Methods and compositions for promoting immunopotentiation

Abstract

This invention discloses immunopotentiating agents which stimulate an immune response. These agents are categorized into single agents that act directly, adjuvants added concurrently with the agents, or heteroconjugates. Heteroconjugate agents elicit or enhance a cellular or humoral immune response which may be specific for an epitope contained within an amino acid sequence. Enhanced hematopoieses by bone marrow stem cell recruitment was also a result of administering some of these agents. Examples of immunopotentiating agents include monoclonal antibodies and proteins derived from microorganisms (e.g., enterotoxins) which activate T cells. One method of treatment disclosed uses only the immunopotentiating agent to stimulate the immune system. Another uses adjuvants in combination with the agent. A third method employs heteroconjugates. Heteroconjugates comprise: (a) an immunopotentiating protein which is characterized as having an ability to stimulate T cells; and (b) a second protein having an amino acid sequence which includes an epitope against which a cellular or humoral response is desired. This invention also relates to a method of preparing the heteroconjugate, and to a method of stimulating the immune system in vivo in a novel way. One route of stimulation is to activate T cells, in some instances, specific subsets of T cells, by administering heteroconjugates containing an immunopotentiating protein and a second protein, to mammals. For this method of treatment, the second protein in the heteroconjugate is derived from abnormal or diseased tissue, or from an infectious agent; alternatively, the second protein is produced synthetically by standard methods of molecular biology. Sources of the second protein include tumors, viruses, bacteria, fungi, protozoal or metozoal parasites. Monoclonal antibodies or T cells prepared from mammals whose immune systems have responded to administration of the heteroconjugate may be produced and administered to induce passive immunity. A method of preparing a hybridoma which secretes said monoclonal antibodies and use of these monoclonal antibodies and T cells, are also disclosed. This invention is also directed to a vaccine comprising the heteroconjugate.

Description

[0001] The government may own certain rights in the present invention pursuant to NIH grant number 5 RO1-CA-49260.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to immunology, and, more specifically, to the preparation and use of immunopotentiating agents which are capable of eliciting, enhancing and / or otherwise modifying immune responses. These agents, through their ability to elicit or enhance cellular or humoral responses, have potential utility in a variety of disease conditions wherein immunotherapy might be expected to provide a benefit. [0004] 2. Description of Related Art [0005] The body's immune system serves as a defense against a variety of conditions, including, e.g., injury, infection and neoplasia, and is mediated by two separate but interrelated systems, the cellular and humoral immune systems. Generally speaking, the humoral system is mediated by soluble products, termed antibodies or immunoglobulins, which have the abilit...

AI Technical Summary

Benefits of technology

[0033] The term “activation” is generally defined to refer to any change induced in the basal or resting state of T or B cells. This includes, but is not limited to, increased cell proliferation and DNA synthesis, lymphokine and cytotoxic cell production, a rapid rise in intracellular calcium, release of water soluble inositol phosphates, increased IL-2 receptor expression, enhanced proliferative response to IL-2, and enhanced responses to foreign antigens or MHC (23). In contrast, the term “immunopotentiating” is classically defined as the ability to produce an effect on the immune system which enhances the system's ability to respond to foreign antigens. Thus, immunopotentiation may affect the cellular response, humoral response, or both. Exemplary indices of immunopotentiation include, but are not limited to, cell-proliferation, increased DNA synthesis, increased production of lymphokines, increased production of cytotoxic cells, calcium efflux, or any other change that raises the cell above the basal or resting state.

[0041] As mentioned, the present invention contemplates the use of these immunopotentiating agents in immunogen containing compositions such as vaccines, where the agents serve as “adjuvants” to improve the immunogenicity of other components of the composition. Thus, it is contemplated that through the use such agents as “adjuvants”, the preparation of useful vaccines using only weakly or non-immunogenic molecules not previously known to function as immunogens is enabled. In such embodiments, the immunopotentiating protein is admixed or otherwise co-administered with the molecule against which an immune response is desired, with the immunopotentiating agent being present in amounts effective to promote potentiation upon administration to the particular subject.

