Matt Gethers/20.380 HIV Project/Meeting Notes/3.18.09 Refine RBC Idea

3.18.09 Meeting: Refine RBC Idea

To Do:

1. Discuss questions everyone was assigned a few weeks ago.
2. What do we want out of John and Darrel tomorrow?

Notes

Rob

• What do we need to put into the person? What stage of progenitor cells? - (done!)
• Immunity issues with progenitor cells? - Rob
• How to couple CD4 expression, etc with RBC differentiation? - Rob
• What to do with HIV once in cell? Do we need it to do anything? - Rob

Courtney

• How are RBCs removed/recycled from body? - Courtney
• Malaria - Courtney

Matt

Can HIV infect progenitor cells?

"Patients with HIV-1 often present with a wide range of hematopoietic abnormalities, some of which may be due to the presence of opportunistic infections and to therapeutic drug treatments. However, many of these abnormalities are directly related to HIV-1 replication in the bone marrow (BM). Although the most primitive hematopoietic progenitor cells (HPCs) are resistant to HIV-1 infection, once these cells begin to differentiate and become committed HPCs they become increasingly susceptible to HIV-1 infection and permissive to viral gene expression and infectious virus production." (Alexaki) Note: there's a figure (1) in this paper that details which cells are susceptible to HIV infection.

1. Alexaki A and Wigdahl B. HIV-1 infection of bone marrow hematopoietic progenitor cells and their role in trafficking and viral dissemination. PLoS Pathog. 2008 Dec;4(12):e1000215. DOI:10.1371/journal.ppat.1000215 |

• Matt Progenitor References

What's necessary and sufficient for HIV infection?

"The notion that a coreceptor is required for HIV-1 entry stemmed from the awareness that CD4 expression is not sufficient to explain HIV-1 tropism for different target cells in vitro (see 4 for review and citations). Two related phenomena led to this conclusion. The first series of findings, initially reported in the mid-1980s and extended through the early 1990s, was based on curious results with recombinant human CD4. The receptor was found to render cells permissive for Env-mediated fusion/entry/infection, but only when expressed on a human cell type. Experiments with cell hybrids supported the conclusion that this restriction was due to the requirement for a cofactor (coreceptor) of unknown identity that is specific to human cells, rather than to the presence of a fusion inhibitor on the nonhuman cells." (Berger)

"Because of its new-found activity in HIV-1 Env-mediated fusion, the protein was named “fusin” (6). Its role as a coreceptor was based on both gain-of-function experiments demonstrating that coexpression of fusin along with CD4 rendered nonhuman cells permissive for Env-mediated cell fusion and infection, and loss-of-function experiments showing that anti-fusin antibodies potently inhibited fusion and infection of primary human CD4+ T lymphocytes. Most importantly, both types of analyses indicated that fusin functioned for TCL-tropic, but not M-tropic, HIV-1 strains. Fusin thus fit the criteria for the TCL-tropic HIV-1 coreceptor." (Berger).

2. Berger EA, Murphy PM, and Farber JM. Chemokine receptors as HIV-1 coreceptors: roles in viral entry, tropism, and disease. Annu Rev Immunol. 1999;17:657-700. DOI:10.1146/annurev.immunol.17.1.657 |

• Matt Infection Mechanism References

Some interesting stuff

• Matt Miscellaneous References

Jessie

• How to prevent HIV from leaving RBC? - Jessie
  • Nothing in the literature indicates anything about an "abandon infection" behavior by the HIV.

• Death switch? - Jessie

David

• Exploding RBCs? - David
• Any natural conditions where RBCs die or explode? - David
  • A normal erythrocyte has a volume of about 90 fL=9.0 X 10^-17 L (a third of which is hemoglobin only freed up if we knock it out)
  • HIV is roughly a sphere of diameter 120nm --> volume of 9.05 X 10^-22 L
  • A normal RBC can theoretically hold a maximum of ~100,000 HIV virions if it has nothing else inside, including water
  • Damaged/misshapen RBCs are naturally destroyed in the spleen (i.e. anything but biconcave cells)
  • There is an entire class of disorders classified as "Hemolytic anemia" where RBCs are broken down prematurely/too much (http://en.wikipedia.org/wiki/Haemolytic_anemia)
  • Some are congenital
    • misshapen membrane
    • metabolic defects
    • sickle-cell anemia
    • thalassaemia
  • Some are acquired
    • autoimmune disorders
    • some drugs (ribavirin)
    • toxins
    • malaria and some other infections
  • Questions:
    • How many copies of HIV do we expect each RBC to hold? (question for modeling)
    • Can't find any papers on what happens when HIV virions aggregate in a small volume (could anything bad/unexpected happen? cross-linking?)
    • If we knock out hemoglobin, do we need to worry about too little osmotic pressure inside? Is Hb just replaced by ions from blood?

Yi

• Take out hemoglobin? Anything else to knock out? - Yi
• Pathologies of RBCs - esp. sickle cell anemia, thalassemia - Yi

Steph

• Ideal concentration of RBC progenitors? - Steph
• How to get into bone marrow? Easy injection method? - Steph
• Role of progenitors? - Steph