Retinoblastoma tumor cell proliferation is negatively associated with an immune gene expression signature and increased immune cells

This study focuses on gene expression differences between early retinal states that ultimately lead to normal development, late onset retinoblastoma, or rapid bilateral retinoblastoma tumors. The late-onset and early-onset retinoblastoma tumor cells are remarkably similar to normally proliferating retinal progenitor cells, but they fail to properly express differentiation markers associated with normal development. Further, early-onset retinoblastoma tumor cells express a robust immune gene expression signature followed by accumulation of dendritic, monocyte, macrophage, and T-lymphocyte cells in the retinoblastoma tumors. This characteristic was not shared by either normal retinae or late-onset retinoblastomas. Comparison of our data with other human and mouse retinoblastoma tumor gene expression significantly confirmed, that the immune signature is present in tumors from each species. Strikingly, we observed that the immune signature in both mouse and human tumors was most highly evident in those with the lowest proliferative capacity. We directly assessed this relationship in human retinoblastoma tumors by co-analyzing proliferation and immune cell recruitment by immunohistochemistry, uncovering a significant inverse relationship between increased immune-cell infiltration in tumors and reduced tumor cell proliferation. Directly inhibiting proliferation with a PI3K/mTOR inhibitor significantly increased the number of CD45+ immune cells in the retina. This work establishes an in vivo model for the rapid recruitment of immune cells to tumorigenic neural tissue.

Retinoblastoma cell-derived Twist protein promotes regulatory T cell development

BACKGROUND

The development of tumor tissue-infiltrating regulatory T cell (Treg) is incompletely understood. This study investigates the role of retinoblastoma cell (Rbc)-derived Twist‑related protein 1 (Twist) in the Treg development.

METHODS

The surgically removed Rb tissues were collected. Rbcs were cultured with CD4⁺ T cells to assess the role of Rbc-derived Twist in the Treg generation.

RESULTS

We found that more than 90% Rbcs expressed Twist. Foxp3⁺ Tregs were detected in the Rb tissues that were positively correlated with the Twist expression in Rbcs, negatively associated with Rb patient survival and sight survival. Treating Rbcs with hypoxia promoted the Twist expression that could be detected in the cytoplasm, nuclei and on the cell surface. Twist activated CD4⁺ T cells by binding the TLR4/myeloid differentiation factor 2 complex and promoted the transforming growth factor-β-inducible early gene 1 product and Foxp3 expression. These Rbc-induced Foxp3⁺ Tregs showed immune-suppressive function on CD8⁺ T cell proliferation.

CONCLUSIONS

Rbcs express Twist, that induces IL-4⁺ Foxp3⁺ Tregs; the latter can inhibit CD8⁺ cytotoxic T cell activities. Therefore, Twist may play an important role in the pathogenesis of Rb.

SYK-targeted dendritic cell-mediated cytotoxic T lymphocytes enhance the effect of immunotherapy on retinoblastoma

PURPOSE

Retinoblastoma (RB) is the most common primary intraocular tumor in children. Chemotherapy is currently the main method of RB treatment. Unfortunately, RB often becomes chemoresistant and turns lethal. Here, we used in vitro cell immunotherapy to explore whether adoptive immunotherapy could be used as a potential treatment for RB. We focused on spleen tyrosine kinase (SYK), which is significantly upregulated in RB cells and serves as a marker for RB cells.

METHODS

Using lentiviruses, we genetically modified dendritic cells (DCs) to express and present the SYK peptide antigen to cytotoxic T lymphocytes (CTLs) in vitro. We used SYK-negative cell lines (MDA-MB-231, MCF-10A, and hTERT-RPE1) and SYK-positive cell lines (MCF-7 and RB-Y79) to evaluate the specificity and cytotoxicity of DC presented CTLs using FACS, live-cell imaging, and RNA interference.

RESULTS

The cytotoxicity of CTLs induced by SYK-overexpressing DCs (SYK-DC-CTLs) was enhanced more than three times in SYK-positive cell lines compared with SYK-negative cell lines. DCs primed with SYK could drive CTL cytotoxicity against SYK-positive cell lines but not against SYK-negative cell lines. Moreover, SYK-silenced RB-Y79 cells successfully evaded the cytotoxic attack from SYK-DC-CTLs. However, SYK-DC-CTLs could target SYK overexpressed hTERT-RPE1 cells, suggesting that SYK is a specific antigen for RB. Furthermore, SYK-DC-CTL exhibited specific cytotoxicity against carboplatin-resistant RB-Y79 cells in vitro.

CONCLUSIONS

Our data showed that SYK could be a potential immunotherapy target mediated by DCs. We propose SYK as a candidate target for treatment of chemoresistant RB.

[Retinoblastoma and "pseudoretinoblastoma" in children: clinical, tomographic and serological features]

Clinical and tomographic features of retinoblastoma and posterior pole inflammatory granuloma ("pseudoretinoblastoma") as well as infectious status in both conditions were assessed in 16 children (32 eyes). The data obtained allow differential diagnosis of neoplastic and inflammatory processes and further adequate treatment.

Human embryonic and neuronal stem cell markers in retinoblastoma

PURPOSE

Retinoblastoma (RB) is the most common intraocular tumor of early childhood. The early onset of RB, coupled with our previous findings of cancer stem cell characteristics in RB, led us to hypothesize that subpopulations of RB tumors harbor markers and behaviors characteristic of embryonic and neuronal origin.

METHODS

Our RB sources included: human pathological tissues, and the human RB cell lines Y79 and WERI-RB27. Microarray screening, single and dual-label immunocytochemistry and RT-PCR were performed to detect embryonic and neuronal stem cell markers, such as Oct3/4, Nanog, CD133, and Musashi-1. To test for functional evidence of stem cell behavior, we examined RB cells for their ability to form neurospheres and retain BrdU label as indicators of self-renewal and slow cell cycling, respectively.

RESULTS

Microarray comparisons of human RB tumors with normal retinal tissue detected upregulation of a number of genes involved in embryonic development that were also present in Y79 cells, including Oct3/4, Nanog, Musashi-1 and Musashi-2, prominin-1 (CD133), Jagged-2, Reelin, Thy-1, nestin, Meis-1,NCAM, Patched, and Notch4. Expression of Musashi-1, Oct3/4 and Nanog was confirmed by immunostaining and RT-PCR analyses of RB tumors and RB cell lines. CD133 expression was confirmed by PCR analysis. Y79 and WERI-RB27 contained populations of Hoechst-dim/ABCG2-positive cells that co-localized with embryonic stem cell markers Oct3/4-ABCG2 and Nanog-ABCG2. Subpopulations of Y79 and WERI-RB27 cells were label-retaining (as seen by BrdU incorporation) and were able to generate neurospheres, both hallmarks of a stem cell phenotype.

