Use of anti-cancer drugs, mitocans, to enhance the immune responses against tumors

Cytotoxic drugs in cancer therapy are used with the expectation of selectively killing and thereby eliminating the offending cancer cells. If they should die in an appropriate manner, the cells can also release danger signals that promote an immune reaction that reinforces the response against the cancer. The identity of these immune-enhancing danger signals, how they work extra- and intracellularly, and the molecular mechanisms by which some anti-cancer drugs induce cell death to bring about the release of danger signals are the major focus of this review. A specific group of mitocans, the vitamin E analogs that act by targeting mitochondria to drive ROS production and also promote a more immunogenic means of cancer cell death exemplify such anti-cancer drugs. The role of reactive oxygen species (ROS) production and the events leading to the activation of the inflammasome and pro-inflammatory mediators induced by dying cancer cell mitochondria are discussed along with the evidence for their contribution to promoting immune responses against cancer. Current knowledge of how the danger signals interact with immune cells to boost the anti-tumor response is also evaluated.

MUC1-specific immune therapy generates a strong anti-tumor response in a MUC1-tolerant colon cancer model

A MUC1-based vaccine was used in a preclinical model of colon cancer. The trial was conducted in a MUC1-tolerant immune competent host injected with MC38 colon cancer cells expressing MUC1. The vaccine included: MHC class I-restricted MUC1 peptides, MHC class II-restricted pan-helper-peptide, unmethylated CpG oligodeoxynucleotide, and granulocyte macrophage-colony stimulating factor. Immunization was successful in breaking MUC1 self-tolerance, and in eliciting a robust anti-tumor response. The vaccine stimulated IFN-gamma-producing CD4(+) helper and CD8(+) cytotoxic T cells against MUC1 and other undefined MC38 tumor antigens. In the prophylactic setting, immunization caused complete rejection of tumor cells, while in the therapeutic regimen, tumor burden was significantly reduced.

Invasion and metastasis of a mammary tumor involves TGF-beta signaling

Several studies have correlated escape from TGF-beta-mediated cell cycle arrest with the tumorigenic phenotype. Most often, this escape from growth control has been linked to dysfunctional TGF-beta receptors or defects in the TGF-beta-mediated SMAD signaling pathway. In this report, we found that highly metastatic 4T1 mammary carcinoma cells express functional TGF-beta receptors capable of initiating SMAD-mediated transcription, yet are not growth inhibited by TGF-beta1. We further observed that TGF-beta directly contributes to the metastatic behavior of this cell line. Exposure to TGF-beta caused 4T1 cells to undergo morphological changes associated with the metastatic phenotype and invade more readily through collagen coated matrices. Furthermore, expression of a dominant negative truncated type II receptor diminished TGF-beta signaling and significantly restricted the ability of 4T1 cells to establish distant metastases. Our results suggest that regardless of 4T1 resistance to TGF-beta-mediated growth inhibition, TGF-beta signaling is required for tumor invasion and metastases formation.

Invasion and metastasis of a mammary tumor involves TGF-beta signaling

Several studies have correlated escape from TGF-beta-mediated cell cycle arrest with the tumorigenic phenotype. Most often, this escape from growth control has been linked to dysfunctional TGF-beta receptors or defects in the TGF-beta-mediated SMAD signaling pathway. In this report, we found that highly metastatic 4T1 mammary carcinoma cells express functional TGF-beta receptors capable of initiating SMAD-mediated transcription, yet are not growth inhibited by TGF-beta1. We further observed that TGF-beta directly contributes to the metastatic behavior of this cell line. Exposure to TGF-beta caused 4T1 cells to undergo morphological changes associated with the metastatic phenotype and invade more readily through collagen coated matrices. Furthermore, expression of a dominant negative truncated type II receptor diminished TGF-beta signaling and significantly restricted the ability of 4T1 cells to establish distant metastases. Our results suggest that regardless of 4T1 resistance to TGF-beta-mediated growth inhibition, TGF-beta signaling is required for tumor invasion and metastases formation.

TCR v(beta) usage and clonality of T cells isolated from progressing and rejected tumor sites before and after in vitro culture

A gelatin sponge model of concomitant tumor immunity was employed in order to examine the clonality of T cells associated with progressing and rejected tumor sites. Here we show that freshly isolated T cells bearing TCR V(beta)1, CDR3 RPGTGN, J(beta)1.1 and TCR V(beta)8, CDR3 GD, J(beta)1.6 predominated progressing and rejected tumor sites. Despite the similarity in T cell populations, the T cells from rejected tumor sites were capable of killing the autologous tumor cells, whereas T cells from progressing tumor sites were not able to do so. The differing cytolytic ability could not be attributed to a difference in TCR zeta chain protein expression levels between both T cell populations. After a 5 day mixed lymphocyte tumor culture the T cells from the progressing tumor site were capable of killing autologous tumor cells, which suggested changes took place within the cell population during in vitro culture. Further TCR analysis revealed T cells bearing TCR V(beta)1, CDR3 RPGTGN, J(beta)1.1 and TCR V(beta)8, CDR3 GD, J(beta)1.6 were not expanded following the in vitro culture. These data suggest that the lack of cytotoxicity of freshly isolated tumor-infiltrating lymphocytes (TIL) was not due to abnormal TCR zeta chain expression or major differences in the TCR V(beta) usage. Additionally, the gain of TIL effector function did not correlate with an expansion of the TCR bearing T cells found to predominate the in vivo response. These data suggest that the predominant TCR V(beta) used by lymphocytes infiltrating regressing or rejected tumors may not represent the tumor reactive T cells that grow in culture or respond to the autologous tumor in vitro.

