Mechanisms of anti-tumor action of Corynebacterium parvum. I. Potentiated tumor-specific immunity and its therapeutic limitations

Adoptive T Cell Therapy Targeting MAGE-A4

MAGE A4 (Melanoma Antigen Gene A4) is a cancer testis antigen (CTA) that is expressed normally in germline cells (testis/embryonic tissues) but absent in somatic cells. The MAGE A4 CTA is expressed in a variety of tumor types, like synovial sarcoma, ovarian cancer and non-small cell lung cancer. Having its expression profile limited to germline cells has made MAGE A4 a sought-after immunotherapeutic target in certain malignancies. In this review, we focus on MAGE-A4's function and expression, current clinical trials involving targeted immunotherapy approaches, and challenges and opportunities facing MAGE-A4's targeted therapeutics.

Tumor Profiling at the Service of Cancer Therapy

Cancer treatment options have evolved significantly in the past few years. From the initial surgical procedures, to the latest next-generation technologies, we are now in the position to analyze and understand tumors in a one-by-one basis and use that to our advantage to provide with individualized treatment options that may increase patient survival. In this review, we will focus on how tumor profiling has evolved over the past decades to deliver more efficient and personalized treatment options, and how novel technologies can help us envisage the future of precision oncology toward a better management and, ultimately, increased survival.

Lymphodepletion strategies to potentiate adoptive T-cell immunotherapy - what are we doing; where are we going?

INTRODUCTION

Adoptive immunotherapy of cancer has evolved from the use of ex vivo expanded lymphokine-activated killer cells and tumor-infiltrating lymphocytes to an increasing array of approaches involving genetically engineered T-cells. A pivotal advance in the enablement of these therapies has been the conditioning of patients with lymphodepleting chemotherapy.A broad range of lymphodepleting regimens has been employed in an effort to improve response rates, without any single consistent approach having emerged. Only a limited number of studies involving small numbers of patients has directly compared two or more regimens, making it challenging to infer which are the preferred agents and dosing schedules. This difficulty is compounded by the fact that both response rate and toxicity appear to be disease-, patient- and T-cell product specific.

EXPERT OPINION

This article surveys clinical experience with lymphodepleting regimens that have been used in conjunction with adoptive T-cell immunotherapy, focussing in particular on studies where different approaches have been employed. Harnessing this limited and evolving clinical experience, we set out to provide potential insights into how an optimal balance may be achieved between efficacy and safety. Intermediate dose fludarabine-based regimens are emerging as an increasingly popular option in an attempt to achieve this goal, although further studies are required to provide definitive evidence.

Propionibacterium acnes Augments Antitumor, Anti-Angiogenesis and Immunomodulatory Effects of Melatonin on Breast Cancer Implanted in Mice

Breast cancer is one of the most invasive cancers with high mortality. The immune stimulating Propionibacterium acnes is a Gram positive bacterium that has the ability to cause inflammation and activate Th1-type cytokine immune response. Antitumor response was associated with the inflammation induced by P. acnes, but the antitumor effect of this bacterium was not evaluated in combination with other agents. The aim of this study was to test the antitumor potential of a combination of melatonin and P. acnes against breast cancer implanted in mice. Balb/C mice were transplanted with EMT6/P cell line and in vivo antitumor effect was assessed for P. acnes, melatonin, and a combination of melatonin and P. acnes. Tumor and organs sections were examined using hematoxylin/eosin staining protocol, and TUNEL colorimetric assay was used to detect apoptosis. The expression of vascular endothelial growth factor (VEGF) was measured in tumor sections and serum levels of INF-γ, and IL-4 were measured to evaluate the immune system function. To evaluate the toxicity of our combination, AST and ALT levels were measured in the serum of treated mice. The combination of melatonin and P. acnes has high efficiency in targeting breast cancer in mice. Forty percent of treated mice were completely cured using this combination and the combination inhibited metastasis of cancer cells to other organs. The combination therapy reduced angiogenesis, exhibited no toxicity, induced apoptosis, and stimulates strong Th1-type cytokine antitumor immune response. The combination of melatonin and P. acnes represents a promising option to treat breast cancer. However, carful preclinical and clinical evaluation is needed before considering this combination for human therapy.

Innate NKT lymphocytes confer superior adaptive immunity via tumor-capturing dendritic cells

If irradiated tumor cells could be rendered immunogenic, they would provide a safe, broad, and patient-specific array of antigens for immunotherapies. Prior approaches have emphasized genetic transduction of live tumor cells to express cytokines, costimulators, and surrogate foreign antigens. We asked if immunity could be achieved by delivering irradiated, major histocompatibility complex–negative plasmacytoma cells to maturing mouse dendritic cells (DCs) within lymphoid organs. Tumor cells injected intravenously (i.v.) were captured by splenic DCs, whereas subcutaneous (s.c.) injection led only to weak uptake in lymph node or spleen. The natural killer T (NKT) cells mobilizing glycolipid α-galactosyl ceramide, used to mature splenic DCs, served as an effective adjuvant to induce protective immunity. This adjuvant function was mimicked by a combination of poly IC and agonistic αCD40 antibody. The adjuvant glycolipid had to be coadministered with tumor cells i.v. rather than s.c. Specific resistance was generated both to a plasmacytoma and lymphoma. The resistance afforded by a single vaccination lasted >2 mo and required both CD4⁺ and CD8⁺ T cells. Mature tumor capturing DCs stimulated the differentiation of P1A tumor antigen-specific, CD8⁺ T cells and uniquely transferred tumor resistance to naive mice. Therefore, the access of dying tumor cells to DCs that are maturing to activated NKT cells efficiently induces long-lived adaptive resistance.

