Immunotherapy in cancer and HIV

Abstract

Two major threats to human health are cancer and human immunodeficiency virus (HIV) infection. In both cases, a feature of progress of the disease is a defective immune function. Immunological mechanisms have evolved whereby transformed cells and HIV-1 infected cells avoid recognition and elimination by the immune system. Efforts to stimulate and restore the immune response against tumor cells or infected cells are collectively called immunotherapy.

In this thesis, we have investigated different types of immunotherapy with a view to stimulate the immune response against cancer cells and HIV-1 infected cells.

In the first study, we aimed at activating specific T-cells and B-cells against the tumor antigen, carcinoembryonic antigen (CEA), which is overexpressed in nearly 50 % of all human cancers. We immunized mice with two different DNA-plasmids, one encoding the wild type, cell surface expressed form of CEA and the other encoding a modified CEA product, expressed intracellularly with an immunostimulatory epitope fused to the protein. The wild type form induced a stronger antibody response than the modified form, but after boosting with a recombinant CEA (rCEA) protein, both constructs induced antibodies. DNAvaccination followed by rCEA boosting also induced cellular responses, as measured by specific production of the cytokines IFN-gamma and IL-2. Thus, a broader humoral and cellular response was induced by the prime boost immunization, compared to DNA or rCEA alone, indicating that a prime boost schedule is preferable.

In the second study, we targeted HIV-1 infected cells by passive immunotherapy with an antiHIV-1 envelope antibody conjugated to a cytotoxic drug called doxorubicin. This antibody conjugate could neutralize HIV-1 IIIB virus and eliminate HIV-1 replication in infected cells in vitro. The in vivo effect was measured in a mouse model, where mice were challenged with a virus consisting of the HIV-1 genome and the mouse leukaemia virus (MuLV) envelope. The anti-HIV-1 doxorubicin-conjugated antibody was capable of eradicating HIV-1IIIB/MuLV infected cells in vivo, since no infectious virus was found in culture supernatant of cells derived from challenged mice treated with the antibody.

In the third study, we aimed at stimulating an innate natural killer (NK) cell response against HIV-1 infected cells, since NK-cells are believed to be important for protection from HIV-1. Results obtained with our HIV-! IIIB/MuLV challenge model suggest that NK-cells contribute to the early defence against HIV-1 infection. We investigated the expression of different NKreceptors of importance for regulating NK-cell function in HIV-1 infected patients and healthy control subjects and found differences between the groups for inhibitory as well as for activating receptors. Efficient killing of leukemic cells has previously been seen in leukemic patients transplanted with bone marrow, expressing killer lg-like receptors (KIR), to which the patient lacks ligands. This is probably because compared to normal cells leukemic cells have a higher expression of ligands to activating NK-cell receptors.

It has been shown that also virally infected cells overexpress these activating ligands. We therefore blocked the interaction between KIRs and their ligands on cells from healthy as well as HIV-1 infected individuals and noted an increased degranulation of the NK-cells. Our aim is to investigate whether blocking of KIRs on NK-cells could be a new immunotherapeutic treatment for HIV-1 infected patients.