CONCLUSIONS

Small subpopulation(s) of RB cells express human embryonic and neuronal stem cell markers. There are also subpopulations that demonstrate functional behavior (label retention and self-renewal) consistent with cancer stem cells. These findings support the hypothesis that RB is a heterogeneous tumor comprised of subpopulation(s) with stem cell-like properties.

Loss of the retinoblastoma tumor suppressor: differential action on transcriptional programs related to cell cycle control and immune function

Functional inactivation of the retinoblastoma tumor suppressor gene product (RB) is a common event in human cancers. Classically, RB functions to constrain cellular proliferation, and loss of RB is proposed to facilitate the hyperplastic proliferation associated with tumorigenesis. To understand the repertoire of regulatory processes governed by RB, two models of RB loss were utilized to perform microarray analysis. In murine embryonic fibroblasts harboring germline loss of RB, there was a striking deregulation of gene expression, wherein distinct biological pathways were altered. Specifically, genes involved in cell cycle control and classically associated with E2F-dependent gene regulation were upregulated via RB loss. In contrast, a program of gene expression associated with immune function and response to pathogens was significantly downregulated with the loss of RB. To determine the specific influence of RB loss during a defined period and without the possibility of developmental compensation as occurs in embryonic fibroblasts, a second system was employed wherein Rb was acutely knocked out in adult fibroblasts. This model confirmed the distinct regulation of cell cycle and immune modulatory genes through RB loss. Analyses of cis-elements supported the hypothesis that the majority of those genes upregulated with RB loss are regulated via the E2F family of transcription factors. In contrast, those genes whose expression was reduced with the loss of RB harbored different promoter elements. Consistent with these analyses, we found that disruption of E2F-binding function of RB was associated with the upregulation of gene expression. In contrast, cells harboring an RB mutant protein (RB-750F) that retains E2F-binding activity, but is specifically deficient in the association with LXCXE-containing proteins, failed to upregulate these same target genes. However, downregulation of genes involved in immune function was readily observed with disruption of the LXCXE-binding function of RB. Thus, these studies demonstrate that RB plays a significant role in both the positive and negative regulations of transcriptional programs and indicate that loss of RB has distinct biological effects related to both cell cycle control and immune function.

Expression of costimulatory molecules on human retinoblastoma cells Y-79: functional expression of CD40 and B7H1

PURPOSE

To examine the expression of various costimulatory molecules on the human retinoblastoma cell line Y-79 and assess the functional roles of selected costimulatory molecules.

METHODS

Y-79 cells were incubated in the presence or absence of IFN-gamma, with or without irradiation (100 Gy). Expression of major histocompatibility complex (MHC) class I molecules, MHC class II, CD80, CD86, CD40, CD70, B7H1, B7DC, B7H2, OX40L, and 4-1BBL on Y-79 cells was measured by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometric analysis. The functional role of CD40-mediated interactions in modifying immune responses to Y-79 was assessed in vitro by using recombinant human CD40 ligand (rhCD40L). The costimulatory effect of B7H1-expressing IFN-gamma-treated Y-79 cells on proliferation of purified T cells was studied in Y-79/T-cell coculture experiments with a blocking anti-B7H1 monoclonal antibody (mAb).

RESULTS

CD40 and B7H2 were consistently detected on Y-79 cells by RT-PCR and flow cytometry. Cell surface expression of CD40 was upregulated on stimulation by IFN-gamma alone, radiation alone, and IFN-gamma combined with radiation. B7H1 expression was induced by IFN-gamma stimulation and increased further when irradiated Y-79 cells were stimulated by IFN-gamma. Treatment of Y-79 cells with rhCD40L enhanced cell surface expression of MHC class I and intercellular adhesion molecule (ICAM)-1 and also stimulated monocyte chemotactic protein (MCP)-1 production. Proliferative response of purified CD3+ T cells costimulated with IFN-gamma-stimulated Y-79 was significantly enhanced by the addition of anti-B7H1 mAb.

CONCLUSIONS

These results suggest that CD40 expressed on Y-79 plays an important role in augmenting antitumor immunity. In contrast, the expression of B7H1 on IFN-gamma-treated Y-79 cells contributes to the suppression of T cells. The dual effects of CD40 and B7H1 on Y-79 cells may contribute to positive or negative regulation of antitumor immune responses in human retinoblastoma.

An aggressive bone marrow evaluation including immunocytology with GD2 for advanced retinoblastoma

There is general agreement that bone marrow (BM) examination for staging in patients with retinoblastoma should be limited to cases with advanced disease. However, there are limited data about the yield of sampling multiple sites with aspirations and biopsies and immunocytology. Our policy for BM examination included: 2 aspirates and 2 biopsies at the posterior iliac crest scheduled only for cases with postlaminar optic nerve extension (n=56), scleral invasion (n=10) or orbital (n=5) or metastatic disease at diagnosis (n=7) or at extraocular relapse (n=18). Immunocytology with the antibodies 3A7 or 3F8 for the ganglioside GD2 was performed. From 1/1994 to 3/2005, 277 newly diagnosed patients and 5 at extraocular relapse were included. BM invasion was not found in any of the 66 patients enucleated with disease confined to the globe, but was found in 11/27 of those with overt extraocular disease. There were 2/11 cases with at least 1 negative aspirate with positive biopsy and/or immunocytology for GD2. GD2 positivity was found in 9/9 cases. A more aggressive BM evaluation has a low yield in enucleated patients with high-risk features but disease limited to the globe. However, in cases with overt extraocular dissemination, the use of BM biopsy and immunocytology for GD2 allowed for the detection of cases that would have been missed by aspirations alone. GD2 was intensively expressed and it may also be used to monitor disease response and the presence of minimal residual disease.

Increased cell proliferation of mouse fibroblast NIH-3T3 in vitro induced by excretory/secretory product(s) from Opisthorchis viverrini

Infection by Opisthorchis viverrini is a strong risk factor for cholangiocarcinoma. However, the mechanism by which the parasite is involved in carcinogenesis is not clear. In addition to the direct damage of the bile duct epithelium via direct contact with O. viverrini, the excretory/secretory (ES) product(s) released from the parasites may play important roles in this process. We therefore investigated the responses of a fibroblast cell line, NIH-3T3, to ES product(s) released from O. viverrini by using a non-contact co-culture technique. In this culture system, the parasites in the upper chamber had no direct contact with the NIH-3T3 cells in the lower chamber of the culture plate. The results indicated a marked increase in NIH-3T3 cell proliferation in the non-contact co-culture condition with either 0% or 10% calf serum in the medium compared with that without parasites. ES product(s) increased cell proliferation by stimulating the expression of phosphorylated retinoblastoma (pRB) and cyclin D1, the key proteins in driving cells through the G1/S transition point of the cell cycle. This led to the induction of cells going into the S-phase of the cell cycle. ES product(s) also changed the morphology of NIH-3T3 cells to a refractive and narrow shape, which allowed the cells to proliferate in the limited culture area. For the first time, we have been able to demonstrate increased cell proliferation induced by the ES product(s) from O. viverrini; this finding may clarify how O. viverrini ES product(s) affect human bile duct epithelium during cholangiocarcinogenesis.

