HIV-1 Vaccine Development: studies in Macaque models

Since its discovery about 15 years ago, human immunodeficiency virus type 1 (HtV-1) continues·to spread at an alarming rate. It is estimated that by the year 2000 between 30 and 40 million people will be infected with this virus worldwide'. Of these, about 90 % live in developing countries. To date, more than six million people have already developed to the fatal acquired immunodeficiency syndrome (AIDS). Despite numerous research efforts no vaccination or generally accessible therapeutic approach has become available yet. In 1981, the first case of AIDS was recognized'. Epidemiologic studies implicated an infectious agent and in 1983, the isolation of a previously unknown human retrovirus called lymphadenopathy-associated virus (LA V) from an AIDS patient was reported by Barre-Sinoussi et al.'. In 1984, Gallo et aI' and Levy et a/s also reported the isolation of retroviruses from AIDS patients which they called human T-Iymphotropic virus type III (HTLV-III) and AIDS-associated retrovirus (ARV), respectively. Soon thereafter, these retroviruses were recognized as members of the Lentivirinae, a subfamily of the Retroviridae, and were indeed identified as the etiological agents of AIDS. In 1986, these retroviruses were named human immunodeficiency virus (HIV). Today, two types of HIV are recognized, HIV-1 and HIV-2. Of these, HIV-1 is the primary etiologic agent of the current AIDS pandemic. The search for an HIV-1 counterpart in other primate species led to the identification of several simian immunodeficiency viruses (SIV), which may cause AIDS like syndromes in monkeys'. Currently, macaque lentivirus infections are considered the most appropriate animal models to study HIV pathogenesis and possible intervention strategies. In the following section, a concise overview is given of the biology of primate lentiviruses, including the host immune response and correlates of immune-mediated protection. Aspects important for vaccine development are highlighted

Chemical inactivation of recombinant vaccinia viruses and the effects on antigenicity and immunogenicity of recombinant simian immunodeficiency virus envelope glycoproteins.

The efficiency of paraformaldehyde (PFA) and binary ethylenimine (BEI) in inactivating recombinant vaccinia virus (rVV), present in baby hamster kidney cells expressing simian immunodeficiency virus envelope glycoproteins (SIV-Env), was measured in a series of inactivation studies. Both compounds were shown to be effective in reducing rVV titres. The use of standard 3-day titration assays proved to be inadequate to measure PFA inactivation, since upon prolonged incubation, residual rVV infectivity was detected in cultures negative at 3 days. Different procedures using PFA or BEI were selected to assess their influence on the antigenicity and immunogenicity or rVV expressed SIV-Env. Antigenicity, as defined by the ability to react with a panel of monoclonal antibodies recognizing major antigenic sites, and immunogenicity, as defined by the ability to induce SIV envelope specific and virus neutralizing serum antibodies in rats, proved to be preserved after either inactivation procedure. These data show that both protocols using

Simian immunodeficiency virus (SIV)-specific CD8+ cytotoxic T lymphocyte responses of naive and vaccinated cynomolgus macaques infected with (SIV)mac32H(J5): quantitative analysis by in vitro antigenic stimulation.

Detailed analyses of simian immunodeficiency virus (SIV)-specific cytotoxic T lymphocyte (CTL) responses in vaccinated and infected macaques may help to clarify the role of CTL immunity in protection against lentiviruses. Here, the optimal conditions for the measurement of SIV Gag-specific CTL were investigated by bulk and limiting dilution assays of peripheral blood mononuclear cells (PBMC) from naive and vaccinated cynomolgus macaques (Macaca fascicularis) infected with SIVmac32H(J5). In vitro restimulation was generally required for CTL detection. Selective activation of CD8+ and MHC-restricted SIV Gag-specific CTL was induced by stimulation with autologous para-formaldehyde-fixed B-lymphoblastoid cell lines infected with a recombinant vaccinia virus expressing SIV Gag. Applied to limiting dilution assays, antigenic stimulation reproducibly demonstrated SIV Gag-specific CTL precursors (CTLp) in PBMC of all animals studied, including those lacking significant responses in standard bulk CTL assays

No Evidence of a Drug-Drug Interaction Between Letermovir (MK-8228) and Mycophenolate Mofetil

Introduction: Letermovir (MK-8228) is a potent, oncedaily inhibitor of the cytomegalovirus (CMV) terminase complex that is being developed for the prophylaxis of CMV infection in transplant patients. This study evaluated the pharmacokinetic interactions, safety, and tolerability of letermovir when coadministered in healthy subjects with mycophenolate mofetil (MMF), which is the morpholinoethyl ester prodrug of mycophenolic acid (MPA). Methods: This was an open-label trial in 14 healthy female subjects that explored the pharmacokinetic parameters of a single 1 g oral dose of MMF administered alone on Day 1 and coadministered on Day 12 with 480 mg oral once-daily letermovir given on Day 5 and from Day 8 continued through Day 16. Letermovir PK was assessed at single dose (Day 5) and at steady state on Day 12 (with MMF) and Day 16 (alone following MMF washout). Results: Coadministration of 480 mg qd letermovir at steady state with a single dose of 1 g of MMF had no effect on the pharmacokinetics of MPA. The MPA AUC0-inf and Cmax geometric mean ratios (GMRs) [90% confidence interval] for the comparison (MMF with letermovir/ MMF alone) were 1.08 [0.96, 1.21] and 0.96 [0.81, 1.13], respectively. Coadministration of a single dose of 1 g MMF with 480 mg qd letermovir at steady state had no clinically meaningful effect on the pharmacokinetics of letermovir, with AUC0-24 and Cmax GMR of 1.18 [1.04, 1.32] and 1.11 [0.93, 1.34], respectively. The letermovir geometric mean accumulation ratio (Day 16/Day 5) and 95% CI were 1.13 [0.90, 1.42] for AUC0-24 and 1.01 [ 0.79, 1.28] f or Cmax, indicating that accumulation of letermovir when administered as daily doses is minimal. All related AEs were reported as mild in severity and resolved. Conclusions: Multiple-dose administration of 480 mg letermovir daily with a single dose of 1 g MMF was generally well tolerated by the healthy subjects in this study. Coadministration of letermovir and MMF had no clinically meaningful effect on the PK of letermovir or MPA. Letermovir and MMF may be coadministered without dose adjustment