The immunoprotective MHC II epitope of a chemically induced tumor harbors a unique mutation in a ribosomal protein

CD4(+) T lymphocyte clones, generated from mice immunized with the methylcholanthrene-induced fibrosarcoma Meth A (H-2(d)), are restricted by I-E(d) and recognize a unique antigen on Meth A. The antigen has been purified and characterized as the ribosomal protein L11. The antigenic epitope is contained within the sequence EYELRKHNFSDTG and is generated by substitution of Asn by His (italic) caused by a single point mutation. The tumor contains the wild-type and the mutated alleles. Immunization of BALB/cJ mice with the mutated epitope but not with the wild-type epitope protects mice against a subsequent challenge with the Meth A sarcoma. Adoptive transfer of CD4(+) clones into BALB/c mice renders the mice specifically resistant to Meth A sarcoma. The mutated L11 epitope is thus shown to be an immunoprotective epitope in vivo by several criteria.

Antitumor Response Elicited by a Superantigen- Transmembrane Sequence Fusion Protein Anchored onto Tumor Cells

Superantigens stimulate T cells bearing certain TCR β-chain variable regions when bound to MHC II molecules. We investigated whether the superantigen toxic shock syndrome toxin-1 (TSST1) could induce an antitumor immune response when anchored onto MHC II-negative tumor cells. Our approach was to facilitate association of TSST1 with cell membranes by fusing its coding region to the transmembrane region (TM) sequence of the proto-oncogene c-erb-B-2. TSST1-TM was expressed in bacteria with an N-terminal histidine tag and purified using nickel-agarose affinity chromatography. Purified TSST1-TM added to cultures of several different MHC II-negative tumor cells spontaneously associated with cell membranes, as detected by flow cytometry. Because superantigens can direct cell-mediated cytotoxicity against MHC II-positive cells, a TM fusion protein lacking the TSST1 MHC II binding domain (TSST88–194-TM) was also constructed. Tumor cells precoated with TSST1-TM or TSST88–194-TM stimulated proliferation of human peripheral blood lymphocytes in vitro whereas uncoated tumor cells did not. Mice preimmunized with TSST1-TM- or TSST88–194-TM-coated tumor cells mounted a systemic response that resulted in significant antitumor immunity as measured by regression of a parental tumor challenge. TSST1-TM and TSST88–194-TM fusion proteins represent a useful new strategy for attaching superantigens or potentially other proteins onto tumor cell surfaces without genetic manipulation.

Considerations for the clinical development of cytokine gene-transduced tumor cell vaccines

In preclinical models, tumor cells genetically altered to secrete cytokines or express costimulatory molecules can generate systemic antitumor immunity. In some studies, these tumor vaccines have been shown to eradicate micrometastases. These results have led to the initiation of numerous phase I clinical trials employing either genetically modified or allogenic tumor vaccines. This article addresses a number of issues related to the clinical development of cytokine gene-transduced tumor cell vaccines including: (1) the production of cytokine-secreting tumor vaccines; and (2) the preclinical feasibility and toxicity studies required for testing these vaccines in patients with cancer.

Sensitizing T-lymphocytes for adoptive immunotherapy by vaccination with wild-type or cytokine gene-transduced melanoma

BACKGROUND

For the relatively nonimmunogenic B16-F10 murine melanoma, it has been found that genetically engineered expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) but not interleukin (IL)-2, IL-4, or interferon-gamma (IFN-gamma) resulted in a vaccine that could induce resistance to rechallenge. Because T cells from lymph nodes draining the sites of some progressive tumors can mediate tumor regression after in vitro activation, it seemed possible that even apparently nonimmunogenic melanoma cells might induce similar preeffector cells in the vaccine-draining lymph nodes (DLNs).

METHODS

C57BL/6 mice were vaccinated with B16-F10 cells that were either unmodified or genetically modified to produce IL-2, IL-4, GM-CSF, or IFN-gamma. DLNs were harvested 10 days after vaccination for adoptive immunotherapy (AIT). The DLN cells were activated with bryostatin 1 and ionomycin (B/I), expanded for 10 days in culture, and transferred to mice with 3-day pulmonary metastases. Pulmonary nodules were counted 14 days after AIT.

RESULTS

Adoptive transfer of expanded DLN lymphocytes sensitized by inoculation of WT B16-F10, or IL-4, GM-CSF, or IFN-gamma expressing cells significantly reduced pulmonary metastases. Despite the spontaneous regression of IL-2-transduced B16-F10 tumors, DLN from mice inoculated with IL-2 producing B16 cells had little or no antitumor activity.

CONCLUSIONS

B16-F10 vaccination strategies that apparently do not induce systemic immunity can effectively sensitize DLN preeffector cells.

Loss of a unique tumor antigen by cytotoxic T lymphocyte immunoselection from a 3-methylcholanthrene-induced mouse sarcoma reveals secondary unique and shared antigens

Most chemically induced tumors of mice express unique antigens that can be recognized by cytotoxic T lymphocytes (CTL) and thereby mediate tumor rejection. The number of different antigens expressed by a single tumor and their interplay during immunization and rejection are largely unexplored. We used CTL clones specific to individual tumor antigens to examine the number and distribution of CTL antigens expressed by cell lines derived from 3-methylcholanthrene-induced sarcomas of (C57BL/6J X SPRET/Ei)F1 mice. Each tumor cell line expressed one or more antigens that were unique, that is, not detected on cell lines from independent sarcomas. Immunoselection against an immunodominant antigen produced both major histocompatibility complex class I antigen and unique tumor antigen loss variants. Immunization of mice with antigen-negative immunoselected variants resulted in CTL that recognized additional antigens that were also expressed by the progenitor tumor. Some CTL recognized additional unique tumor antigen(s); other CTL recognized a shared antigen expressed not only by the immunizing cell line, but also by independent sarcoma cell lines and untransformed myoblastoid cell lines. CTL that recognized the shared antigen were also recovered from mice immunized in vivo with an untransformed myoblastoid cell line. These findings support a model of immunodominance among chemically induced tumor antigens in which shared antigens are masked by unique immunodominant antigens.

