NHLBI-supported extramural AIDS programs encompass basic and clinical research to
ensure the safety of the blood supply and to promote a better understanding of the
pulmonary, hematologic, and cardiac complications of HIV. Each year, findings from these
programs have added to our knowledge of this and related viral diseases, paving the way
to better methods of screening donated blood and organs, understanding the
pathophysiology of opportunistic infections and maternal-fetal transmission of HIV, and
developing new strategies to slow the progression of HIV infection to AIDS. In 1996,
NHLBI-supported research contributed to the landmark discovery that some people are
genetically resistant to HIV infection. The recent identification of specific genes for this
resistance may lead to powerful new AIDS prevention and treatment strategies.
In the years following the emergence of Human Immunodeficiency Virus Type I (HIV-1) as a transfusion-transmitted disease, great progress has been made in screening blood for infectious diseases and in developing new procedures that effectively remove or inactivate viruses in coagulation concentrates. Since the introduction of mandatory screening of the blood supply for the antibody to Human Immunodeficiency Syndrome in 1985, the risk of transfusion-associated HIV infection has fallen to 1 per 500,000 units of blood. (Table 1.) Programs supported by the NHLBI have greatly contributed to these successes.
The last decade has seen the development and implementation of six tests to screen blood: HIV-1, HIV- 2, Human Lymphotropic Virus Type I/II (HTLV-I/II), hepatitis C (HCV), antibody to hepatitis core (anti-HBc), and p24 antigen. Even though pretransfusion testing is better than ever before, patients who require multiple transfusions, some of whom receive hundreds of units of blood over time for chronic conditions, still endure a substantial risk.
The NHLBI currently supports several programs on reducing adverse effects of transfusion. The Transfusion Safety Study (TSS), a large longitudinal study initiated in 1983, was the first study to clarify the nature of HIV transmission by transfusion and the first to show HIV seroconversion in hemophiliacs receiving dry heat-treated Factor VIII from donors who were negative for HIV. The TSS demonstrated that progression to AIDS after transfusion recipients was similar to that reported for homosexual men, that progression of HIV-1 disease in recipients was independent of progression in the donor, and that previously stored blood transmitted HIV less frequently. Findings from the TSS showed that the concentration of viral HIV-1 RNA in the blood of an infected donor correlates with the probability of HIV transmission to recipients. Moreover, the probability of sexual transmission of HIV by infected hemophiliacs was shown to be related to the amount of HIV RNA in their blood.
The Retroviral Epidemiology Donor Study (REDS), another large NHLBI-supported surveillance study of blood donors and their recipients, has examined more than 600,000 samples of blood from the blood donor population. This study has developed and validated methods for PCR analysis of both HIV-1 and HTLV on frozen whole blood and estimated that addition of PCR-based testing to the current battery of pretransfusion tests would further decrease the risk of transmission of HIV from 1:500,000 to 1:1,000,000. In addition, because of recent concern that a new strain of HIV, strain O, could not be detected by the tests commonly used by blood banks, the REDS surveyed 1,072 specimens from blood donors and could detect none that were infected with this strain.
Table 1
Combining donor and recipient questionnaires with screening tests allows researchers to
ascertain donor behavioral patterns that may contribute to the spread of HIV. Recently,
REDS demonstrated that despite efforts to screen blood donors rigorously, 2 percent of
blood donors do not provide accurate answers to blood bank questions about their
behaviors that puts them at risk for HIV. REDS investigators are now seeking additional
information about these donors and why they do not respond accurately to screening
questions.
NHLBI supported AIDS research continues to identify emerging infection agents. Researchers in California have identified a virus believed to cause an AIDS-related cancer in blood donated by a healthy man, but they say the implications of the discovery are unclear. The virus, called human herpes virus 8 (HHV-8), is thought to cause Kaposi's sarcoma, a form of skin cancer that frequently occurs among homosexual men with AIDS. Scientists do not know whether the virus can be transmitted through blood transfusions or whether it poses any health risk to people with normal immune systems. Studies by NHLBI grantees have demonstrated that 2 percent of healthy blood donors test positive for HHV-8. The NHLBI, through use of a repository of blood specimens collected from donors and transfusion recipients, will examine possible transmission of HHV-8 via transfusion.