Expression of Fas ligand in retinoblastoma

BACKGROUND

The importance of the Fas-Fas ligand (FasL) mechanism for the immune evasion by tumors provided a strong rationale for the examination of FasL expression in retinoblastoma. In an earlier publication, the authors reported that invasive retinoblastomas decreased Fas expression. Because to the authors' knowledge there is not much information regarding the effect of FasL expression on retinoblastoma, the authors studied the expression of FasL in retinoblastoma and correlated it with invasiveness.

METHODS

Thirty-six archival retinoblastoma specimens were divided into 2 groups. Group A (n = 17) was comprised of specimens from tumors with no invasion and Group B (n = 19) was comprised of specimens from tumors with invasion of the choroid (focal, diffuse), optic nerve (laminar, postlaminar, surgical end), and orbit. Sections were immunostained with a monoclonal antibody to FasL and the immunoreactivity was assessed.

RESULTS

In Group A, FasL was negative in 100% (17 of 17) of the tumor specimens. In Group B, FasL was expressed in 79% (15 of 19) of the tumor specimens (positive in 9 tumors and heterogeneous in 6 tumors). The difference in FasL expression between the two groups was significant (P < 0.001)

CONCLUSIONS

Increased expression of FasL was observed in specimens taken from patients with aggressive tumors. Thus, Loss of Fas and gain of aberrant FasL expression were common features of malignant transformation. The data suggested that the Fas/FasL pathway is potentially immunosuppressive and may be involved in the escape of retinoblastoma cells from immune destruction.

[An experiment study of in vitro induced antitumor immune responses by vaccination of tumor lysate-pulsed dendritic cells to kill SO-RB(50)]

OBJECTIVE

To investigate induced antitumor immune responses by vaccination of tumor lysate-pulsed dendritic cells (DC) to kill retinoblastoma cells SO-RB(50). We hope to offer new approach for the treatment of patients with retinoblastoma.

METHODS

DC was pulsed with RB tumor lysates in vitro and incubated with autologous lymphocytes to induce antigen specific CTL (cytotoxic T lymphocyte, CTL). SO-RB(50) cells were used as target cells and Raji cells were used as control target cells. Cytotoxicity of CTL was evaluated by MTT method (methyl thiazolyl letrazolium). The specific cytotoxicity of CTL to SO-RB(50) and Raji cells was compared. The cytotoxicity of CTL from RB and normal subjects was compared between these two groups.

RESULTS

Antigen specific CTL showed greater cytotoxicity to SO-RB(50) than Raji cells, the difference was statistically significant, P < 0.01. The cytotoxicity was dose-dependent to the ratio of CTL/target cell. The nonspecific cytotoxicity to Raji cells was the same in CTL from RB patients and normal subjects, P > 0.05. The specific cytotoxicity of CTL from RB patients to SO-RB(50) was weaker than that from the healthy subjects, P < 0.01.

CONCLUSION

DC pulsed with RB tumor lysate in vitro can induce antigen specific CTL which can kill the SO-RB(50) target cells specifically. This method may have potential value of therapy for the RB patients.

Major histocompatibility antigens and antigen-processing molecules in retinoblastoma

BACKGROUND

Malignant transformation of cells is frequently associated with abnormalities in human leukocyte antigen (HLA) expression. These abnormalities may play a role in the clinical course of the disease, because HLAs mediate interactions of tumor cells with cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Retinoblastoma is the most common intraocular malignant tumor in childhood and is characterized by direct spread to the optic nerve and orbit as well as hematogeneous and lymphatic spread. Little is known about the role of HLA expression in the progression of this malignant disease.

METHODS

HLA Class I antigen, beta2-microglobulin (beta2-m), HLA Class II antigens, and the antigen-processing molecules (APMs) of the HLA Class I pathway, including proteasomal subunits (low-molecular mass polypeptide 2 [LMP-2] and LMP-10), the transporter-associated protein (TAP-1) subunit, the binding protein tapasin, and the chaperone molecule calnexin, were studied in 30 archival retinoblastoma specimens by immunohistochemistry. Immunoanalysis was performed based on the International Histocompatibility Working Group Project Description.

RESULTS

HLA Class I antigen, beta2-m, HLA Class II antigen, and APMs were positive in 12 tumors with no invasion and were decreased in 13 tumors with choroidal and optic nerve invasion. The difference in HLA and APM expression between the 2 groups was statistically significant (P < 0.001).

CONCLUSIONS

Decreased expression of HLA was observed in aggressive tumors and in poorly differentiated tumors. The current findings support a role for both CTLs and NK cell-mediated control of tumor growth in the clinical course of retinoblastoma.

Immunohistochemical localization of human pineal tissue antigens in normal retina and retinoblastomas

The normal human retina and retinoblastomas were examined immunohistochemically to assess the localization of pineal antigens in the retina and the oncogenesis and differentiation of retinoblastoma. In the present study, 41 eyes excised from children (aged 4 months to 7 years, all unilateral occurrence) diagnosed to have retinoblastoma and 4 eyes with normal retinas, were used. Retinoblastomas were histopathologically classified into well-differentiated, moderately-differentiated, and poorly-differentiated types. The antibodies used were 9 monoclonal antibodies to human pineal antigens and 6 antibodies to neural tissues. In the normal retina, staining patterns characteristic of retinal cell layers were observed with PP1, PP3, PP5, PP6, PI1, and PI2 antibodies. In retinoblastomas, PP5 antibody, which reacts with horizontal cells and ganglion cells, and PP6 antibody, which reacts with part of the bipolar cells in the inner nuclear layer, showed intense staining in well-differentiated retinoblastomas, but the intensity of staining and the positivity decreased with the degree of dedifferentiation. Antigens recognized by PP3 and PP4 antibodies were positive in all retinoblanstomas. Reactions to GFAP antibody and antibodies that recognize Müller cells were negative. Retinoblanstomas may express markers of not only photoreceptor cells but also other retinal nuclear cells. These results suggest that the retinoblastoma might be developed from visual stem cells, which are common progenitor cells of photoreceptor cells, intermediate neurons, and ganglion cells.