Adoptive immunotherapy of established tumors. Acquisition of radioresistance by tumor-specific T cells after passive transfer into tumor-bearing recipients

The present study was undertaken to determine the sensitivity to ionizing irradiation of T cells from mice immunized against the Meth-A fibrosarcoma and P815 mastocytoma after the transfer of these cells into tumor-bearing recipients. It was found that T cells from memory-immune donors were destroyed by exposing recipients to 500 rad of gamma irradiation up to 48 hr after transfer of the cells, but not thereafter. In contrast, activated immune cells were resistant to irradiation immediately after transfer. T cells were considered to be actively immune if they were harvested from donors in the process of rejecting their tumor, and were replicating, as evidenced by sensitivity to vinblastine. Memory-immune cells, on the other hand, were T cells that were harvested long after rejection of the immunizing tumor and were vinblastine-resistant. Additional results showed that CD8+ memory T cells were needed to cause regression of Meth-A tumor in recipients, whereas CD4+ memory T cells were needed for P815 tumor regression. These results support the idea that T cells that mediate tumor regression in this model of adoptive immunotherapy are radiosensitive while resting, and radioresistant after becoming activated. This knowledge needs to be taken into account when considering ionizing radiation as an immunomodulating agent for tumor immunotherapy.

Tumors with reduced expression of a cytotoxic T lymphocyte recognized antigen lack immunogenicity but retain sensitivity to lysis by cytotoxic T lymphocytes

A murine solid tumor was transfected to express various levels of an allogeneic major histocompatibility complex class I gene (K216), in order to test the effect of the level of antigen expression on immunogenicity and sensitivity to lysis by cytotoxic T lymphocytes (CTL). The growth rates of clones of tumor cells expressing different levels of the transfected gene were similar in vitro and in nude mice. Although all tumor cells, including cells freshly isolated from growing tumors, were equally sensitive to lysis by specific CTL, only tumor cells expressing the highest level of the K216 antigen stimulated CTL and were rejected by normal mice. In contrast, tumor cells expressing lower levels of antigen failed to immunize for CTL and grew progressively in normal mice, despite retaining expression of the transfected gene and remaining fully sensitive to CTL-mediated lysis; thus, the threshold of antigen needed to stimulate CTL responses was considerably higher than that needed to lyse tumor cells. Reduction of K216 antigen expression from 100-fold to 40-fold above background, impaired significantly the ability of the tumor cells to induce a K216-specific immune response, while tumor cells expressing K216 at levels 2-fold above background were as susceptible to CTL-mediated lysis as tumor cells expressing 50-fold more antigen. The important implication of these findings is that some tumors occurring in nature may not be immunogenic but nevertheless express antigens which are potential targets for immune therapy.

Presence of CD4+ T suppressor cells in mice rendered unresponsive to tumor antigens by intravenous injection of irradiated tumor cells

We used in vivo and in vitro assays to determine whether suppressor cells are generated in mice rendered unresponsive to tumor-specific antigens by intravenous (i.v.) injection of non-replicating tumor cells. The results show that a single i.v. injection of 2 x 10(7) irradiated P815 tumor cells resulted in the induction of a state of specific unresponsiveness to tumor-associated antigens, as revealed by the inability of the treated mice to achieve immunologically-mediated regression of an intradermal P815 tumor containing C. parvum, or to generate effector T cells capable of causing rejection of a P815 tumor in T-cell-deficient (T x B) test recipients. Failure to respond to tumor antigens was associated with the presence in spleen of CD4+ T cells capable, on passive transfer, of suppressing adoptive T-cell-mediated tumor regression in T x B recipients. However, the same CD4+ suppressor cells failed to inhibit the generation of tumor-specific cytotoxic T lymphocytes (CTL) in vitro. On the contrary, spleen cells from mice made unresponsive by i.v. injection of tumor cells were primed to generate CTL in response to tumor antigens in vitro. Taken together, our results suggest that unresponsiveness induced by i.v. injection of tumor antigens is an active process mediated, at least in part, by CD4+ T suppressor cells, and that these cells coexist in the spleen with antigen-primed effector T cells with a capacity to generate tumor-specific CTL when released from suppression in vitro.

Immune adjuvants for chemotherapy or radiotherapy in the 9L rat brain tumor model

The therapeutic efficacy and toxicity of three biological response modifiers, Corynebacterium parvum (Cp), Chinese blister beetle extract (CBBE), recombinant human IL-1 alpha (rhIL-1 alpha), used alone or in combination with chemotherapy or radiotherapy, were investigated in the intracerebral (ic) rat 9L brain tumor model. Used alone, Cp (2 mg/rat, ip plus 70 micrograms/rat, ic), CBBE (5 microliters of an ethanol extract, ic), or IL-1 alpha (1 microgram/rat, ic or 1 microgram/rat x 3, q 3 d, ic), had no effect on animal survival compared to the untreated or saline treated controls. When combined with chemotherapy or radiotherapy, the three immunotherapeutic agents did not show any additive effects on survival compared to that observed with systemic BCNU (12 mg/kg), local ic bleomycin (0.25 unit), or local radiotherapy (16 Gy). While ic IL-1 alpha did not produce evident toxicity, there was fatal toxicity caused by ic Cp or CBBE treatment in a few animals. The combination of Cp and bleomycin produced severe neurotoxicity, resulting in the early death of animals. This study demonstrates a lack of efficacy of the nonspecific immune adjuvants IL-1 alpha, Cp or CBBE, used either alone or combined with cytotoxic chemotherapy or radiotherapy, in this rat brain tumor model.

