Following infection with HIV-1, the rate of clinical disease progression varies between individuals. Factors such as host susceptibility, genetics and immune function, [1] health care and co-infections [2] as well as viral genetic variability [3] may affect the rate of progression to the point of needing to take medication in order not to develop AIDS.
A small percentage of HIV-infected individuals rapidly progress to AIDS if they fail to take the medication within four years after primary HIV-infection and are termed Rapid Progressors (RP). [4] Indeed, some individuals have been known to progress to AIDS and death within a year after primo-infection. Rapid progression was originally thought to be continent specific, as some studies reported that disease progression is more rapid in Africa, [4] [5] [6] but others have contested this view. [1] [2] [7] [8]
Another subset of individuals who are persistently infected with HIV-1, but show no signs of disease progression for over 12 years and remain asymptomatic are classified as Long Term Non-Progressors (LTNP). In these individuals, it seems that HIV-infection has been halted with regard to disease progression over an extended period of time. [9] [10] [11] [12] However, the term LTNP is a misnomer as that progression towards AIDS can occur even after 15 years of stable infection. [13] LTNP are not a homogeneous group regarding both viral load and specific immune responses against HIV-1. Some LTNPs are infected with HIV that inefficiently replicates [14] [15] whilst others are infected with HIV that is virally fit and replicates normally, but the infected individual has had a strong and broad set of HIV-specific humoral and cell-mediated responses that seems to delay the progression to AIDS. In some cohorts, individuals who experience signs of progression, but whose clinical and laboratory parameters remain stable over long periods of time, are classified as Long Term Survivors (LTS). [3]
There is another, smaller percentage of individuals who have been recently identified. These are called Highly Exposed Persistently Seronegative (HEPS). This is a small group of individuals and has been observed only in a group of uninfected HIV-negative sex workers in Kenya and in The Gambia. When these individuals' PBMCs are stimulated with HIV-1 peptides, they have lymphoproliferative activity and have HIV-1 specific CD8+ CTL activity suggesting that transient infection may have occurred. [16] [17] [18] [19] This does not occur in unexposed individuals. What is interesting, is that the CTL epitope specificity differs between HEPS and HIV positive individuals, and in HEPS, the maintenance of responses appears to be dependent upon persistent exposure to HIV. [20]
During the initial weeks after HIV infection, qualitative differences in the cell-mediated immune response are observed that correlate with different disease progression rates (i.e., rapid progression to WHO stage 4 and the rapid loss of CD4+ T cell levels versus normal to slow progression to WHO stage 4 and the maintenance of CD4+ T cell counts above 500/μL). The appearance of HIV-1-specific CD8+ cytotoxic T cells (CTLs) early after primo-infection has been correlated with the control of HIV-1 viremia. [21] [22] The virus which escapes this CTL response have been found to have mutations in specific CTL epitopes. [23] [24] [25] [26] Individuals with a broad expansion of the V-beta chain of the T cell receptor of CD8+ T cells during primo-infection appear to have low levels of virus six to twelve months later, which is predictive of relatively slow disease progression. In contrast, individuals with an expansion of only a single subset of the V-beta chain of the CD8+ T cells are not able to control HIV levels over time, and thus have high viral loads six to twelve months later. [27] LTNP’s have also been shown to have a vigorous proliferation of circulating activated HIV-1-specific CD4+ T cell [28] and CTL response [29] [30] against multiple epitopes with no detectable broadly cross-reactive neutralizing antibodies in the setting of an extremely low viral load. [13] However, a few reports have correlated the presence of antibodies against Tat in LTNP status.[ citation needed ]
The HIV-1 subtype that an individual becomes infected with can be a major factor in the rate of progression from sero-conversion to AIDS. Individuals infected with subtypes C, D and G are 8 times more likely to develop AIDS than individuals infected with subtype A. [31] In Uganda, where subtypes A and D are most prevalent, [32] subtype D is associated with faster disease progression compared with subtype A. [33] Age has also been shown to be a major factor in determining survival and the rate of disease progression, with individuals over 40 years of age at sero-conversion being associated with rapid progression. [34] [35] [36] [37]
