Enhancement of tumor outgrowth by tumor-associated blocking factors

Administration of cyclophosphamide changes the immune profile of tumor-bearing mice

Cyclophosphamide (CTX) is often used to create a "window" for more effective therapeutic tumor vaccination. According to a commonly applied protocol, we injected 2 mg CTX intraperitoneally to mice with small (2 to 3 mm diameter) or large (5 to 7 mm, and in one experiment 8 to 10 mm diameter) subcutaneously growing tumors from the SW1 clone of the K1735 melanoma, euthanized the mice 4 days later and studied the composition of lymphoid cells by flow cytometry in both spleens and tumors. Administration of CTX increased the percentage of CD3, CD4, and CD8 cells with the increase in tumors being significantly greater than in spleens, and it also increased the percentage of B cells in spleens and tumors. Furthermore, CTX dramatically increased the frequency of tumor-infiltrating CD4 and CD8 cells containing interferon gamma, of cells expressing NK1.1, and of cells expressing the dendritic cell markers CD11c, CD80, and CD86, with the greatest increases seen among tumor-infiltrating lymphoid cells (TIL) from mice with small tumors. Although CTX decreased the percentage of TIL that expressed CD4 or CD8 together with CD25 and FoxP3 and were therefore considered to be regulatory T cells, it increased the frequency of TIL that stained for Gr1/CD11b, a marker for myeloid-derived suppressor cells. We conclude that the administration of CTX can favorably impact several cell populations that are involved in tumor rejection. However, since CTX has a limited effect on TIL from tumors larger than a few millimeter in diameter and in view of an increased percentage of myeloid-derived suppressor cells among TIL from mice given CTX there is a need for more effective ways to improve tumor vaccination.

Therapeutic vaccination with tumor cells that engage CD137

Therapeutic cancer vaccination is based on the finding that tumors in both humans and experimental animals, such as mice, express potential immunological targets, some of which have high selectivity for cancer cells. In contrast to the successful vaccination against some infectious diseases, where most vaccines induce neutralizing antibodies that act prophylactically, the aim of therapeutic cancer vaccines is to treat established tumors (primarily micrometastases). Since most tumor-destructive immune responses are cell-mediated, therapeutic cancer vaccination needs to induce and expand such responses and also to overcome "escape" mechanisms that allow tumors to evade immunological destruction. Tumor antigens (as with other antigens) are presented by "professional" antigen-presenting cells, most notably dendritic cells (DC). Therefore DC that have been transfected or "pulsed" to present antigen provide a logical source of tumor vaccines, and some encouraging results have been obtained clinically as well as in preclinical models. An alternative and more physiological approach is to develop vaccines that deliver tumor antigen for in vivo uptake and presentation by the DC. Vaccines of the latter type include tumor cells that have been modified to produce certain lymphokines or express costimulatory molecules, as well as cDNAs, recombinant viruses, proteins, peptides and glycolipids which are often given together with an adjuvant. Several studies over the past 5 years have demonstrated dramatic therapeutic responses against established mouse tumors as a result of repeated injections of agonistic monoclonal antibodies (MAbs) to the costimulatory molecule CD137 (4-1BB). However, the clinical use of such MAbs may be problematic since they depress antibody formation, for example, to infectious agents. The alternative approach to transfect tumor cells to express the CD137 ligand (CD137L) increases their immunogenicity, but vaccination with tumor cells expressing CD137L is ineffective in several systems where injection of anti-CD137 MAb produces tumor regression. Recent findings indicate that a more effective way to engage CD137 towards tumor destruction is to transfect tumor cells to express a cell-bound form of anti-CD137 single-chain Fv fragments (scFv). Notably, tumors from melanoma K1735, growing either subcutaneously or in the lung, could be eradicated following vaccination with K1735 cells that expressed anti-CD137 scFv. This was in spite of the fact that K1735, as with many human neoplasms, expresses very low levels of MHC class I and has low immunogenicity. Similar results were subsequently obtained with other tumors of low immunogenicity, including sarcoma Ag104. We hypothesize that the concomitant expression of tumor antigen and anti-CD137 scFv effectively engages NK cells, monocytes and dendritic cells, as well as activated CD4(+) and CD8(+) T cells (all of which express CD137) so as to induce and expand a tumor-destructive Th1 response. While vaccines in the form of transfected tumor cells can be effective, at least in mouse models, the logical next step is to construct vaccines that combine genes that encode molecularly defined tumor antigens with a gene that encodes anti-CD137 scFv. Before planning any clinical trials, vaccines that engage CD137 via scFv need to be compared in demanding mouse models for efficacy and side effects with vaccines that are already being tested clinically, including transfected DC and tumor cells producing granulocyte-macrophage colony-stimulating factor.

