HIV/AIDS

 

Perspective

AIDS is the 7th leading cause of death among 1-4 yr olds, 6th among 15-24 yr olds, and 2nd among 25-44 yr olds in the U.S.  This year marks the 19th year since the beginning of the AIDS epidemic.  The first cases in the U.S. were reported in 1981 in 5 young homosexual males diagnosed with Pneumocystis carinii pneumonia and other opportunistic infections.  Initial conclusions reached were that it was a disease of gay men, particularly those that had many sexual partners.  In 1982, cases of AIDS were reported among hemophiliacs and I.V. drug users.  In 1983 the first documented cases of heterosexual transmission were documented.  Later that year, AIDS were reported in Central Africa with the striking difference that most cases were heterosexually transmitted, rather than homosexually transmitted, as in the U.S. 

            The CDC reacted quite cautiously in 1981 to sound the alarm, for the U.S. citizenry was not quite ready to talk openly about sex, needles, and condoms.  Out awareness heightened by the death of well known individuals, such as Rock Hudson in 1985, but ignorance, apathy, and antagonism prevailed.  Three young hemophiliacs were firebombed out of their Florida home when their neighbors learned they were HIV positive in 1987. 

 

 

 

            In 1985, the epidemic had reached such proportions that scientist, politicians, educators, physicians and concerned individuals started to meet at the International AIDS conference, the most important meeting about AIDS in the world.  Though the meetings were quite small at first, over the years it has grown so large that they have decided to have it every 2 years.  As of 1998, over 410,000 people had died of AIDS.  This represents about 0.2% of the U.S. population.

 

 This conference and many other well-publicized AIDS events have served to educate the public regarding AIDS.  One such device is the AIDS quilt.  It is made up of panels (each one the size of a grave), each one commemorating someone that died of AIDS.  In 1987 it was displayed on the mall in D.C. and covered 2 football fields.  It had 1,920 panels and took less than 2 hours to read.  In 1999, the quilt weighted 55 tons, with 46,000 panels containing 79,000 names.  It covers 25 football fields.  It is the largest piece of folk art in the world.  It was the idea of Cleve Jones of San Francisco.  Every day, more panels arrive to be added to the quilt.

 

June 1981 – CDC reported diseases occurring in gay men that were normally found only in immunosuppressed individuals.  The CDC report said that 5 young men in Los Angeles were diagnosed with Pneumocystis carinii.  They also suggested an association between the disease and the homosexual lifestyle.

 

July 1981 – CDC reported an uncommon cancer, Kaposi’s sarcoma, had been diagnosed in 2 gay men who lived in New York city and California.  Because of the connection with gay men, it was initially called GRID (Gay-Related Immune Deficiency)

 

1982-83 – AIDS was discovered in drug users, hemophiliacs, heterosexuals, and children.  The epidemic was officially recognized. 

 

1981 – Researchers in several laboratories mobilized to try to find the cause of the disease.  This included Robert Gallo’s lab C at the NIH, and Luc Montagnier’s lab at the Pasteur Institute. 

 

 

In January of 1983, Montagnier and colleagues isolated the AIDS virus.  In May of that year, they published the first report on a T cell retrovirus found in a patient with lymphadenoapathy (which is one of the early signs of progression to AIDS).  He named it LAV.  Robert Gallo also claimed to have found the virus which, indeed, he had.  But it was from a mixture of viruses which had accidentally been contaminated with the virus that Montagnier had sent to his lab.  Genetic tests eventually showed that Gallo’s virus (HTLV III) was the same virus as Montagnier’s.  Because of this, the two countries (US and France) negotiated an agreement in which credit was shared between the two men, as well as royalties.  Nevertheless, outside the US (and many people in the US) give credit to Montagnier.  Several years after the discovery, there was an investigation into Gallo’s lab practices and he was censured.  Ultimately, he appealed the censure and it was overturned.