Immunoglobulin superfamily expression in primary retinoblastoma and retinoblastoma cell lines

Retinoblastoma (Rb) is the most common intraocular tumor of childhood. In this study we examined primary Rb specimens and Rb cell lines for the expression of immunoglobulin superfamily (IgSF) antigens: MHC class I and II (MHC-I and MHC-II), neural cell adhesion molecule (NCAM), intercellular adhesion molecule-1 (ICAM-1), and Thy-1, which play an important role in immune system and tumor cell interactions. MHC-I and-II, ICAM-1 (CD54), NCAM (CD56), and Thy-1 (CDw90) immunoreactivity was studied in eight primary Rb biopsy specimens using immunohistochemistry, three using immunoelectron microscopy, and six Rb cell lines using flow cytometry (FCM). Parenchymal and vascular-associated cells, phenotypically similar to retinal microglia, strongly expressed MHC-II immunoreactivity and were distributed throughout primary Rb specimens. However, MHC-II expression on Rb cell lines was similar to nonspecific control levels. Tumor cells in primary Rb specimens displayed high NCAM, moderate Thy-1, and low MHC-I and ICAM-1 immunolabeling. Tumor vasculature expressed low to moderate MHC-I and ICAM-1 immunoreactivity and moderate Thy-1 immunoreactivity. NCAM was not detected on the vasculature of primary Rb specimens. Rb cell lines displayed variable expression of Thy-1, ICAM-1, and MHC-I. NCAM was highly expressed on five of six Rb cell lines. The high levels of constitutive NCAM immunoreactivity on Rb tumor cells confirm the neuroectodermal origins of this tumor. Additionally, the variable expression of Thy-1 may suggest separate neural lineages or differences in the maturational status ofsome Rb tumors. The presence of a population of infiltrating MHC-II-positive cells in primary Rb tumors has implications for immunomodulation of Rb growth.

[Preparation of anti-human retinoblastoma monoclonal antibody by solid tumor cell immunization and study on characteristics of its antigen]

OBJECTIVE

To prepare anti-human retinoblastoma (Rb) monoclonal antibody (McAb) by immunization with solid tumor cells and preliminarily study the characteristics of its antigen.

METHODS

Three Balb/C mice were immunized by intraperitoneal injection of Rb solid tumor cells acquired from enucleation. Spleen lymphocytes were separated from them and fused with myeloma cell line SP2/0. The anti-human Rb McAb was selected by Rb solid tumor cell, SO-Rb(50), SO-Rb(70), etc as antigens. The characteristics of its antigen were preliminarily studied by immunofluorescence, immunohistochemistry and Western blot.

RESULTS

After repeatedly cloning them with micro-manipulation equipment, we successfully established 3 hybridoma cell lines secreting anti-human Rb McAb. Of all, 3C6 hybridoma cells could steadily secrete anti-human Rb McAb after they were frozen, resuscitated and passaged repeatedly for 2 years. Its subgroup was IgG(1). Both immunofluorescence and immunohistochemistry examinations demonstrated that the corresponding antigen of McAb 3C6 was specifically and highly expressed in Rb tumor cell membrane and cytoplasm. The other tumor tissues and human normal eye tissues were negative. Western blot analysis preliminarily demonstrated that McAb 3C6 could bind 25 000 protein band of Rb antigen.

CONCLUSIONS

The anti-human Rb McAb 3C6 established by immunization of solid tumor cells is specifically and highly expressed in Rb tumor cells and has no cross-response with other tumor tissues and normal eyeballs. The antigen molecular weight bounded to this antibody is 25 000 or so, which further shows that it is a possibility for a new unidentified gene to be concerned with the tumor formation of Rb.

Cloning and sequence analysis of light variable region gene of anti-human retinoblastoma monoclonal antibody

PURPOSE

To clone the variable region gene of light chain of monoclonal antibody against human retinoblastoma and to analyze the characterization of its nucleotide sequence as well as amino acid sequence.

METHODS

Total RNA was extracted from 3C6 hybridoma cells secreting specific monoclonal antibody (McAb) against human retinoblastoma (RB), then transcripted reversely into cDNA with olig-dT primers. The variable region of the light chain (VL) gene fragments was amplified using polymerase chain reaction(PCR) and further cloned into pGEM -T Easy vector. Then, 3C6 VL cDNA was sequenced by Sanger's method. Homologous analysis was done by NCBI BLAST.

RESULTS

The complete nucleotide sequence of 3C6 VL cDNA consisted of 321 bp encoding 107 amino acid residues, containing four workframe regions (FRs) and three complementarity-determining regions(CDRs) as well as the typical structure of two cys residues. The sequence is most homological to a member of the Vk9 gene family, and its chain utilizes the Jkl gene segment.

CONCLUSION

The light chain variable region gene of the McAb against human RB was amplified successfully, which belongs to the Vk9 gene family and utilizes Vk-Jkl gene rearrangement. This study lays a good basis for constructing a recombinant antibody and for making a new targeted therapeutic agents against retinoblastoma.

[Amplifying variable region gene of light chain of monoclonal antibody against human retinoblastoma by PCR]

OBJECTIVE

To acquire the variable region gene of light chain of monoclonal antibody against human retinoblastoma.

METHODS

Total RNA were extracted from hybridoma cells secreting specific monoclonal antibody(McAb) against human retinoblastoma(RB), then transcripted reversely into cDNA with random primers. The variable region of the light chain(VL) gene fragments were ampliflied using polymerase chain reaction(PCR) method. Agrose gel electrophoresis was confirmed.

RESULTS

1.5% agrose gel electrophoresis indicated that VL gene was about 340 base pairs.

CONCLUSION

The light chain variable region gene of the McAb against human RB was amplified successfully, which lays a good basis for construction of a recombinant antibody.

CD31 immunoreactivity in small round cell tumors

CD31 has been shown to be a sensitive and specific marker for endothelial differentiation among epithelioid and spindled-pleomorphic human neoplasms. However, the role of this marker in the evaluation of small round cell tumors has not been evaluated. Formalin-fixed, paraffin-embedded tissue sections from 276 small round cell tumors, including 85 Ewing's sarcoma/primitive neuroectodermal tumors (ES/PNET), 52 rhabdomyosarcomas, 10 extraabdominal polyphenotypic small cell tumors, six desmoplastic small cell tumors, 11 neuroblastomas, 23 Wilms' tumors, 20 retinoblastomas, 13 esthesioneuroblastomas, and 56 small cell malignant lymphomas were stained with CD31 (JC/70A, 1:40), using a modified avidinbiotin-peroxidase complex technique, after citrate buffer microwave epitope retrieval. Among nonlymphoid small round cell tumors, four of 85 ES/PNET were at least focally reactive. No other lesion in this group was positive. In contrast, the majority of well-differentiated (11 of 17), intermediately differentiated (two of three), and lymphoblastic lymphomas (three of three) were positive. Small cleaved lymphomas (three of 13 follicular, one of 13 diffuse) were less often reactive, whereas small noncleaved lesions were negative. Although reactivity for CD31 in ES/PNET is uncommon, the presence of platelet/endothelial cell adhesion molecule in a small cell neoplasm should not in isolation be taken as evidence of hematopoietic origin. These results further define the utility of CD31 in the evaluation of human neoplasms.