Immunomodulation in an apparently non-immunogenic murine tumor

Madison lung carcinoma (M109), a murine tumor of spontaneous origin, appears to be non-immunogenic, according to 2 commonly employed tests for tumor immunogenicity. However, C.parvum-induced immunopotentiation during the growth of M109 tumor results in post-excision anti-tumor immunity to M109 tumor implants. The C.parvum-potentiated post-excision immunity to M109 is tumor-specific and T-cell-dependent. T cells from mice whose progressive M109 tumors have been excised are capable, on passive transfer, of inhibiting adoptive immunotherapy of T-cell-deficient recipients by spleen cells from mice immunized with an admixture of M109 cells and C.parvum. The data are interpreted as evidence supporting the hypothesis that the apparent lack of anti-tumor immunity in this tumor model is not due to the absence of tumor-associated antigens. We suggest that, instead, in this model the balance between the effector and suppressor arms of the immune response favors tumor-induced immunosuppression, resulting in a magnitude of anti-tumor immunity insufficient for detection by commonly employed tests for tumor immunogenicity. Our study shows that shifting the balance in favor of the effector arm by means of immunopotentiation results in a measurable immune response to an apparently non-immunogenic tumor.

Production of interferon-gamma by in vivo tumor-sensitized T cells: association with active antitumor immunity

The state of active immunity to Meth A fibrosarcoma in mice immunized with an admixture of Meth A cells and Propionibacterium acnes is associated with possession by the host of spleen cells capable of producing interferon-gamma (IFN-gamma) upon in vitro restimulation with irradiated tumor cells. The ability of spleen cells from immunized mice to produce IFN-gamma in response to irradiated Meth A cells decays as active antitumor immunity is replaced by a state of immunological memory. The IFN-producing cells are L3T4+Ly2+, cyclophosphamide-sensitive and radiosensitive T cells, as determined by their sensitivity to corresponding monoclonal antibodies and complement. The induction of IFN-gamma production by in vivo tumor-sensitized T cells is tumor specific, in that spleen cells from mice immunized against Meth A fibrosarcoma can produce IFN in response to irradiated Meth A cells but not in response to another syngeneic tumor M109 lung carcinoma.

Enhancement and suppression of DTH reactivity to Rauscher murine leukaemia virus induced tumour cell lines

Delayed-type hypersensitivity (DTH) to Rauscher murine leukaemia virus (R-MuLV) encoded or induced determinants was induced in mice by three syngeneic R-MuLV-induced tumour cell lines, i.e. a myeloid tumour, RMB-1, an erythroid tumour, RED-1, and a lymphoid tumour, RLD-1. DTH to subcutaneously (s.c.) administered RMB-1 cells appeared on day 4, with a maximum DTH response on day 6 or 7. The induction of DTH could be prevented by intravenous (i.v.) pre-immunisation with R-MuLV-induced tumour cells several days before the s.c. immunisation. The three R-MuLV-induced tumour cell lines showed cross-reactivity in the DTH assay, whereas no cross-reactivity was found with syngeneic WEHI-3 cells. This indicates that the three R-MuLV-induced tumour cell lines share a virally encoded or induced antigenic determinant, which activates T-cells. When the RMB-1 cells used for immunisation had been cultured in medium supplemented with interferon-gamma (IFN-gamma), the subsequent DTH response was increased. This coincided with an increased expression of the R-MuLV-specific antigenic determinants on RMB-1 cells as demonstrated by Scatchard analysis. Furthermore, IFN-gamma increased the MHC class I antigen expression on RMB-1 cells, whereas the class II antigen expression remained undetectable.

Characterization of a new spontaneously developed murine mammary adenocarcinoma in syngeneic BALB/c hosts

A mouse mammary tumor cell line, designated JC, has been established from a spontaneously developed primary adenocarcinoma of an aged virgin female BALB/c mouse. Isoenzyme analyses including glucose-6-phosphate dehydrogenase, lactate dehydrogenase, and peptidase proved that this cell line is of murine origin and devoid of contamination from other species. Karyotyping revealed that the number of chromosome ranged from 26 to 100, with a modal number of 40. Electron microscopic examination detected the presence of tonofilament and desmosomes confirming its epithelial nature. In addition, no type B or C virus particle was detected, although intracysternal A particle was observed occasionally. Tumorigenicity in immunocompetent syngeneic hosts was easily established by s.c., i.p., and i.v. injection of viable JC tumor cells. A very weak immunogenicity of the JC tumor was demonstrated through its immunization-challenging on syngeneic immunocompetent hosts. Although no rejection of JC tumor was noted, a significant prolongation for the incubation period before an obvious and palpable tumor growth was detected between the experimental and the control animals. Development of a concomitant immunity was also detected. The JC tumor represents a valuable murine mammary tumor model which is different from other available models because of its unique origin, absence of virus particles, very weak immunogenicity, and high tumorigenicity in syngeneic hosts. The cell line has been maintained for more than 5 yr and has been used for experimental immunotherapy in our laboratory.

Effect of intracerebrally injected Corynebacterium parvum on implanted brain tumor in mice

Experiments were performed to determine the effectiveness of Corynebacterium parvum on resistance to growth and development of tumor in the central nervous system. A syngeneic sarcoma was injected intracerebrally into C3H/HeN/MTV-negative female mice that had received intraperitoneal injections of C. parvum or saline prior to tumor inoculation or that received intraperitoneal C. parvum or saline after tumor inoculation. Groups then received an intracerebral injection of C. parvum or saline. Our results reveal that intracerebral C. parvum elicited an intracerebral inflammatory reaction which was enhanced by prior systemic priming with C. parvum. Any inflammatory reaction which was enhanced by prior systemic priming with C. parvum. Any inflammatory reaction produced by C. parvum retarded the growth of intracerebrally-implanted sarcoma and significantly increased the survival of mice bearing such tumors. These results suggest that C. parvum may be an effective therapeutic agent in the treatment of neoplasia of the central nervous system.