Currently, prevention of transfusion-associated viral diseases depends upon pre-donation evaluation of potential donors followed by serologic testing for HIV, HTLV-I/II, HBV and HCV. Although the advent of testing has greatly reduced the transmission of viral diseases by blood products, viruses may still contaminate the blood supply because diagnostic tests may be insensitive during the "window period" before seroconversion of an infected donor. Current estimates of the frequency of viral transmission from blood products on a per unit basis are 1:63,000 for HBV, 1:103,000 for HCV, 1:493,000 for HIV and 1:641,000 for HTLV-I/II.
In 1995, the NHLBI sponsored a consensus conference on use of surrogate markers for pretransfusion screening blood. The consensus panel recommended the institution of direct HIV antigen testing and discontinuation of ALT testing. These recommendations were instituted by most blood banks in the United States.
The NHLBI currently supports a large program to develop and test PCR-based blood testing for pre-transfusion testing and to detect persons in the early stages of infection for whom early antiviral therapy might have an impact. PCR technology permits direct detection of viral RNA in donated blood, organs, and bone marrow. Such a test would significantly narrow the window of uncertainty--the high sensitivity of PCR permits detection of as few as five copies of an RNA strand in a sample, and when HIV is present, so is its RNA.
The NHLBI also supports research devoted to sterilization of blood products. An NHLBI-supported researcher has developed a photochemical treatment (PCT) process to inactivate viruses and bacteria in platelet concentrates utilizing the photochemical reaction of a novel psoralean with nucleic acids mediated by ultraviolet light. This procedure was shown to be effective in destroying the infectivity of HIV as well as a variety of other viruses and bacteria. In vitro platelet function was maintained over 7 days of storage following PCT. In vivo post-transfusion recovery and life-span of treated platelets were comparable to that of untreated cells. In addition, because PCT destroys the leukocytes that are invariably present in platelet concentrates, it may prevent the graft-versus-host disease observed in some transfused patients. Based on the broad spectrum of PCT activity of inactivate infectious agents, the process has the potential to provide protection against new pathogens that may enter the donor population before implementation of effective screening tests. Clinical trials to evaluate the therapeutic efficacy of PCT allogenic platelets in thrombocyctopenic patients requiring platelet transfusion are under way.
The NHLBI is involved in developing therapies which would lead to immunological reconstitution of the infected individual. The NHLBI and the NIAID co-sponsored a trial investigating the effect of HIV immune globulin on HIV-infected infants, and it's ability to prevent infection in the unborn fetus. The treatment proved safe and efficacy is still being evaluated. The NHLBI, along with the Pediatric AIDS Foundation, is also attempting to develop genetically altered blood stem cells derived from cord blood which would be resistant to HIV infection and could potentially be used to treat infected individuals.
Figure 2.
HIV-1 pulmonary disease with resultant respiratory failure is still the leading cause of death in HIV-1-infected patients. Although Pneumocystis pneumonia is a major cause of morbidity in AIDS, other pathogens are becoming more common. Among these are tuberculosis and bacterial pneumonia, both of which have increased incidence in this population. A large multicenter natural history study has demonstrated that bacterial pneumonias occur more frequently in the HIV-1-infected population, particularly in patients with low CD4 counts. These findings should alert physicians to consider this diagnosis more frequently for HIV-infected patients with pneumonia. Other AIDS-related programs are supporting research on pneumocystis, lymphoid interstitial lung diseases, and tuberculosis (TB).
