The cytotoxic T-lymphocyte (CTL) response plays an important role in controlling the severity and duration of viral infections. Immunization by direct in vivo administration of retroviral vector particles represents an efficient means of introducing and expressing genes and, subsequently, the proteins they encode in vivo in mammalian cells. In this manner foreign proteins can be provided to the endogenous, class I major histocompatibility complex antigen presentation pathway leading to CTL activation. A nonreplicating recombinant retroviral vector, encoding the human immunodeficiency virus type 1 (HIV-1) IIIB envelope and rev proteins, has been developed and examined for stimulation of immune responses in mouse, rhesus macaque, and baboon models. Animals were immunized by direct intramuscular injection of the retroviral vector particles. Vector-immunized mice, macaques, and baboons generated long-lived CD8+, major histocompatibility complex-restricted CTL responses that were HIV-1 protein specific. The CTL responses were found to be dependent on the ability of the retroviral vector to transduce cells. The vector also elicited HIV-1 envelope-specific antibody responses in mice and baboons. These studies demonstrate the ability of a retroviral vector encoding HIV-1 proteins to stimulate cellular and humoral immune responses and suggest that retrovector immunization may provide an effective means of inducing or augmenting CTL responses in

Recombinant retroviral vectors can efficiently transduce and express foreign genes in mammalian cells. We have examined the utility of retroviral vector-mediated gene transfer to deliver genes which encode human immunodeficiency virus type I (HIV) antigens capable of stimulating specific immune responses. Murine fibroblast cell lines were transduced with a nonreplicating murine retroviral vector carrying the gene encoding the HIV-IIIB envelope protein and were shown to express the gp160/120 protein. Mice immunized with syngeneic vector-transduced cells developed CD8+, class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) specific for targets expressing the HIV envelope protein. The CTL also exhibited lytic activity on target cells coated with synthetic peptides derived from the gp120 V3 hypervariable region of both the HIV-IIIB and HIV(MN) isolates. Following adoptive transfer in a murine tumor model, these CTL were shown to be effective in vivo by their ability to eliminate established tumor cells expressing the HIV protein. Vector-transduced syngeneic cells were also capable of eliciting HIV envelope-specific antibody responses in immunized mice. Sera obtained from these mice were found to bind to the HIV-IIIB gp160 protein as well as a peptide-defined neutralizing antibody epitope contained within the V3 domain of gp120. These sera exhibited virus-neutralizing activity in that they markedly reduced the ability of HIV to infect and form syncytia of a human T-cell line. This is the first demonstration that cells transduced with a retroviral vector encoding the HIV-IIIB envelope protein are capable of inducing effective HIV-specific cellular and humoral immune responses in mice.

The immune response against human immunodeficiency virus type-1 (HIV-1) is believed to play a role in controlling the early stages of disease progression. The cellular immune response, in particular cytotoxic T lymphocyte (CTL) activity, may be important for eliminating virally infected cells in HIV-1-infected individuals. Genetic immunization using retroviral vectors provides an effective means of introducing antigens into the antigen presentation pathways for T cell stimulation. A nonreplicating, amphotropic murine retroviral vector containing the HIV-1 IIIB env gene has been used to transduce primary rhesus monkey fibroblasts for the expression of HIV-1 antigenic determinants. Rhesus monkeys were immunized with four doses of either vector-transduced autologous fibroblasts (VTAF) expressing the HIV-1 IIIB ENV/REV proteins or nontransduced autologous fibroblasts (NTAF) administered at 2-week intervals. The animals were evaluated for both the induction of HIV-1-specific immune responses and potential toxicity associated with this ex vivo treatment. The VTAF-immunized monkeys generated CTL responses specific for HIV-1 ENV/REV expressing autologous target cells, whereas, NTAF-immunized monkeys showed negligible CTL activity. The cytotoxic activity was mediated by CD8+, major histocompatibility complex (MHC)-restricted CTL. In addition, antibody responses directed against the HIV-1 gp120 protein were also detected in the sera of VTAF-immunized monkeys. Clinical and histopathological evaluation of immunized monkeys showed no evidence of significant adverse events. Several animals that received either VTAF or NTAF had detectable anti-cytoplasmic antibodies, but were not positive for anti-nuclear antibodies or rheumatoid factor. Subsequent evaluation of renal, synovial, and hepatic tissue samples from these monkeys revealed no autoimmune disease-associated lesions. This study demonstrates the safety and ability of autologous retroviral vector-transduced cells expressing HIV-1 IIIB ENV/REV proteins to stimulate immune responses in a non-human primate model, and provides a basis for this form of genetic immunization in HIV-infected humans.

To evaluate the ability of murine anti-human immunodeficiency virus type 1 (HIV-1) IIIB env cytotoxic T lymphocytes (CTL) to recognize and lyse HIV-1-infected cells, we have constructed a human cell line (Hu/Dd) expressing both the CD4 receptor and the murine H-2Dd major histocompatibility complex (MHC) class I protein. This cell line can be productively infected with HIV-1 and can also function as a target for murine CD8+, class I MHC-restricted CTL directed against the envelope glycoprotein of HIV-1 IIIB. The ability of BALB/c anti-HIV-1 IIIB env CTL to specifically recognize and lyse Hu/Dd target cells infected with divergent HIV-1 strains was tested by using both prototypic and clinical HIV-1 strains. CTL generated by immunization of mice with syngeneic cells expressing either the native or V3 loop-deleted (AV3) envelope glycoprotein from HIV-1 IIIB were able to recognize and specifically lyse HuIDd target cells infected with the HIV-1 prototypic isolates IIIB, MN, WMJ II, SF2, and CC as well as several HIV-1 clinical isolates. These results demonstrate that CTL determinants for HIV-1 env exist outside the hypervariable V3 region, anti-HIV-1 IIIB env CTL appear to recognize common determinants on diverse HIV-1 strains, and classification of HIV-1 strains based on neutralizing antibody reactivities does not appear to correspond to CTL recognition and lysis. The results suggest that the cell-mediated components of the immune system may have a broader recognition of divergent HIV-1 strains than do the humoral components.