[0058] As mentioned above, the present invention contemplates that various useful biological products may be derived through the application of the foregoing immunopotentiating compositions. For example, the adjuvant and heteroconjugate embodiments will provide extremely useful means for preparing antibodies, including monclonal antibodies. Moreover, it has been found that immunopotentiating antibodies such as anti-CD3 can serve to promote the recruitment of hematopoetic progenitor cells, presumably by stimulating the release of cytokines and lymphokines from activated T-cells. This lends the possibility that such embodiments may be employed to prepare highly active bone marrow for transplantation, or even for administration to bone marrow transplant recipients or those with depleted bone marrow cells to provide a metabolic boost to the marrow. Moreover, it is contemplated that activated T cells themselves will find some utility, such as in anti-tumor therapy that employs tumor-infiltrating lymphocytes.

Problems solved by technology

One of the major problems in clinical immunology is that the polymorphic antigens of the MHC impose severe restrictions on triggering an immune response.

Another problem is that doses of an invading antigen may be too low to trigger an immune response.

By the time the antigenic level rises, it may be too late for the immune system to save the organism.

The tremendous heterogeneity of the MHC proteins among individuals remains the most serious limiting factor in the clinical application of allograft transplantation.

Attempts to suppress the alloreactivity by drugs or irradiation has resulted in severe side effects that limit their usefulness.

However, the results were often inconsistent due to the inability to standardize individual preparations of antisera.

In addition, the precise nature of the target antigens recognized by the polyclonal reagents could not be defined, thus making scientific analysis difficult.

Although some of these agents, in vitro effects have previously been demonstrated, in vitro activity is often not a reliable predictor of in vivo effects.

One cause of malignant tumor growth is believed to be the inability of the immune system to respond appropriately to tumor antigen.

However, these adjuvants do not selectively act on T cells, or subsets of T cells, and have not been shown capable of overcoming immunodeficiency states.

Unfortunately, current modes of immunotherapy which induce non-specific effector cells are not effective enough in potentiating anti-tumor responses (18).

Immunological responses to HIV infection require the development of both humoral and cell mediated effector mechanisms; however current efforts in treatment and vaccine design have fallen short of success either due to the immunodeficiency associated with the viral infection, or to the low immunogenicity of the vaccine (20).

The development of a safe and effective vaccine against infection with human immunodeficiency virus (HIV) is complicated by a lack of understanding of protective immunity to HIV and disease development, and the absence of an adequate and convenient animal model for studying HIV infection.

In individuals infected with HIV, two components of the immune system are suboptimal and, therefore, the ability to generate an immune response in these individuals has been compromised.

First, the reduced frequency of antigen-reactive CD4+ T cells is apparently not sufficient to mount an appropriate immune response to HIV, especially if the quantity of HIV antigen is low.

Given the tremendous polymorphism of the MHC antigens expressed in the population, and the variation of the HIV virus, developing a successful HIV vaccine for general use is difficult and has not yet been successful.

(f) Problems in Developing Vaccines to Weakly Immunogenic Antigens

The usefulness of certain peptides, proteins or other potential or desired immunogens in vaccines can be limited by several critical factors.

For example, low immunogenicity of the peptide or other structure which one desires to employ can be a difficult problem to overcome, particularly with smaller peptides and those peptides which do not contain appropriately strong B- and / or T-cell potentiating sequences.

It has been difficult to protect against attack by organisms such as the HIV virus or to provide tumor immunity for several reasons.

For example, genetic differences exist among individuals at the major histocompatibility locus, which limits the system's ability to respond to individual small peptides.

Thus, the various components of the immune response, including the T cells and B cells, may not interact appropriately in generating a response to non- or weakly-immunogenic small peptides.

However, prior adjuvants such as these have proven to be inadequate for various reasons, including an inability of the adjuvant to specifically enhance T or B cell activity and the inability of the adjuvant to overcome the severe limitations of MHC restriction.

Although glimpses into the defense mechanisms of the body's own immune system have been provided by in vitro studies and by observation of some in vivo reactions, there is a serious lack of successful therapeutic methods to augment immunity in vivo.

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