Although TB incidence had been decreasing steadily in the years before the advent of the HIV epidemic, there has since been a dramatic reversal of this trend. The number of cases reported in 1996 represented a 19% decrease in the number of cases reported in 1994; this decrease was believed to be related to the substantial efforts of State and Federal Governments. Of even greater concern, is the emergence of drug-resistant TB strains, for which the mortality rate in AIDS patients is 100 percent. This recurrence of TB poses a threat not only to the HIV-infected but also to those free of HIV, including health care workers caring for AIDS patients and the families of people with AIDS.
The NHLBI supports basic research designed to understand the pathogenesis of HIV-related lung disease and offer clues to potential treatment. One investigator has demonstrated the importance of lung surfactant in HIV infected lung in supporting tuberculosis growth. (Figure 2). Another has developed a "suicide" gene for TB which eliminates its ability to grow in culture (Figure 3). Either discovery could lead to development of interventions that could impact on disease development.
The effective treatment of TB requires long-term treatment with poorly tolerated and potentially toxic drugs. NHLBI investigators have developed and tested an aerosolized drug which has few systemic side effects. Aerosolized interferon- was successful in sterilizing infected sputum specimens and in causing clinical improvement in patients with active infection. In 1997, the NHLBI awarded several grants and contracts to support TB research, and in 1998 plans to support many new TB research programs.
The NHLBI conducted a study to examine the cardiac and pulmonary complications of HIV
infection in infants and children born to HIV-infected women. Data from this study have
already been helpful in establishing pediatric criteria for treating HIV-infected children for
Pneumocystis. In infants, low CD4 counts were associated with increased frequency of
Pneumocystis carinii pneumonia. This observation, together with data collected from
other
studies, formed the basis for developing Public Health Service recommendations for
prophylaxis for P. carinii pneumonia. Preliminary data show that prophylactic treatment
of
children with lower CD4 counts substantially reduced the risk of the P. carinii pneumonia
in this group. Another study is investigating the life cycle of Pneumocystis and other
organisms that commonly cause pulmonary disease, such as mycobacteria, Pneumocystis,
and fungi so that rational treatment strategies for these opportunistic infections can be
developed.
Figure 3
Hematologic complications of HIV infection are frequent and contribute to the morbidity associated with AIDS. The risk of neutropenia limits use of antiviral agents and effective chemotherapy in HIV-infected persons with HIV-related cancer. Anemia is the most frequent abnormality and is manifest at time of diagnosis of HIV infection in up to 20 percent of patients. By end-stage disease, 75 to 100 percent of patients become anemic. Thrombocytopenia occurs throughout all stages of AIDS; it is related to increased destruction of platelets in some cases and to decreased production of platelets or megakaryocytes in others.
Although once considered a rare disease, thrombotic thrombocytopenia purpura is now appearing more frequently among individuals infected with HIV. The etiology and the most effective treatment are not yet clear, although some progress has been made. The NHLBI continues to fund investigations related to the etiology and treatment of bone marrow failure in HIV infection. Since 1995 the NHLBI has supported studies on the effects of cytokines on hematopoiesis in HIV infection and the effects of HIV on hematopoiesis.
Heart disease is common and progressive in HIV-infected children and adults, but is often clinically inapparent. Intrinsic cardiomyopathy (as reflected by reduced contractility of the heart) and increased afterload appear to be the causes.
The NHLBI supports a large natural history study of pulmonary and cardiac disease in HIV-infected children. Many of the children in this study did not manifest overt congestive heart failure (CHF), despite decreased left ventricular (LV) function, until an intercurrent illness placed increased demands on their cardiovascular reserves. Thus, the children appeared to be in good health until a febrile episode pushed them into CHF. Many experts caring for these patients fail to appreciate the frequency of LV dysfunction, which results in misdiagnosis of CHF as diffuse pulmonary disease, failure to thrive (idiopathic poor somatic growth), and other conditions. The asymptomatic nature of early HIV-associated heart disease impedes its recognition by the clinical community and is reflected in the low rate of cardiovascular complications reported by the Centers for Disease Control and Prevention's Pediatric Spectrum of Disease Project. Studies that extrapolate data from patient charts seriously underestimate the degree of cardiovascular compromise in young AIDS patients.