Retinoblastoma protein in microphthalmic mice

A microphthalmic strain of mice was used to study immunoresponse of the retinoblastoma protein. Comparing wild-type, heterozygote and homozygote microphthalmic eyes, we found an increasing labelling of phosphorylated retinoblastoma protein (pRb) in the retinal pigment epithelium. Additionally, microphthalmic eyes expressed pRb in the neuroepithelium. Especially rosettes were strongly labelled.

Human retinoblastoma: in vitro differentiation and immunoglobulin superfamily antigen modulation by retinoic acid

Suspension and attachment cultures of Y79 human retinoblastoma cells were treated with all-trans retinoic acid (RA) for up to 10 days to assess its effect on growth and cell-surface expression of immunoglobulin superfamily antigens MHC class I and class II, ICAM-1, NCAM and Thy1. RA up to 10 microM induced growth inhibition, and marked morphological differentiation with extension of prominent processes resembling neurites was seen in attachment cultures. However, above 10 microM RA produced extensive cell death. We also observed increased cell-surface expression of MHC class I, ICAM-1, NCAM and Thy1 on Y79 cells treated with 10 microM over 10 days; constitutive MHC class II expression was not apparent, nor did RA treatment appear to induce Y79 cells to express MHC class immunoreactivity. The up-modulation of cell-adhesion molecules (NCAM, ICAM-1 and Thy1) and immune recognition molecules (NCAM, ICAM-1 and MHC class I), associated with reduced growth and tumour cell differentiation, suggests that RA may have a potential role in regulating the growth and development of retinoblastoma tumours.

Increased chromokinesin immunoreactivity in retinoblastoma cells

chromokinesin is a developmentally down-regulated gene with specific expression in proliferating cells during embryonic chick development. It encodes a DNA-binding motor protein localized along the chromosome arm during mitosis, suggesting that the protein may be a component of the long-observed, yet poorly understood 'ejection force' hypothesized to be involved in controlling the direction and speed of chromosome movement. We have isolated human chromokinesin; with affinity-purified antibodies we demonstrated immunocytochemically that Chromokinesin was present at a much higher level in cultured retinoblastoma cells than in primary cultures of human dermal fibroblasts. The increase in immunoreactivity was particularly prominent in interphase cells, whereas in primary cultures of fibroblasts immunopositive cells were predominantly M-phase cells. These observations imply a deregulation of chromokinesin in retinoblastoma cells. Data presented here may be useful in designing strategies to modulate chromosome movement and cell proliferation with either antisense oligonucleotides or specific antibodies, and hence may set the stage for further investigations of the involvement of chromosome motor molecules in mitosis under normal and pathological conditions.

A study of immunoactivity of retinal S-antigen in retinoblastoma

PURPOSES

To study retinal S-antigen expression in human retinoblastoma and assess if there is a correlation between S-antigen immunoactivity and degree of retinoblastoma cell differentiations.

METHODS

Ten cases of Chinese retinoblastoma parafin-embedded tissues were applied for this study. A strain of monoclonal antibody,MabA9C6, which defines an epitope in S-antigen retained in fixed-tissue sections, was used to study S-antigen expression in 10 cases of retinoblastomas. S-antigen was localized by the biotinavidin indirect immunoperoxidase technique and purified MabA9C6 ascites fluid was used with 1:100 dilution. The whole procedure could be finished within a few hours.

RESULTS

The S-antigen immunoactivity was observed in different patterns: the "normal" photoreceptor elements incorporated in 3 cases of growing tumors; 3 of 4 Fleurettes and E-W rosettes; and scattered tumor cells in 50% of the cases.

CONCLUSIONS

The result suggests that the expression of S-antigen in retinoblastoma may be used to assess the degree of tumor differentiation as another tumor marker in retinoblastoma.

Biochemical characterization and membrane expression of an antigen shared by activated and neoplastic cells of neuroectodermal origin

The reactivity of a mAb (M16) raised against a small cell lung carcinoma line is described. M16 identifies a surface antigen expressed on cells of neuroectodermal origin following activation, as well as neoplastic transformation. M16 antigen expression is increased on retinoblastoma and neuroblastoma cell lines upon 'in vitro' stimulation and it is induced 'in vivo' on glial cells activated following brain injury. Furthermore, glial tumors show levels of M16 molecule expression increasing with the degree of malignancy, and in a retinoblastoma cell line, the expression of M16 was inversely related to the level of HLA-Class I and N-CAM antigens. The M16 antigen may represent a marker of both activation and neoplastic progression for neuroectodermal cells.

[Retinal S-antigen and retinoblastoma--an immunohistochemical study]

A strain of monoclonal antibody, MabAgC6, which defines an epitope in S-antigen, was used to study S-antigen expression in 10 cases of retinoblastoma, where S-antigen immunoactivity was observed in different patterns: the "normal" photoreceptor elements incorporated in 3 cases of growing tumors, 3 of 4 fleurettes and E-W rosettes, and scattered tumor cells in 50% of the cases were stained positive. The results suggest that the expression of S-antigen in retinoblastoma may be used to assess the degree of tumor differentiation, as another of the tumor markers.

[Anti-retinoblastoma reaction developed in vivo through immunization of retinal ganglion neuronotrophic factor]

Isolated retinal ganglion neuronotrophic factor (RGNTF) was used as an antigen to immunize Group A Balb/c mice intraperitoneally prior to the inoculation into the anterior chamber of eye with human retinoblastomal cell line Y-79 (Rb). In Group B mice, Rb cells were inoculated into the eyes before RGNTF immunization. In Group C mice, empty gel without RGNTF was used in immunization 10 days after the Rb inoculation, to serve as a control. The results revealed that the inhibitory rate of Rb tumor development in Group A was 65% (13/20); in Group B only 10% (2/20); and in Group C 0% (0/20). The T-test for difference in the inhibitory rate between Group A and B was statistically significant (T > 2.58; P < 0.01). Sera were collected from these mice and their content of the anti-RGNTF antibody was quantified by ELISA method. The results showed that the anti-RGNTF antibody titer in Group A antisera at 1:600 dilution was measured with an average optical density of 0.156 +/- 0.015; that in Group B 0.103 +/- 0.016; and that in Group C only 0.048 +/- 0.018. Those of controls for normal mouse serum and culture medium were 0.050 +/- 0.008 and 0.043 +/- 0.014, respectively. The t test for difference in the antibody titer measurements between Group A and B was statistically significant (t > t0.05; p < 0.05). Therefore, the above results indicated that active immunization of RGNTF can enhance the specific immunity against the development of retinoblastomal tumor in Balb/c mice, which may have clinical significance in treating human retinoblastoma.

