James E. Talmadge

The effect of experimental conditions on the assessment of T cell immunomodulation by biological response modifiers (thymosin fraction five)

The coculture of spleen cells with specific antigens in the presence of thymosin fraction five (F5) results in the stimulation of the lymphocyte response. To observe the stimulation, a suboptimal responder-to-stimulator ratio must be utilized. Suboptimal assay conditions also are needed in immunization challenge studies in which thymosin F5 acts as an effective immunoadjuvant. The data reported here suggest that to study the efficiency of a biological response modifier, suboptimal assay conditions are best for observation of immunomodulation. We also report that thymosin F5, in addition to exhibiting adjuvantlike activity for T cells, is stimulatory in assays of mixed lymphocyte response and in the in vitro stimulation of cytotoxic T effector cells, following a mixed lymphocyte-tumor culture.

Toxicity of polyinosinic-polycytidylic acid admixed with poly-L-lysine and solubilized with carboxymethylcellulose in mice.

Polyinosinic-polycytidylic acid [poly(I,C)] is a double-stranded RNA that is a potent interferon (IFN) inducer in rodents and, when suitably complexed with poly-L-lysine and carboxymethylcellulose [poly(I,C)-LC], also in primates and humans. In addition, poly(I,C)-LC has shown significant therapeutic activity in a number of preclinical tumor models and significant toxicity in both the preclinical and clinical settings. To better understand the toxicity of this agent, particularly in light of the previously reported bell-shaped dose response curve for immunomodulation and therapeutic activity, we undertook a pharmacological/toxicological study of poly(I,C)-LC. These experiments revealed that the injection of toxic doses of poly(I,C)-LC significantly reduced the body weight of animals and induced serological and histological abnormalities. We found that poly(I,C) is the toxic moiety of poly(I,C)-LC and that both agents induced pulmonary thrombosis as well as hepatic necrosis. The hepatic necrosis was reflected in serum enzyme levels, with significant increases in ornithine carbonyl transferase, serum glutamic oxaloacetic transaminase and serum glutamic pyruvic transaminase levels. In addition, reduced platelet counts indicated a significant increase in platelet consumption in agreement with the thrombosis. There were, however, only minor changes in prothrombin and activated prothrombin times. It was of interest that coincubating poly(I,C)-LC and peritoneal macrophages in vitro resulted in the production of tumor necrosis factor, which has a similar pattern of toxicity; this finding suggests that poly(I,C)-LCs pattern of toxicity may be associated with the induction of TNF and/or IFN.

Biologic and Technical Considerations for the Design of Screening Procedures for the Assessment of Biological Response Modifiers

In this chapter we present the rationale for the design of a meaningful test system for determining the potential value of biological response modifying agents for the treatment of cancer in general, and metastasis in particular. For the last two centuries, numerous efforts have focused on treating neoplastic diseases by the manipulation of the host with agents which we now classify as biological response modifiers (BRMs). An implicit assumption in these studies has been the belief that clinical cancer is the consequence of altered homeostasis, in which host responses to an oncogenic challenge are diminished or absent. Thus, it was reasoned that the successful awakening or boosting of a host’s response to neoplasia should lead to tumor regression. However, clinical immunotherapeutic trials with a variety of agents have yielded discouraging results that are greatly inferior to those obtained in various animal models.

Evaluation of Immunomodulatory and Therapeutic Properties of Biological Response Modifiers: A Comparison of Preclinical and Clinical Studies

Biological response modifiers (BRMs) are those agents or approaches that modify the relationship between the tumor and host by modifying the host’s biological response to the tumor cells with resultant therapeutic effects (1). BRMs may modify the host responses in several ways: 1. increase the host’s antitumor responses through augmentation and/or restoration of effector mechanisms or mediators of the host’s reaction which may be deleterious; 2. increase the host’s defenses by the administration of natural biologicals (or the synthetic-recombinant derivatives thereof) as effectors or mediators of an antitumor response; 3. augment the sensitivity of the host’s tumor cells to endogenous mechanisms for the control of tumor growth; 4. alter the transformed phenotype by increasing the differentiation/maturation of tumor cells; 5. increase the ability of the host to tolerate damage by cytotoxic modalities of cancer treatment.

Comparison of Therapeutic Potential of Cytokines

Biological response modifiers (BRMs) are those agents or approaches that influence the relationship between the tumor and host by modifying the hosts response to tumor cells, with resultant therapeutic activity (9). A series of studies with recombinant cytokines designed to better understand their immunomodulatory and therapeutic properties have been undertaken. The present report discusses recombinant murine interferon-gamma (rM IFN-g), recombinant human tumor necrosis factor (rH TNF), rH interleukin-2 (rH IL-2), and rM colony stimulating factor-gm (rM CSF-gm). We discuss the development of Optimal Therapeutic Protocols (OTP) for preclinical studies and initial clinical trials that have been initiated to test the resultant clinical hypotheses.

Preclinical Evaluation of Individual Biological Response Modifiers

The interferons are a family of proteins and glycoproteins that are synthesized by cells in response to viral infection, antigenic challenge, and a variety of chemical inducers. Interferons can be produced by virtually all eucaryotic cells in response to a variety of stimuli and are capable of acting on homologous and heterologous cells with relative species specificity. The interferons that have been identified are divided into three major classes (alpha, beta, and gamma) according to their antigenic profiles, physiochemical characteristics, and inducing agents. Initially the interferons were categorized according to cell of origin, inductive stimulus, or physiochemical property such as acid lability. Leukocytes produce mainly α-IFN, fibroblasts mainly β-IFN, and T lymphocytes mainly γ-IFN. Interferon units are, at present, determined by a bioassay measuring antiviral activity. Interferons directly affect both malignant and normal cells by slowing their cycling time. This was initially demonstrated with the L-1210 lymphoma, whose growth in vivo as well as in vitro can be inhibited by interferon. Thus, the antiproliferative effects of interferon may account for some of the antitumor effects observed in vivo.