Similar observations have been made in adults, but the extent to which cardiac
involvement occurs in HIV-infected patients varies widely. A 1993 study in Washington,
D.C., found by non-invasive testing that 55 percent of patients had cardiac abnormalities.
Autopsy studies of AIDS patients have revealed a 52 percent incidence of myocarditis. In
San Francisco, investigators observed a slight increase in abnormal cardiac function in
patients with AIDS-Related Complex (ARC) or AIDS, as compared with HIV patients
without ARC or AIDS. At the start of the study, 10 percent of HIV-positive, ARC and AIDS
patients had evidence of cardiovascular disease, and over the follow-up period, which
varied from 6 to 39 months, another 9 percent developed cardiac abnormalities. Two
percent of patients with AIDS had signs of cardiomyopathy at entry into the study and
another 2 percent developed cardiomyopathy during follow-up. In Baltimore, where the
demographics and socioeconomic status of HIV-positive patients are very different, 10-20
percent of patients with HIV infection were found to have symptomatic heart disease and
30-50 percent had clinically silent heart abnormalities.
Figure 4.
In 1996, NHLBI supported AIDS and non-AIDS-related research contributed to the ground- breaking discovery of a human cell-surface receptor, CCR5, that HIV uses to enter cells. (Figure 4). People unable to make normal CCR5 were found to be incapable of infection when exposed to HIV. These people carry a mutation of CCR5 (called *ccr5) that makes the receptor nonfunctional. About 17 percent of Caucasians in the United States carry one copy of the gene. Another 1 percent carry two copies; these individuals cannot make the co-receptor needed by HIV to enter their cells and are resistant to HIV infection.
Further studies revealed that CCR5 is also the receptor for chemokines that block HIV infection. These discoveries are rapidly leading to new avenues of HIV research and new possibilities for combating HIV infection. CCR5 is a key to understanding natural resistance to HIV and mechanisms of HIV activation in the cells of specific organs. Further research is expected to lead to the development of chemokine derivatives capable of blocking HIV infection.
CCR5 is not the only co-receptor for HIV. Some HIV viruses have already been found to use other chemokine receptor molecules in addition to CCR5. Thus far, CCR2b and CCR3 have been identified and more receptors are likely to emerge. As yet, little is known about what cells carry these other receptors, but it is likely that cells in different tissues express different receptors.
Because HIV seems to evolve independently in specific organs, particularly lung and brain, it is important to determine what chemokine receptor cofactors are used by viruses as they adapt to cells in the lung.
Two more important findings followed in 1997. First, a derivative of the chemokine RANTES was discovered which, unlike the parent molecule, cannot attract and activate white blood cells but can block the binding of HIV to CCR5 and other similar receptors. Such an agent has potential as an antiviral substance and opens up the possibility of developing new classes of anti-HIV drugs. The second finding concerns HIV binding to CCR5, a complex process which involves multiple binding sites on the receptor. This complexity was found to be the reason why mouse CCR5, although very similar to human CCR5 (82 percent identity) cannot function as a HIV co-receptor and why HIV cannot enter mouse cells. The investigators were able to construct chimeras, part human receptor and part mouse receptor, that allowed HIV to enter mouse cells. These findings open up the possibility of new transgenic animal models of HIV infection.
The CCR5 co-receptor story was a major breakthrough in understanding the pathophysiology of AIDS. This series of findings has brought together scientists in many disciplines and offers exciting new insights and new hope for combating AIDS as well as new directions for inflammation research. Further investigation of these co-receptors will provide new possibilities for preventing HIV infection, developing better animal models, improving our understanding of how HIV affects the lung and determining the pathways by which inflammatory mediators affect the virus. The NHLBI is expanding its support for investigators in this important area of research.