 

            Over the years, the definition of AIDS has been different.  In 1987, the CDC tried to come up with a consistent definition.  This was later modified in 1993 to anybody having the symptomology and having a T4 cell count less than 200 per ml.  This redefinition caused a large arbitrary increase in the number of people diagnosed with AIDS.  This is very important for the disbursement of medical benefits under insurance and government health programs. 

 

 

 

Prevalence

 

AIDS is currently the 14th leading cause of death in the U.S, lagging far behind heart disease and cancer.

 

Because of increased awareness about the mode of transmission and changing lifestyles, the rate of infection in the U.S. has decreased, but is still very significant at approximately 50,000 people per year.

 

 

 

 

 

The spread of the virus was exponential in  early years before we knew much about it.

 

 

 

As one might expect the percentage of HIV-infected individuals has decreased as a percentage of the US population.

 

 

The majority of people that are infected in the U.S. are in the 25-44 year old age group.

 

 

 

The major at-risk groups in the U.S. are homosexual/bisexual males and intravenous drug users, though heterosexual contact constitutes a significant and growing percentage.

 

 

 

AIDS is still largely a disease of men.  The majority of people that have contracted AIDS in the U.S. have died (60%).  The disease is disproportionately represented in black and Asian ethnic groups.

 

 

AIDS is still a disease that is more likely to be found in urban centers.

 

 

 

In the world, there are approximately 60 million people with AIDS.  The vast majority of these are in sub-Saharan Africa.  Nearly 40% of babies born in this region are born with HIV.

 

 

 

Causal Relationship

            Several well-known scientists have come forward to refute the idea that HIV is the cause of AIDS.  These include Peter Duesberg the scientist that co-discovered cancer-causing genes and Kerry Mullis, Nobel prize winner for the development of the polymerase chain reaction.  Both have written books in which they state their views.  Duesberg, in particular, has paid a high price for these views, losing his government funding and being shunned in the scientific community.  He has even gone so far as to appeal for donations over the internet.  Mullis has suffered less, partially because he is retired to his surfboard.  Some scientists hold his viewpoints as questionable because of his admission in his book, Dancing Naked in the Mind Field, he admits his passion for hallucinogenic drugs and his belief in flying saucers.

 

            Scientists that believe in HIV as the causative agent point out the following:

            a.  the virus has now been identified in virtually all AIDS patients tested.

b.  the virus has been identified by electron microscopy inside and on the surface

of T4 cells in HIV-positive and AIDS patients (see picture below)

            c.  recent work has shown that the genetic material of HIV can be found in as

            many as 1 in 10 blood lymphocytes of persons with HIV disease.

            d.  antibodies against the virus, viral antigens, and HIV RNA have been found in

            HIV-positive and AIDS patients.

            e.  there is an absolute chronological association between the mergence of AIDS

            and the appearance of HIV in humans worldwide

            f.  there is a chronological association of HIV-positive individuals who progress

            to AIDS.  People that are HIV-negative do not get the disease. 

            g.  hemophiliacs from low- and high-risk behavior groups were equally infected

            from HIV-contaminated blood factor VIII concentrates

            h.  the virus is found in HIV-positive and AIDS patents but not in healthy low

            behavioral risk individuals.

            i.  with the exception of persons who had their immune systems suppressed due to

            genetic causes, or by drug therapy, prior to the appearance of the virus, there was

            no known AIDS-like cases.

            j.  an HIV-positive identical twin born to an HIV-positive mother developed

            AIDS, but not the HIV-negative twin.

            k.  only HIV-positive mothers transmit HIV into their fetuses and only HIV-

positive newborns progress to AIDS. HIV-negative newborns from HIV-positive

 mothers do not get AIDS.

            l.  drugs developed specifically to inhibit the replication and/or maturation of

            HIV, thereby lowering the level of HIV found in HIV-infected people, have

            delayed the onset of HIV disease and, for pregnant women, have decreased the

            birth of HIV-infected infants by 66%.

            m.  if HIV does not cause AIDS, how do scientists explain the positive effect of

            drugs used to affect the early and late stages in the life cycle of HIV that have

            lowered viral load to undetectable levels in the blood of those with HIV disease

            and AIDS.

            n.  there are numerous reports in the literature on HIV-infected individuals

            transmitting the virus to their sexual partners, both eventually dying of AIDS.

