Recent developments in clinical trial designs for HIV vaccine research

Vaccination Strategies Against Mycobacterium tuberculosis: BCG and Beyond

Tuberculosis (TB) is a highly contagious disease caused by Mycobacterium tuberculosis (Mtb) and is the major cause of morbidity and mortality across the globe. The clinical outcome of TB infection and susceptibility varies among individuals and even among different populations, contributed by host genetic factors such as polymorphism in the human leukocyte antigen (HLA) alleles as well as in cytokine genes, nutritional differences between populations, immunometabolism, and other environmental factors. Till now, BCG is the only vaccine available to prevent TB but the protection rendered by BCG against pulmonary TB is not uniform. To deliver a vaccine which can give consistent protection against TB is a great challenge with rising burden of drug-resistant TB. Thus, expectations are quite high with new generation vaccines that will improve the efficiency of BCG without showing any discordance for all forms of TB, effective for individual of all ages in all parts of the world. In order to enhance or improve the efficacy of BCG, different strategies are being implemented by considering the immunogenicity of various Mtb virulence factors as well as of the recombinant strains, co-administration with adjuvants and use of appropriate vehicle for delivery. This chapter discusses several such pre-clinical attempts to boost BCG with subunit vaccines tested in murine models and also highlights various recombinant TB vaccines undergoing clinical trials. Promising candidates include new generation of live recombinant BCG (rBCG) vaccines, VPM1002, which are deleted in one or two virulence genes. They encode for the mycobacteria-infected macrophage-inhibitor proteins of host macrophage apoptosis and autophagy, key events in killing and eradication of Mtb. These vaccines are rBCG- ΔureC::hly HM^R, and rBCG-ΔureC::hly ΔnuoG. The former vaccine has passed phase IIb in clinical trials involving South African infants and adults. Thus, with an aim of elimination of TB by 2050, all these cumulative efforts to develop a better TB vaccine possibly is new hope for positive outcomes.

Analyzing cellular immunogenicity in vaccine clinical trials: a new statistical method including non-specific responses for accurate estimation of vaccine effect

Evaluation of immunogenicity is a key step in the clinical development of novel vaccines. T-cell responses to vaccine candidates are typically assessed by intracellular cytokine staining (ICS) using multiparametric flow cytometry. A conventional statistical approach to analyze ICS data is to compare, between vaccine regimens or between baseline and post-vaccination of the same regimen depending on the trial design, the percentages of cells producing a cytokine of interest after ex vivo stimulation of peripheral blood mononuclear cells (PBMC) with vaccine antigens, after subtracting the non-specific response (of unstimulated cells) of each sample. Subtraction of the non-specific response is aimed at capturing the specific response to the antigen, but raises methodological issues related to measurement error and statistical power. We describe here a new statistical approach to analyze ICS data from vaccine trials. We propose a bivariate linear regression model for estimating the non-specific and antigen-specific ICS responses. We benchmarked the performance of the model in terms of both bias and control of type-I and -II errors in comparison with conventional approaches, and applied it to simulated data as well as real pre- and post-vaccination data from two recent HIV vaccine trials (ANRS VRI01 in healthy volunteers and therapeutic VRI02 ANRS 149 LIGHT in HIV-infected participants). The model was as good as the conventional approaches (with or without subtraction of the non-specific response) in all simulation scenarios in terms of statistical performance, whereas the conventional approaches did not provide robust results across all scenarios. The proposed model estimated the T-cell responses to the antigens without any effect of the non-specific response on the specific response, irrespective of the correlation between the non-specific and specific responses. This novel method of analyzing T-cell immunogenicity data based on bivariate modeling is more flexible than conventional methods, and so yields more detailed results and enables accurate interpretation of vaccine-induced response.

A Bayesian design for phase I cancer therapeutic vaccine trials

Phase I clinical trials are the first step in drug development to test a new drug or drug combination on humans. Typical designs of Phase I trials use toxicity as the primary endpoint and aim to find the maximum tolerable dosage. However, these designs are poorly applicable for the development of cancer therapeutic vaccines because the expected safety concerns for these vaccines are not as much as cytotoxic agents. The primary objectives of a cancer therapeutic vaccine phase I trial thus often include determining whether the vaccine shows biologic activity and the minimum dose necessary to achieve a full immune or even clinical response. In this paper, we propose a new Bayesian phase I trial design that allows simultaneous evaluation of safety and immunogenicity outcomes. We demonstrate the proposed clinical trial design by both a numeric study and a therapeutic human papillomavirus vaccine trial.

Early CD4+ T Cell Responses Are Associated with Subsequent CD8+ T Cell Responses to an rAd5-Based Prophylactic Prime-Boost HIV Vaccine Strategy

Introduction

Initial evaluation of a candidate vaccine against HIV includes an assessment of the vaccine’s ability to generate immune responses. However, the dynamics of vaccine-induced immune responses are unclear. We hypothesized that the IFN-γ producing cytotoxic CD8+ (CD8+ IFN-γ+) T cell responses could be predicted by early IL-2 producing CD4+ (CD4+ IL-2+) helper T cell responses, and we evaluated this hypothesis using data from a phase I/II prophylactic HIV vaccine trial. The objective was to assess the dynamics and correlations between CD4+ IL-2+ T cell and CD8+ IFN-γ+ T cell responses after vaccination with a recombinant adenoviral serotype 5 (rAd5) HIV vaccine.

Methods

We analyzed data from the HVTN 068 HIV vaccine trial, which evaluated the immunogenicity of two different strategies for prime and boost vaccination (rAd5-rAd5 vaccine versus DNA-rAd5) in 66 healthy volunteers. Spearman correlations between immunogenicity markers across time-points were calculated. CD8+ IFN-γ+ T cell response in the rAd5-rAd5 arm was modeled as a function of CD4+ IL-2+ T cell response and time using mixed effects regression models.

Results

Moderate to high correlations (r = 0.48–0.76) were observed in the rAd5-rAd5 arm between the CD4+ IL-2+ T cell response at week 2 and later CD8+ IFN-γ+ T cell responses (weeks 2–52). Regression models confirmed this relationship with a significant association between the two markers: for a 1.0% increase in CD4+ IL-2+ T cells at week 2 post-prime, a 0.3% increase in CD8+ IFN-γ+ T cell responses across subsequent time points, including post-boost time points, was observed (p<0.01).

Conclusion

These results suggest an early and leading role of CD4+ T cells in the cellular response to the rAd5-rAd5 vaccine and in particular the stimulation of cytotoxic CD8+ T cell responses. These results could inform better timing of CD4+ T cell measurements in future clinical trials.

Adenoviral vector-based strategies against infectious disease and cancer

Adenoviral vectors are widely employed against infectious diseases or cancers, as they can elicit specific antibody responses and T cell responses when they are armed with foreign genes as vaccine carriers, and induce apoptosis of the cancer cells when they are genetically modified for cancer therapy. In this review, we summarize the biological characteristics of adenovirus (Ad) and the latest development of Ad vector-based strategies for the prevention and control of emerging infectious diseases or cancers. Strategies to circumvent the pre-existing neutralizing antibodies which dampen the immunogenicity of Ad-based vaccines are also discussed.