Dual immunologic property of S-100 protein in normal eyes and eyes with retinoblastoma: a histopathological and immunohistochemical study of 88 cases

To ascertain the cell types expressing S-100 protein in eyes with retinoblastoma, a follow-up study was made on 88 formalin-fixed and paraffin-embedded retinoblastoma specimens histopathologically and immunohistochemically, using antibodies against S-100 protein. In normal retinas and morphologically normal retinas with retinoblastoma, both astrocytes and ganglion cells were stained positively for S-100 protein. In the retinoblastomas, not only the reactive astrocytes in most cases, but also large tumor cells with large cell bodies, prominent nucleoli and well-differentiated figures were positive for S-100 proteins in 2 cases. These large tumor cells were thought to be neuronal and were called ganglion-like cells because they were morphologically and immunohistochemically compatible with the large ganglion cells in normal retina. The results indicate that in eyes with retinoblastoma, S-100 protein has both neuronal and glial immunologic properties and could have a limited value as a glial marker for the histogenesis study of retinoblastoma.

[Immunodiagnosis of retinoblastoma]

To improve the accuracy of early diagnosis of retinoblastoma, the authors have examined a number of cellular and humoral immunity parameters in 188 children with retinoblastomas, in 57 ones with nontumorous conditions of the eyes, and in healthy controls. Stages III-IV retinoblastoma was found associated with reduced blood levels of IgG and IgA and a still more marked reduction of both in the lacrimal fluid (4-fold), with reduced blood T lymphocyte count (by 1.5 times), decreased lymphocyte blastogenesis response to phytohemagglutinin (by 8-9 times), reduced leukocyte migration activity (MI = 79 +/- 10%), reduced serum thymic activity (by 2.5 times). The early (I-II) stage of the disease involves a lowering of only lacrimal fluid IgA (2-fold) and of the leukocyte migration index (MI) (89 +/- 2%). This index was found to be an important specific indicator for the early preoperative diagnosis of retinoblastoma. Leukocyte migration inhibition (MI less than 95%) by retinoblastoma antigens was observed only if this tumor was present. In cases with the nontumorous conditions and in health retinoblastoma antigens as a rule stimulated the leukocyte migration (MI over 95%).

[Second solid tumors in childhood. Review based on three cases]

As children with cancer survive longer, the incidence of second malignant neoplasms has increased considerably. We describe here three cases of second solid tumors after 12, 8 and 2 years of initial diagnosis of cancer: one osteosarcoma of left maxilla in a previously treated child with bilateral retinoblastoma, a temporal astrocytoma associated with acute lymphoblastic leukemia and a glioblastoma multiforme in a girl with neurofibromatosis de Von Recklinghausen, after Non Hodgkin lymphoma, respectively. We review the literature about the influence of genetic, immunologic and therapeutic factors involved in the appearance of these second tumors.

Cytokine-induced modulation of cellular proteins in retinoblastoma. Analysis by flow cytometry

Cytokines are a group of specialized, hormone-like proteins that can exert profound influences on cellular development and on a variety of cellular functions. Retinoblastoma cells are an important model for exploring human malignancy and differentiation. These multipotent embryonic cells are capable of differentiating into neuronal, glial-like and retinal pigment epithelium (RPE)-like elements. This report shows that flow cytometric analysis can be used to measure the expression of both cytoplasmic and cell surface proteins in retinoblastoma cells. The authors used this technique to monitor changes in the expression of selected cellular proteins after exposure to specific cytokines and found that MHC class I molecules were augmented by interferon-alpha (IFN-alpha) and interferon-gamma (IFN-gamma), but not by tumor necrosis factor (TNF). However, the MHC class II molecules were augmented by IFN-gamma but not by IFN-alpha or TNF. The neuronal markers, IRBP and PR-6, the glial-like marker, GFAP, and the RPE cell markers, RPE-9 and RPE-15, were not altered by any of the cytokines tested. Furthermore, IFN-gamma induced a striking enhancement of the expression of the photoreceptor cell protein, S-antigen. In contrast, IFN-alpha and TNF did not affect the expression of S-antigen. These studies show that the cytokine, IFN-gamma, can enhance a distinct cellular protein associated with cells committed to a specific cell lineage.

Effect of lymphokine-activated killer cells on human retinoblastoma cells (Y-79) in vitro: enhancement of the activity by a polysaccharide preparation, krestin

Peripheral blood mononuclear cells (PBMC) cultured in a medium containing interleukin 2 (IL 2) develop the ability to kill fresh tumor cells. This function has been termed lymphokine activated killing (LAK). Recently, cord LAK cell activity was demonstrated to be equally as cytotoxic against similar in vitro targets as adult (peripheral) LAK cells. We investigated the future therapeutic use of LAK adoptive immunotherapy by examining LAK in vitro cytotoxicity from both cord and peripheral blood mononuclear cells against pediatric malignant tumor cell lines Y-79 (retinoblastoma). Cord LAK cells show higher levels of cytotoxicity toward Y-79 targets than do adult LAK cells. Attempts to enhance the rIL 2-induced LAK activity by addition of rIFN-gamma or PSK (krestin) were successful. Furthermore, we found that PSK has a function to enhance rIL 2-induced IFN-gamma and TNF-alpha production. These findings suggest that combined administration of cord LAK cells and PSK may account for the improvement of advanced retinoblastoma in the neonatal period.

Recurrent disseminated retinoblastoma treated by high-dose chemotherapy, total body irradiation, and autologous bone marrow rescue

A case of recurrent, disseminated retinoblastoma is presented. The primary intraocular tumor, a metastatic mass at recurrence, and the tumor cells infiltrating bone marrow were all positive for the anti-GD2 monoclonal antibody (Mab) 3A7. Indirect immunofluorescence using the monoclonal antibody 3A7 was an effective method of detecting residual disease in the marrow. After remission was achieved by conventional therapy, the patient underwent autologous bone marrow transplantation (ABMT). The preparative regimen consisted of VP-16, cisplatinum, high-dose melphalan, and total body irradiation. The autologous marrow inoculum was clean of tumor cells at the detection level of 1:10,000. The transplant course was uneventful, and the patient is well and disease-free 17 months after ABMT. We conclude that high-dose chemotherapy and total body irradiation in an ABMT setting is feasible and a potentially curative approach to disseminated retinoblastoma.

In vitro differentiation of human retinoblastoma cells into neuronal phenotypes

In order to characterize the cell type(s) of origin of human retinoblastoma cells by immunophenotyping, primary cells from seven retinoblastomas and of the corresponding cell lines (RBL lines), as well as four retinoblastoma (RB) lines established by other groups, were compared with rat and human retina cells, and with the adenovirus E1A-transformed human retinoblast cell line HER-Xho1-CC2. Analyses using monoclonal antibodies (Mabs) RB13-2 and RB21-7, originally raised against prenatal rat brain cells and recognizing neural cell surface antigens expressed in a developmental-stage-dependent manner, and three cell-type-specific Mabs (Q211, M501, Mab directed against vimentin) developed by other groups, gave the following results: (i) Retinoblastomas consist of cells expressing differentiated neuronal phenotypes during cultivation in vitro; (ii) All of the newly established RBL lines express neuronal phenotypes; and (iii) Cell lines such as Y79, which have been propagated in vitro for extended periods, do not express antigens specific for the neuronal pathway and cannot, therefore, be considered phenotypically representative of retinoblastoma cells.

