer immunosurveillance controversy and discuss its resolution and evolution into the three Es of cancer immunoediting--elimination, equilibrium, and escape.

The role of chemokines and their receptors in ocular disease

The migration and infiltration of cells into the eye whether blood-borne leucocytes, endothelial or epithelial cells occurs in many ocular diseases. Dysregulation of this process is apparent in chronic inflammation, corneal graft rejection, allergic eye disease and other sight-threatening conditions. Under normal and inflammatory conditions, chemokines and their receptors are important contributors to cell migration. To date, 47 chemokines and 19 chemokine receptors have been identified and characterised. In recent years, investigations into the role of chemokines and their receptors in ocular disease have generated an increasing number of publications. In the eye, the best understood action of these molecules has arisen from the study of their ability to control the infiltration of leucocytes in uveitis. However, the involvement of chemokines in angiogenesis in several ocular conditions and in the survival of corneal transplants demonstrates the multifaceted nature of their effects. Interestingly, the constitutive expression of chemokines and their receptors in ocular tissues suggests that certain chemokines have a homeostatic function. In this review, we discuss the nature and function of chemokines in health and disease, and describe the role of chemokines in the pathogenesis of different ocular conditions.

Mechanisms regulating the recruitment of macrophages into hypoxic areas of tumors and other ischemic tissues

The mechanisms responsible for recruiting monocytes from the bloodstream into solid tumors are now well characterized. However, recent evidence has shown that these cells then differentiate into macrophages and accumulate in large numbers in avascular and necrotic areas where they are exposed to hypoxia. This parallels their tendency to congregate in ischemic areas of other diseased tissues such as atherosclerotic plaques and arthritic joints. In tumors, macrophages appear to undergo marked phenotypic changes when exposed to hypoxia and to switch on their expression of a number of mitogenic and proangiogenic cytokines and enzymes. This then promotes tumor growth, angiogenesis, and metastasis. Here, we compare the various mechanisms responsible for monocyte recruitment into tumors with those regulating the accumulation of macrophages in hypoxic/necrotic areas. Because the latter are best characterized in human tumors, we focus mainly on these but also discuss their relevance to macrophage migration in ischemic areas of other diseased tissues. Finally, we discuss the relevance of these mechanisms to the development of novel cancer therapies, both in providing targets to reduce the proangiogenic contribution made by hypoxic macrophages in tumors and in developing the use of macrophages to deliver therapeutic gene constructs to hypoxic areas of diseased tissues.

Role of infiltrated leucocytes in tumour growth and spread

Leucocytes are a major component of the tumour microenvironment. Recent studies have indicated that the infiltration and activity of these host cells are regulated by the tumour to promote its survival and progression. Through the production of an array of growth factors, proteases and angiogenic mediators, leucocytes in the tumour microenvironment promote tumour growth, angiogenesis and metastasis.

Inhibition of inflammatory angiogenesis by distant subcutaneous tumor in mice

We investigated angiogenesis, inflammatory cells accumulation and endogenous production of cytokines in sponge implants of tumor-bearing mice. Seven days after inoculation of Ehrlich tumor cells (2.5 x 10(6)), sponge discs were implanted subcutaneously in the dorsa of mice to induce the formation of fibrovascular tissue. The implants of tumor-bearing and non tumor-bearing animals were assessed for neovascularization and leukocyte accumulation, together with levels of relevant cytokines, vascular endothelial growth factor VEGF), tumor necrosis factor alpha (TNF-alpha), CXCL1-3/KC and CCL2/JE. In the implants of tumor-bearing animals angiogenesis (assessed by hemoglobin content and VEGF levels in the implants) and leukocyte accumulation (assessed by myeloperoxidase -MPO- and N- acetylglucosaminidase-NAG-enzyme activities) were all significantly less than those in the implants of non tumor-bearing animals. Although the chemokine CXCL1-3/KC was lower in the implants of tumor-bearing animals, the chemokine CCL2/JE was increased in this group. The production of TNF-alpha in the implants was not modified by the presence of the subcutaneous tumor. The combination of the methodologies used in this study has provided a novel approach to investigate the interaction between two distinct proliferating tissues that share common features (angiogenesis, cell recruitment, inflammation) and has shown that the predominant inhibitory effect of a tumor mass over repair process is associated with altered cytokine production.

