Role of class I molecules of the major histocompatibility complex in cytotoxic T-cell function in health and disease

Induction of hepatitis C virus-specific cytotoxic T lymphocytes in mice by immunization with dendritic cells treated with an anthrax toxin fusion protein

As a novel and safe vaccine strategy, the anthrax toxin-mediated antigen delivery system composed of lethal factor (LF) fusion protein and protective antigen (PA) has been studied to prime hepatitis C virus (HCV) core-specific cytotoxic T lymphocytes (CTLs) in vivo. The core epitope fused to LF (LF-core) together with PA induces a negligible core-specific CTL response in mice, whereas core-specific CTL are effectively primed in mice by injecting dendritic cells (DCs) treated in vitro with LF-core and PA. These findings imply that LF fusion protein plus PA in combination with dendritic cells may be useful for a novel T cell vaccine against HCV infection.

Characterization of CD8+ cytotoxic T-lymphocyte responses after genetic immunization with retrovirus vectors expressing different forms of the hepatitis B virus core and e antigens

Cytotoxic T-lymphocyte (CTL) activity appears to play an important role in resolving hepatitis B virus (HBV) infection, and the ability to induce such responses remains an important goal for developing effective immunotherapeutics. A panel of recombinant retrovirus vectors expressing different forms of the HBV core antigen (HBcAg) or e antigen (eAg) were found to induce antigen-specific major histocompatibility complex-restricted CTL responses in both mice and macaques. In addition, a novel retrovirus vector expressing an HBcAg-neomycin phosphotransferase II (HBc-Neo) fusion protein [LHBc-NEO(6A3)], which allows the measurement of the anti-Neo antibody response as a means of directly tracking biological activity of the vector, was generated. Doses greater than 10(7) CFU were necessary to induce CTL responses in H-2(k) mice. Intramuscular injections with 10(8) CFU of the LHBc-NEO(6A3) retrovirus vector into rhesus monkeys induced HBc/eAg-specific antibody production and CD8+ CTLs. The CTL response from one of the two responder rhesus monkeys was directed against a 9-residue peptide, GELMTLATW, at positions 63 to 71 of the HBc/eAg sequence. The CTL response is long lived, being detectable as late as 16 weeks after immunization, and can be boosted upon reimmunization. The potent ability of recombinant retrovirus vectors to induce HBcAg- and eAg-specific CTL responses may prove beneficial as a therapeutic treatment for chronic hepatitis B infection.

H-2Ld-alloreactive T cell hybridomas utilize diverse V alpha and V beta T cell receptor chains

We have sequenced the TCRs from Ld-specific alloreactive T cell hybridomas, whose reactivities we have found to be quite representative of those of a primary dm2 anti-BALB/cJ mixed lymphocyte reaction. We find V beta 6, V beta 7, V beta 8 and V beta 10 gene segments. V alpha usage is diverse, although closely related to that from peptide-specific Ld-restricted CTLs. V alpha-V beta selection provides evidence of preferential pairing. Amino acid frequency analysis shows that the alpha CDR2 region is rich in charged amino acids, in contrast to the beta CDR2 region. Our data suggests the beta chain may be more immunoglobulin-like than the alpha chain, and that charge complementarity may be important in TCR-MHC interactions. We do not consider our results to be contradictory to those previously reported but rather they may represent an early, more diverse response.

Effects of HIV-1 Tat on expression of HLA class I molecules

Tat protein of HIV-1 is a potent transactivator of transcription and essential for HIV-1 replication. In addition, Tat has been proposed to possess immunosuppressive functions, suggesting that Tat may play a direct role in the immune dysfunction associated with AIDS. Recently, it has been reported that Tat represses activity of a major histocompatibility complex (MHC) class I gene promoter. Because HIV infection downmodulates expression of class I molecules, this data strongly suggests that Tat downregulates class I expression and leads to loss of CTL activity. Here, we report effects of Tat on class I expression using a human cell line, T0, expressing Tat (TO-Tat). Northern blot analysis shows that levels of MHC class I transcripts are normal in T0-Tat. Flow cytometry analyses indicate that expression of HLA class I molecules is not substantially downregulated to any great extent by Tat in T0-Tat. Further, pulse-chase experiments followed by Endoglycosidase-H treatment show that the rate of maturation and processing of class I molecules in T0-Tat is indistinguishable from that in the original cell line, T0. Taken together, these data suggest that Tat expression does not necessarily result in downregulation of class I expression.