 

 

Origin

            Some of the more bizarre theories have attributed AIDS to originating from flying saucers, American biological warfare and domestic cats.  In 1989, Louis Farrakhan said, “The spread of international AIDS was an attempt by the U.S. government to decimate the population of central Africa.”.   More plausible, but unsupported, arguments suggest that HIV came from contaminated vaccines (polio, smallpox, hepatitis), the African Green Monkey, African people, their cattle, pigs, and sheep.  Though we think that HIV arose from Africa, the exact method by which this took place is unknown.  Some theories include:

 

a.  HIV entered the human population by the direct inoculation of malaria-HIV-infected blood into human prisoner volunteers

b.  the virus may have come from a variant that infected the Sooty Mangabey (monkey) in west Africa 20-30 years ago.  Many people believe this because it has been shown that the Simian Immunodeficiency Virus can infect humans, though it causes no disease.  Also, the genes found in SIV are very similar to the genes found in HIV.

c.  it may be that the virus has always been endemic to the central part of Africa and because of increased travel through the region in recent years, it has spread.

 

            The first recorded AIDS case in America was that of a 15 year old male prostitute who demonstrated Kaposi’s sarcoma and died in 1969.  Frozen tissue sample contained HIV antibodies.  The first documented case of AIDS in Europe was seen in a Danish surgeon who had worked in Zaire.  She died in 1976.  The earliest known case is believed to be an African man who died in 1959.  Scientists looked for signs of HIV in 1,213 blood samples that were gathered between 1959 and 1982.  They found clear signs of the virus in a Bantu man who lived in Leopoldville, Belgian Congo (Kinshasa).  Based on this finding, and the known rate of change of HIV, it is estimated that HIV crossed into the human population from an animal reservoir between 1924 and 1946. 

 

Characteristics

HIV is a retrovirus of the subfamily Lentivirinae.  The virus contains an enveloped icosahedral helical capsid, which contains two identical RNA molecules.  These RNA molecules are positive in polarity.  The virus possesses a reverse transcriptase, and integrase, as well as other proteins.

 

 

  After entering the cell by membrane fusion the virus RNA is transcribed to a DNA copy.  This DNA migrates to the nucleus where it is integrated into the host chromosome via the viral integrase enzyme.  There are two distinct phases of transcription.  In the early phase, RNA strands or transcripts produced in the cell’s nucleus are snipped into multiple copies of shorter sequences by cellular splicing enzymes.  When these reach the cytoplasm, they are only about 2,000 nucleotides in length.  These early transcripts encode the virus’s regulatory proteins.  In the second phase of transcription, two new size classes of RNA (long and medium [singly spliced]) are made and go to the cytoplasm.  The medium transcripts encode the structural proteins.  The long transcripts (full size) become the encapsidated genome.  HIV encodes nine genes that are put into three classes, 1) Gag, Pol, and Env – the 3 major structural proteins, 2) Tat, and Rev – two regulatory proteins, and 3) Nef, Vif, Vpu, and Vpr – four accessory proteins.   

 

 

 

 

 

 

Pathophysiology

HIV primarily infects CD4+ T cells (i.e., T cells that have a CD4+ receptor).  To some extent monocytes and macrophages can also be infected.  HIV binds to the CD4+ receptor and subsequently to the CCKR5 coreceptor (whose normal function is a chemokine receptor).  It then enters the cell by fusion with the plasma membrane.  It uncoats and the reverse transcriptase makes a DNA copy, which is subsequently used as a template to make a double-stranded DNA.   

 

 

 

 

 

 

One to three weeks after infection most patients exhibit a brief glandular fever-like illness, which is associated with a high titer of virus in the blood and a decline in CD4+ T cells.  A vigorous cellular and humoral immune response commences and within a month or so the viremia declines to near undetectable levels.