Construction of new amplifier expression vectors for high levels of IL-2 gene expression

The success of IL-2 gene therapy in cancer is in part dependent on the development of high level IL-2 gene expression vectors. Currently, expression vectors based on the human cytomegalovirus (CMV) promoter give the highest levels of expression. We have attempted to construct new IL-2 expression vectors to test whether gene expression can be further increased. The first approach was to use the new SR-alpha promoter to control IL-2 gene expression. The second approach was to combine the Tat transcription activator gene and the HIV 1 and 2 promoters in the same construct so that the levels of gene expression can be amplified. Transient transfection results using the human colon cancer cell line SW480 showed that the SR-alpha promoter yields similar levels of activity as the CMV promoter. However, the HIV 1 and 2 promoter-based amplifier constructs produced 11 and 28 times more secreted IL-2 than the CMV promoter control. The augmented activity of the amplifier constructs was dependent on the presence of the Tat gene and the transcriptional units must be placed in the same orientation. Reducing the size of the vectors by elimination of the neomycin selectable marker did not increase the activity of the constructs.

Immunotherapy of advanced malignancy by direct gene transfer of an interleukin-2 DNA/DMRIE/DOPE lipid complex: phase I/II experience

PURPOSE

We have completed a phase I study, followed by three phase I/II studies, in patients with metastatic melanoma, renal cell carcinoma (RCC), and sarcoma in order to evaluate the safety, toxicity, and antitumor activity of Leuvectin (Vical Inc, San Diego, CA), a gene transfer product containing a plasmid encoding human interleukin (IL)-2 formulated with the cationic lipid 1, 2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide/dioleyl-phosphatidyl-ethanolamine (DMRIE/DOPE) and administered intratumorally.

PATIENTS AND METHODS

Twenty-four patients were treated in the phase I study. Leuvectin doses were 10 microg, 30 microg, or 300 microg weekly for 6 weeks. In three subsequent phase I/II studies, a total of 52 patients (18 with melanoma, 17 with RCC, and 17 with sarcoma) were treated with further escalating doses of Leuvectin: 300 microg twice a week for 3 weeks, 750 microg weekly for 6 weeks, and 1,500 microg weekly for 6 weeks.

RESULTS

There were no drug-related grade 4 toxicities and only one grade 3 toxicity, but the majority of patients experienced mild constitutional symptoms after treatment. In the phase I/II studies, 45 patients were assessable for response (14 with RCC, 16 with melanoma, and 15 with sarcoma). Two patients with RCC and one with melanoma have achieved partial responses lasting from 16 to 19 months and continuing. In addition, two RCC, three melanoma, and six sarcoma patients had stable disease lasting from 3 to 18 months and continuing. The plasmid was detected by polymerase chain reaction assay in the posttreatment samples of 29 of 46 evaluated patients. Immunohistochemistry studies on serial biopsy specimens showed increased IL-2 expression and CD8(+) infiltration after treatment in the tumor samples of several patients (12 and 16, respectively).

CONCLUSION

Direct intratumoral injection of Leuvectin is a safe and possibly effective immunotherapeutic approach in the treatment of certain tumor types.

Clinical aspects of intratumoral gene therapy

One of the major obstacles to the development of gene therapy for cancer is our inability to deliver genes to all targets within the body. Thus, effective methodology does not exist to deliver a gene intravenously with the expectation that it will selectively localize within the target tumor, will not localize in other tissues and will be expressed efficiently. While one can take advantage of tissue-specific promoters to activate the gene only in a given target tissue, only a small fraction of the vector will be taken up in the target tissue and expressed. Consequently, since accessible local or regional tumor masses are a major problem in many cancers, there has been a strong emphasis on clinical trials in intratumoral and peritumoral gene delivery.