The Centers for Disease Control and Prevention (CDC) has released findings that genes influence susceptibility to HIV infection and progression to AIDS. HIV enters cells through an interaction with both CD4 and a chemokine receptor of the 7 transmembrane family. They first reviewed the role of genes in encoding chemokine receptors (CCR5 and CCR2) and chemokines (SDF-1). While CCR5 has multiple variants in its coding region, the deletion of a 32-bp segment results in a nonfunctional receptor, thus preventing HIV entry; two copies of this gene provide strong protection against HIV infection, although the protection is not absolute. This allele is found in around 10% of Europeans but is rare in Africans and Asians. Multiple studies of HIV-infected persons have shown that the presence of one copy of this mutation, named CCR5-Δ32 (CCR5 delta 32) delays progression to the condition of AIDS by about 2 years.[ citation needed ]
The National Institute of Health (NIH) has funded research studies to learn more about this genetic mutation. In such research, NIH has found that there exist genetic tests that can determine if a person has this mutation. Implications of a genetic test may in the future allow clinicians to change treatment for the HIV infection according to the genetic makeup of an individual, [38] Currently there exist several at-home tests for the CCR5 mutation in individuals; however, they are not diagnostic tests.[ citation needed ]
A relatively new class of drugs for HIV treatment relies on the genetic makeup of the individual. Entry inhibitors bind to the CCR5 protein to block HIV from binding to the CD4 cell.[ citation needed ]
Coinfections or immunizations may enhance viral replication by inducing a response and activation of the immune system. This activation facilitates the three key stages of the viral life cycle: entry to the cell; reverse transcription and proviral transcription. [39] Chemokine receptors are vital for the entry of HIV into cells. The expression of these receptors is inducible by immune activation caused by infection or immunization, thus augmenting the number of cells that can be infected by HIV-1. [40] [41] Both reverse transcription of the HIV-1 genome and the rate of transcription of proviral DNA rely upon the activation state of the cell and are less likely to be successful in quiescent cells. In activated cells, there is an increase in the cytoplasmic concentrations of mediators required for reverse transcription of the HIV genome. [42] [43] Activated cells also release IFN-alpha which acts on an autocrine and paracrine loop that up-regulates the levels of physiologically active NF-kappa B which activates host cell genes as well as the HIV-1 LTR. [44] [45] The impact of co-infections by micro-organisms such as Mycobacterium tuberculosis can be important in disease progression, particularly for those who have a high prevalence of chronic and recurrent acute infections and poor access to medical care. [46] Often, survival depends upon the initial AIDS-defining illness. [37] Co-infection with DNA viruses such as HTLV-1, herpes simplex virus-2, varicella zoster virus, and cytomegalovirus may enhance proviral DNA transcription and thus viral load as they may encode proteins that can trans-activate the expression of the HIV-1 pro-viral DNA. [47] Frequent exposure to helminth infections, which are endemic in Africa, activates individual immune systems, thereby shifting the cytokine balance away from an initial Th1 cell response against viruses and bacteria which would occur in the uninfected person to a less protective T helper 0/2-type response. [48] HIV-1 also promotes a Th1 to Th0 shift and replicates preferentially in Th2 and Th0 cells. [49] This makes the host more susceptible to and less able to cope with infection with HIV-1, viruses and some types of bacteria. Ironically, exposure to dengue virus seems to slow HIV progression rates temporarily.[ citation needed ]
The human immunodeficiency viruses (HIV) are two species of Lentivirus that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Without treatment, the average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.
An HIV vaccine is a potential vaccine that could be either a preventive vaccine or a therapeutic vaccine, which means it would either protect individuals from being infected with HIV or treat HIV-infected individuals.