 

 

CD8+ cytotoxic T cells, natural killer cells and antibody-dependent cell mediated cytotoxicity may all contribute to this decline by lysing infected cells, while neutralizing antibodies may mop up free virions.  After the initial phase, there is a long asymptomatic period of clinical latency, lasting anywhere from 1 to 15 years.  During this period, only low titers of virus are demonstrable in blood and only a small number of circulating T cells are infected.  However, ten times higher levels are detected in lymph nodes.  As time passes there is a steady decline in CD4+ T cells.  When the T cell count falls below 200-400/ul, opportunistic infections with various microorganisms may occur, and eventually the depleted immune system is unable to cope.  Activation of CD4+ T cells renders them permissive for HIV replication, and other viruses such as HHV-6, CMV, HTLV, and hepatitis B virus.  Death is a result of these and other infections, malignancy, or a cachexia-like state.  The average asymptomatic period is 11 years. 

 

 

 

 

One of the more important questions about HIV is why does it take so long to cause the disease.  After all, within a few weeks of infection there can be a high viral titer in the blood.  The answer, it turns out, it quite complex and not well understood.  Many scientists think that the progression of AIDS is a monumental struggle between the AIDS virus and the immune system.  In the beginning the immune system is primed and reduces the virus to negligible levels.  However, it is not able to totally eradicate the virus because HIV has the advantage of being able to enter the proviral state and exist as nothing more than DNA inside a cell.  It does not replicate in resting T cells and prefers to sequester itself in the lymph notes and not show itself in the bloodstream.  Because of this, it can exist for long periods of time.  It also has the advantage of being able to move from one cell to another by syncytia formation, thereby evading the immune system.  Over a period of time, the virus slowly wins the race and defeats the immune system by destruction of T cells.  This is quite noticeable in lymph nodes, which can be nothing but ravaged hulks by the end of the disease. 

 

The mode of destruction of T cells is not exactly known, but there are many theories.  They include:

            1.  the virus may leave some of its spike attached to the CD4+ receptor, thereby

            impairing T cell function.

            2.  syncytia formation

            3.  HIV may act as a super antigen, which has the effect of depleting T-cell

            populations.

            4.  HIV may trigger apoptosis

            5.  HIV may kill the cell by replication

            6.  HIV may trick the immune system to kill its own T4 cells (autoimmunity)

            7.  Cofactors (such as HHV-6) may aid in T cell killing

 

One of the more interesting AIDS episodes occurred when two gay men came to the NIH and told the researchers that they had had frequent and unprotected sex, yet they were still HIV-negative.  They offered themselves as research models.  Scientists determined that these men had a mutation in the CCKR5 coreceptor gene (R-5).  Therefore, HIV could not easily enter their T cells. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A Personal and Poignant Experience

 

 

 

 

 

Diagnosis

Initial diagnosis is by seroconversion.  Most people seroconvert within 6-18 weeks.  By 6 months, 99% of all individuals have seroconverted.  Once the initial diagnosis has been made, patients (PWAs) are referred to AIDS specialists (if at all possible)  at that time the individuals are carefully monitored on an ongoing basis for T-cell count and viral load.  A useful indicator developed by David Baltimore is the viral RNA circulating in the bloodstream.  This is easily determined via PCR and is directly proportional to viral load, which is much more difficult to assess.  Therefore, you often see graphs which have viral RNA as the indicator, rather than virus.  The physician carefully monitors these two indicators to determine how to administer the anti-AIDS drugs. 

 

 

Epidemiology

AIDS has become a disease of the poor.  Only 1% of AIDS-infected individuals reside in the U.S.  It is rampant, particularly in Africa, but most compete for notoriety with malaria, TB, and measles, all of which are major killers in these populations.