Dipeptidyl peptidase IV activity and/or structure homologues (DASH) and their substrates in cancer

Post-translational modification of proteins is an important regulatory event. Numerous biologically active peptides that play an essential role in cancerogenesis contain an evolutionary conserved proline residue as a proteolytic-processing regulatory element. Proline-specific proteases could therefore be viewed as important "check-points". Limited proteolysis of such peptides may lead to quantitative but, importantly, due to the change of receptor preference, also qualitative changes of their signaling potential. Dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5, identical with CD26) was for many years believed to be a unique cell membrane protease cleaving X-Pro dipeptides from the N-terminal end of peptides and proteins. Subsequently, a number of other molecules were discovered, exhibiting various degree of structural homology and DPP-IV-like enzyme activity, capable of cleaving similar set of substrates. These comprise for example, seprase, fibroblast activation protein alpha, DPP6, DPP8, DPP9, attractin, N-acetylated-alpha-linked-acidic dipeptidases I, II and L, quiescent cell proline dipeptidase, thymus-specific serine protease and DPP IV-beta. It is tempting to speculate their potential participation on DPP-IV biological function(s). Disrupted expression and enzymatic activity of "DPP-IV activity and/or structure homologues" (DASH) might corrupt the message carried by their substrates, promoting abnormal cell behavior. Consequently, modulation of particular enzyme activity using e.g. DASH inhibitors, specific antibodies or DASH expression modification may be an attractive therapeutic concept in cancer treatment. This review summarizes recent information on the interactions between DASH members and their substrates with respect to their possible role in cancer biology.

Chemokine-receptor interactions: GPCRs, glycosaminoglycans and viral chemokine binding proteins

A key feature of the immune system is the migration of leukocytes throughout the organism in an effort to patrol for infectious pathogens, tissue damage, and other physiological insults. This remarkable surveillance system is controlled by a family of proteins called chemokines (chemoattractant cytokines), and their respective receptors. Originally discovered because of their role in cell recruitment during inflammation, it is now well recognized that chemokines are also involved in other diverse processes including lymphocyte development and homing, organogenesis, and neuronal communication. While chemokines have evolved largely for host protection, their ability to induce cell damage and inappropriate cell recruitment, can lead to disease. Thus, there is considerable interest in developing antagonists. In this review we emphasize what is known about the structural biology of chemokines, chemokine receptors, and interactions with cell surface glycosaminoglycans. We also briefly describe their role in certain diseases and strategies for interfering with chemokine function that have emerged from mechanistic and structural understanding of their function. Finally we discuss viral mechanisms for sabotaging or manipulating the chemokine system, in part to illustrate the level of molecular mimicry that viruses have achieved and the evolutionary pressure imposed on the immune system by these pathogens.

Specific recruitment of antigen-presenting cells by chemerin, a novel processed ligand from human inflammatory fluids

Dendritic cells (DCs) and macrophages are professional antigen-presenting cells (APCs) that play key roles in both innate and adaptive immunity. ChemR23 is an orphan G protein–coupled receptor related to chemokine receptors, which is expressed specifically in these cell types. Here we present the characterization of chemerin, a novel chemoattractant protein, which acts through ChemR23 and is abundant in a diverse set of human inflammatory fluids. Chemerin is secreted as a precursor of low biological activity, which upon proteolytic cleavage of its COOH-terminal domain, is converted into a potent and highly specific agonist of ChemR23, the chemerin receptor. Activation of chemerin receptor results in intracellular calcium release, inhibition of cAMP accumulation, and phosphorylation of p42–p44 MAP kinases, through the G_i class of heterotrimeric G proteins. Chemerin is structurally and evolutionary related to the cathelicidin precursors (antibacterial peptides), cystatins (cysteine protease inhibitors), and kininogens. Chemerin was shown to promote calcium mobilization and chemotaxis of immature DCs and macrophages in a ChemR23-dependent manner. Therefore, chemerin appears as a potent chemoattractant protein of a novel class, which requires proteolytic activation and is specific for APCs.