Failure of specific adoptive immunotherapy owing to survival and outgrowth of variant cells

Adoptive immunotherapy, the transfer of spleen cells from immunized mice to mice with a small tumor, was usually curative for mice with the P815 mastocytoma provided that steps were taken to prevent the generation of tumor-induced suppressor cells in the recipient animal. However, failure of adoptive immunotherapy of the P815 tumor, resulting in regrowth of either the primary intradermal or a metastatic tumor, was observed in 10 out of 112 animals receiving graded doses of 7.5 x 10(7) to 3.0 x 10(8) immune spleen cells. Examination of the ten tumors in mice that failed to respond to therapy revealed that seven of them were significantly less susceptible than the original P815 tumor to rejection in vivo by transferred anti-P815-specific effector cells. In addition, nine of the ten therapy-failure tumors were also less susceptible than the original P815 tumor to lysis in vitro by P815-specific, but not DBA/2-specific, cytotoxic T lymphocytes. Sensitivity to lysis by tumor-specific cytotoxic T cells was not, however, strongly correlated with sensitivity to rejection in vivo by P815-specific effector spleen cells. Neither in vivo sensitivity to rejection, nor sensitivity to cytotoxic T cells, was correlated with alterations in class I major histocompatibility complex antigen expression. These results suggest that the survival and outgrowth of variant tumor cells was frequently the cause of failure of specific adoptive immunotherapy of the P815 tumor, and that selection for cells with a reduced sensitivity to killing by cytotoxic T cells was only one mechanism that might lead to an immunotherapeutic failure.

Role of respiratory-burst products from polymorphonuclear leukocytes in the antitumor activity of Propionibacterium acnes vaccine

Tumor cells injected into Balb/c mice together with heat-killed 48-h P. acnes cells were rendered nontumorigenic as early as 12 h after injection, as determined by the inability of the tumor cells to give rise to tumors when transferred to a new host. Determination of tumor cell antigen levels by ELISA indicated that the tumour antigens had virtually disappeared by 24 h after injection of tumor cells and P. acnes. In contrast, in control animals injected with tumor cells only, there was an initial drop in tumor antigen levels at 12 h, after which the level rose steadily and tumors developed in 7-10 days. Since the cellular exudate at 12 h was almost entirely composed of polymorphonuclear leukocytes (PMN), we tested the ability of PMN, stimulated by phagocytosis of 48-h P. acnes cells, to produce substances toxic to tumor cells. Results indicated that the supernatant fluid from a phagocytosis mixture of PMN and P. acnes contained material toxic to tumor cells and also to Chinese hamster ovary cells. Tests with scavengers and inhibitors of oxygen-derived radicals suggested that the toxic material is either hydrogen peroxide (H2O2) or hydroxyl radicals (OH). Suspensions of 12-h P. acnes, P. acnes cells walls, P. freudenreichii, or latex beads were ineffective in preventing tumor growth, and induced little toxicity when phagocytosed. We conclude that in this test system 48-h P. acnes prevents tumor growth by stimulating the production of toxic oxygen metabolites during phagocytosis by PMN.

Immunologically mediated regression of a murine lymphoma after treatment with anti-L3T4 antibody. A consequence of removing L3T4+ suppressor T cells from a host generating predominantly Lyt-2+ T cell-mediated immunity

This study shows that intravenous injection of 1 mg of anti-L3T4 mAb (GK1.5) into thymectomized mice bearing the syngeneic L5178Y lymphoma results, after a delay of 2-3 d, in complete regression of this tumor and in long-term host survival. A flow cytofluorometric examination of the spleen cells of mAb-treated mice revealed that antibody treatment resulted in the elimination of greater than 98% of L3T4+ T cells, but had no effect on the Lyt-2+ T cells subset. Tumor regression was immunologically mediated, because L5178Y lymphoma cells were shown to be L3T4-, and regression of the tumor failed to occur in mice that had been lethally irradiated before anti-L3T4 mAb was given. Tumor regression was mediated by tumor-sensitized Lyt2+ T cells, as evidenced by the finding that treatment of tumor-bearing mice with anti-Lyt-2 mAb alone, or in combination with anti-L3T4 mAb, resulted in enhancement of tumor growth and a significant decrease in host survival time. Moreover, the spleens of mice whose tumors were undergoing regression in response to anti-L3T4 mAb treatment contained Lyt-2+ T cells capable, on passive transfer, of causing regression of a tumor in recipient mice. These results can be interpreted as showing that removal of tumor-induced L3T4+ suppressor T cells results in the release of Lyt-2+ effector T cells from suppression, and consequently in the generation of enough Lyt-2+ T cell-mediated immunity to cause tumor regression. This can only be achieved, however, if immunity to the tumor is mediated exclusively by Lyt-2+ T cells, as is the case for the L5178Y lymphoma. In the case of the P815 mastocytoma, treatment with anti-L3T4 mAb was without a therapeutic effect, and this was in keeping with the finding that immunity to this tumor is mediated by L3T4+, as well by Lyt-2+ T cells.

Cyclophosphamide (Cy)-facilitated adoptive immunotherapy of a Cy-resistant tumour. Evidence that Cy permits the expression of adoptive T-cell mediated immunity by removing suppressor T cells rather than by reducing tumour burden

A cyclophosphamide (Cy)-resistant immunogenic tumour, the L5178Y lymphoma, was used to demonstrate that Cy-treatment of a host bearing this tumour enables passively transferred tumour-sensitized T cells to cause complete tumour regression without any need for Cy to cause a reduction in tumour burden. It was shown that whereas infusion of tumour-sensitized T cells from immune donors had very little effect on growth of the tumour, and whereas treatment with 150 mg/kg of Cy caused appreciable enhancement of tumour growth, combination therapy with Cy plus immune T cells caused complete tumour regression and resulted in long-term survival. Evidence that Cy treatment facilitated the expression of adoptive immunity against the L5178Y lymphoma by eliminating tumour-induced suppressor T cells consisted of the demonstration that tumour regression caused by combination treatment with Cy and immune T cells could be inhibited by infusing the recipient with Cy-sensitive, L3T4+ T cells from tumour-bearing but not from normal donors.