The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs as a strategy to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multiple drugs that act on different viral targets is known as highly active antiretroviral therapy (HAART). HAART decreases the patient's total burden of HIV, maintains function of the immune system, and prevents opportunistic infections that often lead to death. HAART also prevents the transmission of HIV between serodiscordant same-sex and opposite-sex partners so long as the HIV-positive partner maintains an undetectable viral load.
A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens (such as viruses or bacteria), or cells that are damaged in other ways.
The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considered essential in B cell antibody class switching, breaking cross-tolerance in dendritic cells, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages and neutrophils. CD4+ cells are mature Th cells that express the surface protein CD4. Genetic variation in regulatory elements expressed by CD4+ cells determines susceptibility to a broad class of autoimmune diseases.
The spread of HIV/AIDS has affected millions of people worldwide; AIDS is considered a pandemic. The World Health Organization (WHO) estimated that in 2016 there were 36.7 million people worldwide living with HIV/AIDS, with 1.8 million new HIV infections per year and 1 million deaths due to AIDS. Misconceptions about HIV and AIDS arise from several different sources, from simple ignorance and misunderstandings about scientific knowledge regarding HIV infections and the cause of AIDS to misinformation propagated by individuals and groups with ideological stances that deny a causative relationship between HIV infection and the development of AIDS. Below is a list and explanations of some common misconceptions and their rebuttals.
Simian immunodeficiency virus (SIV) is a species of retrovirus that cause persistent infections in at least 45 species of non-human primates. Based on analysis of strains found in four species of monkeys from Bioko Island, which was isolated from the mainland by rising sea levels about 11,000 years ago, it has been concluded that SIV has been present in monkeys and apes for at least 32,000 years, and probably much longer.
C-C chemokine receptor type 5, also known as CCR5 or CD195, is a protein on the surface of white blood cells that is involved in the immune system as it acts as a receptor for chemokines.
AIDS-defining clinical conditions is the list of diseases published by the Centers for Disease Control and Prevention (CDC) that are associated with AIDS and used worldwide as a guideline for AIDS diagnosis. CDC exclusively uses the term AIDS-defining clinical conditions, but the other terms remain in common use.
Envelope glycoprotein GP120 is a glycoprotein exposed on the surface of the HIV envelope. It was discovered by Professors Tun-Hou Lee and Myron "Max" Essex of the Harvard School of Public Health in 1984. The 120 in its name comes from its molecular weight of 120 kDa. Gp120 is essential for virus entry into cells as it plays a vital role in attachment to specific cell surface receptors. These receptors are DC-SIGN, Heparan Sulfate Proteoglycan and a specific interaction with the CD4 receptor, particularly on helper T-cells. Binding to CD4 induces the start of a cascade of conformational changes in gp120 and gp41 that lead to the fusion of the viral membrane with the host cell membrane. Binding to CD4 is mainly electrostatic although there are van der Waals interactions and hydrogen bonds.
HIV-associated neurocognitive disorders (HAND) are neurological disorders associated with HIV infection and AIDS. It is a syndrome of progressive deterioration of memory, cognition, behavior, and motor function in HIV-infected individuals during the late stages of the disease, when immunodeficiency is severe. HAND may include neurological disorders of various severity. HIV-associated neurocognitive disorders are associated with a metabolic encephalopathy induced by HIV infection and fueled by immune activation of macrophages and microglia. These cells are actively infected with HIV and secrete neurotoxins of both host and viral origin. The essential features of HIV-associated dementia (HAD) are disabling cognitive impairment accompanied by motor dysfunction, speech problems and behavioral change. Cognitive impairment is characterised by mental slowness, trouble with memory and poor concentration. Motor symptoms include a loss of fine motor control leading to clumsiness, poor balance and tremors. Behavioral changes may include apathy, lethargy and diminished emotional responses and spontaneity. Histopathologically, it is identified by the infiltration of monocytes and macrophages into the central nervous system (CNS), gliosis, pallor of myelin sheaths, abnormalities of dendritic processes and neuronal loss.