A novel immunological model for the study of prostate cancer

The Dunning R-3327 rat prostatic adenocarcinoma is a widely accepted model for in vivo experimental studies of prostate cancer. We have previously derived phenotypically distinct cell lines from a s.c. tumor resulting from the inoculation of the R-3327-5 subclone into Copenhagen rats. In this study, we report studies using a gelatin sponge model for the delivery of tumor cells and the retrieval of tumor-specific leukocytes responsive to different prostatic cell lines. S.c. preimplanted sponges were inoculated with tumor cells previously selected for differential properties of tumor formation and metastasis and examined for leukocyte content at time points of 1, 3, and 5 weeks after tumor cell inoculation. Cytospin and flow cytometric analyses revealed fewer tumor-associated leukocytes present in sponges inoculated with tumorigenic R-3327-5' and R-3327-5'B lines, with lesser sponge degradation, than in experiments with the nontumorigenic R-3327-5'A line, suggestive of a tumor cell-induced immunomodulatory mechanism. Morphological studies indicate an intermittent tumor growth pattern that gradually disappears in sponges inoculated with the nontumorigenic R-3327-5'A cells but a robust growth pattern in sponges inoculated with the tumorigenic cell lines. Cytokine analyses show the secretion of higher levels of active transforming growth factor-beta by the more invasive and metastatic lines. Total transforming growth factor-beta levels are higher in the epithelial, tumorigenic R-3327-5'B line. Additionally, the more tumorigenic lines secrete interleukin 10, a potent immunosuppressive molecule. In this report, we demonstrate the ability to retrieve viable leukocyte populations from a prostate tumor line bearing sponges, which offers an important model for further in vitro and in vivo manipulations and holds promise for testing adoptive immunotherapeutic strategies.

Interferon gamma and antisense transforming growth factor beta transgenes synergize to enhance the immunogenicity of a murine mammary carcinoma

Transforming growth factor beta (TGFbeta) is an immunosuppressive cytokine that contributes to the immunological escape of tumor cells. In a previous study we demonstrated that inhibition of TGFbeta production by EMT6 murine mammary tumor cells expressing an antisense TGF-beta transgene reduces their tumorigenicity. On the basis of this observation we hypothesized that down-regulation of TGFbeta production coupled with interferon gamma (IFNgamma) stimulation would induce an immune response superior to that generated by either strategy alone. In this study, EMT6 tumor cells expressing antisense TGFbeta were transduced with the murine IFNgamma gene. Tumor cells expressing either or both transgenes grew more slowly than mock-transduced tumors. Dual-transgene-expressing tumor cells were more immunogenic than tumor cells expressing either transgene alone. Studies in mice depleted of T cell subsets indicated that CD8+ T cells are the primary effectors of the antitumor activity observed. These results suggest that down-regulation of immunosuppression combined with cytokine-mediated immune augmentation is a useful strategy to improve antitumor immunity.

Phase I study of immunotherapy of hepatic metastases of colorectal carcinoma by direct gene transfer of an allogeneic histocompatibility antigen, HLA-B7

We have completed a phase I study to test feasibility and toxicity of immunotherapy of hepatic metastases from colorectal carcinoma by direct gene transfer of HLA-B7, a MHC class I gene. Eligible patients were HLA-B7 negative, immunocompetent by PHA lymphocyte stimulation and had at least two measurable hepatic lesions on CT scan for measurement of response of the injected lesion, as well as evaluation of possible distant response. Under ultrasonographic guidance the hepatic lesions were injected with Allovectin-7, a liposomal vector containing the combination of the HLA-B7 gene with beta 2-microglobulin formulated with the lipid DMRIE-DOPE. Eligible patients were injected on two schedules. On the first schedule patients received an injection on day 1 and the injected lesion was biopsied to determine transfection every 2 weeks for 8 weeks. Doses were escalated from 10 micrograms to 50 micrograms to 250 micrograms with three patients treated at each level. The second schedule included multiple injections of 10 micrograms. Three patients received injections on days 1 and 15. Three patients received injections on days 1, 15 and 29. A total of 15 patients have completed treatment. The plasmid DNA was detected in 14 of 15 patients (93%) by PCR. In five of 15 patients (33%) mRNA was also detected. The HLA-B7 protein was detected in five of eight patients (63%) by immunohistochemistry and in seven of 14 patients (50%) tested by fluorescence activated cell sorting (FACS) analysis. There has been no serious toxicity directly attributable to allovectin-7. Our results suggest that liposomal gene transfer by direct injection is feasible and non-toxic. Further studies will be necessary in order to establish the therapeutic efficacy.

Expression of an antisense transforming growth factor-beta1 transgene reduces tumorigenicity of EMT6 mammary tumor cells

Transforming growth factor-beta (TGF-beta) is a potent immunosuppressive cytokine produced by many tumor cells. Secretion of TGF-beta by malignant cells may therefore be a mechanism by which tumor cells escape destruction by tumor-specific T lymphocytes. In order to evaluate the role of tumor-derived TGF-beta on tumor progression, we have inhibited the production of this cytokine by introducing a gene encoding antisense TGF-beta1 into the EMT6 murine mammary tumor cell line using a retroviral vector (Las-TGF-beta1SN). EMT6 cells transduced with this vector (EMT6as-TGF-beta1) stably expressed the antisense gene and secreted 52% less TGF-beta than did tumor cells transduced with the backbone vector alone. Supernatant fluid recovered from tumor cells expressing the antisense TGF-beta1 gene also exhibited a decreased capacity to inhibit alloantigen-specific cytotoxic T-cell responses in vitro. Furthermore, tumor growth in mice injected with EMT6as-TGF-beta1 tumor cells was inhibited compared to mice injected with control tumor cells. These results demonstrate that expression of antisense TGF-beta1 by transduced EMT6 cells decreases their tumorigenicity and suggest that this approach of eliminating immune suppression is a potentially useful strategy to enhance antitumor responses.