Dissociation of Rb-binding and anchorage-independent growth from immortalization and tumorigenicity using SV40 mutants producing N-terminally truncated large T antigens

The large T antigen of SV40 is both necessary and sufficient for conversion of primary mouse cells to cells with fully transformed phenotype. In this investigation, the influence of the N-terminal portion of T antigen on individual transformed cell characteristics was probed by using mutants bearing deletions in the 5'T antigen coding sequence. Specifically, DNA constructs expected to produce T antigens missing the first 109, 127, 150, or 176 amino acids or internal amino acid segments between 117 and 250 were tested for the ability to immortalize C57Bl/6 mouse embryo fibroblasts. The transformed cell properties displayed by clonally derived cell lines were then examined. The results indicated that neither the first 127 amino acids nor amino acids 127-250 of T antigen were necessary for efficient immortalization of primary cells or for their tumorigenicity. Functions mapped within these regions, including binding of the retinoblastoma susceptibility gene product (Rb) and transactivation of heterologous promoters, therefore, were not required to confer either of these growth properties. In addition the results showed that anchorage-independent growth was separable genetically from tumorigenicity and that removal of amino acids within the first 250 residues of T antigen compromised other transformed cell growth properties.

Interferon-gamma enhances the expression of retinal S-antigen, a specific neuronal cell marker

Interferon-gamma (IFN-gamma) is a potent lymphokine which can modify a variety of cellular processes. One of the mechanisms involved in these processes is the ability of IFN-gamma to alter the regulation and expression of cellular proteins. Using analytical flow cytometry, we show that recombinant human IFN-gamma can enhance the expression of retinal S-antigen in retinoblastoma cells. This enhancement was selective since two other retinal cell proteins, interphotoreceptor binding protein (IRBP) and photo-6, were not affected by IFN-gamma treatment. Retinal S-antigen plays an important role in vision and is one of the retinal proteins capable of inducing an inflammatory eye disease called experimental autoimmune uveitis. These studies therefore demonstrate an important role for this lymphokine, that is, the enhanced expression of a neuronal cell protein. This finding may also identify additional mechanisms by which IFN-gamma may participate in immunopathologic events in nervous tissue.

Immunohistological characterisation of retinoblastoma and related ocular tissue

The immunohistological reactivity of six retinoblastomas was investigated by means of 18 monoclonal antibodies and compared with that of adult and fetal retina. The antigenic profiles were found to be characteristic for each cell type studied and indicated that a panel of monoclonal antibodies could achieve a specific immunolocalisation not afforded by any single antibody. Immunohistological comparison between retinoblastoma and adult and fetal retinal cells provided evidence of the histogenesis of the tumour. The data suggest that the tumour arises from an early multipotential cell, which retains the capacity to develop differentiation characteristics associated with inner or outer retinal cell types, resulting in a heterogeneous tumour cell population. A cell with such differentiation potential predominates in the retina prior to the primitive neuroepithelial layer division at eight weeks' gestation.

Unusual sinonasal small-cell neoplasms following radiotherapy for bilateral retinoblastomas

Two patients developed sinonasal small-cell neoplasms that arose 22 years and 37 years, respectively, following radiotherapy for bilateral retinoblastomas. The tumors were composed of small cells with scant cytoplasm and had a few scattered Homer-Wright rosettes. Immunohistochemically, one tumor was positive for keratin (CAM 5.2 and AE1/AE3), epithelial membrane antigen, and neuron-specific enolase. The other neoplasm was immunoreactive for keratin (CAM 5.2 only) and neuron-specific enolase; it also had focal immunopositivity for S-100 protein, desmin, and muscle-specific actin. Both were negative for CEA, vimentin, melanocyte-specific antigen (HMB45), chromogranin A, synaptophysin, Leu-7, 200 kd neurofilament, and retinal S-antigen. Despite aggressive multimodal therapy, the patients died of metastatic tumor 7 months and 10 months following their initial diagnosis, respectively. Although osteosarcoma is the most frequent second cancer following bilateral retinoblastomas, some patients develop clinically aggressive sinonasal small-cell tumors that are difficult to place into conventional classifications. Both of our cases showed evidence of multidirectional differentiation; one tumor labeled with epithelial and neural markers, and the other expressed epithelial, neural, and myogenous antigens.

Specific antitumor immunologic reactivity in patients with retinoblastoma

Retinoblastoma antigen (RbAg) and retinal tissue antigen (RAg) were made from allogeneic retinoblastoma tissues and normal retinal tissue using the 3M KCl method. We have examined leukocyte migration inhibition test (LMIT) and enzyme-linked immunosorbent assay (ELISA) to RbAg and RAg in normal controls and the patients with retinoblastoma, including two spontaneously regressed cases. In LMIT, six out of the 11 patients tested against RhAg showed positive reactivity, in which 4 cases reacted only with RbAg, but not with RAg. All nine control subjects had negative reactivity to the two antigens. In ELISA, 40% of the retinoblastoma patients and 5.56% in normal controls showed positive reaction against RbAg. It was suggested that not only retinal antigens but also retinoblastoma specific antigens present in human retinoblastoma cells. The results also suggested that patients with retinoblastoma and those with spontaneous regression of Rb had both cell-mediated immunologic reactivity and humoral immune response toward retinoblastoma antigen in vitro. These immune responses to RbAg may be responsible for spontaneous regression of retinoblastoma.

Collagen-induced alterations in intercellular adhesion and antigen expression in retinoblastoma cells

Y79 human retinoblastoma cells, which typically grow as suspension cultures in vitro, show increased intercellular and cell-substratum adhesion, and form compact cellular aggregates when cultured on a collagen substratum. Concomitant with collagen-induced formation of compact cellular aggregates, is an increase in the binding of peanut lectin, especially at points of intercellular apposition. In addition, increases in the binding of antibodies against neuron-specific enolase and the cone-specific monoclonal antibody CSA-1 are noted following attachment and growth on collagen. In contrast, a decrease in the binding of antibodies against the glial marker, glial fibrillary acidic protein, is observed in collagen-attached cells. Thus, both the adhesive properties and the biochemical composition of Y79 retinoblastoma cells are altered by their attachment to and growth upon a collagenous substratum.

Immunohistochemistry of retinoblastoma. A review

Various studies which relate to the immunohistochemical identification of neuronal, glial, carbohydrate and nucleic acid associated antigens in retinoblastoma will be reviewed. The majority of these studies appear to support the concept that retinoblastomas arise, in situ, from neuron committed cells and in some cases specifically into photoreceptor-like cells. In selected cases, however, glial cell differentiation may be a feature of the tumor. In addition, the molecular biology of the retinoblastoma gene and the immunohistochemical characterization of its gene product will be discussed.

