This article is a collaboration with Immunology Explained, an initiative by the American Association of Immunologists to connect you to the science that protects your health.
I (Jess) was a teenager when I first watched Philadelphia. Tom Hanks, gaunt and dying, fighting for his dignity in a courtroom while his body failed him. That was 1993, and that was AIDS – a death sentence delivered with a diagnosis. I remember crying during the opera scene and thinking this disease was about endings.
Years later, in graduate school, AIDS became something else entirely – the perfect teaching example for epidemiology students learning about incidence versus prevalence. Our professors would draw those curves on the board: incidence dropping like a stone after 1996, while prevalence climbed steadily upward. It took me a moment to understand what that paradox meant: fewer people were getting HIV, but more people were living with it. They were living with it.
That shift – from death sentence to chronic condition – represents one of the most remarkable scientific victories of our time. And at its heart lies our evolving understanding of the immune system itself...
World AIDS Day is December 1, and a time to honor lives lost, celebrate progress, and recommit to ending the epidemic. Human Immunodeficiency Virus (HIV)/Acquired Immunodeficiency Syndrome (AIDS) was once a global health crisis with no cure and little hope. Today, thanks to decades of scientific breakthroughs and public health action, HIV is no longer a death sentence and is now a manageable chronic condition. But the fight isn’t over. Millions still lack access to treatment, new infections continue, and stigma remains a barrier to care. Ongoing research into HIV’s interaction with the immune system and sustained investment in prevention strategies are critical to protect communities and move closer to long-term control.
Two key pillars strengthen our response to HIV and improve global health:
- Immunology Insights: Understanding how HIV attacks CD4 T cells and how treatments disrupt the virus’s life cycle drives innovation in therapy and prevention.
- Public Health Tools: Strategies like U=U (Undetectable = Untransmittable) and PrEP (Pre-Exposure Prophylaxis) dramatically reduce transmission and protect communities.
The Immunology Behind the Battle: HIV Targets and Weakens the Immune System
HIV is a retrovirus that targets CD4+ helper T cells, the “generals” of the immune system that coordinate immune system defenses. The virus binds to the CD4 receptor and a co-receptor (usually CCR5) to enter the cell and take it over, ultimately resulting in the death of the cell.
Once inside, HIV begins a clever takeover:
Binding and Entry: The virus attaches to CD4 and CCR5, markers on the outer surface of CD4+ T helper cells, and fuses with the cell membrane to enter the cell.
Reverse Transcription: HIV converts its RNA genome into DNA, the nucleic acid of our human genomes, using an enzyme called reverse transcriptase, which it brought with it to ensure cellular takeover. This step – reverse transcription - is a major target for many HIV drugs since human cells do not contain or use this enzyme. It is unique to HIV infected cells.
Integration: The viral DNA is then integrated or woven into the cell’s own genome by another enzyme, provided by the HIV virus itself, called integrase. This viral genome integration into our own DNA makes the infection permanent.
Replication and Release: The hijacked cells become a viral factory, churning out billions of new viruses and eventually dying in the process.
Source: https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/animal-viruses-hiv
By destroying CD4+ T helper T cells, HIV disables the immune system’s command center.
Progression to Acquire Immunodeficiency Syndrome (AIDS)
As CD4 cells are destroyed, the immune system collapses. When CD4 count falls below 200 cells/mm³, AIDS is diagnosed, leaving the body vulnerable to opportunistic infections such as Pneumocystis pneumonia (PCP), tuberculosis, cytomegalovirus, and fungal infections like candidiasis. These illnesses take advantage of a weakened immune system and can be life-threatening without treatment.
The Prevention and Treatment Revolution
Antiretroviral therapy (ART) works by blocking key steps in HIV’s cycle, stopping the virus from multiplying and helping the immune system survive. Different drug classes target specific viral enzymes: reverse transcriptase inhibitors prevent the virus from converting its RNA into DNA, integrase inhibitors stop viral DNA from inserting into the host genome, and protease inhibitors block the assembly of new virus particles. By halting replication at these critical points, ART reduces the amount of virus in the blood to undetectable levels, allowing CD4 T cells to recover and restore immune function.
Ending HIV requires more than science - it demands access, equity, and sustained funding. Progress is being driven by a combination of scientific innovation, effective treatments, and public health strategies that prevent transmission and improve access to care.
The Power of “Know Your Status”
Testing is the entry point to care. Rapid tests and even home kits make it easier than ever to learn your HIV status. This matters because of the UNAIDS 95-95-95 targets for 2025:
- 95% of people living with HIV know their status
- 95% of those diagnosed are on treatment
- 95% of those on treatment achieve viral suppression
Global progress is uneven. Some countries have met these targets, while others lag behind, with testing coverage below 75%.
Undetectable = Untransmittable (U=U)
Science is clear: People living with HIV who maintain an undetectable viral load through ART cannot sexually transmit the virus. This principle, validated by major studies like HPTN 052 and PARTNER, is now endorsed globally. U=U is a cornerstone of HIV prevention that dismantles stigma, empowering people living with HIV to live full, healthy lives.
Comprehensive Prevention Tools
- PrEP (Pre-Exposure Prophylaxis): A daily pill or long-acting injection for HIV-negative individuals to prevent infection. When taken as prescribed, PrEP reduces HIV risk from sex by about 99% and from injection drug use by at least 74%.
- PEP (Post-Exposure Prophylaxis): Emergency medication taken within 72 hours after a possible exposure to HIV.
- Combination Prevention: The most effective approach combines PrEP, U=U, condoms, and harm reduction strategies.
A Future Without AIDS - Science Makes It Possible, Funding Makes It Real
Science only works when programs deliver it. Initiatives like PEPFAR and the Global Fund provide the infrastructure for testing, treatment, and prevention. PEPFAR alone has saved an estimated 26 million lives and enabled millions of babies to be born HIV-free. Sustained investment is essential. Funding prevention and treatment costs far less than managing a growing epidemic and, most importantly, saves lives.
Science and public health have transformed HIV from a fatal disease to a manageable condition. But the finish line of ending AIDS as a public health threat requires action:
- Get tested
- Know U=U
- Advocate for funding and fight stigma
On this World AIDS Day, let’s honor scientific progress and commit to a future where HIV is history by continuing to invest in science, expanding access to life-saving treatments, and fighting stigma so that every person, everywhere, can live free from the threat of HIV.
That teenager watching Philadelphia couldn’t have imagined a world where HIV-positive people would have near-normal life expectancies, where a daily pill could prevent infection, where ‘undetectable’ would equal ‘untransmittable.’ But here we are, living proof that science – particularly immunology – can rewrite even the darkest stories.
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Stay Curious,
Unbiased Science
Jess Steier, DrPH @drjessicasteier is a public health scientist, host of Unbiased Science, and quirky and empathetic science communicator.
Aimee Pugh Bernard, PhD @funsizeimmuninja is an Immunologist, educator, Science Communicator and Science Advocate
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