Phase I study of direct gene transfer of an allogeneic histocompatibility antigen, HLA-B7, in patients with metastatic melanoma

PURPOSE

To determine the safety, toxicity, and efficacy of direct intratumoral injection of an allogeneic major histocompatibility complex (MHC) class I gene, HLA-B7, in a cationic lipid vector (Allovectin-7; Vical Inc, San Diego, CA) in patients with metastatic melanoma.

PATIENTS AND METHODS

Seventeen HLA-B7-negative patients were treated with intralesional injection of Allovectin-7. Twelve patients received a single intralesional injection containing 10 micrograms (four patients), 50 micrograms (five patients), or 250 micrograms (three patients) of plasmid DNA. Five patients received two or three injections of 10 micrograms DNA to a single tumor site at 2-week intervals. Tumor biopsies pretherapy and 2 and 4 weeks after gene injection were obtained to determine expression of the plasmid by polymerase chain reaction (PCR), reverse transcriptase (RT)-PCR, flow cytometry, and immunohistochemistry.

RESULTS

Toxicities were related to technical aspects of the injections or biopsies. These included pain, hemorrhage, pneumothorax, and hypotension. Two patients were hospitalized overnight for observation. Seven patients (50%) had tumor responses insofar as the injected nodule decreased > or = 25% by radiologic or physical examination. One patient with a single site of disease achieved a complete remission. Ninety-three percent of the patients' post-gene therapy biopsies contained HLA-B7 plasmid DNA, mRNA, or protein.

CONCLUSION

Intratumoral injection of the allogeneic histocompatibility gene, HLA-B7, in a lipid vector can be performed safely at plasmid DNA doses < or = 250 micrograms. The safety profile and biologic activity of this therapy warrants further studies to define the mechanism of action, predictors of response, and antitumor efficacy of this approach.

Interferon gamma (IFNgamma) gene transfer of an EMT6 tumor that is poorly responsive to IFNgamma stimulation: increase in tumor immunogenicity is accompanied by induction of a mouse class II transactivator and class II MHC

Abstract Interferon gamma (IFNgamma) is an important cytokine with immunomodulatory properties that include activation of immune cells and induction of class I and class II major histocompatibility complex antigens. In this study a retroviral vector was used to introduce the IFNgamma gene into EMT6 tumor cells to assess the effect of IFNgamma gene expression on tumor immunogenicity. Transfectants were selected in G418-containing tissue-culture medium and were determined to express the inserted IFNgamma gene by reverse transcriptase/polymerase chain reaction. Flow-cytometric analysis revealed that parental unmodified EMT6 cells constitutively expressed only class I MHC and were poorly responsive to exogenous IFNgamma stimulation, whereas class II MHC was induced in IFNgamma-transfected cells. The induction of class II MHC in IFNgamma-transfected cells correlated with the expression of a mouse class II transactivator gene that was dormant in unmodified or mock-transfected cells. In addition, IFNgamma-gene-transfected tumor cells were found to secrete up to 17 ng IFN (equivalent to 75 units/10(6) cells) by enzyme-linked immunosorbent assay (ELISA). Whereas parental EMT6 cells grew unchecked, the growth of genetically modified tumor cells was significantly inhibited in immunocompetent mice. Rechallenge of animals that rejected an IFNgamma-transfected EMT6 clone (EMT6-B17) with parental EMT6 cells resulted in tumor rejection, suggesting that IFNgamma-transfected EMT6 cells were able to induce long-term immunity. Mixing experiments using gene-transfected and unmodified tumor cells demonstrated that 10% of IFNgamma-transfected cells in the population was sufficient to protect mice against subsequent challenge with tumorigenic EMT6 cells. These studies demonstrate that the immunogenicity of tumor cells that are poorly responsive to exogenous IFNgamma can be enhanced by inserting and expressing the IFNgamma transgene. These findings also suggest a role for class II MHC in reducing tumorigenicity of the EMT6 tumor and inducing long-term tumor immunity.

Studies of in vivo recruitment and activation of cytotoxic lymphocytes using a gelatin-sponge model of concomitant tumor immunity

We have earlier described a sponge model of concomitant tumor immunity that permits the capture and isolation of effector T lymphocytes that mediate the rejection of a secondary EMT6 tumor implant. In this study, we have employed the sponge model to study lymphocyte homing and in situ activation during the development of concomitant tumor immunity. Our results demonstrate that EMT6-specific CTL in animals bearing primary EMT6 tumors home preferentially to sponges implanted with EMT6 tumor cells, as compared with contralateral sponges lacking tumor cells or sponges injected with antigenically distinct 168 tumor cells. We further show that recruitment is selective and is not in response to a foreign-body reaction to the sponge. In addition, we show that EMT6-specific CTL were recovered from sponges injected either with intact EMT6 tumor cells or with a mixture of EMT6-derived membranes and supernatant. In contrast, cells accumulating in sponges injected with membranes or supernatant alone were not cytolytic. Thus, maximal recruitment, retention, and activation of CTL precursors require putative chemo-attractive factors secreted by tumor cells as well as interaction with tumor antigen.