[Effect of Propionibacterium granulosum KP-45 on the resistance to Listeria monocytogenes and Salmonella typhimurium infections]

Killed bacterial cells of Propionibacterium granulosum KP-45 were found to be potent modifiers of non-specific resistance of mice against infection with either Listeria monocytogenes or Salmonella typhimurium. Injection of P. granulosum 7 days prior to infection resulted in marked splenomegaly. Disseminated acute inflammatory foci were found histologically in the liver. These mice were apparently less susceptible to infection, since definitely lower bacterial counts were determined. Simultaneous application of both P. granulosum KP-45 and L. monocytogenes resulted, however, in increased susceptibility of mice to infection, since definitely higher bacterial counts were found and the inflammatory reaction to infection was markedly enhanced.

Frequency analysis of augmented CTL production associated with Corynebacterium parvum-induced tumour regression

A limiting-dilution frequency assay was employed to estimate the increased production of cytolytic T lymphocytes (CTL) associated with Corynebacterium parvum-induced regression of the P815 mastocytoma growing subcutaneously in semisyngeneic mice. It was found that intratumour C. parvum functioned to augment greatly the underlying concomitant production of CTL that occurs normally in response to a progressively growing untreated immunogenic tumour. The lymph node draining a C. parvum-treated tumour contained about eight times more CTL than the lymph node draining a control tumour. Intratumour C. parvum also caused a large increase in CTL production in the spleen and an increase in the number of CTL that could accumulate in a peritoneal exudate. At the peak of the anti-tumour response, the largest number of CTL was found in the draining lymph node (1.66 X 10(5], followed by the spleen (3.47 X 10(4) and by a 24-hr casein-induced peritoneal exudate (6.01 X 10(3]. Presumably, this greatly augmented production of CTL explains why C. parvum given intralesionally early enough during tumour growth can cause the regression of the weakly immunogenic P815 mastocytoma.

T cell suppressors of antitumor immunity. The production of Ly-1-,2+ suppressors of delayed sensitivity precedes the production of suppressors of protective immunity

The results of this study show that during growth of the immunogenic Meth A fibrosarcoma, two different types of suppressor T lymphocytes are generated in sequence. One type is generated during early tumor growth, reaches peak number around day 6, and is progressively lost thereafter. It is defined by its ability, upon passive transfer, to suppress the expression of a DTH reaction to tumor antigens in tumor-immunized recipients. It bears the Ly1-,2+ membrane phenotype and is sensitive to relatively low doses of cyclophosphamide. In contrast, the second type of suppressor cell is not detected until after day 9 of tumor growth, and is defined by its ability to inhibit, upon passive transfer, the expression of adoptive immunity against an established tumor in T cell-deficient recipients. According to previous studies it bears the Ly1+,2-, L3T4a+ membrane phenotype and is less sensitive to cyclophosphamide than the T cell suppressor of DTH. It is argued that this second type of suppressor T cell seems likely to be responsible for the escape of immunogenic tumors from antitumor immunity, because it can suppress the expression of a powerful mechanism of antitumor immunity in recipient mice, and is generated progressively as the tumor-bearing host loses concomitant immunity. In contrast, although the Ly-1-,2+ T cell suppressors of DTH can efficiently suppress a DTH reaction to an implant of living tumor cells, they fail to suppress the expression of immunity to the same implant.

Therapy of stage III (optimal) epithelial carcinoma of the ovary with melphalan or melphalan plus Corynebacterium parvum (a Gynecologic Oncology Group Study)

A randomized prospective therapy trial in patients with stage III optimal epithelial carcinoma of the ovary was accomplished by the Gynecologic Oncology Group. Therapy with melphalan or melphalan plus immuno-adjuvant, Corynebacterium parvum (C. parvum), was utilized as adjuvant treatment following surgical therapy. One hundred eight-five patients were eligible for evaluation with 87 patients in the melphalan group and 98 patients in the melphalan plus C. parvum group. The comparison of the treatment regimens showed no differences with respect to either progression-free interval or survival. However, it should be noted that a 50% 3-year survival was obtained. A group was identified, using four prognostic factors that had 80% survival at 3 years. Maximum size of the residual tumor, as well as performance status, was not prognostically significant. This study demonstrates a lack of efficacy of the addition of C. parvum to melphalan for this patient population.

Ly 1+2- suppressor T cells down-regulate the generation of Ly 1-2+ effector T cells during progressive growth of the P815 mastocytoma

It has been shown that progressive growth of the P815 mastocytoma in its semisyngeneic B6D2 host results, between days 6 and 9 of tumour growth, in the generation of Ly 1-2+ T cells which are capable, on passive transfer, of causing the regression of an established tumour in gamma-irradiated recipients, and of T cells which are capable of lysing P815 tumour cells in vitro. After 9 days of tumour growth, these effector T cells are progressively lost; this is associated with the progressive acquisition of Ly 1+2- suppressor T cells which are capable of inhibiting the expression of passively transferred immunity against an established tumour in T-cell deficient recipients. The results are consistent with the hypothesis that this P815 mastocytoma grows progressively, in spite of its immunogenicity, because it evokes the generation of suppressor T cells before enough effector T cells are generated to reject it.

