reply to post by Sinny
On to how we study HIV infection in mice:
I've been doing this every day for over two years and I'm still amazed at what we actually do: we take severely immune compromised mice (we call
these mice NSG for short but they basically contain a variety of mutations that almost completely eliminate their immune systems - we breed and/or buy
them from Jackson Labs: jaxmice.jax.org...
) and give them human immune systems because, as someone pointed out
earlier, no, mice cannot be infected with HIV. The lack of a small animal model for HIV research has severely held back progress on the disease.
However, as the use and experience with humanized mice has improved over the last couple decades, the model has become quite useful for HIV research
and I expect you'll see more and more papers on scientific advances leading towards a cure for HIV. But I digress. The specific mouse strain and
process for humanization varies and we have entire international conferences devoted to trying to clarify this even among the scientists that use it
every day. For this specific study, we used the NSG mice (as opposed to NOD/SCID or Rag2-/- etc). These mice undergo a theoretically
simple/technically challenging survival surgery, in which they receive fetal human thymus and liver and modified "stem cells."
So I know I just said some very disconcerting things. First off, "fetal?" Yes. I was pretty surprised at first, as well. And, fetal tissue is
just as hard to come by as you might think. We have relationships with hospitals and clinics. Patients must be undergoing elective abortions and
they must sign a consent/release form in order to obtain the tissue. Then someone has to procure the proper the tissues, also not an easy job.
Because the human immune system begins in the fetal liver and fetal thymus, we take those tissues.
From the fetal liver, we isolate what are called CD34+ cells. These are hematopoietic (that's just scientist speak for blood) progenitor cells. We
don't actually call them stem cells in the lab because they are not true stem cells. In fact, they are so far away from embryonic stem cells, they
are considered "adult stem cells," which are scientifically called progenitor cells instead of stem cells. These CD34+ cells have the potential to
become every single cell type in our blood, which makes them great cells to study gene therapy for all blood diseases like sickle cell anemia,
hemoglobin disorders and HIV! So we isolate the CD34+ cells and genetically modify them so that they contain the anti-HIV genes we want to express.
To create the humanized mice, we surgically implant a teeny, tiny, itsby, bitsy piece of the fetal liver and thymus under the kidney capsule of the
mouse. Yep. And I was always in awe of human baby/neonate surgeons. Imagine how much harder it is to perform a surgery on a mouse kidney. It is
literally smaller than a kidney bean! So the mouse in under anesthesia, just like a human would be. We make a small incision, find the kidney and
clamp it and the "kidney capsule" is the thin membrane that encircles the kidney. It's literally less than a hair wide! We take our trocar
(surgical needle) that contains the fetal liver and thymus pieces (and sometimes also the genetically modified CD34+ cells) and inject them just under
the kidney capsule but on top the kidney. (We chose the kidney because it has an excellent blood supply.) We close up the mouse and then IV inject
more of the modified CD34+ cells. Some analgesics, etc, wait 8 weeks and begin assaying the mouse for human immune cells. These mice can be infected
with HIV but remember it’s the human immune cells that are actually infected. We’ve never been able to detect HIV in any mouse cells. The human
cells undergo the same depletion we see in humans until the mouse progresses to an AIDS-like disease. We don’t usually wait that long, as we want
to assay the cells before the mouse gets too sick.
And there it is, your primer on humanized mice used for HIV gene therapy!