T lymphocytes infiltrating sites of tumor rejection and progression display identical V beta usage but different cytotoxic activities

Most tumors grow progressively and overwhelm the host. The rare but documented cases of spontaneous regression of primary tumors are indicative of the potential of tumor-bearing hosts to develop a significant antitumor response. Because most tumors grow progressively in the host, it is not surprising that the majority of studies have focused on T lymphocytes that infiltrate these tumors. Although these studies have generated significant and useful information during the period of tumor growth, they can only speculate on the mechanisms that are involved in tumor rejection. We have used a well developed sponge model of concomitant tumor immunity that allows us to compare the immunologic events that occur during tumor progression vs rejection. In this model, an animal harboring a primary EMT6 mammary tumor is challenged with a secondary tumor implant through a pre-implanted gelatin sponge. During the manifestation of concomitant tumor immunity, the secondary tumor is rejected and the effector cells mediating the response are retained within the sponge matrix. Using this model we analyzed the TCR usage, cytotoxic activity of lymphocytes, and cytokine production at both tumor sites. The data revealed that tumor-rejecting lymphocytes isolated from the site of secondary tumor implant were cytotoxic toward EMT6 cells, whereas tumor-infiltrating lymphocytes isolated from the progressing primary tumor were not. Interestingly, the TCR-V beta repertoire of the tumor-infiltrating lymphocytes and tumor-rejecting lymphocytes were identical with V beta 1 and V beta 8 being predominant at both sites. Furthermore, the rejection site showed higher gene expression of IFN-gamma, TNF-alpha, and IL-10 whereas TGF-beta expression was slightly higher in the progressing tumors. These findings suggest that the disparate effector functions observed during tumor progression vs rejection are not caused by different T cell phenotypes but may be due instead to influences exerted by cytokines produced at the tumor sites.

T lymphocytes infiltrating sites of tumor rejection and progression display identical V beta usage but different cytotoxic activities

Most tumors grow progressively and overwhelm the host. The rare but documented cases of spontaneous regression of primary tumors are indicative of the potential of tumor-bearing hosts to develop a significant antitumor response. Because most tumors grow progressively in the host, it is not surprising that the majority of studies have focused on T lymphocytes that infiltrate these tumors. Although these studies have generated significant and useful information during the period of tumor growth, they can only speculate on the mechanisms that are involved in tumor rejection. We have used a well developed sponge model of concomitant tumor immunity that allows us to compare the immunologic events that occur during tumor progression vs rejection. In this model, an animal harboring a primary EMT6 mammary tumor is challenged with a secondary tumor implant through a pre-implanted gelatin sponge. During the manifestation of concomitant tumor immunity, the secondary tumor is rejected and the effector cells mediating the response are retained within the sponge matrix. Using this model we analyzed the TCR usage, cytotoxic activity of lymphocytes, and cytokine production at both tumor sites. The data revealed that tumor-rejecting lymphocytes isolated from the site of secondary tumor implant were cytotoxic toward EMT6 cells, whereas tumor-infiltrating lymphocytes isolated from the progressing primary tumor were not. Interestingly, the TCR-V beta repertoire of the tumor-infiltrating lymphocytes and tumor-rejecting lymphocytes were identical with V beta 1 and V beta 8 being predominant at both sites. Furthermore, the rejection site showed higher gene expression of IFN-gamma, TNF-alpha, and IL-10 whereas TGF-beta expression was slightly higher in the progressing tumors. These findings suggest that the disparate effector functions observed during tumor progression vs rejection are not caused by different T cell phenotypes but may be due instead to influences exerted by cytokines produced at the tumor sites.

Uptake and intracellular survival of Bordetella pertussis in human macrophages

Recent reports have demonstrated that Bordetella pertussis has invasive behavior in vivo and in vitro. In this study, we investigated the ability of a virulent strain, avirulent mutants, and mutants deficient in specific virulence factors to enter and survive intracellularly in human macrophages in vitro. Uptake of virulent B. pertussis was dose dependent and occurred in the absence of serum or specific antibody, with entry occurring via a microfilament-dependent phagocytic process. The virulent wild-type parental strain was internalized and persisted intracellularly over the 3 days of experiments, as determined by transmission electron microscopy and by recovery of viable plate counts. This is the first report of long-term survival of B. pertussis in human macrophages. Avirulent mutants entered macrophages, but at only an average of 1.5% of virulent parental levels, and did not survive intracellularly. Mutants which did not express adenylate cyclase toxin, filamentous hemagglutinin, or pertussis toxin had decreased abilities to enter and to survive inside macrophages. The results suggest that the internalization process, as well as intracellular survival, is virulence dependent and that mutations which inactivate expression of virulence factors may affect both. The ability of B. pertussis to enter and persist inside macrophages may be important not only for survival of the bacteria but also in the pathogenesis of whooping cough.

