Phase I/II Preventive Vaccine Trials: Conference Summary

Impact of adjuvants on the biophysical and functional characteristics of HIV vaccine-elicited antibodies in humans

Adjuvants can alter the magnitude, characteristics, and persistence of the humoral response to protein vaccination. HIV vaccination might benefit from tailored adjuvant choice as raising a durable and protective response to vaccination has been exceptionally challenging. Analysis of trials of partially effective HIV vaccines have identified features of the immune response that correlate with decreased risk, including high titers of V1V2-binding IgG and IgG3 responses with low titers of V1V2-binding IgA responses and enhanced Fc effector functions, notably antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). However, there has been limited opportunity to compare the effect of different adjuvants on these activities in humans. Here, samples from the AVEG015 study, a phase 1 trial in which participants (n = 112) were immunized with gp120SF-2 and one of six different adjuvants or combinations thereof were assessed for antibody titer, biophysical features, and diverse effector functions. Three adjuvants, MF59 + MTP-PE, SAF/2, and SAF/2 + MDP, increased the peak magnitude and durability of antigen-specific IgG3, IgA, FcγR-binding responses and ADCP activity, as compared to alum. While multiple adjuvants increased the titer of IgG, IgG3, and IgA responses, none consistently altered the balance of IgG to IgA or IgG3 to IgA. Linear regression analysis identified biophysical features including gp120-specific IgG and FcγR-binding responses that could predict functional activity, and network analysis identified coordinated aspects of the humoral response. These analyses reveal the ability of adjuvants to drive the character and function of the humoral response despite limitations of small sample size and immune variability in this human clinical trial.

Army Liposome Formulation (ALF) family of vaccine adjuvants

Introduction: From its earliest days, the US. military has embraced the use of vaccines to fight infectious diseases. The Army Liposome Formulation (ALF) has been a pivotal innovation as a vaccine adjuvant that provides excellent safety and potency and could lead to dual-use military and civilian benefits. For protection of personnel against difficult disease threats found in many areas of the world, Army vaccine scientists have created novel liposome-based vaccine adjuvants.Areas covered: ALF consists of liposomes containing saturated phospholipids, cholesterol, and monophosphoryl lipid A (MPLA) as an immunostimulant. ALF exhibited safety and strong potency in many vaccine clinical trials. Improvements based on ALF include: ALF adsorbed to aluminum hydroxide (ALFA); ALF containing QS21 saponin (ALFQ); and ALFQ adsorbed to aluminum hydroxide (ALFQA). Preclinical safety and efficacy studies with ALF, LFA, ALFQ, and ALFQA are discussed in preparation for upcoming vaccine trials targeting malaria, HIV-1, bacterial diarrhea, and opioid addiction.Expert opinion: The introduction of ALF in the 1980s stimulated commercial interest in vaccines to infectious diseases, and therapeutic vaccines to cancer, and Alzheimer's disease. It is likely that ALF, ALFA, and ALFQ, will provide momentum for new types of modern vaccines with improved efficacy and safety.

Long-term safety analysis of preventive HIV-1 vaccines evaluated in AIDS vaccine evaluation group NIAID-sponsored Phase I and II clinical trials

This report evaluates long-term safety data from 3189 human immunodeficiency virus type 1 (HIV-1) uninfected, healthy volunteers who were enrolled into 51 National Institute of Allergy and Infectious Diseases (NIAID)-sponsored Phase I and II multicentred, randomized, double-blind trials of recombinant HIV-1 subunit vaccines (23 studies), synthetic peptide vaccines (7 studies), live vaccinia-vector recombinant envelope vaccines (7 studies), canarypox vector recombinant vaccines (13 studies), a DNA vaccine (1 study), and a Salmonella-vector vaccine (1 study). During the 12,340 person-years of follow-up, participants were monitored for adverse events including immune dysfunction/autoimmunity, anaphylaxis, cancer, death, and vaccine allergy. The analysis provides evidence that a preparation of a C4-V3 polypeptide vaccine emulsified in incomplete Freund's caused serious toxicity, but otherwise no safety problems considered serious were identified for any of the vaccines and adjuvants studied. These data serve to solidify the growing safety base of current vaccine technologies utilized in candidate vaccines for HIV-1 infection.

Factors related to the willingness of young gay men to participate in preventive HIV vaccine trials

Given their high seroincidence, young gay men will be targeted for recruitment into HIV vaccine trials but many challenges stand in the way of enlisting their cooperation. This study examined factors associated with young gay men's willingness to participate in vaccine trials and identified reasons for agreeing or not agreeing to participate. The data come from the Young Men's Survey, a cohort of western U.S. young gay men aged 18 to 29 years, surveyed using mail-back questionnaires. Participants who reported being HIV-negative or who had not been tested for HIV (n = 390) were asked to rate their desire to be given an HIV vaccine and their degree of willingness to participate in a vaccine trial. They also responded to open-ended questions regarding their reasons for participating or not participating. Of these respondents, 91% wanted to be given an HIV vaccine, yet many had serious reservations about participating in a vaccine trial. Men who had engaged in HIV risk behavior reported greater willingness to participate. The most common reasons for wanting to participate were desires to contribute to ending the AIDS epidemic and desire to help others; however, fears for one's own health and safety made many reluctant to participate.

