Can we functionally cure HIV?

Last March, Dr. Deborah Persaud, from the John's Hopkins Children Center, presented a stunning finding at the conference CROI, receiving great resonance across several newscasts: Persaud reported the first case of infant functionally cured of HIV. You can watch Persaud's presentation by downloading the podcast here, it's the seventh talk of the session "Is there hope for HIV eradication?"

Up until this finding, the only living person cured from HIV was the Berlin Patient, who was cured after receiving gene therapy for his underlying leukemia condition. Despite this one successful case, gene therapy is not a feasible way to cure HIV.

What does it mean to be functionally cured?

Once in the host, the HIV virus establishes reservoirs of latent virus: these are viral particles that stay dormant in cells and tissues and have the ability to quickly rebound in the event that therapy is discontinued. That's why it's so important for an HIV infected person to never discontinue the drug regimen, as the rebound virus may be drug resistant. HIV is so efficient at escaping the immune system and therapy that standard practice these days is a lifetime of not just one, but a cocktail of 3-4 antiretroviral drugs.

To be functionally cured means that drugs are no longer needed to keep the viral load (amount of virus in the blood) in check (close or below detection), something that until now had only been achieved by an extremely low number of HIV-positive individuals (less than 1% of infected adults), the so-called "elite controllers." In all other subjects, the reservoirs are never completely weakened and they enable the virus to bounce back once therapy is interrupted.

So, what was different with this child?

The mother went into labor without prenatal care. An HIV test was done during labor and normally, when the test is positive, antiretroviral drugs are administered. This is highly effective in preventing mother-to-infant infections as the only moment when the infant is exposed to the mother's blood is at birth. The antiretroviral drugs keep the viral load so low that the risk of infection becomes very small (around 2%). Unfortunately, in this particular case, the birth was so precipitous that there was no time to administer such drugs. The newborn baby was immediately tested for HIV.

This is my understanding of what was unique about this case: normally a first test is done and, if positive, a second follow-up test is performed and prophylaxis is started once the infection is confirmed. In this case, though, two independent tests were done at the same time and, since both confirmed the HIV infection, prophylactic treatment was started very early, when the baby was 31 hours of age. Also, unique to this case was the fact that a regimen of three drugs, of which one at the therapeutic level instead of the standard prophylactic dosage, was administered during the first week of life. After that, the baby was switched to a standard treatment of antiretroviral drugs (again, my understanding from the CROI talk).

Such regimen successfully brought the child's viral load down to undetectable, which is normal in these cases. Despite this, because of HIV's ability to establish reservoirs, antiretroviral therapy is never discontinued. Like I said before, it is a lifetime therapy. So called "drug holidays" result in more virulent and drug-resistant HIV quasispecies. However, this child was lost to follow-up at 18 months of age and was once again seen by the doctors at 25 months of age, when the caregiver reported discontinuing the therapy. Immediate testing was done to assess the child's viral loads. The child was tested not once, but many times. Genetic testing was also done to make sure it was the same child treated before. The doctors must have been in disbelief as for the first time they were seeing the incredible: after 5 months since discontinuing antiretroviral therapy, the viral load in this child was still undetectable.

What are the consequences? As Dr. Persaud repeated many times during her talk, this is a single case and a proof of concept. We need more cases to be able to generalize (as statistics teach us). However, it points to something that indeed needs to be explored: how early in the infection can we (and should we) intervene? In a 2012 paper [1], Persaud and colleagues studied the dynamics of the latent HIV reservoirs in 17 infants on very early antiretroviral drug therapy (median start age 8 weeks) and found that the size of the reservoirs at age 2 was associated to how early undetectable viral loads were achieved during therapy. The earlier viral load was suppressed through therapy, the smaller the HIV reservoir at age 2. Is there a point, very early into the infection, when the virus is vulnerable and all reservoirs can be not just reduced in size, but actually completely eradicated through potent and prompt intervention?

In rare cases, HIV-infected patients are able to spontaneously maintain their viral load at a very low level without the need of drugs, the so called "elite controllers." What if, when administered early enough, antiretroviral drugs could transfer this type of spontaneous protection to every HIV-infected person?

Shortly after the CROI conference, a French study published in PLoS Pathogens [2] reported 14 cases of what they call "post-treatment controllers," in other words, people whose viral loads remained very low after interrupting treatment. With the exception of mother-to-infant transmissions at birth, it's extremely hard to catch this virus early because people often don't realize they've been infected: symptoms, if any, appear 3-4 weeks later and are often mistaken for a common cold. Twelve of the 14 cases reported in [2] had symptoms that prompted early intervention and start of therapy during the primary infection.

"Post-treatment controllers (PTCs) had a more severe primary infection with higher viral loads and were frequently symptomatic, which may have prompted the early treatment in some cases [. . .] Therefore, our results strongly suggest that the infection control in the PTCs was not achieved spontaneously and was favored by the early onset of therapy. Because the interruption of long-term antiretroviral therapy initiated early during primary infection is not recommended, only a very small proportion (~2%) of the patients in the French Hospital Database on HIV Infection experienced such an interruption, which may explain the rarity of PTCs worldwide [2]."

[1] Persaud, D., Palumbo, P., Ziemniak, C., Hughes, M., Alvero, C., Luzuriaga, K., Yogev, R., Capparelli, E., & Chadwick, E. (2012). Dynamics of the resting CD4+ T-cell latent HIV reservoir in infants initiating HAART less than 6 months of age AIDS, 26 (12), 1483-1490 DOI: 10.1097/QAD.0b013e3283553638

[2] Sáez-Cirión, A., Bacchus, C., Hocqueloux, L., Avettand-Fenoel, V., Girault, I., Lecuroux, C., Potard, V., Versmisse, P., Melard, A., Prazuck, T., Descours, B., Guergnon, J., Viard, J., Boufassa, F., Lambotte, O., Goujard, C., Meyer, L., Costagliola, D., Venet, A., Pancino, G., Autran, B., Rouzioux, C., & , . (2013). Post-Treatment HIV-1 Controllers with a Long-Term Virological Remission after the Interruption of Early Initiated Antiretroviral Therapy ANRS VISCONTI Study PLoS Pathogens, 9 (3) DOI: 10.1371/journal.ppat.1003211