Bordetella pertussis induces respiratory burst activity in human polymorphonuclear leukocytes

Virulent Bordetella pertussis strains survive intracellularly within human polymorphonuclear leukocytes (PMN), at least in part because of inhibition of phagosome-lysosome fusion (L. L. Steed, M. Setareh, and R. L. Friedman, J. Leukocyte Biol. 50:321-330, 1991). Further investigations were done to determine if B. pertussis also inhibited respiratory burst activity of PMN as an additional mechanism of intracellular survival. Chemiluminescence and flow cytometry assays showed that B. pertussis induced significant levels of hydrogen peroxide production. In contrast, ferricytochrome c reduction showed that B. pertussis suppressed extracellular release of superoxide. PMN intracellular reduction of nitroblue tetrazolium verified that superoxide was indeed produced intracellularly during B. pertussis phagocytosis. Therefore, B. pertussis does not inhibit production of superoxide but inhibits only its release. Thus, while phagosome-lysosome fusion is inhibited by B. pertussis, respiratory burst activity of PMN occurs at normal levels.

Gelatin sponge model of effector recruitment: tumoricidal activity of adherent and non-adherent lymphokine-activated killer cells after culture in interleukin-2

This study examined the specific tumoricidal activity of lymphokine-activated killer (LAK) cells derived from tumor-infiltrating lymphocytes that prevent the growth of secondary tumors in animals harboring progressing primary tumors. A pre-implanted gelatin sponge was employed to capture infiltrating host effectors during the expression of concomitant tumor immunity. Additionally, this study compared the cytolytic activity of these sponge-derived cells with those of counterpart splenic lymphocytes. The cells from both sources were cultured for 4 days in IL-2 to generate LAK cells which were further expanded in IL-2-containing medium for up to 11 days. The cytotoxic activities of these cells were measured in a Chromium-51 release assay. The data revealed that the culture of splenic, or sponge-derived lymphocytes results in the emergence of non-adherent and adherent cell populations with LAK activity. The 4-day sponge-derived LAK cells (adherent and non-adherent) exhibited significant cytolysis of EMT6 cells while the spleen-derived counterparts showed minimal cytotoxicity toward these targets. Some NK activity in LAK cells derived from both sources was evident by their lysis of YAC-1 cells. LAK cells from both sources were incapable of lysing histo-compatible EL-4 (H-2b) tumor cells. The lysis of the EMT6 cells by the sponge-derived LAK cells was maintained over an 11-day period of culture in IL-2. Conversely, the spleen-derived LAK cells were unable to significantly lyse EMT6 cells during this period of in vitro culture. These results show the superior specific tumoricidal activity of LAK cells derived from lymphocytes mediating tumor rejection in vivo (sponge-derived) over that of counterpart splenic lymphocytes.

Coxiella burnetii fails to stimulate human neutrophil superoxide anion production

This study investigated the release of superoxide anion (O2-) as an indicator of the oxidative metabolism of human neutrophils during the phagocytosis of Phase I Coxiella burnetti. Human neutrophils were incubated for 1 hr at 37 degrees C with opsonized or unopsonized viable Phase I Coxiella burnetii (MOI was 100 : 1) and superoxide anion formation was measured by the reduction of ferricytochrome C. The data revealed that during its phagocytosis by human neutrophils, C. burnetii (opsonized or unopsonized) fails to stimulate superoxide anion production. In contrast, the uptake of Staphylococcus aureus or zymosan was accompanied by the release of measurable O2-. This release of O2- was abrogated by the addition of 100 micrograms/ml of superoxide dismutase (SOD). These results suggest that the establishment of C. burnetii within neutrophils, as occurs during persistent infection, may be due to the failure to stimulate the metabolic burst during phagocytosis.

Implantation of a gelatin-sponge as a model for effector recruitment. Tumor growth inhibition by T-lymphocytes recovered from a site of tumor rejection

Nylon-wool-eluted lymphocytes, isolated from a site of tumor rejection in Balb/c mice expressing concomitant tumor immunity, were examined for their ability to inhibit the growth of the EMT6 tumor. Tumor growth inhibition was monitored after co-inoculation of lymphocytes and tumor cells into naive mice in a Winn-type adoptive-transfer assay. A pre-implanted gelatin sponge was employed to capture the tumor-infiltrating lymphocytes. Mice harboring primary tumors were implanted 8 days later with gelatin sponges. The pre-implanted sponges were then inoculated with a secondary tumor challenge 2 days after implantation of the sponge (i.e. 10 days after primary tumor challenge). On day 17 (7 days after secondary tumor challenge), the immune sponges were retrieved, digested in collagenase and the T lymphocytes were isolated using a nylon-wool column. Blank sponges (lacking tumor cells), obtained from primary-tumor-bearing or non-tumor-bearing animals, were included for comparison. The data showed that T lymphocytes isolated from immune sponges inhibited tumor growth while T lymphocytes recovered from blank sponges did not. At an effector:target (E:T) ratio of 10:1 the lymphocytes from the immune sponges were able to prevent totally the growth of tumors in all cases (100% inhibition). This ability was reduced (60% inhibition) at an E:T ratio of 1:1. Comparison of the antitumor activities of the immune-sponge-derived cells with those from the spleen of the same animal revealed the superiority of the former. Depletion of immune-sponge-derived cells with anti-Thy1.2, anti-Lyt2.2 or anti-L3T4 and complement resulted in a marked decrease in tumor-inhibitory activity. These results indicate that T lymphocytes, expressing Thy1.2, Lyt2.2 or L3T4 antigens, are involved in conferring protection to Balb/c mice against the EMT6 tumor.