 

AIDS is transmitted by close contact with bodily fluids and secretions.  It can not be transmitted by casual contact or by insect bite.  The proof for this is that many people have lived with HIV-positive individuals (family members) and, except for several instances which had explanations (nosebleeds, sharing razors, bloody fight between brothers), not one person has contracted AIDS.  In addition, scientists have shown that HIV cannot survive the harsh conditions of the insect gut.  AIDS is not transmitted by fomites.  There is, however, one documented case of HIV transmission by kissing.  This is likely to be because HIV is present in saliva at low concentrations.

 

 

The accepted modes of spread are by sexual intercourse, direct injection with HIV-contaminated drugs-needles, etc, and from HIV-infected mother to fetus in utero, during childbirth, from mother to infant, or during breast-feeding.  Even if exposed in this way, it is not a foregone conclusion that a person will contract AIDS.  This depends on several characteristics of donor, recipient, and portal of entry, but the most important variables appear to be viral load, which subtype and variant of HIV, and the recipient’s genetic resistance.  By far the largest two modes of transmission are men having sex with men and IV drug use.  The efficiency of transmission is greater than 90% for blood transfusion, 20-40% for perinatal transmission and approximately 1% for IV drug use and intercourse.  This demonstrates that HIV is not particularly effective at infecting an individual.  There are many other indications to this effect.  Paul Michael Glaser had normal sexual relations with his wife for 5 years prior to her being diagnosed with AIDS.  While their first-born became infected, he did not.  Approximately 50% of people that have regular sex with HIV-infected people do not contract the disease.  This is not a license for unprotected sex, however.  Condoms have been shown to be highly effective at containing the spread of HIV.

 

 

Other documented modes of transmission – acupuncture, human bites, transplants, nosocomial (Romanian orphanages), and medical intervention (Kimberly Bergalis).

 

Little known useless fact:  Every day, 400 liters of HIV-infected semen are ejaculated worldwide.

 

The spread of AIDS in the world is much different, with 70% of it being from heterosexual intercourse, 8% from IV drug use, 9% from perinatal causes, and 3 percent from blood transfusion.

 

Women have a much higher chance of becoming infected from unprotected sex.  This is because during sex women are exposed to semen carrying lymphocytes (whereas men have limited contact with vaginal fluids), the mucosal surface available for HIV penetration is much larger in women, it is much more likely for the tissue lining the vagina to be torn and abraded than the urethral tissue, and there are many more HIV infected men than women (in developed countries its about 6:1).

 

The legal implications of unprotected sex......

 

 

 

Treatment

Evaluation of drugs is usually done on the basis of an increase in T4 or CD4+ cell number or a reduction in viral load.  However, because of day to day variability, these are imperfect indicators (but the best we have).  In particular, viral load is important because it dictates the aggressiveness of the treatment.  In the last 13 years, 15 drugs have received US FDA approval.  These fall into 4 general classes, nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, protease inhibitors, and other.

 

 

Nucleoside reverse transcriptase inhibitors – These are among the first drugs tested and held great promise.  They enter the cell, are taken up by the reverse transcriptase, and thereupon cause termination of synthesis.  However, as monotherapeutic agents, these were quickly shown to have limitations.

a.  they are not 100% effective in stopping the reverse transcriptase

b.  positive clinical effects are short term

c.  each drug has its own set of toxic side effects

d.  individually they do not delay the onset of AIDS

e.  HIV rapidly becomes resistant to each of the drugs.  The mechanism of this development of resistance is through the low fidelity of the reverse transcriptase.  Because it makes so many variation of itself when it is transcribed, there are bound to be variants that are not as inhibited.  These variants make other variants that are even less inhibited and within a short time the drugs are ineffective.

 

Side effects range from severe to moderate:  zidovudine -  anemia, nausea, headache and inhibition of mitochondrial DNA replication, didanosine – peripheral neuropathy (burning pain in hands and feet) and pancreatitis, zalcitabine – peripheral neuropathy and mouth ulcers, stavudine – peripheral neuropathy, lamivudine – hair loss and peripheral neuropathy. 