Antigenicity and immunogenicity of recombinant envelope glycoproteins of SIVmac32H with different in vivo passage histories.

Shortly after infection of two rhesus monkeys (Macaca mulatta) either with a SIVmac32H challenge stock or with the same virus that had been passaged in another rhesus monkey for 11 months, SIV-envelope genes were cloned from their peripheral blood mononuclear cells and subsequently expressed by recombinant vaccinia viruses. The molecular weights and antigenicities of the thus produced envelope glycoproteins were largely identical to those of the native SIV. The envelope glycoprotein derived from the in vivo passaged virus proved to be poorly recognized by virus neutralizing monoclonal antibodies directed against one of the seven antigenic sites for which monoclonal antibodies were available. Immunization studies in rats showed that this protein was also less efficient in inducing antibodies against this antigenic site, and that it induced significantly lower levels of virus neutralizing antibodies than the other SIV-envelope glycoprotein. The immunogenicity of the SIV-envelope glycoprotein incorporated into immune stimulating complexes (iscoms) was compared to that of the same protein presented with Quil A or MDP-tsl

Vaccine-induced virus-neutralizing antibodies and cytotoxic T cells do not protect macaques from experimental infection with simian immunodeficiency virus SIVmac32H (J5).

To gain further insight into the ability of subunit vaccines to protect monkeys from experimental infection with simian immunodeficiency virus (SIV), two groups of cynomolgus macaques were immunized with either recombinant SIVmac32H-derived envelope glycoproteins (Env) incorporated into immune-stimulating complexes (iscoms) (group A) or with these SIV Env iscoms in combination with p27gag iscoms and three Nef lipopeptides (group B). Four monkeys immunized with recombinant feline immunodeficiency virus Env iscoms served as controls (group C). Animals were immunized intramuscularly at weeks 0, 4, 10, and 16. Two weeks after the last immunization, monkeys were challenged intravenously with 50 monkey 50% infectious doses of virus derived from the J5 molecular clone of SIVmac32H propagated in monkey peripheral blood mononuclear cells. High titers of SIV-neutralizing antibodies were induced in the monkeys of groups A and B. In addition, p27gag-specific antibodies were detected in the monkeys of group B. Vaccine-induced cytotoxic-T-lymphocyte precursors against Env, Gag, and Nef were detected on the day of challenge in the monkeys of group B. Env-specific cytotoxic-T-lymphocyte precursors were detected in one monkey from group A. In spite of the observed antibody and T-cell responses, none of the monkeys was protected from experimental infection. In addition, longitudinal determination of cell-associated virus loads at weeks 2, 4, 6, 9, and 12 postchallenge revealed no significant differences between vaccinated and control monkeys. These findings illustrate the need to clarify the roles of the different arms of the immune system in conferring protection against primate lentivirus infections

Decline of simian immunodeficiency virus (SIV)-specific cytotoxic T lymphocytes in the peripheral blood of long-term nonprogressing macaques infected with SIVmac32H-J5.

The evolution of simian immunodeficiency virus (SIV)–specific cytotoxic T lymphocyte precursors (CTLps) and their relationship with virus replication were studied in SIV‐infected macaques. After primary viremia, 3 of 8 macaques l

Complement-Mediated Virus Infectivity Neutralisation by HLA Antibodies Is Associated with Sterilising Immunity to SIV Challenge in the Macaque Model for HIV/AIDS.

Sterilising immunity is a desired outcome for vaccination against human immunodeficiency virus (HIV) and has been observed in the macaque model using inactivated simian immunodeficiency virus (SIV). This protection was attributed to antibodies specific for cell proteins including human leucocyte antigens (HLA) class I and II incorporated into virions during vaccine and challenge virus preparation. We show here, using HLA bead arrays, that vaccinated macaques protected from virus challenge had higher serum antibody reactivity compared with non-protected animals. Moreover, reactivity was shown to be directed against HLA framework determinants. Previous studies failed to correlate serum antibody mediated virus neutralisation with protection and were confounded by cytotoxic effects. Using a virus entry assay based on TZM-bl cells we now report that, in the presence of complement, serum antibody titres that neutralise virus infectivity were higher in protected animals. We propose that complement-augmented virus neutralisation is a key factor in inducing sterilising immunity and may be difficult to achieve with HIV/SIV Env-based vaccines. Understanding how to overcome the apparent block of inactivated SIV vaccines to elicit anti-envelope protein antibodies that effectively engage the complement system could enable novel anti-HIV antibody vaccines that induce potent, virolytic serological response to be developed