Isolation and reactivity of host effectors associated with the manifestation of concomitant tumor immunity

In this study, we have measured the specific tumoricidal activity of tumor-infiltrating lymphocytes that prevent the growth of secondary tumors in animals harboring progressing primary tumors (concomitant immunity). Since no tumor grows at the challenge site when concomitant immunity is established, tumor cells were inoculated into a preimplanted gelatin sponge whose subsequent solubilization in collagenase permitted the retrieval of leukocytes after tumor challenge. Primary progressing EMT6 tumors were established in normal BALB/c mice and 10 days later they were challenged with a secondary tumor inoculum introduced through a preimplanted gelatin sponge. At 3, 7, and 10 days after the administration of the tumor inoculum challenge, a monodispersed suspension of infiltrating leukocytes was recovered by collagenase digestion of the sponge matrix and tested for cytotoxicity toward EMT6 tumor targets. Cytotoxic T-lymphocytes with tumoricidal activity accumulated at the site of the secondary tumor challenge by 3 days. This antitumor activity was maximal 7 days following challenge and decayed thereafter. Splenic lymphocytes from these animals showed little cytotoxicity. In animals harboring a primary tumor, lymphocytes found in sponges that were not inoculated with tumor cells were not cytotoxic. We interpret these data to indicate that cytotoxic lymphocytes migrate to, and accumulate at the site of the tumor but not at other sites and that peripheral sources of lymphocytes in tumor-bearing animals such as the spleen may not be the best source of effector cells for evaluating the host's immune response to its tumor. The approach described here may also be useful in studying the mechanisms for host control of metastatic disease.

A gelatin sponge model for studying tumor growth: quantitation of tumor cells and leukocytes in the CHO tumor

A gelatin sponge model system for tumor cell inoculation and retrieval of tumor-associated leukocytes is described. Gelatin sponges pre-implanted in nude mice harboring tumorigenic Chinese hamster ovary cells (line CHO) were examined at 2 and 11 days after injection of tumor cells for tumor cell content and leukocyte accumulation after digesting the sponge matrix in collagenase solution. The data indicate a progressive influx of host cells consisting primarily of macrophages, neutrophils and lymphocytes. The total number of viable tumor cells as well as the fraction of surviving tumor cells with clonogenic potential also increased with tumor age. Blank sponges not harboring tumor cells elicited an inflammatory response in the animals which did not change appreciably with length of sponge residence. However, when the sponges were harboring tumor cells, the accumulation of host leukocytes far exceeded that which occurred in blank sponges. This observation suggests a host response directed toward the tumor which is absent in animals bearing blank sponges. Apart from providing anchorage for injected cells, the gelatin sponge, by virtue of its digestibility in collagenase, makes possible the easy retrieval and precise quantitation of tumor-associated host cells.

A gelatin sponge model for studying tumor growth: flow cytometric analysis and quantitation of leukocytes and tumor cells in the EMT6 mouse tumor

This study examined the recruitment of host cells into a progressing EMT6 tumor following the inoculation of tumorigenic cells into a preimplanted gelatin sponge. Tumor cell proliferation occurred to a greater extent in sponge tumors than in tumors obtained by direct subcutaneous injection of tumor cells. Blank sponges, lacking tumorigenic cells and used as controls, elicited an inflammatory response characterized by a modest infiltration of granulocytes and macrophages whose numbers, after Day 7 postimplantation, remained unchanged for 21 days of sponge residence in the animal. In contrast, when the sponge contained tumor cells, there was a continuous increase in host cell infiltration that paralleled the increase in tumor cells. Whether in a sponge or not, tumor cells represented more than half of the recovered cells by Day 21 after tumor cell inoculation. Macrophages comprised the greatest fraction of host cells infiltrating the tumors. Flow cytometric analysis and morphological examination of disaggregated tumors indicated that macrophages (19-51%) made up the largest proportion of host cells followed in order by granulocytes (6-18%) and lymphocytes (2-9%). Sorting of marker-labeled cells revealed that 94% of the surface immunoglobulin-bearing cells were macrophages. Twenty-two % of the cells bearing the Thy 1.2 marker were lymphocytes, and 68% were macrophages. The data confirm the occurrence of a cellular host response in the tumor-bearing animal which is distinct from the foreign body reaction elicited by a blank sponge. Additionally, the sponge system described here represents a recoverable environment that would facilitate the study of in vivo host-tumor cell interactions that occur during early tumor development or later during therapy-induced tumor rejection when a palpable tumor is not present.

Cell cycle distribution patterns and generation times of L929 fibroblast cells persistently infected with Coxiella burnetii

Coxiella burnetii established a persistent infection of various cell lines including L929 mouse fibroblasts. Although the basis for such persistence is unknown, the phenomenon does require continual growth, proliferation, and maintenance of viability of the host cells. We examined the effect of short- and long-term infection on the host cell's generation time and cell cycle. Flow cytometric studies of actively growing normal and infected cells stained with mithramycin or propidium iodide revealed no significant difference in cell cycle distribution patterns or changes in ploidy level associated with persistent infection with either phase I or phase II C. burnetii. The population doubling times of infected and normal cells were similar.