CD4+ T cells in cancer stroma, not CD8+ T cells in cancer cell nests, are associated with favorable prognosis in human non-small cell lung cancers

We investigated intratumoral tumor-infiltrating lymphocytes (TILs), including CD4(+) and CD8(+) T cells, in non-small cell lung cancers (NSCLCs) and their relationships with clinicopathological variables and post-operative survival. Tumor specimens from 178 NSCLCs were consecutively obtained by surgery at the Hokkaido University Medical Hospital between 1976 and 1994. CD8(+) T cells, CD4(+) T cells and Ki-67/CD8(+) T cells were visualized immunohistochemically, and counted within cancer cell nests and in cancer stroma. CD8(+) T cells and CD4(+) T cells were observed at higher frequencies within cancer cell nests in moderately and poorly differentiated tumors compared with well differentiated tumors (P < 0.01), and in tumors with high Ki-67 expression compared with low Ki-67 expression (P < 0.01), that showed severe cellular atypia and a higher growth rate. Patients with higher numbers of CD8(+) T cells within cancer cell nests showed significantly shorter survival times compared to those with lower numbers of CD8(+) T cells within cancer cell nests (5-year survival rates, 47% and 60%, respectively; P = 0.03). Moreover, patients with higher labeling index of Ki-67/CD8(+) T cells showed significantly shorter survival than those with lower labeling index of Ki-67/CD8(+) T cells within cancer cell nests (5-year survival rates, 41% and 69%, respectively; P = 0.02), and the labeling index of Ki-67/CD8(+) T cells within cancer cell nests was found to be a significant and independent unfavorable prognostic factor by multivariate analysis (P = 0.01). On the other hand, higher numbers of CD4(+) T cells in cancer stroma, but not within cancer cell nests, were correlated with longer survival times in patients with NSCLC (5-year survival rates, 64% and 43%, respectively; P = 0.04). CD4(+) T cells in cancer stroma might reflect immune responses against cancer cells, while CD8(+) T cells do not appear to work as effectors in tumor tissues of NSCLC. Moreover, the higher labeling index of Ki-67/CD8(+) T cells within cancer cell nests is a strong indicator of unfavorable clinical outcome.

The CC chemokine CCL20 and its receptor CCR6

CCL20, alternatively named liver and activation-regulated chemokine (LARC), macrophage inflammatory protein-3alpha (MIP-3alpha) or Exodus-1, is the only chemokine known to interact with CC chemokine receptor 6 (CCR6), a property shared with the antimicrobial beta-defensins. The ligand-receptor pair CCL20-CCR6 is responsible for the chemoattraction of immature dendritic cells (DC), effector/memory T-cells and B-cells and plays a role at skin and mucosal surfaces under homeostatic and inflammatory conditions, as well as in pathology, including cancer and rheumatoid arthritis. In this review, the discovery, the gene and protein structure, the in vitro biological activities, the cell and inducer specific expression and the tissue distribution of CCL20 and CCR6 are discussed.

G protein-coupled receptors in natural killer cells

Natural killer (NK) cells are capable of killing tumor as well as virally infected cells. How these cells migrate toward the infected sites in the body is not completely understood. Chemokine receptors that belong to the heptahelical family of receptors and characteristically bind heterotrimeric G proteins are present in most NK cells. Recent results showed that resting NK cells highly express constitutive chemokine receptors (CCR4, CCR7, CXCR4, and CX(3)CR1) with low expression of a limited repertoire of inflammatory chemokine receptors (CCR1 and CXCR3). However, only a subset of these cells expressing the CD56(dim) and adhesion molecule(high) phenotype is capable of in vivo binding to vascular endothelium. Under pathological conditions where inflammatory cytokines are present, these cells are induced to express inflammatory chemokine receptors. Resting as well as activated NK cells also express receptors for another member of the heptahelical family of receptors that bind phosphorylated or glycosylated lysolipids. These include sphingosine 1-phosphate (S1P)(1), S1P(4), and S1P(5), the receptors for S1P; lysophosphatidic acid (LPA)(1), LPA(2), and LPA(3), the receptors for LPA; and T cell death-associated gene 8, the receptor for psychosine. Similar to chemokines, S1P, LPA, and psychosine induce the chemotaxis of NK cells through heterotrimeric G proteins. However, in contrast to chemokines, which enhance the cytotoxicity of NK cells, lysolipids inhibit this function. We hope that gaining knowledge regarding the distribution of activated NK cells toward the sites of tumor growth or virally infected sites will give an advantage in designing strategies using these cells as tools for the prevention and treatment of immunodeficiencies.