Entry inhibitors, also known as fusion inhibitors, are a class of antiviral drugs that prevent a virus from entering a cell, for example, by blocking a receptor. Entry inhibitors are used to treat conditions such as HIV and hepatitis D.
HIV superinfection is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. These can form a recombinant strain that co-exists with the strain from the initial infection, as well from reinfection with a new virus strain, and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.
CD4 immunoadhesin is a recombinant fusion protein consisting of a combination of CD4 and the fragment crystallizable region, similarly known as immunoglobulin. It belongs to the antibody (Ig) gene family. CD4 is a surface receptor for human immunodeficiency virus (HIV). The CD4 immunoadhesin molecular fusion allow the protein to possess key functions from each independent subunit. The CD4 specific properties include the gp120-binding and HIV-blocking capabilities. Properties specific to immunoglobulin are the long plasma half-life and Fc receptor binding. The properties of the protein means that it has potential to be used in AIDS therapy as of 2017. Specifically, CD4 immunoadhesin plays a role in antibody-dependent cell-mediated cytotoxicity (ADCC) towards HIV-infected cells. While natural anti-gp120 antibodies exhibit a response towards uninfected CD4-expressing cells that have a soluble gp120 bound to the CD4 on the cell surface, CD4 immunoadhesin, however, will not exhibit a response. One of the most relevant of these possibilities is its ability to cross the placenta.
Long-term nonprogressors (LTNPs), are individuals infected with HIV, who maintain a CD4 count greater than 500 without antiretroviral therapy with a detectable viral load. Many of these patients have been HIV positive for 30 years without progressing to the point of needing to take medication in order not to develop AIDS. They have been the subject of a great deal of research, since an understanding of their ability to control HIV infection may lead to the development of immune therapies or a therapeutic vaccine. The classification "Long-term non-progressor" is not permanent, because some patients in this category have gone on to develop AIDS.
AntiViral-HyperActivation Limiting Therapeutics (AV-HALTs) are an investigational class of antiretroviral drugs used to treat Human Immunodeficiency Virus (HIV) infection. Unlike other antiretroviral agents given to reduce viral replication, AV-HALTs are single or combination drugs designed to reduce the rate of viral replication while, at the same time, also directly reducing the state of immune system hyperactivation now believed to drive the loss of CD4+ T helper cells leading to disease progression and Acquired Immunodeficiency Syndrome (AIDS).
HIV/AIDS research includes all medical research that attempts to prevent, treat, or cure HIV/AIDS, as well as fundamental research about the nature of HIV as an infectious agent and AIDS as the disease caused by HIV.
A small proportion of humans show partial or apparently complete innate resistance to HIV, the virus that causes AIDS. The main mechanism is a mutation of the gene encoding CCR5, which acts as a co-receptor for HIV. It is estimated that the proportion of people with some form of resistance to HIV is under 10%.
Gene Martin Shearer is an American immunologist who works at the National Institutes of Health (NIH). He first achieved fame for his discovery in 1974 that T lymphocytes recognized chemically modified surface antigens only in the context of self major histocompatibility complex (MHC) encoded molecules, identifying the central feature of antigen recognition by T lymphocytes known as MHC restriction. His discovery of MHC restriction using chemically modified surface antigens was simultaneous with the discovery of MHC restricted T lymphocyte recognition of virus infected cells by Rolf Zinkernagel and Peter Doherty, who received the 1996 Nobel Prize in Physiology or Medicine.
M. Juliana “Julie” McElrath is a senior vice president and director of the vaccine and infection disease division at Fred Hutchinson Cancer Research Center and the principal investigator of the HIV Vaccine Trials Network Laboratory Center in Seattle, Washington. She is also a professor at the University of Washington.