Anti-tumour effect of humoral and cellular immunities mediated by a bacterial immunopotentiator, Lactobacillus casei, in mice

Administration of a mixture containing Lactobacillus casei YIT 9018 (LC9018) and methylcholanthrene-induced fibrosarcoma (Meth A) cells into the peritoneum of syngeneic BALB/c mice suppressed the tumour growth and protected the mice from tumour death. With the appearance of the anti-tumour activity, serum complement-dependent tumour cytotoxic (CDC) antibody was induced on the 5th day after the administration as a result of the adjuvant effect. The cytotoxic antibody was not found in serum on the 5th day after inoculation of Meth A cells alone, but it was induced before the mice died of the tumours. Adjuvant induction of the cytotoxic serum antibody at an early time was also observed using Kirsten murine sarcoma virus-transformed tumour (K234) cells. Both of these cytotoxic antibodies in sera from Meth A-suppressed and the tumour-bearing mice were specific for the tumour cells and were IgM class, since they were absorbed with rabbit anti-mouse IgM antibody. However, the cytotoxic antibody was not found in the peritoneal cavity which was the tumour inoculation site, but binding antibody against the tumour cells was faintly detected in the region using an enzyme-linked immunoabsorbent assay (ELISA). In neutralization tests, the cytotoxic antibody did not exert anti-tumour activity in recipient mice when it was administered to the mice along with the tumour cells or when it was administered i.v. at the time of tumour inoculation. Moreover, the cytotoxic antibody was not available for the antibody-dependent cell-mediated cytotoxicity (ADCC). These results suggest that the cytotoxic antibody did not exert anti-tumour activity in the tumour-suppressed mice. In contrast, peritoneal exudate cells (PEC) on the 5th day, and PEC and spleen cells on the 15th day after i.p. administration of the mixture exerted strong anti-tumour activity as measured by the Winn test. In conclusion, the adjuvant effect of LC9018 induced tumour-specific humoral and cellular immunities but the anti-tumour activity was dependent only on the cellular effectors of the host. The possible use of LC9018 in tumour immunotherapy is discussed.

Immunomodulation of NK and ADCC by Corynebacterium parvum in acute myeloid leukaemia patients

Natural killer (NK)- and antibody dependent cellular cytotoxicity assays were performed using cryopreserved effector cells in AML patients receiving i.c. and s.c. injections of Corynebacterium parvum. A dose related increase in NK could be demonstrated with peaks in NK at day 1 with full Cp dosage and at day 14 with 50% doses. This increase was attributable to the Cp vaccine since normal donors receiving tetanus toxoid or pneumococcal polysaccharide and AML patients randomized not to receive Cp did not show similar NK boosting. The increase was probably due to interferon induction in vivo and could be demonstrated with purified T- and non-T-lymphocyte subsets. However, longitudinal measurements showed that the ability of Cp to boost NK was gradually lost over 4-6 months. ADCC studies showed that while lymphocyte-ADCC was not consistently affected by Cp, monocyte-ADCC was enhanced with maximal cytotoxicity at day 14.

Comparison of antitumor activity of Lactobacillus casei with other bacterial immunopotentiators

Antitumor activity of Lactobacillus casei YIT 9018 (LC9018) was demonstrated by intralesional (i.l.) or intravenous (i.v.) administration into tumor-bearing mice which were inoculated with methylcholanthrene-induced fibrosarcoma (Meth A) or Kirsten murine sarcoma virus-transformed tumor (K234) cells. Its activity was significantly superior to the activity of two other species of lactobacilli but was nearly the same as that of Corynebacterium parvum or Mycobacterium bovis Bacille Calmette-Guérin (BCG). I.l. or i.v. administration of LC9018 into the tumor bearers caused local transient swelling or hepatosplenomegaly but did not cause other pronounced lesions. There was no significant difference in the degree of hepatosplenomegaly in LC9018 and that in other immunopotentiators. In mice whose tumors had regressed as a result of administration of LC9018 or the other immunopotentiators, the phytohemagglutinin P (PHA-P) response of the spleen cells was less than that of mice whose tumors progressed, and approached the normal level. The PHA-P response of popliteal lymph node cells proximal to the tumor lesion was fairly low compared with the splenic PHA-P response and there was no difference between the lymphocytes from mice whose tumors had regressed or progressed. Adjuvant activity of LC9018 in inducing tumor immunity was demonstrated by administering a mixture of LC9018 and Meth A cells to mice. This adjuvant activity was of the same efficiency as that of C. parvum and BCG. The presence of the antitumor activity of LC9018 in cell wall components was deduced from fact that removal of its cell wall by endo-N-acetylmuramidase (M-1 enzyme) abolished the activity. The possible availability of LC9018 for immunotherapy of tumors is discussed.

Generation and decay of the immune response to a progressive fibrosarcoma. I. Ly-1+2- suppressor T cells down-regulate the generation of Ly-1-2+ effector T cells

It was shown that the progressive growth of the immunogenic meth A fibrosarcoma in its semisyngeneic host results in the generation of concomitant immunity to the growth of a tumor implant. The generation of immunity occurred between days 6 and 9 of tumor growth and was associated with the generation of sensitized T cells that were capable, on passive transfer, of causing regression of a 3-d tumor in gamma-irradiated recipients. After day 9 of tumor growth, concomitant immunity and the T cells able to passively transfer it were progressively lost, and this was associated with the generation of splenic suppressor T cells able to suppress the expression of adoptive immunity against an established tumor in T cell-deficient ( TXB ) recipients. The T cells that passively transferred concomitant immunity were shown to be of the Ly-1-2+ phenotype, in contrast to the T cells that transferred suppression, which were shown with the same reagents to be Ly-1+2-. The results are consistent with the hypothesis that the progressive growth of an immunogenic tumor results in the generation of Ly-1-2+-sensitized effector T cells that fail to reach a number sufficient to destroy the tumor because their generation is down-regulated by tumor-induced Ly-1+2- suppressor T cells.

Augmentation of antitumor resistance by a strain of unicellular green algae, Chlorella vulgaris

Growth of Meth-A tumor in CDF1 mice was inhibited significantly by injection of a hot water extract of a strain of Chlorella vulgaris (CE) into the tumor or into the subcutaneous tissue near the tumor. The augmentation of resistance by CE may require the participation of T cells and macrophages, since it was abolished or reduced in athymic nude mice or mice treated with carrageenan, a macrophage blocker. Mice treated with CE exhibited antigen-specific augmented resistance against rechallenge with tumor. Moreover, the antitumor effect of CE was comparable with that of Corynebacterium parvum, but its mechanism of effect might be different.