Role of homeostatic chemokine and sphingosine-1-phosphate receptors in the organization of lymphoid tissue

Chemokines regulate both homeostatic leukocyte recirculation and trafficking to sites of infection and inflammation. Apart from the well-established physiological functions, chemokines receive growing interest for their role in pathophysiological processes such as autoimmune diseases, cancer, and allograft rejection. The chemokine receptor CCR7, which is responsible for directing T cells, B cells, and dendritic cells (DCs) into secondary lymphoid organs and their precise positioning therein, has already been implicated in lymphoid organ infiltration by neoplastic cells and the localization of metastasis formation. We have shown that the differential expression of CCR7 by neoplastic cells in two entities of Hodgkin's disease (HD), classic HD (cHD) and the nodular lymphocyte predominant HD (NLPHD), may account for the differences observed in tumor cell dissemination within the affected lymph nodes. Because of the prominent role of the chemokine receptors CCR7 and CXCR5 in lymphocyte homing to secondary lymphoid organs, we hypothesized that they may also be involved in the action of FTY720, a synthetic immunosuppressant inducing lymphopenia. By using CXCR5 and CCR7 knockout mice, we have tested for a possible function of these receptors in the FTY720-induced migration of lymphocytes into Peyer's patches (PPs) and peripheral lymph nodes (PLNs). Lymphopenia is noticeably delayed in mice lacking CCR7, whereas CXCR5 knockout mice show a significant reduction of lymphocyte accumulation in secondary lymphoid organs that are infrequently present in these mice. However, FTY720-induced lymphocyte sequestration appears to be essentially independent of CCR7 and CXCR5.

Cathepsin D specifically cleaves the chemokines macrophage inflammatory protein-1 alpha, macrophage inflammatory protein-1 beta, and SLC that are expressed in human breast cancer

Cathepsin D (Cath-D) expression in human primary breast cancer has been associated with a poor prognosis. In search of a better understanding of the Cath-D substrates possibly involved in cancer invasiveness and metastasis, we investigated the potential interactions between this protease and chemokines. Here we report that purified Cath-D, as well as culture supernatants from the human breast carcinoma cell lines MCF-7 and T47D, selectively degrade macrophage inflammatory protein (MIP)-1 alpha (CCL3), MIP-1 beta (CCL4), and SLC (CCL21). Proteolysis was totally blocked by the protease inhibitor pepstatin A, and specificity of Cath-D cleavage was demonstrated using a large chemokine panel. Whereas MIP-1 alpha and MIP-1 beta degradation was rapid and complete, cleavage of SLC was slow and not complete. Mass spectrometry analysis showed that Cath-D cleaves the Leu(58) to Trp(59) bond of SLC producing two functionally inactive fragments. Analysis of Cath-D proteolysis of a series of monocyte chemoattractant protein-3/MIP-1 beta hybrids indicated that processing of MIP-1 beta might start by cleaving off amino acids located in the C-terminal domain. In situ hybridization studies revealed MIP-1 alpha, MIP-1 beta, and Cath-D gene expression mainly in the stromal compartment of breast cancers whereas SLC transcripts were found in endothelial cells of capillaries and venules within the neoplastic tissues. Cath-D production in the breast carcinoma cell lines MCF-7 and T47D, as assessed by enzyme-linked immunosorbent assay of culture supernatants and cell lysates, was not affected by stimulation with chemokines such as interleukin-8 (CXCL8), SDF-1 (CXCL12), and SLC. These data suggest that inactivation of chemokines by Cath-D possibly influences regulatory mechanisms in the tumoral extracellular microenvironment that in turn may affect the generation of the antitumoral immune response, the migration of cancer cells, or both processes.

Infection and cancer: the common vein

The role of infectious agents in the development of cancer is well documented. The pathogenesis of various human neoplasms ranging from non-Hodgkin lymphoma (NHL) to cervical carcinoma frequently involves a chronic, most often viral, infection. At the same time, there is compelling evidence that certain acute infections result in the inhibition of neoplastic growth. The basis for this phenomenon is often thought to be concomitant anti-tumor immunity. Yet, experimental data supporting this hypothesis are scarce, and other non-immune anti-tumor factors could be involved. For instance, since virtually all aggressive tumors outstrip their blood supply, development of new vessels, or angiogenesis, is a limiting factor during neoplastic growth. In this review, we will discuss recent studies that implicate anti-angiogenesis in infection-mediated tumor suppression and suggest that this mechanism could also complement cytotoxic immunity arising from the use of cancer vaccines.