Characterization of subsets of bone marrow-derived macrophages by flow cytometry analysis

Normal C3H bone marrow cells were grown 7 days in medium containing L cell-derived colony stimulating factor-1 (CSF-1). During the first 4 days of culture, erythroid and granulocytic cells decreased while macrophages increased exponentially with a doubling time of about 31 hr. Only 0.3% of all cells in the initial bone marrow suspension formed discrete colonies of mononuclear phagocytes, but by day 6 60% of the nonadherent cells were capable of forming macrophage colonies, representing a 200-fold enrichment of the original progenitor population. Using flow cytometry, mononuclear phagocytes obtained after 4 days of culture were separated into two distinct phenotypes based on their autofluorescence. Nonadherent cells were a discrete population of small cells exhibiting low autofluorescence, and the adherent cells were a broad heterogeneous population of large cells exhibiting high autofluorescence. A panel of currently available rat monoclonal antibodies (MABs) against murine hematopoietic cells were used to determine whether unique subsets of macrophages could be resolved. The MABs RA 31B6 and H-11 stained virtually all the nonadherent cells but not adherent cells. The MABs E-2 and 11-4.1 (anti-H-2Kk) stained almost all the adherent cells and demonstrated no significant staining of nonadherent cells. Nearly all the nonadherent and adherent cells were stained by the MABs DNL 4.4 and MAC-1. Additionally, the data suggest that the epitopes for MAC-2 and MAC-3 and gamma 2a Fc receptors develop late in nonadherent progenitor cells as they mature into adherent macrophages.

Cultivation of murine bone marrow macrophages in sponges: a method that permits recovery of viable cultured cells

Various investigators have cultured murine bone marrow or peritoneal cells in vitro on glass or plastic surfaces with the ultimate aim of retrieving adherent macrophages for morphologic and functional evaluation. The removal of these adherent macrophages by conventional techniques has been consistently accompanied by low yield and significant cell damage. We report here a simple technique for culturing murine bone marrow cells in gelatin sponges (Spongostan and Gelfoam) in growth medium containing 10% fetal bovine serum and 10% L-cell conditioned medium. Viable cells were retrieved from the sponges in 10 min by digestion with collagenase. The in situ growth kinetics were similar to those found for cells cultured on plastic dishes. The recovered cells were adherent, phagocytic, positive for Fc gamma receptors, and had esterase activity.

Lysosomal response of a murine macrophage-like cell line persistently infected with Coxiella burnetii

The lysosomal response of a murine macrophage-like tumor cell line (J774) during persistent infection with Coxiella burnettii was examined. By using acid phosphatase as a lysosomal marker, it was shown that phagosome-lysosome fusion occurred in J774 cells persistently infected with C. burnetii. This observation was verified using thorium dioxide, an electron-dense compound that is sequestered in secondary lysosomes. The phagolysosomes contained viable replicating rickettsiae. Spectrofluorometric analysis indicated that the phagolysosomal pH of persistently infected cells was acidic. In attempts to correlate rickettsial survival with lysosome function, the activities of several lysosomal enzymes were assayed in both infected and uninfected cells. Activities of acid phosphatase and beta-acetylglucosaminidase were not significantly altered during infection. However, infected cells appeared to display slightly higher intracellular lysozyme, beta-glucuronidase, and beta-galactosidase activities.

Superoxide anion production and superoxide dismutase and catalase activities in Coxiella burnetii

Coxiella burnetii was examined for superoxide anion (O2-) production and superoxide dismutase and catalase activities. The organism generated O2- at pH 4.5 but not at pH 7.4. The rickettsia displayed superoxide dismutase activity distinguishable from that of the host cell (L-929 mouse fibroblast). Catalase activity was maximal at pH 7.0 and diminished at pH 4.5. These enzymes may account, in part, for the ability of this obligate intracellular parasite to survive within phagocytes.

Fate of phase I and phase II Coxiella burnetii in several macrophage-like tumor cell lines

Several macrophage-like tumor cell lines of murine origin were exposed to phase I and phase II Coxiella burnetii, and the subsequent fate of the parasites was determined by electron and bright-field microscopy. Phase I C. burnetii proliferated within and established a persistent infection of P388D1, J774, and PU-5-IR cell lines but not of WEHI-3 and WEHI-274 cell lines. Phase II C. burnetii, however, entered into and persistently infected all five cell lines. The parasites proliferated within vacuoles. Macrophage cell lines persistently infected with phase I and phase II C. burnetii were maintained for over 200 and 100 days, respectively. Within P388D1 cells, the phase I C. burnetii converted, in part, to phase II; phase II organisms remained in the phase II state. The differential fate of the two rickettsial phases after exposure to the WEHI-3 and WEHI-274 cells may be attributable to surface differences such as lipopolysaccharide content.