 

For a short time it was thought that these drugs could be made more effective by using them in a multidrug cocktail.  While this does increase their efficacy slightly, in the end the result is the same.

 

It is expensive to bring new drugs to market!!   Merck estimates that they spent $1,000,000,000 over 10 years to bring Crixivan to market.  Recently, it has been found that Crixivan loses it’s efficacy and has more side effects than a newer competitor... so it is likely that it will not be used within a few years time.

 

Non-nucleoside reverse transcriptase inhibitors – Though they work at the same site (RT), these differ from nucleoside reverse transcriptase inhibitors in that these are not incorporated (thereby stopping chain elongation), but work directly on the enzyme, causing noncompetitive inhibition.  Like the nucleosdie RT inhibitors, this action is short-lived because variants of the enzyme are rapidly selected.  Combination therapies on nucleoside RT inhibitors and non-nucleoside RT inhibitors have shown some success in that they lengthen the time of the asymptomatic period, but they do not increase the survival time.  Their main function in therapy is to delay use of protease inhibitors.

 

Protease inhbitors  - in HIV replication a specific protease is necessary to process the precursor proteins of  reverse transcriptase, integrase, and envelope proteins.  If the protease is missing or inactive, noninfectious HIV are produced.  Scientists found that the HIV protease is distinctly different from human proteases, opening the door for drugs that would inhibit the viral protease, but not human proteases.  These have been very effective in some cases.  There are about 20 HIV protease-inhibiting drugs under study, six in clinical trials and six that have received approval.  It should be noted however that at least 15% of the people must give up protease inhibitors because of severe side effects.  Likewise, about 15% of the people do not respond to protease inhibitors.  Finally, it has recently been shown that protease inhibitors fail to suppress HIV replication in about half of the people in treatment after 1-3 years.  The average cost of protease inhibitors on the market is about $600 per month.  Protease inhibitor side effects are different for each drug, but range from rash diarrhea, stomach discomfort, anorexia, headaches, fatigue, kidney stones.

 

Combination therapy – though each drug has its failing, if these drugs are used in combination (for instance, a protease inhibitor, a nucleoside analog, and a non-nucleoside analog), they can produce significant results, rescuing people from the brink of death.  In one instance the viral load went from 98,600 copies per ml of serum to undetectable within 2 weeks.   Combination therapy is based on simple probability.  If there is a in 100,000 chance of the virus developing resistance to a single drug, then there is a 100,000 X 100,000 chance (1/10,000,000,000) of a virus developing resistance to two drugs, and a 100,000 X 100,000 X 100,000 chance of a virus developing resistance to three drugs.  The cost, however, is significant and substantial.  The patients must adhere to a strict regimen of pills (anywhere from 10 to 72 pills per day).  If they miss a pill, it can severely hurt their therapy.  If they take a pill too early or  take too much, it can cause debilitating side effects.  The monetary cost is also daunting.  For a person that is HIV-positive, but has not yet shown additional symptoms the cost may be approximately $20,000 per year.  For a person that has AIDS, the cost may go as high as $150,000 per year.  The acronym given for this type of combination therapy is HAART (Highly Active Antiretrovial Therapy).

 

 

 

 

 

 

 

Anecdotal story:  A recovering patient in San Francisco had no measurable HIV in his blood for the 89 weeks he was on the protease inhibitor-AIDS cocktail.  He decided to stop the drug therapy; the virus became measurable within 1 week.

 

AIDS Prevention

Common sense

 

Vaccine -  No vaccine has yet made it through Phase III trials, and there is only one candidate even in Phase III (AIDSVAX).  The primary issues appears to be that cellular immunity is much more important for HIV destruction than previously thought.  Most vaccines focus on initiating antibody production.  Moreover, HIV mutates very rapidly, overcoming the antibody response.  Many of the early vaccines did not stimulate the cellular response strongly enough. 

 

Currently, there are approximately 60 vaccine candidates in various stages of testing.