Safety profile of phase I and II preventive HIV type 1 envelope vaccination: experience of the NIAID AIDS Vaccine Evaluation Group

The NIAID-sponsored AIDS Vaccine Evaluation Group was established in 1988 to perform phase I/II clinical trials with candidate preventive HIV-1 vaccines. This report includes safety data from 1398 HIV-negative, healthy volunteers who were enrolled into 25 phase I and 1 phase H multicentered, randomized, double-blind studies evaluating seven recombinant HIV-1 envelope vaccines, two V3 loop synthetic peptide vaccines, and two live poxvirus-vectored recombinant envelope vaccines. All studies but three were placebo controlled; the placebo was either the adjuvant alone or, in studies of recombinant poxvirus vaccines, it was the vector with no gene insert or a non-HIV gene insert. All candidate vaccines were generally well tolerated. The only adverse effects that were clearly related to vaccination were occasional acute local and systemic reactions that were associated with the adjuvants. Three adjuvants in particular were associated with moderate to severe local reactions: alum plus deoxycholate (ImmunoAg), MTP-PE (Biocine Corp.), and QS21 (Genentech, Inc.). MTP-PE was also associated with self-limited severe systemic reactions. There were no serious adverse laboratory toxicities and no evidence of significant immunosuppressive events after receipt of the candidate vaccines. A few volunteers experienced symptoms that might relate to an underlying immunopathologic mechanism (rash, hemolytic anemia, arthralgia), but their presentations were mild and their incidence was low. Eleven volunteers were diagnosed with malignancies during or after their participation, which was within the 95% confidence interval of the number of cases predicted by the National Cancer Institute SEER (Program for cancer surveillance, epidemiology, and end result reporting) database. In conclusion, the envelope-based recombinant or synthetic candidate HIV-1 vaccines appear to be safe and this work has prepared the way for the testing of increasingly complex candidate HIV-1 vaccines.

T-cell response to HIV in natural infection: optimized culture conditions for detecting responses to gag peptides

The proliferative responses to four gag peptides were examined in 24 HIV-seropositive patients whose CD4 counts ranged between 500 and 1400 cells/mm3. To overcome some of the limitations imposed by HIV infection on the T-cell proliferative assay, recombinant interleukin 2 (rIL-2) was added to the cultures, and the culture time of the cells was increased from the standard 6 to 8 or 10 days. Four of 24 patients responded to one or more core peptides, aa180-194, 208-217, 267-286, and 287-306 by the standard 6-day culture: this increased to 13 of 24 using the optimized culture approach. The greatest number and magnitude of responses occurred after cells were in culture for 8 days. Eight patients responded to gag 180-194, which has not been identified previously as a TH epitope in humans but has considerable homology with a TH epitope recognized by cloned T cells from macaques immunized with simian immunodeficiency virus (SIV). We have identified four T-cell epitopes on the HIV core protein p24, using synthetic peptides as immunogens. Three of the peptides would not have been considered immunogenic had the standard assay system been used to detect T-cell responsiveness. We have also shown that a region of the core protein encompassed by aa180-194 is recognized by TH cells in humans.

Willingness to participate in HIV-1 vaccine efficacy trials and the effect of media events among gay and bisexual men in New York City: Project ACHIEVE

Efficacy trials of candidate HIV-1 vaccines require study populations at high risk of infection who adhere to study protocols and who are willing to participate. Data from HIV-1 antibody-negative men (n = 698) enrolled in Project ACHIEVE in New York City were analyzed to assess willingness to participate in efficacy trials, factors influencing willingness, and the effect on willingness of the June 1994 media events about the decision not to proceed with phase III trials and about breakthrough infections during phase I and II vaccine trials. Sixty-eight percent indicated they would definitely or probably be willing to participate. Men enrolled during the time of media events were significantly less willing compared with men enrolled during other periods. These men were also more likely to mention safety of the vaccine, fear or mistrust of research or government, and social risks as important factors in their decision compared with men enrolled during other periods. The most frequently cited motivator for participation was altruism (57%); the most frequently cited barriers were vaccine safety (36%) and vaccine-induced seropositivity (19%). A substantial proportion of this cohort was willing to participate in future vaccine efficacy trials. However, because willingness may be affected by issues of vaccine safety, vaccine-induced seropositivity, and media coverage of these issues, significant efforts are needed for participant and community education, and specific concerns must be addressed in the design and implementation of trials.