Chemokine biology in cancer

Many human cancers possess a complex chemokine network that may influence the extent and phenotype of the leukocyte infiltrate, angiogenesis, tumor cell growth, survival and migration. Restricted expression of chemokine receptors on leukocytes may allow concise control of cell movement and retention at the tumor site. Restricted and specific expression of chemokine receptors on tumor cells may be involved in the characteristic patterns of metastasis, and may promote tumor cell growth and survival. Detailed study of chemokine and chemokine receptor antagonists in experimental cancer models is warranted. Manipulation of the tumor chemokine network could have therapeutic potential in malignant disease.

Inflammation and cancer

Recent data have expanded the concept that inflammation is a critical component of tumour progression. Many cancers arise from sites of infection, chronic irritation and inflammation. It is now becoming clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an indispensable participant in the neoplastic process, fostering proliferation, survival and migration. In addition, tumour cells have co-opted some of the signalling molecules of the innate immune system, such as selectins, chemokines and their receptors for invasion, migration and metastasis. These insights are fostering new anti-inflammatory therapeutic approaches to cancer development.

Inflammation and cancer

Recent data have expanded the concept that inflammation is a critical component of tumour progression. Many cancers arise from sites of infection, chronic irritation and inflammation. It is now becoming clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an indispensable participant in the neoplastic process, fostering proliferation, survival and migration. In addition, tumour cells have co-opted some of the signalling molecules of the innate immune system, such as selectins, chemokines and their receptors for invasion, migration and metastasis. These insights are fostering new anti-inflammatory therapeutic approaches to cancer development.

Inflammation and cancer

Recent data have expanded the concept that inflammation is a critical component of tumour progression. Many cancers arise from sites of infection, chronic irritation and inflammation. It is now becoming clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an indispensable participant in the neoplastic process, fostering proliferation, survival and migration. In addition, tumour cells have co-opted some of the signalling molecules of the innate immune system, such as selectins, chemokines and their receptors for invasion, migration and metastasis. These insights are fostering new anti-inflammatory therapeutic approaches to cancer development.

Armed therapeutic viruses: strategies and challenges to arming oncolytic viruses with therapeutic genes

Oncolytic viruses are attractive therapeutics for cancer because they selectively amplify, through replication and spread, the input dose of virus in the target tumor. To date, clinical trials have demonstrated marked safety but have not realized their theoretical efficacy potential. In this review, we consider the potential of armed therapeutic viruses, whose lytic potential is enhanced by genetically engineered therapeutic transgene expression from the virus, as potential vehicles to increase the potency of these agents. Several classes of therapeutic genes are outlined, and potential synergies and hurdles to their delivery from replicating viruses are discussed.

Photopheresis: clinical applications and mechanism of action

Photopheresis is a leukapheresis-based therapy that utilizes 8-methoxypsoralen and ultraviolet A irradiation. Photopheresis is currently available at approximately 150 medical centers worldwide. Recent evidence suggests that this therapy used as a single agent may significantly prolong life, as well as induce a 50%-75% response rate among individuals with advanced cutaneous T cell lymphoma (CTCL). Furthermore, a 20%-25% complete response rate with photopheresis alone, or in combination with other biologic response modifiers, has been obtained at our institution among patients with Sezary syndrome. These complete responses have been characterized by the complete disappearance of morphologically atypical cells from the skin and blood. The use of sensitive molecular techniques has also confirmed the sustained disappearance of the malignant T cell clone from the blood of patients with complete responses. In addition to the treatment of CTCL, numerous reports indicate that photopheresis is a potent agent in the therapy of acute allograft rejection among cardiac, lung, and renal transplant recipients. Chronic graft versus host disease also appears to be quite responsive to photopheresis therapy. Likewise, there may also be a potential role for photopheresis in the therapy of certain autoimmune diseases that are poorly responsive to conventional therapy. The immunologic basis for the responses of patients with these conditions is likely due to the induction of anticlonotypic immunity directed against pathogenic clones of T lymphocytes. Treatment-induced apoptotic death of pathogenic T cells and activation of antigen presenting cells are postulated to have important effects in this therapeutic process.