Transforming growth factor-beta inhibits the in vitro generation of lymphokine-activated killer cells and cytotoxic T cells

The effect(s) of purified transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF) on the induction and function of lymphokine-activated killer (LAK) cells and cytotoxic T lymphocytes (CTL) was examined. The addition of TGF-beta, but not PDGF, to cultures containing fresh C57BL/6 mouse splenocytes or human peripheral blood lymphocytes plus recombinant interleukin-2 markedly inhibited the development of mouse and human LAK cell activity (measured after 3 days for cytotoxicity against cultured or fresh tumor targets in 4-h 51Cr release assays). The addition of TGF-beta, but not PDGF, to a one-way, C57BL/6 anti-DBA/2, mixed lymphocyte reaction effectively blocked the generation of allospecific CTL as well. However, TGF-beta did not inhibit the effector function of LAK cells or of allospecific CTL when added directly to the short-term cytolytic assay. A second form of homodimeric TGF-beta, type 2, was also found to be suppressive on the development of murine LAK cells and allospecific CTL. Collectively, these data demonstrate that the peptide TGF-beta is a potent inhibitor of LAK cell and CTL generation in vitro.

Thymic factor-induced reduction of pulmonary metastases in mice with FSA-1 fibrosarcoma

The biological activities of two thymic factors, serum thymic factor thymulin normally present in serum and thymosin alpha-1 (Ta-1) extracted from the thymus gland, have been studied. The effects of the factors on the growth of pulmonary metastases and survival of mice were evaluated in pathogen-free C3H/fSed males. Mice were injected i.v. with the single cell suspension of the syngeneic methylcholanthrene-induced fibrosarcoma. The treatment with thymulin and Ta-1 started two days after injection of 5 x 10(4) to 2 x 10(5) tumor cells per mouse. Different doses of the thymic factors were administered S.C. in sets of 5 daily injections through a period of 2 or 3 weeks. Numbers of tumor colonies in the lung were determined two weeks after the cell injection. Treatment with 0.1 micrograms Ta-1 per injection through the period of two or three weeks, prolonged the survival of tumor-injected mice. Similar effects were observed in mice treated with 0.01 microgram thymulin per injection. Numbers of tumor colonies in lungs of these mice two weeks after the cell injection were also reduced in comparison with saline-treated controls. These findings correlated with prolonged survival time of identically treated mice. The effectiveness of thymic factors in reducing tumor growth was dependent on the tumour load. In addition, the effects induced by Ta-1 persisted longer than observed in thymulin-treated mice. Mice challenged 150 days after the primary tumor cell injection and treatment with Ta-1 demonstrated increased resistance to tumor, while mice treated with other factors behaved as saline-treated controls. The results indicate that both factors exert beneficial effects against tumor growth, although mode of action for each factor may be different.

Inhibition of sensitized leukocyte's in vitro reactivity by circulating immune complexes in prostate cancer

Circulating immune complexes in the sera of patients with confirmed histological diagnosis of carcinoma of the prostate, were found to interfere in the sensitized leukocyte's in vitro reactivity to prostate cancer associated antigen as evaluated by tube leukocyte adherence inhibition assay, thereby suggesting an inhibitory role of such serum factors in host's anti tumor cell mediated immune responses.

Immunosuppressor control as a modality of cancer treatment: effect of plasma adsorption with Staphylococcus aureus protein A

In tumor-bearing hosts both cellular and humoral tumor-growth-enhancing factors are present. They cause immunosuppression and facilitate the growth of tumors. Very early during tumor growth these factors are either elicited by the tumor cells or induced by the host immunocytes. Among these immunosuppressive agents, circulating immune complexes appear to play a predominant role. They also activate suppressor cell activity. Plasma adsorption of CIC and IgG by protein A of Staphylococcus aureus has been reported to cause tumor regression. Plasma adsorption with protein A-collodion charcoal, protein A-silica, or protein A-Sepharose also induced tumorilytic reactions. Even direct infusion of protein A induced tumor regressions in rat mammary tumors. Recent studies showing tumor regressions following S. aureus Wood 46 plasma adsorption or infusion of normal plasma adsorbed over S. aureus indicate that specific blocking factor removal by plasma adsorption may not be the mechanism for causing tumor destruction. Results indicate that S. aureus plasma adsorption leaches a number of staphylococcal agents. Thus, it appears that staphylococcal agents, protein A, enterotoxin, and other factors are responsible for the induction of reactions leading to tumor destruction. A unified mechanism explaining the results obtained with plasma adsorption using protein A of S. aureus, or S. aureus Wood, or direct protein A infusion, was presented.

