A study published on February 9th reported yet another case of “HIV cure” after the patient received a specific type of bone marrow or stem cell transplant. It is a 53-year-old man, who the researchers christened the “Düsseldorf patient”. He underwent treatment in 2013 and has been monitored ever since.
The term “cured” is complicated, after all, although researchers are no longer able to detect the virus in the patient’s body, it cannot be said with certainty that it is no longer present. That is why it is called “remission”.
Until now, both the “Düsseldorf patient” and the so-called “Berlin patient” and “London patient”, all reported to be in HIV remission, shared common characteristics: they were positive for HIV type 1 (HIV-1) and they had potentially lethal types of cancer, such as leukemia or lymphoma.
All of them also received bone marrow or, more precisely, allogeneic hematopoietic stem cell transplants.
The transplants were intended to treat cancer, but the donors in these three cases had a very rare mutation in a gene called CCR5, which essentially makes them resistant to HIV-1.
What are hematopoietic stem cells?
In this context, bone marrow and stem cells are often used interchangeably, because in our bone marrow there are indeed stem cells called hematopoietic stem cells (HSC) or stem cells.
HSCs are a cell-producing machinery that can give rise to blood and immune system cells, a process called hematopoiesis, which comes from the Greek for “blood production”.
About 300 billion new cells are produced every day by HSCs in our bone marrow.
Stem cells: broader definition
Strictly speaking, however, “stem cell” is a generic term that refers to cells that are constantly dividing and have the potential to form different types of other cells.
Most of our cells are very specialized and cannot change. They can be heart muscle cells, neurons, or gut wall cells, just to name a few.
In contrast, stem cells are like teenagers about to graduate from high school.
They can become practically anything after that: lawyers, workers, nurses, scientists, journalists, influencers, tiktokers – they just need to adapt to new trends.
Different types of cells-stem
But not all teens are equally flexible when it comes to choosing what to be when they grow up. Some may be very into the arts, while others may be passionate about science and unable to draw a tree.
Stem cells also have different types of, say, affinities, in the sense of the diversity of cell types they can generate.
Stem cells that can produce all the different types of cells needed for an embryo to develop are called pluripotent. Multipotent cells can only generate certain types of cells.
Adult human beings have multipotent stem cells in many other places, such as the skin, bones, or gonads, because these cells need constant replenishment.
It is possible, however, to induce already differentiated cells to become pluripotent again, in a process called “cell reprogramming”, a discovery that earned the Nobel Prize in Medicine in 2012.
This potential to develop any type of cell and create new tissues was precisely what made stem cell therapy an extremely active field of research.
Hematopoietic stem cell transplantation
There are several types of stem cell therapies, but bone marrow transplantation or hematopoietic stem cell transplantation (HSCT) is the most popular. But it’s also a tough and risky procedure, used to try to repair diseased bone marrow by replacing it with healthy bone marrow.
This transplant is often intended to treat life-threatening conditions, such as bone marrow-related cancers such as leukemia or lymphomas, or blood/immune disorders such as sickle cell disease.
There are different types of stem cell transplants depending on where they come from. If it comes from the same person being treated, for example it is called autologous, if it comes from another person it is called allogeneic.
All three “HIV cured” patients received an allogeneic HSCT for cancer treatment.
A high-risk transplant
But before the transplant can take place, the patient must undergo a conditioning regimen that may include chemotherapy and radiation therapy.
Both chemotherapy and radiotherapy can have serious side effects, such as infections, organ dysfunction, and even death.
The conditioning regimen is designed to destroy the patient’s diseased bone marrow and heavily suppress their immune system so that the transplant can integrate properly.
If the treatment is successful, the transplanted cells will trigger an immune reaction against any residual cancer cells, helping to eliminate them, in what is called the “graft versus tumor effect”.
But things can go wrong. In some cases, the donor’s transplanted immune cells may begin to recognize the recipient’s body as foreign and attack it, leading to graft-versus-host disease.
It is not HIV treatment
Graft-versus-host disease can affect the skin, intestines, and liver. In some cases, it can even be fatal.
In a similar process, transplanted immune cells can also work to advantage, triggering an immune reaction and helping to eliminate any residual cancer cells, in what is called the “graft versus tumor effect”.
Due to its high risk, the researchers of the three HIV remission studies repeatedly warned that HSC transplants should not be seen as a therapy against HIV, whose recommended treatment is still the retroviral.
(Article written by Esteban Pardo, journalist specializing in science communication)