Metastatic retinoblastoma successfully treated with immunomagnetic purged autologous bone marrow transplantation

There are no documented cases of long-term, disease-free survival in retinoblastoma (RB) metastatic to the bone marrow. The following study details successful outcome in a 3-year-old child with extensive marrow replacement 7 months postenucleation in an otherwise untreated group V RB. Therapy consisted of combinations of vincristine, doxorubicin, and cyclophosphamide for 3 months. After demonstrating cross-reactivity by a panel of six monoclonal neuroblastoma (NB) antibodies with the patient's RB cells, her marrow was purged by using microsphere-linked monoclonal antibodies, and then reinfused as rescue therapy after ablative doses of etoposide and cyclophosphamide. The authors conclude that short-term induction therapy followed by marrow ablative combination chemotherapy and immunomagnetically purged autologous marrow rescue can (1) effect successful outcome in widely metastatic RB, and (2) eliminate the risk of therapy-induced second malignancies.

Detection of gangliosides as N-glycolylneuraminic acid-specific tumor-associated Hanganutziu-Deicher antigen in human retinoblastoma cells

Gangliosides were shown to bear the tumor-associated N-glycolylneuraminic acid (NeuGc)-specific Hanganutziu-Deicher (HD) antigen expressed in human retinoblastoma cells. HD antigenic gangliosides were detected by thin-layer chromatography/enzyme-immunostaining using affinity-purified chicken antibody against GM3 containing NeuGc and horseradish peroxidase-conjugated anti-chicken IgG. One to four species of the antigenic gangliosides were detected from all of 4 cell lines, Y79, WERI-Rb1, TOTL1, and YK, as well as freshly cultured retinoblastoma cells and isolated tumor tissue. All cases contained GM3(NeuGc) as an HD antigen. No HD antigenic ganglioside was detected in normal retinal tissues by the same procedure.

Coexpression of neuronal, glial, and major histocompatibility complex class II antigens on retinoblastoma cells

This study identifies the presence of major histocompatibility complex class II antigens on retinoblastoma cells. In addition, the modulation of HLA-DR by interferon-gamma as well as the preferential expression of this major histocompatibility complex molecule over HLA-DQ is described. Double labeling experiments revealed that HLA-DR antigen is shared concomitantly with cells of glial and neuronal character. Investigations such as these underscore the possibility that expression of major histocompatibility complex class II antigens may function as immunological components in the host or play a role in the cellular differentiation of these tumor cells.

Immunohistochemical characterization of human retinoblastomas in situ with multiple markers

We studied paraffin-embedded specimens from 18 surgically enucleated eyes with retinoblastoma by peroxidase-antiperoxidase immunohistochemistry with antibodies against glial fibrillary acidic protein, S-100 protein, Leu 7 epitopes, neuron-specific enolase, the 200-kilodalton subunit of the neurofilament triplet polypeptide, and retinal S-antigen. We found that (1) glial fibrillary acidic protein, S-100 protein, and Leu 7 epitopes were detected only in well-differentiated glial cells that were interpreted as reactive and not neoplastic, (2) undifferentiated neoplastic cells expressed both neuron-specific enolase and retinal S-antigen immunoreactivity, and (3) differentiated cells forming Flexner-Wintersteiner rosettes were found to express neuron-specific enolase, retinal S-antigen, and, occasionally, neurofilament protein. These results support the view that retinoblastomas are composed of neuron-committed cells and favor the origin of these tumors from photoreceptor progenitor cells. We did not find any morphologic or immunohistochemical evidence of glial differentiation from tumor cells that would support the concept that retinoblastoma arises from a primitive neuroectodermal cell capable of divergent differentiation along neuronal and glial lines.

Electron microscopy and HLA expression of a new cell line of retinoblastoma

A new continuous retinoblastoma cell line (Rb 355-7) derived from a nonfamilial unilaterally-affected child was studied morphologically and with regard to HLA expression. The tumor was compared with two older and widely studied cell lines, the Y-79 and WERI-Rb1 strains. The Rb 355-7 line grew in tissue culture in clusters and chains. Its doubling time was calculated to be 4.4 days. In contrast to the Y-79 and WERI-Rb1 cell lines, the Rb 355-7 showed a paucity of HLA expression.

Retinoblastoma. Immunohistochemistry and cell differentiation

Tumor from eight enucleated eyes was analyzed by immunohistochemistry, using a panel of specific antibodies including interphotoreceptor retinoid-binding protein (IRBP), S-antigen (S-Ag), opsin, neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), laminin, and vimentin. In addition, immunoelectron microscopy and enzyme-linked immunosorbent assay (ELISA) for IRBP were performed. Immunohistochemical staining disclosed the most pronounced labeling of tumor cells with NSE and IRBP antibodies. A correlation was found between the degree of tumor differentiation and amount of IRBP, a protein specifically synthesized by photoreceptor cells. Moderate labeling of the better differentiated tumors was also observed with antibodies against S-Ag and focal labeling in a few tumors with opsin antibodies. Anti-GFAP labeling was limited to a smaller number of reactive glial cells and perivascular glial cells. These data indicate the essential neuronal nature of retinoblastoma tumor cells in situ as well as at least partial photoreceptor-like features, as shown by the presence of recognized photoreceptor cell markers (IRBP, S-Ag, opsin). Tissue culture studies using the human Y-79 retinoblastoma cell line also demonstrate that the tumor cells are primitive multipotential retinoblasts capable of at least partial differentiation along neuronal, glial, or pigment epithelial cell lines.

Heterogenous expression of antigenic markers on retinoblasts

Using a large panel of monoclonal antibodies to antigenic determinants specific for photoreceptor outer segments (S-Ag), for cells of neural (Leu-7) bipolar and/or ganglion cell (A2B5), glial/astrocytic (LN-1) or Muller's cell (M.M.) and two polyclonal antibodies to S-Ag and S-100 protein, the authors studied the expression of these antigenic determinants in four newly established retinoblastoma cell cultures and in cells derived from the Y-79 cell line. All four newly established retinoblastoma cell cultures demonstrated antigenic determinants specific for photoreceptors, astrocyte/glial and Muller's cells. The population of cells derived from the Y-79 cell line reacted mainly with the polyclonal antibody to S-100 protein, reflecting the homogeneity of its cell population mainly harboring antigenic determinants specific for astrocyte/glial cells. The heterogeneic staining of the newly established retinoblastoma cell cultures may reflect the multipotential-embryonic origin of these cells demonstrated by their ability to express antigenic determinants specific for the different cellular elements of the mature neuro-retina while the strictly glial staining of the Y-79 may be the result of cloning of this cell line.