Immunologic enhancement of experimental metastasis in the rat

Using a series of immunologically cross-reactive metastatic tumor variants, we demonstrate that serum from animals bearing pulmonary tumor colonies possesses enhancing properties in the experimental metastasis (lung colony) assay. Enhancement is produced by chronic serum administration and promotes the growth of tumor cells arrested in the lungs which would not otherwise proliferate to form grossly detectable lung nodules. Tumor-bearer serum from animals with lung colonies derived from the most highly metastatic variant examined is shown to possess enhancing properties in both BD-IX(H-1d) and BD-IV(H-1d) rat strains, while tumor-bearer serum from animals with lung colonies derived from the less metastatic parent tumor cell line possesses enhancing properties in the BD-IX rat strain only. Removal of immunoglobulin from enhancing serum by affinity column chromatography simultaneously removes the enhancing factor(s), and enhancing activity correlates with the presence of increased levels of Clq-binding immune complexes in the serum. Serum levels of immune complexes are shown to be more elevated in serum from animals bearing lung colonies derived from the most highly metastatic variant. The enhancing moieties are shown to bind to concanavalin A, but not to staphylococcal protein A, and the active fraction elutes from concanavalin A-Sepharose with alpha-methyl-mannoside. Consideration of immunoprecipitation studies on whole and fractionated enhancing sera, along with studies on affinity purified isotype fractions reveals that the activity resides with antibodies of IgG2b subclass.

Partial characterization of serum suppressor factors in patients with cervical squamous carcinoma

A cell-mediated cytotoxicity system was used to characterize the suppressor factors in sera from patients with invasive squamous cell carcinoma of the uterine cervix. The immunoglobulin-M fraction of the sera of 17 patients with different stages of invasive squamous cell carcinoma of the cervix, separated by Sephadex gel filtration, were tested. All showed marked cytotoxic suppressor activity, including two cases in which sera showed only mild activity. The immunoglobulin-G fraction of sera from 13 patients with invasive squamous cell carcinoma of the cervix was separated by ion exchange chromatography. The cytotoxic suppressor activity of the immunoglobulin-G fraction proved to be comparable in effect to that of the whole sera. By using increasing dilutions of IgG and IgM fractions, it could be demonstrated that IgM fraction retained its activity at 0.01 +/- 0.005 mg/ml whereas IgG fraction was devoid of activity at this concentration, suggesting that these two immunoglobulin fractions act independently. It is suggested that the cytotoxic suppressor activity in sera from patients with invasive squamous cell carcinoma of the cervix resides in the gamma globulin fraction and that both immunoglobulin-M and immunoglobulin-G of their sera manifest the cytotoxic suppressor activity independently. (Am J Reprod Immunol. 2:199-203.)

Immunoselection of tumor variants resistant to antibody-mediated cytotoxicity. Their immunologic and metastatic characterization

The immunological characteristics of two series of metastatic variants of restricted genetic origin were related to their lung-colony-forming potential. A series of metastatic variants was isolated from a tumor-cell population in which heterogeneity appeared following short-term in vivo passage, while a second series of variants were immunoselected in vitro for resistance to antibody-complement-mediated cell lysis. In the case of the first series, the sensitivity of the individual variants to cell-mediated and antibody-complement-mediated cytotoxicity appeared to be partly determined by the number and rate of loss of antibody-binding sites on the cell surface. These characteristics also correlated with the efficiency of experimental metastasis in the animal. We compared the results reported herein with our previous studies of nonimmune parameters for this series of metastatic variants, and we conclude that immunological differences can be important to the efficiency of lung-colony formation. However, in the case of the second series of variants, despite selection in vitro for resistance to antibody-complement-mediated cell lysis, the behavior of these variants in the lung colony assay could not be predicted by the immunologic parameters examined.

Cytotoxic blocking activity in invasive squamous cell carcinoma of the human uterine cervix

A cell-mediated cytotoxicity assay was used to evaluate the specific reactivity of patients with squamous cell carcinoma to an established cell line derived from squamous cell carcinoma of the cervix. Heat inactivated sera from patients with squamous cell carcinoma could very effectively nullify this specific cytotoxicity (P less than 0.01). There was no significant difference between the cytotoxic blocking activity of the sera from patients with different stages of the cancer in this experimental setup.