Hepatitis B vaccination of high risk pregnant women: A clinical trial at Parkland Memorial Hospital

Hepatitis B infection is a major public health problem of global proportions. It is estimated that 2 billion people worldwide are infected by the Hepatitis B virus (HBV) at some point, and 350 million are chronic carriers. The Centers for Disease Control and Prevention (CDC) report an incidence in the United States of 140,000–320,000 infections each year (asymptomatic and symptomatic), and estimate 1–1.25 million people are chronically infected. Hepatitis B and its chronic complications (cirrhosis of the liver, liver failure, hepatocellular carcinoma) responsible for 4,000–5,000 deaths in America each year. ^ One quarter of those who become chronic carriers develop progressive liver disease, and chronic HBV infection is thought to be responsible for 60 million cases of cirrhosis worldwide, surpassing alcohol as a cause of liver disease. Since there are few treatment options for the person chronically infected with Hepatitis B, and what is available is expensive, prevention is clearly best strategy for combating this disease. ^ Since the approval of the Hepatitis B vaccine in 1981, national and international vaccination campaigns have been undertaken for the prevention of Hepatitis B. Despite encouraging results, however, studies indicate that prevalence rates of Hepatitis B infection have not been significantly reduced in certain high risk populations because vaccination campaigns targeting those groups do not exist and opportunities for vaccination by individual physicians in clinical settings are often missed. Many of the high-risk individuals who go unvaccinated are women of childbearing age, and a significant proportion of these women become infected with the Hepatitis B virus (HBV) during pregnancy. Though these women are often seen annually or for prenatal care (because of the close spacing of their children and their high rate of fertility), the Hepatitis B vaccine series is seldom recommended by their health care provider. In 1993, ACOG issued a statement recommending Hepatitis B vaccination of pregnant women who were defined as high-risk by diagnosis of a sexually transmitted disease. ^ Hepatitis B vaccine has been extensively studied in the non-pregnant population. The overall efficacy of the vaccine in infants, children and adults is greater than 90%. In the small clinical trials to date, the vaccine seemed to be effective in those pregnant women receiving 3 doses; however, by using the usual 0, 1 and 6 month regimen, most pregnant women were unable to complete a full series during pregnancy. There is data now available supporting the use of an "accelerated" dosing schedule at 0, 1 and 4 months. This has not been evaluated in pregnant women. A clinical trial proving the efficacy of the 0, 1, 4 schedule and its feasibility in this population would add significantly to the body of research in this area, and would have implications for public health policy. Such a trial was undertaken in the Parkland Memorial Hospital Obstetrical Infectious Diseases clinic. In this study, the vaccine was very well tolerated with no major adverse events reported, 90% of fully vaccinated patients achieved immunity, and only Body Mass Index (BMI) was found to be a significant factor affecting efficacy. This thesis will report the results of the trial and compare it to previous trials, and will discuss barriers to implementation, lessons learned and implications for future trials. ^

THE CYTOPLASMIC TAIL OF MHC CLASS I MOLECULES PLAYS A CRITICAL ROLE IN DENDRITIC CELL-INDUCED T CELL IMMUNITY

The presentation of MHC class I (MHC-I)/peptide complexes by dendritic cells (DCs) is critical for the maintenance of central tolerance to self and for the regulation of cytotoxic T lymphocytes (CTL)-mediated adaptive immune responses against pathogens and cancer cells. Interestingly, several findings have suggested that the cytoplasmic tail of MHC class I plays a functional role in the regulation of CTL immune responses. For example, our previous studies demonstrated that exon 7-deleted MHC-I molecules not only showed extended DC cell surface half-lives but also induced significantly increased CTL responses to viral challange invivo. Although exon 7-deleted variant of MHC-I does not occur naturally in humans, the animal studies prompted us to examine whether exon 7-deleted MHC-I molecules could generate augmented CTL responses in a therapeutic DC-based vaccine setting. To examine the stimulatory capacity of exon 7-deleted MHC-I molecules, we generated a lentivirus-mediated gene transfer system to induce the expression of different MHC-I cytoplasmic tail isoforms in both mouse and human DCs. These DCs were then used as vaccines in a melanoma mouse tumor model and in a human invitro co-culture system. In this thesis, we show that DCs expressing exon 7-deleted MHC-I molecules, stimulated remarkably higher levels of T-cell cytokine production and significantly increased the proliferation of meanoma-specific (Pmel-1) T cells compared with DCs expressing wild type MHC-I. We also demonstrate that, in combination with adoptive transfer of Pmel-1 T-cell, DCs expressing exon 7-deleted Db molecules induced greater anti-tumor responses against established B16 melanoma tumors, significantly extending mouse survival as compared to DCs expressing wild-type Db molecules. Moreover, we also observed that human DCs expressing exon 7-deleted HLA-A2 molecules showed similarly augmented CTL stimulatory ability. Mechanistic studies suggest that exon 7-deleted MHC-I molecules showed impaired lateral membrane movement and extended cell surface half-lives within the DC/T-cell interface, leading to increased spatial availability of MHC-I/peptide complexes for recognition by CD8+ T cells. Collectively, these results suggesr that targeting exon 7 within the cytoplasmic tail of MHC-I molecules in DC vaccines has the potential to enhance CD8+ T cell stimulatory capacity and improve clinical outcomes in patients with cancer or viral infections.