Gamma-irradiation facilitates the expression of adoptive immunity against established tumors by eliminating suppressor T cells

It was found that sublethal (550 rad) whole-body gamma-irradiation of mice bearing established immunogenic tumors enabled tumor-sensitized spleen cells infused intravenously 1 h later to cause complete tumor regression in all mice. In contrast, gamma-irradiation alone caused only a temporary halt in tumor growth, and immune cells gave practically no therapeutic effect at all. This result was obtained with the SA1 sarcoma, Meth A fibrosarcoma, P815 mastocytoma, and P388 lymphoma. Additional experiments with the Meth A fibrosarcoma revealed that the spleen cells from tumor-immune donors that caused tumor regression in gamma-irradiated recipients were T cells, as evidenced by their functional elimination by treatment with anti-Thy-1.2 antibody and complement. It was shown next that adoptive T-cell-mediated regression of tumors in gamma-irradiated recipients was inhibited by an intravenous infusion of spleen cells from donors with established tumors, but not by spleen cells from normal donors. The spleen cells that suppressed the expression of adoptive immunity were functionally eliminated by treatment with anti-Thy-1.2 antibody and complement. Moreover, they were destroyed by exposing the tumor-bearing donors to 500 rad of gamma-radiation 24 h before harvesting their spleen cells. The results are consistent with the interpretation that gamma-radiation facilitates the expression of adoptive T-cell-mediated immunity against established tumors by eliminating a population of tumor-induced suppressor T cells from the tumor-bearing recipient.

Expression of passively transferred immunity against an established tumor depends on generation of cytolytic T cells in recipient. Inhibition by suppressor T cells

The results of this study with the P815 mastocytoma confirm the results of previous studies that showed that the passive transfer of tumor-sensitized T cells from immunized donors can cause the regression of tumors growing in T cell-deficient (TXB) recipients, but not in normal recipients. The key additional finding was that the expression of adoptive immunity against tumors growing in TXB recipients is immediately preceded by a substantial production of cytolytic T cells in the recipients' draining lymph node. On the other hand, failure of adoptive immunity to be expressed against tumors growing in normal recipients was associated with a cytolytic T cell response of much lower magnitude, and a similar low magnitude response was generated in TXB recipients infused with normal spleen cells and in tumor-bearing control mice. Because the passively transferred sensitized T cells possessed no cytolytic activity of their own, the results indicate that the 6-8-d delay before adoptive immunity is expressed represents the time needed for passively transferred helper or memory T cells to give rise to a cytolytic T cell response of sufficient magnitude to destroy the recipient's tumor. In support of this interpretation was the additional finding that inhibition of the expression of adoptive immunity by the passive transfer of suppressor T cells from tumor-bearing donors was associated with a substantially reduced cytolytic T cell response in the recipient's draining lymph node. The results serve to illustrate that interpretation of the results of adoptive immunization experiments requires a knowledge of the events that take place in the adoptively immunized recipient. They support the interpretation that suppressor T cells function in this model to "down-regulate" the production of cytolytic effector T cells.

Cyclophosphamide-facilitated adoptive immunotherapy of an established tumor depends on elimination of tumor-induced suppressor T cells

On the basis of preceding studies showing that tumor-induced, T cell-mediated immunosuppression serves as an obstacle to adoptive immunotherapy of the Meth A fibrosarcoma, it was predicted that cyclophosphamide treatment of tumor bearers would remove this obstacle and allow passively transferred immune T cells to cause tumor regression. It was found that infusion of immune spleen cells alone had no effect on tumor growth, and cyclophosphamide alone caused a temporary halt in tumor progression. In contrast, combination therapy consisting of intravenous injection of 100 mg/kg of cyclophosphamide followed 1 h later by intravenous infusion of tumor-immune spleen cells caused small, as well as large tumors, to completely and permanently regress. Tumor regression caused by combination therapy was completely inhibited by intravenous infusion of splenic T cells from donors with established tumors, but not by spleen cells from normal donors. These suppressor T cells were eliminated from the spleen by treating the tumor-bearing donors with 100 mg/kg of cyclophosphamide. Immune T cells, in contrast, were resistant to this dose of cyclophosphamide. These results show that failure of intravenously-infused, tumor-sensitized T cells to cause regression of the Meth A fibrosarcoma growing in its syngeneic or semi-syngeneic host is caused by the presence of a tumor-induced population of cyclophosphamide-sensitive suppressor T cells.

Mechanisms of anti-tumor action of Corynebacterium parvum. II. Potentiated cytolytic T cell response and its tumor-induced suppression

It was shown that subcutaneous implantation of P815 tumor cells admixed with Corynebacterium parvum resulted in the emergence of a tumor that grew for 9-10 d and then regressed. The onset of tumor aggression was preceded by the substantial generation in the draining lymph node and spleen of T cells capable of specifically lysing P815 target cells in vitro. The finding that the magnitude of this cytolytic response was much greater than the cytolytic response to a control tumor that grew progressively is consistent with the hypothesis that the anti-tumor action of C. parvum is based on its capacity to augment the production of T cells sensitized to tumor-specific transplantation antigens. This adjuvant action of C. parvum was revealed by additional experiments in which irradiated, nonreplicating tumor cells were substituted for living tumor cells in the admixture. The results support the conclusion that the potentiated cytolytic response to subcutaneous injection of an admixture of irradiated tumor cells and C. parvum is responsible for the ability of this admixture to cause the regression of a test tumor growing at a distant site. Finally, it was shown that the failure of the therapeutic admixture to cause the regression of distant test tumors above a certain size was associated with a failure of the admixture to cause a potentiated, anti-tumor cytolytic response. We discussed the possibility that this failure was caused by the presence of a tumor-induced state of immunosuppression.